Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 190238

Area Forecast Discussion
National Weather Service Huntsville AL
938 PM CDT Fri Aug 18 2017

.NEAR TERM...(Rest of tonight)
Issued at 938 PM CDT Fri Aug 18 2017

Quiet weather conditions exist across the CWFA this evening, and
should persist overnight as a weak surface ridge translates eastward
in the wake of the cold frontal passage earlier today. Well to the
northwest of our region, a mid-level shortwave trough is forecast to
dig southeastward...reaching the southern Great Lakes and lower OH
Valley by 19/12Z. Scattered mid and high-level clouds preceding the
trough will begin to spread eastward across the TN Valley after
Midnight, and may inhibit radiational cooling just enough to prevent
the development of widespread fog...especially given the advection of
drier air into the region earlier this afternoon. Nonetheless,
conditions will be favorable for fog formation in river valleys and
near large bodies of water...especially between 08-13Z...and this has
been included in the updated weather grids. Other elements of the
forecast appear to be on track at this point, with only a minor
increase in minimum temps made to reflect the introduction of more
clouds after Midnight.

.SHORT TERM...(Saturday through Sunday night)
Issued at 247 PM CDT Fri Aug 18 2017

The upper trough axis will move east of the forecast area by the
afternoon hours on Saturday. Despite the slight increase in
moisture, little in the way of forcing is expected and therefore do
not anticipate any showers and thunderstorms developing during the
day. Meanwhile, a cold front to our north will shift through the
area, bringing a reinforcing shot of drier air across the region.
Models are hinting at an MCS moving across the western section of
the forecast area late Saturday afternoon, however due to the dry
air in place, do not feel confident enough to add showers and
thunderstorms back into the forecast. By Sunday, the axis of an
upper level ridge will begin to build northward across the area,
with light flow keeping moisture advection limited. Thus, another
dry day is expected again on Sunday. Temperatures through the period
will generally be near seasonal norms. Skies are expected to remain
mostly clear and with slight height rises, highs will warm into the
upper 80s to lower 90s. Meanwhile, overnight lows will drop into the
upper 60s to lower 70s.

.LONG TERM...(Monday through Thursday)
Issued at 247 PM CDT Fri Aug 18 2017

The extended will start off with the most anticipated forecast of
the week...for the eclipse. Eclipse viewers across our area should be
in good shape with mostly clear skies and isolated coverage of
diurnal showers and thunderstorms. A ridge building westward across
the Southeast on Monday will bring back southerly flow and keep temps
in the lower 90s. On Tuesday, with additional moisture and temps
still in the lower 90s, scattered coverage of diurnal shower/storms
are expected with a heat index around 100 degrees.

As a sfc low lifts into the Great Lakes Tuesday night/Wednesday, the
trailing cold front will make way into the TN Valley by Wednesday
night/Thursday. This will bring a greater coverage of showers and
thunderstorms across the area Wednesday/Wednesday night. Behind the
front, temps will be a few degrees lower in the upper 80s, but
looking more forward to the dewpoints dropping into the 60s!


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 711 PM CDT Fri Aug 18 2017

VFR/SKC conditions will persist at both HSV/MSL this evening in the
wake of a cold front which pushed swd thru the region earlier today.
However...a high-level trough currently across the upper MS valley is
expected to spread esewd into the central Appalachians over the
course of this TAF period. Sct-ocnly bkn altostratus associated with
the trough should begin to move across the region after Midnight.
Although cloud bases will likely be in the 10-15 kft range, the
presence of these clouds coupled with a drier boundary layer should
reduce the threat for fog. Occasional/minor vsby reductions in lgt br
will still be psbl btwn 08-13Z, and will monitor trends this evening
in the event that br/fg needs to be included in the next set of
TAFs. Sct cu should develop arnd 17Z as low-level moisture slowly
returns to the region ahead of the trough passing by to our north. A
few shra/tsra will also be psbl tomorrow aftn as the trough makes
its closest approach to our region, but threat is too remote to
include in forecast attm. Sfc winds will remain vrb and at speeds
below 5 kts.





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