Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 290347 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1047 PM CDT Tue Mar 28 2017

.DISCUSSION...Updated for latest aviation discussion below.


06Z issuance...Am still expecting fog development along and just
north of the I10 corridor overnight. 11-3.9 satellite shot is
starting to show stratus development over mainly the Fl panhandle
attm. Wild-card for dense fog development is a patch of mid/upper
level clouds moving over eastern LA attm. At this point, the
patch of stratus appears to be small enough to quickly pass early
in the forecast and allow denser fog to form closer to sunrise.
After sunrise Wednesday, am expecting VFR conditions, but a return
of low end MVFR/IFR level conditions well after sunset, late in
the forecast.



.PREV DISCUSSION... /issued 624 PM CDT Tue Mar 28 2017/

DISCUSSION...Updated for latest aviation discussion below.

00Z issuance...VFR CIGS/VISBYS will drop overnight into IFR
levels overnight as temps cool. Latest guidance is painting best
chance of IFR or lower CIGS/VISBYS east of Mobile Bay and along
I-10 overnight. Did stick with previous forecast of lower values
over area coastal counties inland from the coast and problematic
western portions of Mobile Bay. After sunrise, any fog should mix
out quickly and do not anticipate any significant SHRA coverage


PREV DISCUSSION... /issued 350 PM CDT Tue Mar 28 2017/

NEAR TERM /Now Through Wednesday/...A bit early to see, but see
nonetheless, a coastal sea-breeze boundary being the source of
focus for a few showers and storms along the I-10 corridor over
the northwest Florida panhandle. A few of these could linger into
the early evening, but chances are very slim (around 10%) as
instability decreases. Thereafter, chances of rain diminish to
less than 5% thru the remainder of the night.

Short-wave high level ridge moves eastward over the southeast
tonight with surface high from the northern Bahamas to the central
Gulf coast maintaining a light, warm, and moist southerly flow.
Due to the persistent type pattern, areas of fog likely to re-
develop overnight. Fog could become locally dense in some areas.
Overnight lows also will follow a persistence approach, ranging
from a mild to muggy mid to upper 60s. For Wednesday, look to be
in a transition between weather systems, with little in the way of
rainfall expected and highs ranging in the lower to mid 80s for
much of the local area. /10

SHORT TERM /Wednesday night Through Friday night/...A potentially
significant weather event is still forecast for Thursday and
Thursday night as a strong storm system approaching the region
from the west moves across the area. An upper level trough with
embedded closed low pressure area will advance eastward over the
southern Great Plains Wednesday night and Thursday. The closed low
is forecast to be over the eastern portions of Kansas and
Oklahoma Thursday morning and advance eastward, reaching the mid
Atlantic states by Friday night. Meanwhile the southern portion
of the trough is expected to swing quicker to the east, aided by a
90 to 110 knot jet streak over the western Gulf of Mexico, and
possibly become slightly negatively tilted over the region late
Thursday night. A surface low pressure area is expected to be
over eastern Oklahoma Wednesday evening and move eastward, also
reaching the mid Atlantic states by Friday night. An associated
cold front approaching the region from the west Thursday evening
will sweep through the forecast area after midnight.

A deep southerly wind flow ahead of the system will advect
moisture northward across the region, with precipitable water
values climbing to between 1.5 to 1.8 inches Thursday afternoon
and evening. The severe weather parameters in the GFS and NAM
models are similar, and both are higher when compared to the
ECMWF, with MLCAPE values between 700 to 1000 J/KG Thursday
afternoon and evening compared to 300 to 600 J/KG from the ECMWF.
SFC-1km storm relative helicity values from all models range from
80 to 180 m2/s2. A 35 to 45 knot low level jet is also expected
to accompany this system. Mid and upper level lapse rates are
still expected to be in 7 to 7.5 C/KM range. The pre-storm
environment still favors the development of strong to severe
thunderstorms throughout the day Thursday into Thursday night as a
line of numerous storms advances east through the region.
Damaging winds, large hail, and isolated tornadoes are all
possible with this system. Heavy rainfall will also occur with
widespread 1 to 2 inches likely, with locally higher amounts.

It will be dry Wednesday night ahead of the system with patchy
fog developing across the area, and dry Friday afternoon through
Friday night in the wake of the cold front.

Low temperatures Wednesday and Thursday nights will range from 58
to 62 degrees inland areas, with mid 60s along the beaches. Low
temperatures Friday night behind the cold front will range from 52
to 57 degrees inland areas, with upper 50s along the beaches. Very
warm temperatures will continue on Wednesday with highs ranging
from 82 to 87 degrees inland areas, with upper 70s to lower 80s
along the coastal sections. Slightly cooler high temperatures are
forecast for Thursday and Friday, but still above normal. /22

LONG TERM /Saturday Through Tuesday/...The dry period will then
persist through much of the weekend as an upper ridge and surface
high pressure dominate the southeast states. Precipitation
chances will increase once again starting Sunday evening as yet
another upper level trough develops to our west and advances east
over the southern plains, with scattered to numerous showers and
thunderstorms forecast for Sunday night through Monday night. At
this time it appears there could be some strong to possibly severe
thunderstorms associated with this system, along with heavy
rainfall. Above normal temperatures will continue through the
long term. /22

MARINE...Surface high pressure to the east maintains onshore flow
thru Wednesday, increasing on Thursday as a front approaches from
the west. Due to the increase and duration of the southerly fetch
Thursday and Thursday night, seas build. Thunderstorms increase
in coverage, bringing locally higher winds, waves, seas and
frequent cloud to water lightning activity. The front looks to
make passage early Friday morning, bringing a moderate westerly
flow during the day Friday in its wake. Onshore flow returns over
the weekend and shows a greater increase by Sunday. /10




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