Saturday, March 30, 2013

April 10-12 Potential Storm

American GFS model MSLP anomaly forecast for 10 days

European ECMWF model 500mb anomaly forecast for 10 days
Medium-range model guidance is in unusually good agreement on a storm system digging into the Southwest US as a closed low before making its way east and affecting areas east of the Front Range. Below normal anomalies for the model's respective fields shown above depict the storm system, while the warmer colors in both images indicate high pressure. European model is considerably further north with this storm system over the American GFS. Because the European model only forecasts out to 10 days, we cannot see how far in the future the European takes it. However, the American model DOES go through the full timeframe of this storm, and we will examine its forecast a little later on.

General atmospheric flow in both images is highly meridional, and the lack of a positive tilt (highest vorticity pointing towards the southwest) means that this system should quickly occlude and shoot north into the Plains towards Canada. When this occlusion happens, an accompanying cold front is likely to begin forcing the massive high pressure system out. Based on temperature forecasts from American model and European ensemble system, temperatures surpassing 60 would be common in and south of the Great Lakes. This could set the stage for a severe weather event. European model itself has cities like Chicago and Des Moines flirting with the upper 70's as the high pressure system takes over as illustrated in the above images, while the American model has those cities closer to the 60's.

Precipitation forecast on April 12th suggests the suspicions of a severe weather event may verify, as a heavy precipitation event looks to impact the southern Plains, likely encompassing stronger storms in the typical cold front's linear storm formation. Time will tell if this linear formation ends up being a squall line or just pockets of heavy rain. Lighter amounts also exist further to the north, stretching as far north as far northern Wisconsin. Examination of severe weather parameters for this timeframe reveal rather high deep level shear conducive for at least marginally strong thunderstorms. Lack of widespread instability across southern Plains is something to watch, although elevated instability immediately onshore of the Gulf Coast would allow for some solidly strong thunderstorms to thrive.


April 5-6 Potential Storm

There is potential for a coastal storm in the Northeast from April 5-6.

Fresh model data indicates a storm system will form in the Southeast and manifest itself to move northeast, just offshore of New England. The system will not be close enough to provide an opportunity for snow, and the presence of warm air along coastal cities means any snow potential will be dashed there by a chilly rain. Lake effect snowfall may be possible in western New York, but this looks to be a rather marginal opportunity for any accumulating snow. Best chances for accumulation reside in western New York as a result of the lake effect snow, and those accumulations may be very light. There remains time for this situation to change, but right now I'm seeing a non-event as far as snowstorm potential goes.


Summer Warmth On The Way

The latest run of a member of the European ensemble set has summertime warmth flooding the nation just 10 days from now.

The image above is from the European ensemble control run, which is a member of the ensemble set that has its parameters unchanged. As you may recall, ensemble members are forecasts from the model itself, but their starting parameters are slightly changed in one way or another. The control run does not have its parameters changed. This forecast, valid for the evening of April 8th, has a massive warm-up across much of the nation, with every state east of the Colorado Front Range (except a few select New England states) reaching full-on spring or summertime warmth.

Cities like Houston, Orlando and Atlanta would have temperatures very similar to those in Chicago, St. Louis and Detroit. The massive warm-up would not reach northern ND, MN, WI or the Upper Peninsula of Michigan, although a forecast 240 hours out is not nearly written in stone.

The unusually warm temperatures following this unusually cold start to spring would most likely be a byproduct of an intense ridge of high pressure sitting across the Great Lakes, Midwest and Plains. Latest indications are that this warmth would be wiped out a few days later as the storm system you see in the Southwest moves on through the nation, but the incredible expanse of the high pressure system means the warmth would not go down without a fight. Time will most certainly tell if this warmth comes to fruition, but this forecast certainly warms the heart of those frowning upon the cool and snowy start to spring.