International Falls, Minnesota: Frigid Begets Super-Frigid

By: 24hourprof , 9:48 PM GMT on December 12, 2013

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The temperature at International Falls, Minnesota, plummeted to minus 33 degrees Fahrenheit early Tuesday morning (Climate Summary for December 10). The low occurred between 4 and 5 A.M. CST on December 10, but, if you were a rookie forecaster working during the evening of December 9, you might not have predicted such an extreme minimum.


A portion of the 00Z surface analysis on December 10 (6 P.M. CST on December 9). Full analysis. Courtesy of WPC.

Indeed, a low-pressure system was slated to move southeastward and pass to the south of International Falls...see 00Z surface analysis on December 10 above (6 P.M. CST on December 9; full analysis.). Even so, frost points to the west and north of International Falls were not even in shouting distance of minus 33 degrees. By way of background, weather forecasters use the dew point (frost point) as an estimate for the nighttime low temperature on clear nights with light winds...the air temperature can't really fall below the dew point (frost point) (unless a cloud forms, but, even then, there's an imperceptibly tiny difference between the two).


The METARS at International Falls, MN, from 00Z to 15Z on December 10 (6 P.M. on December 9 to 9 A.M. on December 10). I underlined, in blue, the frost points at 00Z and 10Z. I also indicated the low temperature (minus 36.1 Celsius = minus 33 degrees Fahrenheit). Courtesy of NOAA.

One look at the METARS (hourly weather observations) at the International Falls Airport (above) indicate that the frost point fell from minus 27.8 degrees Celsius (minus 18 degrees Fahrenheit) at 00Z to minus 37.2 degrees Celsius (minus 35 degrees Fahrenheit) at 10Z (4 A.M. CST) early on December 10.


The METARS at International Falls, MN, from 00Z to 15Z on December 10 (6 P.M. on December 9 to 9 A.M. on December 10). I outlined, in blue, the wind speeds (in knots) from the evening to early the next morning. Courtesy of NOAA.

Moreover, if you look closely at wind speeds above (in knots), you can see that winds were either calm or blew from the southwest at six knots or less. This observation should convince you that any quick answer involving the advection (wind transport) of really dry air is simply not reasonable.

The meteogram below graphically summarizes the points I'm making here. Note how the frost point (green curve on the uppermost plot) decreases dramatically during the early morning hours of the 10th, even though winds were calm (zero dry advection). The low temperature (minus 33 degrees Fahrenheit) obviously occurred between hourly observations.


The meteogram at International Falls from 1255Z on December 9 to 1255Z on December 10, 2013. Note how the frost point (green curve in the uppermost plot) decreases dramatically during the early morning hours of the 10th, even though winds were calm (zero dry advection). The low temperature (minus 33 degrees Fahrenheit) obviously occurred between hourly observations. Courtesy of the University of Wyoming.

So how did the frost point get so low during the nighttime hours? Whatever the answer, the air temperature followed the lead of the frost point and plummeted to minus 33 degrees. Okay, I'll divulge the answer.

During winter, when International Falls is deep in an Arctic air mass, there is a lot of frost deposition on exposed surfaces such as cars, light poles, etc. This process takes water vapor in the air near the ground out of the air, thus lowering the frost point. Water vapor also likely deposited on the cold snow cover, which was reported to be 12 inches deep on December 10. The bottom line here that deposition likely took water vapor out of low-level air, decreasing frost points, and, with a mainly clear sky and light winds, the temperature "chased" the falling frost points, plummeting to an absolutely frigid minus 33 degrees Fahrenheit before sunrise.

There are also many winter nights in International Falls when ice deposition occurs in the air (in addition to exposed surfaces, snow cover, etc.). When I lived in Montreal during graduate school, ice crystals sometimes fell out of the air even though the sky was clear. Thus, I hesitate to call these hydrometeors "snow," but, technically, they are. I've seen this kind of precipitation reported as light snow (-SN) on METARS in frigid places like International Falls.


An example of an ice crystal in the shape of a hollow, hexagonal column. Courtesy of Kenneth G. Libbrecht, Caltech.

For the record, these ice crystals are often thin plates or columns (above) that form in the temperature regime from minus 20 degrees Celsius to minus 40 degrees Celsius. Even with a temperature and frost point of, say, minus 29 degrees Celsius and minus 34 degrees Celsius (respectively), the air is likely saturated with respect to ice. As a result, the deposition process readily occurs because all sorts of ice nuclei become "activated" in the lower troposphere. These activated ice nuclei grow as water vapor deposits onto them, removing water vapor from the air and lowering the frost point.

Having discussed this process, I admit there weren't ice crystals reported on the METARS at International Falls. There were, however, reports of ice crystals within 50 miles of International Falls. If they occurred, more water vapor would have been removed from the layer of air above the ground, and the frost point would have lowered.

The bottom line here is that deposition likely occurred on exposed surfaces and the cold snow cover, paving the way for frost points to dramatically decrease, even though there wasn't any dry advection. In turn, temperatures plummeting under a mainly clear sky and light winds. In effect, frigid begat super-frigid.

Lee

P.S. This is my last blog for Wunderground (it's difficult for me to comprehend that I've already been here for an entire year). I cannot adequately express my gratitude to Jeff Masters for this wonderful opportunity. Jeff...I always anxiously looked forward to writing my blogs. And many thanks to my colleagues at Wunderground for supporting me and helping me whenever I had technical difficulties. Finally, to my faithful Wunderground readers, I couldn't have done it without you. Thanks a million to everybody.

Best,

Lee

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63. WunderAlertBot (Admin)
1:55 PM GMT on May 07, 2014
24hourprof has created a new entry.
62. VirginIslandsVisitor
2:52 AM GMT on February 12, 2014
Hi Lee

If you do pop in once in a while, just know that I thoroughly enjoyed your blog with your never ending patience in explaining things and your lively chats with other bloggers.

I'm so sorry to see that you have left and hope to see you back again some day!

Lindy
Member Since: July 30, 2011 Posts: 2 Comments: 620
61. georgevandenberghe
10:06 PM GMT on January 31, 2014
Quoting 60. DonnieBwkGA:
From the Jacksonville wx discussion on the afternoon of January 24th, 2014.

TONIGHT...ANOTHER TRICKY FORECAST WITH THE PROSPECTS FOR INCREASED CLOUD COVER PROVIDING A BLANKET ON TEMP FALLS TONIGHT.


If you still visit your blog I thought you'd be amused. Or dismayed.



So prospects now behave like radiating bodies and
affect temperatures??!! :-)

To paraphrase (all too often) my english teachers of the early 70s

"We're going to need a bigger red pen!"

Just to be clear this is directed to JAX, not DonnieBwkGA
Member Since: February 1, 2012 Posts: 17 Comments: 1721
60. DonnieBwkGA
8:29 PM GMT on January 24, 2014
From the Jacksonville wx discussion on the afternoon of January 24th, 2014.

TONIGHT...ANOTHER TRICKY FORECAST WITH THE PROSPECTS FOR INCREASED CLOUD COVER PROVIDING A BLANKET ON TEMP FALLS TONIGHT.


If you still visit your blog I thought you'd be amused. Or dismayed.
Member Since: June 29, 2013 Posts: 28 Comments: 2034
59. josF
2:06 PM GMT on January 12, 2014
Lee, I will miss your insightful commentary.
Sad to see you go.
Peace.
Member Since: August 25, 2011 Posts: 0 Comments: 60
58. georgevandenberghe
4:15 AM GMT on January 03, 2014
Quoting 57. Bruzote:
georgevandenberghe - Good thing your car started. In the winter of '93-'94 (Jan 20th) my car did NOT start after a record cold night at Walker Building (-18 F at the building). I owned a trickle charger, so I used it to charge the car battery inside Walker Bldg. My gloves were bulky, so I had to use my bare hands to disconnect the battery cable and lift out the battery. It was at 6AM. I wanted to be in bed, not in the dark touching bitterly cold car metal. At least I didn't freeze to the metal.

It's a good thing I wasn't in the Pine Barrens. Some guys went out the next (similar) night and measured -36F! Check out the obs card comments from the 21st: www.meteo.psu.edu/~wjs1/wxstn//ObsCards/1994/JAN_9 4.pdf.

I knew it was cold when the roll-up vinyl wrap for my end wrench set just cracked all over as I unravelled it. I still have that old cracked vinyl holder twenty years later! Fortunately, my fingers didn't suffer the same outcome (at least not until middle age caught up with them).



{sigh!} Some things never change!

In early January 1981 flying back from Christmas break, I tried to start my car at the State College airport. It was about -5F with wind in midafternoon. No luck and I got mild frostbite on three fingers detaching the battery to charge it inside because I also carried a charger. After the third attempt to charge it (Cold batteries charge very slowly by the way), I finally got started.

One trick to get a lot more current out of a battery.. warm it!. It also charges several times faster also.

In the DC area in 1994, I got to -5F with wind. But my cars were in good condition and I had no troubles with them. My sump pump discharge at home froze, a water main broke nearby, a glacier advanced slowly to the foundation of my house and then ran down to the sump collector and flooded it so I had to rush out and get a second pump (faster than sawing through the line and rerouting it which my wife wouldn't let me do anyway!). The ground was covered with 1.5-2" of smooth ice, even grassy areas were unwalkable! To top it off my father lost power in Waynesboro PA (actually way out in the sticks near there) and I decided I needed to go rescue him. His car fuel line was frozen so he couldn't drive out even if he had been able to get through the 2.5' of snow in his area. So I went and got him, hiking the last 200 meters to his house. I remember seeing -15F at 2PM on a bank thermometer near Waynesboro.
Member Since: February 1, 2012 Posts: 17 Comments: 1721
57. Bruzote
10:47 PM GMT on December 30, 2013
georgevandenberghe - Good thing your car started. In the winter of '93-'94 (Jan 20th) my car did NOT start after a record cold night at Walker Building (-18 F at the building). I owned a trickle charger, so I used it to charge the car battery inside Walker Bldg. My gloves were bulky, so I had to use my bare hands to disconnect the battery cable and lift out the battery. It was at 6AM. I wanted to be in bed, not in the dark touching bitterly cold car metal. At least I didn't freeze to the metal.

It's a good thing I wasn't in the Pine Barrens. Some guys went out the next (similar) night and measured -36F! Check out the obs card comments from the 21st: www.meteo.psu.edu/~wjs1/wxstn//ObsCards/1994/JAN_9 4.pdf.

I knew it was cold when the roll-up vinyl wrap for my end wrench set just cracked all over as I unravelled it. I still have that old cracked vinyl holder twenty years later! Fortunately, my fingers didn't suffer the same outcome (at least not until middle age caught up with them).
Member Since: March 1, 2013 Posts: 0 Comments: 11
56. georgevandenberghe
7:15 PM GMT on December 21, 2013
Quoting 54. Astrometeor:
Hello Lee, just wanted to let you know that I've received an acceptance letter from Penn State University to study meteorology as an undergrad.


Congratulations! I did my undergraduate work at Penn State December 1978-May 1981 after doing my first two years at VPI and losing some credits in transfer (the benefit of the classes was not lost, just the credits)


Member Since: February 1, 2012 Posts: 17 Comments: 1721
55. wxdude714
11:09 AM GMT on December 21, 2013
I have to say with tremendous thanks, thank you for all your hard work. I've loved reading your blogs and articles going back to my high school freshman days reading Weatherwise magazine. Some of those articles had me laughing and taking meteorology more seriously vs accepting buzz phases such as "frontal boundary" commonly aired on TWC.
Although no one has been able to explain to me where these #'s, shapes, pictures and drawing are coming from on satellite photos and the subsequent collapse of precipitation, I have to say I've done some deep research into the matter and it revolves around the KH series of satellites in the early 80's particularly Ops 2849 as it's starting point.
In the Aug/Sept 1996 issue of Weatherwise you wrote an article called "Plain Geometry"...if you still think I'm nuts examine Figure #1 Sat photo 15:15Z 5/28/96 and pay attention to what is over Southwestern VA...the initials "RWL" are clearly present. These are the signatures I'm referring too...these are clearly man made and created not by changing of scale. They appeared frequently over tropical disturbances in the Atlantic last hurricane season with a sudden rapid decrease in convection. There's a clear smoking gun here...
Your my favorite meteorologist of all time and I wish my parents had the money to send me to Penn State in 1999-2001...It would have been an honor to be in one of your classes.

Sincerely,
Paul Harris
Member Since: October 9, 2010 Posts: 0 Comments: 22
54. Astrometeor
12:18 AM GMT on December 21, 2013
Hello Lee, just wanted to let you know that I've received an acceptance letter from Penn State University to study meteorology as an undergrad.
Member Since: July 2, 2012 Posts: 100 Comments: 10234
53. 24hourprof
6:11 PM GMT on December 18, 2013
Quoting 51. auburn:
Sure gonna miss your blog,always informative and detailed.
Wishing you the best and thank you!!!


Many, many thanks for your kind words.

Best,

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
52. 24hourprof
6:11 PM GMT on December 18, 2013
Quoting 50. beell:
Morning, Lee
...And I just knew that at some point you would tackle diffluence/divergence. I shall remain forever ignorant and it's all your fault...
:)


LOL!!!

It's on my list!!!!!

Thanks for everything.

Best,

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
51. auburn (Mod)
4:59 PM GMT on December 18, 2013
Sure gonna miss your blog,always informative and detailed.
Wishing you the best and thank you!!!
Member Since: August 27, 2006 Posts: 546 Comments: 50598
50. beell
1:32 PM GMT on December 18, 2013
Morning, Lee
...And I just knew that at some point you would tackle diffluence/divergence. I shall remain forever ignorant and it's all your fault...
:)
Member Since: September 11, 2007 Posts: 142 Comments: 16496
49. 24hourprof
1:24 PM GMT on December 18, 2013
Quoting 48. Skyepony:
Lee~ Your blogs are going to be really missed.. I do hope you will fill in for Jeff if he calls on you. Few has been able to fill that space in his absence like you have.


Very, very kind. Thanks so much.

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
48. Skyepony (Mod)
3:49 AM GMT on December 18, 2013
Lee~ Your blogs are going to be really missed.. I do hope you will fill in for Jeff if he calls on you. Few has been able to fill that space in his absence like you have.
Member Since: August 10, 2005 Posts: 162 Comments: 37822
47. 24hourprof
8:23 PM GMT on December 17, 2013
Quoting 45. Barefootontherocks:
What...? What? I second DocNDswamp @29.
I will miss your blogs, Lee. The detailed explanations and the time and patience you gave to wu members are much appreciated.

Wish you the best, and, like DocSwamp, I hope you have the time/inclination to write a blog once in a while.


You are very kind to say that. I already miss blogging. My days seem empty.

Take care.

And thanks for everything!

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
46. 24hourprof
8:22 PM GMT on December 17, 2013
Quoting 44. redseatrough:


i will miss you a lot,fan of your nice blogs from Persia!


Thanks so much. You are very kind.

Best,

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
45. Barefootontherocks
6:22 PM GMT on December 17, 2013
What...? What? I second DocNDswamp @29.
I will miss your blogs, Lee. The detailed explanations and the time and patience you gave to wu members are much appreciated.

Wish you the best, and, like DocSwamp, I hope you have the time/inclination to write a blog once in a while.
Member Since: April 29, 2006 Posts: 152 Comments: 18563
44. redseatrough
3:56 PM GMT on December 17, 2013
Quoting 41. 24hourprof:


That's a great idea. I think Chris looked at that event, so take a look at his most recent blog (I posted my last blog at WU last week).

Best,

Lee


i will miss you a lot,fan of your nice blogs from Persia!
Member Since: March 25, 2013 Posts: 0 Comments: 3
43. 24hourprof
5:42 PM GMT on December 16, 2013
Quoting 42. wvjohn123:
Thanks you so much for your blogs! I'm and long time lurker/learner at WU and I've really enjoyed your blogs and learned a lot from them. Best of luck in whatever you do next!


Many thanks and much appreciated.

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
42. wvjohn123
2:00 PM GMT on December 16, 2013
Thanks you so much for your blogs! I'm and long time lurker/learner at WU and I've really enjoyed your blogs and learned a lot from them. Best of luck in whatever you do next!
Member Since: August 23, 2010 Posts: 0 Comments: 20
41. 24hourprof
1:30 PM GMT on December 16, 2013
Quoting 38. redseatrough:
Hi dear Professor Grenci,would you please take a look at Alexa snow storm in the middle east and publish an analysis about that in your blog?,we had about 40-50 inches of snow in western parts of iran!thanks a lot


That's a great idea. I think Chris looked at that event, so take a look at his most recent blog (I posted my last blog at WU last week).

Best,

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
40. 24hourprof
1:29 PM GMT on December 16, 2013
Quoting 37. trHUrrIXC5MMX:
Lee, you were given the privilege many times to write the main blog to which most of us go everyday. Like the main highway all cars from all roads come to get on to to get to their far away destination

Im very thankful for having you here to guide us. I won't forget the retired senior lecturer and forecaster, the only one, to have ever taken the time to quote me back.
I felt so privileged.

We will miss you. Have a great time out there whereever you are and wherever you go

- Max


Many, many thanks, Max.

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
38. redseatrough
9:27 AM GMT on December 16, 2013
Hi dear Professor Grenci,would you please take a look at Alexa snow storm in the middle east and publish an analysis about that in your blog?,we had about 40-50 inches of snow in western parts of iran!thanks a lot
Member Since: March 25, 2013 Posts: 0 Comments: 3
37. trHUrrIXC5MMX
12:25 AM GMT on December 16, 2013
Lee, you were given the privilege many times to write the main blog to which most of us go everyday. Like the main highway all cars from all roads come to get on to to get to their far away destination

Im very thankful for having you here to guide us. I won't forget the retired senior lecturer and forecaster, the only one, to have ever taken the time to quote me back.
I felt so privileged.

We will miss you. Have a great time out there whereever you are and wherever you go

- Max
Member Since: April 23, 2011 Posts: 104 Comments: 14873
36. 24hourprof
2:27 PM GMT on December 15, 2013
Quoting 32. georgevandenberghe:
I hope you'll post relevant comment on other blog threads particularly Jeff Masters' where the weather watchers seem to group. I'll look forward to it.



George,

It's like when I retired from competitive softball...I didn't like going back to the field because I didn't trust myself not to play again.

:-)
Member Since: October 24, 2012 Posts: 91 Comments: 803
35. 24hourprof
2:25 PM GMT on December 15, 2013
Quoting 33. DocNDswamp:
Lee,
You do realize, once you've joined Wunderground it's kinda like da Mafia... or Hotel California - you can check out but never really leave!
;)


LOL!!!
Member Since: October 24, 2012 Posts: 91 Comments: 803
34. DocNDswamp
8:22 PM GMT on December 14, 2013
re: 12. georgevandenberghe 8:51 PM CST on December 12, 2013
Quoting georgevandenberghe:
On the topic of clear air ice crystals I remember a 2" gentle snowfall in January 1979 at PSU where the moon was hazily visible throughout and the sky looked milky but not cloudy. The ice crystals were condensing out of only very thinly cloudy air. It was a cold storm, but I don't remember 850mb temps. It was my fifth or sixth week at PSU and I started tracking 850mb temps about a month later.


George, thanks for all your contributions here too!
Always informative...

re: 850 mb temps.
You probably have access to other sources but one I use is Plymouth State's Upper Air Archive Data 1957-1998... and 1999 to Present... several available variables and multi regional mapping options. A caveat or so, have noted dubious projections / artifacts at times over data-sparse oceanic regions... and sometimes wrong projection loads, re-click.

Compared my local wx data (SE LA) for January '79 coldest period, might that have been Jan 2-3 event that you recall? Plymouth data charts of Southeast region indicate 850 mb isotherms to -10C nosing in over N FL by 0Z 3rd. On related note, seems infrequently we have 850 mb temps at or exceeding -10C encompass Louisiana and dig well down over the N Gulf, i.e. Dec 1983 and '89. Another date with very cold 850 mb anomalies (for Louisiana, to -15C) was Mar 2-3 1980 - set March all-time record low 23F here (Houma, 29.6N 90.7W). And of course, Superstorm '93 is incredible evolution to review, the values by 0Z 14th are insane.

EDIT: LOL, just realized after all that, you were talking about Penn State, NOT Tallahassee / FSU!
My bad...
Member Since: September 21, 2005 Posts: 94 Comments: 4794
33. DocNDswamp
8:17 PM GMT on December 14, 2013
Lee,
You do realize, once you've joined Wunderground it's kinda like da Mafia... or Hotel California - you can check out but never really leave!
;)
Member Since: September 21, 2005 Posts: 94 Comments: 4794
32. georgevandenberghe
4:19 PM GMT on December 14, 2013
I hope you'll post relevant comment on other blog threads particularly Jeff Masters' where the weather watchers seem to group. I'll look forward to it.

Member Since: February 1, 2012 Posts: 17 Comments: 1721
31. 24hourprof
12:43 PM GMT on December 14, 2013
Quoting 29. DocNDswamp:
Howdy Lee,
Well darn, just when I thought Friday 13th wasn't bad, reading this might be your last blog on WU just made the day a bummer... :(

That said, really appreciate the time you devoted and expertise generously shared with us here. Even more so, that you always politely acknowledged your readers, corresponded back / forth with answers, point clarity and additional (related or off topic) side notes, made for a delightful educational experience. Best meteorology blog, indeed!

Rest assured, your blog has been a must-read on my list since inception, absorbing each one. I've commented infrequently of late, but do know been reading along, looking forward to each with same interest and anticipation as did decades ago with your articles in Weatherwise... 'cept I didn't have to wait a whole month for the next installment here, lol! And you betcha, still have (and re-read) those dog-eared journals. ;)

Lee, hope you might reconsider offering an occasional blog post in the future. Yet regardless, thanks for the wealth of knowledge you've contributed!
Best wishes,
- Rand


Rand,

You're very kind. Thank you.

You never know...I might be back as a guest blogger now and then.

Take care, Rand, and thanks again.

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
30. 24hourprof
12:41 PM GMT on December 14, 2013
Quoting 28. vis0:
my self, spirit & soul thanks you - Professor.


You're very welcome! Thanks!
Member Since: October 24, 2012 Posts: 91 Comments: 803
29. DocNDswamp
6:32 AM GMT on December 14, 2013
Howdy Lee,
Well darn, just when I thought Friday 13th wasn't bad, reading this might be your last blog on WU just made the day a bummer... :(

That said, really appreciate the time you devoted and expertise generously shared with us here. Even more so, that you always politely acknowledged your readers, corresponded back / forth with answers, point clarity and additional (related or off topic) side notes, made for a delightful educational experience. Best meteorology blog, indeed!

Rest assured, your blog has been a must-read on my list since inception, absorbing each one. I've commented infrequently of late, but do know been reading along, looking forward to each with same interest and anticipation as did decades ago with your articles in Weatherwise... 'cept I didn't have to wait a whole month for the next installment here, lol! And you betcha, still have (and re-read) those dog-eared journals. ;)

Lee, hope you might reconsider offering an occasional blog post in the future. Yet regardless, thanks for the wealth of knowledge you've contributed!
Best wishes,
- Rand
Member Since: September 21, 2005 Posts: 94 Comments: 4794
28. vis0
1:26 AM GMT on December 14, 2013
my self, spirit & soul thanks you - Professor.
Member Since: December 15, 2006 Posts: 247 Comments: 420
27. georgevandenberghe
11:48 PM GMT on December 13, 2013
Quoting Lee
See...the old man still has some neurons firing!!! :-)


end quote from Lee


Sometimes I worry about my own. GWV

Stephen King once referred to the terror of memory loss as not losing memories but finding out that what you remembered just wasn't what happened.. your memory had been corrupted.
Member Since: February 1, 2012 Posts: 17 Comments: 1721
26. georgevandenberghe
10:28 PM GMT on December 13, 2013
Quoting 25. 24hourprof:


George...

There is indeed cold-air drainage into KTLH as I expected. Here's the Local Climate Data (pdf file)...scroll down to the last page and the text summary and you'll see the reference to cold-air drainage at KTLH. I think I remember now how I knew this...KTLH was once in the National Collegiate Forecasting contest.

See...the old man still has some neurons firing!!! :-)

Lee



The quote from the document is

"During the winter, topographic effects and cold
air drainage into lower elevations produce a wide
variation of low temperatures on cold, clear and
calm nights. Freezing temperatures at the airport
and surrounding suburban areas average about
thirty-six occurrences each winter, but freezing
temperatures in the city are about half that
number. Temperatures of 25 degrees or lower in the
suburban areas average about twelve times per
winter, with temperatures dropping into the teens
on occasions."

************************************************* ***************

The southern portions of the area (where the airport is) are colder
but I maintain the airport is not in a frost pocket.. the whole southern exurban region is flat and colder on radiation nights. Drainage there is kilometers in scale The northern portions are not as cold and minima are notably warmer in extreme south Georgia.

That said, the airport does run colder than surrounding stations. Those to the north have higher heat capacity soils and more relief and you don't have to go much further south before the Gulf of Mexico has local effects.

I'll look for a topographic map to see if the airport is in a bowl with too slight curvature to perceive with the naked eye. These can be colder even though they look flat. I just remember my first 29 and 28 years prior experiences in 1984 and 1985 finding that a lot of the area south of the city (including my rental garden) behaved like the airport. My own apartment next to the university was much warmer on radiation nights ( light wind nights where radiative cooling dominated the temperature forecast).

If I got this wrong I'll be embarrassed.

Note Tallahassee is the FROSTIEST place I have ever gardened with risk deep into the growing season on both ends. The April minimum in 1987 stated in the PDF document, destroyed my lettuce which was heading and of superb quality. It also destroyed tasselling corn which I try to get early wherever I live.


In 1986 there was scattered frost reported in the area on or about April 24. The airport got to 33 and stayed at 33 for several hours.
Nothing of mine froze but I heard anecdotes from locals to the west of significant garden damage. (Max temps on the 23'd and 24'th were 72 and 80. but the airmass was very dry with afternoon dewpoints on the 23'd of about 20F)


Member Since: February 1, 2012 Posts: 17 Comments: 1721
25. 24hourprof
9:29 PM GMT on December 13, 2013
Quoting 24. georgevandenberghe:


My memories are 26 years old but I do not remember any relief features at the station. It is just flat. My memories of trees are hazy but I think it was widely spaced palmetto and pine and mostly grass and sparse shrubs. Just to the north one finds typical eastern deciduous woodland trees (color season is thanksgiving to early December) but they aren't as lush as in more temperate regions. I used to say in spring that when they leafed out they looked like we feel when awakened at 3AM after not going to bed till midnight. It's not a rapid lush green burst forth like in our regions.


George...

There is indeed cold-air drainage into KTLH as I expected. Here's the Local Climate Data (pdf file)...scroll down to the last page and the text summary and you'll see the reference to cold-air drainage at KTLH. I think I remember now how I knew this...KTLH was once in the National Collegiate Forecasting contest.

See...the old man still has some neurons firing!!! :-)

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
24. georgevandenberghe
2:34 PM GMT on December 13, 2013
Quoting 23. 24hourprof:


Yep. I'm not surprised, George. Sandy soil is key to dramatic nocturnal cooling on clear, calm nights. Thanks for the lesson!


My memories are 26 years old but I do not remember any relief features at the station. It is just flat. My memories of trees are hazy but I think it was widely spaced palmetto and pine and mostly grass and sparse shrubs. Just to the north one finds typical eastern deciduous woodland trees (color season is thanksgiving to early December) but they aren't as lush as in more temperate regions. I used to say in spring that when they leafed out they looked like we feel when awakened at 3AM after not going to bed till midnight. It's not a rapid lush green burst forth like in our regions.
Member Since: February 1, 2012 Posts: 17 Comments: 1721
23. 24hourprof
2:01 PM GMT on December 13, 2013
Quoting 22. georgevandenberghe:

KTLH is in a flat sandy region with scrubby vegetation and no trees. It is more typical of the area than most people realize. It is far enough from town though that there is no heat island effect. I had a garden plot a few miles away that had similar nighttime temperatures. The transition from sand to clay occurs just north of town and vegetation is more developed there. Soils are often very dry also in spring and late fall with a bimodal rain distribution in winter and (especially) summer. KTLH is to the southwest of town.


Yep. I'm not surprised, George. Sandy soil is key to dramatic nocturnal cooling on clear, calm nights. Thanks for the lesson!
Member Since: October 24, 2012 Posts: 91 Comments: 803
22. georgevandenberghe
1:52 PM GMT on December 13, 2013
Quoting 20. 24hourprof:


George,

As I recall, isn't KTLH in sort of a "hole" so that there's a lot of cold-air drainage? Also, the type of soil makes a big difference. If I remember correctly, the soil at the Barrens is rather sandy.

And, yes, fresh snow is key. The night I went out to the Barrens came in the immediate aftermath of a February snowstorm, so the snow cover was quite fresh (and quite deep).

I hope I remember right; it's been 26 years but I remember KTLH being in a flat sandy region with scrubby vegetation and no trees (tree density is something I don't remember for sure). It is more typical of the area than most people realize. It is far enough from town though that there is no heat island effect. I had a garden plot a few miles away that had similar nighttime temperatures. The transition from sand to clay occurs just north of town and vegetation is more developed there. Soils are often very dry also in spring and late fall with a bimodal rain distribution in winter and (especially) summer. KTLH is to the southwest of town. And yes that low heat capacity dry sand makes it very cold on dry nights.
Member Since: February 1, 2012 Posts: 17 Comments: 1721
21. 24hourprof
1:36 PM GMT on December 13, 2013
Folks,

I added the relevant meteogram at International Falls so you can get another perspective of what occurred.

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
20. 24hourprof
1:10 PM GMT on December 13, 2013
Quoting 11. georgevandenberghe:


"Two inches of snow" was not often relevant in TLH.

I also learned most stuff in nature is close to black in infrared and about the insulating property of snow and have noted that freshness of the cover is also important since a fresh snow cover has more insulating air in between the crystals and conducts much less. I took a few trips out to the barrens in summer to observe the vegetation but stayed away in winter. If I'd spent a second summer at PSU I would have experimented with frost hardy plants in large containers out there.. visited and observed perhaps weekly. My student colleagues who did go in winter also were careful not to turn off their cars. One observed on a -34F night (-10F at Walker) that he could not maintain engine temperature.. the indicator dial just sank to C. (I suspect though he had a stuck thermostat). My own car was very reliable at -17C. It would reliably not start unless I warmed the battery. This again was not an issue at FSU.



George,

As I recall, isn't KTLH in sort of a "hole" so that there's a lot of cold-air drainage? Also, the type of soil makes a big difference. If I remember correctly, the soil at the Barrens is rather sandy.

And, yes, fresh snow is key. The night I went out to the Barrens came in the immediate aftermath of a February snowstorm, so the snow cover was quite fresh (and quite deep).
Member Since: October 24, 2012 Posts: 91 Comments: 803
19. 24hourprof
1:05 PM GMT on December 13, 2013
Quoting 15. Some1Has2BtheRookie:
Lee, I certainly hate see this blog come to an end. I have learned much from you and I certainly appreciate the efforts that you have taken here. Thanks to you we have been able to better our knowledge on the subject. We will miss your lessons and I hope that you return to do guest blogs from time to time? (Sure you will. Where else can party with the crazies and still not end up being crazy yourself?)

Mike


Mike,

Thank you. You always asked perceptive, great questions, and I will miss being challenged to explain the science you sought to learn.

Thanks for everything.

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
18. 24hourprof
1:04 PM GMT on December 13, 2013
Quoting 14. Astrometeor:
Woah. You're leaving WU Lee? Is that even legal? What are you going to do now? I have a million questions!

:( Thanks for your teachings Lee, your short time spent here has made such a tremendous impact on everyone here, thanks for everything!

Well wishes to you and your future,
-Nathan


Nathan,

Thank you. I will sorely miss our discussions. I always had a few readers I was always hoping would reply, and you were one of them.

Many, many thanks.

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
17. 24hourprof
1:02 PM GMT on December 13, 2013
Quoting 13. beell:
Lee,
I will sorely miss the "finest weather blog on the internet" but am thankful for the meteorological treasures you brought us here over the last year.

This is bad news for a weather geek!

I have revisited many of your previous blogs on more than one occasion. Each re-read brought a better understanding of the subject presented. As long as you and WU allow, I will continue to visit your blogs. So in a sense, "Here endeth the lesson" is incorrect.

If the mark of a great writer and/or teacher is to "leave 'em wanting more", you have succeeded in my estimation.

Thanks, and best wishes. Give us a guest appearance here and there if you can.


Very, very kind. Thank you. Your comments mean a great deal to me.

Thanks again.

Lee
Member Since: October 24, 2012 Posts: 91 Comments: 803
16. georgevandenberghe
5:20 AM GMT on December 13, 2013
More evidence of temperatures crashing through the dew point. On calm clear nights with a shallow moist layer and dewpoints somewhat above the melting point, a lot of dew will deposit as dewdrops on exposed surfaces. As cooling continues more dew will deposit and eventually the dew will freeze as a solid clear layer of ice. Frost then deposits on top of this layer. I've seen over a mm of dew deposit this way before it freezes and frost starts depositing.
Member Since: February 1, 2012 Posts: 17 Comments: 1721
15. Some1Has2BtheRookie
5:08 AM GMT on December 13, 2013
Lee, I certainly hate see this blog come to an end. I have learned much from you and I certainly appreciate the efforts that you have taken here. Thanks to you we have been able to better our knowledge on the subject. We will miss your lessons and I hope that you return to do guest blogs from time to time? (Sure you will. Where else can party with the crazies and still not end up being crazy yourself?)

Mike
Member Since: August 24, 2010 Posts: 0 Comments: 4737
14. Astrometeor
4:55 AM GMT on December 13, 2013
Woah. You're leaving WU Lee? Is that even legal? What are you going to do now? I have a million questions!

:( Thanks for your teachings Lee, your short time spent here has made such a tremendous impact on everyone here, thanks for everything!

Well wishes to you and your future,
-Nathan
Member Since: July 2, 2012 Posts: 100 Comments: 10234
13. beell
3:27 AM GMT on December 13, 2013
Lee,
I will sorely miss the "finest weather blog on the internet" but am thankful for the meteorological treasures you brought us here over the last year.

This is bad news for a weather geek!

I have revisited many of your previous blogs on more than one occasion. Each re-read brought a better understanding of the subject presented. As long as you and WU allow, I will continue to visit your blogs. So in a sense, "Here endeth the lesson" is incorrect.

If the mark of a great writer and/or teacher is to "leave 'em wanting more", you have succeeded in my estimation.

Thanks, and best wishes. Give us a guest appearance here and there if you can.
Member Since: September 11, 2007 Posts: 142 Comments: 16496

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Retired senior lecturer in the Department of Meteorology at Penn State, where he was lead faculty for PSU's online certificate in forecasting.

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