583 
fxus62 kmfl 201857 
afdmfl 


Area forecast discussion 
National Weather Service Miami Florida 
257 PM EDT Sat Mar 20 2010 


..warmer/mostly dry through Sunday, then wet Sun night/Monday... 


Synopsis...mid/upper low and associated surface low over OK/Arkansas will 
move east across the deep south (ms/al/ga) Sunday night-Monday before 
moving to the Middle Atlantic States and off the eastern Seaboard 
Tue-Wed. The cold front trailing the low will move across South Florida 
late Sun night/early Monday morning with high pressure slowly building 
into the area from the northwest in its wake. 


&& 


Discussion...today Marks the first day of Spring. The Vernal 
equinox (or when the earths axis is neither tilted toward nor away 
from the sun) officially occurred at 1:32 PM EDT this afternoon. 
Pleasant Spring weather will continue across South Florida tonight 
through Sunday. Temperatures will warm...with lows holding in the 60s 
Atlantic coast tonight and staying in the 50s elsewhere. Highs on 
Sunday will be at or slightly above normal for a change...reaching 
into the lower 80s at most locales...except upper 70s along the Gulf 
Coast and immediate Atlantic coast. 


Mostly dry weather will prevail through Sunday. Have lowered probability of precipitation to 
slight chance everywhere Sunday afternoon...as GFS/NAM forecast 
soundings both show a very pronounced cap at around 5k 
feet...probably an eml (elevated mixed layer) from the Mexican 
plateau. This along with a continued rather dry profile is 
expected to keep conditions mostly dry on Sunday...with the more 
active weather remaining just north of Lake Okeechobee. 
Strengthening southeast wind flow/moisture advection underneath the cap 
will lead to considerable cloudiness on Sunday. A gusty warm 
breeze will ensue Sunday as well...with gusts of 25 to 30 miles per hour 
expected. 


The atmosphere really moistens Sunday night and the cap 
erodes...leading to better instability. Precipitable waters  rise to about 1.75 
inches and cape reaches near 1000 j/kg along with impressive 0-6 km 
shear values in the 50-60 knots range. However...the time of day does 
not Bode well for the generation and maintenance of thunderstorms 
locally (climatologically speaking)...especially given that the 
main upper level support will be to our north. GFS/NAM also only 
show 850 mb winds generally 20-30 knots...with the low level jet axis 
aligned over central Florida. So will continue with just slight chance 
of thunderstorms in the forecast as believe the Prospect for 
strong/severe looks very minimal. The Storm Prediction Center does 
mention South Florida in their day 2 outlook...but with much 
uncertainty. Later shifts can further assess with updated model 
runs to see if any mention needs to be included in the hazardous 
weather outlook. 


Although the front clears the area Monday morning...isentropic lift 
will occur in a moist environment immediately behind the front to 
result in a not-so-springlike day on Monday. Cloudy and cool 
conditions are expected with scattered showers...and even the 
possibility of a steady light rain for a time Monday. Increased probability of precipitation 
for Monday...with likely probability of precipitation East Coast and chance probability of precipitation elsewhere. 
The clouds/showers will hold temperatures down...likely significantly on 
Monday. Favored the cooler nammos guidance for Monday...which is 
5-7f degrees cooler than gfsmos. Will also significantly undercut 
both GFS/nammos for Naples...by some 5f degrees due to a west wind 
off of the rather cold Gulf waters...more in line with nam12 temperature 
depiction...just not quite as cold (which shows a high at Naples in 
the lower 60s Monday.) 


Below normal temperatures will continue through middle week...but will warm by 
late next week as a ridge slowly builds. Latest GFS though shows 
some flattening of the ridge next weekend with another impulse 
riding through the area. Made no changes to the extended forecast as 
slight chance of showers by next weekend looks good at this time. 


&& 


Marine...winds will be on the increase overnight and especially 
on Sunday. In fact...a Small Craft Advisory may be needed for 
the Atlantic waters and Biscayne Bay on Sunday. Winds will 
gradually subside by Monday-Tuesday as winds turn west-northwest behind the cold 
front. 


&& 


Fire weather...southeast wind/moisture advection is winning out this 
afternoon over mixing. This is leading to rh's not as low as 
previously forecast. Rh's are expected to fall to near 35 percent 
for a few hours this afternoon over Glades...Hendry...and inland 
Collier counties...but not long enough of a duration to meet red 
flag conditions. Therefore...we will be cancelling the red flag 
warning. Moisture will be on the increase over the next few 
days...with no relative humidity concerns. 


&& 


Preliminary point temps/pops... 
West Palm Beach 66 81 60 72 / - 20 70 60 
Fort Lauderdale 67 80 63 72 / - 10 70 60 
Miami 66 81 63 72 / - 10 70 60 
Naples 60 76 61 67 / 0 20 70 50 


&& 


Mfl watches/warnings/advisories... 
Florida...none. 
Am...none. 
GM...none. 
&& 


$$ 


Long term...57/dg 
short term/aviation...30/kob