Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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210
FXUS63 KOAX 170405
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1005 PM CST Sat Dec 16 2017

.UPDATE...
Issued at 956 PM CST Sat Dec 16 2017

Mades some tweaks to the clouds...temps...and dewpoints based on
latest trends and tight temperature gradient in parts of southwest
Iowa near the front. The HRRR/RAP/SPC HRRR hinting at some light
precip a little farther west initially toward 11Z, however the
general trend is for the light precip to be confined southeast
Nebraska and farth southwest Iowa. Still mention rain, however a
mix is possible on the northwest edge of the precipitation area
Sunday morning.

&&

.SHORT TERM...(Tonight through Tuesday)
Issued at 230 PM CST Sat Dec 16 2017

Potential for light precipitation late tonight into Sunday morning
and temperatures through the period are the main forecast concerns
through Tuesday.

Closed low at 500 mb which was over Mexico at 12Z this morning
continued to lift northeast across TX early this afternoon, while
the kicker shortwave trough was digging toward northern Baja. Mid
level height falls this morning were strongest over CA but also
stretched up farther to the northeast with the wave in the
northern stream across Canada. A fairly decent mid level
temperature gradient was setting up from the central Rockies out
in the Plains, while at 850 mb a warm airmass extended from the
desert southwest into KS and NE. Cooler air was pushing southeast
though behind a surface cold front that should extend from
northern IL back to southeast CO by early this evening.

Lift and moisture will be on the increase later tonight across
the southern part of the forecast area. Some of the high resolution
and other models (GFS and ECMWF) bring some light precipitation
north from KS into our southern zones prior to 6 am Sunday. Will
keep some low chances going there, and continue those through late
Sunday morning. This looks like mainly a light rain event with a
potential for a mix on the northern fringes of the precipitation
shield. Of some concern is amount of low level moisture that could
result in holding down temperatures for Sunday. At this time, have
highs close to a blend of GFS and NAM.

Longer range models are in fairly good agreement that the rest of
the day Sunday and then into Tuesday should be mainly dry. Mild
air will again spread east across the region for Monday, with
highs in the lower and mid 50s. A weak cold front pushes through
the area Monday night which will put highs in the 45 to 50 degree
range in our northern zones but still in the lower 50s near the KS
and MO borders.

.LONG TERM...(Tuesday night through Saturday)
Issued at 230 PM CST Sat Dec 16 2017

Precipitation chances starting late Wednesday night and continuing
through Thursday night will be the main concern in the long term.

At the start of this period there will be a weak closed low
tracking east across the southern Plains and a pretty strong wave
extending from southwest Canada to off the coasts of WA and OR.
That feature then pushes southeast toward the northern Plains and
central Rockies through Wednesday. Wednesday night the flow
becomes more split, with some energy dropping south which forms a
weak circulation that starts to close off over UT. To the north, a
piece of energy will track across the northern Plains, helping
force a cold front through the region. Mid level forcing and
moisture should be adequate for some light rain and light snow
initially, then as the column cools it will turn to all snow.
There are hints of a coupled jet structure Thursday, with the main
jetstreak over the Great Lakes region and a secondary max from
southern AZ toward western KS. The 12Z model guidance was
generally in better agreement than it was this time yesterday, in
regards to snow amounts. The GFS, ECMWF and Canadian models all
bring at least some light snow to the region. This will be
accompanied by much colder air and north winds from 15 to 30 mph.

Temperatures Thursday should be falling through the day, bottoming
out in the 5 to 10 degree range in northeast NE and from about 9
to 15 degrees for southeast NE and southwest IA Friday morning.
Then it looks like temperatures should remain below normal into
Saturday and Sunday. There are signals for light precipitation
next weekend, but those signals are weak and will not include
anything at this time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 530 PM CST Sat Dec 16 2017

VFR conditions are expected to deteriorate to MVFR/IFR between
07Z-12Z at all through sites. Reinforcing cool and moist air will
settle in from the north, meanwhile...a storm system will track
across Kansas. There is some uncertainty with a narrow area of
subsidence between the systems that may hold clouds in the VFR
category...thus this will need to be watched for KLNK and KOMA.
The precipitation from the Kansas will approach KLNK and KOMA
however is currently not forecast to reach them.


&&

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

$$

UPDATE...Zapotocny
SHORT TERM...Miller
LONG TERM...Miller
AVIATION...Zapotocny



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