Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 162300

Area Forecast Discussion
National Weather Service Omaha/Valley NE
600 PM CDT Sat Sep 16 2017

.SHORT TERM...(Tonight through Tuesday)
Issued at 242 PM CDT Sat Sep 16 2017

A potent shortwave trough will eject east-northeast across the
Dakotas and the ND-MN Red River Valley this afternoon into tonight
with the southern fringe of mid-level height falls glancing the
forecast area. At the same time, a cold front will steadily
advance south through the remainder of southeast NE and southwest
IA, ushering a cooler and drier air mass into the region.

Pre-frontal showers and thunderstorms have limited the degree
of destabilization within warm sector so far today. However,
pockets of stronger heating will yield a moderately unstable and
weakly capped environment by mid to late afternoon when surface-
based storms will become increasingly likely. Latest convection-
allowing model guidance suggests that this scenario is most likely
to unfold across far southeast NE into southwest IA after 4 PM
with additional storms forming nearer to the 850-mb front along
and south of I-80 this evening. The most intense storms are
expected to be those forming along the surface front where
instability will be greater. Large hail and damaging wind gusts
will be the primary hazards. A strong storm or two is also
possible later this evening with the elevated activity mentioned
above, and some hail cannot be ruled out.

Precipitation will end from north to south tonight and the
majority of Sunday looks to remain dry as high pressure builds
through the area.

On Sunday night into Monday, low-level warm advection will
strengthen ahead of a low-amplitude shortwave trough tracking from
the Rockies into northern and central Plains. This process in
conjunction with deeper-layer forcing attendant to the approaching
mid-level wave will support a good chance of showers and
thunderstorms across much of the area. Locally heavy rainfall is
possible, especially nearer to the NE-KS border. Both
precipitation and clouds should diminish during the afternoon on
Monday as the mid-level impulse shifts east of the region.

Monday night into Tuesday, another powerful jet streak and
associated shortwave trough will migrate from the Interior West
into the northern High Plains. This will drive the deepening of a
lee cyclone and the eastward advance of a cold front through the
High Plains. This large-scale pattern evolution will support
afternoon temperatures warming well into the 80s and perhaps lower
90s with breezy to windy conditions.

.LONG TERM...(Tuesday night through Saturday)
Issued at 242 PM CDT Sat Sep 16 2017

The above-mentioned shortwave trough will traverse the northern
Plains and upper-MS Valley Tuesday night into Wednesday with the
associated surface cold front weakening as it moves into the mid-
MO Valley. Thereafter, medium-range guidance is suggestive that a
longer-wavelength trough will become established over western
North America by late week before edging east toward the Great
Plains next weekend. Ahead of this trough, we will likely see near
to above-normal temperatures with increasing precipitation chances
by the weekend.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 559 PM CDT Sat Sep 16 2017

The surface cold front continues south through far southeast NE
and southwest IA as of early evening with a trailing band of MVFR
stratus across much of the area. Radar data indicate a gradual
deepening of convection to the north of the surface boundary from
KTQE to near KLNK. Latest model guidance suggests that some of
this activity will further evolve into thunderstorms over the next
couple of hours. As such, have mentioned VCTS at KOMA and KLNK
through 03z. Otherwise, expect the MVFR ceiling to erode from
northwest to southeast with surface winds diminishing and veering
to northeast.




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