Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 191146 AAA

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
546 AM CST Mon Feb 19 2018

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


12Z issuance...Patches of LIFR to IFR ceilings over the area at
the beginning of the period, along with a few patches of thick
fog over the interior Florida panhandle, transition to VFR
conditions for the entire area by mid morning. An IFR/MVFR
ceiling develops this evening with the potential for VLIFR/LIFR
conditions in low ceilings and fog at some locations. Light
southeast winds increase to 10 to 15 knots through midday then
diminish to a light southeast flow again tonight. /29


.PREV DISCUSSION... /issued 434 AM CST Mon Feb 19 2018/

NEAR TERM /Now Through Monday night/...An upper ridge extending
from the northern Gulf into the western Atlantic amplifies
significantly through the period as a longwave trof advances
across the western states. A series of shortwaves moving through
the southwest flow aloft ahead of the advancing upper trof lead to
a series of surface lows moving from the Plains and off to the
northeast, along a slowly advancing cold front. A surface ridge
oriented near the northern Gulf coast strengthens somewhat today
in response to the slowly advancing front/series of surface lows
resulting in light southeast winds near 5 knots currently over the
area increasing to 10 to 15 knots by midday. This modestly increasing
southerly flow is expected to limit fog development to patchy at
best early this morning. Another unseasonably warm day is expected
today with near record highs. The forecast high for Mobile is 80, and
the record is 83 set in 2017. The forecast high for Pensacola is
78, and the record is 81, also set last year. Other than some
isolated light showers possible over the western portion of the
area today, dry conditions are expected through tonight. /29

SHORT TERM /Tuesday Through Wednesday night/...Upper ridging
continues to build over the western Atlantic and southeastern U.S.
through the short term, with broad troughing maintained over the
western CONUS. This pattern leaves us beneath the back edge of the
upper trough, near the periphery of a wide band of southwest
upper-level flow extending from Mexico northeast into eastern
Canada. Meanwhile, at the surface, high pressure continues to
ridge from the western Atlantic into the southeastern U.S. and
eastern Gulf, maintaining a warm and moist onshore flow across
our area. The combination of anomalous mid- and upper-level
ridging and warm onshore flow result in high temperatures
remaining around or even just above record levels Tuesday and
Wednesday. This will especially be the case in areas that can see
sunshine peek through the clouds.

The mid-level ridge axis over the northern Gulf elongates and
pushes east late Tuesday into Wednesday in response to the
advancing western CONUS trough. With this shift, subsidence over
our area weakens enough for some showers to form Tuesday
afternoon. Rain chances continue into Wednesday, especially over
our northwestern counties, as the upper trough slowly advances
eastward and pushes a surface front into the lower Mississippi
River Valley. Models also remain in fair agreement in developing
enough instability across our area Wednesday afternoon to include
a mention of thunder mixed in with the rain showers. /49

LONG TERM /Thursday Through Sunday/...The midweek surface front
ultimately stalls to our northwest, keeping the axis of heaviest
rainfall out of our area except for areas generally west of I-65,
which could see some scattered showers and storms continue into
Thursday afternoon. The front then lifts off to the north Thursday
night as another mid-level ridge builds back over the area. The
resulting subsidence beneath this ridge will help suppress rain
chances Friday.

Eventually, the upper ridge that blocked the western CONUS trough
all week dampens and pushes south, leaving a primarily zonal flow
pattern across much of the eastern CONUS over the weekend.
Meanwhile, mid-level southwest flow continues from Mexico up into
eastern Canada as a potent shortwave digs into the Desert
Southwest. The resulting cyclogenesis in the lee of the southern
Rockies develops a surface low over the south Plains, which kicks
quickly northeast into the Great Lakes region by Sunday. This low
drags another front southeast towards our area, stalling it
across our inland counties and bringing rain chances back to the
area both Saturday and Sunday.

In terms of temperature, expect the near-record high temps to
continue Thursday and Friday thanks to the anomalous mid-level
ridge and associated subsidence. This will be especially true for
areas east of I-65 on Thursday, away from the showers and storms
near the stalled front. Temperatures then cool a little (but
remain well above seasonal normals) over the weekend as the next
front stalls nearby and overcast skies return. /49

MARINE...A light to moderate southeasterly flow prevails through
the end of the week, except occasionally stronger well offshore
through mid week. Patchy fog development will be possible late each
night into the early morning hours over the bay waters. /29




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