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2013 Fall Medium Range Discussion


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Long-Lived Winter of 2012-13 Nearing its End...

 

After a record-setting February-March in terms of snowfall in parts of New England, a February KU blizzard, a near KU snowstorm in early March, and a historic Palm Sunday snowstorm across Missouri and parts of Illinois, the winter season is now coming to a close.

 

In large part, the revival of winter and then its long-duration in parts of North America was the result of a blocking regime that has now lasted 52 days. That exceptional blocking regime brought the AO below -5.000 for the first time on record after mid-March. Moreover, through today, the AO has averaged -3.173 for March and a figure below -3.000 is extremely likely when the month ends in two more days. That will surpass the current March record of -2.858 from 1958.

 

Since 1950, there have been only two years during which the March AO averaged -2.500 (1958 and 1962) or lower and only 5 on which it averaged -2.000 or lower (1957, 1958, 1962, 1970, and 1984). The general consensus of the pattern evolution from those years is that April witnessed a break in the cold pattern, with most of those years favoring warmer readings for the second half of the month in large parts where cool anomalies had begun the month.

 

AprilTransition2013_zps9f8e65b1.jpg

 

All said, that pattern evolution supports the idea coming out in the teleconnection analogs of a dramatic pattern change that will likely see the second half of April wind up warmer than normal in much of the area currently enjoying generally colder than normal readings. It appears that the second week of April could witness the start of that transition.

 

Before then, winter may launch a last-ditch bid to carve its legacy into the memories of those who experienced some of its highlights. The possibility for at least some accumulation of snow exists in such cities as Chicago, Cleveland, Toronto, Ottawa, Montreal, Worcester, and perhaps even Boston. A small chance exists for at least some snowflakes in parts of Pennsylvania eastward to New York City, though that's not assured. An increasingly rare April freeze is also a possibility in New York City. The last time there was a freeze in April there occurred in 2007.

 

In sum, Spring 2013 appears likely to begin to take hold in the extended range.

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The 00Z Global Ensembles continue to advertise a potential severe weather episode developing the second week of April across the Plains. This appears to be the first legitimate severe weather event of the Spring Season and will be worth monitoring in the days ahead.

 

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the Tampa bay Tornado in 1966 came on the 4th when the AO was at a record low for this time of year...Yesterday had severe storms in south Florida with the ao nearing record low levels...todays storm in the mid atlantic was blocked from coming north as forecast earlier in the week...With the block we have now more severe storms from cold fronts will cross the south and Florida until it moves...

http://en.wikipedia.org/wiki/1966_Tampa_tornado_family

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The 00Z suite of operational and ensemble guidance appears to be converging on a fairly wide spread significant severe episode for the Central/Southern Plains into the Middle and Lower Mississippi Valley Region next week. For those interested, we have an ongoing Topic in the Central/Western sub forum discussing the potential...

 

http://www.americanwx.com/bb/index.php/topic/39881-pattern-change-and-severe-weather-opportunities/

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The 04/11 00Z Global ensemble mean suggest a rather deep trough developing once again across the West and Great Plains late next week. While there remain some timing issues, there is a bit of agreement that a general stormy and cooler pattern will return to the Western 2/3rd of the CONUS as we head toward late April.

 

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  • 2 weeks later...

Both of the medium range GFS and ECMWF are depicting what I can only describe as one of the most anomalous patterns I've ever seen in early May. Take for example this day 7 plot of the GFS 850 hPa standardized temperature anomalies.

 

850temp_stdanom_namer_85.gifThats -5 sigma at 850 hPa over a large area of the southeast... the 0 degree isotherm at 850 hPa is in the GULF OF MEXICO! 

 

 

The ECMWF isn't quite that anomalous... but its very reminiscent of a pattern that occurred in late October of last year... I'll let you guys fill in the blanks.

 

ECMWF.png

 

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Both of the medium range GFS and ECMWF are depicting what I can only describe as one of the most anomalous patterns I've ever seen in early May. Take for example this day 7 plot of the GFS 850 hPa standardized temperature anomalies.

 

Thats -5 sigma at 850 hPa over a large area of the southeast... the 0 degree isotherm at 850 hPa is in the GULF OF MEXICO! 

 

 

The ECMWF isn't quite that anomalous... but its very reminiscent of a pattern that occurred in late October of last year... I'll let you guys fill in the blanks.

 

 

 

It's funny you should mention it Phil, because a 100 kt easterly jet off of Newfoundland is an extremely anomalous event, but also occurred during the last week of Oct 2012. 

 

Of course, before making any further comparisons (exciting too many weenies), we should mention that if anything develops in the Gulf / N. Caribbean, it would be strictly subtropical and not even a particularly strong subtropical entity.  Doesn't mean it can't be a big rain maker tho. 

 

post-378-0-32101000-1367016223_thumb.gif

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It's funny you should mention it Phil, because a 100 kt easterly jet off of Newfoundland is an extremely anomalous event, but also occurred during the last week of Oct 2012. 

 

Of course, before making any further comparisons (exciting too many weenies), we should mention that if anything develops in the Gulf / N. Caribbean, it would be strictly subtropical and not even a particularly strong subtropical entity.  Doesn't mean it can't be a big rain maker tho. 

 

attachicon.gifgfs_atlantic_162_250_wnd_ht.gif

 

Yes of course... I probably will stir the pot more than intended, but from a synoptic perspective, late October 2012 and the upcoming day 7 forecast have remarkable similarities. Of course the major difference here is that its very unlikely we will have the same magnitude disturbance in the Caribbean/Gulf of Mexico/Bahamas. Thats not to say it can't aid in robust cyclogenesis if the cutoff cyclone located over the Ohio valley moves further east. 

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Interesting Spring, record to near record late to get to 70 for places like Rockford, and I believe Fargo was very late even on reaching 50... Duluth has seen it's snowiest April yet, and after this transient warm-up, another bout of Negative 500mb height anomalies shows up again with a cut-off L. The recent 500mb pattern over NA has been represented quite well by the Positive Phase variant of the TNH (Tropical Northern Hemispheric) Pattern teleconnection. Even though the TNH is not calculated in April (only in the DJF Winter period) is is showing up quite well as of late in our most recent pattern.

 

post-204-0-22732200-1367165603_thumb.png

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Yes of course... I probably will stir the pot more than intended, but from a synoptic perspective, late October 2012 and the upcoming day 7 forecast have remarkable similarities. Of course the major difference here is that its very unlikely we will have the same magnitude disturbance in the Caribbean/Gulf of Mexico/Bahamas. Thats not to say it can't aid in robust cyclogenesis if the cutoff cyclone located over the Ohio valley moves further east. 

 

 

Weather pattern should still be interesting, but not looking quite as anomalous as it once was.  Two things I immediately notice are 1) the cutoff low isn't bringing nearly as much cold air with it as was modeled 2 days ago, limiting temperature gradients / baroclinic energy, and 2) precipitable water values are lower over the Gulf with less moisture feed from the Caribbean, making sustained deep convection and subtropical development more difficult.  I suppose something subtropical could still form with those low heights over the Gulf, but I'd probably bet against it at this point. 

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Both of the medium range GFS and ECMWF are depicting what I can only describe as one of the most anomalous patterns I've ever seen in early May. Take for example this day 7 plot of the GFS 850 hPa standardized temperature anomalies.

 

Thats -5 sigma at 850 hPa over a large area of the southeast... the 0 degree isotherm at 850 hPa is in the GULF OF MEXICO! 

 

 

 

Phil, you weren't too far off! I saw 0º 850's into Louisiana today!

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  • 2 weeks later...

TORCH... The GWO indicating we might finally dip to negative AAM values. Haven't seen this since mid-Feb- I'm thinking a period of upper 80s, lower 90s over the central U.S. next week, later followed by mid-to-upper 80s, lower 90s from DCA to BOS late in the week. Too bad Memorial Day wasn't one week later...

 

gfsgwo_1.png

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TORCH... The GWO indicating we might finally dip to negative AAM values. Haven't seen this since mid-Feb- I'm thinking a period of upper 80s, lower 90s over the central U.S. next week, later followed by mid-to-upper 80s, lower 90s from DCA to BOS late in the week. Too bad Memorial Day wasn't one week later...

 

gfsgwo_1.png

 

Looks like this is going to be a good call Mike! (+3 to 5 sigma 1000 hPa temperature anomalies in the far northeast projected this weekend). First real heat of the season for this part of the country. 

 

wloh09.gif

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  • 2 weeks later...

So does anyone have an idea of how hot July and August will be in NJ?

 

I'm seeing an overall warm pattern developing over the Northeast between July 7-15. The warm signal looks to fade thereafter, but redevelop over the Midwest... likely to push back across the Northeast late in the month. 

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I'm seeing an overall warm pattern developing over the Northeast between July 7-15. The warm signal looks to fade thereafter, but redevelop over the Midwest... likely to push back across the Northeast late in the month. 

The models have really captured onto a solid heat event across the Midwest/Northeast heading through next week..I'm having trouble figuring out how the MJO signal out there (and how the models are predicting it to progress) has played into these developments, if at all. Long range GFS really wants to continue the torch as well while the euro ensembles have a strong ridge out west and closer to normal further east. These differences have been pretty consistent for 2-3 days now.

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The models have really captured onto a solid heat event across the Midwest/Northeast heading through next week..I'm having trouble figuring out how the MJO signal out there (and how the models are predicting it to progress) has played into these developments, if at all. Long range GFS really wants to continue the torch as well while the euro ensembles have a strong ridge out west and closer to normal further east. These differences have been pretty consistent for 2-3 days now.

Still there too, as of 0Z.

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