Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 211842 AAA

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1242 PM CST Tue Jan 21 2020

.DISCUSSION...See updated information for land areas and aviation
discussion below.


.NEAR TERM /Now Through Wednesday Night/...A very dry deep layer
airmass will continue to spread into our region through this
evening along northwesterly flow aloft between a departing trough
of low pressure near the southeast U.S. coast and a building ridge
over the Plains and Mississippi Valley region. A cold surface
ridge of high pressure will also continue to build southward into
the area overnight. Clear skies are expected through this
evening. Highs this afternoon still appear on track to only reach
into the lower to mid 40s across much of the region, which is
about 15 degrees below normal for late January. Another freeze is
expected to impact much of the region again tonight, and overnight
lows preliminarily look to range from the lower to mid 20s over
much of our interior, and in the upper 20s to lower 30s closer to
the coast.

A deep layer dry and subsident airmass will persist into Wednesday
as the upper level ridge builds eastward over the forecast area.
However, high clouds should begin to increase in coverage through
Wednesday afternoon as the upper ridge shifts east of our region
and as flow aloft transitions more southwesterly ahead of the next
trough of low pressure moving across the Plains states. The
surface ridge of high pressure also continues to shift toward the
Eastern Seaboard Wednesday through Wednesday night, allowing
surface flow to become more easterly across our region. High
temperatures should modify into the lower 50s Wednesday afternoon.
Deep layer moisture may tend to increase over western parts of our
CWA late Wednesday night as the trough axis approaches the
Mississippi Valley region. The increased moisture and perhaps some
weak isentropic ascent could allow for the development of a few
showers over southern portions of our area late Wednesday night.
Overnight lows will range from the mid to upper 30s inland to the
lower to mid 40s over southern portions of the area. /21


18Z issuance...VFR conditions are expected through the next 24
hours. Clear skies are expected through early this evening before
high clouds increase in coverage late tonight into Wednesday
morning. Northerly winds will remain elevated between 10-15 knots
with occasional gusts around 20 knots this afternoon as surface
high pressure continues to build into our region. Lighter
northerly to northeasterly winds are expected tonight, becoming
more easterly on Wednesday. /21


.PREV DISCUSSION... /issued 536 AM CST Tue Jan 21 2020/

DISCUSSION...Updated for latest aviation discussion below.

12Z issuance...VFR ceiling and visibility will persist through
22.12z. The northerly winds of around 12 knots will continue
toady with occasional wind gusts to near 20 knots near the coast.
Winds will diminish once again in the evening hours and overnight.

PREV DISCUSSION... /issued 448 AM CST Tue Jan 21 2020/

NEAR TERM /Now Through Tuesday night/...A dry low/mid northerly
wind flow will remain through this afternoon as a large upper
level trough over the region and a 1040mb surface high pressure
system centered over the mid Mississippi River move eastward. Cold
air advection will remain across the forecast area throughout the
day due to the northerly flow, resulting in high temperatures
much below normal despite the sunny skies. Expect high
temperatures 13 to 17 degrees below normal, ranging from 41 to 46
degrees. The surface high pressure and upper level trough will
continue to shift east overnight, while a medium amplified upper
level ridge over the nations midsection moves east of the
Mississippi River after midnight. Cirrus clouds spilling over the
ridge will begin to move into over the region from the west-
northwest tonight, with very cold overnight temperatures. Low
temperatures will be 10 to 15 degrees below normal, ranging from
22 to 27 degrees inland areas and 28 to 33 degrees along the
coast. /22

SHORT TERM /Wednesday Through Thursday night/...The short term
period will begin Wednesday as upper level ridging takes hold
over the region. Meanwhile, an upper level trough will begin to
advance over the central CONUS. By Thursday afternoon, this
feature will progress towards the southeastern CONUS, with a
closed low forming over the upper Mississippi Valley. At the
surface, high pressure that brought dry weather to the area for
the near term period will begin to shift eastward as a low
pressure system develops over Texas and the lower Plains. The low
will continue to move eastward, with a warm front expected to
progress over Lousiana and a cold front over southeastern Texas on
Thursday morning. The warm front will continue to lift and pass
over our area Thursday afternoon, with the cold front passing
through late Thursday night.

This low pressure system is expected to bring between 0.50 to 1.5
inches of rain over our area from Thursday morning through
Thursday night, with the heavier amounts over the NW Florida
panhandle. Not expecting much thunderstorm activity during this
time, though. This is due to meager CAPE values shown by model
guidance (although some CAPE, 300 J/kg or less, is shown near the
coast) as well as lapse rates generally around 6 C/km. There will
be some shear present, but this is expected to be 30 knots or less
through Thursday night. Thus, any thunderstorms will likely be
concentrated over the open Gulf waters and near the coast.

Highs Wednesday will remain below normal, with temperatures in
the lower to mid 50s. Lows Wednesday night into Thursday will also
be chilly as temperatures drop into the mid to upper 30s farther
inland and closer to 40 degrees near the coast. Highs Thursday
will be a touch warmer but will still be below normal, in the mid
to upper 50s inland to around 60 degrees along the coast.
Temperatures will then return to above normal (low) values
overnight, as lows only drop to the mid to upper 40s inland to
around 50 degrees near the coast.

Lastly, a moderate risk of rip currents is in effect for
Wednesday and Wednesday night; however, this will become a high
risk come Thursday and continue through Thursday night. /26

LONG TERM /Friday Through Monday/...The upper level closed low over
the upper Mississippi Valley will continue to progress eastward
through late week. By the weekend, it will move up into the
northeastern CONUS while zonal flow develops over the northern
Gulf coast. Zonal flow will then persist through Sunday afternoon
before a shortwave traverses the northern Gulf coast Sunday
evening through early Monday morning. Meanwhile, the surface cold
front that brought rain to the area for the short term will
quickly progress out of our area by Friday afternoon. High
pressure will then build in over the region from the northwest and
maintain its hold through early next week. This will lead to some
lingering chances for showers in our east through Friday
afternoon, but by Friday evening, generally dry conditions will
return and persist through Monday. Mostly clear skies will also
return Friday evening. However, the passing shortwave aloft will
increase cloud cover once again for late weekend. Skies will then
clear to start the new work week.

Temperatures will run at or just below normal Friday through
Sunday, with highs in the upper 50s to lower 60s. By Monday, highs
will warm to be in the lower 60s area-wide. Low temperatures will
increase slightly over the weekend. Lows will start out in the
mid to upper 30s inland to around 40 degrees near the coast Friday
night into Saturday morning. By Monday morning, lows will
generally be in the lower 40s inland to the mid 40s along the
coast. /26

MARINE...Moderate to strong northerly winds and elevated seas will
persist into Tuesday as a strong surface high pressure system
builds over the eastern half of the country. As the high continues
its eastward advance, winds become a light to moderate easterly.
A low pressure system and associated cold front tracks eastward
over the Gulf coast late Thursday into Friday morning, bringing
the next round of unsettled weather. Offshore flow and drier
conditions set up Friday and continues into the weekend following
the passage of this weather system. /22


GM...Small Craft Advisory until 3 AM CST Wednesday for GMZ670-675.



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