Unsettled weather on the horizon...

By: Zachary Labe , 9:33 PM GMT on July 14, 2010

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After a period of dry weather and near term isolated drought conditions, a recent change in the jet stream pattern has aided in a relocation of the heat ridge allowing for cold fronts to penetrate across the northern Middle Atlantic and washing out to the south in Virginia. 500mb analysis indicates a relocation of the Bermudian high slightly farther south and east in the Atlantic. But above normal temperatures will continue across the region courtesy of global abnormal thermal heights. Cold air is very absent across much of the globe, especially in the north Arctic where sea ice conditions are down at a record negative pace.

The upcoming pattern will continue favor above normal temperatures, but slightly enhanced precipitation in the rainfall department courtesy of an anomalous flow out of the Gulf of Mexico. Recent heavy rain during the past three days is courtesy of enhanced PWATs originating from the south with a near +2SD. SREF guidance quickly pinpointed to the higher 700mb moisture anomalies several days in advance of the heavy rain. Local groundwater conditions continued to heed below normal values especially in localized areas across northcentral Maryland and parts of the middle Susquehanna Valley in Pennsylvania where drought conditions on the Palmer Index entered D1. With soil moisture anomalies well below normal, the threat of flash flooding actually increases as the water washes quick away into urban areas and is not allowed to soak into the ground. FFG at the time was a general 4in/12hr across much of the state, but global model guidance indicated a heavy rain threat several days in advance. GFS meteograms for KMDT indicated nearly 1.5in of rain with local 4km WRF output near 6in for parts of southeastern Pennsylvania, likely courtesy of convective error. Monday, 14 July 2010, produced an interesting weather day across much of central Pennsylvania where near stationary convection developed on an axis of instability on a surface front ahead of the general cold front. PWATs near 2in with CAPE values near 2000j/kg produced a complex of thunderstorms on the leeward side of the Alleghanies with a general storm track and momentum to the east-northeast at 75degrees.

30knot wind shear 0-6km aloft allowed high echo tops from thunderstorms to bring down some higher wind gusts. Widespread wind damage was reported along a narrow corridor along the lower and middle Susquehanna River. General damage reports were courtesy of wet downbursts and straightline winds. Heavy rainfall rates were also reported ranging from 4-7in/hr for short periods of time courtesy of tapping into near tropical air aloft in the lower troposphere. Rainfall totals from the training thunderstorms were reported ranging from 1-4in. These complexes of thunderstorms later tracked into eastern Pennsylvania, but in a slow general weakening state by evening.

As the potent upper level trough lifts out of the region, the general shortwave will move offshore. Taking a near tropical depression outlook on local satellite imagery, the deformation axis of precipitation will move offshore by Wednesday evening with additional QPF generally .1in for eastern Pennsylvania. High pressure will return with an anti-cyclonic flow, but the airmass has non-polar origins therefore continuing the above normal temperature pattern. As the 1020mb high pressure moves offshore by Thursday evening, the clear skies featured on Thursday will be invaded by higher cirrus by 6z Friday. 2m temperatures look to be a general 90-95F for most locations in Pennsylvania, Maryland, and Delaware below 1000ft. Across the higher elevations such as the Laurels, Poconos, and Northwest highs will be a less salty 80-85F.

12z 7/14/10 GFS indicates an approaching cold front by Friday as a 1004mb low pressure moves through Ontario. A bubble of higher H85 thermals near 20C will center over the northern Middle Atlantic for Friday with very warm temperatures topping well over 90F for most locations outside the higher elevations. Southern urban locations such as Washington DC will feature highs in the upper 90s with widespread haze and poor air quality. 2m dewpoints are estimated to be regionwide in the 70s for a very oppressive day. Heat indices will approach 100-110F during the 11am-4pm heat of the day.

NAM/GFS QPF fields indicate the highest probability of rain occuring in northwestern portions of Pennsylvania. Increasing SBCAPE Friday afternoon near 2000j/kg with winds aloft near 40knots will allow for stronger convection to accompany the front in broken lines. EHI values approach 1-2 will also allow for the threat for a few rotating low levels in the strong thunderstorms. The highest threat for severe weather on Friday exists for northwestern Pennsylvania, but as convection seeps southwards Friday night, isolated wind damage may still occur as far south as northern Maryland. Not all areas will receive rain with southern areas progged at below .1in QPF. The latest 7/14/10 18z NAM remains especially dry for areas south of I-80.

Of interesting note, the GFS has recent gone under a major upgrade and this will take effect in the coming week. First expected to debut in June, recent delays in enhancing resolution has caused a slight later date.

TECHNICAL IMPLEMENTATION NOTICE 10-15
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
853 AM EDT FRI APR 2 2010

EFFECTIVE JUNE 22 2010...BEGINNING WITH THE 1200 COORDINATED
UNIVERSAL TIME /UTC/ RUN...THE NATIONAL CENTERS FOR
ENVIRONMENTAL PREDICTION /NCEP/ WILL UPGRADE THE GLOBAL
FORECAST SYSTEM /GFS/. THE RESOLUTION OF THE GLOBAL FORECAST
MODEL WILL BE INCREASED FROM T382 /35 KM/ TO T574 /27 KM/.
THE HIGH RESOLUTION PORTION OF THE FORECAST WILL BE EXTENDED
FROM 180 HRS TO 192 HRS. WITH THIS EXTENSION 3 HOURLY OUTPUT
WILL BE MADE AVAILABLE OUT TO 192 HOURS... Link.

A seconday cold front is progged by latest GFS to move across the northern Middle Atlantic and wash out over northern Maryland. This will allow for another day of convection, some of which could be severe. Strong areas of lift in the right front entrance of the low level jet will allow for higher winds aloft to be reached by strong thunderstorm echo tops. Highs will once again reach 90F for many areas outside the higher elevations, but will be 4-6F cooler than Friday. Humidity levels remain high with PWATs near 2.0in. Models diverge on solutions for the beginning of next week, with the ECMWF bringing the cold front boundary northward as a warm front as early as Sunday with accompanying showers, but the GFS delays this northward progression. In any case unsettled conditions will continue through the middle of next week with a boundary located over the northern Middle Atlantic. This will allow for daily diurnal convection and accompanying threats of flash flooding. Meanwhile the fast zonal jet streamal flow will promote a rapid progression of a strong shortwave early next week across the northern tier. For now this ring of fire looks to be north of the northern Middle Atlantic, but details remain uncertain. At this time, it appears the threat of a widespread wind damage outbreak from a derecho is possible across the northern tier United States. SPC already highlighting the threat in their long term outlook...

ZCZC SPCSWOD48 ALL
ACUS48 KWNS 140850
SPC AC 140850

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0350 AM CDT WED JUL 14 2010

VALID 171200Z - 221200Z

...SEVERE WEATHER EPISODE FROM THE NRN PLAINS ACROSS THE GREAT LAKES
AND INTO THE NERN STATES POSSIBLE DAYS 4-6...

MEDIUM RANGE GUIDANCE IS COMING INTO BETTER AGREEMENT MOVING A SHORT
WAVE TROUGH RAPIDLY EWD ACROSS THE NRN TIER OF A STATES FROM ND
ACROSS THE GREAT LAKES AND TOWARD NEW ENGLAND DURING DAY 4 /JUL 17/
THROUGH DAY 6 /JUL 19/. LATEST SEVERAL RUNS OF THE GFS AND ECMWF
SHOW QUITE SIMILAR TIMING AND AMPLITUDE OF THE SYSTEM...AND ARE
CONSISTENT WITH THE 12Z ECMWF ENSEMBLE MEAN SOLUTIONS. STRONG LOW
AND MID LEVEL JETS ARE FORECAST TO TRANSLATE EWD IN ASSOCIATION WITH
THE FAST MOVING FRONTAL SYSTEM...WITH GUIDANCE INDICATING AMPLE LOW
LEVEL MOISTURE/INSTABILITY AND STRONG VERTICAL SHEAR ACCOMPANYING
THE SYSTEM. SEVERE STORMS ARE EXPECTED TO DEVELOP DURING DAY 4 /JUL
17/ OVER THE ERN DAKOTAS AND SPREAD EWD ACROSS THE UPPER MS
VALLEY...WITH THE SYSTEM CONTINUING EWD ACROSS THE GREAT LAKES AREA
ON DAY 5 /JUL 18/. BY DAY 6 /JUL 19/ THE CONVECTIVE SYSTEM IS
EXPECTED TO CONTINUE EWD ACROSS PARTS OF THE NERN STATES. OVERALL
JET PATTERN SUGGESTS POTENTIAL FOR A MORE WIDESPREAD DAMAGING WIND
EVENT DURING THIS PERIOD ALTHOUGH IT IS TOO EARLY TO PROVIDE DETAILS
OF THE CONVECTIVE EVOLUTION.

For the time being the excessive dry and hot weather will remain absent from the northern Middle Atlantic allowing for a more active weather pattern to resume. Heavy rain and near term flash flooding will be primary threats in the coming seven days. Recent Mt. Holly rainfall analysis indicates excessive rainfall over much of the eastern half of the northern Middle Atlantic.

Heavy rains have also impacted the Philadelphia metropolitan region...
As of 5 PM... Philadelphia International Airport reported nearly 3 inches of rain today... 2.88 inches to be exact... most of that occurring in a 2 hour period this afternoon.
A quick recap for the forecast for the coming few days across most areas in the northern Middle Atlantic...

Thursday- General sunshine with high pressure dominating, but temperatures remain mild in the lower 90s.
Friday- A shortwave and accompanying cold front approach from the northwest with an increase in humidity and heat. Thunderstorms are also possible over the region with the highest threat during the late afternoon over northwestern Pennsylvania. A few storms may be severe. Highs in the mid 90s.
Saturday- A seconday cold front approaches with more showers and thunderstorms with mostly cloudy skies and highs in the upper 80s to low 90s.
Sunday- Chance of spotty showers/thunderstorms with mostly cloudy skies and highs in the 80s.

Regional updating radar...


"Here north of Harrisburg 2010 statistics"
(Severe Weather Stats...)
Severe Thunderstorm Watches- 6
Severe Thunderstorm Warnings- 7
Tornado Watches- 1
Tornado Warnings- 0
Total Thunderstorms- 13

(Precipitation Stats...)
Flood Watches- 3
Flood Warnings- 1
Monthly Precipitation- 4.09inches
Yearly Precipitation- 21.19inches

(Temperature Stats...)
Heat Advisories- 2
Excessive Heat Warnings- 0
90degree days- 22
Highest Temperature- 101F (x2)

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86. TheRasberryPatch
7:21 PM GMT on July 20, 2010
i got 0.12" from that shower. at least we are getting some rain to help with the grass. i still have at least 1/3 of my yard that is still brown
Member Since: January 26, 2007 Posts: 72 Comments: 6255
85. originalLT
6:42 PM GMT on July 20, 2010
Oh well, I over-estimated again!
Member Since: January 31, 2009 Posts: 0 Comments: 7451
84. Zachary Labe
6:29 PM GMT on July 20, 2010
.16in of rain here from today. New blog coming today!
Member Since: December 14, 2007 Posts: 282 Comments: 15099
80. originalLT
3:54 PM GMT on July 20, 2010
Blizz looks like your area is being hit by some pretty good showers or storms right now. I'm going to guess you'll get about 1/3" or so from this cluster!
Member Since: January 31, 2009 Posts: 0 Comments: 7451
79. goofyrider
2:26 PM GMT on July 20, 2010
Post 78

PWS @ Bradley Beach shows a wind gust +/- 40 mph about 1030 yesterday not good for anyone sailing
Member Since: February 27, 2009 Posts: 0 Comments: 2743
76. TheRasberryPatch
2:17 AM GMT on July 20, 2010
Hoy....for my Droid i have weatherbug....it's ok. the radar doesn't move. if you have the iphone wunderground has an app.
Member Since: January 26, 2007 Posts: 72 Comments: 6255
75. Hoynieva
1:21 AM GMT on July 20, 2010
Yeah, seeing some pretty lightning from out my window as well. I'm hoping one of those cells pass over us, but i've hoped that a lot this summer and it rarely happens.

Does anyone use weather apps for their phone? I was just wondering what you guys find to be a good quality app worth paying for, as I've never paid for an app yet. I'd do it if it's got high quality maps and radar which are up to date.
Member Since: January 20, 2009 Posts: 0 Comments: 1503
73. originalLT
11:42 PM GMT on July 19, 2010
Nice to see PalmyraP. around, its like reverse hybernation with him!
Member Since: January 31, 2009 Posts: 0 Comments: 7451
72. originalLT
11:30 PM GMT on July 19, 2010
Hey Zotty, looks like you really got "clocked" by that 7-7:30pm storm!
Member Since: January 31, 2009 Posts: 0 Comments: 7451
71. pittsburghnurse
11:23 PM GMT on July 19, 2010
Quoting TheRasberryPatch:
P451 - i have one for you that used to be on tv way back and it was a public service annoucement..."It's 11PM...do you know where your children are?"


Haha now you're really bringing me back.
Member Since: October 14, 2006 Posts: 1 Comments: 639
70. goofyrider
10:48 PM GMT on July 19, 2010
Check out the ft dix radar

look at the Heat Lightning in advance of the front
Member Since: February 27, 2009 Posts: 0 Comments: 2743
69. PalmyraPunishment
7:38 PM GMT on July 19, 2010
Zotty, no it doesn't mean that lol. It just means that I found a few minutes to post. I've said on here multiple times, Summer is a time when I tend to back away from a computer (aside from work, and all) and it's rare that I post here. I do read the blog regularly, just don't post.

Don't sweat it... it's still July. And it's still too hot.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
68. zotty
7:35 PM GMT on July 19, 2010
Quoting PalmyraPunishment:


They used that one last night on Fox 10 news. Only replacing 11:00 PM with 10:00 PM.


PP! Whats happening? Does your presence mean there is only six more months before our first winter storm?

P451- The storm did look like it was rotating. Is that of particular significance?
Member Since: August 19, 2009 Posts: 0 Comments: 729
67. PalmyraPunishment
7:15 PM GMT on July 19, 2010
Quoting TheRasberryPatch:
"It's 11PM...do you know where your children are?"


They used that one last night on Fox 10 news. Only replacing 11:00 PM with 10:00 PM.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
66. TheF1Man
6:34 PM GMT on July 19, 2010
LT i obviously had those same 2 rounds and probably got around the 1 inch mark which was really good for the grass, etc. During the first round the thunder was so loud and the storm so violent, the china in one of the cabinets was shaking, i couldn't believe it. i'm not sure how we didn't lose power.

no im not exaggerating...
Member Since: February 23, 2010 Posts: 0 Comments: 676
65. TheRasberryPatch
6:30 PM GMT on July 19, 2010
P451 - i have one for you that used to be on tv way back and it was a public service annoucement..."It's 11PM...do you know where your children are?"

Blizz - it looks like we might be getting a pop-up if it holds together
Member Since: January 26, 2007 Posts: 72 Comments: 6255
62. originalLT
4:21 PM GMT on July 19, 2010
Hi Zotty, yeah, I think you are right, but Blizz could explain that. Conditions must be very good for those storms to survive overnight or in the early morning, since they don't have any heating by the sun for energy. I got two rounds, first was the strongest, 0.70" and lots of lightning around9AM, thenanother round, heavy downpour but no lightning at about 11AM. Total from that one 0.30". Grand total 1".
Member Since: January 31, 2009 Posts: 0 Comments: 7451
61. zotty
3:05 PM GMT on July 19, 2010
Hey Blizz- I like the more frequent and shorter blogs. Thanks!

Driving to work (White Plains NY) today I looked west and saw a line, or more like a wall many thousands of feet high, stretching clear across the western horizon. I don't think I've seen anything like it before, and that includes some time at sea. We had a great deal of lightning, but no hail, though I understand there were reports of hail in the area.

Those storms that last through the night into the morning always seem to have a lot of punch. Am I imaging things, or is there something to that?
Member Since: August 19, 2009 Posts: 0 Comments: 729
60. Zachary Labe
1:24 PM GMT on July 19, 2010
Thanks all! Nice storm here this morning just before 5am with about .42in of rain. More widespread storms are likely today with a few storms severe.
Member Since: December 14, 2007 Posts: 282 Comments: 15099
59. TheRasberryPatch
1:19 PM GMT on July 19, 2010
that's a pretty neat saying goofyrider.

P451 - I am a bit older at 48 and had very similar channels living just north of Baltimore, I consider myself kind of lucky when it came to tv. we could watch Baltimore and DC programming. both network channels and DC had 2 independents with Baltimore having 1 independent and of course they each had a PBS that was on a couple different frequencies. Then on a good night you could tune in a channel from West Virginia or farther. I can remember my dad spinning the UHF dial slowly to fine tune a channel and in a somewhat clear channel watch bullfights.
Member Since: January 26, 2007 Posts: 72 Comments: 6255
58. originalLT
1:01 PM GMT on July 19, 2010
Great call Blizz about the morning T.Storms, we are getting one now, NONE of the locals called for this last night, they just said afternoon and evening storms.
Member Since: January 31, 2009 Posts: 0 Comments: 7451
57. goofyrider
12:39 PM GMT on July 19, 2010
Back in Spring Lake

Found this in an article by KC Heidorn

An old folk saying goes:

"Yeller gal, Yeller gal, flashing through the night, Summer storms will pass you, unless the lightning's white."
Member Since: February 27, 2009 Posts: 0 Comments: 2743
53. TheRasberryPatch
11:32 AM GMT on July 19, 2010
thanks for the heads up Blizz. i got 0.36" from the thunder storm. the lightning was not near me though. most of the thunder was not loud and seconds from the lightning
Member Since: January 26, 2007 Posts: 72 Comments: 6255
52. TheRasberryPatch
11:22 AM GMT on July 19, 2010
P451 - you have to remember it hasn't been that long before tv was introduced as well as radar and other technology for the weather. a lot of baby boomers grew up with people calling what you described as heat lightning. I would guess that was a term passed down through the ages. You just can't change the terminology just like that, overnight especially with people that are content with getting their weather info from the local mets
Member Since: January 26, 2007 Posts: 72 Comments: 6255
51. originalLT
4:30 AM GMT on July 19, 2010
Just looked it up, Wikipedia calls it "dry lightning", what I just mentioned.
Member Since: January 31, 2009 Posts: 0 Comments: 7451
50. originalLT
4:22 AM GMT on July 19, 2010
Hi P451, have to admit growing up I used that term too untill I realized that there isn't such a thing! Lightning is produced from a T. Storm so its raining somewhere. But in the SW especially, I do believe there can be a thunder storm with very little rain reaching the ground, it evaporates as it is falling, so in a sense its like the dreaded term 'Heat Lightning"! Please comment if I am wrong.
Member Since: January 31, 2009 Posts: 0 Comments: 7451
48. baxtheweatherman
9:57 PM GMT on July 18, 2010
On the turnpike coming back from Pittsburgh last night (like 12:30 to 2am), I watched lighting out the window to the north. Then moving up I-99, the show really began. It constantly was streaking across the sky and I was sure that it was raining at home but it wasn't when we arrived. Later we got a sprinkle, which was very disappointing due to the incredible amount of lighting.
Member Since: December 31, 2007 Posts: 0 Comments: 118
47. Zachary Labe
1:47 PM GMT on July 18, 2010
Chance of severe weather later tonight. Storms may form late tonight with impressive dynamics over western Pennsylvania and track into eastern Pennsylvania possibly in the early morning hours.
Member Since: December 14, 2007 Posts: 282 Comments: 15099
45. Zachary Labe
1:54 AM GMT on July 18, 2010
TheRasberryPatch- La Nina temperatures correlations are usually mild winters and cooler summers. Spring and Fall are typically variable with loose if any correlations. Now this summer will rank in the top warmest most likely for several eastern cities, but that is due to the lingering effects of one of the strongest El Ninos since 1998.

wxgeek723- I'll be honest, hahaha, I have done little winter preparation forecasts. I have looked up zero analogs at this time. The only thing I have been tracking is the southern osciallation, a few global teleconnections, and upstream blocking. But I have not begun to link any pieces to the puzzle yet.
Member Since: December 14, 2007 Posts: 282 Comments: 15099
44. wxgeek723
1:45 AM GMT on July 18, 2010
One more question Blizz. Do you know of any analog winters that paint a better picture of how this upcoming one may turn out?
Member Since: August 28, 2008 Posts: 79 Comments: 3486
43. weathergeek5
7:47 PM GMT on July 17, 2010
Quoting TrentonThunder:
No way I would have issued a heat advisory in the Mount Holly region today or tomorrow. Maybe a watch for Monday. I think the advisories have been too sensative at times this summer. They need to be saved for when really needed for people without air conditioning etc...

There may be more heat advisories issued from Mount Holly than anywhere else in the country.

Looks like we are warm and dry again from this Tuesday thrugh the rest of the month.


Mount Holly canceled the heat advisories. I think they read this post.
Member Since: December 25, 2005 Posts: 0 Comments: 1744
42. TheRasberryPatch
7:28 PM GMT on July 17, 2010
what does la nina mean to temperatures? i thought i read it means the fall will be cooler, which right not sounds good to me...hahahaha
Member Since: January 26, 2007 Posts: 72 Comments: 6255
41. wxgeek723
7:13 PM GMT on July 17, 2010
Shame. I guess it's back to reality for snow lovers around here, lol.
Member Since: August 28, 2008 Posts: 79 Comments: 3486
40. Zachary Labe
7:06 PM GMT on July 17, 2010
TrentonThunder- Yep it is ridiculous. Advisories among other things are over used greatly. The SPC now seems to issue slight risks every other day. I used to remember when they actually meant something interesting.

wxgeek723- It actually is not too early despite what some may believe... Unfortunately it is not looking too great. Developing La Nina, unfavorable QBO, relaxing blocking, etc are not going well for snowlovers. We need to see some improvements in the next few months, which can happen...
Member Since: December 14, 2007 Posts: 282 Comments: 15099
39. wxgeek723
6:52 PM GMT on July 17, 2010
We did have some minor thunderstorms down in South Jersey in the early morning hours around 4-4:30. There was little rain. However, there was persistent thunder that rarely got too loud. It makes sense though, because the lightning spectacle was spectacular.

I think the heat is far from over, but I believe the hottest has passed. I doubt Philly will surpass 103F back on July 7. That was the hottest in fifteen years, and August is typically slightly cooler.

I know it's extremely early, but I have to ask, lol. Bliz, do you have any early thoughts on the upcoming winter 2010-2011?
Member Since: August 28, 2008 Posts: 79 Comments: 3486
38. TrentonThunder
5:03 PM GMT on July 17, 2010
No way I would have issued a heat advisory in the Mount Holly region today or tomorrow. Maybe a watch for Monday. I think the advisories have been too sensative at times this summer. They need to be saved for when really needed for people without air conditioning etc...

There may be more heat advisories issued from Mount Holly than anywhere else in the country.

Looks like we are warm and dry again from this Tuesday thrugh the rest of the month.
Member Since: December 17, 2009 Posts: 0 Comments: 796
37. originalLT
3:43 PM GMT on July 17, 2010
Hi Blizz, yeah I read that movie is this years MATRIX, complicated but very good!
Member Since: January 31, 2009 Posts: 0 Comments: 7451
36. TrentonThunder
3:30 PM GMT on July 17, 2010
I believe we have officialy entered La Nina criteria within the last week or two. The tropics have been relatively quiet so far, but i was reading in Jeff Masters blog that we've had similar El Nino to La Nina setups where the season started slow and picked up later. I believe that's what I was reading (scanning) anyway.
Member Since: December 17, 2009 Posts: 0 Comments: 796

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Cornell University- Atmospheric Sciences Undergrad; Research Assist.- Onset of Spring Indices Toolbox; Interests- Small spatial scale climatolology

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