Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 161125 AAA

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
525 AM CST Sat Dec 16 2017

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


12Z issuance...General VFR CIGs/VISBYs expected today into this
evening under general easterly flow. As the low level flow becomes
a more southeast to southerly tonight, CIGs are expected to drop,
especially over southeast Mississippi and southwest Alabama. Winds
are expected to remain strong enough to keep CIGs at MVFR levels,



.PREV DISCUSSION... /issued 453 AM CST Sat Dec 16 2017/

NEAR TERM /Now Through Saturday night/...Shortwave energy that
has stalled over the southern Plains the end of the week will
begin to organize, then move northeast. This energy organizes a
weak surface low over the western Gulf, then moves it onshore over
Louisiana. Surface high pressure over the Southeast shifts east,
to over the Carolina coast, and with that, shift low level flow
from northeast/east to southeast/south by Sunday morning. This
will allow the stalled front over the northern Gulf to begin to
move north as a warm front. For the first 24hrs of the forecast,
the more organized flow remains west of the forecast area, and any
initial moisture return. Guidance is advertising mainly shra to
the west, and see no reason to argue at this point. Have started
precip returning to western portions of the area the last few
hours of tonight`s period as a result. With instability
essentially non-existent, have left out any wording of rumbles
with the initial shra. Temps today will be warmer than yesterday,
but are still expected to be below seasonal with mostly cloud to
cloudy skies limiting today`s insolation, and any warming onshore
flow not quite in effect. With the onshore flow returning tonight,
overnight lows above seasonal average returns, with a steady
warming through the night from the low temps for the night
expected to occur in the evening hours. /16

SHORT TERM /Sunday Through Monday night/...A 1026mb surface
high pressure area moving east across the western Atlantic will
set up a southerly return flow on Sunday. An upper level shortwave
over the central plains will move quickly toward the northeast
conus and dissipate along the northern periphery of the upper
high pressure area centered over the Bahamas by midnight Sunday.
The upper high will then drift slowly southwestward through the
reminder of the short term, while an upper cutoff low over the
southwest conus/northwest Mexico border drifts slowly eastward.
Deep layer moisture will continue to increase across the region,
with precipitable water values climbing to between 1.5 to 1.9
inches by Sunday evening.

Numerous to definite rain showers along with embedded
thunderstorms will spread from west to east to the I-65 corridor
on Sunday, with scattered coverage expected to the east of I-65 as
upper level impulses associated with on the ejecting upper wave
traverse the region. Scattered to numerous rain showers along with
embedded thunderstorms will follow through Monday afternoon as
additional upper level impulses move over the region. Lower rain
chances will occur Monday night.

Widespread rainfall amounts through the short term will range
from 1 to 2 inches west of the Alabama River, with locally high
amounts near 3 inches possible across inland southeast
Mississippi. Widespread rainfall amounts east of the Alabama
River will range from 0.50 to 1 inch, with locally high amounts
near 2 inches possible. Areas of dense advection sea fog are
expected to develop across our southern zones Sunday night through
Monday night as surface dewpoints in the mid to upper 60s move
northward over the cool gulf and bay waters. /22

LONG TERM /Tuesday Through Friday/...The pattern remains
complicated through the long term as the cutoff upper low
pressure area moves slowly eastward and also evolves into an open
wave before reaching the southeast conus. The ECMWF and GFS models
are more in line passing the shortwave just north of the forecast
area on Wednesday. However, timing and spacial differences of
upper level impulses east of the wave between the two models
remain, so confidence remains low on exactly when the higher
chances of precipitation will occur.

Additional widespread rainfall amounts Tuesday through Friday are
expected to range from 0.50 to 1 inch, with locally high amounts
near 2 inches possible. /22




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