"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, November 15, 2011

Chance of Showers and Possible Thunder Mid-Afternoon Toward Sunset

Pre-Sunrise Radar image showers some light to moderate showers working from south to north along the east coast. The area outlined in white toward the east side is a very general depicture of those areas which received measurable rainfall from late yesterday through early today. The red "x" is the center of what appeared to be a weak vort max or nearly a microscale convective vortex which was apparent when radar was animated. This area moved north and into the low level ridge axis at which point the more appreciable rainfall abated.

RECAP: Overall, not much change from yesterday's reasoning. Fog was reported in many areas across interior South Central to west central and over much of North Florida this morning. Rainshowers worked up the coast from as far south as Southern Palm Beach County early last evening but also occurred concurrently toward East Brevard and Indian River. Overnight, what appeared to be a weak low level vort max evolving from the activity over Palm Beach County organized as it worked up the coast, especially after 4AM across Eastern Brevard County but spreading the wealth into Osceola and Orange Counties as well. Heaviest rainfall reported per CoCoRAHS volunteers was from Eastern Indian River County to Cape Canaveral (where the highest total of .57" was reported, albeit this report was a little conservative and could have been a bit higher).  It appears from my perspective only from what I've read that this rain was 'convectively' driven but resided a bit elevated (not solely surface based) above a shallow inversion around 500-800 ft), and was limited in vertical extent due to drier air aloft in the absence of greater instability and/or external forces or boundaries. Fog quickly formed in some locations toward Ft Pierce "post rains", with the now fully saturated low level atmosphere and ground from earlier rains still present under neath the shallow inversion as the vort max lifted north (and likely, some subsidence behind it as well). By the time the area of showers lifted north the sun was up and daytime, diurnal mechanisms were already in play precluding fog over most of Brevard. DAB also had some fog well north of the approaching vort max and under the low level inversion. all cases, the inversion was very shallow and not impressively strong.

TODAY: Per model guidance sounding forecasts, the low level inversion present at the time of this writing should be breaking up between 10:45AM - 12:15PM. Partly cloudy skies as cloud types transform to a mix of stratocu and cumulus with sufficient breaks , especially across South Florida for highs to reach the lower/mid 80Fs in a few locations. Expecting more clouds Central and North to refrain above the lower 80Fs to near 80F at the coast south of Cape Canaveral where a slight on-shore or side-shore wind closer to the water will tone highs down a few unsubstantial degrees.  Current LDIS plots, latest RUC, and morning NAM indicate present and future convective instability to be in place by 2pm this after from just north of I-4 to all of South Florida. Surface and low level ridge will be located across South Central with the mid-level ridge not far from the same position. The only differences with the runs is 1) RUC has mostly early shower activity in the area shown (below), which would preclude any thunder. On the other hand 2) NAM/GFS are holding off on any rain until after 2:30pm (at least) if not later, which at this point I'm more likely to favor. In other words, the RUC which showed nothing earlier might be jumping the gun. With that said, better heating over South Florida to transport instability northward toward   I-4. With forecast CAPE of near 1700 j2/kg2 (RUC) and now near or above 2000 j2/kg2 (NAM) , see no reason not to include the chance of thunderstorms in the post, especially from near or just east of MCO and along I-4 to DAB southward toward Vero Beach and eastern Osceola Counties. There is a smaller chance near West Palm, but believe any earlier activity in this area as depicted by the latest RUC will be showers.

Lastly, all forecast plots show the inversion in the lowest few thousand or even hundreds of feet to break, with none present by late afternoon. This should allow ample sunshine and the west coast sea breeze to work inland and modify while traversing the heated , and dry grounds now in place on the west side of the state.  

In closing for today, The Storm Prediction Center nor any official offices are discussing thunder today, and barely even showers, at least not as of the time of this perhaps all of the above should be taken with a large grain of salt and dash of pepper over the left shoulder. Models have been very consistent with showing showers today though, and with higher CAPE now forecast than previous day, I'm willing to roll the dice and take the leap to thunder. Main con will be lack of low level forcing and no truly discernible trigger . But again, sufficient low to mid-level vertical (upward) motions are shown, especially toward Southern Volusia and all of Brevard.

TONIGHT:  Showers to end by mid-late evening if not sooner. Low clouds again possible with mild temperatures much like last night.

WEDNESDAY: Stacked ridge axis across South Central in the absence of apparent triggers should yield rainfree skies, cloudy to partly cloudy by afternoon with highs in the lower 80Fs, and some mid-80Fs where the best cloud breaks occur.

THURSDAY/FRIDAY: Frontal boundary to work down the state, and reach dead central shortly after  nightfall. Showers and maybe some thunder to accompany the boundary, reaching the CDL toward late day. Best chances of rain extends as far south as Sebastian to Vero. Frontal passage accompanied by a quick wind shift over the course of 4-8hrs to the NE and eventually ENE Friday. The boundary could work as far south as West Palm ...underdeath the mid-level ridge which will remain locked in place. Any rains from  Friday morning through Saturday will be post-frontal under speed convergence and some instability behind (north) of the boundary.

SATURDAY: Latest GFS is falling back in line with many of its previous runs with a good chance of showers working back north late Friday through Saturday. The prime culprit appears to be a vort max and associated moisture evolving NE of the Bahamas that rotates around the western periphery of the midlevel high pressure over South Florida. This area is forecast to move into East Central and finally taper and wane toward NW Florida Saturday night. Thus, rain chances seem to be a good bet from Ft. Pierce and north from Friday mid-day and working toward St. Augustine and inland during the day Saturday into early Sunday.

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