Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 221502 AAB

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
902 AM CST Sun Jan 22 2017

.NEAR TERM...(Rest of Today)
Issued at 839 AM CST Sun Jan 22 2017

The latest surface analysis shows a very strong double barrel low
structure with centers situated across central Arkansas and the north
Central Gulf. The minimum central pressure was noted at 994 millibars
with a large expanse of the region at sub 1000 millibars. Regional
radars and satellite imagery this morning show a significant severe
weather event continuing to unfold with convection extending from
southern Georgia through the Florida panhandle and southern Alabama.

Closer to home, after a very loud/stormy night thanks to MCS
activity we have been in a bit of a lull this morning. However,
expect precipitation to fill back in rather quickly today as the
upper low approaches and the surface low continues to deepen across
the state. In fact we are already seeing an increase in rainfall
across Mississippi.

Primary questions will be rainfall amounts and potential for
thunderstorms. Lapse rates will steepen quickly with time today as
the low approaches. Despite minimal boundary layer heating, we could
see sufficient instability for low topped embedded cells. These
structures aided by the increasing low level cyclonic curvature may
even exhibit discrete/mini-supercellular characteristics and will
need to be monitored closely. Otherwise, moisture convergence will be
maximized along with the divergence associated with the LF quadrant
of the u/l jet to enhance precipitation potential especially across
our eastern areas late this afternoon and this evening.

Although beyond the "near term", will likely go ahead and issue a
wind advisory for late tonight though Monday as the gradient tightens
substantially and the 925 mb winds increase to greater than 40 knots.

.SHORT TERM...(Tonight through Tuesday)
Issued at 202 AM CST Sun Jan 22 2017

The exact position of the deformation field this evening still
remains uncertain with the GFS a bit further northwest with the low
track. Consequently, it also places the heaviest QPF of 2-3 inches
over our area. With rather wet top soils noted in our area, and
noticing recent within bank rises on area streams, there is growing
potential for some flooding if this indeed occurs. The strong trowal
and steep lapse rates resulting in large -divQ values suggest ample
support for sustained rainfall, some of it heavy at times.

Still looking at windy conditions developing late Sunday night into
Monday as the upper/surface low phases. We may see a 8-10 mb pressure
gradient on Monday morning east-west over our area. Have included
gusts over 40 mph due to momentum transfer in our higher terrain,
with 30-35 mph elsewhere and could see higher if this indeed verifies.
Will hold off an High Wind Watch or Advisory until the convective
threat moves out today, but future shifts will likely need to hoist
something later today or tonight. The precip area should shift east
of the area completely by Monday evening with a ridge quickly moving
in and diminishing flow. Lows will be below 40 degrees Tuesday
morning the for first time since the 9th of January! Then we should
recover nicely into the upper 50s to lower 60s with warm advection
returning in earnest Tuesday.

.LONG TERM...(Tuesday night through Saturday)
Issued at 202 AM CST Sun Jan 22 2017

No major changes planned in the extended forecast. A broad west-
southwest flow pattern develops by mid week with another Pacific
front arrives Tuesday Night into Wednesday. Moisture return will not
be plentiful, but low QPF is forecast along the frontal band. The
strong vorticity/trough axis at 500 mb drops southeast on Thursday
with a secondary push of colder air. However, it appears it will go
through dry. Lows Friday morning (Jan 27th) will be at or just below
freezing. That would be 3rd longest stretch in January on record for
days above freezing at KHSV. A dry forecast will run through days 6-7
as well with temps running a bit below normal for a change.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 537 AM CST Sun Jan 22 2017

Prevailing conditions suggest VFR thru midday as one round of rain/
low clouds exits to the NE while the next takes shape. However,
satellite and obs hint at lingering patchy IFR clouds so the TAFs
will keep a TEMPO thru 14Z. Rain (and MVFR ceilings/vis) will
redevelop by 19-20Z this aftn; vis/ceiling heights could fall farther
than forecast, and TSRA could be more of an issue than indicated, but
timing is problematic and amendments will be needed. The low
pressure will exit the region slowly tonight, with NW winds picking
up sharply around 02Z at KMSL and 04Z at KHSV. Ceilings will fall to
near-IFR at that point and stay there thru 12Z.





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