Scientific Forecaster Discussion
fxus62 ktbw 260717
Area forecast discussion
National Weather Service Tampa Bay Ruskin Florida
317 am EDT Mon Jun 26 2017
07z water vapor and h4 rap analysis shows an amplified upper level
pattern over the Continental U.S....comprised of ridging over the inter-
mountain west, and broad longwave troughing covering the country to
the east of the Continental Divide. The Florida Peninsula resides at
the base of this longwave trough underneath a weakening upper level
ridge. This ridge has kept a rather warm column aloft with meager
lapse rates, and somewhat tapered convection the past couple
of days. As the upper ridge begins to break down today into
Tuesday, we will see these mid-level thermodynamics improve
somewhat in the favor of deep convection, leading in
partial manner to a greater coverage of diurnal storms
compared to what we have seen in recent days. The 00z ktbw
sounding profile continued to show a rather impressive
subsidence inversion under the upper ridge around 600mb,
however, forecast soundings from all the reliable guidance
members show a weakening and eventual disappearance of this
warmer layer aloft during the next 12-18 hours. This all
results in slightly steeper lapse rates (widening cape
profiles) through the mid-levels.
At the surface... subtropical ridge axis has been shifted southward
to the lower half of the Florida Peninsula, as a weak frontal
boundary lies across the Northern Peninsula. This front should not be
considered something with a change in temperatures, but for our
purposes will only act as a low level source of focus/convergence as
it slowly migrates toward the I-4 corridor during today.
Short term (today through tuesday)...
today...the surface gradient over our area is going to remain weak,
and this should allow the sea-breeze to form along the entire West
Coast and push inland this afternoon.
The day starts out with a few storms lying offshore along the land
breeze, but generally a dry morning for the bulk of our area. Only
exception this morning might be up toward Citrus/Levy County in
closer proximity to the surface front. Some indications that a few
showers forced along this boundary will migrate onshore into these
zones before midday. Otherwise, look for sct convection to develop
along the inland propagating sea-breeze by early/mid
afternoon...with an eventual consolidation of storms inland from the
I-75 corridor this evening. This is how the pops will evolve through
the day in the forecast. The sea-breeze will eventually interact
with the surface front during the late day hours, and may very well
further enhance the convective coverage. As mentioned in the synopsis
above, mid-level temperature profiles will be more favorable toward
deep convection by this afternoon/evening than we have seen in
previous days. In addition to higher coverage of storms, this fact
may also allow for a few more vigorous updrafts and stronger storms
as well. What is most uncertain later today is whether outflow moves
back toward the coast for a second round of later evening
convection. While the sea-breeze will be in place, it will not be
strong, and vigorous enough outflow will push back against it. This
will just have to be something that is followed through the day, and
hopefully some of the hires guidance will hint at its likelihood.
Look for a mix of sun and clouds becoming mostly cloudy by the later
half of the afternoon/evening hours as convection and convective
high level anvils overspread much of the region. High temperatures
reaching the upper 80s to lower 90s today.
Tonight...evening convection slowly dissipates, with little left
over the landmass by midnight. The gradient remains quite weak
allowing a feeble land-breeze to form and move offshore. Should see
a few more late night storms form over the coastal waters,
especially offshore of the Nature Coast where some enhancement from
the now quasi-stationary surface boundary is more likely.
Depending on how the flow sets up, some potential to see a
few of these showers migrate back toward the coasts of
Citrus/Levy toward dawn, and will represent this potential
in the forecast after 09z.
Tuesday... fairly similar overall conditions remain in place. The
quasi-stationary frontal boundary will still lie across the
peninsula, but be washing out with time. The mid-levels will
continue to cool (perhaps another degree), further increasing the
thermodynamic favorability for deep convection. A generally dry
morning under a mix of sun and clouds will become increasingly
active in terms of storms during the afternoon, with a consolidation
of storms inland by the early evening hours.
A more easterly synoptic flow is then expected to commence
beyond Tuesday, returning the best convective potential
back toward the Florida West Coast during the later part of
Wednesday and Thursday. More on this part of the forecast in
the long term section below.
Long term (wednesday - monday)...
for the long term period, a typical Summer time pattern will
continue over the region. Upper level ridging extends over the
Bahamas westward through the Florida Peninsula and into the Gulf of
Mexico. This pattern will hold through the period with very little
variation through the week. On the surface, subtropical high
pressure near Bermuda ridges west-southwest over southern Florida. A
weak frontal boundary over northern Florida washes out and
dissipates as high pressure moves off the southeast coast by
Wednesday afternoon. This will keep a general east-southeast wind
flow over the region through the week. Rain chances will be typical
for the Summer time with 50-70 pops each day through the week.
Temperatures will remain near seasonal averages with upper 80's
during the day and overnight lows in the mid 70's.
Aviation (26/08z through 27/06z)...residual showers still
around early this morning. May see a brief showers at
klal/ksrq through 09z...but no significant restrictions
expected. Prevailing VFR conditions through the morning
hours. The potential for showers and storms increase after
17-18z and move progressively inland through the later
afternoon hours. Brief restrictions can be expected at any
of the terminals with passing storms, but otherwise expect
VFR to prevail through the taf period.
a light pressure gradient and resulting winds will remain
over the forecast waters through the middle of the week.
Each morning will likely feature widely scattered storms
developing in the pre-dawn hours and fading by midday as
storms develop inland.
no significant fire weather concerns are expected through
the next several days as relative humidity values remain
well above critical levels, the potential for wetting
rainfall remains high, and winds remain generally low,
outside of thunderstorms.
Fog potential...no significant area of fog or visibility
reduction are anticipated through the next several days.
Preliminary point temps/pops...
tpa 90 77 90 76 / 50 10 50 20
fmy 92 75 90 75 / 40 30 40 20
gif 92 74 91 73 / 60 60 70 30
srq 87 77 86 75 / 40 10 40 10
bkv 89 72 90 72 / 50 20 50 20
spg 89 78 90 77 / 50 10 50 20