Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 201733 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1133 AM CST Sat Jan 20 2018

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


18Z issuance...VFR conditions will prevail through the period,
with only a SCT to BKN mid and/or upper cloud deck. Southeasterly
surface winds 6 to 12 knots today, becoming mainly east around 5
knots tonight. Patchy late night fog is possible, but not enough
to add to the TAF forecast at this time. /22


.PREV DISCUSSION... /issued 538 AM CST Sat Jan 20 2018/

DISCUSSION...Updated for latest aviation discussion below.

20/12Z issuance...Mostly VFR conditions through the period, but
expect SCT to BKN mid and/or upper cloud deck today. Surface winds
primarily southeasterly 5 to 10 knots today, around 5 knots
tonight. 12/DS

PREV DISCUSSION... /issued 407 AM CST Sat Jan 20 2018/

NEAR TERM /Now Through Saturday night/...A slightly positive tilted
shortwave trof in the flow aloft over Louisiana early this morning
will weaken and drift east across the forecast area today and
tonight. Expect increasing mid/upper level cloudiness with this
feature, but still relatively dry in the lower levels of the
atmosphere. In fact, as the cloud cover moves over some of our
northwestern counties early this morning, temperatures have
recovered into the 40s, but generally remain in the 30s over our
eastern zones. At the surface, the high pressure area that has been
bringing the cold conditions to our area is finally moving off to
the east, and will be situated over the southeast Atlantic coastal
area and offshore over the Atlantic by late tonight. This will bring
an continued moderating trend to the area, especially this afternoon
and tonight as low level flow becomes primarily southeasterly. A few
showers are noted over Louisiana underneath the approaching upper
trof this morning where return flow has previously been earlier
established, but airmass over our area won`t begin to modify
substantially until today. As a result, low level moisture probably
wont be enough to include a slight chance of showers for our area
today, although a few isolated showers may occur over western
portions of the forecast area (southeast Mississippi zones). Highs
today warming into the lower 60s across most of the area today,
perhaps some mid 60s over Mississippi zones where the return flow
becomes more established. Much warmer tonight, with lows ranging from
upper 30s far northeastern counties, to the mid and even a few
upper 40s southwestern and coastal counties. 12/DS

SHORT TERM /Sunday Through Monday night/...Sunday through Sunday
night, a shortwave system moves from over the Four Corners region
to the Central Plains. In the process, it moves a surface low
that has developed on the east side of the Co Rockies east-
northeastward. A surface front gets pushed east-southeast across
the plains to near the Lower Mississippi River Valley in the
process. Southerly flow off the Gulf strengthens through Sunday
night ahead of the front, increasing deep layer moisture over the
Lower Mississippi River Valley and western portions of the
Southeast. Temps well above seasonal continue, with a return of
highs bumping 70 some areas Sunday afternoon. Guidance has backed
off on the fog coverage Sunday night, leaning more towards stratus
due to the stronger winds near the surface especially over
western portions of the forecast area. Weaker winds east will
allow fog to develop, with a better chance of dense fog. Am not
differentiating dense or not, with timing inconsistencies in
previous model runs of the stronger winds ahead of the front.

Monday through Monday night, guidance is more consistent in its
timing in the front moving across the forecast area late Monday
through Monday night. The upper system now taking a more
northeastward movement due to a building upper ridge off the East
Coast, but is less so than previous runs. This allows more upper
support from mid/upper level jets swirling around the south side
of the main system. Guidance is advertising MU-Capes rising to
around 500 J/KG, with 0-3km helicities rising above 250m^2/s^2,
enough for some strong to severe storms. Previous runs have been
advertising less upper support due to a more northward path of the
upper dynamics and a bit less instability, so at this point,
agree with an SPC painted marginal risk, mainly for the afternoon
into evening hours. Will need to monitor in case the more
southward track of the upper dynamics continues.

Looking at temps, well above seasonal temps continue for the area,
with highs above 70. With cooler, drier air moving over the
forecast area behind the front Monday night, a closer to seasonal
lows west to well above east gradient is expected across the
forecast area for lows.


LONG TERM /Tuesday Through Friday/...A weakly organized upper
system moves slowly east over the Southern PLains and Lower
Mississippi River Valley, pushing a surface high slowly east from
the Mississippi River to over the Carolinas. This keeps the
forecast area under dry northerly flow until Friday, dropping
temps a bit below seasonal levels for mind-week. Temps slowly
moderate upwards to a bit above seasonal through the rest of the
week, with the next chance of rain being Friday into Friday night.


MARINE...No hazards in the near term. The cold front approaches
the marine area from the west on Monday bringing an increased chance
of showers and embedded storms late Monday and Monday night. Ahead
of the front, a more established onshore wind allows a gradual build
in seas late in the weekend continuing into Monday. Another
potential concern is warmer, moist Gulf air flowing atop cooler
water near the coast, possibly resulting in dense fog formation over
the nearshore waters could pose some problems late this weekend
before the front arrives. A strong offshore flow and continued high
seas expected through mid week. 12/DS




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