Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 161955
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
355 PM EDT Wed Apr 16 2014
.Near Term [Through Tonight]...
With the very chilly start to the day with lows ranging from the mid
30s to the mid 40s, temperatures have struggled to climb through the
50s and into the 60s during the afternoon despite plenty of
insolation. The gusty NE winds have also aided in keeping the
temperatures down, but these should diminish over most areas by
sunset. For tonight, temps may initially fall fairly quickly under
the still dry air, mostly clear skies, and lighter winds, but should
then level off and possibly even rise during the overnight hours as
low level moisture and low cloudiness begin to increase over the
region from the southeast. That said, expect minimum temperatures to
reach the lower to mid 40s over the NW half of the CWA, to the upper
40s to lower 50s further to the SE. Also, besides putting a cap on
the temperatures, once the low level clouds become more widespread
(especially in the remaining hours before sunrise), a few sprinkles
will be possible across much of the FL Big Bend and eastern
Panhandle and near the Valdosta area in GA where the moisture
advection will initially be greatest. The chance for sprinkles (or
even some measurable light rain) will be even greater across the
marine area late tonight.
.Short Term [Thursday through Saturday]...
Much of the focus in the short term period was centered around the
evolution of a Gulf low from Thursday Night onward, and the amount
of rain that it will produce in our area. Numerical models have
begun to converge on a similar solution as the digging shortwaves
that will eventually lead to surface cyclogenesis are finally
being sampled by the upper air network over the western US.
Generally speaking, a low-amplitude shortwave trough in the mid-
upper levels will dig ESE to around 90W longitude by 00z Friday.
This will place the base of the shortwave trough and RFQ of a
strengthening upper level jet streak over the north-central Gulf
of Mexico, setting the stage for a surface low to develop. The low
should then move in the general direction of the I-4 corridor in
the Florida Peninsula by Saturday morning.
On Thursday and into Thursday evening, low-level isentropic ascent
will gradually increase, paired with a trend for higher RH and
lower condensation pressure deficits. This should lead to the
development of scattered showers in that time period, and perhaps
an isolated thunderstorm over the southern part of the area.
By late Thursday Night and early Friday, cyclogenesis over the
Gulf will be well underway. Model forecast cross sections NE of
the low from DHN-TPA show increasing mid-level frontogenesis over
our forecast area around 18z Friday. There is good model agreement
showing the development of a band of heavy rain around that time,
especially over the southeastern half of our forecast area.
Overall, the instability levels seem to be very limited so this
looks to be more of a general rain event forced by a combination
of isentropic ascent and mid-level FGEN. With PWATs expected to be
around 1.6-1.7 inches in the southeast part of our area (around +2
standard deviations above normal) and very strong forcing for
ascent, the ingredients are there for heavy rainfall. Given the
lack of instability and the long duration of rain (12-24 hours),
it seems like river and areal flooding threats would be higher in
this event than flash flooding. QPF totals are relatively close to
a model consensus and range from 2-4 inches over much of the
Florida Big Bend region and adjacent far southern Georgia, to
around 1 inch in southeast Alabama. The 16Apr.12z runs of the
ECMWF, UKMET, GFS, CMC, and NAM all show a band of 3-4 inches of
rainfall across the southeast part of our area. We did not issue a
Flood Watch yet, but one could become necessary overnight if model
consensus continues to grow around this particular solution.
.Long Term [Saturday Night through Wednesday]...
By Sunday, slight ridging will begin to settle in the area allowing
for a break from precipitation. The next chance of rain occurs
Tuesday when the flow will become more zonal and a shortwave to the
north of our area will bring a slight chance of rain and isolated
thunderstorms to the northern counties. Throughout the entire period,
temperatures will be near climatology with highs in the lower 80s,
and lows in the upper 50s.
[Through 18Z Thursday] VFR conditions will hold at the terminals
through the remainder of this afternoon and much of tonight, with
the gusty NE winds diminishing by sunset. However, by very late
tonight and into Thursday morning, MVFR level CIGS may be poised to
overtake the TAF sites from SE to NW, as low level moisture is
expected to quickly return to the region from the southeast.
After a brief break in the Advisory level conditions this afternoon,
winds and seas will be back on the increase tonight out of the east
to northeast as the pressure pattern tightens once again. Therefore,
issued a new Small Craft Advisory which will begin at 8 pm EDT this
evening for the easternmost legs, and at 2 am EDT overnight for the
rest of the marine area. This Advisory will remain in effect until 8
am EDT Friday morning, but will very likely need to be extended for
some time into the upcoming weekend, as a new low pressure system
develops in the northern Gulf of Mexico.
After the brief shot of much cooler and drier air over the region
today, low level moisture will quickly be on the increase once again
on Thursday and Friday. A developing low pressure system in the Gulf
of Mexico will then lead to yet another batch of rain over the area
on Friday and into the upcoming weekend. These inclement conditions
will ensure no fire weather concerns during the next several days
across the Tri-state area.
Heavy rains across the FL Panhandle yesterday resulted in sharp
rises on the Chipola River where the Altha gage is cresting about
two feet above moderate flood stage. Only minor rises occurred on
the Choctawhatchee, Apalachicola and Ochlockonee Rivers. Most of
the area rivers have crested and are falling steadily, except for
the Choctawhatchee River near Bruce, which is currently at its
crest but will remain in moderate flood stage until Sunday. More
rain is expected Friday. Rain totals of 1 to 3 inches are possible
with 2 to 4 inches possible in the Florida Big Bend region.
Isolated areas may see higher totals.
As rain rates should be more gradual, with the above rainfall
totals expected to fall over 12-24 hours, the flooding threat with
this next round of rain should be of the areal/river variety.
The flash flooding threat should be lower. In other words, areas
of existing high water or flooding may worsen... and areas of
high water could also develop in places like fields or low-lying
areas. River flooding will also be possible - particularly in
rivers around the Florida Big Bend and Apalachee Bay region.
The most up-to-date river forecast information can always be found
on our AHPS page (below):
.Preliminary Point Temps/PoPs...
Tallahassee 49 70 61 67 55 / 10 30 70 80 80
Panama City 49 71 63 67 58 / 10 30 80 80 60
Dothan 44 68 57 65 53 / 0 10 50 60 50
Albany 44 70 55 66 52 / 0 10 50 70 50
Valdosta 49 70 59 67 56 / 10 20 60 80 80
Cross City 53 74 63 73 57 / 10 30 60 80 80
Apalachicola 49 70 65 68 60 / 10 30 80 80 80
FL...High Rip Current Risk until Midnight EDT tonight for Coastal
GM...Small Craft Advisory from 8 PM this evening to 8 AM EDT Friday
for Apalachee Bay-Coastal waters from Suwannee River to
Keaton Beach FL out 20 NM.
Small Craft Advisory from 2 AM Thursday to 8 AM EDT Friday for
Coastal waters From Ochlockonee River to Apalachicola FL
out to 20 NM-Coastal waters from Apalachicola to Destin FL
out 20 NM-Waters from Suwannee River to Apalachicola FL
from 20 to 60 NM-Waters from Apalachicola to Destin FL from
20 to 60 NM.