Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 292000
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
300 PM CDT MON AUG 29 2016

.SHORT TERM...(tonight through Thursday)
Issued at 241 PM CDT MON AUG 29 2016

Conditions are primed in some areas for additional flash flooding
tonight, primarily for those areas that received from 1 to 5
inches of rain last night in slow moving thunderstorms. Thus a
flash flood watch was issued for portions of southeast NE and
southwest IA where flash flood guidance was lowered as a result.

Environmentally, things are not that different from last night.
The atmosphere remains tropically moist being fed by a moist water
vapor plume that can be traced to the western coast of Mexico. PW
values this morning were around 1.8", which climatologically is
right at the maximum moving average for this time of year. This
moisture is also 1-2 standard deviations above normal based on
NAEFS climatological means, thus we have a lot of water to work
with. The upper low across the central Rockies will continue to
very slowly fill then lift across the plains through Tuesday. The
main westerlies are well north of the region, thus storm motions
are quite slow, only 10-15 mph at times. Due to the abundant
moisture, rainfall rates could easily reach 1-2" per hour. Storms
have begun to fire with the heat of the day with surface based
CAPE ranging 2000-3500 J/kg. Effective shear is very marginal
though, generally less than 20 knots. While freezing levels around
13300 could be conducive for hail, wet bulb zero levels are
extremely high around 12650. With the lack of higher storm scale
rotation and very marginal mid level lapse rates, hail will be a
struggle, but there does appear some wet microburst potential for
any storms that can develop a cold pool.

The wet pattern continues into Tuesday with conditions nearly
identical, but perhaps more coverage of storms as the upper trough
axis remains in place across the region, then slowly drifts south
of the area by early Wednesday. Will maintain likely Pops
along/south of I80 late tonight into Tuesday, then end precip from
north to south Wednesday morning, then go dry and mild for
Thursday.

.LONG TERM...(Thursday night through Monday)
Issued at 241 PM CDT MON AUG 29 2016

Dry conditions continue Friday with an upper ridge remaining in
place across the central US, but rain chances return for the
holiday weekend as the ridge shifts east, and a series of upper
level weather disturbances move into the area Saturday and Sunday,
along with a cold front on Labor Day.

&&

.AVIATION...(18Z TAFS for KOFK...KLNK and KOMA.)
Issued at 1230 PM CDT MON AUG 29 2016

Current water vapor imagery depicts a pronounced moisture plume
originating from the sub-tropical Pacific and stretching through
the mid Missouri Valley. This moisture extends through a deep
layer with the 12z OAX sounding sampling above 90th percentile PW
values when compared to climatology for this date. The upshot is
that we expect this moisture to fuel scattered showers and
thunderstorms this afternoon into tonight. Confidence in a
thunderstorm occurrence at any TAF location remains low, so we
will only include a vicinity mention in the near term, and use
PROB30 groups for tonight. Expect prevailing VFR conditions
outside of thunderstorm areas with restrictions in visibility and
variably gusty winds possible in and near the stronger storms.

&&

.OAX Watches/Warnings/Advisories...
NE...Flash Flood Watch through Tuesday afternoon for NEZ068-078-
     088>093.

IA...Flash Flood Watch through Tuesday afternoon for IAZ090-091.

&&

$$

SHORT TERM...DeWald
LONG TERM...DeWald
AVIATION...Mead



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