Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus64 khun 190503 

Area forecast discussion
National Weather Service Huntsville Alabama
1203 am CDT Mon Aug 19 2019

for 06z tafs.


Near term...(rest of tonight)
issued at 922 PM CDT sun Aug 18 2019

Latest near term model guidance continues to suggest that a
weakening mid-level vort Max (currently across the lower great lakes)
will advance eastward into the central Appalachians region by
19/12z. The trailing trough axis is expected to drift more slowly
southeastward across the Tennessee Valley, and although lift directly
related to this feature will be rather weak, it could be sufficient
to generate isolated showers/thunderstorms based on the amount of
elevated cape evident in point forecast soundings. We have introduced
a slight chance pop for all forecast zones beginning late this
evening to address this potential, and also indicated the development
of patchy fog across portions of the County warning forecast area between 08-13z. Due to the
anticipated development of a steep inversion in the boundary layer
across our region, any storms that form should be slightly elevated,
with the main threats coming from lightning and locally heavy
rainfall. Otherwise, we expect slightly warmer and more humid
conditions overnight as compared to previous nights, with lows in the
l-M 70s.

Short term...(monday through tuesday)
issued at 210 PM CDT sun Aug 18 2019

The start of the new work week will be much the same as we've
experience the last few days. The ridge over the southwestern Continental U.S.
Will build eastward, while surface flow remains light. This will
limit the deep layer moisture return across the Tennessee Valley, while
weak subsidence provides for an even lesser chance for showers and
thunderstorms on Monday. Despite this, there may be just enough
moisture in the lower levels for an isolated thunderstorm to develop
during our peak heating hours Monday afternoon. By Monday night, a
weak area of low pressure will lift northward from the northeastern
Gulf of Mexico and slowly drift through Georgia on Tuesday. This
feature doesn't look to impact the Tennessee Valley much before it
dissipates, however we could see some of the associated moisture
filter into the forecast area. Given this increase in moisture, the
coverage to thunderstorms will be slightly higher than those
observed on Monday, but pops will still be in the lower chance range.

Temperatures will be a couple of degrees above normal for this time
of year. Highs on Monday and Tuesday will depend on the coverage of
storms, but with a relatively low coverage expected, temps should
warm into the mid 90s. Am not overly confident on how much of the
area will see the upper 90s, but with the building ridge, temps may
be a degree or two too low. Model dewpoints have been a little on the
high side, so those were lowered with this forecast package, which in
turn lowed the relative humidities forecast for Monday and Tuesday.
So, with all of that said, heat index values are forecast to stay
just below criteria but hot nonetheless. Overnight lows will be mild,
with temps falling into the lower 70s Monday night and Tuesday

Long term...(tuesday night through saturday)
issued at 210 PM CDT sun Aug 18 2019

The upper ridge will linger of the region on Wednesday, before it
breaks down in response to an upper low swinging into the Great Lakes
region. Wednesday will be fairly similar to Tuesday, though with more
moisture over the area, thunderstorm coverage will be a bit higher.
Thunderstorm chances really begin to increase on Thursday, as flow
aloft weakens further and guidance suggests several weak waves moving
through the area. Given the uncertainty with this type of pattern in
the extended period, pops were capped at chance on Thursday. On
Friday, a strong shortwave is expected to move through the region
which will provide a greater focus for convective development during
the afternoon. Thus, likely pops were kept in the forecast. The upper
level pattern will remain fairly zonal headed into next weekend, with
scattered thunderstorms possible again on Saturday. Overnight,
confidence is on the lower side with regard to the forecast through
the long term period, as forecast guidance diverge quite a bit.

Temperatures through the extended will be near to slightly above
normal for this time of year. Highs will warm into the lower to mid
90s each day, with overnight lows in the lower 70s.


Aviation...(for the 06z tafs through 06z Monday night)
issued at 1101 PM CDT sun Aug 18 2019

Bkn-ovc layers of as/cs debris clouds will continue to spread east-
southeastward across the region overnight. Although this may result
in occasional cigs above fl150, we expect conds to remain VFR at the
terminals, as remnant precipitation across western Tennessee will likely not
reach either mean sea level or hsv. Patchy fog will be possible across portions
of the Tennessee Valley btwn 08-13z, but confidence remains too low to
introduce vsby reductions in the tafs at this point. Sct diurnal cu
field will develop by 16z and dissipate around 02z, with isolated
thunderstorms and rain possible during the afternoon hours. However, probability of
direct impacts from thunderstorms and rain is too low to include thunderstorms in the vicinity in the forecast


Hun watches/warnings/advisories...



Near term...70/dd
short term...73

National Weather Service Glossary of Abbreviations