AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
432 AM EDT SAT Jul 7 2012
SYNOPSIS...
The 03 UTC regional surface analysis showed an extremely weak
PRESSURE pattern over the Southeast, dominated by small scale
features like MESO highs and OUTFLOW/sea breeze boundaries. The
TROUGH to our north the past FEW days can no longer be identified.
Local radars showed a fairly large cluster of loosely-organized
storms over central GA & AL this early morning, but unlike last
NIGHT, (so far) these storms have moved very slowly and stayed just
north of our County WARNING Area. Vapor imagery and upper AIR data
showed a broad, flat area of higher heights over much of the CONUS,
with a maximum near Iowa. Probably the most interesting feature for
our concern is a region of drier air developing from east to west
over our forecast area. Based on our 00 UTC KTAE SOUNDING, most of
this dry air was above 700 MB.

&&

.SHORT TERM...
(Today through Monday) The global models, which AS of 00 UTC Friday
were showing a gradual drying trend in the MID TROPOSPHERE this
weekend, appear to be on TRACK with their latest runs. This warmer,
drier air aloft is expected to greatly limit the amount of deep
moist CONVECTION over our forecast area today. The 00 UTC GFS and
NAM MOS have picked up on this in their POP forecast, and our PoP
(which also takes into account a blend of several Convection
Allowing Models) is only 20% for today. The main focus for
convection initiation today will be the sea breeze FRONT and any
residual outflow boundaries from the ongoing STORM clusters to our
north. The poor THERMODYNAMICS will make strong updrafts hard to
come by, so the PROBABILITY of severe storms today, while not zero,
is very LOW.

The warm dry air aloft is LIKELY to continue through at least
Sunday, then gradually retreat to the east ahead of a deep layer
trough. Despite the normally wet, onshore WIND (from 1000 to 700 mb)
expected Sunday, the poor thermodynamics will continue to inhibit
deep moist convection. Our PoP will remain well below average at
only 20%. The PoP will begin to return to more average levels Monday
from Tallahassee westward, where there will be an increase in deep
layer MOISTURE.

With the decrease in clouds and showers, HIGH temperatures will
return to above average levels through Monday. We expect highs to
REACH" onClick="return popup(this, 'notes')">REACH the mid 90s at most inland sites, with a few upper 90s
possible (especially around Valdosta, which reached a surprising 98
degrees on Friday afternoon). Slightly drier air is expected to mix
into the boundary layer each afternoon, allowing dewpoints to drop
into the upper 60s inland. This may not sound like much, but it will
probably be enough to prevent us from reaching heat ADVISORY
criteria.

.LONG TERM [Monday Night through next Saturday]...
Once again, the reasoning for the extended period of the forecast
from last night still looks mostly valid, and not a lot has changed
on the latest 07.00z suite of global models. At the beginning of the
period (around 00z Tue 10 July) the available models and ENSEMBLE
members are all in very good agreement on the synoptic pattern; it
features an upper level RIDGE that has already split with the highs
aloft centered in the Intermountain West and near Bermuda. They also
show a weak and ill-defined trough or upper level low near LA/MS,
and low AMPLITUDE and progressive trough in the Northeast that
should develop east quickly. As we mentioned last night, this will
probably leave a mid-upper level trough to linger in weak steering
FLOW over the Southeast through the remainder of the week.

Initially, for Monday Night and Tuesday, the pocket of drier air
(discussed in the "short term" portion above) may be lingering over
parts of our area - especially the FL Big Bend and into SC Georgia.
This would be due to a continued weakness in the flow near a ridge
axis extending across north Florida. However, as that remaining
portion of the ridge erodes into Tuesday Night and Wednesday, the
ECMWF and GFS both show deeper S-SE flow opening up and increasing
mixing ratios, particularly in the lowest 2-3km AGL" onClick="return popup(this, 'notes')">AGL. Therefore, the
trend of lower POPS in the south and east from Monday was kept into
Tuesday, with PoPs finally increasing areawide (to around 50% in the
afternoons) on Wednesday. These PoP distributions were then
maintained through the remainder of the forecast. Confidence is not
quite high enough yet to merit inclusion of 60% or greater PoPs,
which would change the RAIN mentions from "CHANCE" to "likely".
12-hour PoPs of 50% are just above climatological normals for this
time of YEAR during the daytime hours. However, if models continue
to hone in on an long stretch of S-SE flow, we may need to continue
nudging up the PoPs. Local sea-breeze regime climatologies alone
have PoPs for S-SE flow in the 60-70% RANGE over our Florida zones.
The TEMPERATURE OUTLOOK" onClick="return popup(this, 'notes')">OUTLOOK is still close to CLIMATOLOGY, although if
abundant rain and CLOUD cover indeed does materialize, we could be
looking at highs more in the upper 80s.

&&

.AVIATION [through 06z Sunday]...
Once again tonight, there has been an overnight development and
maintenance of THUNDERSTORM activity off to the north of our area -
currently around Auburn, AL (KAU0) and Columbus, GA (KCSG). While
storms last night developed close to these locations and then
progressed south through DHN terminal around 08-09z, initially these
storms seem to be pushing a bit further off to the west. However,
there is a southward moving outflow boundary probably producing some
brief northerly gusts around 10-20 knots. If this held together, it
would reach DHN terminal around 0930z. Such a boundary may also lead
to the development of additional ISOLATED-SCATTERED storms, so VCTS
group with a northerly wind was included from 0930-11z at DHN.
Elsewhere, IFR to MVFR FOG was mentioned in the previous SET of TAFs
and that seems reasonable so no major changes were made (except at
ABY where mid-high clouds from developing storms may limit fog).

&&

.MARINE...
The typically low summertime values of winds and SEAS will continue
through much of this work week as the marine area remains north of
the western extent of the West Atlantic ridge. South to southwest
winds will be the predominant direction. Brief increases in the
winds and seas are likely near the coast each afternoon and evening
due to the sea breeze enhancement, but peak sustained wind speeds
are unlikely to exceed 15 KT. Since isolated showers and storms are
likely to develop near and just off the FL Panhandle coast this
morning, there could be a brief WATERSPOUT or two, which was the
case Friday morning.

&&

.FIRE WEATHER...
Even with slightly drier air aloft and lower rain chances the next
few days, abundant low-level moisture will keep afternoon minimum
relative HUMIDITY at or above 40 percent. Therefore, critical fire
weather conditions are not anticipated.