Area Forecast Discussion
Issued by NWS Mobile, AL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS64 KMOB 190526 AAB
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1126 PM CST Mon Feb 18 2019

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

&&

.AVIATION...
06Z issuance...Radar shows isolated -shra lifting northward over
southern MS/Southern AL. No flight impacts from these as any
measurable rain will be light. A solid sheet of overcast cigs from
4 to 6 kft holds over the deep south. Near term forecast calls
for cigs to remain around these levels overnight. Northeast winds
continue overnight and will be gusty at times. Vsby ok. By
Tuesday afternoon, cigs are forecast to lower to lower end MVFR
categories. Isolated to scattered passing -shra. /10

&&

.PREV DISCUSSION... /issued 523 PM CST Mon Feb 18 2019/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
00Z issuance...Radar shows isolated -shra lifting northward off
the Gulf. No flight impacts from these as any measurable rain
will be light. A solid sheet of overcast cigs at around 4 kft.
Near term forecast calls for cigs to remain around these levels
overnight. Northeast winds will be gusty at times. Vsby ok. By
afternoon on Monday, cigs are forecast to lower to lower end MVFR
categories. Isolated to scattered passing -shra. /10

PREV DISCUSSION... /issued 352 PM CST Mon Feb 18 2019/

NEAR TERM /Now Through Tuesday/...Latest radar loops continue
to show long bands of light to moderate rain streaming mostly to
the northeast across the north central gulf region in the wake of
a shallow layered cold front that moved south of the coast early
this morning. Latest model soundings support this reasoning
showing a moderate to strong northeast flow generally below 5k ft
with a moderate to strong southwest flow aloft combined with a
rather moist layer lingering roughly between 3k and 10kft. This
pattern is expected to continue over the region through mid to
late Tue afternoon with a weak warm front approaching from the
south, eventually moving onshore generally from Pensacola FL to
Mobile AL by late Tue afternoon. Better low level moisture is
expected to return to lower parts of the forecast area as the warm
front moves onshore with surface dewpts climbing to the upper 50s
to lower 60s. As result coastal areas of Al and NWFL could see
the onset of marine or advection fog along the coast by late Tue
afternoon gradually spreading inland overnight. Rainfall totals
through the next 24 hours will be low, generally ranging from
about .01 to .10 inches across the entire forecast area through
Tue afternoon.

With mostly cloudy skies through the next 24 hours temperatures will
continue to be affected with lows ranging 3 to 5 degrees above
seasonal norms tonight and 2 to 3 degrees below seasonal norms on
Tue. Lows tonight will range from the mid 40s to lower 50s generally
along and north of highway 84 and the lower to middle 50s further
south stretching to the immediate coast. Highs Tue will range from
the upper 50s to lower 60s generally along and north of highway 84
and the lower to middle 60s for all other locations further south
stretching to immediate coast. 32/ee

SHORT TERM /Tuesday night Through Thursday night/...An upper trof
advances across the central states then shears out across the
Great Lakes region Wednesday night, deflected by a large upper
ridge centered over the Bahamas region. A surface low associated
with the upper trof will be located near the Texas coast Tuesday
evening then moves off to the Great Lakes region. An old frontal
boundary over the northern Gulf moves northward as a warm front
through the forecast area Tuesday evening through midday
Wednesday. The frontal passage occurs first over the western
portion then the eastern portion later, delayed by a slowly
retreating strong surface ridge over the extreme southeast
states. The surface low later brings a trailing cold front slowly
into the western portion of the forecast area Wednesday night
which moves slightly to near the I-65 corridor on Thursday while
the upper ridge remains in place and another upper trof reloads
over the western states.

Very high amounts of deep layer moisture will be present over
much of the area through Wednesday with precipitable water values
of 1.5 to 1.8 inches, although the lower range values will be
over the eastern portion of the area due to subsidence on the
periphery of the upper ridge. Precipitable water values around 1.5
inches are expected for the entire area on Thursday. These values
during the period will be 200-250% of normal and portend highly
efficient rain production with convection. The position of the
upper ridge continues to play a key role over the forecast area,
as while a series of shortwaves move across the region in the
southwest flow aloft, these shortwaves and the best deep layer
forcing will be mainly along and west of the I-65 corridor at
least through Thursday. The best rainfall amounts through the
period will likewise be oriented west of the I-65 where totals
of about 1.0 to 3.0 inches are expected. We have expanded a
Limited Threat of Flooding to include much of the area west of
I-65 where localized flash flooding is possible mainly during the
Wednesday into Wednesday night timeframe. As a generalization,
pops through Thursday will include likely to categorical pops
along and west of I-65 with chance to good chance pops further to
the east, then pops will be a bit lower overall Thursday night as
the stronger shortwaves affect areas well west and north of the
area.

As the warm front lifts northward through the area, MLCAPE values
of 700-1000 J/kg develop on Wednesday with similar values expected
again on Thursday. For Wednesday, a 35-45 knot 850 mb jet results
in 0-1 km Helicity values of 200+ over southeast Mississippi and
interior southwestern Alabama. Much lower shear values follow for
Thursday as the weak cold front moves slowly into the area. An
examination of model soundings on Wednesday shows a less
favorable lapse rate below 600 mb over the eastern portion of the
area due to subsidence warming associated with the upper ridge,
while further to the east more favorable lapse rates will exist.
Considering the environment, the current outlook for Wednesday of
a Marginal Risk of Severe Storms over southeast Mississippi and a
small portion of interior southwest Alabama looks reasonable, and
actually some eastward expansion of this risk area could be
considered. The decreasing shear on Thursday should preclude a
potential for severe storms. A high risk of rip currents is
expected through Wednesday night, then a moderate risk follows for
Thursday. /29

LONG TERM /Friday Through Monday/...The western states upper trof
moves across the central Plains then shears out across the Great
Lakes area through Sunday, much like the SHORT TERM system, while
the strong upper ridge centered over the Bahamas begins to weaken.
The frontal boundary previously near the I-65 corridor moves
slowly northward out of the forecast area through Friday evening
while a surface low develops over the southern Plains in response
to the upper trof. Will have chance to likely pops on Friday
(highest over the northwest portion) then slight chance to chance
pops follow for Saturday.  The surface low deepens significantly
while moving off to the Great Lakes on Sunday and brings another
cold front through the forecast area. The cold front is expected
to stall over the northern Gulf on Monday while the upper ridge
continues to weaken with an essentially zonal flow pattern
developing over the south central and southeastern states. As the
front approaches and moves through, have gone with chance to
likely pops for Saturday night then chance to good chance pops
follow for Sunday along with slightly lower pops on Monday. /29

MARINE...A moderate to strong northeast wind flow will persist
through early Tue then shift mostly east then southeast and diminish
through Wed afternoon as high pressure to the north shifts east. A
light to moderate southerly wind flow will continue through the
remainder of the week as the ridge high pressure continues along the
eastern seaboard combined with a weakening cold front approaching
from the west. With the better onshore flow by Tue afternoon
continuing through much of the week expect the return of fog mainly
over the near waters of both AL and NWFL likely becoming dense at
times especially during the overnight and morning hours. Small craft
advisories for the open gulf waters of AL and NWFL out to 60 nm
including lower Mobile Bay and MS Sound east of Pascagoula will
continue through 3 AM Wed morning. 32/ee

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...High Rip Current Risk from Tuesday afternoon through Wednesday
     afternoon for ALZ265-266.

FL...High Rip Current Risk from Tuesday afternoon through Wednesday
     afternoon for FLZ202-204-206.

MS...None.
GM...Small Craft Advisory until 3 AM CST Wednesday for GMZ631-632-650-
     655-670-675.

&&

$$

This product is also available on the web at:
http://weather.gov/mob


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.