Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 052021
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
221 PM CST Mon Dec 5 2016

.NEAR TERM...(Tonight)
Issued at 221 PM CST Mon Dec 5 2016

Widespread showers continued over the Tennessee Valley, as another
round of precipitation moves across the region. This activity was
preceding an upper low, now moving to the NE across the Edwards
Plateau of central Texas. The trough axis as it moves ENE across
the Mississippi Delta will take on a slight negative tilt later this
afternoon through the overnight. The upper low should move across the
forecast area Tuesday morning, reaching the Mid Atlantic coast early
Wednesday.

A surface low spawned by this trough was developing over the NW Gulf,
now south of the Sabine River. A warm front extending east of this
low should move further northward across central Alabama during the
overnight, with the cold/warm front becoming occluded as it moves
across the Tennessee Valley region near daybreak Tuesday. Widespread
showers this evening could be accompanied by isolated/embedded
thunderstorms. Some of the mesoscale models were hinting at a heavier
line of precipitation - not quite a squall line moving west to east
across the region during the overnight. This is when the heaviest
showers are expected. The stronger storms/showers during the
overnight should bring locally heavy downpours, small hail, and gusty
winds. Both the NAM/GFS BUFR soundings indicate strong lower level
shear, but hardly any instability - typical of a high shear/low CAPE
event. Overnight lows will range in the low/mid 50s.


.SHORT TERM...(Tuesday through Wednesday)
Issued at 221 PM CST Mon Dec 5 2016

The surface low should be north and east of the region after
daybreak Tuesday. This should end the heavier showers and storms.
The NAM was hinting at ducting/wake low formation occurring mainly
just to our east. This could result in gusty easterly winds Tuesday
morning over our far eastern areas. Shower activity otherwise should
end from west to east during the course of the day. Rainfall amounts
from this system should range from 1-2 inches, with locally higher
amounts. The rain will definitely help with the drought situation
most of the area has been under as of late. Somewhat greater
hydrological response is possible from this next system; as the
ground is a little wetter than before. Cloudy skies otherwise will
continue with highs in the mid/upper 50s.

Dry weather is forecast Tuesday night - with the area between
systems. An Arctic cold front and clipper type system headed ESE from
the Front Range region will bring more clouds and a chance of rain
during Wednesday, mainly in the afternoon. Colder air from the
northwest will filter in, bringing lows into the low/mid 30s. Some
light snow may mix in with the rains over our northern areas before
daybreak Thursday. Given a warm and wet ground, no accumulation
issues are expected.


.LONG TERM...(Wednesday night through Sunday)
Issued at 221 PM CST Mon Dec 5 2016

The Arctic front continues to track southeast across the area by 12z
Thursday and the precip associated with it is looking drier with each
model run. Both GFS/ECMWF this morning had maybe a few sprinkles
across the area. Will keep the blended pops right now (chance in the
SE counties to slight chance to the NW) but they are less than
previous runs and it should probably continue to decrease as we get
closer to the event. It should also be breezy with the frontal
passage as the gradient tightens with wind gusts of 15-20 mph
possible. Lows will be near normal and in the middle 30s.

The front should be through the whole area by 00z Friday, earlier in
the NW parts of the area. GFS is much quicker with the dry air and
the colder air and is a few degrees colder than other models. This
would lead to cooler high temps. It does look like the GFS is the
slight outlier with the blends and other individual guidance a bit
warmer so will stick with the blended temps at this time which puts
highs in the lower 40s. Won`t be surprised if it ends up colder
thanks to strong cold advection that will be occurring.

Thursday night will be the coldest we have seen this season with
lows dropping to around 18-20 degrees. With a 5-10mph wind, the wind
chills will drop to around 9-12 degrees. The cold air continues to
move in Friday with the coldest highs of the year expected, in the
middle 30s. The record minimum max temps are 30 degrees for both
Huntsville and Muscle Shoals so that record does not look to be
broken. Clear skies and light winds Friday night will help drop
temps again to around 18-20 degrees but with light winds, the wind
chills will only be a couple degrees cooler.

Synoptic differences become evident starting Saturday with the
location of a developing front over the midwest. This could bring
showers and maybe thunderstorms Saturday night through Monday,
depending on which model you choose. Given the uncertainty, kept the
blended pops and kept all rain. With southerly flow returning
though, a warming trend will start with highs back into the upper
50s by Monday.


&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1158 AM CST Mon Dec 5 2016

Inclement flying weather will continue, as another storm system
forming over the NW Gulf moves towards the forecast area. Through the
period, MVFR CIG/VIS values or lower will prevail. The heaviest
showers with embedded thunderstorms will impact the region tonight,
beginning in the mid/late evening over NW Alabama, then progress to
the east during the overnight. As such, set timing for thunder
affecting KMSL at 03Z...and KHSV an hour later. Gusty winds and lower
CIG/VIS values are possible with the heavier showers/stronger storms.
Generally IFR conditions are otherwise expected for the predawn and
Tuesday morning with light rain and fog.


&&

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

$$

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


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at weather.gov/huntsville.



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