Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 161707
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1207 PM CDT Tue May 16 2017

.SHORT TERM...(Today through Thursday)
Issued at 345 AM CDT Tue May 16 2017

Forecast concerns in the short term will be lingering
showers/thunderstorms early this morning...then re-development of
thunderstorms this afternoon and tonight with potential for
severe weather and locally heavy rain...with unsettled weather
continuing on and off into the first part of the weekend.

Showers and thunderstorms were ongoing early this morning. A
surface warm front stretched from northern Nebraska toward the
MN/IA border. The bulk of the thunderstorms were near or north of
the boundary...however additional storms were over northern
Nebraska with a cluster of storms in north central Kansas. A
coupled jet was noted on the upper air maps with upper level
divergence overnight over the forecast area along with a shortwave
in the southwest flow aloft. Broad 20 to 40m ht falls were over
the southwest U.S. Very steep mid level lapse rates were noted on
the OAX sounding with MLCape of 1000-2000J/kg and moisture of
1-1.5" PWAT. Surface temperatures were in the 60s and 70s locally
with the warm front to the north...and dewpoints were in the 50s
and 60s.

Warmer mid-level temperatures over the western High Plains is
forecast to shift eastward into the forecast area this
morning...thus limiting surface based convection. This
afternoon...the closed h5 low over southern CA/NV is forecast to
shift east into CO/NM. Warm air advection will be ongoing this
morning...however the 40 to 50kt h85 wind is forecast to weaken to
20 to 30kt. Elevated showers and thunderstorms are
possible...however the coverage at this time looks very
limited...thus trended downward for the morning hours. This
afternoon...the RAP/HRRR/EC/Canadian trend toward increasing
thunderstorm chances in the 22-00Z time period in southeast
Nebraska...the GFS is closer to the front in northeast
Nebraska...while the NAM holds off until the 00-03Z. Instability
increases to 2-5KJ/kg with 0-6km bulk shear of 40 to 55kts. SPC
has our area in the enhanced outlook for severe storms and this
seems reasonable with the instability/shear and very steep lapse
rates and probability for hail and wind. The forecast soundings
show decent storm motions of 20 to 30kts and forward propagating
motion vectors to the northeast...however training of storms in
the moisture rich environment could lead to locally heavy rain.
WPC has added our forecast area to the slight risk for excessive
rainfall.

As the main mid tropospheric trough arrives Wed...showers and
thunderstorms will be likely for parts of the area...decreasing
across the south near the KS border Wednesday night.

.LONG TERM...(Thursday night through Monday)
Issued at 345 AM CDT Tue May 16 2017

Unsettled weather with periods of showers and thunderstorms is
forecast as the next closed h5 trough is progged to encompass
parts of UT/CO/WY Friday night then slowly move across the rockies
into the Plains through Friday...becoming an open wave as it
lifts into the Northern Plain Friday night then gradually lifting
far enough north Saturday that the precipitation will end. In the
extended...the potential for severe weather will depend on the
track of the surface low with the backed flow more pronounced for
parts of southeast Neb. and southwest IA with the GFS/NAM
compared to the EC. and there is good 0-6KM Bulk Shear. The CFS
chiclets had some signal for this period...however recently backed
off somewhat...however the expected synoptic pattern still
supports keeping a close eye on the track. Temperatures look to be
in the 50s-70s Friday. A more northern stream wave will bring a
chance for showers and thunderstorms Sunday night into Tuesday.
High should be mostly in the 60s and 70s Saturday through Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1207 PM CDT Tue May 16 2017

Gusty south winds will continue this afternoon across eastern
Nebraska with scattered-broken clouds at around FL040.
Thunderstorms are expected to form to the west this afternoon
before moving into the area this evening. Short-term model
guidance remains in good agreement in suggesting that a bowing
line of storms will affect the Lincoln and Omaha areas between
about 01 and 04z. As such, a mention of strong wind gusts have
been included in the TAFs during that time frame. Otherwise,
expect episodic showers and thunderstorms overnight into Wednesday
morning with the potential for more widespread MVFR ceilings
developing late tonight.


&&

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

$$

SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...Mead



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