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fxus64 kmob 210535 aab 

Area forecast discussion...updated
National Weather Service Mobile Alabama
1135 PM CST Wed Nov 20 2019

Discussion...updated for latest aviation discussion below.


06z issuance...VFR conditions are expected to prevail through
Thursday, except for the potential for MVFR ceilings to develop
Thursday evening. Light and variable winds tonight become
southeasterly 5 to 10 knots on Thursday, then decrease to a light
southerly flow Thursday evening. /29


Previous discussion... /issued 525 PM CST Wed Nov 20 2019/

Discussion...updated for latest aviation discussion below.

00z issuance...VFR conditions prevail for the next 24 hours. Light
and variable winds tonight become southeasterly 5 to 10 knots on
Thursday. /29

Previous discussion... /issued 328 PM CST Wed Nov 20 2019/

Near term /now through Thursday/...upper level ridging will
continue to build over the southeastern Continental U.S. Through Thursday.
This, coupled with surface high pressure, will keep dry and mostly
clear conditions through the near term period. However, by Thursday
afternoon, surface high pressure will begin to move off to the east,
giving way to a cold front slated to move through the region early
this weekend. An increase in cloud cover is expected into Thursday
evening as well with the transition of airmass.

Temperatures will be just above the seasonal norm through tomorrow,
with overnight lows in the mid to upper 40s inland to around 50
degrees along the coast. Furthermore, the formation of sea fog is
possible through dawn, particularly form Mobile Bay westward. This
is due to a sufficient land/ocean temperature gradient along the
coast as well as winds beginning to shift to the southeast. Highs
tomorrow afternoon will then be similar to this afternoon, with
temperatures in the lower 70s. /26

Short term /Thursday night through Saturday night/ a surface
anticyclone continues moving off to the east of our region, a
low-level return flow will remain in progress until a cold front
passage sometime on Saturday (currently we are expecting the cold
front to pass west of I-65 during the morning hours of Saturday
and east of I-65 during the afternoon). Some sea fog could form
Friday evening and into early Saturday morning from Mobile Bay
westward (and out to 20-30 nm) as the warm surface air flowing
over shelf waters that are will be about 10 deg(f) colder at that
time, could aid in the formation. Would expect this to end from
west to east once the precipitation moves in ahead of the front
after midnight. We are not expecting severe thunderstorms with
the passage of this system, however a few isolated storms will be
possible both along and ahead of the front. The thermodynamic
instability is very limited, despite a recent trend in the models
to increase the value of surface dewpoints into the low and middle
60s deg(f). Also the incoming mid- and upper trough trough weakly
forcing this event will possess a very positive-tilt nature and
this is not favor to downstream pre- cursor deep-layer
differential divergence to enhance narrow mesoscale ascent along
and ahead of the cold front (better north of our area in central
al). For what little bit of thermodynamic instability there is, it
is out of phase with the best vertical wind shear. By the time
the best instability arrives, what were once veering local wind
profiles become more unidirectional and this has been persistent
consensus for the past several days in several models. Both cold
and dry air advection commences Saturday night and skies clear
from the west. Sunday morning's lows will be in the 40s deg(f).
/23 jmm

Long term /Sunday through Wednesday/...dry high pressure and
persistent upper troughing persists through Monday night. Between
Sunday and Tuesday, a series of shortwaves move through the broad
mean longwave trough and re-enforce existing conditions. After
that time, there is much uncertainty in a couple of systems that
try to form in the Lee of The Rockies. Given this uncertainty in
their development, it is hard to pinpoint how far south any
associated cold fronts (and associated rainbands) would make it
as these systems move south out into the plains and deepen, only
to quickly re-curve sharply northward. This high degree of
uncertainty is supported by large spread in the gefs ensemble
members for the 500 hpa geopotential height field. At this point,
looks like a west-northwest flow aloft becomes more zonal Tuesday and even
SW by Wednesday. This would be a mainly dry pattern whereby high
clouds may stream across the region with near normal temperatures
(i.E., 60s and perhaps lower 70s deg(f) for highs and nighttime
lows in the 40s and 50s deg(f)). /23 jmm

Marine...surface high pressure will continue over the southeast
today, but begin to shift off to the east tomorrow. Winds during
this time will shift from being easterly to being from the
southeast. A cold front will then advance towards the southeastern
Continental U.S. Friday morning, with passage expected on Saturday. A few
thunderstorms will also be possible along and ahead of the surface
front. In addition, winds will shift to be southwesterly,
increasing in intensity, before frontal passage Saturday. Winds
are then expected to shift to be out of the northwest through the
evening Saturday after frontal passage. Thus, a Small Craft
Advisory is likely this weekend, given this scenario. Winds are
then expected to decrease by early next week as surface high
pressure returns for the region. /26


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