FXUS64 KMOB 232340

Area Forecast Discussion
National Weather Service Mobile AL
640 PM CDT Tue Oct 23 2018

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


23/00Z issuance...Widespread light rain axis that had been streaming
east over the northern Gulf coast area today is slowly drifting
offshore and expected to decrease in coverage this evening. A few
scattered clouds around 1000 feet early this evening near the
coast, but expect full VFR ceilings overnight with primarily
broken mid to upper level clouds. VFR ceilings continue into
Wednesday morning as the mid and upper clouds continue to
dissipate. Light north-northeast surface winds tonight, gradually
becoming more northeast-east during the morning hours on
Wednesday. 12/DS


.PREV DISCUSSION... /issued 402 PM CDT Tue Oct 23 2018/

NEAR TERM /Now Through Wednesday/...The period is a transitional
one between the current rain ending and the next system. First
item to deal with is rain ending. A digging upper trough over the
Northeast will push the northern edge of an upper ridge over the
Gulf of Mexico south a bit, directing shortwave energy that is
moving east along the northern edge of said ridge south a bit.
This digging trough also pushes drier air south over the eastern
Conus. The result is the band of rain shifting south overnight
tonight. With the clouds over the area decreasing overnight,
radiational cooling will allow temps to drop lower as compared to
last night. With more cooling over areas north of Highway 84
overnight, a significant north/south temp gradient will result,
with upper 40s north to upper 50s closer to the coast expected.

Wednesday...as an upper ridge gets pushed east over the Plains and
Mississippi River Valley, a surface ridge over the Mississippi River
Valley shifts east and starts to bring increasing isentropic upglide
to areas to our west. Am expecting mid/upper level clouds from
precip activity to our west to increase in coverage through the day,
decreasing daytime heating across the area. With a relatively dry
airmass over the area to heat during the day, highs a bit above
seasonal are expected, and with greatest amount of heating over
eastern parts of the forecast area, a gradient of high temps is
expected, with mid 70s west to near 80 east. Could see a few light
showers attempt to dampen southwestern parts of the forecast area
late in the afternoon, but at this point, guidance generally
keeps any precip west of the forecast area.

SHORT TERM /Wednesday night Through Friday night/...An active
weather pattern will return to our forecast area Wednesday night
into Thursday. Deep moisture associated with the remnants of
Hurricane Willa will lift northeast across Mexico tonight and
gradually phase with an upper level trough translating over the
central and southern Plains on Wednesday. This upper level trough
axis is forecast to progress eastward across the Mississippi
Valley Wednesday night and eventually across the Gulf Coast states
through the day Thursday. An associated area of surface low
pressure is still forecast to deepen over the northwestern Gulf of
Mexico Wednesday night and propagate eastward along the immediate
Gulf Coast through Thursday night, before lifting northeastward
into northern Florida and southern Georgia Friday morning. Large
scale ascent ahead of these features will bring numerous to
widespread rain showers across southeast Mississippi and adjacent
southwest Alabama after midnight Wednesday night, with widespread
rain showers then expanding across the remainder of the forecast
area during the day Thursday. The rich deep layer moisture will
especially spread across central and southern portions of our
forecast area during the day Thursday, where precipitable water
values may range around or just a little above 2 inches. Heavy
rainfall will be possible across the forecast area Thursday, and
the forecast generally continues to call for widespread total
rainfall amounts between 1-2" on average over northern portions of
the CWA, and between 2-3" (possibly locally 4"+) closer to the
immediate coast. We have included mention of locally heavy
rainfall in the forecast grids Thursday, with categorical POPs in
the 90-100% range. Guidance continues to show instability
remaining very weak and mainly confined near the immediate coast,
with slightly better instability located offshore over the
northern Gulf to the south of the warm front. SPC Day 3 outlook
has roughly our southern and eastern areas highlighted in a
general thunderstorm potential Thursday, which looks reasonable
at this time. Kept a slight mention of thunderstorms over this
portion of the area.

A good chance of rain will linger over our eastern zones Thursday
night, before precipitation is expected to quickly taper Friday
morning as the trough axis lifts east and a dry slot moves into
the region along the base of the large scale trough axis. Cooler
and drier conditions are expected Friday night. The temperature
forecast for this period was generally trended close to the
blended guidance numbers. /21

LONG TERM /Saturday Through Tuesday/...The pattern will remain
amplified over the CONUS this weekend into early next week as a
mean large scale trough encompasses the eastern CONUS, while
ridging aloft gradually builds across the western and central U.S.
Our forecast area generally remains with northwest flow aloft
between these features through the extended period. A couple of
shortwaves rounding the base of the larger trough axis could
bring a slight chance of rain to portions of our area this
weekend, but a dry pattern looks in store for Monday and Tuesday.
Overnight lows should otherwise remain cool and a few degrees
below normal each night, with daytime highs near to slightly below
seasonal averages for this time of year. /21

MARINE...A surface ridge shifts from over the Mississippi River
Valley east to over the East Coast by Friday. A surface low develops
off the Texas coast Wednesday afternoon into Wednesday night, then
moves east along an old surface boundary over the northern Gulf.
Moderate to at times strong easterly flow over area coastal waters
will become more variable in direction as the surface low passes
Thursday night into Friday. Moderate to strong offshore flow follows
for Friday, lasting through Saturday before easing Sunday. /16




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