"But seeing they could not See; hearing they could not Hear"
“The views expressed herein are those of the author and do not necessarily represent those of the National Weather Service or affiliate/related organizations. Please consult .gov sites for official information”

"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, April 4, 2011

Thunderstorms (Some Strong to Severe) Tuesday Beginning Early

Above is the latest official forecast issued by the Storm Prediction Center today for Tuesday issued this morning with a questionable area in the black box. However, continue below regarding this discrepancy. Note that the above is valid thru 8am Tuesday morning.

TODAY: Very pleasant and breezy along the East Coast, particularly of Indian River, Brevard, and Volusia Counties mid-late afternoon. Winds SSE 12-20mph with gusts to near 25mph later this afternoon up the intracoastal waterway. Otherwise, partly cloudy skies with humidity levels on the rise today, particularly near the east coast. Chance of a mid-late afternoon showers in the vicinity of Gainesville into Ocala, possibly west Flagler County into the early evening.

TONIGHT: Strong surface boundary of various atmospheric temperature and wind gradients within a deep full latitudinal 500mb trough is sweeping across the Mississippi River Valley/Ohio River Valley Basins this afternoon, and into through the Deep South. Several tornado and severe thunderstorm watch boxes encompass this region as of noon. Mainly tornado watches as we can see below:

Tornado Watches in Affect. Nearly 400 severe weather related reports have already been logged since early  evening of Sunday night with this storm system as it progresses east. Mainly from high wind and large hail

OVERNIGHT: Here is a time of contention is POSSIBLE (not definitie) for North Central and a portion of South Central Florida.  Note that at the time I started this post, , Florida was not within a threat for severe weather, per the graphic at the top in the 8AM time frame.

However, by all appearances, there was that area in the black box that really drew my interest. In this area I checked forecast soundings from two different models for the time period along with a VAST plethora of other atmospheric parameters and come to the conclusion that the region in the box, or roughly Flager, Volusia, and the North Half of Brevard County as well as parts of Orange and Seminole Counties stand a shot of severe weather during the hours of 6-8AM. Kind of odd considering the actual surface boundary of contention (the cold front), will still be way back in the panhandle.

Based on sounding data and all the other goodies used to make this determination, it appears a squall line composed of high bulk shear and cold air aloft along with moderately strong very low level wind speeds, partly from a suddenly developing low level nocturnal jet streak will blossom during a 'transition time'.

What is the 'transition time'?  Guidance has indicated for 3 runs that the full latitudinal 500mb trough will begin to acquire a 'negative tilt' where the base of the trough will swing forward ahead at its apex and be aligned a bit from NNW-SSE other words the base will proceed the axis of averaged flows in lower levels of the atmosphere. 

During this time a subtropical jet across the Southern Gulf of Mexico will be working northward from over South Florida...the two are SUPPOSEDLY going to phase together right as a 500mb vorticity maximum swoops through the base of the continental trough...strongly across Central Florida. If this occurs, expect rapid storm develop between the hours of 3-4:30AM which will move almost generally E-ESE and strengthen with time while approaching the coast an hour or two before dawn through sunrise to just after sunrise.

There actually is a few locations that it could be especially nasty...for instance..over North Brevard surface instability will be greater prior to this event than that further north, with dew points approaching 70F degrees right long the Brevard County coast to the Port. As I write, the SSE winds of today are advecting this juicy air up the coast and into this region.  This low level instability does not appear will reach north of Brevard County. However, further north into Volusia and Flagler Counties...winds aloft are a bit more strongly stacked ...with higher bulk shear throughout the 'bulk' of the atmosphere. 

Therefore, I drew in the box as noted at the top of this post...even though this area was not outlooked for active weather during this time frame by official outlets. It looks like, should this occur, the activity will have cleared the area by 9AM, if not sooner. Straight line winds of 60mph and hail of 1-1.5" inches are possible (although stronger winds are possible).  Forecast soundings also show a bit of a "dry slot" just above the ground...which will be conducive for the cold, denser air aloft to descend and accelerate through the drier air as it reaches the ground. 

Vertical velocities (upward motions) through the low and mid levels during this time frame are conducive for the formation of hail as well...the number (hail size) is  just a gander, based on the fact that  the lifting condensation levels will be very low during this time frame. In other words, condensation of moisture into rising air parcels will begin close to the ground at the same time the anticipated low level nocturnal jet will be in play.

It is also interesting in that this is all supposed to occur in an area of relatively high convective inhibition. (an atmosphere NOT conducive for storms)..thus...THIS EVENT IS ONLY POSSIBLE...NOT a Given.

While typing this post, a new Day2 Severe Weather Outlook has been issued...with a starting valid time of we see below:


In conclusion, perhaps all that is written above wasn't so far off base after all. The above graphic is valid through all of Tuesday.

OUTSIDE OF THE POSSIBLE EARLY MORNING EVENT: The NAM and GFS models are almost in perfect harmony with timing of the frontal passage proper. They both agree the front will cross Florida 3 hours LATER than previously proposed in all of the model runs the past two days up until just before this post, with the front barely clearing Brevard County at dusk as virtually every wind field, instability, and related parameter ia swept offshore. The front lingers over South Brevard before simply dropping through the remainder of the state with little fanfare.

However, there may be another round of thunder storms with the frontal boundary itself as far south as South Brevard. The front is forecast to cross through Volusia around 2-3pm and slide into South Brevard around 4-5pm before losing much of its dynamic energy. Then, in the process of the sunset and the energy having departed...quickly clears the remaining southern portion of the state in the following 3-5 hours.

BE ADVISED THOUGH: This is only one possible scenario, and it could quickly change with the next run of models. The later frontal passage does not surprise me in the least though.

SOUTH FLORIDA: Totally different bag of tricks. The same vorticity pattern that is set to ignite the prefrontal squall line further north will cross into South Florida in the following hours after sunrise where thermal instability will already be well in place. Wind profiles aloft south of Brevard County quickly become weaker but the air aloft remains cold, so strong winds of 55mph or greater are possible, as is small hail, but timing of such is difficult to narrow down beyond writing that it will be sometime after 10AM, possible much sooner.

Rains/Storms will end all areas, the far east coast last, by 8pm for the most part...and in most areas much sooner than that.

IN SUMMARY: Mostly cloudy tomorrow except over South Florida through mid morning, with a near 100% chance of rain. Showers and thunderstorms, some of which could be pretty strong, or even severe.

TORNADOES: At this time, they do not look likely, but one could occur, as it often the case in Florida with strong or severe thunderstorms. Lips are sealed on where I think those have a 2% better chance of occurring than other as not to raise either a red flag of warning, nor to put folks at ease in thinking the are out of the woods in this regard. Simply know way of knowing.  Even South Florida without the wind fields, could experience somewhat of a mesoscale accident along storm outflows, especially once the anticipated squally area further north could potentially send an OFB (outflow boundary) into the region.

BEYOND TUESDAY: Very pleasant through the remainder of the week. Behind the cold front it is very nice to know there really isn't much cold air! Return to normal or slightly below normal temperatures for a day or two...and that's it. Dry.

Two more potential systems loom on the horizon going into the next 12 days.

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