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fxus64 kmob 270612 aaa 
afdmob

Area forecast discussion...updated
National Weather Service Mobile Alabama
112 am CDT Mon Mar 27 2017

Discussion...updated for latest aviation discussion below.

&&

Aviation...
06z issuance...MVFR to IFR cigs and visibilities through about
27.14z followed by MVFR to VFR cigs through about 28.03z followed
by MVFR to VFR cigs through 28.06z. Lower cigs and visibilities
mainly in patchy fog and low status generally through mid morning
followed by isolated to scattered showers and thunderstorms
through mid to late afternoon...then more patchy fog and low
stratus by late this evening. Winds will be southeast to south at
8 to 14 knots with through early this evening diminishing to 4 to
6 knots by late this evening. Higher gusts up to around 20 knots
will also be possible mainly during the late morning and afternoon
hours. 32/ee

&&

Previous discussion... /issued 841 PM CDT sun Mar 26 2017/

Discussion...see updated information for land areas below.

Update...early this evening our region is being affected by a
deep southerly surface fetch that is the return flow around an
approximate 1026 hpa surface anticyclone located just east of the
NC Outer Banks. GOES-r fog product wonderfully showing developing
low stratus already forming mainly along and south of the I-10.
Current forecast has it clouding over overnight - so that is one
track with patch fog becoming areas of fog later tonight. Forecast
lows in the low to mid 60s also looks on track.

Next main focus for our region will be on tomorrow afternoon's
thunderstorms, some possible containing large hail and damaging
straight line winds, mainly north of the Highway 84 corridor (and
west of I-65). The main mid- and upper wave (currently associated
with the severe thunderstorms over the southern plains) will pass
fairly far to our north and also fill somewhat on its track from
the plains, across MO and into the western Ohio Valley. As it currently
stands we are only forecasting isolated to scattered thunderstorm
coverage given the more northerly track of the aforementioned
feature. Wayne, Choctaw, Clarke and Wilcox counties are expected
to receive the greatest coverage. There is a significant thermal
cold pool advecting by as the wave passes to our north (-14 to
-16 deg(c) forecast at 500 hpa) and low wet bulb zero hgts (close
to 8-9 kft). Thus any storms that form would likely stand a good
chance of locally damaging winds and severe hail (>1" than
diameter) for a brief period tomorrow afternoon. Mitigating
factors for this event would be relatively lower values of
absolute moisture than what we normally see. This would limit the
amount of thermodynamic instability and thus further limit
thunderstorm coverage and intensity (so, considering the
pros/cons, we are looking for about 800-1100 j/kg of MLCAPE -
which would still cause concern). 40 knots of bulk 0-6 km vws will
also exist tomorrow afternoon (using Choctaw co, Alabama as a proxy)
which will help to organize newly developing updrafts but this
will be offset somewhat by relatively weaker low-level sr inflow
which would stifle the intensity of newer and subsequent updraft
growth.

Summarizing, there is relatively high forecast confidence the
mid- and upper wave will track more to our north and this would act to
limit the amount of thunderstorm activity (so we concur with
where Storm Prediction Center has placed the southernmost limit of the mrgnl risk on
their latest day 2 outlook). The thunderstorms are forecast to
end during the 6-9 PM time frame altogether and we will be dealing
with patchy dense fog again tomorrow night regionwide.

Regarding rip currents, we closely analyzed everything this
afternoon and have decided, once again like yesterday, to extend
the 'high' risk of rip currents through late Monday (despite
coming into a neap cycle). Area beaches were also continuing to
fly red flags this afternoon. The wave period is still relatively
high (7 sec) with higher values to the south and the wind fetch
is still causing wave energy to disperse northward from the
central and southern Glfmex. It is just going to take a while for
the swell to subside. Synoptically the pattern is non-changing, so
this is what you would expect until something does indeed change.
Have all ideas that by tomorrow afternoon we will be in a better
place. /23 jmm

Previous discussion... /issued 643 PM CDT sun Mar 26 2017/

Discussion...updated for latest aviation discussion below.

Aviation...
00z issuance...patchy dense fog and low clouds develop late
tonight into early Sunday morning, particularly during the pre-
dawn hours, with cigs/vis dipping to IFR/LIFR levels. Scattered
to broken cu field with VFR (to potentially MVFR near the coast)
cigs develops Monday afternoon and evening, with scattered shra
near the coast and tsra across the interior. Gusty winds, heavy
downpours, and large hail possible in the strongest storms. /49

Previous discussion... /issued 348 PM CDT sun Mar 26 2017/

Near term /now through Monday/...persistent light southerly flow
on the western periphery of a surface high positioned off the
mid- Atlantic coast maintains a fairly steady state surface
dewpoint profile in the lower to mid 60s overnight. Surface based
moisture and wind direction favors the development of late night
fog. This is supported by the latest rap/hrrr and short range
ensembles. Fog could become locally dense in spots. Overnight lows
mild, ranging in the lower to mid 60s.

Next upper level storm system, ejecting out of the plains states
across the lower MS River Valley Monday morning, makes steady
eastward progression across the Tennessee River valley thru the day. This
feature allows a frontal boundary to approach the mid-south by
Monday afternoon. East of the larger scale dynamics and surface
front, precipitable water values hold near an inch. Considering
passage of modest deep layer ascent and sufficient daily
instability, a return chance of showers and storms remains in the
forecast Monday. The Storm Prediction Center places a better
chance (slight risk of severe weather) to our north from the Tennessee
River valley, southward to northern MS/northern Alabama on Monday.
However, with amount of instability and wet-bulb zero heights down
to 8 to 9 kft, cannot rule out some strong to a few severe storms
containing marginally severe hail (quarter size or so) and
localized damaging wind gusts, mainly over the northwest half of
zones. It is these zones that are within a marginal risk of severe
weather that extends south of the slight risk area, with an area
defined along and west of a line from Thomasville Alabama to Richton
MS. Daytime highs Monday lower to mid 80s interior to mid to upper
70s beaches. /10

Short term /Monday night through Wednesday night/...the upper
level trough over the southeast conus will shift eastward and
weaken before moving over the western Atlantic by late Tuesday
afternoon. Meanwhile an upper level ridge over the Southern
Plains will move east and build northward, with the central axis
moving over the region. This upper level ridge will extend from
the southeastern Gulf of Mexico to south central Canada by Tuesday
evening and shift eastward through midweek, while a large upper
level trough exiting the Rocky Mountains moves over the Great
Plains. The surface high pressure ridge across the southeastern
states and eastern Gulf will remain largely intact as a surface
low across the Ohio River valley region moves east and weakens.
A weak cold front associated with the surface low will approach
the region from the northwest just reaching the northern portion
of the forecast area and stall. Other then a few isolated showers
across our far northern zones Monday night near the front and
isolated development on Tuesday north of I-10, it will be dry
through midweek.

Low temperatures each night will range from 58 to 62 degrees
inland areas, with mid 60s along the beaches. Warm temperatures
will continue on Tuesday and Wednesday with highs ranging from 80
to 85 degrees inland areas, with mid to upper 70s along the
coastal sections. /22

Long term /Thursday through Sunday/...the large upper level
trough over the Great Plains will shift eastward, with an
embedded upper low pressure area within the trough over the
eastern portions of Kansas and Oklahoma lifting northeast. The
southern extent of the upper trough will swing eastward across
the deep south. The surface high pressure ridge across the
southeastern states and eastern Gulf will move eastward as a
surface low forming across the Southern Plains lifts northeast to
the Great Lakes region. A weak cold front associated with the
surface low will approach the forecast area from the west Thursday
night. Scattered to numerous showers and thunderstorms will
accompany this next system on Thursday and Thursday night, with
the potential of strong to severe thunderstorms. The precipitation
will then taper off from west to east on Friday in the wake of
the front followed by high pressure building in from the west.
Above normal temperatures will continue through the long term. /22

Marine...high pressure off the mid-Atlantic coast Monday and
Tuesday sinks southward to the northern Bahamas on Wednesday. A
general light onshore flow persists for the next several days.
Onshore flow strengthens and seas build on Thursday in response
to a strong low pressure system lifting up across the mid MS River
Valley and associated frontal boundary approaching from the west.
Chances of storms increase Thursday and Thursday night, some of
which could become strong. /10

&&

Mob watches/warnings/advisories...
Alabama...high rip current risk through this evening for alz265-266.

Florida...high rip current risk through this evening for flz202-204-206.

MS...none.
GM...none.
&&

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