Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 191115

Area Forecast Discussion
National Weather Service Mobile AL
615 AM CDT Fri Oct 19 2018

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


12Z issuance...VFR conditions expected across much of the area
throughout today. Cloud cover increases as winds shift to
southerly this afternoon, with a few isolated showers possible
primarily along the coast. Low stratus and patchy fog, possibly
dense at times, will develop late tonight into early Saturday
morning. /49


.PREV DISCUSSION... /issued 341 AM CDT Fri Oct 19 2018/

NEAR TERM /Now Through Friday night/...An upper ridge currently
over the eastern CONUS pushes over the western Atlantic through
the next 24 hours ahead of a deep longwave trough digging across
central Canada and the northern CONUS. Beneath the upper ridge, a
surface high also pushes east over the Atlantic and a moist
southeast flow develops across the northern Gulf coast. Moisture
gradually improves as a result, with PWATs reaching 1.5 to 1.75
inches across the area. This should be enough to support a few
showers along the sea breeze today, starting along the coast
during the late morning and early afternoon hours and moving
inland before dissipating after sunset. Instability will be a bit
limited, but cannot rule out a few rumbles of thunder in cells
over SW AL and the far western FL panhandle, where hi-res guidance
suggests a nose of ~1000 MLCAPE develops this afternoon.
Temperatures will trend a bit warmer as well, with highs reaching
the mid 80s this afternoon and lows tonight in the upper 60s and
lower 70s. /49

SHORT TERM /Saturday Through Sunday night/...An upper trof
amplifies over the eastern states on Saturday then slowly moves
off into the western Atlantic on Sunday. An associated deep
surface low well off to the northeast brings a strong cold front
southward into the region, which moves through the forecast area
during the day on Saturday. In the wake of the front, a dome of
cool and dry high pressure builds from the Plains and into the
eastern states through Sunday, bringing fall-like temperatures to
the area. Will have chance to good chance pops for most of the
area on Saturday as the front moves through, then dry conditions
follow for the remainder of the period. Highs on Saturday range
from the lower 80s over the southern portion of the area to
lower/mid 70s well inland as cooler air begins to flow into the
area. Highs on Sunday will be up to several degrees below normal
and range from the lower 70s over the southern portion of the area
to the mid/upper 60s well inland. Sunday night looks to be coolest
night of the entire forecast period, with lower 40s well inland
ranging to near 50 at the coast. /29

LONG TERM /Monday Through Thursday/...Another upper trof swings
out of Canada and into the interior eastern states on Monday,
then slowly moves off into the western Atlantic by Wednesday.
While one would typically expect at least broad upper ridging to
build into the region in the wake of the upper trof, a complex
series of southern stream shortwaves will instead affect the
region during much of the period. The first set of these
shortwaves are expected to advance from Texas to across the
northern Gulf coast area Monday night into Tuesday. This is
followed by another series of shortwaves (ejected from an upper
trof over the southwestern states) which move across Texas and
then across the northern Gulf coast area Wednesday into Wednesday
night. In response to the series of shortwaves, an inverted
surface trof develops near the Texas coast/western Gulf on Monday,
then is expected to evolve into a surface low which advances
eastward across the northern Gulf or into the north central Gulf
coastal states later in the period. While the timing and placement
of this surface low is highly uncertain, the overall pattern at
least supports a return of rain chances to the forecast. For now,
will have dry conditions for most of the area on Monday then
slight chance to chance pops follow for Tuesday and Wednesday and
have gone with good chance pops for Thursday. Temperatures during
the period will generally be near seasonable values. /29

MARINE...A lighter onshore flow develops today and tonight as high
surface pressure north of the area pushes east over the western
Atlantic and the local pressure gradient weakens. Another cold front
passes through on Saturday, with a moderate to strong offshore flow
returning in its wake and lasting through Sunday night. Winds will
be strongest Saturday night into early Sunday and a Small Craft
Advisory may be needed for that period. Winds then shift to easterly
(but remain at SCEC levels) early next week as high pressure builds
back in north of the marine area. Seas expected to be around 2 feet
today and Saturday, then increase to 3 to 5 feet nearshore and 5 to
7 feet well offshore in the wake of the front Saturday night into
early next week. /49




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