Daweathablog

Charles E. Roop giving his own forecasts, weather discussions, photos and adventures for the Starkville, MS area, Florida, and beyond.

Sunday, April 25, 2010

Slight Severe Weather Threat Today

The SPC has continued labeling north and central Florida as a slight risk category for today and tonight. The dynamics look decent, but there are a few limitations to the threat.

Skew-T (upper-air sounding) from Jacksonville at 8 am ET (Source: Unisys Weather)

The KJAX skew-t (shown above) gives a snapshot profile of the air above the surface. Shear profiles look good and, according to NWS-JAX, helicity values look good for possible rotation. The lifted index is about -2, which is slightly decent for severe weather formation. There are moist conditions at the surface, but dry at about 900 mb and higher. This might be a sign of convective instability but we would need some daytime heating to get things going. The SPC mesoscale analysis does hint at divergence over the area, which is another factor for making things unstable.

However, the NWS is noting low lapse rates as a limiting factor. Also, the cloudcover over northern Florida would limit daytime heating in the area. However, that could change later on.

Florida visible satellite image (Source: WeatherTap.com)

As for timing and arrival, NWS-JAX wrote this at 9:38 this morning...
THE LINE IS EXPECTED TO SPLINTER AS IT APPROACHES THE COAST THIS AFTN...THEN REDEVELOPMENT OCCURS ACRS THE SRN PORTION LATER IN THE AFTN AS STORMS MOVE IN DIRECTLY FROM THE GULF. EVEN SO THE COASTAL ZONES AND REMAINDER OF NE FL ARE NOT OUT OF THE WOODS AS STRONG TO SEVERE STORMS ARE POSSIBLE AND RISK FOR TORNADOES STILL EXISTS.
Based on the sounding and profile readings, storm motion should be out of the west-southwest at about 30-40 knots.

So, it's a wait and see. Keep an eye on the Twitter feed during the day as I try to both watch this and study for a physics final exam. Stay tuned.

Saturday, April 24, 2010

Slight Severe Weather Risk in North Florida on Sunday

Severe weather risk for today. (Source: SPC/NOAA)

Good morning, everyone. Today isn't (or is) a good day to be in the southeast (depending if you are a weather nut or a storm chaser). There is a very-rare high risk for severe weather in parts of Alabama and Mississippi according to the Storm Prediction Center (SPC). A low over the Midwest with an associated cold front, a sufficient low-level jet, steep lapse rate potential, a negative tilting trough, and many other factors are allowing for this rare weather setup across the deep south. Multiple tornado watches are in effect along with many tornado warnings currently in effect. Reports of possible tornado and thunderstorm wind damage are flooding my Twitter feed as I write this.

This same storms system will continue to move on into the east and will affect areas from central Florida to the mid-Atlantic states on Sunday. The SPC has issued a slight risk of severe weather for the aforementioned area. Here are some factors the SPC is laying out for the risk (with links to their definitions by meteorologist Jeff Haby):

- Southerly to Southwesterly low-level jet within the pre-frontal warm sector
- MLCAPE of 1000 to 2000 J/Kg
- Increased dynamic forcing ahead of a upper trough
- Increased wind shear environment

Severe Weather Risk for Sunday (Source: SPC/NOAA)

Among these, daytime heating will help enhance the setup as the day advances. The National Weather Service in Jacksonville also noted in their last full Area Forecast Discussion (AFD) that the southern jet stream will also strengthen tonight. As Sunday begins, multiple lifting mechanisms (cold front, upper-level divergence - which allows more air to replace the diverged air in the upper levels - smaller impulses and disturbances) will add to the potential.

We will have to wait until Sunday morning when more data comes in and forecasts solidify before determining what exactly will happen. Timing will also be key since the intensity will depend on how much daytime heating would be allowed. So much for focusing on the Physics II final exam.

There may be an update on this blog Sunday morning or as early as tonight. Keep an eye on my Twitter feed for the latest information.