Area Forecast Discussion
Issued by NWS Huntsville, AL

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099
FXUS64 KHUN 210451
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1151 PM CDT Sun Aug 20 2017

.UPDATE...
For 06Z TAFS.

&&

.NEAR TERM...(Tonight)
Issued at 912 PM CDT Sun Aug 20 2017

Temps have fallen off nicely this evening into the mid/upper 70s
from their earlier highs in the lower/mid 90s under predom partly
cloudy skies. A passing upper disturbance embedded within a W to E
flow pattern will likely keep some cloud cover around heading into
the overnight hrs, before skies become mostly clr early Mon morning.
With dew pt trends mainly in the lower 70s as well, temps will prob
only fall a few more degrees, or more into the lower 70s/near 70F
mark, provided dew pts mix out a degree or two more. No real changes
were needed to the ongoing forecast other than to refresh some of the
hourly grids based on these latest trends.

.SHORT TERM...(Monday through Tuesday)
Issued at 300 PM CDT Sun Aug 20 2017

Attention quickly turns to the historical Total Solar Eclipse event
for Monday. The good news for folks in the Tennessee Valley is that
the upper-level ridge should help to promote fairly decent viewing
conditions. However, a look at model soundings suggests a fair bit
of moisture present at 850 mb, which may support a higher CU field
than previously thought. Additionally, would not be shocked to see a
few isolated showers along the plateau later in the afternoon (though
was not confident enough to mention in the forecast at this time).
Still, viewing conditions should be fairly good, with scattered CU
potentially causing some visibility issues, locally, at the peak
obscuration. The other interesting trend to watch will be
temperatures will would normally peak in the low to mid 90s, but may
drop 3-5 degrees during this event due to the interruption of
normalized heating. Have reflected this in the forecast. Thus, we
may see our actual high around 5 PM local time due to this event.

Southerly flow around the ridge will continue to push more Gulf
moisture underneath it on Tuesday. With this ridge slowly weakening
and shifting further south, a weaker CAP may allow for isolated to
scattered convection to form in the afternoon. The main interest,
though, will be late Tuesday night as a prefrontal trough is progged
to trigger a line of storms over Middle Tennessee. Latest model
guidance suggests this could approach and move into the Southern
Middle Tennessee and far Northern Alabama 09-12z Wednesday. Most of
this activity should weaken and remain below severe limits given the
lack of appreciable instability. However, have adjusted rain/thunder
chances up during this period to account for the possibility of an
earlier arrival time. The NAM is more bullish than the GFS, CMC, and
ECMWF -- but all show some convective, QPF signals at our doorstep by
12z Wednesday. We will continue to monitor this over the coming
days.

.LONG TERM...(Tuesday night through Saturday)
Issued at 300 PM CDT Sun Aug 20 2017

On Wednesday, the upper-level trough will continue to dig through
the Great Lakes and into Quebec with the sfc low slightly ahead of
it. Models are hinting that the trailing cold front will now move
into the TN Valley earlier than what previous runs were depicting due
to a short wave rounding the base of the trough. This would bring
the front in closer to Wednesday afternoon, developing numerous
showers and thunderstorms across the TN Valley. Daytime heating will
provide additional instability, and with bulk shear ~20kts and PWATs
hovering just under 2 inches, will not rule out a strong storm or two
with gusty winds and locally heavy rainfall as the primary threats.
Precip chances will taper off as the front pushes southeast heading
into Wednesday night. Cooler and drier air will filter in behind the
front where both the highs and lows will be slightly below normal.
Thursday will be the coolest day of the week, literally, with highs
in the low/mid 80s and overnight lows in the lower 60s with possibly
some upper 50s in southern middle TN! High pressure across the Great
Lakes will build into the region on Thursday and Friday keeping us
dry. Isolated showers and storms are possible again on Saturday as
the pattern deamplifies and wedging along the Appalachians develops.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1151 PM CDT Sun Aug 20 2017

With high pressure layered across the mid/srn Atlantic Coast, VFR
conds are xpcted thru the TAF period.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

NEAR TERM...09
SHORT TERM...AMP.24
LONG TERM...JMS
AVIATION...09


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