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.



Anonymous said...

Have you examined any other dynamics? Or are you making a call for severe weather after looking at only the precipitation forecast and the temperature forecast?

Andrew said...

Anonymous at 6:28: Other parameters, such as shearing and instability, were examined.