Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 171952

Area Forecast Discussion
National Weather Service Omaha/Valley NE
252 PM CDT Sun Sep 17 2017

.SHORT TERM...(Tonight through Wednesday)
Issued at 251 PM CDT Sun Sep 17 2017

More active weather will continue, with a roller coaster of
temperatures. Subjective 12Z upper-air analysis indicates an upper-
level ow centered near the MB/SK border, with 500mb height falls
centered in noe northwestern Great Lakes. Another shortwave trough
was evident in the Pacific Northwest through the Baja, along with a
weak remnant wave in the mid-Atlantic. An 850mb cold front extended
from a now in western ON through the mid-MS river valley and toward
the TX/OK panhandles, with much of the moisture shunted ahead of it.
Surface high at 19Z was centered near the SD-MN and NE-IA border
area, with temperatures well below normal today.

Main forecast concern is shower/thunderstorm potential this evening
through Monday across the area, with another brush of the northern
CWA possible on Tuesday night. Mid-level flow and moisture already
are returning to the High Plains, with advection returning eastward
this evneing. As a weak but broad upper-level shortwave passes
through the central Plains, showers and a few embedded thunderstorms
should develop later this evening from southeast to central NE,
spreading northeastward through the night and continuing on Monday,
before finally shunting away to the east later Monday. MUCAPE
profile is not very impressive, with weak 500-1000 J/kg MUCAPE
possible tonight through Monday morning, perhaps around 1000-1500
J/kg in the southeastern CWA by afternoon, and skinny CAPE profile.
Clouds and rain will hold temperatures down again on Monday, despite
a return of warm air advection.

In wake of the Monday showers/storms, rising 500mb heights should
keep things quiet on Monday night and Tuesday as a deeper upper-
level trough digs into the Rockies. With continued warm air
advection, temperatures on Tuesday should pop well above normal
again. An ejecting shortwave trough on Tuesday night across the
Dakotas will bring another round of thunderstorms, but do think the
activity will struggle to get southward into northeast NE/northwest
IA as the upper-level support pulls away to the north and with
rather substantial mid-level cap. If it did sneak into the area,
there is some potential for storms to be on the strong to severe
side. Associated cold front will bring a return to near-normal
temperatures to the area on Wednesday.

.LONG TERM...(Wednesday night through Sunday)
Issued at 251 PM CDT Sun Sep 17 2017

A deep upper-level low is progged to dig into the Rockies late this
week and through the weekend (and likely beyond), with an upper-
level high parked over the Great Lakes.  The persistent pattern will
keep the central US under an active weather regime, with the
potential for several consecutive days of moderate rainfall slowly
moving across the area from Saturday into early next week.
Temperatures are likely to be quite a bit above normal to our east,
below normal to our west, and something in between here in the
middle, with rainier days likely to be on the cooler side.  ECMWF is
quite a bit slower than GFS to bring the slow-moving front and
associated moderate to heavy rainfall into the area. Ultimately, the
weekend looks cool and rainy, with well above normal temperatures on
Thursday and Friday ahead of the digging low and advancing front,
along with dry weather on Thursday and potentially on Friday,
depending on the speed of the advancing front.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1209 PM CDT Sun Sep 17 2017

Surface high pressure will quickly build through the area today
with strengthening warm advection already yielding a growing cloud
shield to the immediate west. A low-amplitude perturbation will
emerge from the Rockies tonight, combining with the warm-advection
pattern to foster numerous showers and thunderstorms which will
affect the area from after midnight until about midday Monday.
Ceilings will gradually lower from south to north with prevail MVFR
conditions anticipated late tonight into Monday morning at all
three TAF sites.




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