"But seeing they could not See; hearing they could not Hear"
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"From its chamber comes the whirlwind, and cold from the scattering winds." - Job 37:9.

"The wind blows to the south and turns to the north; round and round it goes, ever returning on its course".

Monday, January 17, 2011

Tornado Watch All of South Half Of Florida

Quick Micro-post: Two tornado watches have been issued for South Half of Florida, and as expected the severe threat has shifted further north and now stretches south of line running from Tampa Bay to Titusville. The watch is in effect until 7pm, as hypothesized the time constraint would be in the previous post. A tornado was spotted near Port St. John with a debris cloud visible by a certified spotter.

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Rotating/Severe Storms Still Possible South/Central Florida Today

Images: Forecast Convective Available Potential Energy (CAPE) Values for 4pm, Storm Relative helicity values for 4pm, Current Tampa Vertical Azimuth Display (VAD) from Doppler Radar, Current LDIS plot showing Low Level Wind Shear. Note the shear values near Tampa Bay as storms were in this area at the time.

NOW: Surface low pressure in the East Central Gulf now in place this morning well WSW of Sarasota at sunrise will make slow progress initially ENE-NE ward through early afternoon. There appears to be perhaps two definitive 'fronts' (per se) of warm frontal nature extending east from the low, the first is a slightly elevated warm front stretched from Tampa Bay to just north of the Kennedy Space Center. The more defined surface warm front is across South Florida. In looking at dew points, 60F dewpoint air is now as far north as Cape Canaveral along the coast with a SE surface wind taking shape, with low - mid 60F dew point air over South Florida. Lightning strikes are occurring both along and north of a line from Tampa Bay to Orlando -Sanford along the secondary warm front with more around the keys and into the Gulf along the other boundary. Activity is moving ENE.

TODAY: We see in the RUC forecast that the greatest helicity values are restricted to along and north of the warm front, whereas the greatest surface based instability is south of the warm front in the warmer air - makes sense. In an organized severe weather event these two features would normally be closely overlaid which will not be the case today. Either way, we see that CAPE values in the 500-1000 j/kg air will be south of a line from Tampa to Titusville at 4mph (in this forecast from the RUC model) as the directional wind shear values cross east central and NE Florida late afternoon along and north of the slightly elevated warm front described above.

The thing that has my interest the most is that the surface low may linger in the Gulf slower than what overnight model runs have depicted. If this is the case, the warm front now over South Florida will have time to 'jump' north to a North Tampa Bay - Titusville line during the midafternoon hours. This would jive with the forecasted higher CAPE values extending that far north as noted above and as shown in the first image. Again, note the helicity values/location for the 4pm time frame per the last RUC model output.

The Storm Prediction Center (SPC) has South and South Central Florida in a 'slight risk' for severe weather today with tornadoes possible. Believe this line on the east side of the state 'could' (in my mind' be taken north a bit to KSC considering that richer dew point air (and as such, higher CAPE values) coincident with high helicity values rotating along the warm front and over running this air mass coupled with backed surface winds (particularly at the coast) could possibly all fall in line between the hours of 2 pm -6:00pm as the low pressure system moves in.

It is important to note that, as is typical when a storm system approaches and features become more discernible, that several spokes of energy will rotate through, with the whole configuration in constant 'morph mode'. In fact, as I type, storm activity on radar has changed tremendously over the past hour , with some passing over the Orlando NOW. All activity so far has been along and north of the most northern 'warm front' and is just missing Central Brevard in passing just to the north by not too far at all.

In short, best stay advised for the strongest of activity any time over South and Central Florida from 1:30m - 7pm (discounting the Keys where some activity is already in progress), with a narrowed down time range of 1pm - 5:30pm. South Florida will have more time to destabilize due to the fact that a great expanse of rain coverage is not in that area at this time, but by the time the peak of destabilization is reached there winds may become more unidirectional with height except along the East side of the state, regardless, speed shear will be in place supplying storms greater potential to gain vertical upward momentum (rising air currents). Additionally, thermal instability, as relatively minimal as it may be forecast for today in comparison to a big severe weather event, might be even less due to cloud cover. Still, some severe weather cannot be disregarded as a very real possibility.

TONIGHT: Looks like the core of the worst potential for a strong storm(s) will have passed within one hour after sunset and thermal instability is lost due to lack of sunlight/heating all areas with all rains clearing out overnight, last to exit the east side of the state.

TUESDAY/BEYOND: Not much change from yesterday's post with two more fronts to cross Central Florida with significantly less impact than today's brouhaha. Fog areas or low clouds possible in the morning as a high pressure bubble passes over head behind the system, with a west wind on Tuesday and remaining pleasant in regards to temperatures. Will refine the outlook for the remainder of the week tomorrow, considering the more immediate short term, and might add continuously evolving and on-going weather scenario now in progress through the remainder of the daylight hours.

But, if interested, the outlook in regards to temperatures is looking rosier (warmer) , even from yesterday's post. Same low temperature regime in regards to locations of the coldest air remains, but now even warmer with mainly 40s in the coldest spots Saturday or Sunday morning with the east coast from Cape Canaveral to Miami (and the Keys) remaining the warmest over night. Coldest North Central-North Florida.

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