Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 131424 AAA

Area Forecast Discussion...UPDATED
National Weather Service Miami FL
924 AM EST Wed Dec 13 2017

The issue for consideration with this update is tonight`s
low temp forecast. Model consensus and blends are in line with
the official forecast. However, over the past few days, and in
particular during the coldest nights, the blends have shown a warm
bias to the point that during two of the nights patchy frost was
reported as far south as inland farming sections of Miami Dade.
For tonight, the consensus of the guidance brings surface dew
points into the mid 30s across most of the inland areas away from
both the west and east coasts. The synoptic pattern places the
surface high right across the region leading to complete
decoupling. This combined with clear skies should set the stage
for good radiotional cooling taking place. There will be some
moisture increase along with some clouds returning tomorrow from
west to east and depending how early that start it could hamper
the radional cooling potential. But odds favor this happening
after peak radiotional cooling time in the early morning hours.
So lowered the temps inland a bit with forecast lows now dipping
into the upper 30s in traditionally cooler spots inland during
this kind of event. This means there is a chance that patchy
frost, at the very least, could be observed in coldest spots given
ground temps would be slightly colder than forecast and that
there is about a 1 in 10 chance temps could end up even colder
than forecast. This would impact cold sensitive crops.

No other updates are planned at this time.


.PREV DISCUSSION... /issued 554 AM EST Wed Dec 13 2017/

High pressure is settling in behind last nights cold front. The
wind is forecast to continue to be northwesterly through the day.
This evening expect light and variable conditions shortly after
sunset. Skies are forecast to be clear to mostly clear through the
TAF period.

PREV DISCUSSION... /issued 413 AM EST Wed Dec 13 2017/

Latest WPC surface analysis shows the center of a well defined low
pressure system over Maine, with a cold front extending south
southwest, draped across the far tip of South Florida. IR
satellite imagery depicts clear skies across the region, with mid-level
alto cu spreading over the Florida Straights. Behind this
feature, winds have turned northwest, generally 10 to 15 mph over
land with breezier conditions over the local waters. Minimum
temperatures are on track to plummet into the low 40s near Lake
Okeechobee this morning, to around 50 along the east coast metro.
By this afternoon, winds will ease, trending weaker with time.
With a very cool and dry atmospheric behind the frontal passage,
maximum temperatures will struggle to reach the mid/upper 60s,
nearly 10 degrees below normal for this time of year.

Thursday through Friday: Through the mid range forecast, zonal
flow will remain in place over the peninsula. This synoptic pattern
should continue the light west or southwest flow, along with dry
and cool conditions. However, 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. Expect dry atmospheric conditions, with PWAT values
progged to remain well below 0.75". Thus, not anticipating any
precipitation during this period.

Friday through Monday: Long range models are in better agreement
now, washing out a weak cold front over northern Florida early in
the weekend and keeping our CWA mainly dry. Both high pressure
aloft and at the surface will begin to build to the north of our
region Sunday into Monday, which will act to shift winds to the
southeast and continue the warming trend. Forecast temperatures on
Sunday and Monday climb into the low to mid 80s, within a few
degrees of daily records.

Gusty northwest winds behind a dry frontal boundary
will continue to bring hazardous boating conditions through early
this morning, weakening slightly by this afternoon. Seas will
generally be 3 to 5 feet today. Late Saturday into Sunday, high
pressure will build to the north, leading to breezy easterly
winds over the coastal waters.

A dry front will continue to push through the region through early this
morning with high pressure building overhead. The resulting light
winds will lead to poor dispersions, with the reinforcing dry airmass
allowing RH values to near or drop below critical thresholds for
several hours this afternoon. However, according to the Florida
Forest Service, ERC values are expected to remain below critical

West Palm Beach  68  45  70  55 /   0   0   0   0
Fort Lauderdale  68  49  71  59 /   0   0   0   0
Miami            69  49  72  59 /   0   0   0   0
Naples           68  49  72  57 /   0   0   0   0



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