Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 161748
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1148 AM CST Sat Dec 16 2017

.SHORT TERM...(Today through Monday)
Issued at 249 AM CST Sat Dec 16 2017

Mild weather today and Monday, bracketing a cooler Sunday and a
small chance for precipitation in our far southeast.

A couple of features of note will be affecting our weather over the
next couple of days. The first is an area of surface low pressure in
the eastern Dakotas this morning, which is forecast to dive
southeast into eastern Iowa this afternoon. Attendant cold front was
developing across South Dakota this morning, and will settle south
into eastern Nebraska and western Iowa this morning. Ahead of the
front, southwest low level flow and 850 temperatures close to 10C
will help to warm temperatures well into the 50s over much of our
southern CWA today. However, with cooling behind front and a
switch to north or northeast surface flow, the northern part of
our area will likely hold in the upper 40s. But still, these
temperatures are well above-normal for the middle of December.

Meanwhile a mid level low pressure area currently in western Mexico
is expected to eject northeast toward the Plains as a stronger
kicker trough settles south along the West Coast and into the Baja.
Significant dampening of ejecting wave as it approaches our area is
shown by model output this morning, with a continued trend to a more
southerly track shown the last few model runs. Thus only a glancing
blow for any precipitation, favoring far southeast Nebraska and
southwest Iowa Sunday morning.

The other affect with this system will to maintain north to
northeast low level winds across eastern Nebraska and southwest Iowa
through Sunday, keeping temperatures much colder than today, but
still close to normal mid-December readings.

Surface winds turn southwest again Sunday night into Monday as a
series of shortwaves roll across the Northern Plains where strong
mid level flow is expected. Plenty of sunshine and favorable
surface flow should push highs toward 50 once again Monday afternoon.

.LONG TERM...(Monday night through Friday)
Issued at 249 AM CST Sat Dec 16 2017

Continued above-normal temperatures will take us through the middle
of the week before a dramatic cooldown and decent chance for
accumulating snow enters the forecast Thursday.

Strongest mid level flow will remain north of Mid America through mid
week, arcing from the Pacific Northwest through the Northern Plains
and into the Great Lakes. A broad shortwave swinging through the
flow will nudge a cold front into the Plains Monday night, turning
winds to northerly here and cooling temperatures into the 40s
Tuesday. Then effects of next significant wave will begin to be
felt as shortwave ridging ahead of it and southerly low level flow
nudge temps back into the 50s Wednesday afternoon.

But then things change drastically. Strong mid level trough, which
is currently a deep closed low just off the west coast of Alaska,
will march southeast as a deep trough into the Northern Plains and
Rockies by Thursday morning. Associated cold push will be entering
northeast Nebraska at that time, with 850 temps forecast to drop 20C
or more from Wednesday evening to Thursday afternoon on strong
northerly winds. We could very well see falling temperatures
Thursday with wind chills dropping toward zero by the evening.

Meanwhile, strong upper level winds greater than 100kt will place
our area under lift of favorable right entrance region early in the
day, then an even more favorable coupled jet regime later. All
models develop significant precipitation, but the exact details are
still way too far out to nail down. Suffice it to say, temperatures
will support snow or a quick change to snow across all of eastern
Nebraska and southwest Iowa, with a good chance of accumulating
snows until dynamics wane late Thursday night. Temperatures will
struggle to reach 30 on Friday, and that may be generous if
significant snow cover materializes.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1138 AM CST Sat Dec 16 2017

VFR likely through at least 03z at all sites. After 03z, broken
IFR conditions moving in from northwest to southeast. Ceilings
will likely begin to lift to MVFR from north to south after 12z.
Primary uncertainties are in overall cloud coverage and timing of
height changes.

&&

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

$$

SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...Barjenbruch/Dusselier



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