|Fig 1 -- Surface temperature (colors) and pressure (contours) at 11Z, March 31, 2011. From the HOOT website.|
Of course, as cold air moves south, so does the jet stream. Remember that the jets above are directly tied to temperature gradients below through the thermal wind relation. So, as the gradient of temperature between arctic air to the north and warm subtropical air to the south moves south, so do the jet streams above. Here's this morning's 500mb chart (from College of DuPage--the HOOT site seems to be behind on its graphics). The yellow contours are isotachs showing wind speed.
|Fig 2 -- 500mb geopotential height (blue contours) and winds (yellow dashed contours) for 12Z, March 31, 2011. From the College of DuPage.|
|Fig 3 -- Base reflectivity composite over the southeastern US from 1808Z, March 31, 2011. From weather.gov.|
But the end is in sight! The European model shows that the broad trough over the eastern US is going to start moving eastward. Here's the 500mb forecast for Friday morning:
|Fig 4 -- ECMWF 24-hour forecast of 500mb winds (colors) and geopotential height (contours) for 12Z, Friday, April 1, 2011. From the HOOT website.|
The pattern is forecast to continue to be progressive, with the next shortwave moving through on Sunday into Monday.
|Fig 5 -- ECMWF 96-hour forecast of 500mb winds (colors) and geopotential height (contours) for 00Z, Monday, April 4, 2011. From the HOOT website.|
|Fig 6 -- ECMWF 120-hour forecast of 500mb winds (colors) and geopotential height (contours) for 00Z, Tuesday, April 5, 2011. From the HOOT website.|
Models begin to diverge in their long-range outlook past Monday night. First, the forecast from the ECMWF for 500mb on Tuesday night (00Z, Wednesday):
|Fig 7 -- ECMWF 144-hour forecast of 500mb winds (colors) and geopotential height (contours) for 00Z, Wednesday, April 6, 2011. From the HOOT website.|
Now let's take a look at the GFS forecast for the same time:
|Fig 8 -- GFS 132-hour forecast of 500mb winds (colors) and geopotential height (contours) for 00Z, Wednesday, April 6, 2011. From the HOOT website.|
So what does this all mean? We know that the rounds of storms in Florida look to be coming to a close very shortly. The flow will begin to flatten out as troughing moves off the east coast this weekend. Then, a new shortwave is forecast to dig in out of the desert southwest and onto the plains from Sunday into Monday. From there on out--things get dicey. Trying to time this shortwave for its impacts on the east coast is very difficult right now.
Even trying to figure out what kind of precipitation type is going to fall is somewhat of a mystery. The long-range forecast from the Climate Prediction Center is forecast a "heavy snow event" for the northern plains and upper midwest on Sunday into Monday.
|Fig 9 -- CPC precipitation hazards forecast for Apr 2-13, 2011. As of March 30, 2011. From the CPC.|
|Fig 10 -- GFS 4.5 day forecast of critical thickness values for 00Z Tuesday (Monday evening), Apr. 5, 2011. From the College of DuPage.|
And given the disagreements in the models after Monday, it doesn't seem very useful to try and look at any more diagnostics past this point.
So...this weekend will be the test. Will the models come into better agreement? Or will we still by guessing by the time Monday rolls around?