Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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452
FXUS63 KOAX 182004
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
304 PM CDT Mon Sep 18 2017

.SHORT TERM...(Tonight through Thursday)
Issued at 304 PM CDT Mon Sep 18 2017

Showers are exiting the area this afternoon. Subjective 12Z upper-
air analysis indicates west-northwesterly upper-level flow across
the central US, with a few weak ripples through the flow and with
ridging in the eastern US. Mid-level warm and moist air advection
had brought dewpoints of 12C+ into eastern NE/southwest IA, with
southwesterly winds and continuing warm air advection. Surface high
at 19Z was centered in southern MO, with a surface low in central MT
and a relatively weak pressure gradient between the two.

Main forecast concerns through Thursday include a chance of storms
on Tuesday evening/night. Showers and clouds will continue to exit
the area this evening and tonight. Given recent rain and relatively
rich low-level moisture, along with decreasing winds and clearing
skies, would not be surprised by at least patchy fog anywhere in the
area, with dense fog not out of the question. For now, have included
patchy fog mention in the few hours on either side of daybreak.
Temperatures will warm up in earnest tomorrow under good mixing
conditions. As a shortwave trough slides across the Dakotas on
Tuesday afternoon/evening, bringing a cold front with it,
showers/storms are likely to develop in SD in the afternoon/evening.
Wind shear is quite strong, given backed low-level winds and very
looping low-level hodographs, along with abundant shear at 0-3km and
effective bulk layers. However, capping inversion will limit
southward extent of convective development, with most likely
southward extent just reaching northeast NE into northwest IA.
Should storms reach into the area, they will carry the risk of
severe weather, including gusty winds, hail, and perhaps even a
tornado.

Front will progress through the area on Tuesday night, bringing
cooler temperatures on Wednesday, as well as the risk of
showers/storms redeveloping on the front on Wednesday afternoon and
evening, mainly in southwest Iowa. Quick temperature recovery to
readings well above normal is expected on Thursday as return flow
again brings much warmer mid-level temperatures, with southerly
winds providing good mixing.

.LONG TERM...(Thursday night through Monday)
Issued at 304 PM CDT Mon Sep 18 2017

As an upper-level low digs into the western US - there to stay for
the rest of the forecast period - prolonged moderate to heavy
rainfall is possible this weekend. Warm air advection and good pre-
frontal mixing will continue on Friday, and the area should remain
ahead of the surface trough and associated precipitation at least
through Friday night. Do have some POPs in northeast NE beginning on
Friday afternoon, but honestly think chances really will hold off
until Saturday in northeast NE and possibly Saturday night/Sunday in
the rest of the forecast area, as models are trending toward the
slower ECMWF solution in this stagnant pattern. Once precipitation
does arrive, it is not likely to progress out until at least Monday
and potentially beyond. Strong frontogenetical forcing and unstable
(convectively and conditionally) airmass should foster efficient
rainfall production. Combined with slow progression of heavier rain
areas, the potential for heavy rainfall and perhaps some areas of
flooding is possible if the scenario does materialize.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1215 PM CDT Mon Sep 18 2017

Scattered showers and isolated thunderstorms from David City and
Lincoln to Omaha as of 17z will continue east this afternoon. This
precipitation should move east of KLNK within the next hour or
two, but will linger in the KOMA vicinity through much of the
afternoon. MVFR to local IFR conditions are expected to trend
toward VFR by mid afternoon into early evening before
transitioning back to MVFR overnight, especially at KOMA and KOFK.
Some patchy fog is also possible at those two locations toward
daybreak on Tuesday.


&&

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

$$

SHORT TERM...Mayes
LONG TERM...Mayes
AVIATION...Mead



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