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000
FXUS64 KHUN 211857
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1257 PM CST Thu Nov 21 2019

.UPDATE...
For Near Term and 18Z TAFS.

&&

.NEAR TERM...(Remainder of Today)
Issued at 1257 PM CST Thu Nov 21 2019

A deamplifying 500-mb ridge will continue to shift eastward and away
from the TN Valley today, with deep-layer west-southwesterly flow
becoming more established to the north of a subtropical ridge over
the southern Gulf of Mexico and to the east of a cutoff upper low
moving slowly eastward across the southwestern deserts. At the
surface, light south-southeasterly winds will slowly veer to the
south-southwest and strengthen as a low-level ridge spreads
southeastward across NC/SC and a cold front approaches the region
from the northwest. Adequate lift in the resulting lower-tropospheric
WAA regime has been sufficient to sustain light rain moving into the
region from the west-southwest, and we expect this trend to persist
throughout the afternoon. POPs have been adjusted to reflect a higher
coverage of measurable precipitation, but rainfall amounts should be
very light. Otherwise, we made minor downward adjustments to the max
temperature grid to reflect the earlier onset of thicker clouds and
precipitation.

.SHORT TERM...(Tonight through Saturday Night)
Issued at 227 AM CST Thu Nov 21 2019

Expect an increase in shower activity through the overnight hours, as
the aforementioned frontal boundary tracks closer to the Valley.
Guidance seems to be in fairly good agreement about a frontal wave
forming near the ArkLaTex region around 18z, stalling the frontal
boundary near southern TN, keeping us soggy on the warm side of the
front. High temperatures will remain close to seasonal norms, ranging
from the low to middle 60s. Expect the heaviest rain to come Friday
night and Saturday morning, as the frontal wave tracks near the
northwest corner of AL and eventually pushes a cold front east of the
Valley by late Saturday. Looking at thermodynamic profiles, have
continued a slight chance of thunder Saturday morning as some
marginal elevated instability looks to be present, especially across
northwest AL. With that said, do not expect thunderstorms to be
widespread but an occasional rumble or two of thunder cannot be ruled
out. Expect shower activity to clear northeast AL by sunset
Saturday, with rainfall amounts totaling between 1.5-2.0". While
widespread flooding issues are not anticipated at this time, some
ponding of water on roadways will be possible during periods of
heavier showers, especially Friday night and Saturday morning.
Exercise caution especially if traveling during this time.

After another mild day of highs in the low to mid 60s, temperatures
will fall steadily behind the front as cooler, drier air is ushered
in and high pressure moves into the area. Overnight lows will fall
back into the mid to upper 30s Saturday night/Sunday morning.

.LONG TERM...(Sunday through Wednesday)
Issued at 227 AM CST Thu Nov 21 2019

High pressure will quickly move into the area Sunday and Monday in
wake of the frontal system, resulting in a brief period of fair
weather and dry conditions early next week. On Sunday, northerly flow
will reinforce a cool, post frontal air mass. Thus, despite the
abundant sunshine, highs will struggle to climb above the lower 50s.
As high pressure slides off to the east of the region on Monday,
we`ll see some air mass recovery as southwest flow helps push
temperatures into the 60s. Subsidence from the ridge will prevent
anything in the way of cloud cover developing, so expect another
sunny and dry day.

This bout of quiet weather will be short-lived as we transition back
into a more active pattern as a developing low pressure system shifts
from the Southern Plains into the Mississippi Valley on Tuesday,
eventually moving into the Great Lakes Tuesday night into Wednesday
morning. A surface cold front will track eastward into the
Mississippi Valley on Tuesday and push into the Tennessee Valley
region Tuesday night, clearing the area by Wednesday morning. Models
have changed their thinking regarding the evolution of this system.
Earlier runs indicated the northern stream trough merging with a
closed low across Baja California and the Desert Southwest. It now
appears that this northern wave may be a little too far removed to
accomplish this, and thus, expect this next system to move through
the Ohio/Tennessee Valley region as more of an open wave, rather than
a dynamic, deep upper cyclone.

Moisture recovery ahead of this frontal system will be very slow
significantly limiting instability and the onset of precipitation
somewhat on Tuesday. For this reason, think that the thunderstorm
threat during this period is quite low and have maintained a forecast
of rain showers. However, we should get a good slug of moisture
right along the front as it moves in Tuesday afternoon/evening and
Tuesday night. Thus, we should get another appreciable round of
moderate to locally heavy rainfall during the window of the frontal
passage Tuesday night. Thereafter, the boundary will shift east of
the area on Wednesday as high pressure moves in from the west,
bringing an end to the rainfall by midday Wednesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1257 PM CST Thu Nov 21 2019

VFR altostratus cigs arnd 15 kft will continue to slowly descend
through the aftn, as lift strengthens ahead of an approaching cold
front and light rain spreads northeastward into the TN Valley.
However, model consensus indicates that a more rapid deterioration in
conditions will occur at the terminals arnd 22/09Z as cigs become
established in the 1500-2500 ft layer. Both coverage and intensity of
rainfall will increase around or shortly after 12Z as the cold front
drifts southeastward into the region and stalls. Thus, we have
indicated both MVFR vsby reductions in heavier precipitation and IFR
cigs. Sfc winds will oscillate btwn SSE-SSW at speeds of 5-10 knots
through 12-14Z, before becoming lgt/vrbl as the pressure gradient
diminishes with the approach of the cold front.

&&

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

&&

$$

NEAR TERM...70/DD
SHORT TERM...25
LONG TERM...AMP.24
AVIATION...70/DD

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at weather.gov/huntsville.