WEATHERAmerica Newsletter, Sunday, February 3, 2008, 8:10 P.M. CT

WEATHER HAZARDS (During The Next 24 Hours)

SEVERE WEATHER OUTLOOK
(potential for tornadoes, damaging winds, and large hail within the next 24 hours)
Some Thunderstorms may APPROACH Severe Limits
AZ....NM

ISOLATED Severe Thunderstorms
(Microbursts, Large Hail)
NE TX....C, S AR....N MS....N AL....W, C TN....W KY


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

Isolated Locations In
AZ....NM
(QPF 1 - 2")

Isolated Locations in
NE TX....C, S AR....N MS....N AL....W, C TN....W KY
(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
ND....SD....extreme N IA....MN....N, C WI....Upper MI
(Snow; 4 - 12")

Isolated Locations In
E OR....N NV....ID....UT....W, C CO....W WY....MT
(Snow; 4 - 8")

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)



The Proverbial "One-Two Punch"


The storm which is currently taking shape over the Intermountain Region is not the only item to watch in the near term. If you look at GOES imagery over the Gulf of Alaska, you will see another, and stronger, impulse digging southeastward. So after the initial low dumps its outlay of heavy or severe thunderstorms across the lower Great Plains and Mississippi Valley during the following 36-48 hours, cyclogenesis will get underway in the TX Panhandle. Positioned just below a tongue of cold advection (and that is serious Arctic air dropping out of Canada), the low will follow a fairly typical Panhandle Hook B path and draw in some of the colder values. A band of convergence is forecast to set up from E OK into New England, which I expect to be the focus for heavy precipitation. Warm sector severe thunderstorms may fire from TX into VA, but the major concerns are heavy rainfall over melting snow and ice in the Corn Belt and the threat for a prolonged ice to snow episode in an arc from Kansas City MO through Chicago IL and Detroit MI during Tuesday night and Wednesday. An argument can be made for an additional 4 to 8 inches of snow in parts of Lower MI and the ON Peninsula, after a period of glazing.

Colder Than You Would Think (North Of Interstate 70, That Is)

The much-ballyhooed warming trend for the Great Plains, Midwest, and Northeast is just that, an overrated one or two days of temperature rises that will reach its peak on Tuesday over the lower Ohio and Tennessee Valleys. In truth, cold air is prevalent across the northern half of the nation, and will again advance southeastward beginning on Day 3.

....But Still Quite Warm In the Southeast

One section where the warming WILL be impressive is the Gulf Coast and Southeast, where the 80 deg F isotherm will reappear in the lower right quadrant of the developing Panhandle Hook storm. This supply of warm and moist air is a good thing; as the cold front slams into the unstable domain, strong thunderstorms will dump heavy rainfall on locations long afflicted with drought.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

That Old Devil Subtropical Jet Stream

Yes, the subtropical jet stream is strong, and about to strengthen further as a disturbance ejects from the equatorial Pacific Ocean. No, this has nothing to do with the ongoing La Nina episode (see below). The presence of the impulse near the Hawaiian islands makes the case for another huge storm to hit the West Coast within 96 hours, then spread its effects into the lower 48 states by Days 6 and 7.

A "Northern Tier' Storm Of Note?

If the vigorous disturbance that has just exited the Japan Trench succeeds in linking with the subtropical jet stream near HI (likely), we could have the makings of yet another major winter storm. So far, the computer forecasts indicate a mainly west to east progression of any formative low center (something akin to a Colorado/Trinidad system). There is some potential for such a low center to reform off of the shoreline of the Northeast by Day 10 (the ECMWF scenario), but the progressive nature of the 500MB longwave pattern would argue against such redevelopment. Still, precipitation potential is likely underdone by the numerical versions after February 10, and frozen types could be an issue for parts of the Midwest, Great Lakes, and northern New England.

Major (And Temporary) Warm-Up In Western, Central U.S.

The northward shift in the storm track could result in importation of Mexican air into the Southwest and Great Plains. many of the computer forecasts have spotlighted a spell of very mild to warm weather, reaching as far north as the Upper Mississippi Valley in about 7 or 8 days. I must emphasize that, with the progressive nature of the jet stream configuration, any radical rise in temperature in the U.S. will not be of long duration.

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

There Might Be A -NAO In Your Future....
Many of the numerical models covering the Day 11-15 day period have been hinting at a developing negative phase of the North Atlantic Oscillation, and a breakdown of the current positive formation in the related Arctic Oscillation (dissolution of a broad circumpolar vortex). If the Day 10-11 storm complex is as strong as the GFS and ECMWF suites seems to indicate, a cAk vortex could form near Newfoundland. This gyre, in turn, would advect warmer and more stable values into Greenland, perhaps even attaching on the positive height anomaly seen on model depictions over Scandinavia.

....And, For That Matter, A +PNA, Too!
With the formation of two prominent motherlodes in the Arctic Circle, the separation between the vortices may give rise to an anticyclonic axis over Alaska at some point in the extended period. Notice that on the European and American model panels covering Days 13 - 16, the Siberian cold pool is digging toward the Aleutian Islands. If this storm complex continues to lose latitude and settles between AK and HI, a strong case can be made that a +PNA ridge complex of a blocking nature may arise near the West Coast into the Yukon Territory.

La Nina And MJO Watch


While the La Nina episode over the equatorial Pacific Basin is the strongest in ten years, it must be stated that this -ENSO occurrence is NOT producing the classic effects of a typical cold anomaly. consider the ongoing occurrence of the subtropical jet stream, with numerous cases of lower latitude heavy precipitation events. Add the volatile nature of temperature transitions seen this winter (if you disregard the usual whinings about anomalies, which are based on 30 year averages), and it HAS been a crazy winter, NOT a warm one...). The conditions across the U.S. are indicative of frequent interaction between the three active bands of the westerlies. Note that the thermal signal is very weak over the eastern sectors toward Ecuador, but strong in the central quadrants. With time the colder water will start to moderate, resulting in an effectively neutral ENSO environment by early April. In the process, we could see some of our most interesting (that is cold and stormy) conditions in the U.S. between now and the end of calendar winter.

Much has been written about the effect of the Madden Julian Oscillation on apparent weather in North America. Although the full effects of the MJO are by no means well understood, some have opined that any warmth in the U.S. (especially the Northeast....grins....) is because of a certain phases of the oscillation. What is documented about MJO is that there is less impact during stronger La Nina events, and that exacerbation of impulses (Kelvin waves) increases as the largest convective clusters build out of the Indian Ocean toward the International Dateline). This appears to be happening now, with the cloud grouping sliding over Malaysia and Indonesia (I usually ignore the MJO phase charts/diagrams, which often appear to be out of sync with actual conditions). If linkage with the polar westerlies does occur, we could see more amplification of the jet stream, and more wintry conditions across the eastern two-thirds of the continent in the last two weeks of February.

Watching The Volcano

The expected eruption of a tall volcanic mountain in Ecuador could have a major impact on global weather. Positioned near the equator, a vertical (as opposed to lateral or fanned) blast into the stratosphere could eject loads of particulate matter. Reducing sunlight, alterations in temperature and weather could last as much as two years depending on the power and nature of the plume distribution.

Prepared by Meteorologist LARRY COSGROVE on
Sunday, February 3, 2008, 8:10 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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