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WEATHERAmerica Newsletter Saturday, February 6, 2010 at 6:00 P.M. CT Rate Topic: -----

#1 User offline   LarryCosgrove Icon

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Posted 07 February 2010 - 01:19 AM

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)
E QB....NL (Labrador)

STRONG WINDS
(Pressure Gradient Derived)
S MB....ND....C, E MT....AB....W SK

Some Thunderstorms May APPROACH Severe Limits
S CA Deserts....S NV....AZ....NM


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

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


WINTER WEATHER OUTLOOK
(potential for minimum temperature to drop below 20 deg F, or for snow and/or ice impeding travel within the next 24 hours)

Scattered Locations In
E QB....N ME....NB....PEI....NL (Labrador and N Newfoundland Island)
(Snow; Near-Blizzard; 4 - 12")

Scattered Locations In
W WA....W OR....N CA....NV....N AZ....N NM....CO....KS....E NE....NW MO....W, C IA
W, C MN....ON Boundary Waters....S MB....E ND....E SD
(Snow; 3 - 6")

GLOBAL WEATHER SUMMARY
(a review of key weather features around the world)

Powerful mAk vortex just east of Hokkaido bodes ill for downstream locations in North America. This gyre is mobile and will likely not come to a stop until reaching an area below the Aleutian Islands. That position almost always favors strong -EPO/+PNA/-AO ridging, and with it colder air into Canada and the U.S. Shortwave entering Mongolia may produce excessive snowfalls in that nation, Manchuria, and Korea in the next 4 days. Australia is settling into a drier pattern.

GOES WEST full disk image shows why residents of the U.S. ought to be VERY concerned through the next two weeks. Huge Kelvin wave complex straddles phases 8, 1, and 2 and is fueling intense subtropical jet stream moving once again toward Mexico. At the same time, convection is feeding very energetic, suppressed storm sequence through Pacific Ocean that will produce major precipitation and cold impacts (ridge building above the storms) across the nation.

Spectacular winter storm shows up on GOES EAST data, with subtropical jet stream linkage to eastern equatorial Pacific Ocean. Drainage of bitter cold cAk regime from Canada follows this cyclone. Not the approach of another large disturbance straddling the West Coast. Plentiful diurnal and tropical convection seen across much of South America in broad 500MB weakness between heat ridges.

Massive storm complex across northern Atlantic Ocean appears to be inducing new ridge formation in Scandinavia. Large winter storm in vicinity of Balkan Peninsula and Asia Minor will have both severe weather impacts (The Levant and Mesopotamia) and snowfall (Caucasus region and Ukraine) in coming days. See also that important convection is below the equator in Africa, while northern half of continent is dry. This arrangement does NOT favor either an early or active hurricane season in the Atlantic Basin.

Most of Asia is marked by intense cold in Russia east of the Ural Mountains, and a strong area of low pressure in the Tien Shan range. Aside from showers and thunderstorms (and mountain snows) in Afghanistan and parts of Pakistan, the southern reaches of the Eurasian supercontinent are essentially mild and dry.

SHORT RANGE OUTLOOK
(Through The Next 72 Hours)

Intense Cold Will Follow Intense (Yes, Historic) Winter Storm Over Eastern Half Of U.S.

Hurricane eye. 40 inches of snow with locally higher amounts in spots. Covering three regions. Crippling tree, power, and home damage from wet snow and ice. The Mid-Atlantic region (think a line from Harpers Ferry WV to Atlantic City NJ and 100 miles either side of that arc) won the prize for most snowfall. And now comes the cold.

This bombastic was, like most historic events, seen in the computer models two weeks ago (if you don't believe me, check out the extended outlook from January 23....). Of course, the odd quirks like virtually no snow for New York City and Long Island were not detected even 12 hours before onset. But the compressed gradient for snowfall across Pennsylvania and New Jersey was visible even last Wednesday, a product of an anchored cAk motherlode that created a weird 100 mile space of virga (snow on radar did not reach the ground; the dry air ate up the flakes produced aloft).

Now this deep snowpack will act as a refrigerant for the Arctic domain that is following the gyre. The entire near term forecast for all of the Midwest and Northeast will be about 20 degrees below seasonal normal. And even more bitter cold air is on the way!

Yet Another Huge Storm Is Developing Over The West....

If you look closely at the GOES WEST satellite view of western North America, you can see TWO distinct centers of cyclonic energy. One, in Alberta and Saskatchewan, is associated with a descending motherlode of rarified Arctic values. The other is now bringing heavy rainfall (and higher elevation snows) to much of the West. During the next 48 hours, these disparate systems will merge into one entity, spreading important snow and ice across the Great Plains and eventually the Midwest. It is this combinant feature that could set up yet another blizzard across parts of the Mid-Atlantic and coastal New England regions.

....While Bitter Arctic Motherlode In Prairie Provinces Takes Aim At Lower 48 States

Besides providing some more snow for the already whitened ground across the Great lakes and Corn Belt, the latest storm to take shape from the West and in Canada will be accompanied by some brutal Arctic cold. The Southeast could warm up briefly on Tuesday ahead of the virulent disturbance. But by the middle of the week, the various blocking signatures at high latitudes and the full-latitude storm and trough complex across the eastern two-thirds of the U.S. will allow the cold domain to occupy much of Mexico and the lower 48 states.

MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)

"Snowmageddon: New York" Takes A Slightly More North Track (Hello Great Lakes, Northeast!!!)

Storms occurring in phased motion with a cAk vortex are very rare. That said, just such a disturbance (sort of an Alberta Clipper on steroids) is taking shape in western Canada. Soon to link with the everpresent, intense subtropical jet stream, this deepening system will likely undergo bombogenesis when it reaches the southern tip of the Delmarva Peninsula late on the evening of February 10.

With the impressive vorticity burst in its upper left quadrant, much of the Great Lakes region will get clocked with wind-driven bone-chilling 6 - 12" of snowfall before either secondary cyclogenesis or a center jump take the deepest vertical velocities into middle Appalachia and the Atlantic Coastal Plain on late Tuesday and Wednesday. While not in the same league as its historic predecessor, it is my feeling that a blizzard may develop as the core of cyclonic energy consolidates with the reformed center. Heavy snows may fall as far south as Fredericksburg VA and Seaford DE, but as of now the star of this snowfall show looks to be the Interstate 95 corridor from Wilmington DE to New Haven CT (along with currently snow-deprived Long Island NY). New York City, which somehow largely dodged the bullet from the recent white bonanza, should be the focal point of this system, with amounts in the 10 - 15 inch range. Possibly more!

There now, are all of you NYC snow hounds satisfied? As for Boston, there may be enough cold air infiltration to suppress snow amounts somewhat next go round. Like they say, some got to win, some got to lose!

+PNA/-AO/-NAO Configuration Yields Mild Weather In Canada And Western U.S., Cold Elsewhere

Persistent blocking signatures over western North America, northern Canada and Greenland look stronger than ever on all of the computer models in the 6 - 10 day period. Against a very strong but suppressed (into Mexico, then to Florida) subtropical jet stream, that configuration almost guarantees two things in any forecast for the U.S. One is an active southern tier track, which should produce a major snow/ice/heavy rain event across Texas and the Dixie states on February 13 - 15 (with more to follow in the longer term). Another is more outlandish cold that will grip the nation to the right of the Continental Divide. This second aspect is important because at a time when the California and Deep South agricultural markets should be making plans for planting seasonal crops and making citrus harvests, the cold will be plentiful and strong enough to destroy seedlings.

EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)

"For Those Who Like Extensive Cold And Frozen Precipitation"

Now if you are one of those folks who crave winter in all its delights (or tortures, depending on your perspective on such matters), you will love this forecast for the period February 17 -21. High-latitude blocking looks to be quite strong until some easement on Days 15 and 16, working with an energetic (and vastly suppressed) southern branch. In general, most of the West outside of California will be dry and mild. But from the Great Plains to the East Coast, the potential exists for perhaps TWO major winter storms of the Miller A family, with brutal cold following the disturbances. If the GFS and ECMWF model suites are correct, the Interstate 20 corridor (Dallas TX to Atlanta GA) has a decent chance at seeing major snowfall. The European equation package suggest that the cAk domain will grip the Midwest and Northeast for the duration of the longer term. If you ask "why?", just check out the attached maps showing strongly positive 500MB height anomalies in the +PNA, -AO, and -NAO positions.

It is going to be very cold. And snowy. And icy. In a lot of places.

Class dismissed!

The Vexing Question: When Will This Highly Amplified Jet Stream Configuration End?

Readers of this forecast discussion are probably split into two camps. Namely, those who are tired of the incessant cold intrusions and abundant episodes of snow and ice versus those who never want the pattern to end! Now, while it may appear obvious that the next two weeks will be the proverbial "winter wonderland" across much of the U.S. outside of a portion of the Intermountain Region, I can see the probable terminus to "SnowFest 2010".

When I make a longer term forecast, I look at a number of variables. First and foremost is the array of computer models at my disposal. Secondly is climatology, what the weather should be doing in North America aloft and at surface based on 30 year averages (the ESRL site ESRL : PSD : CDC Interactive Plotting and Analysis Pages is superb for making these checks). Third is persistence, namely any observed trends seen in the winter, month, or week so far. An important step is locating the forcing mechanisms, such as the Madden-Julian Oscillation with its attendant Kelvin wave location/linkage, and also mountain torque events over central and eastern Asia. Once you roll all of this into one very unruly ball of synoptic features, trough/ridge placement (as well as associated air masses) will become apparent through the next 15 days. One thing that should NEVER be included (in my opinion) are MJO forecasts, which are in their infancy and are seldom accurate with regard to position, intensity, and linkage to the polar westerlies (especially this last aspect).

From what I see, the MJO is the driver in the recent crazed "snow + cold" configuration across the northern two-thirds of the U.S. (and soon to be most anywhere save for the Pacific northwest). look at the broad convective complex marking the position of the Kelvin wave. This particular size and alignment of a tropical warming/lifting mechanism has not been seen so far this winter, covering Phase 8 and 1 positions and visibly moving eastward. Most of the disturbed areas in the past 90 days have generally broken up after long stays in the vicinity of the International Dateline. From that position, disturbances in the polar jet stream have been energized by tapping into the thunderstorm groupings (the same result can happen if a trough picks up a typhoon), with warm advection building persistent, though sometimes chaotic, blocking signals in all positions favorable to cold transport into the U.S. (-EPO, +PNA, -AO, -NAO).

I suspect that this Kelvin wave will continue to march eastward and weaken slowly. So after another 15 days of bombastic cold shots, potent disturbances in the subtropical jet stream and insane moisture advection from the equatorial regions, we will start to see erosion of the brutal Arctic regimes (from west to east) across the U.S. So that at some point between February 24 and March 1, we will (generally speaking) say goodbye to winter east of the Rocky Mountains.



Prepared by Meteorologist LARRY COSGROVE on
Saturday, February 6, 2010 at 6:00 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 2009 by Larry Cosgrove

All rights reserved.

This publication may not be reproduced or redistributed in whole or in part without the expressed written consent of the author.

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