AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
430 AM EDT Wed Jul 4 2012
SYNOPSIS and Short Term (Rest of Tonight through Friday)...After a
one day break in the evening and overnight MCS Cycle on Monday with
a generally suppressed day of CONVECTION, we certainly made up for
lost ground late Tuesday afternoon and tonight, AS another MCS
barreled down into our CWA from the north. The main difference
between tonight`s MCS and Sunday NIGHT`s was the earlier begin and
end times of the deep convection, as just a FEW spots of light RAIN
are lingering across parts of our GA zones as of 1230 AM EDT.
Otherwise, the remainder of the CWA is essentially just blanketed in
a CIRRUS Deck which should gradually dissipate as the night GOES on.
Although we have somewhat regrettably held off on a clear, concise,
and deterministic forecast for today and tonight, (which obviously
includes all of the important 4th of July festivities and
celebrations,) FCST confidence is finally beginning to increase.
Typically, unless we are in a very steep Upper Level TROF Axis
(which does not appear to be in the cards until Thursday and
Friday), it is more common to get MCS development on an every other
day type basis, as the ATMOSPHERE takes more time to recover from
the most recent destabilization. This could be very good news for
today and tonight, as the Bulk of Global and HI-Res Models (that
have come in thus far) are now more indicative of SCT afternoon and
evening Sea Breeze induced showers and thunderstorms. However, even
with the POPS now more LIKELY to occur in the afternoon and early
evening (before much of the fireworks displays), the 1000-700 MB
MEAN Layer Vector WIND (MLVW) is very light today, and it could be
argued as either a Type 1 or LOW End Type 4 Sea Breeze Day. This is
important because any showers or storms that do develop could be
fairly slow movers and thus potentially dump some locally heavy
RAINFALL where they do occur. Although, no Severe Storms are
expected at this time, a potential strong STORM or two with gusty
winds cannot be ruled out either at this time.
One other interesting note is that both new 00 UTC NCEP WRF runs
have arrived, and they have both reverted back to NE to SW moving
MCSs through our CWA in a very similar manner in which they
attempted to do on Monday Night. Since these earlier solutions never
came remotely close to verifying, will discount them at this time,
but will need to be cognizant just in case the 12 UTC runs (as well
as our local 06 UTC run) come in with similar solutions. Also, it
should be pointed out that these MCSs have a much earlier begin and
end time than those prognosticated for Monday Night, and are also
significantly weaker in nature.
For Thursday through Friday, expect the dominant Upper Level RIDGE
which was responsible for our most recent Heat Wave, to continue to
build further off to our NW which should allow the Upper Trof Axis
to SET up across our CWA. This should lead to a more UNSETTLED
pattern over our area with cooler afternoon HIGH Temperatures,
Higher PoPs, and more CLOUD cover both day and night.
.LONG TERM [Friday Night through next Wednesday]...The general
trend in the extended part of the forecast will be for a gradually
retrograding upper level ridge axis - from the Midwest over the
weekend to the Intermountain West by the middle of next week. This
will be forced in part by an amplifying longwave TROUGH and falling
MID-upper level heights in the Northeast and Eastern US. There are
some differences in the 04.00z runs of the GFS and ECMWF. The ECMWF
develops the trough axis at our latitudes much further west next
week (over MS/LA). This would set up a prolonged period of
weak-moderate southwesterly FLOW. The GFS, on the other hand, keeps
the primary trough axis along the Atlantic coast with the ridge
still having influence over the Lower Mississippi River Valley. The
CMC seems to side with the GFS in this regard. As we are headed into
the season where sea-breeze convection usually has great influence
on the forecast, the differences in the flow regime matter.
For the weekend, it doesn`t seem to matter quite as much as model
consensus is on weak-moderate S-SW flow. A blend of HPC PoPs and
local sea-breeze CLIMATOLOGY for regime 4 was used from Saturday
into Monday as a result. This focused 40% PoPs across our Florida
zones in the afternoons, with 30% PoPs north across Alabama and
Georgia. For Tuesday and Wednesday, the GFS would transition us to
more northwesterly flow. However, the 04.00z GFS ENSEMBLE mean shows
the possible approach of a low-level cold FRONT by that time frame,
so PoPs were kept around 40% over most of the area. High TEMPS look
to be in the low-mid 90s for much of the extended.
.Marine...A few Land Breeze showers were able to form over the
Coastal Waters last night which has been a fairly rare occurrence
thus far. Other than increasing chances for showers and
thunderstorms over the Marine Area during the next couple of days,
generally light winds will continue with an onshore component along
with low SEAS through the forecast period.
.AVIATION...[through 06z Thursday]...
There will be the potential for some FOG overnight, particularly as
mid-level cloud cover lingering from earlier storms diminishes by
around 08-09z. For now, we included 2-3 hours of IFR VISIBILITY just
before SUNRISE at TLH, VLD, and ABY, with MVFR at the SAME time at
DHN and ECP. Some brief reductions to LIFR (below 1 mile) cannot be
ruled out, particularly at TLH which received heavy rainfall today,
but confidence is not high enough to include in the 06z TAFs. It
looks like afternoon storms may develop more along the sea breeze
today so VCTS was included at TLH, ECP, and VLD for now. Confidence
in coverage further north was lower, but some TS may need to be
included at ABY and DHN pending later trends.
.FIRE WEATHER...There are no fire weather concerns over the next 7
days as relative HUMIDITY levels should generally remain above 45%.