Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 291857

Area Forecast Discussion
National Weather Service Huntsville AL
157 PM CDT Wed Mar 29 2017

.NEAR TERM...(Tonight)
Issued at 109 PM CDT Wed Mar 29 2017

Early afternoon surface analysis shows the low situated across
northeast Oklahoma/southeast Kansas with the warm front extending
from central Arkansas through west Tennessee and into northern
Alabama. Temperatures across the region have warmed nicely today
under mostly sunny skies with readings in the mid to upper 70s. Also
interesting to note that dewpoints ranged from the lower 60s across
northwest Alabama to lower/mid 50s across northeast Alabama/southern

For this afternoon into tonight, cumulus/stratocumulus has slowly
been building with time and you can actually see the location of the
warm front in the vicinity of the cumulus buildup. Expect quiet but
very mild conditions tonight as southerly winds become established
ahead of approaching/deepening surface low. Significant convection
should be ongoing late tonight from southern Illinois well south
through Mississippi River Valley.

.SHORT TERM...(Thursday through Friday)
Issued at 109 PM CDT Wed Mar 29 2017

Business will be picking up across the Tennessee Valley early in the
short term period. Although detail/mesoscale uncertainties continue
within the model guidance, the majority of the models have converged
on a deepening mid latitude cyclone moving through the Missouri
Valley on Thursday and taking on a negative tilt as it rotates into
the lower Great Lakes on Friday. This system will aid in deepening a
surface low across the Mid Mississippi Valley on Thursday.

Late tonight into early Thursday, a line of strong/intense convection
will be crossing the Mississippi River and potentially impacting the
JAN/MEG County Warning Areas. The guidance handles the evolution of
this line/convection differently with time and it will have impact on
later storms. The NAM and some of the higher resolution guidance
weakens this line quickly/efficiently as it approaches NW Alabama
tomorrow morning. The GFS and to a lesser extent the ECMWF/CMC
bringer a more dense blowoff shield/remnant trash convection across
the area. If the latter verifies, it will have some negative impact
on the instability and potentially lower level thermodynamics for
afternoon storms.

Having said that, the NAM/high res windows including the CAMs point
toward a potentially volatile setup tomorrow afternoon. As the upper
system approaches from the west, the region will come under an
increasingly diffluent upper flow due to a coupled jet structure at
250 millibars. The combination of enhanced ascent aloft with
increasing low/mid level jet dynamics (70 knot mid level jet) will
set the stage for sufficient forcing for another round of
afternoon/evening convection. The kinematic profiles shows
significant veering atop a backed low level flow. With the daytime
heating and sufficient low level moisture we have the potential for
an unstable airmass (MLCAPE ~1500 J/kg) coupled with the shear
profiles sufficient for rotating supercells. The primary timing for
the afternoon/evening event would be from 22z (west) to 05z (exiting
in the east).

The afternoon/evening activity should be fairly progressive in
nature, but given the recent heavy rainfall some isolated flash
flooding would not be out of the question. The one key to remember
right now is that there`s potential for the afternoon storms to be
signficant, but there`s also a lot of questions marks leding up to it
that could throw a monkey wrench into the setup. Conditions will
improve quickly after Midnight tomorrow night and into Friday with a
dry but mild day expected for Friday.

.LONG TERM...(Friday night through Tuesday)
Issued at 130 PM CDT Wed Mar 29 2017

Progressive upper level flow will persist across the region through
the extended period. The weekend looks quiet currently with the
Tennessee Valley in between systems and ridging building across the
area. We may see an increase in cloud cover on Sunday as the lower
tropospheric winds become southerly and a warm front lifts toward the
region. Moisture will return rather rapidly late Sunday, especially
after dark, but will hold off on pops until after 00z.

A fast moving, bowling ball type low, will roll across the Deep
South Monday into Tuesday. Overall, this system will bring
substantial moisture to a large portion of the Gulf Coast and points
inland. However, given the southerly latitude expect the warm sector
and best potential for severe storms to remain south of the region.
Having said that, the lapse rates aloft and thermodynamics alone
would be sufficient for strong storms and widespread convection with
this system.

Conditions should improve briefly from late Tuesday into early
Wednesday before the next system approaches from the west. Currently
this system looks rather weak and somewhat vertically stacked. Will
include low chance pops for convection for now given that we are
looking at the Day 7/8 period.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1249 PM CDT Wed Mar 29 2017

VFR conditions will prevail across North Alabama this afternoon
through the overnight hours tonight. As a storm system approaches
from the west on Thursday morning, lower clouds are expected to
develop and move quickly northeastward affecting KMSL as early as
12z. Have trended toward MVFR cigs in the planning period for MSL and
HSV, but don`t have enough confidence yet to include any VCSH or RA
in the TAF at this time. Additional showers and storms are expected
to develop into the afternoon and evening hours on Thursday, and
move eastward across North Alabama. Inclusion of VCTS and TSRA will
be needed in subsequent TAF updates.





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