WEATHERAmerica Newsletter, Sunday, January 27, 2008 at 7:50 P.M. CT

TODAY'S FUN LINK: Weather Refdesk.com

WEATHER HAZARDS (During The Next 24 Hours)

SEVERE WEATHER OUTLOOK
(potential for tornadoes, damaging winds, and large hail within the next 24 hours)
STRONG WINDS
(Pressure Gradient Derived)
Coastal MA, NH....ME....NB....PEI....NS....NL (NWF)

STRONG WINDS
(Pressure Gradient Derived)
W MT....N ID....W, C BC

STRONG WINDS
(Pressure Gradient Derived)
MO....IL....IN....MI....C, E ON

STRONG WINDS
(Pressure Gradient Derived)
MB....SK....ND


HEAVY RAINFALL OUTLOOK
(potential for an inch or more total rainfall within the next 24 hours)

Isolated Locations In
WA....OR....CA....S NV....AZ....W NM
(QPF 1 - 2")


FROZEN PRECIPITATION OUTLOOK
(potential for accumulation of ice rime, freezing rain, sleet or more than 3" total snowfall within the next 24 hours)

Scattered Locations In
Coastal NH, ME....NB....PEI....NS
(Snow; 4 - 18"; Blizzard)

Scattered Locations In
WA....OR....CA....NV....AZ....W NM....W CO....UT....ID....W, C MT....W WY
(Snow; 4 - 36")

Isolated Locations In
SE BC....S AB....SK....N, C MB....N ON
(Snow; 4 - 8")

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)


The "Almost Nor'easter"

While the major storm winding up east of the MA Islands will have an impact on coastal New England and most of the Maritime Provinces with snow and wind, the formation of the low was too far north to allow for major snow amounts along much of the Interstate 95 corridor. This feature will turn into a genuine blizzard impacting much of ME, NB, and PEI (snow changing to rain in NS), but exit for the open waters of the northern Atlantic Ocean by sunset on Monday, with no discernible impacts on the 500MB longwave pattern.

California Deluge Is On The Move....

Aided by a phenomenal (considering this is a La Nina winter) subtropical jet stream as well as a classic 500MB cold pool, the huge low pressure center moving into California tonight will spread all kinds of crazy weather. Heavy mountain snowfall, even more rainfall at lower elevations and even ongoing severe weather threats for parts of CA, NV, and AZ during the next 24 hours. There will be a break in the precipitation beginning Tuesday, when the mean storm track shifts a bit northward and bypasses the Golden State.

....With Mild Air And Severe Weather A Concern East Of The Great Plains


The shift of the West Coast storm complex into the Great Plains and Prairie Provinces will trigger major changes in sensible weather east of the Rocky Mountains. Much warmer air will be drawn northward; both tropical and continental elements will be present, making for a very unstable, thunderstorm-friendly environment from coastal TX into the Ohio Valley and Great Lakes. As the surface low undergoes redevelopment over the Ozark Plateau on Tuesday morning, convection should become more focused across parts of the Corn and Tobacco Belts. Afterwards, a sweep of much colder air will temporarily lower readings across much of the Midwest on Wednesday.

Another Storm Threatens The Pacific Northwest


A couplet of intense storms now over the northwestern Pacific Ocean (associated with a Kamchatka mA vortex) will target the Pacific Northwest on Tuesday and again by later next week. Largely bypassing California, these impulses will trigger widespread heavy rain, higher elevation snow, and strong winds through BC, WA, OR, and ID before digging into the lower Great Plains at the start of the medium range.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

Vicious Panhandle Hook Storm With Variety Of Weather Extremes

The low scheduled to make landfall in the pacific Northwest of Tuesday will be a major concern for the rest of the nation as well. NWP outlooks suggest that this feature will dig into CO and NM by 96 hours, then swing northeastward in a parabolic northeastward manner before reaching maximum intensity over the St. Lawrence Valley on Day 6. There are many complications that could be associated with this feature. For one, the various equations have been very consistent with outlay of excessive precipitation in most sectors of the cyclone. this includes a prominent severe thunderstorm threat in Dixie; heavy rains through the Ohio and Tennessee Valleys into the Northeast; and a huge outlay of snow and ice along and north of the storm track. The most recent forecasts would seem to favor (albeit tenuously) a heavy snowfall event for the Chicago IL metro, with glazing threats in and near St. Louis MO and Detroit MI. While the exact track of the low is still uncertain, the prediction of a widespread extreme weather event is not. Many communities from the Ozark Mountains into the lower Great Lakes will go through three shifts in precipitation type before the storm is over. And straight line winds and colder temperatures will be another side effect from the low as it makes its move into Quebec around February 2.

Alternation Between Warm And Cold Across The U.S.


Just as major warming will occur ahead of the storms moving through the U.S., so will shots of colder air (generally cA+cPk) be felt after passage of the cyclones. Consider that on Tuesday, the 70 deg F surface isotherm may climb into the Mid-South. Conversely, cold values may return to areas below 35 N Latitude for a time on Wednesday and again during the weekend. All of this without benefit of blocking, and much of the constant changes due to a classic +AO configuration with the polar stream disturbances spinning about an entrenched, singular circumpolar vortex.

Yet Another Strong Low Out Of Texas In About 7 - 9 Days!

Those wishing for more "storm action" may regret that want, as the current 500MB longwave pattern favors a fast-and-furious sequence of intense disturbances tracking from the lower High Plains into the Quebec Eastern Townships. Following on the heels of the Days 4 - 6 system will be yet another violent impulse, this one a hybrid-type feature that (early model information indicates) could be a major severe thunderstorm producer for much of the Old South and Midwest around February 5 - 6.

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

500MB Longwave Pattern Destined To Change By Mid-Month

The computer outlooks are now favoring a shift in the 500MB longwave pattern by mid-February. A disturbance now over eastern China is predicted to move northward over a flat ridge covering the eastern Pacific Ocean and part of the western U.S. This weak +PNA signature (not a block) allows the mean trough to shift from the western and central portions of the continent into the eastern third of North America. In the process, the Chinese system deepens into an Arctic vortex over the Great Lakes, with a shot of cAk values dropping across the eastern half of the country after February 10. A word of warning: ensembles of all models have been especially bullish on this feature, indicating the potential for a memorable weather event with much precipitation and wind affecting a large part of the nation and Canada. Stay tuned....

Look Closely At The La Nina Signature


This is not a classic "strong" La Nina, despite the number of individuals in the world of weather who make it out to be. And, it must be added, a close look at SST anomalies in the equatorial Pacific Basin will show that the episode is past peak, and should start to slowly decline within the next month or so.

Consider: when have we ever seen a -ENSO with a basin-wide subtropical jet stream that helps to bring heavy rainfall top southern California? And with an equatorial breach that signifies an extensive low-latitude storm? You are correct if you realize that the ongoing 500MB longwave pattern has much more in common with last winter and its collapsed El Nino than with a so-called "strong" La Nina. The problem is that many who judge the event look at ONLY the central (3,4) sector and not at the foundation (1,2) eastern territory near the Galapagos Islands, where readings are getting closer to normal.

Bottom line: La Nina should continue to decline, probably washing out in April. And, in the process, winter weather may stick around a lot longer with cold and frozen precipitation effects through the last four weeks of calendar winter.

Prepared by Meteorologist LARRY COSGROVE on
Sunday, January 27, 2008 at 7:50 P.M. CT

Disclaimer:

The previous statements are my opinions only, and should not be construed as definitive fact. Links provided on this newsletter are not affiliated with WEATHERAmerica and the publisher is not responsible for content posted or associated with those sites.

Copyright 2008 by Larry Cosgrove

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