Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 132337
AFDMFL

Area Forecast Discussion
National Weather Service Miami FL
637 PM EST Wed Dec 13 2017

.AVIATION...
VFR through the period with generally light wind. In the morning,
a northerly to northwesterly drainage flow is expected that will
shift southerly to southwesterly during the day. The flow is light
enough the directional variability can be expected though speeds
should remain in the 5 to 8 kt range.

&&

.UPDATE...With sunset, winds are quickly becoming calm with
temperatures dropping through the 50s. Some cirrus is already
moving into the area, which will serve to arrest the best
radiational cooling. However, still expect a relatively chilly
night across the region.

Temperatures expected to drop into the upper 30s/around 40 near
Lake Okeechobee with low 40s for the remainder of the interior.
The Gulf coast and western portions of the east coast metro will
dip into the mid 40s, though wouldn`t be surprised for a few low
40s in the coldest spots in these areas. The remainder of the east
coast will stay in the upper 40s to around 50 east of I-95.

No significant changes to the ongoing forecast.

&&

.PREV DISCUSSION... /issued 318 PM EST Wed Dec 13 2017/

DISCUSSION...

THIS AFTERNOON AND TONIGHT: Another cool day across South Florida
with temperatures currently maxing out in the low to mid 60s across
the region. Dewpoints are generally in the mid-upper 30s with a few
low 40s in spots, showing just how dry the airmass is across the
area.

The surface high over the Gulf is expected to slide east this
evening, centered directly over South Florida overnight. This should
allow temperatures to decouple quickly after sunset, becoming calm
or nearly so. This, coupled with the dry air and mostly clear skies
will set the stage for excellent radiational cooling. The one curve
ball in temperatures freefalling overnight is the cirrus that
visible satellite currently shows over the Central Gulf. Depending
on when and how much of this cirrus moves overhead, which models
differ slightly about, peak radiational cooling potential may not be
achieved. Tonight`s forecast will lean on the cooler side of
guidance, with temperatures dipping into the upper 30s around Lake
Okeechobee and low 40s for the remainder of the interior. Gulf coast
and western portions of the east coast metro will dip into the mid
40s, though wouldn`t be surprised for a few low 40s in the coldest
spots in these areas. The remainder of the east coast will stay in
the upper 40s to around 50 east of I-95.

THURSDAY AND FRIDAY: High pressure center will slide across the
region on Thursday and off to our east on Friday, keeping very light
low level southwesterly flow in place. Dry and cool conditions
continue, though with slowly rising 500 mb heights, a slight warming
trend will ensue. Maximum temperatures Thursday are forecast to rise
to the low 70s, then mid to upper 70s by Friday. Overnight lows will
be range from the upper 40s across the far interior to low 60s
Thursday night, with 50s and 60s for everyone Friday night.

SATURDAY THROUGH MONDAY: The threat for any appreciable
precipitation has all but evaporated with the last two model runs.
12Z models keep the upper level ridge in place just to our
southeast, limiting any significant southward progress of the
shortwaves moving through the southern US. It looks like another
dry frontal passage Friday night, but unlike the previous few
fronts, the airmass will be modified by the time it arrives along
with winds quickly veering east-northeast. As a result
temperatures will be near normal in the mid-upper 70s on Saturday
and low 80s on Sunday. South-southeasterly flow on Monday may
allow temps to climb to near record levels in the mid 80s.

MARINE...Northwesterly winds will continue to diminish this
afternoon as high pressure builds across the region through the end
of the week. Except light and variable winds tonight into Thursday,
with flow becoming south-southwest on Friday though at less than
10kts. Weak frontal passage on Saturday will bring a little stronger
northeasterly flow with winds around 15kts, veering east on Sunday.
Seas highest this afternoon and evening at 2-4ft in the Gulf and 3-
5ft in the Atlantic, then subsiding to 2ft or less late Thursday.

FIRE WEATHER...High pressure will build across the region from
the Gulf the next few days, leading to light winds and poor
dispersions. RH values will bottom out in the mid 30s this
afternoon for most locations. A little more low level moisture is
expected to keep RHs above critical values the next few days,
though a few locations may drop into the upper 30s on Thursday. No
appreciable rain chances are expected through the period.

&&

.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach  44  71  56  77 /   0   0   0   0
Fort Lauderdale  49  71  58  76 /   0   0   0   0
Miami            50  72  56  76 /   0   0   0   0
Naples           47  73  55  76 /   0   0   0   0

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...None.
GM...None.

&&

UPDATE...88/ALM
AVIATION...02/RAG



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