Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 211143

Area Forecast Discussion
National Weather Service Huntsville AL
643 AM CDT Sat Apr 21 2018

For 12Z TAFS.


.NEAR TERM...(Today)
Issued at 420 AM CDT Sat Apr 21 2018

Surface high pressure situated over the Great Lakes was the main
controlling feature regarding the regional current weather. Across
the greater North American domain, a split flow pattern was in place.
A stream of tropical/subtropical moisture was heading to the NE from
SW of the Baja. This moisture was feeding south of a developing
upper low situated over SE Colorado - with its surface reflection
over West Texas. This system will move eastward and bring a wet
period beginning later tonight to the Tennessee Valley.

Before then, this week will end on a dry and warm note, as surface
high pressure northeast of us builds to the Mid Atlantic coast by
the evening. A southeast flow around this ridge and more sun than
clouds (at least into the early/mid afternoon)  will result in high
temperatures rising a bit higher than yesterday, into the low/mid
70s. Today will be one to enjoy the great outdoors and finish any
tasks that need completing, as things will change tonight.

.SHORT TERM...(Tonight through Monday)
Issued at 420 AM CDT Sat Apr 21 2018

The above noted system will travel in an easterly direction tonight
and on Sunday. Clouds preceding it will overspread the Valley this
evening, with showers beginning after midnight (mainly across the
region west of I-65). Have rain chances increasing to near 100
percent on Sunday, as a comma head portion of the system affects
the region. Even though the main surface low should track and remain
south of this region, enough shear and minimal instability will keep
an isolated thunderstorm or two in the forecast. Storms that form
should remain "general" in intensity, and be mainly embedded within
more widespread showers.

Precipitable water amounts rising into the 1 to 1.5 inch range, and
decent upglide of deep moisture from the Gulf could result in locally
heavy rainfall. Rainfall amounts from the various models range in the
2-4" range into late Monday. This could result in excessive rainfall
overrunning and producing mainly hydrological issues, aka stream,
creek, river rises. Flash flooding could not be totally ruled out,
but given we`re on the northern side of this next system, short-term
intense rainfall is not as likely. After a warm day today, clouds and
showers will keep high temperatures on Sunday/Monday almost 10
degrees cooler, in the mid 60s. Very good rain chances will continue
on Monday, as the system slows its eastward progress, and remains
over the Tennessee Valley and Deep South.

.LONG TERM...(Monday night through Friday)
Issued at 420 AM CDT Sat Apr 21 2018

Fairly messy forecast will continue into the new week for the cntrl
TN Valley. Potent upper low/trough axis pretty much centered over the
mid TN Valley will continue to gradually translate ewd Mon night
into Tue, as the attendant sfc low S of the local area lifts into the
mid/srn Atlantic Basins. As the trough pattern begins to lift newd
away from the area, it is xpcted to weaken or open more into a broad
upper trough axis across the mid Atlantic states. Rainfall/showers
look to be ongoing over parts of the area thru Tue as these systems
exit the region. Rainfall may then taper off quickly from the W Tue
evening, as drier air above H85 briefly filters into the area.
Overall temps at least look to remain near seasonal for the first
half of next week, with highs on Tue mainly in the upper 60s/near 70F
while lows Mon/Tue nights trend predom in the lower/mid 50s.

Unfortunately, the dry spell looks to be short lived, as another
upper trough axis and attendant cold front out of the nrn/mid Plains
dives sewd into the Midwest/Lower MS Valley regions on Wed. Forecast
time heights indicate a rapid increase in moisture along/just ahead
of this next front, which should translate into more sct showers
spreading ewd into the TN Valley Wed/Wed night. Weak dynamic forcing
increasing along the approaching cold front should aid in the shower
development across the area. Even with more clouds/rain moving into
the region, little change in overall temps is xpcted, with highs on
Wed again mainly in the upper 60s/around 70F and lows early Thu
morning near 50F for most locations.

Another brief reprieve in the rainfall may then develop late Thu into
Thu evening, with the passage of this next front, as drier air above
H7 quickly mixes into the area. This will be followed though by
another rapid increase in moisture to close out the work week, as
yet another cold front out of the Plains states dives swd into the
region. This should at least result in more sct showers spreading
into parts of the area on Fri along/ahead of this next front. This
cold front however may have a bit more cold air advection with its
passage, as highs Fri struggle to climb higher than the upper 60s
while lows that night fall more into the lower/mid 40s.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 643 AM CDT Sat Apr 21 2018

VFR weather should continue into the evening. However a developing
storm system over the southern High Plains will approach the region,
resulting in increasing clouds, and cloud bases gradually lowering,
especially after midnight. Light east winds at 12Z will become SE and
increase into the 5-15 kt range a few hours after sunrise. Winds will
be on the higher end of the scale east of I-65. Scattered cirrus this
morning will become broken in the later afternoon, with lower clouds
moving in after sunset. CIGs lowering to MVFR ~2500ft AGL and light
showers are possible late in the TAF at KMSL.





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