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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 160915

Area Forecast Discussion
National Weather Service Huntsville AL
415 AM CDT Thu Aug 16 2018

.NEAR TERM...(Today)
Issued at 415 AM CDT Thu Aug 16 2018

Area radars are showing a large mass of light/mod showers, with some
embedded tstms, spreading ewd into much of west TN this early Thu
morning. This activity looks to be associated with a weak upper level
impulse embedded within a weak shrtwv axis traversing ewd into the OH
Valley/Mid South regions. This convection is also developing ahead of
a weak frontal boundary located from the Midwest into the srn Plains.
Closer to home, high pressure at the sfc remains fairly stagnant over
the srn Atlantic Basin, which is translating into a return flow
pattern across much of the region. Latest model suites continue the
convective development trend over the Mid South area later today as 
it spreads more to the east. The upper shrtwv axis to the north/west 
looks to become even more sheared to the NE later today, thereby 
helping to keep much of the shower/tstm activity displaced just to 
the north. However, trailing bands of energy back to the SW may be
enough to result in iso/sct showers/tstms forming across parts of the
cntrl TN Valley later today, especially for areas along/north of the
TN River. Even with the chc of rainfall and associated cloud cover,
afternoon temps again look to be seasonably warm for this time of the
yr, with highs mainly in the lower/mid 90s for most locations.

.SHORT TERM...(Tonight through Saturday)
Issued at 415 AM CDT Thu Aug 16 2018

Lingering iso/sct showers/tstms may continue into the evening hrs, as
weak upper disturbances continue to move ewd across the region. Most
of the rainfall though should taper off by the onset of the overnight
period, with early morning lows Fri falling mainly into the lower/mid
70s. Rain chances are then xpcted to increase heading into Fri, as a
stronger upper trough pattern out of the Great Lakes drops into the
Midwest/OH Valley states. The weak frontal boundary to the NW may
also drift sewd, but it is xpcted to stall well north of the local
area. With moisture increasing into the region from the WSW, sct/num
showers/tstms look to develop thru the day Fri and continue into Fri
night. With SBCAPE values increasing into the 2-3K J/kg range coupled
with 25-30kt of 0-6km Bulk Shear, a few strong/marginally svr tstms
capable of brief damaging wind gusts and hail cannot be ruled out Fri
afternoon/evening. Not much change is then xpcted for Sat, with the
upper trough axis remaining fairly stagnant across the region. This
should again result in num showers/tstms Sat, with a few of these 
storms potentially strong in nature. With the increase in cloud 
cover/rainfall, afternoon temps Fri/Sat may trend a little bit
cooler, with highs more in the mid/upper 80s for most areas.

.LONG TERM...(Saturday night through Wednesday)
Issued at 415 AM CDT Thu Aug 16 2018

Unsettled weather will continue for the start of another week. At 
the surface, high pressure situated off of the southeast coast will 
maintain a moisture laden S-SW surface flow across the region. This 
moist flow, upgliding in the 305K region (800-900mb), and the 
approach of a frontal boundary from the northwest, will result in 
more clouds than sun, and scattered showers and thunderstorms on 
Sunday and Sunday night. Along with the surface features, a more 
southward extent of the polar jet moving in from the northwest, will 
bring a trough across the Ohio/Tennessee Valley region early next 
week, helping to raise rain chances even more during Monday. 
Precipitable water amounts range in the 1.7 to 2.1 inches in this 
timeframe, which will result in locally heavy rainfall. Forecast 
soundings indicate surface based CAPE values rise into the 2-3K 
range, but with little shear. Inverted-V signature with high 
instability values could result in microburst type wind from
collapsing storms, and frequent lightning.

The above noted upper system will help to develop a surface low over
the mid Mississippi Valley on Monday. This low will move to the 
northeast during Tuesday. A cold front trailing from this low should 
move across the forecast area during Tuesday. The passage of this 
front should bring drier air across the region, with lowering rain 
chances Tuesday night, and dry conditions for Wednesday. High 
temperatures for most of the extended period should range in the 
mid/upper 80s through Tuesday, then "only" into the low/mid 80s next 
Wednesday, with lower thickness values and a dry northerly surfaced 


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1220 AM CDT Thu Aug 16 2018

With weak high pressure remaining in place over the srn Atlantic
states, VFR conds are xpcted thru the TAF period. Mid/high clouds
will again spread into the area from the west heading into the
morning hrs Thu, but cigs are xpcted to remain above VFR levels.





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