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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 161108

Area Forecast Discussion
National Weather Service Huntsville AL
508 AM CST Fri Nov 16 2018

.NEAR TERM...(Today)
Issued at 508 AM CST Fri Nov 16 2018

Seasonably strong west-northwest flow aloft continues across the TN 
Valley this morning, in the wake of a departing shortwave trough 
across the mid-Atlantic region. However, near term guidance suggests 
that this flow will back to the west and diminish throughout the 
afternoon as a weaker mid-level disturbance over southeastern TX 
shifts east-northeastward into the central Gulf coast, weakening the 
height gradient aloft. Scattered-broken cirroform cloud cover ahead 
of the wave to our southwest has already begun to overspread the 
region, likely reducing the efficiency of radiational cooling this 
morning. Furthermore, a gradual increase in low-level southwesterly 
winds is expected over the next couple hours, as a cold front sweeps 
eastward into the lower Great Lakes region, and these factors should 
ensure no significant change in temperatures between now and sunrise.
Although environmental conditions are not ideal, patchy freezing fog
has recently been reported in a few locations and will remain a 
possibility across portions of the region through 13-14Z.

After sunrise, winds should veer to the west-southwest as the region
will become more influenced by a broad ridge of high pressure 
centered along the Gulf coast. Stronger insolation and light west- 
southwest flow will result in afternoon highs roughly 20-25 degrees 
warmer than yesterday, although based on the expected coverage of 
high clouds we have kept maxes in the l-m 50s.

.SHORT TERM...(Tonight through Sunday night)
Issued at 508 AM CST Fri Nov 16 2018

Mid and high level flow will back further to the west-southwest and 
begin to increase overnight, downstream from a well-defined vort max 
progged to drop southeastward into the northern Rockies. This feature
is expected to shift steadily southeastward into the central Plains 
by 00Z Monday, becoming increasingly sheared as it enters a region of
confluent flow to the north of the subtropical jet. Periods of high 
clouds will be possible in this regime at any time, but should 
gradually become thicker and more widespread from Saturday night into
Sunday as very weak synoptic scale forcing for ascent begins to 
overspread the region from the west. Based on expectations that high 
cloud cover will briefly dissipate after Midnight tonight, we feel 
that conditions will be favorable for radiational cooling once again,
with an attendant threat for fog (and freezing fog across portions 
of the CWFA). Thicker high clouds should limit both temperature falls
and the threat for fog on Saturday night/Sunday morning, with lows 
expected to only reach the u30s-l40s. Highs on Saturday and Sunday 
will be pleasantly warm compared to the past few days, reaching the 
l-m 60s for most of the area.

By Sunday night/Monday morning, models suggest that the mid-level 
shear axis over the central Plains will be approaching our region 
from the northwest. Although lift associated with this disturbance 
will be quite weak, it may be sufficient for the development of a few
showers along or immediately in the wake of a weak cold progged to 
enter the region during this period. Due to the weak nature of the 
lift and evidence of dry air in the subcloud layer, we have only 
included a slight-low chance POP at this point. Due to an increase in
lower cloud cover late Sunday afternoon, min temps should only reach
u30s-l40s once again Monday morning.

.LONG TERM...(Monday through Thursday)
Issued at 508 AM CST Fri Nov 16 2018

Models have changed little concerning details of the forecast on 
Monday. It looks as though a weak pre-frontal boundary ahead of a 
very weak cold front will move east into northern Alabama and 
southern middle Tennessee on Monday. Forcing along this convergence 
feature ahead of the front remains weak in most models. A fairly 
moisture starved atmosphere is in place along and ahead of it. 
However, they continue to show just enough moisture for isolated 
shower development as this boundary continues to move into locations 
west of I-65 into southern middle Tennessee Monday morning. Most 
models continue to further dry out the airmass ahead of the front and
along this pre-frontal boundary as they push the boundaries further 
east during the afternoon hours, only allowing some virga to develop.
Thus kept less than 20 pop in the forecast during that period. 
Mostly cloudy conditions are expected to occur with these features 
Monday morning through the evening hours, before starting to clear 
out towards daybreak on Tuesday. The dissipating cloud cover and 
persistent winds around 5 mph should keep low temperatures from 
really bottoming out. It does look cool though with lows dropping 
into the upper 30s.

Despite more abundant sunshine on Tuesday, some cold air advection 
behind the front should keep the high temperatures in the lower to 
mid 50s. Winds remaining around 5 mph or a little higher should keep 
similar temperature trends in the forecast, despite clear skies 
overnight. Lows in the lower to mid 30s with highs in the mid 50s 
look reasonable on Wednesday.

With a more zonal to slightly southwesterly flow developing ahead of
some upper level energy moving across eastern Texas, it should be 
warmer late Wednesday night into Thursday (lows in the mid/upper 30s 
and highs in the upper 50s/around 60 degrees). This trend continues 
into the weekend, as weather conditions change little through Friday 
afternoon. Some isolated to scattered showers may push east into the 
area ahead the afore-mentioned upper level energy as it approaches 
the area.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1138 PM CST Thu Nov 15 2018

VFR conditions will prevail at each terminal through the period, 
with a mostly clear sky and light winds.





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at weather.gov/huntsville.