Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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613
FXUS63 KOAX 211723
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1223 PM CDT Sun May 21 2017

.SHORT TERM...(Today through Tuesday)
Issued at 335 AM CDT Sun May 21 2017

Finally a dry day with decreasing clouds today, but thunderstorm
chances return for Monday.

Upper low that caused our widespread and continued rains the last
several days was drifting northeast into Minnesota this morning.
Northwest flow at the surface and aloft behind this system will
continue to spread low and mid level cloud cover from South Dakota
into eastern Nebraska and southwest Iowa early in the day, but a
gradual clearing trend from southwest to northeast is expected as
low moves farther away. Thus plenty of sunshine is forecast this
afternoon, helping to push temperatures back into the 60s most
areas.

Strong mid level trough rotating south on back side of this system
is still slated to arrive over our area Monday afternoon. A weak
impulse ahead of that trough is forecast to roll out of the High
Plains tonight, and may trigger scattered showers over southeast
Nebraska late tonight and Monday morning. Otherwise most of eastern
Nebraska and southwest Iowa will wait until Monday afternoon when
stronger trough enters the region. Significant cooling aloft will
combine with surface temperatures climbing into the 70s to
produce moderately steep lapse rates in the afternoon. Moisture
will be somewhat limited with surface dew points in the low to mid
50s near and south of I-80 just ahead of expected afternoon cold
front position. GFS suggests SBCAPE will top 1000 J/kg with modest
bulk shear approaching 40kt. Given cooling aloft, convective
temperatures will easily be met, leading to scattered showers and
at least isolated thunderstorms all areas in the afternoon. Higher
instability and focusing low level boundary in our south may
yield more robust storms which could produce hail and gusty winds.
We remain in a marginal risk for severe as per SPC`s day 2
outlook.

Convection should wane through the evening with loss of daytime
heating, but won`t end until after midnight in the southeast when
upper trough finally swings southeast. A secondary shortwave trough
is forecast to drop into the region again Tuesday afternoon, with
associated steepening lapse rates again popping some afternoon
showers. Instability and shear forecasts are much lower then, so
thunder chance is low.

.LONG TERM...(Tuesday night through Saturday)
Issued at 335 AM CDT Sun May 21 2017

The longer term will begin relatively benign as upper low from the
western Great Lakes sinks southeast into the Ohio Valley region,
then swings northeast toward New England by Thursday night.
Meanwhile, another upper low progress southeast from the Gulf of
Alaska into the Pacific Northwest, then settles into southern
Saskatchewan by Thursday. A general rising heights regime in the
Plains will lead to warmer temperatures Wednesday through
Saturday, with highs back into the 70s or higher. However several
mid level impulses rotating around Canadian low are expected to
eject through the Rockies and into the Plains beginning Thursday
night, leading to several chances for showers and thunderstorms
through Saturday. Moisture return appears to be limited ahead of
these impulses, so widespread severe seems unlikely at this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1222 PM CDT Sun May 21 2017

VFR conditions through the period. Northwest winds at 14 knots
with gusts up to 22 knots to about 23-24z. Then winds back and
southwest through the remainder of the period. There is some mid
level moisture approaching the area tonight and Monday. This could
trigger spotty showers or sprinkles, but not confident enough to
mention at any of the TAF locations.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...DeWald



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