Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 200001 AAA

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
601 PM CST Mon Feb 19 2018

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


00Z issuance...VFR conditions will continue through the evening
before decreasing overnight as low clouds and patchy fog develop.
Some of the fog could be dense at times with LIFR/IFR conditions
possible late tonight. VFR conditions redevelop by late Tuesday
morning. /13


.PREV DISCUSSION... /issued 358 PM CST Mon Feb 19 2018/

NEAR TERM /Now Through Tuesday/...An upper trough over the
western Conus deepens as an upper high located off the Carolina
coast builds. Energy moving through the western trough pushes a
surface front south across the Mid Mississippi River Valley as the
building upper high builds a surface ridge stretching west across
the Southeast even more, strengthening low level flow off the Gulf
over the Southeast. After a initial drier slug of air moves inland
over the Southeast early tonight, deep layer moisture increases
significantly later tonight through Tuesday. Guidance is advertising
precip h20 values reaching 1.5-1.75" by the end of the day
Tuesday(well above seasonal levels). Combined with a shortwave
approaching the northern Gulf coast Tuesday, will see an increase in
precip, with these being mainly low level showers in the morning as
any convective activity will have a seriously hard time breaking a
serious subsidence inversion from the upper high. By Tuesday
afternoon, as the shortwave approaches the coast, the moist unstable
airmass is expected to combine with added upper instability to over-
ride the synoptic scale subsidence from the upper high and have some
tsra begin to mix in.

With temps, subsidence from the the upper ridge remains firmly in
control of temps, with well above seasonal temps expected to
continue.With record highs for tomorrow generally around 80F,
chances are very good that these records will be tied or bested.

With the onshore flow continuing, there is a moderate risk of rip
currents Tuesday. A neap tidal cycle is the only thing holding back
from a high risk attm. /16

SHORT TERM /Tuesday night Through Thursday night/...A
southwesterly mid level flow pattern will prevail across the
central Gulf Coast region through the short term period between a
large ridge of high pressure that will be oriented from the
western Atlantic Ocean through the eastern Gulf of Mexico and a
broad trough over the western CONUS. Much above normal temperatures
will persist across our area through Thursday night as warm and
moist southeasterly to southerly low level flow persists between a
surface ridge of high pressure over the western Atlantic and a
slow moving cold front moving from the Plains states toward the
Mississippi and Tennessee Valley regions. Near record or potentially
record high temperatures remain possible Wednesday and Thursday.
A slight increase in deep layer moisture along with ascent
provided by a shortwave trough lifting northward from the Gulf of
Mexico through our forecast area on the western periphery of the
ridge will provide a chance of rain showers to the area Tuesday
night, and will keep POPs around 30% over most locations.
Conditions also remain favorable for at least some patchy fog
formation again across the forecast area again Tuesday night and
will include mention in the forecast after midnight.

An axis of deeper moisture will become oriented across our
northwestern zones on Wednesday within increasing southwest flow
aloft ahead of the aforementioned front. The best chance of POPs
will therefore be favored generally along and west of I-65 during
the day Wednesday, though we will keep at least a slight chance
in place over eastern and southern portions of the area. There may
be enough weak instability for a few rumbles of thunder again
Wednesday, particularly over the western/northwestern portions of
the area, so have also included mention of a slight chance of
thunderstorms. The axis of moisture actually looks to retrograde
northwestward with time Wednesday night into Thursday as the upper
level ridge of high pressure builds westward into much of Florida
and the adjacent eastern Gulf of Mexico. POPs should decrease
over central and eastern areas Wednesday night and Thursday as a
drier and more subsident airmass arrives over this portion of the
region, but will maintain low POPs in the west/northwest zones.
The drier airmass should be in place over our entire region
Thursday night, so will maintain a dry forecast area wide then.
The warm and muggy weather pattern otherwise prevails into
Thursday night. /21

LONG TERM /Friday Through Monday/...Southwesterly mid level flow
will increase across our forecast area late Friday through the
weekend as the upper level trough advances eastward across the
Plains and toward the Mississippi Valley region. Friday looks to
remain dry except for perhaps our far western zones, where enough
moisture/lift could arrive to provide isolated showers over
southeast Mississippi. The chance for showers and a few
thunderstorms will increase this weekend as a zone of deeper
moisture arrives over our area ahead of the approaching cold
front. Current model trends favor frontal passage across our CWA
late Saturday night into Sunday. The front may become stationary
or diffuse near the coast Sunday night into Monday. There are some
indications that additional shortwave troughs may propagate over
our area along the stalled/diffuse boundary Sunday night into
Monday, so will maintain a chance of POPs into Monday. The streak
of much above normal temperatures continues into Saturday.
Slightly cooler temperatures may arrive behind the front Sunday
into Monday, though readings still trend above normal into early
next week. /21




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