Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 201558

Area Forecast Discussion
National Weather Service Huntsville AL
1058 AM CDT Thu Jul 20 2017

.NEAR TERM...(Rest of Today)
Issued at 1058 AM CDT Thu Jul 20 2017

Temp trends are rebounding with authority across much of the cntrl TN
Valley this late Thu morning, from their earlier lows mainly in the
lower/mid 70s. Temps in many locations have already reached the upper
80s, with a few spots hitting the 90F mark. Unfortunately, dew pts
are also trending in the lower/mid 70s for many areas, which is not
making it very comfortable as far as the humidity goes. Dew pts may
be able to lower a couple of degrees thru the afternoon as low level
mixing increases. However, afternoon highs are still xpcted to climb
well into the mid/upper 90s, mainly across the cntrl/wrn zones. This
still looks to translate into maximum heat indices around 105F or
higher for a few hrs this afternoon, and a Heat Advisory remains in
effect for NW AL and now Madison Co thru 7 PM CDT. Low chances for
showers/tstms also remain in place mainly for areas along/e of the
I-65 corridor later today, as weak upper disturbances traverse swd
along the ern fringe of the upper ridge pattern centered over the
Midwest/Mid South regions.

.SHORT TERM...(Tonight through Saturday)
Issued at 412 AM CDT Thu Jul 20 2017

A few isolated showers or thunderstorms could linger in Cullman
northeast through Dekalb counties this evening, before dissipating.
Depending on how widespread the rainfall, more and possibly denser
fog could form late Thursday night into Friday morning. Lows in the
70 to 75 degree range should continue, low level moisture recovers
Thursday night (as we lose mixing of drier air aloft).

Friday could see a few isolated showers or storms move northward.
However, overall much more sunshine should allow temperatures to
reach the 95 to 99 degree range over most of the area. With
temperatures still around 70 degrees, heat index values may climb
into the 105 to 107 degree over a larger area of northern Alabama and
Southern Middle Tennessee, before dewpoints mix out later in the
afternoon. Thus, a heat advisory may be needed for a larger portion
of the area on Friday.

By Saturday, although it will be more humid models show an inverted
trough axis extending northward from the western Gulf of Mexico. This
should increase shower/storm chances to scattered again and keep high
temperatures in the 90 to 95 degree range, keeping heat index values
lower around 100 degrees. Little shear with this inverted trough axis
so although instability will be there, only gusty winds and frequent
lightning are expected in stronger storms.

.LONG TERM...(Saturday night through Wednesday)
Issued at 412 AM CDT Thu Jul 20 2017

The inverted trough axis holds over the southeast, producing enough
lift for isolated showers and storms to continue overnight on

By Sunday, models increase forcing over the area, as a cold front
approaches from the north. Likely chances of rain were included in
the forecast. Although not much shear is present, dry air aloft
should allow for the development of stronger thunderstorms capable of
producing gusty winds. There is a bit better shear and ample
instability with this feature as it pushes southeast through the area
Monday into Tuesday. Thus have highest chances of showers and
thunderstorms during this period. At this point, strong storms
capable of producing gusty winds look like the main threat Monday and
Tuesday as well, with dry air entrainment aloft and better
shear. There is some uncertainty concerning how quickly this
boundary will move south. However, general consensus seems to be
Tuesday through early Wednesday. Regardless, this will be a welcome
respite from the hot temperatures, with highs returning back to the
85 to 90 degree range mostly Sunday through Tuesday.

A dry and warm period returns to the forecast by Wednesday, as high
climb back into the upper 80s to lower 90s.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 615 AM CDT Thu Jul 20 2017

VFR conditions are expected through most of the TAF period. BKN/SCT
Cigs around 5000 feet are expected to develop this morning at both
terminals and continue into the mid-afternoon hours. Isolated to
scattered -TSRA are expected to develop also near KHSV. For now left
TSRA or VCTS out of the KHSV TAF, since coverage is expected to be so
low. If a TSRA does directly affect KHSV, cigs and vsbys could
become MVFR (1500-3000 feet) or IFR(2 SM). Otherwise, VFR cigs will
return this evening, as fog drops vbsbys to MVFR (4SM) late tonight
through daybreak on Friday.


AL...Heat Advisory until 7 PM CDT this evening for ALZ001>006.




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