Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 211500
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1000 AM CDT Sat Oct 21 2017

.NEAR TERM...(Rest of Today)
Issued at 1000 AM CDT Sat Oct 21 2017

Temperatures have risen to between 59 and 63 degrees in most
locations at 9 AM. A bit more moist air has been advecting into the
region from southern Georgia and the eastern Florida panhandle. This
will continue through the day accompanied by some weak warm air
advection.

Scattered areas of mostly cloudy conditions (mainly thin and high in
nature) can be seen in morning satellite imagery near/east of I-65.
Further west lower and thicker cloud cover is in place over the MS/AL
border in northern Alabama. The RAP seems to be handling this cloud
cover pretty well. It keeps some mostly cloudy conditions in place
over northwestern Alabama through much of the day, but doesn`t move
it much further east (keeps it west of the I-65 corridor). Trended
cloudy conditions toward this output west of I-65 today. RAP and
many other models develop more partly to mostly cloudy conditions
this afternoon near and east of I-65, but models indicate that this
will be primarily high/thin cloud cover. Thus, do not expect much
impact from these clouds in those areas. Highs in the mid to upper
70s still look possible, despite cloud cover. Maybe some 81 or 82
degree temperatures at Decatur or Huntsville. In contrast, with the
more persistent, thicker cloud cover over portions of northwestern
Alabama, have gone a degree or two below guidance there (78 to 80
degrees). Winds should pick up a bit this afternoon, with sustained
winds 5-10 mph with gusts to between 15 and 20 mph.

.SHORT TERM...(Tonight through Monday)
Issued at 359 AM CDT Sat Oct 21 2017

Complicated forecast for Sunday and Monday as the pattern quickly
changes. The aforementioned high will continue to move well east into
the Atlantic and a deepening upper-trough will quickly swing into the
Tennessee valley on Sunday, bringing scattered showers and
thunderstorms across most of the region by the afternoon. This
activity will become more widespread and numerous by the evening and
overnight as a cold front advances into the area.

Some model solutions (GFS, NAM) indicate this trough will strengthen
into a cut-off low over south MS/AL as it quickly advances through
the Deep South Sunday Night into Monday. It is during this period
where PoPs and QPF will be greatest, especially on Monday when a LLJ
ramps up ahead of the deepening upper-cyclone. Given the moisture in
place (with PWATs increasing to near 2 inches) and the dynamic lift
associated with this storm system, locally heavy rainfall is expected
with this storm system -- especially in the Sunday night through
Monday afternoon period. Though we have been fairly dry of late, the
need for some flash and areal flooding will need to be monitored in
the coming days. This is especially true given the abnormally high
PWATs and the potential for training of cells along and parallel to
the advancing cold front. Storm total rainfall of 2 to 3 inches seems
likely, with some locally higher amounts.

The primary uncertainty lies with the timing. The ECMWF is weaker
and more progressive, still showing an open wave quickly shifting NE
of the region by 00z Tuesday. The NAM is slowest and doesn`t want to
move in the best precip chances until Monday afternoon, evening --
while the GFS is somewhere in the middle. For now, have favored more
the GFS/ECMWF solutions which have had better continuity -- though
will need to watch the notable slower model trend of the NAM and
some of the other mesoscale guidance.

One last note: it going to feel noticeably colder behind this
frontal system. Highs may run 10 degrees to perhaps 15 degrees
lower on Monday, in the upper 60s to around 70 degrees.

.LONG TERM...(Monday night through Friday)
Issued at 359 AM CDT Sat Oct 21 2017

The coolest air this season is on the way to the TN Valley. As
previously mentioned in the short term, a cold front will pass
through the TN Valley on Monday. A few wrap around showers from the
backside of the system are possible early Tuesday as it lifts
northeast. Otherwise the rest of the day will be quite breezy with a
northwesterly wind 10-15kts and gusts up to 20kts filtering in
cooler and drier air. A second, stronger, front will arrive Tuesday
afternoon, bringing in a reinforcing shot of cooler air. Daytime
highs for Tuesday will be quite cool and only reach the lower 60s!
Overnight lows will be chilly in the upper 30s to lower 40s across
the TN Valley.

To further reinforce the cooler air, an upper-level trough will dig
all the way into the Southeast Tuesday night into Wednesday. Daytime
highs on Wednesday will be in the upper 50s to lower 60s with
overnight lows also in the upper 30s to lower 40s. If you are not a
fan of the cooler weather, temperatures will warm up a little bit on
Thursday and Friday as a weak upper-level ridge builds into the
region. Temps will reach the upper 60s, maybe 70 degrees with
overnight lows in the upper 40s. The ridge is quickly pushed eastward
by the next system moving across the Midwest. This system will bring
another cold front and our next round of showers and thunderstorms
to the area next weekend, however there is still a lot of model
disagreement to overcome.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 623 AM CDT Sat Oct 21 2017

VFR conditions will be the predominant flight category at each
terminal through the period. Passing cirrus will filter through the
region during the day and evening ahead of an approaching upper-level
storm system. These ceilings will lower and clouds will become
denser overnight, but remain well about reduced category limits.


&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

NEAR TERM...KTW
SHORT TERM...AMP.24
LONG TERM...JMS
AVIATION...AMP.24


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