FXUS64 KHUN 201919

Area Forecast Discussion
National Weather Service Huntsville AL
219 PM CDT Wed Sep 20 2017

.NEAR TERM...(Tonight)
Issued at 219 PM CDT Wed Sep 20 2017

A surface ridge axis was sitting along the spine of the Appalachians
into the deep South. This can be noted in the visible imagery as
well with more robust cumulus remaining further west of this axis
over middle TN, northwest AL into MS. Just a few showers were
popping up thus far in middle TN and north MS. At this time, will go
with a dry forecast after 7 pm as loss of heating should decay any
development that occurs in our forecast area this afternoon. If
this changes, will make slight adjustments into the evening hours.
Once again, dense valley fog is expected late tonight into early
Thursday morning.

.SHORT TERM...(Thursday through Friday)
Issued at 219 PM CDT Wed Sep 20 2017

Through Friday, the 850-500mb ridge will build over the OH and MS
Valleys. Along the eastern fringe of the ridge, weak vorticity
waves will continue to drop south. These along with local forcing
along the Plateau and Mountains may induce scattered
shower/thunderstorm development on Thursday and perhaps on Friday as
well. Otherwise, will go with near persistence temperature
forecasts both days with highs in the mid 80s to around 90. Will
also maintain patchy valley fog both Thursday and Friday Nights as

.LONG TERM...(Friday night through Tuesday)
Issued at 219 PM CDT Wed Sep 20 2017

Upper-ridge over the Tennessee Valley will shift north into the
Great Lakes by Saturday as a weak area of low pressure along FL/AL
the Gulf Coast becomes more magnified as it drifts into Central
Alabama. The increased lift, along with sufficient boundary layer
moisture will allow for scattered thunderstorms to develop during
the afternoon and evening, with the best coverage along and south of
the Tennessee River. This feature will linger around the region
enough on Sunday and Monday to also warrant a few isolated afternoon
storms. In general through, the broad ridge over the eastern CONUS
should promote a fairly dry and mostly clear forecast each day
through at least the middle of the upcoming work week. Highs in the
85-90 degree range are expected each day, with nighttime lows in the
low to mid 60s. As is typical this time of year, the mostly clear
sky and light winds may result in patchy fog development near
rivers/lakes overnight as well.

Late in the period, a longwave trough will push east from the Rocky
Mountains into the Ohio Valley. This feature will likely bring with
it a stronger front into the Tennessee and lower Mississippi River
valleys -- and perhaps some better chances for storms. Additionally,
this could usher in a cooler, more autumn-like air mass to end
September and start October. Still some differences in the model
with respect to timing 7-8 days out, so did not get too specific
with the details this far out. Stay tuned!


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1136 AM CDT Wed Sep 20 2017

VFR flight weather conditions are expected this afternoon into this
evening. An isolated thunderstorm is possible in northwest AL this
afternoon, but the probability is too low to include in the TAF at
this time. Valley fog is once again expected to develop by 10Z, and
expect visibility to drop to around 5SM, with a good chance of 1-2SM
at KMSL and 2SM at KHSV. After the fog dissipate by 14Z, expect a
clear sky and VFR weather.





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