Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 232349

Area Forecast Discussion
National Weather Service Huntsville AL
649 PM CDT Sun Apr 23 2017

For 00Z TAFS.


.NEAR TERM...(Tonight)
Issued at 307 PM CDT Sun Apr 23 2017

Quite a change in the weather across the Tennessee Valley compared
to yesterday and the days before - especially regarding temperatures.
Highs of at least 80F or more have occurred since April 9th, with
highs today getting to near 60 as of this writing under cloudy skies.
Along with the clouds, light showers (some too low in elevation to be
detected by radar) were also present. To our north where rather steep
mid level lapse rates in the 6-7C/km and 500mb air temps ~ -15C, have
resulted in a few lightning strikes over portions of western and
middle Tennessee.

Given the track of the upper system (moderating somewhat as it moves
to the SE), have held off on convection so far this forecast area.
Even if no lightning occurs, isolated to scattered showers look
possible tonight. The models for the most part indicate light rain
chances overnight. Given 1000/500 mb thickness values around 550
decameters and the colder air in place, night time lows should cool
to around 50 most spots, a bit cooler in our higher elevated spots.
Shower activity for the most part should diminish from NW to SE as
the system exits the region. Given that big picture rainfall in the
1-2 inch rainfall occur across the area, included patchy fog in for
the late and overnight.

.SHORT TERM...(Monday through Tuesday)
Issued at 307 PM CDT Sun Apr 23 2017

The new work week should start off dry but with patchy morning fog.
This fog should fade shortly after sunrise. Given the expansive size
of the cloud shield around the departing system, took a slower
approach with clouds decreasing mainly in the afternoon. With more
slackened cold air advection, highs should warm into the mid 60s
mountains to lower 70s NW Alabama (where more solar insolation is

Similarly cool conditions are forecast Monday night with lows around
50. Held off on fog development this issuance, but given the amounts
of recent rain, could get more patchy fog before daybreak Tuesday.
Tuesday otherwise should feature mostly sunny skies, with high
temperatures recovering to around 80.

.LONG TERM...(Wednesday through Saturday)
Issued at 307 PM CDT Sun Apr 23 2017

The extended starts midweek with the warm up still in
progress as the upper level ridge displaced just off to our east.
Highs will be in the lower 80s with lows in the lower 60s under
mostly clear skies. The trough out in the Midwest will lift NE
towards the Great Lakes as the sfc low pulls a cold front into the
TN Valley Wed Night into Thursday. With southward progress, the
front will weaken, however it will still produce scattered showers
and thunderstorms.

On Friday, what is left of the front will lift northward as a warm
front. There is still model disagreement on the coverage and
intensity of the convection that would occur. If the low level cap
holds that the GFS shows, the large area of convection the ECMWF is
displaying will really be out to lunch. Until better agreement
arises, took a blend of the two for POPs. High pressure off the east
coast strengthens on Saturday, but disturbances will still round the
western edge, allowing for lingering chances of showers and storms
in the forecast. Highs will be in the mid 80s! Both solutions have
slowed down on the timing for Sunday`s system so made adjustments to
POPs to accommodate.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 649 PM CDT Sun Apr 23 2017

MVFR conditions (mainly due to low ceilings) may continue for
another 3-5 hours. Ceilings will lower to ~700 ft around that time.
Scattered showers or drizzle will persist through early Monday
morning (at least through 12Z); some changes to visibility are likely
but IFR should dominate. Some modest improvement back to low-end
MVFR will occur 16-17Z Monday, and the rain/drizzle will be over by
then. However, little additional improvement is expected beyond that
through 00Z/25; earlier clearing can`t be ruled out but the TAFs
assume a more pessimistic scenario.





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