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fxus63 koax 210525 

Area forecast discussion
National Weather Service Omaha/valley NE
1125 PM CST Wed Nov 20 2019

..updated aviation forecast discussion...

issued at 251 PM CST Wed Nov 20 2019

showers and perhaps a few thunderstorms will overspread the area
tonight. There is a small chance for a strong storm over southeast
Nebraska and southwest Iowa. Precipitation could change over to
light snow before ending late tonight into Thursday morning over
northeast Nebraska. Accumulations should remain less than half an
inch. The next chance for precipitation will be next Monday night
into Wednesday. Above normal temperatures today will drop to below
normal through Friday before rising back above normal this
weekend into early next week.

Tonight into Thursday morning:
a short-wave trough over the southern High Plains early this
afternoon will eject northeast through the mid MO valley tonight
in advance of a strong upper-level low moving through Southern California
into the lower Colorado valley. In the low levels, a surface low
analyzed over western Kansas will develop into south-central NE by
this evening before reaching north-central Iowa by Thursday morning.
Ahead of the surface low, a 40-50 kt low-level jet will continue
to promote the poleward flux on an increasingly moist air mass
into the region. That process is occurring beneath a
northeastward-advecting elevated-mixed layer (reference the 12z
ddc sounding), eventually resulting in pockets of weak instability
(i.E. MUCAPE at or below 700-800 j/kg) this evening within the
system warm sector.

The gradual destabilization process should allow an ongoing
cluster of showers and thunderstorms over western OK and southern
Kansas to move into our area this evening into tonight, in tandem with
the surface low and short-wave trough. Given the expected
development of only weak instability, severe weather is
improbable. However, forecast soundings across southeast NE into
southwest Iowa do suggest some potential for marginally buoyant,
surface-based parcels amidst a kinematic environment featuring
quite strong low-level shear. As such, there is a small risk for
a strong storm or two from about 10 PM to 2 am. Thereafter,
columnar cooling within the deformation axis of the passing
weather system could yield a period of light snow over portions of
northeast NE late tonight into Thursday morning. Any snow
accumulation should remain less than a half inch.

Thursday afternoon through friday:
the passage of a strong short-wave trough through the upper MS
valley and upper Great Lakes will deposit a surface high across
the mid MO valley. At the same time, a subtropical-branch mid to
upper-level low will track from the southern rockies into the
central and Southern Plains. It currently appears that the best
precipitation chances associated with the subtropical-branch
system will remain to our immediate south on Thursday night into
Friday. However, we will see cooler temperatures with highs in the
mid 30s to mid 40s on Thursday, and around 40 on Friday.

Saturday and sunday:
the above-mentioned mid-level system over the central and Southern
Plains will accelerate east in response to the development of a
strong upper-level jet from the northeastern Pacific into northern
High Plains. An increasingly zonal, mid-level wind component
across northern rockies will encourage a downslope-induced warming
pattern to overspread our area with highs in the 40s on Saturday
and 50s on Sunday.

Monday into wednesday:
while there is general model agreement in the evolution of a broad
trough across much of the U.S. Early next, notable difference
exist in the amplitude and location of embedded perturbations. The
12z GFS deterministic solution depicts the development of an
intense deep-layer cyclone over the Central Plains on Tuesday,
which would yield impactful weather for our area. In contrast, the
deterministic runs of the European model (ecmwf) and Canadian models suggest a
lower-amplitude mid-level pattern, weaker surface low development,
and lighter precipitation. The take away is that potential exists
for a winter-weather precipitation event. However, specific
detail remain highly uncertain.


Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1123 PM CST Wed Nov 20 2019

Rain showers continue to move through the taf sites, but will end
by 11-13z. MVFR and temporary IFR conditions initially with the
rain, but improving to VFR by 20-22z. South winds at 15 to 25 mph,
becoming northwest at koma before 08z, and northwesterly winds at
klnk at taf issuance. There could still be an isolated lightning
strike within the next couple of hours, but that would remain
southeast of the klnk/koma locations.


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