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Posted at 10:46 AM ET, 03/06/2012

Mild March forecast on target for much of U.S.: big warming possible next week

After experiencing one of the mildest winters in modern times, the Lower 48 is staring down …you guessed it … a warm start to Spring. Earlier long-range forecasts for above average temperatures in March are now supported by multi-week predictions from the global weather models. Fortunately, as outlined by the Storm Prediction Center (SPC), severe weather prospects appear limited through the next week at least.

Temperature anomalies expected Thursday from the GFS ensemble mean. (Penn State)
Overall, the pattern is quieting down across the country after the ferocious outbreak of tornadoes on March 2nd. It is also warming up relative to average. As shown to the right, much of the country east of the Rockies will see temperatures 5-15°F above climatology tomorrow and Thursday.

Highs should easily make it into the 60s both days in the DC area. Even today, it will be in the 70s in St. Louis, Kansas City, and nearby locations in the Central and Southern Plains.

As the weekend approaches, a trough (dip in the jet stream) at high altitudes over the Southwest will split from the faster westerly jet stream to its north (outlined in black below) and slowly wobble around in the same general region for several days. The image below identifies this feature by an X, and shows its expected position on Friday.

Upper-level winds, pressures, and temperatures predicted by the ECMWF weather model for Friday. The black X marks the “cutoff” upper low, and the black arrows outline the main jet stream (ECMWF)
Ostensibly, a setup like this one is not that dissimilar from an efficient severe weather maker. Upper-level lows like the one shown above can increase wind shear (increase the difference in wind speed and/or direction with height) and reduce static stability (cool the upper levels while warm up surface temperatures) over the same locations simultaneously, and thereby increase the likelihood of severe storms.

But in this case, the necessary ingredients probably won’t optimally overlap.

Outside of a slight chance for severe storms on Thursday over a small area in Texas, we may be looking at a long-duration heavy rain event for the balance of the event (see map below) over a large area from the mid-South southwestward to the western Gulf States … beginning Thursday and lasting through the weekend.

GFS forecast of 2 ½-day accumulated rain (inches) ending early Sunday (NOAA)
Thunderstorms will almost certainly accompany these rains, but widespread severe weather appears unlikely at this point. Of course, stay tuned to SPC for later adjustments to their outlooks.

Looking to next week, one of the big stories will be the warmth in the eastern two-thirds of the country, particularly across the Plains. As ridging (warm air) aloft overspreads much of the country (red shading below), spectacularly-warm temperature anomalies will surge into the Northern Plains.

High-altitude temperatures for next week predicted by ECMWF (left) and GFS (right). Red shading indicates anomalous ridging. (Penn State)
It is not out of the question that record highs will be set in some locations there. In Minnesota, for example, temperatures may very well be more than 20°F above average next Wednesday. Though records may be harder to reach farther south, 70s and 80s should still be common across the Central and Southern Plains.

Temperature probability map for March. Areas in red are more likely than not to be warmer-than-average. (NOAA CPC)
After a brief cool down over the weekend in the East, locations there will also join the mid-Spring weather. Anomalies in the +5 to +15°F range are probable next week all the way from Maine to the Carolinas.

The bottom line is that Spring is here, even though its astronomical start date is nearly three weeks away. And present indications make it hard to quarrel with the Climate Prediction Center’s (CPC) temperature probability map for March.

By  |  10:46 AM ET, 03/06/2012

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