881 
fxus62 kmfl 220113 
afdmfl 


Area forecast discussion 
National Weather Service Miami Florida 
913 PM EDT sun Mar 21 2010 


Update...significantly reduced probability of precipitation area wide as land stability 
is a major inhibitor to convection being maintained...as evidenced 
by radar/lightning data which shows a solid line of convection 
off east central Florida extending SW to just off the Palm Beach 
coast...then another band of convection over Florida Bay with just a 
few showers over the Mainland. The Miami sounding shows two 
inversions remaining...one at near 8k feet...and the other more 
significant one at near 17k feet. K-index is -13...precipitable water only 1.44 
inches. Cape though is around 1300 j/kg. Still...given 
trends...took probability of precipitation down from categorical...and lowered to 50% East 
Coast to 30% Gulf Coast. Most of the activity will be 
showers...but a few storms will remain possible tonight. 
However...will tone down hazardous weather outlook. /Gregoria 


&& 


Previous discussion... /issued 737 PM EDT sun Mar 21 2010/ 


Aviation...mostly cloudy skies will prevail as a frontal boundary 
moves across South Florida tonight. Most of the activity is 
expected to remain near kpbi...but kept vcsh/thunderstorms in the vicinity at all terminals 
overnight due to uncertainty. Will amend if necessary. Kept SW flow 
at all terminals slowing down overnight and picking up speed by 
22/11z. 


Previous discussion... /issued 617 PM EDT sun Mar 21 2010/ 


Update... 
the line of showers and thunderstorms that has been approaching 
the northern and western areas of South Florida this afternoon is 
starting to stall from about the West Palm Beach southwest to 
Naples area early this evening. The latest models are still 
showing the line should stall over the northern areas this evening 
as the steering flow becomes southwest...before moving slowly 
south through rest of the County Warning Area late tonight into Monday morning 
with the passage of the cold front. So will continue with categorical 
probability of precipitation tonight over the County Warning Area...with the highest probability of precipitation over the 
northern areas this evening shifting to the southern areas after 
midnight. 


There could still be a few strong storms tonight over the 
County Warning Area...due to the same reason mention below in paragraph 6. 


So no changes are plan at this time...except to remove the 
afternoon and evening wording. 


Update...54/bnb 


Previous discussion... /issued 330 PM EDT sun Mar 21 2010/ 


Rain likely tonight with a few strong storms possible... 


Discussion... 
a low pressure system was located over the Mississippi Valley with a 
trailing southward cold front southward into the eastern Gulf of 
Mexico early this afternoon. A pre frontal trough of low pressure 
was located from about Orlando southwest through Fort Myers into 
the southeast Gulf of Mexico where showers and thunderstorms were 
occurring. 


The pre-frontal trough will continue to move east but become 
stationary over the northern areas of the County Warning Area this evening...as 
the steering flow become parolee to the trough. So the showers and 
thunderstorms should push into the northern areas...before 
becoming stationary from about West Palm Beach southwest to Naples 
area this evening. 


Some showers have also develop over the western ares of the County Warning Area 
this afternoon...due to the heating and unstable air ahead of 
the pre-frontal trough. Showers and even a thunderstorm or two 
should develop over the County Warning Area through the afternoon hours ahead of 
the trough of low pressure. 


So have up the probability of precipitation to likely over the northern interior 
areas...with chance Cat over rest of the County Warning Area for this afternoon 
into this evening. There is also a thunder threat now over the 
County Warning Area...with the highest treat over the northern portions of the County Warning Area. 


The low pressure mention above will also move slowly east into the 
southeast United States tonight pushing the cold front slowly east 
and through South Florida mainly after midnight. This will help to 
push the line of showers and thunderstorms over the northern areas 
slowly southward after midnight...and should be over the southeast 
metropolitan areas by sunrise Monday or just offshore. Therefore...have 
up the probability of precipitation to categorical over the County Warning Area for tonight...with the 
northern areas see the highest probability of precipitation this evening before shifting 
into the southern areas after midnight. 


A short wave over the Yucatan Peninsula this afternoon will also 
move northeast and through South Florida tonight along the front. 
There will also be middle to upper level jet of 100 to 120 knots 
moving through central Florida which will put South Florida in the 
right rear quadrant of the jet...and the middle levels of the 
atmosphere will also be cooling down into the -10 to -13 degrees 
range late tonight. This usually means that there could be some 
strong to severe storms in this type of environment. 
However...there is no low level jet and the timing of the line of 
showers and thunderstorms is at night which is usually weaker due 
to the lack of heating. Storm Prediction Center also only have US in a see text for 
tonight. So at this time will mention a few strong storms over 
South Florida tonight in the severe weather potential statement product with the primary impacts 
being gusty winds and small hail...and continue to monitor the 
latest model runs for tonight. 


The low will continue to move slowly east on Monday into the 
western Atlantic waters pushing the cold front east into the 
western Atlantic waters and away from South Florida. This will 
allow for the showers and thunderstorms to slowly dissipate Monday 
morning into early Monday afternoon over the County Warning Area. So will continue 
with a chance of probability of precipitation over the northern areas to likely probability of precipitation over 
the southern areas Monday morning...before tapering down to 
slight chance north to chance south for early Monday afternoon. 


High pressure will then build into Florida Peninsula Monday night 
into Wednesday. This will allow for dry conditions along with 
cooler air to work into the County Warning Area from the north. 


Extended forecast... 
the high will then move east into the Atlantic waters late this 
week into next weekend allowing for another weak cold front to 
move through the area. So will continue the chance of showers 
over the County Warning Area Friday and slight chance of showers early next 
weekend...before going dry for the second half of next weekend. 


Marine... 
the winds early this afternoon have been coming from the south to 
southeast around 20 knots with gusts up to around 30 knots. The 
southerly winds will become southwest this evening before going 
westerly late tonight into Monday. The speeds will also decrease 
from 15 to 20 knots this evening to 10 to 15 knots by late tonight 
into Monday. So the Atlantic seas will slowly fall from 4 to 6 
feet this afternoon to less than 6 feet by late tonight into Monday. 


For the Gulf side...a northwest swell of 1 to 2 feet will work 
into these waters overnight into Monday. This will allow for the 
seas to build from less than 6 feet this afternoon to 5 to 7 feet 
Monday morning in the Gulf waters and 3 to 5 feet near-shore. The 
northeast swell will continue to increase to 2 to 3 feet on Monday 
allowing for the seas to build to 7 to 9 feet offshore and 4 to 6 
fee near-shore. 


So will continue the Small Craft Advisory for all waters until this evening before 
changing the Small Craft Advisory to a scec. The only exception is to keep the Small Craft Advisory for 
the offshore Gulf waters due to the seas building overnight into 
Monday. 


There is also a high risk of rip currents this afternoon along the 
East Coast beaches of South Florida. So will headline this in the 
afternoon zones. 


Fire weather... 
the relative humidities will remain above the critical value of 35 
percent on Monday due to the cooler temperatures. However...on 
Tuesday the relative humidities could fall approach the 35 percent 
over the northwest interior areas...due to lower dew points and 
higher temperatures. So will continue to monitor the relative 
humidities for Tuesday in the latest model runs to see if a Fire 
Weather Watch will be needed for the northwest interior areas on 
Monday for Tuesday. 


&& 


Preliminary point temps/pops... 
West Palm Beach 62 73 56 76 / 50 50 10 - 
Fort Lauderdale 65 74 58 77 / 50 50 10 - 
Miami 64 75 59 78 / 50 50 10 - 
Naples 60 69 57 76 / 30 30 10 - 


&& 


Mfl watches/warnings/advisories... 
Florida...none. 
Am...none. 
GM...Small Craft Advisory until 8 am EDT Tuesday for Gulf waters from 
Chokoloskee to Bonita Beach, Florida extending from 20 to 60 nm. 


&& 


$$ 


Long term...57/dg 
short term/aviation...17/era 

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