Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 181721

Area Forecast Discussion
National Weather Service Huntsville AL
1121 AM CST Thu Jan 18 2018

For 18Z TAFS.


.NEAR TERM...(Rest of Today)
Issued at 908 AM CST Thu Jan 18 2018

Thursday dawned clear but cold across the Tennessee Valley. Most area
low temperatures were in the single digits to around 10 degrees, but
with sunrise, those have rebounded to around 20 as of 10 AM/15Z.

Sunny conditions will continue today, and winds will veer around to
the west, allowing temperatures to rise above freezing for the first
time since late Monday. While MOS is slightly cooler, most blended
guidance supports highs in the mid-upper 30s, in line with the
existing forecast. Aside from the usual tweaks to hourly grids, few
changes are needed to the forecast.

.SHORT TERM...(Tonight through Saturday)
Issued at 320 AM CST Thu Jan 18 2018

Temps will again turn unseasonably cold later tonight under optimal
radiational cooling conditions coupled with dew pt values predom in
the lower teens. Lows again look to fall mainly into the mid/upper
teens, but should be a few degrees warmer than the past couple of
nights. Even warmer temps are then xpcted on Fri, as the sfc high
settles more into the region and sfc winds back further to the SW.
Afternoon highs on Fri look to climb well into the mid/perhaps upper
40s for most locations, under continued mostly sunny skies. The sfc
high should then begin to move E of the region Sat closer to the srn
Atlantic Coast, as return flow develops and some moisture begins to
stream nwd into the mid TN Valley. Afternoon highs on Sat again look
to climb a few degrees higher, as temps reach the lower 50s for most
areas under increasing clouds.

.LONG TERM...(Saturday night through Wednesday)
Issued at 320 AM CST Thu Jan 18 2018

A slow warming trend that occurred in the shorter term will continue
Saturday night. The area of high pressure that brought very chilly
air to the region earlier this week, by Saturday night should be
moving off of the Southeast Coast, bringing a southerly flow across
the Tennessee Valley. This flow and Gulf moisture (albeit worked
over by the Arctic high) will begin returning to the region. Night
time temperatures Saturday night for most of the area should remain
above freezing, a first time in a good while - with lows ranging
from the low/mid 30s over northeast Alabama to around 40 over NW
Alabama. Above normal temperatures will greet the start of a new
week, as the southerly flow becomes more established, helping raise
high temperatures into the lower 60s most locations. Lows across the
area Sunday night will only be in the low/mid 40s.

A powerful storm system now west of the Alaska Panhandle/British
Colombia will continue ashore over the next day. A speed max/upper
disturbance south of it will move across the northern California
coast tonight and on Friday, developing into a major winter storm
over the western CONUS during Saturday. As this system`s upper
trough in a neutral tilt swings across the Divide region late
Saturday, it will induce development of a surface low across the
High Plains on Sunday. This next low will deepen as it heads toward
the Great Lakes in the Mon/Tue timeframe. It will bring a Pacific
front (rather than Arctic front) across the forecast area during
Monday, bringing rain chances back to the region.

This looks like another high shear/low instability system. There
remains enough instability to keep a mention of thunder mixed in
with more predominate showers. Given rather strong storm relative
helicity values and decent diffluent upper flow, a few storms could
become strong, with gusty winds the main threat. Unlike last night,
the models were in better agreement timing wise, bringing the front
across during the latter half of Monday. Temperatures a tad above,
but closer to seasonable norms are expected on Tue/Wed, as a Pacific
based high pressure builds in from the west - unlike the very chilly
conditions Canadian and Arctic based ridges previously brought to
the region.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1121 AM CST Thu Jan 18 2018

VFR conditions are expected through 18Z/19. Winds will decouple & go
calm after 00Z, then pick back up out of the SW around mid-morning





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