Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 270300

Area Forecast Discussion
National Weather Service Huntsville AL
1000 PM CDT Wed Jul 26 2017

.NEAR TERM...(Rest of tonight)
Issued at 1000 PM CDT Wed Jul 26 2017

Current water vapor satellite imagery confirms the presence of a weak
mid-level shortwave trough over the southwestern Great Lakes/upper
Midwest. This feature is expected to travel southeastward into the
upper OH Valley by sunrise and begin the process of gradually
weakening the subtropical high that has been in place over the region
for the last several days. Although this by itself should not result
in the redevelopment of convection early tomorrow morning, guidance
does suggest the passage of a weaker disturbance to the immediate
northeast of the CWFA...with a subtle veering trend in 850-700 mb
flow between 09-12Z. This may be sufficient for the development of
isolated showers/thunderstorms -- particularly across the eastern
third of the forecast area -- before sunrise and a low POP has been
included for this reason. Otherwise, we are expecting another warm
and muggy night with lows once again in the l/m 70s. Due to sporadic
nature of afternoon/early evening precipitation...patchy fog has been
included for the entire forecast area between 06-12Z.

.SHORT TERM...(Thursday through Friday)
Issued at 209 PM CDT Wed Jul 26 2017

Expect Thursday to generally be a carbon copy of today with very warm
and humid conditions again. Will hold off on extending the heat
advisory, but later shifts may need to re-evaluate that. The ridge
axis does weaken a bit and with the boundary layer profiles remaining
very warm/moist the areal coverage may be slightly higher. Again,
any storms that form could be strong with gusty outflow winds.

The guidance diverges somewhat in the handling of a strong shortwave
trough and attendant front progged to impact the region late
Thursday night into Friday. The operational NAM and to a lesser
extent the 12z GFS bring a rather robust convective complex/MCS
southward toward the Tennessee Valley along a prefrontal boundary
Thursday night. Meanwhile, the high res windows keep the area dry
with the convection remaining to the north through sunrise Friday.

Give the model uncertainties am inclined to keep the Thursday night
pops in the chance category for now. All the guidance agrees on
convection be fairly widespread on Friday ahead of the approaching
system. The Friday model proximity soundings indicate a potentially
unstable airmass with some contribution from a mid level jet as the
eastern CONUS trough deepens. SPC has placed the entire area in the
slight risk and this seems reasonable given the combination of
thermodynamics/kinematics but also the uncertainties with timing and
extent of convection (and quality of the airmass).

The bulk of the convection should shift south of the region late on
Friday. Tough call on the Friday max temperatures but it won`t take
much to reach upper 80s/near 90 so trended toward the higher end of
the blends. Also, maintained chance pops for Friday night though
later shifts may be able to reduce/tweak those given the trends.

.LONG TERM...(Saturday through Tuesday)
Issued at 209 PM CDT Wed Jul 26 2017

We will start off the weekend with the front to our south and sfc
high pressure that`s anchored back up in the Great Lakes building
into the region. This will provide us the opportunity to look forward
to a dry and cooler late July weekend. Daytime highs will be in the
low/mid 80s while overnight lows cool towards the low/mid 60s! triple digit heat index values!

Heading back into the workweek, temps will start to climb back up
towards 90 degrees and precip returns to the forecast. As the upper-
level trough to our east shifts into the Atlantic, northwesterly
flow aloft will weaken. However, weak disturbances will still stream
towards the TN Valley. Combined with daytime heating, isolated
showers/storms are possible Monday and Tuesday.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 710 PM CDT Wed Jul 26 2017

Latest radar data suggests that isold shra/tsra continue to
diminish across the region early this evening. Although a few shra
may persist to the south of the TN River beyond 27/01-02Z, threat for
impacts at HSV/MSL is too low to warrant VCSH/VCTS. Isold-wdly sct
convection should develop once again tomorrow...perhaps as early as
15Z...but with a greater coverage anticipated to the north/east of
both airports we will not indicate precip invof of either terminal.
Regarding cigs/vsby, sct cu arnd 5 kft will likely prevail thru late
this evening beneath sct ci. Gradual clearing is expected beyond 05Z
and may lead to development of patchy early-morning fog in areas that
received rainfall this aftn, but based on lack of rainfall at the
terminals and expectations of a sw wind arnd 4 kts this potential is
too low to include in either TAF. Sct high-based cu should develop
once again by 15Z beneath a layer of altocumulus clouds. Sfc winds
will veer to wsw and gradually increase by tomorrow aftn.





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