Flash Flood Warning 27, NWS Tallahassee, FL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
332 PM EDT Sat Jul 13 2013

...Unsettled Weather Pattern to Continue...

.NEAR TERM [Through Tonight]...
An unusual retrograding mid/upper low centered over the Midwest
is providing the Southeast and the northern Gulf with broad
troughing. In fact, there may even be another (weaker) closed low
over the northern Gulf based on VWP data. At the surface, similar
to aloft, broad troughing covers the Gulf Coast states on into the
northern Gulf. Within the broad trough there appears to be two
closed circulations, one off the southeast Louisiana coastline,
and one just southwest of buoy 42039. Additionally, a notable
surface trough embedded in the large area of low pressure extends
from the closed circulation east to the western Florida Peninsula
coastline, northeast up the eastern Georgia coastline. In this
area, steady convection has been ongoing throughout the day.
Further to the west, a stationary boundary divides a very dry vs.
very moist airmass essentially along the Mississippi/Alabama state
line, with another weak trough extending north out of the Gulf
ahead of the front. This is another area where storms have focused
this afternoon. Locally, scattered convection and light rain
plague the Tri-State area where convergence is maximized on the
eastern edge of the main low/mid level circulation. Expect this
general pattern to remain in place through the day, with the low
moving slowly north and west later tonight. Thus, expect the best
chances of rain to gradually slide slightly west through the
night.

&&

.SHORT TERM [Sunday Through Monday Night]...
The weak surface low in the Gulf of Mexico will be pulled
northwestward toward the Mississippi coast on Sunday by the
retrograding upper level low moving into the Southern Plains. Deep
layer tropical moisture will continue to be pulled northward into
the area with precipitable water values well over 2 inches. PoPs
will be in the high likely category. We will also see increasing
southeasterly shear. While the degree of destabilization will likely
be mitigated by abundant cloud cover and convective coverage, deep
layer shear will be sufficient (25-30kt) to produce isolated strong
to severe storms in any areas that get a bit of sunshine. SPC has
the region in a 5% risk area for severe with damaging winds and
perhaps even a tornado the potential threats. The upper low will
reach the TX Panhandle by Monday. This will allow a big upper high
centered over eastern PA Sunday morning to slide west to Indiana by
Monday. Beneath the ridge, a tropical wave will approach and cross
FL on Monday and this will keep PoPs elevated in the likely range,
despite the building ridge to the north. Max temps will be kept
below guidance and several degrees below normal due to anticipated
cloud cover and the numerous showers and storms.

&&

.LONG TERM [Tuesday through Friday]...
By the start of the period, the upper low will have retrograded all
the way to eastern New Mexico with a 598-dm high centered over
Indiana. This high will lose amplitude as it drifts to the southwest
toward the Great Plains. By the end of the week, a broad trough will
be in place across the Northeast and Mid Atlantic. At the surface, a
tropical wave will move west of the forecast area Tuesday and
Tuesday night. After that, the subtropical ridge will reestablish
itself over the Southeast with the axis slipping south of the region
by Friday and Saturday. Despite the influence of the upper ridge,
PoPs will be close to climatology on Tuesday due to the passing
wave. The ridge will win out on Wednesday with below normal PoPs and
above normal temps (a rare thing this summer). By Friday and
Saturday, temps and PoPs will be very close to normal July values as
the once familiar subtropical ridge pattern sets up the more typical
sea-breeze induced thunderstorms each day.

&&

.AVIATION...
[Through 18 UTC Sunday] Scattered showers and thunderstorms will
generally spread westward through the day as a developing low
pressure in the Gulf of Mexico drifts northwest. From latest
satellite imagery, it appears MVFR ceilings, where currently
present, will likely lift early in the period. Overnight and early
tomorrow morning, expect MVFR ceilings to develop and persist
through most of the morning. Although possible, we don't have
enough confidence to lower ceilings to IFR/LIFR restrictions
before sunrise, so will defer to next TAF package.

&&

.MARINE...
Weak low pressure over the north central Gulf of Mexico will drift
northwest toward the Alabama or Mississippi coast through Sunday
night. Winds will generally be in the exercise caution range across
the western legs. High pressure will then become established north
of the area from Monday through midweek. This will set up diurnal
easterly surges over the marine area bringing winds to near
cautionary levels during the overnight and morning hours. Showers
and thunderstorms will remain numerous through Monday.

&&

.FIRE WEATHER...
Red flag conditions are not expected through the period.

&&

.HYDROLOGY...
Rainfall amounts today have been rather insignificant thus far, with
the exception of the Southeast Big Bend earlier this morning, where
3 to 5 inches of rain fell, mostly over Dixie and Lafayette
counties. Although we will be in a rather wet stretch, average
rainfall totals for the next couple of days should peak around 2
inches. However, locally higher amounts are certainly possible (e.g.
2 to 3 inches fell in one storm across western Walton county earlier
today). Should any of these locally higher amounts fall over any of
our warned basins, it could result in some rather sharp rises. In
general however, expect area rivers and streams to remain in a
rather steady state over the next few days. Please refer to our
River Forecast page (below) for more detailed information.

http://water.weather.gov/ahps2/index.php?wfo=tae

&&

.PRELIMINARY POINT TEMPS/POPS...
Tallahassee   83  71  86  72  87 / 80  50  70  40  60
Panama City   85  74  85  75  87 / 60  60  70  40  60
Dothan        89  71  84  72  85 / 60  60  70  40  60
Albany        84  70  86  72  87 / 80  50  70  30  60
Valdosta      82  71  87  72  87 / 90  40  70  30  60
Cross City    84  72  87  71  87 / 90  40  70  40  60
Apalachicola  84  77  85  75  87 / 80  60  70  50  60

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AL...None.
GM...None.

&&

Hydrology...Godsey/Harrigan
Short Term/Long Term/Marine...Wool
Rest of Discussion...Harrigan