"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".

Tuesday, October 11, 2011

Scattered Showers, Isolated Thunder Mainly Central and North

Image from the NWS, Melbourne. Link shown in lower left of image. This plot is the 1km helicity and low level winds, which was used because it shows
in the most simple terms today's scenario at the surface. A weak surface low is near Panama City, whereas  a mid level low is much further north. A weak surface trough extends just off the Florida West Coast, as another across the Panhandle to just west of Jacksonville. Colors are explained further down in the post.

As shown above, there is a surface low near Panama City ( I did not draw it in but it can be seen by following the direction the wind barbs are pointing) , and a mid-level low further north. This can be seen by the infrared satellite image below. The mid level low is expected to lift N-NNE to the Great Lakes while the low level surface reflection rotates around it to the ENE-NE toward coastal South Carolina in the next 24-48 hours.
The surface reflection should ride up the eastern Sea board while the mid-level reflection lifts toward the Great lakes region by Friday. In the image above:

1. Green, mainly showers
2. Yellow, Chance of  Very Isolated Thunder before 6pm
3. Orange, Chance of  isolated thunder until 8pm
4. Best chance of there being thunder, Red

Using a blend of the RUC and 2AM GFS, it appears the showers moving into SW Florida and north are a result of cooler upper level temperatures and higher PWAT (precipitable water) air, but thermal instability is greatly limited due to poor lapse rates and lack of heating at this time of day. It is not expected we will warm up all that much today, and the sun angle is getting lower (have you noticed lately?). 

 The best chance of thunder will be right at peak heating toward 9pm. CAPE (convective available potential energy) is not looking to get much above 1500 Js/kgs which supports the weaker low level lapse rate theory, which is barely considered moderate instability. Most of the instability today will be in the mid-levels.

 Lack of deeper moisture and more unidirectional winds further weakens the thunder chances. The best chance of thunder will be along the east coast sea breeze boundary which will be stuck close to the coast toward I-95 and East , developing after 2pm (earlier SE Florida).  Drier air is trying to move into South Florida, but showers and who knows, maybe a thunder could occur near the same location as where some occurred late yesterday (near West Palm Beach). (That area will be   more favored  Wed/Thursday)
INFRARED FROM 8:45 AM EST. The low level low pressure area in the Panhandle is barely discernible in this image, being composed of only low clouds in this infrared image which uses cloud top temperatures to provide a picture of what is going on. The white and brighter the cloud tops, the colder (and higher) the clouds. You can barely see the clouds over the Panhandle of Florida because they are 'warm' by comparison to those north and out over the Atlantic . The large mid-upper level low is more easily seen because it is composed of colder clouds (tops), which the satellite can detect (N. Georgia). There is a pseudo warm and cold front couplet
extending from the surface reflection as noted by the dotted white lines, per the wind fields. The blue lines point toward where most of the moisture will be heading today to support more showers and possibly isolated thunderstorms during and after peak heating toward mid-evening.
This is VISIBLE satellite imagery taken just as the sun had risen enough to reflect off of the cloud tops. Note the dense combination of clouds in the low through upper levels over Georgia. By Pensacola toward Panama City most of these clouds are only low level clouds as noted in the previous image. Showers can be seen moving from the Gulf toward Sarasota with stronger showers just to the north along the dashed , white 'cold front' portion of this system. 

MORE ON TODAY: The surface reflection low will move toward the NE-ENE today. Best chance of thunder will be along the weak trough axis toward NE Florida as far south as interior Volusia County, with a secondary area further south where it could become more unstable toward Central Brevard county and toward the interior, but mainly along to just west of I-95 and eastward.

WEDNESDAY/THURSDAY: The tag team of lows will lift north, with the surface low shifting toward off the SE U.S coast while the main feature low lifts north to the Great Lakes in response to a another system moving into the Pacific NW. This ensemble will be a trouble maker through most of the weekend in the NE States, with a severe weather threat possible in association with the surface reflection near the East Coast states as it lifts north.

Otherwise, the trough associated with the surface low shown by the dotted white line will cross Florida on Wednesday as thought yesterday. However, jet stream level winds will be the driving factor to scoot it along, and with those winds models are indicating a plume of upper level moisture, which would mean abundant 'cirrus clouds' . Those clouds stabilize the atmosphere because they prevent the sun from shining fully. Otherwise, this could have been a good day for stronger thunderstorms considering the wind fields.

Wednesday could end up being cloudy for most of the state due to high cirrus clouds with less clouds to none in the lower levels. The area from South Lake Okeechobee to Miami might escape the worst of it, so a storm/more likely a shower could form toward Palm Beach or Broward Counties. This will have to be all re-evaluated tomorrow morning.

WEEKEND: Cold front to pass through early Friday followed quickly by NNE-NE winds at the surface and West winds just above the deck. The surface front should be forced south toward the Florida  straits if not to Cuba.

Behind the front, morning lows from Orlando and West and interior Osceola County could get into the mid-upper 50s, but the beaches will remain in the 70Fs, with afternoon highs in the low to mid-80Fs inland both days.

BEYOND: Winds will remain from the ENE-E for much of early next week with some stratocumulus clouds working in and spreading across the state during the late morning through early evening hours. Some sprinkles are possible, esp. toward South Florida, but no big deal. Another cold front will quickly move in mid-week with a rapid wind shift toward the South and a chance of Thunderstorms around Wednesday or Thursday.

WEDNESDAY/THURSDAY and 'THE GREAT BEYOND': It gets very sticky from here on out. Next weekend is not looking so great at this time for outside activities of full day duration. The SECOND front, has as been advertised now by the GFS for several runs, is the beginning of what could be something 'big', in regard to weather / rain producing capabilities.

This front could stretch out well, well, WELL east into the Atlantic along an even latitude and remain nearly stationary across the peninsula as it gets squeezed in behind high pressure behind the previous front that will go through on Friday. The subtropical southern branch jet could lift out as well, leading to little progress of any low level features as low pressure in the Caribbean toward the extreme SW Gulf is 'triggered' along the prior frontal boundary  of this weekend.

It becomes quite complex from this point on. Reliability in terms of 'something' evolving in the Southern Gulf toward all of The Caribbean is looking more certain at this point, since this is not all so far out in time, but it remains sketchy and varies from run to model run on just exactly how, where, and why things will evolve.

The trend has been to focus the attention more toward the SW Gulf and the Yucatan rather than Jamaica. For example only, the GFS is now tracking a large tropical storm from the SW tip of Cuba that forms in the BOY (Bay of Yucatan) to Ft Myers, crossing near Melbourne, FL and then lifting into coastal South Carolina as we enter the last week of October (around the 22-24th time frame). This scenario will change in   a vast array of parameters in each and every model run of the GFS as well as other models.

Point is, the period from October 19th -27th could be turbulent either over Florida and/or the Carribean and Gulf of Mexico with a tropical threat anywhere east of the Mississippi River. Watch the BOY.

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