Area Forecast Discussion
Issued by NWS
FXUS62 KTAE 031430
Area Forecast Discussion
National Weather Service Tallahassee FL
930 AM EST Sat Dec 3 2016
.NEAR TERM [Through Today]...
A large closed low centered over Baja California, is not quite
disconnected from the northern stream and is gradually moving east
into mainland Mexico. Ahead, and in response to it, flow is
veering through the troposphere. Locally, the low-levels are still
quite dry, especially below 850mb. There is enough moisture in the
305K-315K window (~7000-12000ft) to generate showers that are
spreading northeast through the Tri-State region. However, due to
the dry low-level air, most are evaporating before reaching the
surface. The low levels will gradually moisten from west to east
through the day, but likely a little too late to produce
measurable rain from the showers seen on radar this morning. It
appears we will become saturated enough by tonight to start
introducing rain into the forecast (primarily west of the
Apalachicola and Chattahoochee rivers). High temperatures this
afternoon are forecast to climb into the low 70s across the
southeast Big Bend of Florida, gradually cooling to the northwest
into the middle 60s across southeast Alabama.
.PREV DISCUSSION [645 AM EST]...
.SHORT TERM [Tonight Through Monday]...
Near zonal flow aloft will become more southerly Sunday ahead of
a strong closed upper level low that was situated across the
southwest CONUS this morning. In addition, the easterly flow at
the surface also will become more southerly as the surface high
weakens ahead of the next system and a warm front lifts north.
This southerly flow will bring increased moisture to the CWA and
help to contribute to the increased rain chances for particularly
the second half of the short term. While the main system remains
well to the west tonight, isentropic lift and moisture increase
across the CWA for the second half of the night and thus will
start to see some light showers moving in early on Sunday.
Initially CAPE is limited so have just advertised showers in the
grids until Sunday afternoon when instability is enough to mention
a slight chance across the western portion of the CWA.
By Monday, the upper level low lifts into Texas while the surface
low tracks along the western Gulf coast. As this occurs, moisture
increases across the CWA with PW values in the 1.8-1.9 inch range
allowing for the best rain chances in the short term Sunday night
into Monday. While instability increases with CAPE values nearing
1000 J/kg, the low level shear is on the low side so while expect
some thunderstorms on Monday, it appears better chance of strong
to severe weather will hold off through the short term. Main
focus is more on the heavy rain potential with these near 2 inch
PW values which are well above average.
With a warm front lifting across the CWA in the short term,
temperatures will remain above normal. Highs will range from the
upper 60s across a small area well inland to the mid 70s across
much of the area and the upper 70s across the southeast Big Bend.
Low temperatures will increase from the low to mid 50s tonight to
the 60s Monday morning. Based on the current forecast, we could
possibly break the high minimum temperature record for Monday
.LONG TERM [Monday Night Through Saturday]...
By Monday night, the aforementioned upper level low will be
lifting across the lower Mississippi Valley and into the
Tennessee Valley while the surface low also lifts northeast. The
CWA will be in the warm sector Monday night with instability still
around 1000 J/kg, but will see an increase in both deep layer and
low level shear that this appears to be the main time period to
watch for an isolated strong to severe storm. SPC has included the
western portion of the CWA in a slight risk with the majority of
the remainder of the area in the marginal risk. While the shear
decreases slightly on Tuesday, instability remains similar and
thus expect the thunderstorms to continue into Tuesday,
particularly mid-day across the eastern half of the CWA. Based on
the timing of the system, this could still change though. The
heavy rain threat will continue through Monday night as PW values
remain near 2 inches.
The actual front will push through the CWA on Tuesday and clear
the area by Tuesday evening.
Differences remain between models in the second half of the
extended. While both the GFS and ECMWF push a cold front into the
southeast on Thursday, the GFS weakens it with little to no precip
across the area. On the other hand, the ECMWF pushes a wet front
through the CWA. Given the differences, PoPs are limited to chance
for Thursday. Behind this front, significantly colder air is
expected to move into the CWA.
.AVIATION [Through 12Z Sunday]...
VFR conditions will continue through the remainder of the period
at all terminals. East-northeasterly winds will generally remain
between 5 and 10 knots with a few higher gusts possible, mainly
at ECP and DHN. A few light rain showers are possible in the
afternoon around DHN, but visibility will not be significantly
Small Craft Advisory level winds will continue across much of the
marine zone this morning and while there will be a brief time
period of less than 20 knots this afternoon, they will quickly
increase again tonight with these stronger winds persisting into
Sunday afternoon. Winds will be more marginal for Sunday night.
Expect an increase again Monday night ahead of a front that will
move through on Tuesday. Will see a significant increase in chance
of rain across the marine area for Monday and Monday night ahead
of the cold front.
Minimum RH values could dip to the upper 20s and lower 30s this
afternoon, but combined with light winds and fairly low dispersion
values do not anticipate fire weather concerns. Increasing moisture
and periods of rain will prevent any fire weather issues from Sunday
through the middle of next week.
The chance of showers and thunderstorms will increase for Sunday
through Tuesday with widespread rainfall totals of 1 to 3 inches
still expected across the area. Higher rainfall totals are
possible and with WPC including the area in a Day 2 marginal risk
and Day 3 slight risk for the Excessive Rainfall Outlook, it will
remain important to continue to monitor the forecast in terms of
the higher rainfall amounts as the event gets closer.
.PRELIMINARY POINT TEMPS/POPS...
Tallahassee 71 54 74 68 76 / 0 10 30 60 60
Panama City 68 58 74 69 76 / 10 20 50 70 60
Dothan 65 51 68 61 73 / 30 30 60 70 70
Albany 66 51 68 61 72 / 20 10 40 70 70
Valdosta 69 51 75 65 76 / 0 10 20 40 50
Cross City 72 52 78 65 78 / 0 10 10 20 40
Apalachicola 68 60 73 69 76 / 0 10 30 60 50
GM...Small Craft Advisory until 2 PM EST Sunday 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.