Weather outlook for this week February 25, 2013

Hello everyone. I know it has been roughly a month since my last post, due to coursework and other commitments.  I apologize for the delay. However, I am back and this next post includes a very interesting topic for us here in south Florida. Next week’s weather will be quite interesting and the pattern will possibly trickle into the following week.

As we approach the end of the winter season, we are in the midst of what is one of the warmest winters on record for a majority of the region. Steering currents have favored a persistent southeast wind flow which has helped to keep cold fronts at bay. Astronomically speaking, the winter season for the northern hemisphere ends on March 20th, and we usually get one last strong front around this time or slightly before it. That case seems to be increasingly likely, for a late season strong cold front is looming in the forecast.

SHORT TERM:

Before we take a look at the pending cold front, we will have to deal with increasing instability in the upper levels of the atmosphere. In other words, returning to what Florida knows best to make in the summer months: Thunderstorms.

MSL 1 ECMWF

MSL 1 GFS

This is the Mean Sea Level (MSL) model map, which shows the average pressure of the surrounding airmasses. This model is also a good indication of precipitation and detecting low and mid-latitude cyclones (seen in the green/mustard yellow blob east of the Carolinas). The top image is the MSL from the European Centre for Medium-range Weather Forecasts (ECMWF) model, while the bottom image is the MSL from the Global Forecasting System (GFS) model, both taken at 72 and 66 hours from the most recent run, respectively. Both models indicate a shortwave trough moving across the east coast and is expected to stall just to the southeast of us. This should create enough instability to generate showers and thunderstorms. Increasing chances for rain are expected to start Tuesday morning, with the best chance for any activity coming on Wednesday evening/Thursday morning.

 

LONG TERM:

 

This is where the weather patterns will become real interesting and bears close monitoring. All signs point to a late season cold front pushing through the area. However, both of the models differ significantly in the evolution and movement of the mid-latitude cyclone set to form over the Midwest states.

GFS 2-24 1

GFS 2-24 2

GFS 2-24 3

GFS 2-24 4

 

This is the GFS model measured at the 850 mb level (about 5,000 feet above the surface). These images span from 117 hours to 192 hours from the most recent full run. The GFS is leaning to a more aggressive frontal system that will send colder air deep to the south, with near freezing (aqua colored or darker) approaching much of the area. This translates into potential 30s and 40s for inland areas, and low 50s along immediate coastal areas. With the GFS, it is expected to last for more than 3 days, possibly more than 5 days at the current predictions.

 

ECMWF 2-24 1

ECMWF 2-24 2

 

This is the ECMWF prediction of the 850 mb temperatures. Due to the lack of data that was available, the two images span a time frame of 114-135 hours from the most recent full run. What separates this from the GFS is how deep the trough extends into S. FLA. With this model run, the ECMWF keeps the coldest of the air just to the north of S. FLA, sending cool, but nowhere near as much cool air as the GFS predicts. To translate this map, most inland areas would level out in the 40s, with mid-upper 50s across most of the coastal areas.

 

There is a similarity between both models. If you notice the arrows on the map, those are wind vectors that estimate potential wind speeds at the 850 mb level. Winds may increase noticeably out of the northwest as the front passes, and this is the tell-tale sign of how long the cool airmass will last.

 

SUMMARY:

 

In short, the information that is known so far is limited, but what can be said is a shot of cooler and drier air is increasingly likely to start off March. The last significant March cold front dates back all the way to the 1993 Superstorm of March 12-14. Going with the ECMWF would indicate more moderate temperatures; going with the GFS would spell sharply cooler air and potential record low temperatures in isolated areas for given days in March.

 

I will be posting a blog later this week with an update to the situation.

 

Onward and upward,

 

Brian Matilla

 

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