"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".

Tuesday, October 18, 2011

Tornado Watch (s) Likely This Afternoon/Tonight


VERY COMPLEX SITUATION WHICH WILL LIKELY MORPH AND ADJUST THROUGH 11PM TONIGHT. FROM LEFT TO RIGHT: COLD FRONT, TWO PREFRONTAL TROUGHS, DEVELOPING LOW IN THE CENTRAL GULF WITH A SMALLER LOW TO ITS SOUTH. PURPLE IS WHERE SIGNIFICANT TORNADO PARAMETERS ARE SHOWING UP NOW. A series of impulses ahead of the low pressure area and with it, along with several boundaries to develop going into tonight will likely further complicate the situation tonight

SIG TOR PARAMETER in bottom central portion of image. Total TOR threat through event I believe is between the purple lines, with an earlier threat over South Florida and spreading north toward sunset through midnight. Image is directly from the Mesoscale Analysis page at  

TODAY: Tornado Threat increasing per the latest Rapid Update Cycle and mesoscale analysis page. The Storm Prediction Center will likely issue a watch box in the next hour across portions of South and South Central Florida. However, an additional risk area could develop later today/tonight further north based on the RUC.

Watches are issued by The Storm Prediction Center based in Norman, OK. WARNINGS are issued by the National  Weather Service offices in the state, of which there are 6 in Florida. 

Be aware that even if you are not in a watch box, adverse conditions can occur outside of the boxed area. 

Based on RUC and NAM models blend: Surface low could strengthen/organize substantially as upper level trough and associated height falls move across the Northern Gulf early this evening. In the meantime, SE winds are working up the east coast of Florida, and the RUC implies that instability off the SE coast and around the Keys and the Bahamas could be drawn northward from the Western Bahamas to as far north as I-4 by midnight.

In fact, the RUC model predicts the temperature late tonight will be warmer than it is this afternoon as the low draws very warm and moist air with very high precipitable water values over 2.1" as far north as I-10.

As the low pressure area begins to incorporate wind shear elements of the approaching upper level trough, bulk shear will increase across the peninsula from the surface up to 20,000 ft, with the greatest bulk shear eventually to evolve in the lower levels across the South Half of the state between 8pm to midnight.

Meanwhile, unstable air could be drawn further north within this area of bulk shear and helicity in the 200-450 m2/s2 range from the surface to 3KM (possibly higher than that which is significant), particularly along and south of the Beachline as far south as Indian River a low level jet also increases to 40-50kts after dark across all of South Central.

Granted, when we start throwing terms around like CAPE, shear, BULK shear, and helicity it gets a bit Aesopian..but to the meteorologist it all has significant meaning. Such as a new found archaeological dig would be to a historian.

The storm prediction center will likely be issuing a watch box shortly, but based on values 'on paper only', the parameters for why this watch will be issued are not as 'significant' compared to those of tonight if the RUC model verifies. Conditions could change rapidly toward sunset, so it is best to at least be aware of this fact prior to dinner time.

It is possible that at least one more watch box, if not two, could be issued later today through post-midnight as the situation develops further (if it does).

The SPC is eyeing this area. Go to the web site at for latest updates and discussions, and click on mesoscale convective discussions.

OUTSIDE of the Tornado Threat, stronger storms with winds in excess of 60mph are possible across the peninsula late this afternoon through 3AM, decreasing from North to South with time, and last to exit South Florida tomorrow morning before noon, but likely much sooner. Winds just 2000 ft above ground are forecast to increase from JAX to VERO after 11pm, and any heavy rain storm to form in this environmental set up will be capable of bringing these winds to the ground. These winds are most likely on the EAST side of the state from JAX to Vero...then working south with time toward MIA by morning, but decreasing further south.

However, there is one key factor to negate a much, MUCH greater potential...that being the temperatures aloft. Gratefully, they are not forecast to be extremely cold. In fact, during the rain event of a week or so ago they were much colder (which was one reason for all of the rain).  This series of POTENTIAL events is all about the strong wind fields just over head to well aloft and the direction from which they blow at different levels of the atmosphere. Hence, bulk shear. It is also about vorticity (disturbances) and helicity (helical rotation ) in the horizontal being pulled upward and further twisted by diverse  speed shear and directional shear through the atmosphere combined.

AFTER TONIGHT: Cold front will finally clear Central Florida between 3pm -6pm tomorrow, perhaps a bit later.  It will be breezy on Wednesday behind and ahead of the front, with a few sprinkles along a prefrontal boundary and/or the front, but in between those boundaries it will be partly cloudy with mainly lower fast moving low topped cumulus clouds but before then we could see some 80Fs tomorrow before the front goes through. 

THURSDAY/FRIDAY: Winds gradually calming down with very cool evenings. Lows in the 50Fs to mid-upper 40Fs further north and highs in the upper 60Fs to low 70Fs. The coolest to cold morning will be Friday as winds taper off the most and possible atmospheric decoupling can occur.

As noted previously, it does not look like the mid-upper level trough will even completely clear the state, so rapid recovery is expected in the temperature department by Saturday morning into afternoon as winds turn more NE, but light. Any future rain chance will be held at bay until at least Monday, and will be light along the coast.

At least one more front could develop next week later in the week, but pass through dry with little fanfare, although the GFS in the long range is showing some very strange placements of troughs and ridges toward the last week of the month which raises an eyebrow, but so far nothing significant is expected to develop.

TODAY'S /TONIGHT'S/EARLY WEDNESDAY THREATS: Mainly possible tornadoes and strong wind gusts. Rainfall is not expected to be excessive, although heavy but brief rainfall could pose a problem for those areas still recovering from previous rains such as across Polk/Osceola Counties for example.

It is also possible a squall line will from overnight in association with the main low pressure area as it crosses North Central/Central Florida in tandem with a mid-level low toward Apalachicola Bay area, and eventually into South Florida.  It remains yet to be seen based on paper, whether or not such a line will develop, even in the short term models.

In fact, it might be that only the tornado watch which could be issued this afternoon will be the only one required. The above stated/written presents a worse case scenario.

If it remains to appear that a greater storm threat will be possible toward later tonight, a very brief post might be written up. Right now, it appears there is a  50/50 chance.

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