Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mobile Alabama
703 am CDT Sat Aug 1 2015
Aviation update...1200z issuance...skies have scattered out as the
weak frontal boundary has shifted east and south for now. As a
result...patchy fog conditions...mostly MVFR...have developed over
the Florida Panhandle and south central and coastal Alabama where
rainfall occurred yesterday. Otherwise...a drier airmass has invaded
the region creating fair skies. However the front is expected to waffle
inland along the Florida Panhandle and perhaps south central Alabama this
afternoon with the afternoon sea breeze push. Expect scattered to
numerous thunderstorms to trigger along the southern boundary over
the Panhandle with isolated to scattered activity over coastal
Alabama as well as south central and southeastern Alabama. Storms should
move offshore by early evening as the boundary shifts southward over
the northern Gulf.
Previous discussion... /issued 505 am CDT Sat Aug 1 2015/
Short term...(today through monday)...for today through tonight...
the weak...quasi-stationary frontal boundary will linger along the
coast through the weekend. The boundary currently extends southward
through Crenshaw and Covington County Alabama then through Okaloosa
County Florida and then west southwestward over our coastal waters.
East and south of the boundary deep layer moisture exists with precipitable waters
of around 2.0 inches while on the dry side of the boundary over our
southeast MS and interior SW Alabama counties precipitable waters fall to 1.0 to 1.3 inches.
Boundary will become the focus for convection this afternoon with
most activity occurring over the moderately unstable...moist side of
the boundary. Though the bulk of the rainfall will fall over the Gulf
and east of our area today. Surface temperatures should heat up into the
middle 90s away from the coast which will help establish an afternoon
sea breeze which will cause the boundary to nudge temporarily a
little further inland before sagging off the coast in the early
evening. Heat indices today will be highest along the Florida
Panhandle in the moisture rich air...but showers and afternoon cloud
cover will keep area below heat advisory criteria again. Expect
indices near the coast to reach the low to middle 100s while more
interior locations in the much drier air...will experience upper 90s
to low 100s. Overnight lows will remain in the middle 70s along the
coast and generally 70s elsewhere...except for portions of southeast MS and
our more interior Alabama counties where lows will fall into the 60s. /08
This afternoon's wet microburst risk is moderate along Alabama and
Florida coastal counties.
Sunday through Monday...a vorticity lobe swings around the base of an
upper low near Hudson Bay. This allows the upper trough over the
eastern Continental U.S. To weaken...with the surface ridge stretching west over
the Gulf of mex building as a result...especially over the western
Gulf of mex. This will help to re-establish south to southwesterly
flow over the northwest and northcentral Gulf of mex by Monday and
begin to mix the dry airmass over the lower miss River Valley and
western half of the southeastern states out.
With the weakening of the eastern trough...the upper ridge over the
southwestern states and Southern Plains builds east a bit...with
temperatures moderating upward a bit. Combined with the dry airmass over
mainly inland portions of the forecast area...temperatures in the upper 90s return
Monday...though do not see heat indices reaching critical values(except
for near coastal areas seeing daytime heat indices around 105).
With the surface boundary south of the coast...best chance for rain
will be south of the coast this part of the forecast. Did put a
slight chance for areas along and south of i10...mainly due tot he
possibility of northward propagation of any activity that forms
along and south of the coast.
Long term...(monday night on)...Monday night through Tuesday
night...the upper ridge over the southwestern states sees some
manipulation by a pair of shortwave moving over the western ridge and
a vorticity lobe swinging around the Hudson Bay low. This re-digs the
eastern upper trough...mainly over the southeastern quarter of the
Continental U.S.. the surface ridge over the Gulf shifts north...to over the
northcentral and northeastern Gulf Coast...and bringing a more direct
flow off the Gulf. Need less to say...this increases moisture
levels...with the chance of rain beginning to increase. Temperatures remain
above seasonal...but show a slight downward trend in daytime temperatures...
with areas closer to the coast seeing the largest drop. Overnight
temperatures moderate upward a bit...but generally remain around seasonal.
Wednesday into Friday...a strong shortwave moves into the eastern
trough (and passing over the forecast area thursday)...bringing a better chance
for rain...especially Thursday into Thursday night. Temperatures fall with
the increased cloud-cover/rainfall...to a bit below seasonal levels.
The surface ridge that has moved over the northern Gulf Coast sees
some squeezing as a surface trough passes over the southeastern
states...and ultimately by Friday...the direct onshore flow becomes
Friday night through Saturday...a second shortwave moves into the
eastern upper trough...bringing a surface front south across the tenn
River Valley to northern/central portions of miss/al/GA. This front
may provide enhancement to the rain chances for next weekend...but with
this being the end of the forecast...and guidance inconsistent in
the front's position...am leaning towards a seasonal forecast.
Marine...a weak frontal boundary will continue to linger near the coast.
Showers and thunderstorms can be expected along and south of the front through
early next week. Generally a light to moderate onshore flow develops
each afternoon becoming an offshore flow overnight. /08 jw
Preliminary point temps/pops...
Mobile 95 71 95 72 96 / 10 10 20 10 20
Pensacola 91 75 94 75 95 / 50 30 20 10 20
Destin 90 77 92 78 91 / 60 40 30 10 20
Evergreen 96 71 97 65 97 / 20 10 10 10 00
Waynesboro 95 67 97 67 97 / 05 05 05 05 00
Camden 96 69 97 65 97 / 10 05 05 10 00
Crestview 93 73 97 67 96 / 60 40 20 10 20