Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 221722
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1122 AM CST Thu Feb 22 2018

.UPDATE...
For 18Z TAFS.

&&

.NEAR TERM...(Rest of Today)
Issued at 1031 AM CST Thu Feb 22 2018

A very amplified upper level pattern continued across the greater
North American domain; with rather deep troughing over the western
lower-48, and abnormally strong upper ridging situated off of the
southeast coast. A near 595 decameter 500mb upper high is very
impressive for this time of year. At the surface, a cold front that
made an intrusion across parts of the Tennessee Valley yesterday
afternoon and evening, continued to retreat to the north and west as
a warm front - another unusual event for winter time. A strong SW
upper flow rounding the western side of the upper ridge, and east
side of trough was helping to shunt the coldest air from the surface
high over the northern Rockies more to the northeast than south.

In regards to the local weather setup, a very moist plume of high
precipitable water amounts (in the 1.4 to 1.5 inch range, which is
in the top 90s percentile range for this time of year. Thus the
showers and storms over NW Alabama this morning will be capable of
producing locally heavy rainfall. However, new high resolution
models, as well as the new NAM are in good agreement decreasing rain
chances from SE to NW during the afternoon, as the surface ridge to
our SE helps push the frontal boundary further to the north and west
of here.

A decrease in rain chances, but variable cloud cover makes for a
tricky forecast regarding high temperatures later today. We`ve kept
high temps for most of the area in the mid/upper 70s most spots.
Standing record highs in Muscle Shoals and Huntsville are 79-1909 and
76-1909/1980 respectively. Think the record high at Huntsville will
be challenged given less rainfall there and a potential for more
heating.

.SHORT TERM...(Friday through Saturday)
Issued at 337 AM CST Thu Feb 22 2018

Another warm and dry day is expected Friday with highs reaching
the upper 70s to around 80. There will be a weak 8h trof/wind shift
lifting northward by Friday evening with deeper low level moisture
increasing behind this feature. This will bring showers late Friday
night into Saturday. The GFS is quite a bit more aggressive with
this feature, but will leave at chance for now until this becomes
more definitive. Several weak 7-5h shortwave will keep at least a
chance of showers or even a thunderstorm through Saturday, but it is
difficult to pin down specific timing. On Saturday, the chance will
be slightly higher northwest closer to the stronger mid level flow.
As such, the clouds and scattered showers will keep temperatures in
the 70s.

.LONG TERM...(Saturday night through Wednesday)
Issued at 337 AM CST Thu Feb 22 2018

The extended forecast will start off with the front finally moving
through the TN Valley Saturday night into Sunday morning, entering NW
AL around 06Z. The front will be moving into an environment with
plentiful moisture and unseasonably warm temperatures set up by the
persistent southerly flow of the anchored ridge off to our east.

Since the front will be moving in during the overnight hours,
instability will be limited and will have to see what will be left
from earlier in the day which has its own limiting factors: cloud
cover and convection ahead of the front. There should be enough
instability for thunderstorms as soundings continue to show a couple
hundred J of MU CAPE. Shear values will increase to 30-40kts (0-1km)
and 40-50kts (0-6km). Not to mention there will be a LLJ of 50-60kts
moving in just before 06Z, helping storms develop along and ahead of
the front. This could support strong to maybe severe storms within
the line, with damaging winds as the primary hazard at this time. The
GFS continues to be a little bit stronger with the front due to it
still holding on to the solution of a more amplified upper-level
trough and deeper sfc low lifting into the Great Lakes over the
weekend. Not fully giving this solution yet, but will not rule it
out. Otherwise, models are more so in agreement.

The front will weaken as it moves across the forecast area on
Sunday, with precip chances decreasing throughout the day from west
to east. Isolated precip chances will linger into Monday as weak
disturbances glide into the region and the front stalls in Central
AL. `Cooler` temps return behind the front, however they will still
be warmer than normal. The work week will start off with daytime
highs in the 60s and overnight lows in the 40s. This temp trend will
linger through the first half of the week. Enjoy the pleasant day
expected on Tuesday before the rain returns late Tuesday night into
Wednesday!

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1120 AM CST Thu Feb 22 2018

A line of showers with a few embedded storms is moving across the TN
Valley as of 17z. Gusty SW winds up to 35kts and reductions of vis
down to 1-3SM are possible along the leading edge of the line.
Behind the line winds return back to the south with vsbys climbing
back above 5SM. Could see some brief periods of MVFR vsbys as
additional showers in northern MS move towards the terminals.
Otherwise, expect VFR conditions to continue through about 09z when
drop towards 1,500ft. After 15z Friday mixing should allow cigs to
increase back to VFR.

&&

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

$$

NEAR TERM...RSB
SHORT TERM...17
LONG TERM...JMS
AVIATION...Stumpf


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at weather.gov/huntsville.



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