Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 220443
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1143 PM CDT Wed Oct 21 2020

...Updated for 06Z Aviation Forecast Discussion...

.DISCUSSION...
Issued at 341 PM CDT Wed Oct 21 2020

Forecast Summary:

Increasing chances for rain and drizzle are in the forecast
overnight before a strong cold front brings a chance for some
thunderstorms on Thursday. Much colder air invading behind that
front will certainly bring a hard freeze to all of eastern Nebraska
and southwest Iowa by Saturday morning. The cold temperatures will
get even colder as another strong system brings a chance for snow by
Sunday, with highs averaging almost 30 degrees below normal to start
next week.

Tonight through Thursday night:

Cool easterly low level flow and plenty of cloud cover has kept
temperatures near or below 50 this afternoon. A strong mid level
storm system diving through the Northern Rockies this afternoon will
induce strong isentropic upglide over cooler surface layer beginning
this evening and continuing overnight. Potent theta-e advection on
southerly 850 mb winds approaching 50kt overspreads eastern
Nebraska and southwest Iowa this evening, leading to widespread
areas of at least light rain and drizzle slowly spreading north
through the CWA. Mean SREF MUCAPE of 1000-1500 J/kg suggest some
elevated thunderstorms are possible overnight as well.

On Thursday, surface low strengthens in western Kansas while
baroclinicity increases across eastern Nebraska and western Iowa
along frontal boundary stretching southwest to northeast across
southeast Nebraska and southwest Iowa. Modest instability along and
east of this front should lead to potentially strong thunderstorms,
however models have sped things up a bit and now suggest the
instability axis and front will be exiting our southeast counties by
21Z when initiation is expected. Thus, SPC has moved marginal severe
risk nearly out of our counties. Still could see thunder Thursday
afternoon even behind the front, but risk of severe is low.

System swings to the east Thursday night taking precipitation with
it before sunrise Friday. Strong cold advection behind the front
will provide us a wide range of afternoon temperatures Thursday,
ranging from the 40s in northeast Nebraska to the mid to upper 70s
in far southeast Nebraska and southwest Iowa.

Friday and Saturday:

Cold advection continues Friday, and despite more sunshine, highs
several degrees either side of 40 is all we`ll manage. Then surface
high pressure settling into the region along with cold airmass and
decreasing winds should allow temperatures to bottom out in the 20s
all areas Saturday morning. This will end the growing season across
eastern Nebraska and southwest Iowa.

Increasing clouds and little mixing on southeast low level flow
should keep highs Saturday near 40 again.

Sunday through Wednesday:

Another potent mid level system dropping through the Rockies will
bring our next chance of snow by Sunday, with much colder air to
follow for next week. A majority of model ensemble members show we
will see snow with this system, but there remain differences in
regards to axis of highest snowfall. Most of the ECMWF members
suggest most of the snow will occur Sunday and to our north, with
GEFS a bit farther south and an earlier transition to snow. Our
forecast is a blend of these solutions, with snow beginning Saturday
night in our northern CWA with a gradual change from rain to snow
over the rest of the area later on Sunday. And most solutions keep
snow falling into Monday morning when impacts could be amplified
with the return to work and school.

After snow ends on Monday, much colder air filters south behind
exiting system. We will likely see highs only in the 30s both Monday
and Tuesday before some moderation into the 40s by Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1143 PM CDT Wed Oct 21 2020

IFR conditions settled over the area earlier in the evening and
should remain in place much of the next 18 hours at least. -SHRA
and isolated TSRA will be possible overnight, mainly at KOMA. LIFR
conditions may occur at times later tonight into the mid morning
hours. Some low level wind shear is likely at KOMA and KLNK before
the frontal passage. Gusty north/northwest winds will occur behind
the cold front, with ceilings slowly increasing.

&&

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

$$

DISCUSSION...Dergan
AVIATION...Mead



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