Area Forecast Discussion
Issued by NWS Melbourne, FL

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FXUS62 KMLB 081453
AFDMLB

East Central Florida Forecast Discussion
National Weather Service Melbourne FL
953 AM EST Fri Dec 8 2017

.DISCUSSION...
...Slight Chance for Severe Storms this Evening and Overnight...
...Turning Much Colder This Weekend...

Today-Tonight... Upstream convection is developing over the eastern
gulf with local winds increasing on the Air Force 915 mhz profiler
network based near XMR. Low clouds have been hanging tough at mid
morning across much of the area, however as the warm sector thickens
there should be an opportunity for SB instability to develop during
the course of the afternoon. The vigorous disturbance approaching
from the gulf today will be the main player in development of
organized storms.

modified prev disc...

Models have continued to trend a tad slower with the approaching
system. A weak wave of low pressure will move along quasi-stationary
frontal boundary in the Gulf of Mexico through this evening then
transition northeast of the area after midnight. This will pivot a
cold front southeastward through northern sections late tonight with
the 00z GFS showing it reaching the Treasure Coast by about daybreak
Sat. This is slightly slower than 24 hours ago.

Warm temps will develop in the increasing southwest flow with higher
theta air working well northward across central FL. As a result,
would expect some late day convection to initiate due to boundary
interactions well ahead of cold front.

By tonight, we expect a band of storms along the cold front to
approach northern sections and move steadily eastward across the
rest of the area through the overnight hours.  Deep layer shear will
be increasing ahead of an approaching shortwave trough aloft,
allowing for some organization of storms within a band of pre-
frontal convection. Increasing southerly flow will advect quite
high dewpoints near 70 degrees into the central peninsula, while
divergence aloft provides storm evacuation. This looks supportive
of the overnight convection being maintained as it traverses the
peninsula.

The Storm Prediction Center has much of east central Florida within
a slight risk for severe weather. Damaging wind gusts will be the
main threat, though a slight chance for tornadoes also exists.  We
generally expect a steady progression of the squall line across the
area during the overnight hours. More recent HRRR model runs suggest
the line could be approaching Lake county around 9-10 PM, moving
east around 30 mph. This is within a reasonable couple hours of GFS.
Any pre-frontal band of convection becomes more prominent over the
Gulf, we`ll be able to give better estimates of the squall line`s
timing.

Sat-Sat Night...
Early in the period a cold front will lie south of the Cape with
ongoing showers and isolated storms across ECFL. Aloft, an upper
trough extending from the FL Panhandle southwestward through the
GOMEX will advance eastward and into north-central FL by sunset
Sat evening. This upper wave will continue to weaken through the
night as it ventures into south FL. Diffluence aloft from the tail
end of a 120-130kt upper jet will aid the shower/isolated storm
activity. Highest PoPs from north Osceola-Cape southward,
initially 70-90pct will decrease from north to south during the
day. PoPs north of here 50-70pct and will end much quicker during
the morning/early afternoon as the activity spreads southeastward.
A few strong storms during the morning cannot be ruled out,
especially south of Melbourne. Gusty winds, lightning, coin-size
hail, and torrential downpours the main threats. Winds will become
west- northwesterly behind the front. Wind speeds will approach
15-20 mph with frequent higher gusts, at times, during the day.
Speeds will decrease during the evening/overnight but may remain
elevated near 10 mph.

Temperatures on this day will range from the M50s to L60s near/north
of I-4. Southward generally 60s, but may see some temperatures
around 70 degrees along the St. Lucie/Martin coasts. Cold air
advection pours down the peninsula Sat overnight. Lows for most
areas may realize down into the 30s, except L-M40s immediate St.
Lucie/Martin coasts, and some larger metropolitan areas may be
closer to around 40 degrees. Elevated winds Sat night should keep
frost concerns low, but lowest wind chills after midnight and
towards sunrise Sun morning will be in the L-M30s almost areawide. A
Wind Chill Advisory may be necessary for Sat overnight across much
of the area.
&&

.AVIATION...
During the late afternoon and early evening there will be a chance
of showers and slight chance of storms but the main threat for
strong-severe storms looks to begin tonight. The HRRR model is
starting to show the line of storms approaching KLEE around 02-03z,
moving east near 25 knots.  This would sweep the line through KISM-
KMCO-KSFB-KDAB by about 04z, reaching KTIX-KMLB by 06-07z and KVRB-
KSUA early Saturday morning.

&&

.MARINE...
Today-Tonight...South/southwest flow is progged at 10-15 knots
then the gradient will tighten tonight as a weak wave of low
pressure in the Gulf of Mexico approaches. Speeds will pick up to
15-20 knots by midnight and 20-25 knots offshore before sunrise
Sat behind a cold front. This will necessitate an exercise caution
statement this evening and a Small Craft Advisory offshore late.
There is a slight chance for offshore moving storms late this
afternoon into evening. An organized line of storms is expected to
traverse the waters late tonight through the pre-dawn hours of
Sat. These storms will be capable of producing wind gusts over 40
knots.

&&

.MLB WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...Small Craft Advisory from 4 AM Saturday to 10 AM EST Sunday for
     Flagler Beach to Volusia-Brevard County Line 20-60 nm-
     Sebastian Inlet to Jupiter Inlet 20-60 nm-Volusia-Brevard
     County Line to Sebastian Inlet 20-60 nm.

&&

$$

JP


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