Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tallahassee Florida
433 PM EDT Sat Apr 25 2015
..isolated severe storms possible through this evening...
Near term [through tonight]...
the noon EDT regional surface analysis showed a weak warm front
exiting our forecast area to the northeast (across central ga), and
a ridge along the west Florida coast. There was a 1008 mb low over
southeast la, associated with an mesoscale convective system. Vapor imagery and upper air
data sowed a +pv anomaly (near the aforementioned warm front)
exiting off the southeast coast. It was this feature (along with the
warm front) that helped to generate the deep moist convection this
morning. As of 3 PM EDT, the storms over our region had decreased
and were rather isolated, being primarily driven by mesoscale
boundary interactions and a conditionally unstable air mass.
There was another +pv anomaly over southeast la that will
translate quickly eastward through this evening. We expect some of
the deep moist convection associated with this feature (currently
the mesoscale convective system in southeast la) to reach our forecast area by late
afternoon and early this evening.
Recent rap analyses still showed 0-6 bulk shear values of 50 to 60
knots across our region. Coupled with a moist, moderately unstable
air mass, there could still be isolated severe storms across our
region through sunset. Damaging wind gusts and hail are the main
threats, but there is just enough 0-1 km shear (25 kt) to support a
low-end tornado threat as well, especially along mesoscale
boundaries. After sunset the cape will decrease and the forcing will
diminish, so we expect the rain to taper off from west to east by
Short term [sunday through Monday night]...
at upper levels, the elongate east-west oriented trough over New England
and the Great Lakes will amplify southward as it sweeps off the East
Coast. Meanwhile, an upper level low will cut off over New Mexico on
Sunday and move east to Oklahoma by Monday night. The Gulf Coast
region will remain under fairly zonal fast flow with the seemingly
ever-present subtropical jet firmly in place on Sunday. This
feature will lift temporarily northward on Monday. At the
surface, a cold front will drop south from the Tennessee Valley on
Sunday to off our coastline by Monday. Enough dry air will work
itself into our northern zones by Sunday to preclude convective
development there. Areas south of a Dothan to Tifton line will see
isolated to scattered storm development on Sunday afternoon with
coverage increasing as you head south. 50-55 knots of deep layer
shear will overlay sbcapes in excess of 1200 j/kg (along and S of
I-10) which will support organized convetion and another severe
weather threat. Storm Prediction Center has the entire forecast area outlined for a
marginal risk of severe storms. However, we feel that the best
threat for severe will be limited to the southern half of the
forecast area with damaging wind and hail the primary threat. By
Monday, increased dry air and lower cape will preclude a severe
weather threat, although isolated to scattered storms are still
possible south of the Florida line.
Long term [tuesday through next saturday]...
the upper low over the plains will open up as it moves east
across the Mississippi Valley, but some remnant energy will be
left behind and eventually deepen into another cut-off closed low
somewhere in the vicinity of Texas or la. There are large differences
in how the models evolve the low eastward with the GFS more
progressive than the Euro. There will be a surface reflection of
this feature somewhere in the vicinity of the north central Gulf
Coast by Tuesday. Again, there are model differences as to what
latitude the low will track eastward along. A more northerly track
would favor more thunderstorms and severe threat while a more
southerly Route would mean mainly showers. These details will need
to be worked out in future forecasts when we will hopefully see a
model consensus develop. One thing that is certain is that the the
Tuesday through Wednesday period will be the most unsettled with
highest probability of precipitation. Later in the week, the Euro dries US out and the GFS
develops another Gulf low. To address the uncertainty we have
slight to low chance probability of precipitation in for Friday through Saturday.
[through 18z sunday] MVFR to VFR conditions this evening will
deteriorate to IFR overnight as low ceilings set in around midnight.
Low visibilities will also be possible at tlh and vld around sunrise.
Winds from the west-southwest will be quite gusty today and
tomorrow at most sites, around 10-15 kts with gusts to around 20
kts occasionally, though they will be lighter overnight.
winds will increase to cautionary levels tonight as a cold front
drifts south toward the waters. These winds will remain elevated
across the eastern waters into Sunday night. The front will slide
south in the waters by Monday morning briefly switching winds to
offshore. The forecast from Tuesday Onward is highly dependent on
the development of and track of a Gulf low through Thursday. For
now the forecast reflects moderate easterly flow on Tuesday
switching to stronger northwesterly flow on Wednesday. This
forecast is subject to change.
moist conditions will persist through the next few days keeping
relative humidity values well above critical levels. Rain chances
remain in the forecast through Wednesday...with the potential for
locally heavy rainfall from a stronger storm system Tuesday and
an active weather pattern has left many of our area rivers in
action stage, with a few that reached flood stage. The
Choctawhatchee River at Bruce and the Apalachicola River at
Blountstown are the only two sites remaining in flood stage and
have both peaked and will continue to fall over the next few days.
Additional rainfall today and tomorrow is not forecast to cause
any further flooding, however a round of heavy rain on Tuesday in
North Florida may cause some area rivers to rise to action or
flood stage by middle-week next week. Currently the most vulnerable
sites would be the Choctawhatchee at Bruce and Caryville and the
Apalachicola River at Blountstown again.
Preliminary point temps/pops...
Tallahassee 73 89 69 86 64 / 30 30 20 20 30
Panama City 74 81 71 79 65 / 20 30 20 30 40
Dothan 70 87 64 83 59 / 10 10 10 10 20
Albany 70 87 64 81 57 / 30 10 10 10 10
Valdosta 71 88 66 82 62 / 40 30 20 20 20
Cross City 73 85 69 84 64 / 30 40 30 40 30
Apalachicola 75 83 71 81 68 / 20 40 20 40 40
Florida...high rip current risk until 2 am EDT Sunday for coastal Bay.