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fxus62 kmfl 211124 
afdmfl 


Area forecast discussion 
National Weather Service Miami Florida 
624 am EST Sat Nov 21 2009 


Aviation...mostly VFR conditions are expected through the period, 
however apf, pbi, and tmb will continue to see reduced visible through 
13z with br. This may occur again tonight. Nearly calm winds will 
gradually increase to near 10kts by middle morning from the NE. 




&& 


Previous discussion... /issued 458 am EST Sat Nov 21 2009/ 


Discussion... 
current reflectivity data from kamx continues to show isolated 
light/moderate showers activity affecting primarily the Palm 
Beach coast and adjacent waters...where low-level convergence 
continue to be maximized between easterly flow to the south and 
northerly flow off the coast of east central Florida. Across 
inland areas...the combination of generally clear skies...calm 
winds...and nearly saturated conditions has allowed for the 
formation of fog...and a dense fog advisory has been issued for 
interior zones through 8 am EST. Models indicate that a very 
diffuse zones of low-level convergence will exist across the 
northern half of the forecast area today...and this may very well 
be the focus for isolated afternoon shower activity...as precipitable waters  are 
expected to remain in the 1.25-1.5 inch range. With this in 
mind...and increasing southerly component to steering flow...will 
keep highest probability of precipitation across the northern interior today. 


Models continue to suggest that southeasterly flow will strengthen 
across the entire area overnight...as surface cyclone over the 
western Gulf lifts east-northeastward toward the central Gulf 
Coast. This will support at least isolated/widely scattered shower 
activity across the local Gulf waters...and with lower rain 
chances along the southeast coast...and generally dry conditions 
expected inland. Large scale ascent associated with a broad low- 
level warm advection regime will be in place over the area on 
Sunday...and should be sufficient to promote the development of 
scattered showers area-wide...as deep layer moisture will also 
increase...with precipitable water values increasing to 1.5-1.75 inches for most 
locations. Will continue trend of low-end chance probability of precipitation...although 
rain chances may actually be slightly higher for eastern zones 
with southwest steering flow regime in place. Some lingering 
shower activity is possible on Sunday night/Monday morning... 
especially across the East Coast where a weak prefrontal wind 
shift axis may ignite development as it gradually shifts eastward 
and offshore. The trailing cold front still appears as if it will 
loos its identity rather quickly as it drifts southeastward across 
central Florida and toward the Lake Okeechobee region on Monday. 
However...it may provide enough low- level convergence to focus 
development of showers over the northwest counties Monday 
afternoon...especially given high levels of residual moisture. 
Although South Florida will be in the warm sector of the 
cyclone...and the threat for thunderstorms is non-zero...will not 
mention isolated thunder at this time...given weak lapse rates and 
limited instability. As far as temperatures are concerned...will 
use close to a persistence forecast for highs today...with east- 
southeast flow leading to warmest temperatures along the Gulf Coast this 
afternoon...and along the Atlantic coast overnight. Temperature 
forecast is a little trickier on Sunday and Sunday night...with at 
least some maritime influence possible along both coasts. 


Medium range guidance from the European model (ecmwf)/GFS has not changed much 
since last night...with the general trend of a weak front 
stalling in the vicinity of South Florida on Monday continuing. 
This diffuse boundary may very well linger in the area for much of 
next week...providing the focus for scattered showers...especially 
along the East Coast where moisture will remain deeper and low- 
level flow will be primarily from the east. A strong upper low is 
still forecast to dig southeastward across the northern plains 
early in the week...with another strong clipper type system 
expected to phase with it and develop a potent long wave trough 
across the eastern U.S. By middle/late week. It still appears as if 
the clipper system will provide enough forcing to drive a strong 
cold front across the area on Thanksgiving day...bringing an end 
to scattered shower chances... and resulting in much cooler/drier 
and blustery conditions from Thanksgiving night through next 
weekend. 


Marine... 
latest wave watch guidance indicates that a small...1-3 foot 
northeast swell will continue to affect the local Atlantic 
waters through the end of the weekend...contributing to a locally 
higher threat for rip currents along the Palm Beach County coast 
and combined seas of 1-3 feet. Otherwise...there are no marine 
weather concerns...through mid-week...when northeast flow will 
increase to around 15 knots and allow seas to increase to 3-5 feet 
for most of the Atlantic/Gulf marine zones. Stronger north to 
northwest winds are anticipated following passage of a cold front 
on Thanksgiving day...with increasingly rough conditions lasting 
through next weekend. 


Fire weather... 
there are no fire weather concerns through the middle of next 
week...with low-level moisture values remaining sufficiently 
high for minimum afternoon relative humidity values of 50-55 percent. A much 
drier air mass following passage of a strong cold front may result 
in lower relative humidity values and increasing fire weather concerns toward the 
end of next week. 


&& 


Preliminary point temps/pops... 
West Palm Beach 83 71 83 69 / 10 20 40 40 
Fort Lauderdale 84 74 83 72 / 10 20 30 30 
Miami 85 73 84 72 / 10 20 30 30 
Naples 86 68 84 69 / 10 20 40 30 


&& 


Mfl watches/warnings/advisories... 
Florida...dense fog advisory until 8 am EST this morning for flz063-flz066- 
flz067-flz070-flz071-flz073. 


Am...none. 
GM...none. 
&& 


$$ 


Long term...70/dd 
short term/aviation...04/at