Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 191715 AAA

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
1215 PM CDT Mon Mar 19 2018

For 18Z TAFS.


.NEAR TERM...(Rest of Today)
Issued at 1000 AM CDT Mon Mar 19 2018

Latest GOES-16 Infrared image shows several clusters of convection
extending from northwest Georgia to extreme northern Mississippi and
western Tennessee. This activity is generally situated just north of
the surface-925 mb warm front with the true warm sector airmass
(dewpoints in the lower 60s and remnant nocturnal stratus) noted from
the Clarksdale to Jasper to Macon.

The latest high resolution guidance indicate no significant changes
in terms of timing/evolution of the anticipated sensible weather
later today. The approaching 500 millibar trough/associated low will
rotate across the Ozarks today with a slowly strengthening surface
low passing to our northwest. The hi res windows/NAM/HRRR are in fair
agreement with the synoptic fields with a favorable kinematic
setup between roughly 20z and 03z. With the upper trough passing just
to our north and the area getting into the warm sector later today
the low/mid level lapse rates will be more than sufficient for rotating
updrafts and large hail production.

As always, in terms of pinpointing specific severe weather threats
the devil is in the details. The NAM continues to be the most
aggressive in terms of buoyancy potential with an ensemble
approaching so a more realistic high shear/moderate CAPE environment
late this afternoon. Given the progged location of the surface low
and potential for some (note some) deepening the surface winds may
experience enough backing to enhance the sub 1km helicity. This would
result in an enhanced tornado potential especially in a corridor
along and east to Athens to Decatur to Cullman where strong
tornadoes are possible.

An update will be issued shortly but not planning any significant
changes overall. All in all, a potential volatile setup this
afternoon and folks should take this one very seriously.

.SHORT TERM...(Tonight through Wednesday Night)
Issued at 300 AM CDT Mon Mar 19 2018

Behind the line of storms, clouds likely will not clear out much as
quick cooling at the surface traps the clouds under an inversion but
the rain should quickly end. Rain could be done in NW AL by 00z,
central N AL by 1-3z and out of NE AL by 4-6z. Lows will be mild, in
the upper 40s.

Models are slow to move the surface low east once it moves into
eastern Tennessee and the Carolinas. However, good cold air advection
is in place behind the cold front by Tuesday morning. Also, a strong
deformation band looks to develop just to the west and northwest of
the surface low further east over eastern TN and western North
Carolina. Luckily, most models have the low far enough east that this
strong deformation band will likely setup over the north
Carolina/eastern TN border and extend southwest to near Chattanooga.
This would produce a band of heavier and more persistent
precipitation over those areas and keep rain chances lower over
northern Alabama and towards Moore county, TN. However, will still
see some higher chance pops in our southern middle Tennessee and
northeastern counties Tuesday afternoon into Tuesday evening. The
strong cold air advection mentioned earlier will drop temperatures
from the lower 50s /west of I-65/ to near 60 degrees /east of I-65/
around daybreak into the lower 40s/upper 30s by the early evening
hours. It will be fairly breezy and cloudy with a stiff northwest
wind sustained at around 15 mph with gusts to between 20 and 30 mph,
given a strong 30 to 35 knot 850 mb jet aloft Tuesday and Tuesday

Precipitation chances should lower a bit more around and
after midnight. However, as temperatures drop into the mid 30s around
midnight, this precipitation looks to be in the form of a mix of
very light rain and snow (but surface temperatures stay at least a
few degrees above freezing which should keep any accumulation from
occurring). As precipitation chances become more isolated before
moving east into Georgia around daybreak on Wednesday, this could
briefly change to all snow as temperatures drop to near freezing.
However, this period of all snow looks to be too brief and isolated
in nature for any snowfall accumulation. However some slick conditons
may develop around daybreak as temperatures drop near or just below
32 degrees east of I-65.

A return to cold temperatures and clear skies are expected on
Wednesday, as high pressure builds toward the area. Highs in the mid
40s to lower 50s are expected.

.LONG TERM...(Thursday through Sunday)
Issued at 300 AM CDT Mon Mar 19 2018

A gradual warm up will commence on Thursday as a trough builds
initially into the western CONUS and a ridge with deepening S-SW
flow develops in the Plains States and moves eastward. Some
discrepancies exist as expected between the next upr wave and cold
front expected to impact the region. But, the global models indicate
a rather quick transition from a developing ridge to a near zonal
flow pattern by the early weekend, with low pressure moving rapidly
across the OH Valley region on Saturday. What is appearing likely is
that at least a part of the west CONUS trough will be ejected into
the Plains and Midwest, but what is not easy to determine yet is the
southern extent of its influence, including on the TN Valley.
Nevertheless, this has been a persistent large scale feature and thus
some POPs are retained for the weekend period. Weak instability during
the period may produce a few thunderstorms, but only slight chances
were mentioned owing to the generally weak instability and forcing
over our region.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1209 PM CDT Mon Mar 19 2018

Active weather anticipated at both terminal locations over the next
24 hours. Currently IFR ceilings were noted due to a large expanse of
stratus covering the region. This stratus will very slowly diminish
and lift through the early afternoon hours as a warm front lifts
northward. However, conditions will become more favorable for
convection/thunder ahead of an approaching cold front and have
included VCTS for this aftn/early evening at both locations. Also
included a TEMPO window for more significant convection and
associated wind gusts. Storms may be capable of producing damaging
hail but did not include in TAFs. The storms are anticipated to
swing east of the area after 03z with some clearing noted late
evening/overnight. However, stratus is once again expected to
overspread the area toward Tuesday morning.





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