Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 061428
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
928 AM EST Thu Mar 6 2014
.Near Term [Through Today]...
The latest regional radar mosaics at 14z indicated that the back
edge of a large area of rain was just about reaching the western
boundary of our forecast area - roughly a MGM-DTS line. Model
guidance is in excellent agreement that this will slowly clear
east today. Given the good agreement, we sharpened up the drying
trend in hourly weather grids and PoPs, but otherwise left the
forecast generally unchanged. Even with the rain gradually coming
to an end, we expect that low stratus may hang in through much of
the day keeping temperatures cool. The best chance for some breaks
of sun would be in the western part of the area. We shouldn`t set
any low maximum temperature records, but highs should be around 20
degrees below normal.
The main concern otherwise is related to the possibility of a wake
low developing on the trailing edge of the rain as it clears
through the area today. Some of the high-resolution model guidance
explicitly generates a wake low late this morning and early this
afternoon, including our local 4km WRF and the HRRR. The WRF shows
a sharp 1hr pressure fall and rise couplet with magnitudes up to
about 4mb or so. The largest pressure fluctuations on the models
tend to be in SE AL or SW GA, and that is where the stronger
easterly low-level flow (925-850mb) is as well. Therefore, those
are the locations we would expect to see the stronger wind gusts
if the wake low does in fact materialize. There is some evidence
that one is beginning to develop as of 14z with a well defined
pressure trough extending north from the Gulf low roughly right
along the back edge of the rain (DTS-MGM). Some observations in SE
Alabama and coastal Bay County have gusted to between 20 and 30
knots in the past hour or so. Based on the available information,
we wouldn`t be surprised to see some easterly gusts to 30-40mph
late this morning or early this afternoon as rain comes to an end
in SE Alabama or SW Georgia. We will keep an eye out for any
higher values in the event a Wind Advisory is needed. For now, we
increased gusts in the forecast to around 35 mph.
.Prev Discussion [624 AM EST]...
.Short Term [Tonight Through Saturday]...
The 500 mb flow pattern will become a bit more amplified/phased,
which will put an end (for the time being) to the systems that
have been training quickly along the Gulf Coast this past week. By
tonight a large, intense dry slot will be wrapping around most of
the 500 mb low, which will be propagating slowly east-
northeastward over GA. It`s curious that all of the various
dynamical models and MOS forecast such high PoP and relatively
high QPF for our forecast area tonight and early Friday, as the
vast majority of the time when we get "dry slotted" the rain just
stops. In particular, the 00 UTC GFS QPF bullseye over southwest GA
(with an inch of rain) would be unprecedented for this type of
synoptic pattern. Based on the climatology of these systems, we`ve
undercut the guidance consensus PoP and QPF a bit, though that
still leaves much of our region with a 50-60% PoP overnight. The
rain will end from west to east during the day on Friday, but the
SREF ceiling guidance holds on to the cloud cover until later
Friday afternoon. This, along with the relatively cold nature of
this system, will keep highs below average on Friday (lower to mid
50s around Tifton, upper 50s to lower 60s elsewhere). 500 mb
heights will rise dramatically Friday night and Saturday, as an
area of surface high pressure becomes centered over our region.
With clearing skies, calm winds, and a dry boundary layer, lows
will fall into the upper 30s in the normally colder inland
locations away from the beaches Friday night. On Saturday a
warming trend will begin, with highs in the lower 70s (mid 60s at
the beaches, as the Gulf waters are still rather cool).
.Long Term [Saturday Night Through Thursday]...
We should finally see some warming to around normal levels.
Unsettled weather will move back into the area by mid week ahead
of yet another system. There remain differences between the
operational GFS and Euro with this next system as the Euro phases
with a nrn stream impulse and GFS does not. However, both bring
another shot of rain during the mid week period. Expect highs in
the 70s through mid week.
[Through 12z Friday] Rather poor conditions will continue through
the period with prevailing IFR/LIFR cigs and widespread rain as an
area of low pressure develops south of the area. Rain may decrease
some during the afternoon around KDHN and KECP with a potential
dry slot, but conditions are expected to remain below VFR through
the period. Winds could be gusty at times today, especially at
KDHN and KABY.
Some of the NWP guidance has underestimated the wind speeds over our
coastal waters this early morning, which they tend to do sometimes
when there is a high pressure "wedge" just to our north and a
quasi-stationary front (with developing frontal cyclone) to our
south. In fact, winds were very close to advisory levels. We relied
more on the higher-resolution NWP guidance for today, as these
models have verified a little better thus far. Winds will weaken
slightly this afternoon, but still remain at moderate levels from
the north or northeast through Friday. Much lower winds and seas are
expected this weekend as an area of high pressure becomes centered
over the marine area.
Red flag conditions are not expected over the next several days,
though dispersions will remain low today with widespread rain.
Most of the rainfall on Wednesday was 0.25 in or less, with
isolated amounts between 0.50 to 1.0 in. Rainfall totals for this
next system (today through Friday) will average between 1.0 and
1.5 inches, with the heaviest amounts likely across the FL Big
Bend and South Central GA. These amounts are unlikely to cause
flash flooding, even though isolated heavier amounts could cause
some standing water in poor drainage areas. However, this will add
a fairly large volume of water to several rivers that already
exhibited above-normal flow. The latest GFS, CMC, and SREF based
hydrologic ensembles (MMEFS) continue to forecast several sites to
reach action stage over the next several days. This is a common
scenario this time of year when there is an El Nino pattern. This
means that many of the local rivers will essentially be "primed"
for flooding, if they get another round(s) of soaking rain in the
next week or two.
.Preliminary Point Temps/PoPs...
Tallahassee 55 43 57 38 70 / 100 60 20 0 0
Panama City 58 43 61 48 67 / 100 50 10 0 0
Dothan 50 38 58 41 71 / 100 60 20 0 0
Albany 47 38 54 40 71 / 100 60 40 0 0
Valdosta 52 41 55 40 70 / 100 60 40 0 0
Cross City 60 46 61 38 71 / 100 40 20 0 0
Apalachicola 63 44 61 47 66 / 100 50 10 0 0
GM...Small Craft Advisory until 5 PM EST this afternoon for
all zones of the coastal waters.