Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tampa Bay Ruskin Florida
503 am EDT sun Mar 16 2014
Synopsis...08z WV imagery shows a vigorous upper low rotating across
the north central Texas/Oklahoma border tonight...with an expansive
area of moisture being carried downstream. WV imagery shows a
deepening middle level trough across the southern rockies...moving into
the Southern Plains states. This trough will eject out of the plains
into the southern states during the day Monday...as high pressure
that has been anchored over the western Atlantic the past several
days slides eastward and loses its influence on our weather.
Across our area this morning...light winds prevail under mostly
clear skies. Dewpoints have begun to tick back up since Saturday
afternoon...with ktbw soundings since then indicating increasing
precipitable water values under the influence of moist lowlevel southerly flow.
Most models have come into better agreement tonight regarding
evolution of the upstream trough...related surface features...and
timing of impacts across west central Florida. NAM was the
outlier...lagging GFS...European...and sref mean field with timing
of frontal passage. NAM was also much more aggressive with its
severe threat on Monday/Monday night due to its slower progression
which allowed the convection to be more coincident with the
strengthening low level wind fields. For now...chose GFS/sref mean
field blend for the forecast...but even those solutions would
suggest a modest severe weather threat Monday/Monday evening for
much of west-central Florida.
All indications point to a slowly progressing upper pattern and
surface frontal boundary...with abundant moisture streaming ahead as
it moves across the Gulf. It is beginning to look quite wet for US
here in west central Florida to start out the work week as rain and
storms build/expand south and east with time from the Nature Coast
tonight into the rest of the forecast area through the day on
Short term (today-tuesday)...
today...the area will remain mostly rain free today as strong
southerly flow develops ahead of our approaching system. Just a
slight chance of a late afternoon shower up toward Levy
County...although approaching synoptic lift fields would suggest
most of the activity up toward Chiefland will hold off until after
Tonight...impressive upper level diffluence associated with an
advancing jet core will increase as the upper shortwave begins to pivot
along the northern Gulf Coast. At the same time the frontal boundary
moves slowly eastward across the Florida Panhandle and northern Gulf
waters. Scattered to numerous showers develop across the Nature
Coast zones during the overnight...with increasing chances for
thunder toward morning. Although a few scattered showers are
possible late tonight further south...it appears a fairly sharp
cut-off in rain chances will exist around the I-4 corridor by
sunrise. Widespread showers and storms will be ongoing north of
Tampa Bay by this time...with probability of precipitation quickly decreasing with southward
extend. Best low level jet will also be in place across the Nature
Coast bringing the threat for a few damaging wind gusts with the
thunderstorms before the night is through.
Monday/Monday night...widespread to numerous thunderstorms will begin
to expand south and east through the day. However...it does look
like this will be a slow process. The Tampa Bay area is likely to
get into the action fairly early...but down toward Fort Myers...the
steadier rains/storms may hold off until much later. Models often
struggle with convective blowups over The Loop current when strong
impulse cross the Gulf. These convective blowups are difficult to
predict...but if they occur...than rain can arrive over our southern
zones (fort Myers vicinity) much earlier than previously though.
Will be watching this potential tonight and Monday morning. As
mentioned above...some disagreement with the mass fields progressing
with this system between models and how they relate to our severe
threat. All models showing at least a modest threat for damaging
winds ahead of the cold front Monday into Monday night although the
timing will be difficult to pin down. Have a longer period of severe
weather mentioned in the forecast than normal due to the less
organized features well ahead of the main impulse. The storm
predictions center has outlooked much of our area in a slight risk
for severe weather Monday into Monday night. Now keep in mind...that
a slight risk should not be thought of in the same manner as "a
slight chance of showers". A slight risk of severe weather implies
that severe weather is expected...just with less coverage than would
be implied from a moderate or high risk. This outlook seems quite
reasonable given the strength of the low level jet and sufficient
deep layer shear to support organized convection.
The prolonged elevated southerly flow will bring with it an elevated
rip current risk for Monday and Monday night along the coast from
Pinellas County southward.
The threat for severe weather looks to continue into at least the
first half of Monday night...with the threat then passing east with
the cold front. Although the surface front will eventually cross and
end the threat for severe storms...plenty of residual column
moisture for the potent shortwave to interact with will almost
certainly support continued shower activity in the Post frontal
environment and keep likely rain chances in through the night for all
zones. In fact...the GFS/NAM/ec all show a very impressive swath of
q-vector convergence over the region the second half of the night.
Tuesday...cold front will continue to pass off to our east through
the day as the upper shortwave passes over early and then itself is
gone. A few scattered showers likely to still be around for the
morning...but optimistic that we can see a mostly dry afternoon with
more and more sun through the afternoon.
Long term (tuesday night - next saturday)...
flow aloft the Gulf region becomes more zonal as a short wave trough
exits to the open Atlantic. The zonal flow continues through the
period while a short wave trough passes by to the north Thursday. At the
surface high pressure over the plains states builds into the Gulf
and tracks east to the Atlantic as a weak front/boundary moves
through Thursday...in response to the short wave trough. The
GFS/ECMWF/CMC are all similar aloft but to a lesser extent with
surface features. The European model (ecmwf) has a more moist front...although it
dries out before reaching Florida...while the GFS is dry and the CMC is
in between. The pressure field of the GFS is the most robust while
the European model (ecmwf) and CMC are more relaxed. Have opted to lean toward the
GFS and will have a dry forecast. Temperatures start off Wednesday morning
near or below normal...especially across the Nature Coast...but
gradually warm to above normal by Sat.
Aviation...16/00z-17/06z: VFR as clouds increase to broken at middle
and high levels. Light mostly southeast winds become southerly...and
gusty through the afternoon.
a slow moving storm system will bring elevated winds and seas to the
eastern Gulf of Mexico through Monday night. A cold frontal passage
Monday night will bring improved conditions for the middle portion
of the week. Cautionary to advisory level winds expected today. Any
advisory level winds should end this evening...however cautionary
level wind and seas are expected to last through Monday night.
increasing moisture levels will prevent any red flag concerns the
next couple of days.
Preliminary point temps/pops...
tpa 82 70 76 65 / 0 50 90 80
fmy 86 70 84 70 / 0 10 50 70
gif 84 67 81 67 / 0 30 70 80
srq 83 69 77 67 / 0 40 80 80
bkv 83 68 76 61 / 10 60 90 80
spg 81 69 76 65 / 0 50 90 80
Florida...Lake Wind Advisory from 11 am this morning to 7 PM EDT
this evening for coastal Charlotte-coastal Citrus-
coastal Hernando-coastal Hillsborough-coastal Lee-
coastal Levy-coastal Manatee-coastal Pasco-coastal
inland Citrus-inland Hernando-inland Hillsborough-
inland Lee-inland Levy-inland Manatee-inland Pasco-
Gulf waters...Small Craft Advisory from 8 am this morning to
5 PM EDT this afternoon for Englewood to Tarpon Springs
out 20 to 60 nm-Tarpon Springs to Suwannee River out
20 to 60 nm.
Short term/marine/fire weather...14/mroczka