947 
FXUS63 KOAX 181722
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1122 AM CST Thu Feb 18 2021

...Updated mainly for 18Z Aviation Forecast Discussion...

.UPDATE...
Issued at 1122 AM CST Thu Feb 18 2021

Made a few changes to the forecast to add some flurries for some
locations today. Cloud temperatures are favorable for ice crystals
to grow easily. Also added some POPs tonight for light snow, in
line with the RAP model output which suggests a bit of light snow
moving from west to east through the area tonight. Otherwise just
tweaked winds and temperatures today a bit. 

&&

.DISCUSSION...
Issued at 328 AM CST Thu Feb 18 2021

Forecast Summary:

Our gradual warming trend for high temperatures increasing from the 
teens today to the 40s by Tuesday remains on track. Precipitation 
chances will be negligible outside of Saturday night and Sunday when 
there is a chance for minor accumulations of light snow. 

Today through Saturday:

Deep mid level trough remained over the central CONUS this morning, 
keeping a fairly cold airmass in place across a good part of the 
country. A series of shortwaves within the larger flow pattern will 
affect our weather the next couple of days, but nothing too 
substantial.

A weak shortwave lifting northeast through western Iowa was 
triggering a few flurries across eastern Nebraska and southwest 
Iowa, but those should end early this morning. A second shortwave 
was noted diving southeast through eastern North Dakota on its way 
to Wisconsin later tonight. This wave will nudge a wind shift 
through our area today, helping to reinforce the cool air already 
here. By Friday mid level heights will begin to rise as main trough 
axis swings toward the Atlantic Coast, with shallow mid level 
ridging developing in the Plains by Saturday.

Clouds covered most of our area this morning, helping to hold 
temperatures in double digits, but single digits were noted where 
clouds had cleared. Expect clouds to start breaking up this morning 
as better mixing accompanies wind shift. But given cool advection, 
highs should remain in the teens despite more sunshine. Winds turn 
southwesterly on Friday, then southerly Saturday, with airmass 
warming significantly as heights rise. 850 temps colder than -10C 
today actually swing to above 0C on Saturday. Thus we should gain a 
few degrees each day, with 20s Friday and near 30 on Saturday.

Sunday through Wednesday:

Another mid level trough is scheduled to progress through the Plains 
Saturday night and Sunday. There is fairly decent agreement among 
model output showing light precipitation breaking out in eastern 
Nebraska and western Iowa Saturday night in warm advection zone 
ahead of wave. There is some question whether ice nucleation will 
occur given lack of mid level moisture shown on forecast soundings.
Therefore both light snow and freezing drizzle are both possible 
Saturday night through Sunday morning before wave exits to the 
east. Average QPF is fairly low, only a few hundredths of an inch,
so any snow or ice accumulation should be minor.

A quick shot of cold advection follows shortwave for Sunday, but 
deeper mixing, afternoon sunshine and a return to westerly low
level winds suggest highs back in the 30s are likely.

For Monday through Wednesday, quasi-zonal mid level flow is 
advertised until Wednesday when a shallow trough enters the Plains. 
A warmer airmass characterized by 850 temps over 5C and favorable 
low level flow puts temps close to or above 40 Monday and Tuesday,
then a little cooler for Wednesday with shallow troughing.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1122 AM CST Thu Feb 18 2021

Some MVFR ceilings and flurries will be possible this afternoon,
mainly at KOFK. More widespread ceilings of 3000-5000 feet along
with areas of MVFR are expected tonight with some light snow or
snow flurries. Highest chances seem to be at KOFK and KOMA. Expect
a return to VFR conditions by sunrise or so Friday.

&&

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

$$

UPDATE...Miller
DISCUSSION...Dergan
AVIATION...Miller