Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 260915
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
315 AM CST Sat Nov 26 2016

.SHORT TERM...(today through Monday)
Issued at 311 AM CST Sat Nov 26 2016

Return of precipitation Sunday and Sunday night is the primary
forecast concern.

High pressure settled south of our area during the day Friday,
allowing light west then south winds to return to the region.
Despite the lack of mixing with those light winds, plenty of
sunshine helped push temperatures into the lower and middle 50s
Friday afternoon. Even warmer conditions are forecast this afternoon
as favorable southwest low level flow under building mid level
heights and lots of sunshine combine to push highs well into the 50s
or even some lower 60s. Decreasing winds and clear skies this
evening will allow temperatures to drop relatively quickly before
high clouds begin to increase later tonight ahead of our next system
scheduled to arrive on Sunday.

That system was taking shape off the West Coast this morning as an
upper trough approaching the Pacific Northwest. The trough is
forecast to move into the Northern Rockies later tonight as a strong
70-80kt mid level jet rotates into AZ/NM early Sunday, and then will
approach eastern Nebraska late in the afternoon. Increasingly
diffluent upper flow pattern across the Plains suggests strong
low/mid level theta-e advection should saturate initially dry lower
atmosphere, leading to eventual widespread precipitation in eastern
Nebraska and western Iowa by late Sunday morning and afternoon. Also
by Sunday afternoon, upper trough is expected to close off a low
center in western South Dakota with attendant surface low tracking
northeast through north central or northeast Nebraska. Late-
arriving low 50s surface dew points are forecast into eastern
Nebraska Sunday afternoon under steepening lapse rates in left
exit region of mid level jet. Strong 0-6km bulk shear over 50kt is
expected as well. Despite the scant low level moisture leading to
relatively low MUCAPE values (models show 300-500 j/kg), high
shear in veering low/mid level wind profiles suggests the
potential for low-topped supercell storms and attendant risk for a
few strong storms, especially over eastern Nebraska during the
afternoon.

Given strong forcing environment, will continue with fairly high
precipitation chances Sunday afternoon into the evening before mid
level jet punches northeast of our area after midnight. Strong south
winds during the day will become southwest then west as Pacific cold
front rotates around northward-drifting upper low. Much colder
airmass is forecast to surge south on back side of the system for
Monday when 850 temperatures drop below 0C in our north. Cyclonic
flow regime and minor waves rotating around low may trigger a few
showers there Monday afternoon. Otherwise expect temperatures in the
50s Sunday to drop into the 40s or lower 50s Monday before the
coldest air settles in later in the week.

.LONG TERM...(Monday night through Friday)
Issued at 311 AM CST Sat Nov 26 2016

Location and progression of upper low in and through the Northern
Plains will be the primary factor in precipitation chances for much
of the work week. GFS and ECMWF are still widely spaced in regards
to initial placement of upper low Monday night, with GFS still
farther north in North Dakota and ECMWF closer to home in eastern
South Dakota. The Canadian model offers a compromise between those
other two models, but as far as sensible weather is concerned,
probably not a whole lot of difference.

The overall weather story next week will be colder temperatures as
all models basically keep our area under broad trough regime at
least until Thursday. And they all allow colder air characterized by
850 temperatures in the 5-10C below range to set up shop in the
middle of the country much of the week. Thus highs in the 30s and
lower 40s much of the week are likely, with potentially colder
readings in our north where the likelihood of more cloud cover will
exist from time to time.

As far as precipitation goes, northeast Nebraska will have the
highest chances for a rain or snow shower into mid week where
juxtaposition of layer moisture and lift in cyclonic flow regime
will be sufficient for at least slight chances into Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1055 PM CST Fri Nov 25 2016

VFR conditions will continue through the period as surface high
moves off to the southeast and upper ridge moves over the plains
region.


&&

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

$$

SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...Fobert



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