Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 182335
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
535 PM CST Wed Jan 18 2017

.UPDATE...
For 00Z TAFS.

&&

.NEAR TERM...(Tonight)
Issued at 301 PM CST Wed Jan 18 2017

For this afternoon, dry weather prevailed across the greater
Tennessee Valley, thanks to drier air north of a cold front filtering
southward. This frontal boundary was becoming quasi-stationary,
extending from near Meridian to Atlanta. To the SW, an area of low
pressure was developing over SE Texas. Showers and a few
thunderstorms forming with this system extended eastward across
southern Arkansas and northern Louisiana. Otherwise generally mid to
high level clouds were present across the greater Tennessee Valley.
Mid afternoon temperatures have risen into the upper 50s to lower 60s
with light and variable winds.

The above noted showers to our southwest will continue moving towards
the northeast. This activity should reach far NW Alabama during the
late evening, and overspread the remainder of the area during the
overnight. More instability/lift will be realized during the later
night too; so introduced a slight chance of thunder in with more
predominate showers. Lows tonight should only cool into the upper 40s
to mid 50s. Normal low temperatures this time of year are around 31.

.SHORT TERM...(Thursday through Friday night)
Issued at 301 PM CST Wed Jan 18 2017

The warm front should by the late morning be located across our
northern areas, placing the forecast area in a rich southerly flow
form the Gulf. This increase of moisture and instability, and the
approach of a cold front will bring more widespread showers and
thunderstorms during Thursday. Model output overall is in reasonably
good agreement, bringing the heaviest axis of rainfall across our
western areas in the later morning and early afternoon, and the
central and eastern area during the afternoon hours.

Convective numbers suggest some of the storms could become "strong"
with locally heavy rainfall and wind gusts in the 40-50 mph.
Thunderstorms into the morning will be generally embedded within
widespread showers, then more numerous during the afternoon/evening
as the cold front approaches from the west. This front should move
across the region during the overnight of Thursday night/Friday
morning. Rain coverage and intensity should tapering off during the
day Friday. Rainfall totals should range into the 1-2 inch range
with this system. Only have a slight chance of rain in for our SE
area Friday afternoon. Also kept a slight chance of rain in for
Friday night, mainly for areas south of the Tennessee River.

.LONG TERM...(Saturday through Tuesday)
Issued at 301 PM CST Wed Jan 18 2017

Models continue to forecast various shortwaves pushing northeast
over the Tennessee Valley on Saturday. This is all ahead of another
upper low that swings northeast from Oklahoma into Iowa/Nebraska
during the day on Saturday. However, at the same time, the front to
the south of the Tennessee Valley continues to remain over the
Florida panhandle west into southern Mississippi. This should keep
deeper moisture advection well south of northern Alabama through
Saturday. 925 mb temperatures are progged to climb to between 15 and
16 degrees, so highs in the upper 60s to around 70 degrees look
good.

By Saturday night, models are in better agreement that a shortwave
impulse deepens into a surface low as it moves from central Alabama
northeast into northern Georgia/extreme eastern Tennessee. This
could produce some strong to severe storms during the evening and
overnight hours, as wet-bulb zero values around 7000 feet and CAPE ~
between 500 and 1000 J/KG is forecast to be in place by most models.
Luckily, not much helicity is forecast, so tornadoes do not look very
possible Saturday night. More of this activity may remain east of
I-65 and closer to Cullman to Dekalb counties, but this could change.

Models are in fairly good agreement snaking a warm front from near
northeastern Alabama southwest into central Mississippi before
extending it further northwest to the occluded surface low near
Memphis by Sunday morning. Not much instability shown by models, due
to the location of the warm front. However, as the surface low near
Memphis pushes east later in the morning, some models do show a band
of shower/storms developing just ahead of the surface low. If this
occurs, there is a brief window for additional strong thunderstorms,
but severe threat does not look very good. Some storms could produce
gusty winds to 50 mph and small hail, but instability and helicity
are not impressive. Regardless an additional 1 to 2 inches of
rainfall looks possible Saturday through Sunday, especially east of
I-65. Due to continued cloud cover and additional shower/storm
development, highs will be hard pressed to climb above the lower 60s.
Due to the slow moving and large area of upper level forcing progged
by the models Sunday night into Monday, keeping likely to a good
chance of showers in the forecast. Cooler and drier air will move in
behind the front Monday and Tuesday with highs in the 50s to lower
60s.

Expect a break from the rainfall by Tuesday Tuesday night, as high
pressure builds over the Tennessee Valley.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 533 PM CST Wed Jan 18 2017

Complicated TAF forecast through the next 24 hours. Ceilings are
currently VFR with CIGS around 5kft in eastern MS moving east
towards the area. CIGS and visibilities will lower through the
overnight and into Thursday, getting to IFR (around 1000ft) by Thu
afternoon. They could drop even lower but confidence is not high
enough to go much lower at this time.

Light rain will move in after midnight and be off/on through the
morning. Heavier rain will move in after 16-18z west to east.
Thunderstorms are possible after 19-20z and have included a Tempo
group at this time.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

NEAR TERM...RSB
SHORT TERM...RSB
LONG TERM...KTW
AVIATION...LN


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