Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 210921
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
421 AM CDT Wed Oct 21 2020

...Updated Forecast Discussion...

.DISCUSSION...
Issued at 420 AM CDT Wed Oct 21 2020

Wednesday and Wednesday night...

Lots of moving parts in the forecast today. System responsible for
record early season snow across parts of Minnesota is now pushing
through Great Lakes and is losing its influence over the CWA.
Quiet northerly surface winds have aided in the development of
some dense fog this morning in southwest Iowa. The fog should lift
by mid- morning. Those winds will turn east over the course of
the day as surface high slides east behind ejecting wave.

At H85, southerly winds will develop by mid-morning and lead to
some stiff WAA. Still not expecting it to mix to surface and have
continued trend of pushing expected highs lower. May manage low
50s at best. Cyclogenesis from ejecting mid-Rockies wave begins
Wednesday night. Frontogenesis at H85 and H7 will produce a band
of rain this evening. Some elevated convection may be enough to
initiate a couple of rumbles of thunder, but generally expecting
just a welcomed rain. Have backed off QPF a bit, but still
expecting 0.2 to 0.4" in southeastern Nebraska and southwestern
Iowa. Expect more closer to DSM.

Under the clouds and continued WAA, temps will slip only
minimally... and in fact may begin to warm after midnight.


Thursday....

WAA from quick southerly winds (20 kts) will race the cold front
approaching from the NW to get as much of CWA into warm sector.
I`ve cooled most highs down from previous forecasts as front
looks quicker to push south. 80F along the Missouri state line is
still possible... but expect northern tier of counties to fall shy
of 50F. With the warmer temps comes dew points of over 60F
allowing CAPE values to climb. Dependent on front timing, could
see CAPE of up to 1500-2000 J/kg, though something closer to 500
is also possible. Shear will be near 40kts either way... so
adequate there. There is an EML to overcome, but potent front is
expected to give it enough of a nudge. Severe hail and winds
possible as the cold air is swept southeast.

NBM continues to underestimate winds on Thursday so have
maintained 30kt gusts both ahead and behind front. But if
anything, I too am on the low side.


Friday and beyond...

Cold air continues to pour in on Friday with north winds 10-20
kts. Temps in the 40s will translate to afternoon apparent
temperatures in the 20s at times. Friday night lows should fall
into the 20s in most locations... the last straw for begonias and
the growing season.

Zonal flow on Saturday will be interrupted by a large trof Sunday.
This will bring another reinforcing shot of cold air and a chance
of both rain and snow... especially over the northern half of the
CWA. Accumulating snow is on the table, though isn`t exactly a
sure bet this far south at this point.

High temps will remain well below normal through the first half of
next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1237 AM CDT Wed Oct 21 2020

The presence of light winds, wet soil, and a moist boundary layer
has yielded areas of dense fog along the MO River, which will
likely persist through daybreak. The possible exception is if
denser cloud cover can move in from the west, decreasing the
amount of outbound radiation. As such, we will maintain the LIFR
conditions at KOMA and adjust upward if conditions warrant.
Otherwise, precipitation chances will increase on Wednesday
afternoon --and moreso into evening-- at KLNK and KOMA owing to
strengthening warm advection across the area.


&&

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

$$

DISCUSSION...Nicolaisen
AVIATION...Mead



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