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afdhun

Area forecast discussion
National Weather Service Huntsville Alabama
538 am CST Wed Dec 11 2019

Update...
for 12z tafs.

&&

Near term...(today)
issued at 515 am CST Wed Dec 11 2019

Cloud cover lingering over northeastern Alabama will exit into
Georgia and southeastern Alabama by daybreak. Based on current
temperatures, clear skies, and dewpoints in place and upstream,
temperatures should drop into a range of 23 to 28 degrees in most
locations. Sunny skies will help temperatures climb above freezing
everywhere between 8 and 10 am. With some residual moisture remaining
from melted snowfall, black ice will continue to be a problem
through 10 am. Though closer to 10 am, this should be the case
primarily in southern middle Tennessee. So be careful on the morning
commute and be alert for slick areas due to black ice.

Most locations near and north of a line from Scottsboro to Cullman
received at least a trace to 1 inch of snowfall with this system
(mainly on elevated and grassy surfaces). The exceptions to this
generally occurred near and just to the northeast of the I-65
corridor, where some localized amounts between 1 and 1.5 inches
occurred. The highest total around 2.5 inches occurred in the Sewanee
area, likely due to less melting (a longer period of near or below
freezing temperatures due to its elevation).

Evaporation of the remaining moisture is expected during the day
with sunny skies and breezy conditions putting an end to any threats
of black ice tonight. It will be noticeably colder with highs only
reaching the mid 40s east of the I-65 corridor and 50 degrees in
northwestern Alabama. Northerly winds from 5 to 10 mph with gusts to
around 20 mph are possible later this morning into the afternoon
hours. So despite air temperatures, it will feel like it will barely
get out of the 40s. So remember to take a good jacket if venturing
outside. Another cool night in store with lows dropping into the
upper 20s to lower 30s. Winds should remain just high enough with
clear skies overnight to keep freezing fog from forming.

Short term...(tonight through friday)
issued at 515 am CST Wed Dec 11 2019

Temperatures will warm slightly on Thursday, despite increasing
cloud cover ahead of a weak approaching front (stretching from the
western Great Lakes region into western arkansas). Cloud cover will
move north into northern Alabama and southern middle Tennessee ahead
of it, mainly in the afternoon. Highs in upper 40s to lower 50s look
reasonable despite cloud cover.

By Thursday evening, enough convergence and deep enough moisture
look to be in place for at least some scattered rainfall to develop.
At this point, soundings and guidance look too warm for any wintry
precipitation.

The strength of warm air advection on Friday will increase as the
front moves closer to the Tennessee Valley. Highs look similar to
Thursday, just a tad warmer maybe. Little instability is shown in
guidance, either aloft or surface based. Strong forcing though should
produce a brief period of moderate to heavy rainfall during the day
on Friday over northern Alabama and southern middle Tennessee.
Despite the strong forcing, overall around 1 inches or less looks
reasonable as this moves quickly east in most guidance.

Long term...(friday night through tuesday)
issued at 515 am CST Wed Dec 11 2019

Extended range model guidance continues to suggest that a
significant shortwave trough will lift northeastward from northern
la/southern Arkansas into Alabama/Georgia on Friday night, within a belt of cyclonic
flow aloft encompassing the Continental U.S.. strong lift and moisture advection
to the east of this system should allow for a fairly widespread
coverage of showers during the evening hours, with this activity
expected to shift eastward overnight as the system's deepening
surface low tracks up the southeastern Atlantic coast. Low stratus
clouds and light showers/pockets of drizzle will be possible
throughout the morning hours on Saturday, before a secondary mid-
level disturbance drops southeastward into the Cumberland Plateau
region of Tennessee/KY, allowing low clouds to lift/scatter during the
afternoon. A separate round of more scattered shower activity may
accompany the passage of this disturbance, but at this point we feel
that this activity may just clip the northeastern portion of the County warning forecast area
(if it does so at all). Due to the expected coverage of low clouds,
min temps will remain rather mild and in the l-M 40s on Saturday
morning, with around a 10-15 degree increase in these values expected
by the afternoon.

A zonal flow regime aloft will develop across the Tennessee Valley Saturday
night/Sunday, providing a brief period of dry conditions. It is
becoming more apparent with latest model guidance that an intrusion
of modified Canadian air will occur on Saturday night, providing
cooler morning temps in the mid 30s on Sunday. Temperatures will
recover into the l-M 50s Sunday afternoon, but a steady increase in
mid/high-level cloudiness is also anticipated to occur during this
period as flow aloft backs to the west-southwest downstream from a
shortwave trough digging into the central/southern rockies.

Model consensus indicates that the aforementioned shortwave trough
will partially phase with a northern stream disturbance over the
Central Plains on Sunday night, beginning the process of carving out
another amplified longwave trough which will approach the region from
the northwest by Tuesday evening. A sharpening surface trough
related to this system will extend from south Texas northeastward into
the mid-south region early Monday morning, and should focus the
development of widespread showers and perhaps a few elevated
thunderstorms that may impact northwestern Alabama/southern Tennessee prior to
daybreak. Although the trough will move little during the day on
Monday, the regime of widespread rainfall will spread eastward, as a
deepening wave of low pressure tracking northeastward into
southwestern Kentucky enhances low-level warm air advection across our forecast area. As
the surface low races northeastward Monday night, a powerful cold
front will sweep southeastward, ending the threat for precipitation
during the early morning hours on Tuesday. It is important to mention
that strong low-level wind shear will accompany this system and
could support a risk of severe weather on Monday/Monday evening, if
dewpoints rise into the lower 60s as advertised by model guidance.
However, due to limited instability, we have omitted thunderstorms
from the forecast at this point, but this threat will continue to be
monitored over the next several days. Locally heavy rainfall appears
to be a much greater hazard, with most of the area receiving perhaps
as much as 2 inches of rainfall from Sunday night-Monday night. Dry
conditions are expected in the wake of the front on Tuesday, although
temperatures will struggle to reach the mid 40s.

&&

Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 535 am CST Wed Dec 11 2019

VFR conditions are expected throughout the taf period.

&&

Hun watches/warnings/advisories...
Alabama...none.
Tennessee...none.
&&

$$

Near term...ktw
short term...ktw
long term...70/dd
aviation...ktw

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