Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 171439 AAA
AFDOAX

Area Forecast Discussion...UPDATED
National Weather Service Omaha/Valley NE
839 AM CST Sun Dec 17 2017

.UPDATE...
Issued at 840 AM CST Sun Dec 17 2017

Messy morning forecast with mixed rain, freezing rain, sleet and
snow. Expanded chances farther north, and kept POPs higher a bit
longer based on recent RAP13 model output. Minor changes to winds
and temperatures.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 306 AM CST Sun Dec 17 2017

A quick shot of light precipitation across southeast Nebraska and
southwest Iowa this morning, and cooler temperatures this afternoon,
will give way to warmer conditions the first part of the work week.

Strong shortwave was shown on water vapor satellite loops lifting
through western Kansas this morning. Broad diffluent flow ahead of
it inducing lift into southeast Nebraska and southwest Iowa was
producing light radar returns approaching the Kansas border, with
more moderate precipitation in central through eastern Kansas.
Precipitation will continue spreading northeast this morning as wave
tracks into southern Iowa. Most short-range hi-res model output was
a little bearish when compared to current radar, but overall trend
in precipitation track and intensity seemed okay. Thus played a
persistence forecast based on current radar and model trends. Will
have northwest edge of precipitation hugging Interstate 80 in
southeast Nebraska, with highest chances closer to the Kansas border
and on into southwest Iowa. Surface temperatures were generally in
the lower to middle 30s in southeast Nebraska, but had fallen below
freezing in southwest Iowa. Meanwhile temperatures aloft were above
freezing and should remain there until wave passes and precipitation
is ending. So we should see a mainly rain or freezing rain event
based on surface temperatures, with a brief mix with sleet or snow
where miso-scale lift is maximized. Am not expecting widespread
impacts with any freezing rain as amounts should be light and
infusion of moisture to surface layer will tend to warm temps toward
freezing or above.

Precipitation will be moving east of the area by noon with gradually
decreasing clouds. Persistent northeast low level flow will maintain
our cooler airmass, keeping temperatures at or below 40 for highs
most areas.

Then a warming trend is expected Monday as southwest low level flow
develops when mid level shortwave trough tracks across the Northern
Plains. Warming 850 temps toward 8C and sunshine should help highs
top 50 once again.

Another cold front will trail Northern Plains shortwave, settling
into our area Monday night, and bringing northerly winds and cooler
airmass for Tuesday. Still not a dramatic cooldown with temperatures
again some 10 degrees above normal for this time of December.

.LONG TERM...(Tuesday night through Saturday)
Issued at 306 AM CST Sun Dec 17 2017

A dramatic shift in upper air pattern will evolve for the end of the
week, with our first chance in a long time for accumulating snow and
much colder temperatures.

Generally zonal mid level flow will remain in place for Wednesday
before strong upper trough dives into the Plains for Thursday
through Saturday time frame. Southerly surface winds and 850 temps
pushing 10C Wednesday afternoon should push highs into the 50s,
perhaps the last time for quite some time.

Then approach of upper trough will induce lowering surface pressures
in the High Plains Wednesday night. Moisture return on strong
southerly winds suggests areas of stratus, drizzle, and maybe light
rain could develop through Thursday morning. Strong cold advection
will commence later Thursday morning when upper trough settles
southeast, pushing arctic frontal boundary through the region.
Potent upper level jet riding over colder surface air will lead to
widespread precipitation across the region Thursday into Thursday
night. Forecast soundings show northeast Nebraska should see all
snow from the beginning of the event as cold air arrives there
before significant precip develops. However the rest of eastern
Nebraska and southwest Iowa will likely see a transition of rain to
a mix to snow through the afternoon and evening. The main trend in
model solutions the last couple of days is to slow this system a
bit, thus keeping more of our area in warm sector longer which
would cut down on potential snow amounts. Still, accumulating snow
is likely over a good part of eastern Nebraska and southwest
Iowa, but it is impossible to put a number on amounts at this
time.

Much colder air will follow after precipitation ends Friday morning.
Highs in the 20s appear likely right into the weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 639 AM CST Sun Dec 17 2017

MVFR conditions are possible this morning at KOMA and KLNK as area
of rain and snow lift northeast bwtween 12z and 14Z at at KLNK and
KOMA between 14Z and 16Z. Ceilings will improve this afternoon to
VFR.

&&

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

$$

UPDATE...Miller
SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...Smith


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