FXUS64 KMOB 180529 AAC

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1129 PM CST Sun Feb 17 2019

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


06Z issuance...Frontal boundary has made passage over MOB and
will soon do so over BFM and PNS. Some light shra expected but
nothing that brings impacts. Other than some isolated instances
of MVFR vsby, vsby expected to be ok overnight with the passage of
the front. A northwest to northerly component to the wind follows
in the wake of the front. Winds expected to become gusty at
times carrying over into the day Monday. CIGs at IFR to MVFR
categories. /10


.PREV DISCUSSION... /issued 958 PM CST Sun Feb 17 2019/

DISCUSSION...See updated information for land areas below.

UPDATE...Area radars detecting only a thin line of light rain
showers along the I-65 corridor ahead of a cold front. While a
few light showers remain possible behind the front, updated the
grids and public forecasts to lower the precipitation chances to
40 percent or less for the remainder of the night. Kept patchy fog
along the coast through midnight, prior to the passage of the cold
front. /22

PREV DISCUSSION... /issued 541 PM CST Sun Feb 17 2019/

DISCUSSION...Updated for latest aviation discussion below.

00Z issuance...Cold front was draped over from northern AL to off
the southwest coast of LA to open up the TAF period. Ahead of the
boundary, MVFR to IFR cig bases forecast this evening with vsby
also expected to trend lower to IFR, to perhaps LIFR categories
in fog. Scattered light shra possible. Front makes passage late in
the night, bringing wind shift and gusty conditions with cig
bases lifting to MVFR categories. /10

PREV DISCUSSION... /issued 401 PM CST Sun Feb 17 2019/

NEAR TERM /Now Through Monday/...A broad upper trof located over
much of the western conus stretching northeast over parts of the
northern plains and lower Canada will shift slightly east through
the next 24 hours as a continued series of potent mid level
impulses continue to dive south and round the base of the main
upper system. Well to the east a large blocking ridge of high
pressure stretching from the central Atlantic to the southwest
Gulf and western Caribbean will move little through Mon helping to
maintain unseasonal moisture content for many locations further
west or generally across much of the eastern U.S. Near the surface
a shallow cold front currently located from the TX/LA border
stretching northeast across central parts of LA and MS and
northern AL will continue to shift southeast moving across western
and northern sections of the forecast area by 06z or midnight
tonight then further south moving off the AL and NWFL coast by 12z
or 6 am Sun morning. Ahead and along the front expect scattered
to numerous showers to move south and east across the forecast
area tonight and early Mon followed by more low clouds and
scattered areas of light rain in the wake of the front moving
across the forecast area through midday Mon. Also, for this
evening expect more low clouds mixed with dense fog occurring
mainly along the immediate coast mixing out with the wind shift
along the front late tonight and early Mon morning. Dense fog,
mostly patchy, could also spread further inland after sunset this
evening possibly reaching areas along and south of the I-10
corridor mainly through about midnight, possibly lingering over
most areas of the western FL Panhandle and coastal sections of AL
through about 3 AM Mon morning. A this time with the lack of
significant forcing aloft combined with limited instability in the
lower levels of the boundary layer no thunderstorm development is
expected through tonight. Although some heavy rainfall may occur
later this evening and overnight especially over western and
northern sections of the forecast area ahead and along the front
no significant or widespread flooding is expected.

Temperatures will continue to be mild through most of tonight
running about 4 to 8 degrees above seasonal norms then about 2 to 4
degrees below seasonal norms during the day on Mon. Lows tonight
will range from the mid to upper 40s to lower 50s generally along
and north of highway 84 and the middle 50s to lower 60s further
south stretching to the immediate coast. Highs Mon will range from
the lower 60s generally north of highway 84 and the middle 60s
further south and east stretching to the immediate coast. 32/ee

SHORT TERM /Monday night Through Wednesday night/...Within a
5-Wave scale pattern over the western states/Baja area, an upper
trof moves across the central states then shears out across the
Great Lakes region during the period while a large, stubborn
upper ridge remains centered over the Bahamas. A massive surface
high over much of the eastern half of the CONUS gradually retreats
into the easternmost states through Tuesday night but leaves
strong ridging in place over the extreme southeast states while a
surface low associated with the upper trof moves from the Texas
coast northeastward roughly along the Mississippi river valley.
The surface low brings an old frontal boundary over the northern
Gulf northward as a warm front through the forecast area Tuesday
afternoon through Wednesday morning, with the passage occurring
first over the western portion but will be delayed over the
eastern portion until Wednesday morning due to the surface ridge
over the extreme southeast states. The surface low ends up near
the eastern Great Lakes region Wednesday night, meanwhile bringing
a trailing cold front slowly into the western portion of the
forecast area as the surface ridging gradually weakens over the
extreme southeast states. Deep layer moisture increases
dramatically during the period, with precipitable water values
initially ranging from 0.5 to 1.25 inches over the area Monday
evening increasing to around 1.5 inches Tuesday morning then to
1.5-1.9 inches on Wednesday. To put this in perspective, this
means values increase from 90 to 150% of normal to around 250% of
normal during the period.

One important characteristic of this pattern for the forecast area
is the stubborn upper ridge centered over the Bahamas will tend to
deflect passing shortwaves in the southwest flow over the region
along with fringe subsidence effects. So, during the period pops
will be higher generally along/west of I-65 compared to further to
the east while the warm front progresses through the area
followed by the trailing cold front moving into the area Wednesday
night. Isentropic lift in the 295-305K layer will support slight
chance to chance pops Monday night. Good chance to likely pops
generally follow for Tuesday into Tuesday night west of I-65 as
the warm front progresses through this portion within an
environment of increasing deep layer moisture along with some
support from passing shortwaves, while further to the east expect
chance pops. By Wednesday, pops increase to likely/categorical
along/west of I-65 as another series of shortwaves affect the area
while chance pops continue further to the east, then similar pops
follow for Wednesday night as the trailing cold front begins to
moves into the area.

Rainfall amounts from Monday night through Wednesday night range
from about 0.75 to 1.75 inches along/west of I-65 with amounts of
0.25 to 0.75 east of I-65. These amounts might lead to some
nuisance type flooding over interior southeast Mississippi and
interior southwest Alabama and will need to monitor. Lows Monday
night range from the mid 40s well inland to the lower 50s near the
coast then near seasonable daytime highs follow for Tuesday,
ranging from lower 60s well inland to mid 60s over the southern
half. Tuesday night will be warm and range from 55-60 well inland
to mid 60s closer to the coast, then Wednesday night will be in
the mid 60s for essentially the entire area. Highs on Wednesday
will be well above seasonable levels with mid 70s prevailing. A
high risk of rip currents is expected through much of the period.

LONG TERM /Thursday Through Sunday/...The stubborn upper ridge
remains centered over the Bahamas through Friday while an upper
trof slowly advances from the western states. The frontal boundary
which had advanced into the western portion of the area Wednesday
night remains near this position on Thursday then moves slowly
into central Alabama/Mississippi on Friday. The upper ridge
finally breaks down during the remainder of the period as the
upper trof advances across the central states then weakens to a
shortwave trof while moving across the eastern states. The frontal
boundary moves well north of the area on Saturday as a surface
low develops over Texas, then the surface low moves quickly off to
the northeast states and brings another cold front through the
forecast area. Will have likely pops for much of the area Thursday
then rain chances decrease to slight chance to chance pops by Saturday
as the frontal boundary moves north of the area leaving a light
southerly flow pattern over the area. Chance pops are expected on
Sunday as the front moves through, but higher pops could
eventually be supported once confidence increases with the timing
of the frontal passage. /29

MARINE...A light to moderate southerly wind flow will continue
through this evening as a cold front approaches from the west. A
moderate to strong northerly flow will develop in the wake of the
front late tonight through Monday then gradually shift east by early
Tuesday. A moderate to strong easterly flow is expected on Tuesday
followed by a light to moderate southerly flow Wednesday into
Thursday in response to another cold front slowing approaching from
the west. Areas of fog mostly over the near shore waters of Alabama
will redevelop this evening then clear with the windshift overnight.
Patchy dense fog will also be possible further east occurring mostly
over the near waters of Northwest Florida through early Monday
morning. 32/ee


GM...Small Craft Advisory from 4 AM Monday to 6 AM CST Tuesday for

Dense Fog Advisory until midnight CST tonight for GMZ630>632.



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