Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 231957

Area Forecast Discussion
National Weather Service Huntsville AL
257 PM CDT Sun Jul 23 2017

.NEAR TERM...(Tonight)
Issued at 257 PM CDT Sun Jul 23 2017

The Heat Advisory in effect for much of the area will be allowed to
continue until 7 PM this evening. Temperatures and heat indices for
the most part are cooler this afternoon than they were earlier this
weekend, but given isolated to scattered nature of on-going showers,
will keep the advisory going.

Hot and humid conditions continued across the greater Tennessee
Valley region, as broad upper level ridging to our north and west
slowly breaks down. Warm air aloft associated with the upper ridge
for the most part has kept convection overall tamped down. But the
activity that has formed for the most part has remained short lived,
while drifting slowly eastward this afternoon (compared with moving
to the southwest yesterday). Locations under this convection could
experience gusty, at times strong winds, very heavy rainfall and
frequent lightning.

Shower activity will continue tonight, as a series of weak upper
disturbances move by. Stayed with scattered rather than isolated rain
chances, especially with the models overall painting some precip
across the region for the overnight. Despite more clouds and showers,
low temperatures will only cool in the low/mid 70s with light winds.

.SHORT TERM...(Monday through Tuesday)
Issued at 257 PM CDT Sun Jul 23 2017

The NAM model over the past few days has been indicating an outflow
boundary or wave moving southward across the region late tonight and
during Monday morning. The GFS/ECMWF were showing this but not as
strongly. As such, will keep rain chances going, but at a chance, not
likely range. With the rains being convective, chances of a location
with good odds of getting wet will not be high enough to support
higher PoPs. With more clouds than sun, temperatures to start a new
work week will be a bit cooler, "only" in the upper 80s to around 90.
Even with dewpoints in the lower 70s, they should not be high enough
to warrant Heat Advisories - at least this issuance.

Similarly very to hot conditions will continue on Tuesday, as high
precipitable water amounts continue. PW amounts in the 1.8 to 2
inches should continue, which will keep a threat of locally heavy
rains, gusty winds, and electrically active storms. A front moving
southward with a dip in the northern stream will approach the area on
Tuesday, but should remain north of the region.

.LONG TERM...(Tuesday night through Saturday)
Issued at 257 PM CDT Sun Jul 23 2017

The Tennessee Valley will be pinched between systems on Wednesday
with a shear axis/remnant low situated across the southeast and a
front well to the northwest across the Great Lakes/Midwest. Hard to
pinpoint significant synoptic forcing in this particular regime but
given the very moist airmass in place expect widely scattered diurnal
convection will be a good bet once again.

The evolution of the longwave pattern becomes a bit questionable as
we head toward the latter part of the work week and toward next
weekend. The ECMWF maintains generally northwest flow across the
Tennessee Valley and eventually slides the aforementioned front
toward the area on Friday/Saturday. This would maintain a rather
unsettled regime with increasing rain chances late week. The GFS
meanwhile has a higher amplitude eastern US trough by late week. In
turn, the 12z GFS meanwhile drives a stronger front through on Friday
with more pronounced energy in the southern stream.

This would point toward cooler weather toward next weekend. This
particular solution has been fairly consistent in the last several
runs. Looking at the blend of medium range guidance, the more
progressive solution may be preferred. Eventually we may see the
remnant upper energy cut off/retrograde back into the area Sunday
night/Monday, but that`s beyond this forecast period.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1235 PM CDT Sun Jul 23 2017

Strong daytime heating and abundant moisture in the atmosphere will
result in isolated to scattered convection this afternoon and early
evening. Strong erratic wind gusts over 40 kts, locally very heavy
rains with reduced CIG/VIS values to MVFR (possibly lower at times),
and frequent lightning could accompany the stronger convection.
Shower activity should wane with a loss of daytime heating this
evening. Light winds and mostly clear skies could cause patchy fog
to form, especially if a wetting rain occurs over or near a terminal.
An upper level system approaching from the north will return a risk
for more convection late Monday morning.


AL...Heat Advisory until 7 PM CDT this evening for ALZ001>008-016.

TN...Heat Advisory until 7 PM CDT this evening for TNZ076-096.




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