Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 171722 AAC

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
1222 PM CDT Thu Aug 17 2017

For 18Z TAFS.


.NEAR TERM...(Rest of Today)
Issued at 924 AM CDT Thu Aug 17 2017

Clouds continue to increase from the West this morning ahead of
convection ongoing across portions of the ArklaMiss upward into the
Mo Bootheel. This activity is associated with an approaching cold
front draped SW to NE in this general vicinity. Short-term/HIRES
models continue to show this activity dissipating with further Ewrd
progression, with perhaps a little redevelopment along the actual
front itself this aftn over our area thanks to insolation/peak
heating upon its arrival.

Otherwise, temp/dewpoint trends are on track with current temps in
the upper 70s/lower 80s (despite the increasing cloud cover) and
dewpoints in the middle 70s. This is making for rather soupy
conditions today, with Heat Index Values approaching Advisory
criteria in a few spots in NW AL. Overall, HI values will remain in
the low 100s W/upper 90s to ~100 E. Will monitor conditions and
reassess if a Heat Advisory is warranted should any major breaks
in the clouds develop later today (especially W of I-65).

No changes were warranted with the public forecast update this
morning. The current forecast is handling both observational and
expected trends very well.

.SHORT TERM...(Tonight through Saturday night)
Issued at 211 AM CDT Thu Aug 17 2017

Models are all in good agreement in pushing the boundary into the
area late this evening through early Friday morning. Convection
should be focused along this boundary and based on model soundings
will be primarily elevated. But with PWATs still near 2 inches expect
very heavy rainfall from storms. Due to the parent low associated
with the boundary being so far north, the movement of the boundary
through the area will be slow and won`t be south of the area until
Friday afternoon. So, areas east of I-65 could see a slight increase
in the coverage of storms Friday morning as we begin to warm up.

Winds at the surface and aloft begin to shift to the NW behind the
boundary and drier air will filter into the area. PWATs drop down to
around 1.2 inches and dewpoints should drop below 70 degrees! So,
some relief from the humid conditions is expected as we head into the
weekend. With these drier conditions and clear skies Friday
night/Saturday morning the northern half of the area could see lows
in the low to mid 60s. The rest of the area should remain in the mid
to upper 60s.

A trough is forecast to drop SE out of the northern Plains and move
through the OH Valley Saturday. While there will be better forcing
with the trough, the continued NW winds and dry air advection will
result in little if any instability. So, with that in mind have kept
a rain free forecast going for Saturday. Winds begin to shift back
to the south Saturday night into Sunday with dewpoints climbing back
into the lower 70s. This increase in moisture will keep temps Sunday
morning a few degrees warmer compared to Saturday morning.

.LONG TERM...(Sunday through Wednesday)
Issued at 211 AM CDT Thu Aug 17 2017

The forecast for Days 4-5 (Sun-Mon) have been adjusted for lower
rain chances as the TUTT low is now progged to migrate further west
as an upper ridge (500 mb heights of up to 597 dam) builds westward
into GA and AL. This will suppress convective development on Sunday.
A weak wave extension of the TUTT low may try to migrate north and
northeast around the ridge into the lower MS/TN valley on Monday, but
have kept the PoP at only 20 percent at this time. A weak surface
convergence boundary begins to lift northward on monday afternoon
into southern and perhaps central AL where convection should be more

On Days 6-7, the upper ridge will shift further west along the Gulf
states allowing upper troughing to take place over much of the
eastern CONUS.  Tuesday should bring typical summertime afternoon
thunderstorms that should diminish during the evening. By mid week,
vorticity impulses will flow southeast within the northwest flow
aloft. One arrives on Wednesday coinciding with a weakening cold
front.  There will certainly be sufficient moisture and instability
to produce at least scattered showers and thunderstorms Wednesday
into Wednesday evening. Highs should stay close or just above
seasonal normals next week.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1217 PM CDT Thu Aug 17 2017

VFR conds are generally expected through the TAF period at both
terminals, with the exception of the low clouds currently arnd 2kft
at KMSL. Otherwise, expect convection to develop shortly in the
vicinity of both terminals, lingering through the early evening hours
tonight. Clouds in place should limit fog potential, but this may
need to be added in with the 00Z issuance depending on if either
terminal is directly affected with +RA this aftn. Skies will begin to
clear by the end of the TAF period, with winds becoming more NWrly.





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