Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 161742
AFDMOB

Area Forecast Discussion
National Weather Service Mobile AL
1242 PM CDT Mon Jul 16 2018

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

&&

.AVIATION...
16/18Z issuance...VFR CIGs/VISBYs this morning will see increasing
chances of MVFR levels late this morning through the afternoon
with increasing coverage of tsra. Operations are expected to be
impacted at times. VFR conditions return this evening as convective
activity increases near area TAF sites. Brief periods of IFR conditions
near the stronger showers and storms this afternoon, perhaps lingering
into the early evening hours in some locations. Prevailing VFR conditions
again expected overnight. Another round of showers and thunderstorms
expected over much of the area again Tuesday afternoon. Surface
winds generally light and somewhat variable, with a light offshore
flow possible overnight and more light onshore during the afternoon
hours. Winds gusty and stronger gusts near stronger storms. 12/DS

&&

.PREV DISCUSSION... /issued 615 AM CDT Mon Jul 16 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
12Z issuance...VFR CIGs/VISBYs this morning will see increasing
chances of MVFR levels late this morning through the afternoon
with increasing coverage of tsra. Operations are expected to be
impacted at times. VFR conditions return this evening as
convective activity decreases near area TAF sites.

/16

PREV DISCUSSION... /issued 450 AM CDT Mon Jul 16 2018/

NEAR TERM /Now Through Monday night/...Shortwave energy swings
around the base of an upper low located north of the Great Lakes.
This energy digs an upper trough over the eastern Conus. Increased
mid/upper level instability combined with a weak surface trough
over the southeast and a very moist airmass ( precip h20 values of
2"- 2.4" ), well above seasonal chances of rain are expected
again today. With temps close to seasonal levels, instability
across the forecast area is expected to rise to levels allowing
for a few strong to severe storms (MuCapes of 2500-3000j/kg). Just
as important, the very moist airmass allows for very efficient
rain production in the stronger storms. Storm motion to the south
is expected to be relatively slow, allowing the higher rainfall
amounts to be more localized and bring a possibility of localized
ponding/nuisance flooding to the forecast area today. WPC has
outlined the entire forecast area in a marginal chance of rainfall
amounts exceeding FFG values.

Focusing on temps, with the axis of the upper trough setting up
east of the forecast area, the high moisture levels combined with
good heating this morning, temperatures are expected to rise close
to seasonal levels before increasing cloud and rain cuts off
heating across the area. With the hot temps and moist airmass,
another item to consider is heat indices. At this point, heat
indices rising into the 100 to 105 degree range are expected
before cooling off. For lows tonight, high moisture levels and
residual cloud cover will counterbalance radiational cooling. Lows
a bit above seasonal are expected as a result. /16

SHORT TERM /Tuesday Through Wednesday night/...An upper level
shortwave trough just east of the Appalachian Mountains will move
eastward over the western Atlantic, while the base of a much
larger upper level trough over southeast Canada and the Great
lakes region digs southeast over the northeast conus. However, the
southern portion of the first upper level shortwave over the
southeast states and northeast Gulf of Mexico will remain in place
through the short term. Meanwhile, the surface ridge extending
from the western Atlantic across the Gulf of Mexico will remain
intact, keeping a light, moist west to southwest surface wind
across the forecast area.

With the presence of the upper level weakness, deep moisture with
precipitable water values ranging from 2.0 to 2.4 inches and
decreasing daytime stability, numerous to definite showers and
thunderstorms will occur across the entire forecast area Tuesday.
Scattered to numerous showers and thunderstorms will follow
Tuesday night, with the highest coverage occurring across our
southern zones. Numerous to definite showers and thunderstorms
will develop once again across the entire forecast area on
Wednesday, with the precipitation tapering off from north to
south Wednesday night as drier air finally filters in from the
north. /22

LONG TERM /Thursday Through Sunday/...The upper level trough over
the southeast states and northeast Gulf of Mexico will persist
through Thursday, and then shift slightly eastward late in the
week and into Sunday. This will allow an upper level ridge to
very slowly build into the western portions of the forecast area.
Meanwhile, a closed upper low pressure system developing over the
northern Great Plains Thursday morning will expand and move east-
southeast over the Great lakes and Ohio River Valley regions over
the weekend. The southern base of the upper low is expected to
reach into the southeast states. The surface ridge extending
westward from the western Atlantic across the Gulf of Mexico will
remain intact, keeping a moist, light west to southwest wind flow
across the forecast area. Scattered to numerous showers and
thunderstorms will occur each day through the long term, with
isolated to scattered numerous showers and thunderstorms each
night. With less cloud coverage and lower rain chances, heat
indices will rebound back to between 100 and 107 degrees. /22

MARINE...A surface ridge organizes over the central Gulf of
Mexico today, bringing a more organized southwest to westerly
flow. A surface front pushes south across the Southeast mid
week, pushing the surface ridge over the Gulf south a bit as it
moves south of the I20 corridor and brings a more westerly flow to
area waters. More moderate wind speeds are expected, especially
over unprotected waters. The gradient eases later in the week into
the weekend, but flow remains a general westerly. /16

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...None.
FL...None.
MS...None.
GM...None.
&&

$$

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