Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 100526
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1126 PM CST Sat Dec 9 2017

.SHORT TERM...(Tonight through Tuesday)
Issued at 306 PM CST Sat Dec 9 2017

Our dry forecast continues the next several days with a warm end to
the weekend followed by cooling trend through Tuesday.

Mostly sunny skies were noted across eastern Nebraska and southwest
Iowa this afternoon. Temperatures had rebounded into the 40s in our
west, but struggled to reach the lower and middle 30s in southwest
Iowa. Brisk north winds gusting over 20 mph kept wind chills in the
20s in many spots.

Mid level flow pattern featured a deep mean trough to our east,
extending from Hudson Bay into the Deep South, and a ridge to the
west, extending from the Baja through western Canada. This leaves
our part of the country under north to northwest flow aloft, which
is forecast to remain wholly unchanged much of the coming week.
Perturbations dropping through that flow will help reinforce our
cooler temperature regime, with only modest warming ahead of each
shortwave.

The first shortwave of consequence was noted topping ridge in
northern British Columbia this afternoon, and is forecast to drop
southeast toward the western Great Lakes on Sunday. Main sensible
weather affect in our area will be modest warm advection regime
induced in the Plains to the west of the track, characterized by 850
temps warming some 10C from this afternoon into Sunday. We`ll still
see some weak cool advection Sunday afternoon and an increase in mid
and high level cloud cover, but temperatures should top 50 in much
of our CWA.

A second and more potent shortwave was currently tracking northeast
through the Gulf of Alaska, and is expected to top ridge and race
south into the Plains on Monday. Strong warm advection ahead of this
wave will come mainly during the overnight period Sunday night with
strong cold advection commencing Monday morning and continuing into
Monday night. Thus it is quite likely a non-diurnal temperature
trace will result with rising temperatures after midnight Sunday
night, then falling afternoon temps on Monday.

Strong winds approaching advisory levels are likely on Monday as
well. Unidirectional flow increasing with height and steep low level
lapse rates behind cold front suggest efficient momentum transfer of
40 mph average boundary layer winds to the surface. A few sprinkles
or flurries are possible as well given steep lapse rates, but
nothing of any consequence.

Cooler temperatures will follow for Tuesday, but still rebounding
toward normal for this time in December.

.LONG TERM...(Tuesday night through Saturday)
Issued at 306 PM CST Sat Dec 9 2017

Western ridge/eastern trough upper air pattern will remain in place
until late week before a pattern shift is advertised by all major
long-range guidance.

Another strong shortwave diving into the Plains Wednesday will again
push temperatures upward Tuesday night before strong cold advection
ensues during the day Wednesday. GFS is fastest with this wave while
Canadian and ECMWF delay arrival a bit, allowing some rebound in
temperatures on Wednesday before cooling takes hold. A weak
secondary shortwave follows closely behind for Wednesday night and
Thursday, but behind these waves, mid level flow begins to shift for
the weekend.

Eastern upper trough flattens over the eastern half of the CONUS
Friday into Saturday as last of shortwaves rotates off the East
Coast. Meanwhile, western ridge is flattened by a series of
shortwaves suppressing heights. One of those waves will be entering
the Rockies on Friday and moving into our part of the world on
Saturday. With overall height rises, expect warming potential to
increase accordingly. However increased mid and upper level clouds
in mid level warm advection regime will likely hinder maximum
warming on Saturday. There is at least a small chance light
precipitation may be squeezed out of this system, but most model
output is pretty bearish on this. Thus will maintain a dry forecast
for now.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1125 PM CST Sat Dec 9 2017

Expect VFR conditions through the period with mainly some mid and
high level clouds. Winds will turn to the northwest and increase
mid to late Sunday morning with some gusts around 20 to 25 knots,
then winds will decrease toward sunset.

&&

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

$$

SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...Miller



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