Supplement To The WEATHERAmerica Newsletter, January 29, 2009

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Negative-Tilt+Triple Phase+Vortex Formation = Impressive Blizzard On February 2 - 4
I have not changed my thinking about the system forecast to affect the eastern half of the U.S. and Canada during the February 1 - 4, 2009 time frame. My thoughts are still mirrored in the STORM TRACK and APPARENT WEATHER Graphic in the previous day comments, with the possibility for:

- Near- blizzard conditions from parts of the Mid-South into the Ohio Valley and Lower Great Lakes

- Significant Icing in parts of Appalachia, particularly the Shenandoah and Susquehanna Valleys

- Heavy rainfall with thunderstorms from the central and eastern Gulf Coast into southern New England

I will likely come up with an accumulation total depiction when I release the newsletter on Saturday afternoon. For now, the only real changes that I see concern the structure of the system (vertical) and the possibility of a north-northwest bend into the QB Eastern Townships on the afternoon of February 3 (still not a certainty, but increasingly likely).

You may have noticed the trend in the computer models to come into agreement on the 500MB makeup of the storm. When sudden height falls occur in the upper levels of a storm, rapid deepening can occur. Most of the intensification results from rapid evacuation of air from the surface to make up the deficit aloft. Convection can aid in this "boost" in strength, as can the addition of a tropical energy and moisture source. While this storm is not anywhere close to the 1993 Superstorm in terms of potential, I am convinced it will be historic for many regions. A tap of deep moisture accompanies the merger of three distinct jet streams (Arctic, Polar, Subtropical) at 250MB to form a true cAk vortex that gets as far south as Louisville KY early on February 3! A more typical position for such a gyre is Hudson Bay. So the snow and cold generation with this feature will be something special, albeit along and west of the Appalachian Mountains.

Forcing from the southern branch component will likely lead an initial burst of precipitation over most of Dixie (east of Interstate 35 in TX) on Sunday night and Monday, with snow from ice-stricken AR into W TN, W KY and S IL by Monday afternoon. As the 500MB gyre motherlode approaches, more heavy snow bands will begin to form over IL and IN and progress into KY, OH and WV. The merger process should be more or less complete by the time the surface low passes into PA (near Lancaster) and then rolls northward toward SE QB or ME. I noticed that the 250MB jet axis is positioned in such a way to take the lowest pressures into the Gulf of St. Lawrence, which would keep most of QB in snow and limit the ice/glaze threat to interior New England. Unless something changes dramatically, the major cities of the Interstate 95 corridor will see mainly rain, with perhaps some potential for snow squalls with the edge of the Arctic intrusion immediately following the passage of the surface storm.

The clear leaders in the "Blizzard of 2009" snow derby? Probably Lexington KY, Cincinnati OH, Huntington WV, Pittsburgh PA, Buffalo NY, and Toronto ON. More on this threat in the Saturday edition.

Strong Intrusion Of Arctic Air Accompanies Intense Piedmont Cyclone


The invasion of bitter cold air from Nunavut AR into the U.S. may last only 48 - 72 hours, but it will be impressive. With winds exceeding 40 mph (some higher gusts are probable in the lower Great Lakes, Northeast and Quebec on February 3), the chill factor will be dropping sharply within the western quadrants of the storm. Arctic air, in modified form, will even reach southern Florida by midweek!

Brief Period Of Warming East Of Rocky Mountains During February 8 - 12....



Warmer air will return over the eastern two-thirds of the continent later in the medium range. Even though the jet stream configuration remains in a largely -AO and -NAO alignment, the westerlies will split and progress across the lower 48 states, delivering air of Pacific Ocean origin. Eventually, however, the large positive height anomaly over northern Canada and Greenland will exert an influence. Disturbances will be forced to take a track from California into Texas, then consolidate off of the East Coast. The mildest air should be felt over the Midwest and Northeast (major positive thermal anomalies drift into Ontario and Quebec beneath the ridge complex), with a slow drop in readings likely to set in by mid-February.

....But Stratospheric Warming Episode, Madden Julian Oscillation Combine For Cold In Mid-February



While the MJO is flaring strongly over the equatorial Indian and Pacific Basins, satellite imagery shows a lack of connection of tropical convection and the polar westerlies. With no linkage to the powerful energy and moisture supply, the trough complex over eastern Asia will not become an mAk vortex. With lower than average 500MB heights the result over Alaska, the idea of a more moderate air mass presentation in the eastern two-thirds of the U.S. between February 8 and 12 gains credence. Free-moving disturbances reaching the West Coast, of course, would act to lower temperatures through most of the Intermountain Region.

Consider, however, that the core of the thunderstorm development will progress out of Sri Lanka and the Bay of Bengal through Indonesia and the southwestern Pacific Ocean in about ten days. At the same time, the effects of the recent surge in stratospheric warming will be having an effect on apparent weather in North America. The core of 10MB warming has been over Baffin Island recently; since it takes about two weeks for highest-level features to translate to the 500MB level, the prospect of a dominant -AO/-NAO jet stream configuration seems likely (and this is reflected in many of the ensemble forecasts). Projecting ahead, the addition of an MJO contribution to the upper low and trough undercutting the ridge complex could produce a) an immense winter storm affecting much of the lower 48 states during a February 10 to 13 time frame and b) a brutal display of Arctic cold following that system from the west to the east.