Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 200803

Area Forecast Discussion
National Weather Service Miami FL
403 AM EDT Tue Mar 20 2018


TODAY AND TONIGHT: Unsettled 24 hours setting up across the state
as compact upper level low current traversing the OH Valley moves
eastward into the northeastern US later this morning. Behind it,
strong upper level jet diving into the Deep South will drive digging
trough that is forecast to move into the eastern Gulf late this

Last night`s activity has diminished across the state as the first
upper low has pulled out, but expect activity to re-energize along
a diffuse boundary across North Florida later this morning. The
front is expected to push through the state and into South Florida
towards sunset this evening.

Lingering dry air in the midlevels and lack of an organized
forcing mechanism to initiate convection should keep at least the
first half of the day dry despite the relatively unstable
atmosphere in place with dewpoints in the 60s and 70s and near
record highs across most of the area.

Best chances for convection will be late this afternoon into this
evening as the boundary moves into the far northwest/Lake region.
This activity will be developing with a 35-50kt low level
southwesterly jet in place along with lingering midlevel dry air.

The primary severe weather threat is expected to be strong to
severe straight line wind gusts. However, large hail and rotating
storms can`t be ruled out especially if the boundary arrives
slightly earlier and can better utilize peak daytime heating. The
outlook from SPC places area north of I-75 in a marginal risk for
severe thunderstorms, with a slight risk around the Lake
Okeechobee region.

As the front moves further into South Florida during the late
evening and overnight hours, the shortwave trough will be departing
the region, bringing increasing subsidence and tending to suppress
deep moist convection with time. The weakening surface convergence
along the front may be just enough for an isolated gusty shower to
persist as the front reaches south of I-75 later tonight, but
coverage is expected to be low.

WEDNESDAY AND BEYOND: Strong trough evolving into an upper level low
across the OH Valley and Mid Atlantic will shift the evolving low
pressure system up the east coast on Wednesday. This will crank the
frontal boundary through South Florida, with even most most
conservative model clearing out the region by daybreak Wednesday.

Another cool and dry airmass will overspread the region behind the
front for the remainder of the week into the upcoming weekend.
Daytime highs Wednesday through Friday will be in the low to mid
70s, climbing back to a more seasonable upper 70s and low 80s for
the weekend as flow veers easterly. A return of chilly overnight
lows is expected with low ranging from the mid 40s to mid 50s
Wednesday and Thursday night, with a gradual warmup into the


.MARINE...Winds are expected to pick up to 15-20kts out of the
south-southwest over all the water later this morning ahead of an
approaching system. Expect showers and storms ahead of and along the
front from early afternoon through most of the overnight, with the
best coverage generally over the Gulf waters and Lake Okeechobee.
Stronger storms necessitating Special Marine Warnings can not be
ruled out.

Winds veer northwesterly Wednesday morning behind the front, with
speeds continuing to hover around 15-20kts into Thursday. Local
Atlantic waters may see steady 20kts at times through this
timeframe. The increase in winds will drive an increase in seas,
coming up to 6-7ft over the local Gulf waters by daybreak Wednesday.
Atlantic waters will see seas coming up to 6-8ft in the Gulf Stream
on Thursday.

Conditions steadily improve Friday into the weekend as high pressure
moves over the region.


.AVIATION...KAPF and remainder of interior may see periods of IFR
vsbys/cigs in fog through 14Z. Light SW winds increase to
15G25KT late this morning ahead of front. VCSH after 17/18Z for
KAPF, KFLL, KFXE, and KPBI as front approaches late this
afternoon. Few TSTMS possible, especially vcnty KPBI and KAPF, but
as threat would most likely be after 00Z will keep out of TAFs
for now.


.BEACH FORECAST...Breezy south-southwesterly winds will lead to a
moderate risk of rip currents at the Gulf Beaches today, with the
potential for the risk to become high Wednesday and Thursday with
breezy northwesterly winds behind a front. North, and eventually
northeasterly flow, in combination with a 1-3 foot swell may lead to
an enhanced risk of rip currents along the Atlantic beaches into
this weekend.


.FIRE WEATHER...Gusty south-southwesterly flow ahead of a frontal
boundary will lead to excellent dispersions across much of South
Florida this afternoon. Showers and storms are expected across the
area this afternoon and overnight with the front, with wetting rains
expected for most of the region.

Another very dry air mass will move into the region behind the cold
front Wednesday. Minimum RH Wednesday afternoon will be in the 30-35
range over parts of the interior, and in the 20-30 percent range
over most of the region Thursday and Friday afternoons, before
increasing to 35 percent or higher this weekend. At this time, winds
above 15 mph are not expected to coincide with the low RH periods,
so headlines are not required.


Near record highs are possible along the east coast today.

City           Forecast / Record High (Year)
Miami             89        89 (2008)
Ft. Lauderdale    88        91 (1965)
W. Palm Beach     91        92 (1965)
Naples            83        90 (1977)


West Palm Beach  91  61  79  52 /  10  30   0   0
Fort Lauderdale  88  66  81  55 /  10  30   0   0
Miami            89  68  81  54 /  10  30   0   0
Naples           83  66  73  53 /  50  40   0   0




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