From the Lee Side

Look out Loretta!

Posted by: Lee Grenci, 4:04 PM GMT on March 05, 2013

When I was a graduate student at McGill University in Montreal, I became an avid fan of the Montreal Canadiens (professional hockey). After I graduated and moved back to Pennsylvania, my allegiance switched to the Pittsburgh Penquins, especially during the early 1990s when Mario Lemieux led the team to the Stanley Cup. Like most Penquin fans, I loved to listen to play-by-pay announcer, Mike Lange, and all of his hilarious quips after the Penquins scored a goal...Scratch my back with a hacksaw; Buy Sam a drink and get his dog one, too; Call Arnold Slick from Turtle Crick;..the list goes on.

But of all of Mike Lange's quips, my favorite was "Look out Loretta!" I even used it on WPSX-TV (now WPSU) whenever I was the forecaster on Weather World and a big storm was threatening. With a new storm looming over the West by the end of this week, I decided to take a trip down memory lane (thus, the title of this blog).

The 72-hour GFS ensemble mean forecast of 500-mb heights (dark contours) and 500-mb height anomalies (in decameters), valid at 06Z on Friday, March 8. Courtesy of Penn State and NCEP.

The 72-hour GFS ensemble mean of 500-mb heights from the 06Z runs this morning (above), valid at 06Z on March 8 (Friday), shows a closed low centered over northern California, with 500-mb heights predicted to be roughly 180 meters (give or take) below average. For the record, the GFS ensemble has 12 members.

Given how cold it will be aloft (check out, below, the operational GFS 72-hour forecast of 500-mb temperatures in degrees Celsius; larger image), thunderstorms are possible along and near the California Coast as early as Thursday of this week. Perhaps a few will produce small hail. Keep in mind that winter and early spring is typically thunderstorm season along the West Coast of North America. That's when most of these kinds of cold upper-level lows swing inland from the Pacific (the jet stream is, on average, farther south during the cold season).

The operational 72-hour GFS forecast for 500-mb temperatures, in degrees Celsius, valid at 06Z on Friday, March 8, 2013 (from the 06Z run this morning). Larger image. Courtesy of Penn State.

The 120-hour GFS ensemble mean of 500-mb heights (and spaghetti), valid at 06Z March 10 (Sunday) indicates that the closed 500-mb low will be centered along the Colorado-Kansas border (by the way, it's not a cut-off low).

To the east of the closed 500-mb low, the corresponding surface low taking shape over the western High Plains is slated to produce an upslope snowstorm along the Front Range of the Rockies. For confirmation, check out the 120-hour forecasts of the 12 GFS ensemble members, valid 06Z Sunday, of MSL isobars, 12-hour precipitation ending out 06Z in March 10, and the 1000-500-mb thickness. One of the ensemble members (zoom-in) has a large precipitation maximum near Denver (the 510-, 540- and 570-decameter thicknesses appear as dashed, red contours). Note the orientation of the isobars in northeast Colorado, indicating a component of the wind that upslopes the higher terrain. Again, this is a 120-hour forecast, so details are a bit premature, but it's reasonable to assume, at least at this point, that a portion of the Front Range of the Rockies might get clobbered by snow this weekend.

As the surface low heads east and draws moist air northward from the Gulf of Mexico, the stage will be set for thunderstorms over the Deep South, some of which will spawn severe weather. Indeed, most of the GFS ensemble members on the 144-hour forecast of MSL isobars, 12-hour precipitation ending out 06Z on March 11 (Monday), and the 1000-500-mb thickness indicate precipitation patterns consistent with a line of thunderstorms, some of which could spawn severe weather as the cold front associated with this system barrels eastward over the Deep South (here is the corresponding GFS mean ensemble forecast of 500-mb heights. Moreover, the 144-hour forecast suggests the possibility of a snowstorm over portions of the Upper Middle West.

If you look closely at the overall message from all of the individual members on the 144-hour forecast, you get the impression that timing issues are very uncertain at this time. After all, these forecasts fall into the medium-range category, so looking at details in such situations is definitely beyond our skill. But it's our responsibility as forecasters to talk about these storms in general terms beyond Day 3 of the forecast period in order to alert the public of the regional patterns of weather that might affect them in the medium range forecasting period.

No matter how you slice it, a potentially newsworthy storm will come ashore along the West Coast later this week and pivot northeastward toward the Upper Middle West. As Mike Lange often quipped, "Get in the fast lane, Grandma, the bingo game's ready to roll!"

Lee

Categories: Synoptic Meteorology Medium-Range Forecasting

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1. DelWeather 4:49 PM GMT on March 05, 2013
Ah phooey. You posted while I was commenting on your last blog. Hope you get a chance to read that off-topic post, as I'd like to know whether I've misunderstood your previous posts. I'd love to know what is meant by a cut-off low. And what it means when you say "closed low." What would make it an open low? Thanks! Mark Member Since: October 9, 2012 Posts: 0 Comments: 50

2. Lee Grenci, Retired Senior Lecturer and Forecaster 5:07 PM GMT on March 05, 2013
Quoting DelWeather: Ah phooey. You posted while I was commenting on your last blog. Hope you get a chance to read that off-topic post, as I'd like to know whether I've misunderstood your previous posts. I'd love to know what is meant by a cut-off low. And what it means when you say "closed low." What would make it an open low? Thanks! Mark I'll go check it out and respond. Member Since: October 24, 2012 Posts: 53 Comments: 445

3. Lee Grenci, Retired Senior Lecturer and Forecaster 5:14 PM GMT on March 05, 2013
Quoting DelWeather: Ah phooey. You posted while I was commenting on your last blog. Hope you get a chance to read that off-topic post, as I'd like to know whether I've misunderstood your previous posts. I'd love to know what is meant by a cut-off low. And what it means when you say "closed low." What would make it an open low? Thanks! Mark Okay, I replied to your post about the blue sky. I think we're both on the same wavelength here, pun intended. Check out my comment. And thanks! Member Since: October 24, 2012 Posts: 53 Comments: 445

4. Lee Grenci, Retired Senior Lecturer and Forecaster 5:37 PM GMT on March 05, 2013
Quoting DelWeather: Ah phooey. You posted while I was commenting on your last blog. Hope you get a chance to read that off-topic post, as I'd like to know whether I've misunderstood your previous posts. I'd love to know what is meant by a cut-off low. And what it means when you say "closed low." What would make it an open low? Thanks! Mark Regarding your question about cut-off lows, check out the image below (larger image)? Hope this helps. Thanks so much for your interest and for you great analysis on the blue sky. Member Since: October 24, 2012 Posts: 53 Comments: 445

5. vis0 12:29 AM GMT on March 06, 2013
Whew, i thought the blog's title was the The Weather Ch. was now naming FRONTS and Loretta was the most recent. Once i read on, i understood its 'bout the human experience and the ingredients that make life exciting, (Wx & Sports of course) "Now go out there, stay sober and lean on the bar". Just made that up, means go out and check/maintain the barometer. i'm a proponent of naming storms, just prefer using numbers & ancient styles, as Male, clod...i mean cold core , to blends i.e. super storms, extra tropical for winter storms AND Tropical storms names to be female names (as they were) warm core, warm core to blends. i'm not a politically correct guy, am a scientifically correct FAIR guy...or try to. Member Since: December 15, 2006 Posts: 150 Comments: 109

6. Lee Grenci, Retired Senior Lecturer and Forecaster 11:50 AM GMT on March 06, 2013
Quoting vis0: Whew, i thought the blog's title was the The Weather Ch. was now naming FRONTS and Loretta was the most recent. That's hysterical! You made me laugh out loud. Member Since: October 24, 2012 Posts: 53 Comments:** 445

7. DelWeather 9:07 PM GMT on March 06, 2013
Quoting 24hourprof: Hope this helps. It helps a lot. I guess I didn't realize that without at least one closed isobar you would even say you had a low. And the cut-off low... I have to laugh at myself there. I thought the low was cutting something off... not that it was the low itself that is cut-off from the main westerly flow of air! Live and learn! Mark Member Since: October 9, 2012 Posts: 0 Comments: 50

8. Lee Grenci, Retired Senior Lecturer and Forecaster 11:46 AM GMT on March 07, 2013
Quoting DelWeather: It helps a lot. I guess I didn't realize that without at least one closed isobar you would even say you had a low. And the cut-off low... I have to laugh at myself there. I thought the low was cutting something off... not that it was the low itself that is cut-off from the main westerly flow of air! Live and learn! Mark Mark, I laugh a lot at myself too. Glad I could help. Member Since: October 24, 2012 Posts: 53 Comments: 445

9. georgevandenberghe 5:00 PM GMT on March 08, 2013
You can have a low without a closed isobar. It's then an open wave. By the way I'm a Caps fan and my son is a rabid Caps fan. I do sometimes remind him that the Caps can usually plan on being out on the Golf course by late April while the Penguins maybe aren't done with their work for the year :-) Member Since: February 1, 2012 Posts: 3 Comments: 297

10. WunderAlertBot (Admin) 12:40 PM GMT on March 09, 2013
24hourprof has created a new entry.

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About 24hourprof

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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