Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 172300

Area Forecast Discussion
National Weather Service Omaha/Valley NE
500 PM CST Fri Feb 17 2017

.SHORT TERM...(Tonight through Monday)
Issued at 305 PM CST Fri Feb 17 2017

Early-afternoon water vapor imagery depicted a polar-branch
short-wave trough over the Dakotas with a sub-tropical-branch mid
to upper-level low over the southern Plains. The former
disturbance will continue northeast into the upper MS Valley
tonight, supporting the equatorward advance of a surface cold
front through the mid MO Valley. This boundary will dissipate on
Saturday to our south as a weak surface high moves through the
area. Slightly cooler low-level thermodynamic profiles and
shallower boundary-layer mixing will result in highs generally in
the lower to mid 60s.

Saturday night into Sunday, a sub-tropical-branch short-wave
trough will track from the lower CO Valley and northern Baja into
the central and southern Rockies, inducing the deepening of a lee
trough over the High Plains. A resultant strengthening of
southerly low-level winds and the concurrent poleward flux of an
increasingly moist boundary-layer will commence with patchy fog
possible late Sunday night into Saturday morning. It still appears
that this low-latitude trough will tap into a plume of mid to
high-level moisture originating over the sub-tropical Pacific,
yielding mostly cloudy skies on Sunday with highs in the lower to
mid 60s.

Sunday night into Monday, aforementioned short-wave trough will
continue northeast into the central Plains, gradually phasing with
a polar-branch disturbance moving into the Dakotas. Strengthening
forcing for ascent coupled with the continued low-level
moistening/destabilization occurring ahead of the system cold
front will result in increased chances of showers and a few
thunderstorms, mainly late Sunday night through midday Monday.
Relatively poor mid-level lapse rates will limit the degree of
destabilization and no severe weather is currently anticipated.

.LONG TERM...(Monday night through Friday)
Issued at 305 PM CST Fri Feb 17 2017

The mid-level flow pattern will transition to quasi-zonal in the
Tuesday-Wednesday time frame, in the wake of the trough moving
through the MS Valley, and ahead of the next trough evolving over
the Interior West. Southwest to west, downslope winds will enhance
warming potential on Tuesday with temperatures rising into the
mid 60s to lower 70s. Readings may be a bit cooler on Wednesday
--especially over our northern counties-- as a weak cold front
settles south into the area.

Thursday into Friday, attention then turns to a potent mid-level
trough emerging into the Great Plains from the Rockies. Differences
exist amongst 12z model guidance with respect to the amplitude
and track of this system. The deterministic GFS is most
progressive with this synoptic system, indicating the associated
surface low over eastern NE by midday Thursday, prior to pushing
the trailing cold front through the entire forecast area by
Thursday evening. The ECMWF and Canadian deterministic models as
well as the GEFS mean suggest a slower progression of the synoptic
wave; which is the direction we are inclined to lean with the
forecast at this point. Under the slower scenario, we would see
increasing chances of showers and thunderstorms on Thursday
afternoon and continuing into Thursday evening. Thursday night
into early Friday, a change over from rain to snow is possible.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 500 PM CST Fri Feb 17 2017

Expect VFR conditions through the period. Some small potential for
a little fog toward sunrise, but a little better chance of low
clouds or fog late Saturday night.




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