Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 241758

Area Forecast Discussion
National Weather Service Miami FL
158 PM EDT Tue Apr 24 2018

Showers and thunderstorms are developing N/W of terminals this
afternoon and will likely spread east and impact in the vicinity
of terminals from 19z through at least early evening. Will likely
need to add TEMPO groups as timing/coverage confidence
increases,especially for PBI and Broward sites. Atlantic breeze
could temporarily turn winds SSE at KFLL and possible other sites,
but generally SW wind 10 KT will prevail. Cold front passes
tonight, turning winds to NW at 5 - 10 KT, which will continue
into Wednesday as skies clear.


.PREV DISCUSSION... /issued 1101 AM EDT Tue Apr 24 2018/

Showers are beginning to develop over Hendry and Glades counties,
and this activity is likely to become stronger and more numerous
into the afternoon as it moves eastward toward Palm Beach County.
CAMs depict widespread convection over and near Palm Beach County,
then diminishing coverage and intensity to the south and west,
with no precipitation close to the Gulf Coast. Have adjusted POPs
accordingly, raising risk over Palm Beach County and lowering it
in the S/W. 12Z RAOB analysis shows evolving unstable atmosphere,
with plenty of cold air aloft to support some strong
thunderstorms. Feel that northeast parts of South Florida could
have near-severe wind gusts and some hail, isolated in nature.
Will also have to monitor for a potential Atlantic breeze
development, which would lead to backed winds, much enhanced shear
and potential for an isolated tornado. This still appears unlikely
but potential appears to have increased slightly from earlier
guidance. Also, decreased cloud cover this morning, otherwise no
changes to previous forecast.

PREV DISCUSSION... /issued 334 AM EDT Tue Apr 24 2018/


TODAY: Slow moving upper level low that has been driving our weather
the past few days continues to gradually meander northeastwards
across the TN and OH valleys this morning. Satellite derived PWATs
trace out the path of its associated surface front quite well, with
a sharp demarcation between the 1.6-1.7" values across south and
eastern Florida and the 0.5-1" values across the Panhandle and
northeastern Gulf.

Timing is consistent between models in bringing the front into South
Florida just after midday. Before then, expect most land areas to
remain fairly dry, other than a rouge shower or two, with most
activity over the waters.

Several factors come together in addition to the front`s arrival for
another fairly active afternoon across South Florida. Temperatures
aloft remain cool, around -9 to -10C, contributing to steep lapse
rates as surface temperatures will climb back into the mid to
upper 80s and low 90s. We are expected to remain in the moist
sector through this afternoon, with values well above normal.
80-90kt upper level jet and vort max are expected to dip far
enough south to give upper level support to any development.
Potential for weak Atlantic seabreeze development will also aide
surface convergence.

Best coverage should favor Lake Okeechobee and the east coast,
following the best surface convergence, through the afternoon and
early evening hours. Lightning and heavy rain remain the biggest
threats, though strong wind gusts, hail, and potential for
waterspouts/landspouts can`t be ruled out given the environment.

TONIGHT: Upper level low is expected to weaken and merge into the
larger trough overnight, bringing its accompanying surface low up
the east coast. As the main axis of the upper trough moves east of
the state, it should drive the surface front south of the area,
leaving only a few lingering showers across the local Atlantic
waters by daybreak Wednesday.

WEDNESDAY AND THURSDAY: A few days of dry weather are expected
behind the front for midweek. No appreciable change in highs
temperatures are expected, with values continuing in the mid to
upper 80s both days. Lower humidities will allow cooler overnight
lows ranging from the upper 50s over the interior and mid to upper
60s along the coasts.

FRIDAY INTO NEXT WEEKEND: Larger east coast trough is expected to
continue to dominate the pattern into the extended. Several
shortwaves are expected to rotate around its base through the
Northern Gulf coast/Deep South, potentially driving the development
of another weak surface low and some manner of front that slides
down the FL peninsula this weekend.

Over South Florida, we look to see a gradual increase in moisture
from south to north as the old frontal boundary drifts back into the
region. Expect the threat for showers to return to the forecast,
potentially lingering through most of the weekend depending on the
exact evolution of the features further to our north. Daytime highs
look to remain the same, with overnight lows gradually warming back
into the 60s and low 70s.

MARINE...Moderate south-southwest winds today as a frontal boundary
makes its way through the region, veering west-northwest by daybreak
behind the boundary. Expect west-northwest winds around 10kts to
linger into the upcoming weekend. Speeds will be light enough to
generally allow the Atlantic seabreeze to develop near the coast
each afternoon, bringing winds out of the south-southeast.

Showers and storms will be numerous again this afternoon, especially
across Lake Okeechobee and the local Atlantic. Drier conditions are
expected through midweek, with a few showers returning to the
forecast by the upcoming weekend.

West Palm Beach  66  84  67  82 /  30   0  10   0
Fort Lauderdale  70  86  69  86 /  30  10   0   0
Miami            70  85  69  86 /  20  10   0   0
Naples           67  81  64  81 /  10  10   0   0



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