Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 191737

Area Forecast Discussion
National Weather Service Huntsville AL
1237 PM CDT Thu Oct 19 2017

For 18Z TAFS.


.NEAR TERM...(Rest of Today)
Issued at 936 AM CDT Thu Oct 19 2017

Another cool fall morning with temperatures already rising into the
low to mid 50s as of 930AM this morning underneath a high pressure
system centered over western NC.

Meanwhile, patchy dense fog has once again developed near the TN
river over Jackson county (Scottsboro to Stevenson area) and in some
other valley, river, lake locations. Currently, GOES 16 VIS
satellite imagery and observations continue to show fog over eastern
Jackson county along the TN river. Made an adjustment to the forecast
to keep patchy dense fog in the forecast through 16Z/11AM.

Otherwise, satellite imagery does show high cirrus from upstream weak
shortwave trough over the southern Plains that may move over the
Southeast later today. Made some minor trend adjustments to the
dewpoints and temperatures, but daytime highs in the low to mid 70s
with dewpoints in the upper 40s/near 50 are on track.

.SHORT TERM...(Tonight through Saturday)
Issued at 315 AM CDT Thu Oct 19 2017

Clear skies, light winds, cool temperatures and residual moisture
will lead to patchy fog development again, mainly near bodies of
water and in the more sheltered valleys. For this issuance, stayed
with just patchy wording; will let later shifts add dense wording if
it appears appropriate for the situation.

The system carving a trough over the western CONUS will lead to a
troughing west/ridging east setup by Saturday. With upper ridging
along the east coast and a surface high over the Mid Atlantic, a dry
and warm trend will continue across the Tennessee Valley for the rest
of the week. High temperatures for Friday/Saturday should warm into
mid/upper 70s both days. I cannot rule out an 80-82 high for the
warmest spots, especially on Saturday. "Normal" highs on Saturday are
73 for what it is worth. As the system out west advances further
eastward, clouds associated with it should overspread the region,
with sunny skies on Friday, becoming partly cloudy east - to mostly
cloudy west during Saturday.

.LONG TERM...(Saturday night through Wednesday)
Issued at 315 AM CDT Thu Oct 19 2017

The latter half of the forecast period begins with both high pressure
at the sfc and an upper ridge axis exiting the Atlantic Seaboard to
the E, as a large upper trough pattern digs across the Plains
states. With the approaching upper trough pattern, a cold front is
still xpcted to sweep ewd into much of the ern CONUS Sun/Sun night,
along and ahead of the upper level feature. A little bit of
consistency exists this morning between the 00Z ECMWF/GFS, with both
models now showing some type of closed upper low developing along the
base of the trough over the wrn/cntrl Gulf Coast, as the trough axis
lags just behind the sfc boundary into Mon. What this means is
perhaps a slower frontal passage into the day on Mon, with quite a
bit of shower/tstm activity occurring along/ahead of the front
starting late Sun afternoon into Sun night. The models are actually
hinting at PWs increasing near 1.70 inches by early Mon morning,
which is certainly suggestive of locally heavy rainfall given some
fairly descent low level convergence/dynamical forcing along/just
ahead of the advancing front. Buoyancy/SBCAPE values are not that
overly impressive, with max values near 1500 J/kg while Bulk Shear
values hover just below 40KT. This may suggest a couple of strong
tstms within the heavier rainfall, but prob nothing more.

The latter half of the model suites then have the front exiting the
local area to the E late Mon afternoon, with a trailing band of
rainfall moving thru the area Mon night into Tue, as the upper trough
axis translates ewd across much of the region. A thickness stream
diving straight into the nrn Gulf suggests a notably cooler surge
into the region from the N, as thermal advection lowers temps around
10-15F going into the middle of next week, with clearing skies.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1236 PM CDT Thu Oct 19 2017

VFR conditions are expected to continue across north Alabama/southern
middle Tennessee for the next 24 hours. There may be fog over
northeast Alabama/southern middle Tennessee between 20/10Z-20/14Z
near rivers, lakes, valleys which could reduce visibility to MVFR or
lower. This fog may affect KHSV briefly but not expecting a drop in
VIS to affect aircraft operations.





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