Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 221045 AAA

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
445 AM CST Thu Feb 22 2018

For 12Z TAFS.


.NEAR TERM...(Today and Tonight)
Issued at 337 AM CST Thu Feb 22 2018

The QLCS entering NW AL is taking advantage of LLJ intensification,
and is showing small bowing signatures/RINs that may be indicative
of stronger wind gusts. However, the line is elevated behind the
cold front at this, but may become more surface based as the line
pushes further east. The HREF shows a narrow nose of SBCAPE values
of 200-500 J/KG nosing in our northwest AL counties. The earlier 03Z
UAH SWIRLL sounding indicated a strongly curved low level hodograph
with 1km SRH values in excess of 300 m2/s2. Thus, we will have to
monitor for possible intensification. The showers and thunderstorms
should make good progress eastward through southern middle TN and far
north AL, with weakening expected as the low level jet weakens
during the day. There will be a cutoff in precipitation further
southeast, with areas along I-59 likely staying dry.

The frontal boundary will be to lift northwest as a warm front today,
but the NAM suggests additional showers and thunderstorms that will
track across far northwest AL into middle TN. This will keep the
boundary in this area until this evening. Rain chances look very
minimal further southeast in the warm sector. Rain chances should
virtually end areawide by 03Z this evening. With lower clouds likely
moving back in this morning, temperatures may not be as warm as
Wednesday, but still should see highs in the upper 70s southeast of
the boundary proximity. Near the boundary, highs should be around 70
in far northwest AL and lower 70s in southern TN.

.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 moreso 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


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 445 AM CST Thu Feb 22 2018

Flight weather conditions will likely be MVFR due to ceilings of
015-020agl through 18-20Z. Showers will persist at times, with
locally +RA possible. Ceilings should scatter out this afternoon with
south flow gusting at 15-20kt through 00Z. Then winds should diminish
with VFR conditions expected until more low clouds (MVFR ceilings
~015agl) arrive by 09Z.





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