982 
FXUS63 KOAX 191715
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1215 PM CDT Tue Oct 19 2021

...Updated Aviation Forecast Discussion...

.DISCUSSION...
Issued at 327 AM CDT Tue Oct 19 2021

Forecast Summary:

We'll see one more warm and windy day today before strong low 
pressure system brings a chance for showers and thunderstorms 
overnight into Wednesday. Much cooler air will follow this system to 
end the week. We should warm a bit for the weekend, but rain chances 
return by Saturday night as well.

Today through Wednesday:

Upper low scheduled to move into the region tonight and Wednesday 
was noted on water vapor and RAP objective analysis spinning east 
through Utah this morning. Broad diffluent mid level flow ahead of 
it was evident across the Plains as a mid level accas field was 
growing from central Kansas into Nebraska. Paltry moisture this 
morning should keep any precipitation at bay through the afternoon. 

Surface cyclogenesis was beginning in northeast Colorado this 
morning, and will deepen through the afternoon as it moves toward 
central Nebraska and Kansas. Thus strong southerly winds will again 
occur today across eastern Nebraska and southwest Iowa. Surface dew 
points this morning were in the lower 40s, and are advertised to 
increase toward 50 this afternoon. Therefore minimum humidities 
should remain above 30 percent and less favorable for any fire 
weather concerns today despite strong surface winds.

As upper low moves closer this evening, strong theta-e advection 
will ride isentropically through eastern Nebraska, converging near 
SD/NE border region after midnight where cold core of upper low will 
be approaching. Lapse rates over 8 C/km are advertised by 09Z, with 
mid level instability (MUCAPE) ranging from near 500 J/kg near I-80 
to close to 1500 J/kg near the SD border. Strong cloud-layer shear 
is noted as well, suggesting some supercell structures could occur 
if storms fire late tonight. Given elevated nature of storms, hail 
will be the primary threat.

Cold core drifts east during the day Wednesday, keeping lapse rates 
steep across at least our northern CWA and an attendant chance for 
convection through the afternoon. Though better forcing will 
translate eastward into northern Iowa through the day.

Temperatures will be lucky to gain much from overnight lows in 
northeast Nebraska where strong cold advection and cloud cover will 
be prominent through the day. Farther south we may rebound a bit 
with more sunshine, but likely topping out early in the afternoon 
before slipping a bit late in the day.

Thursday and Friday:

A cooler atmosphere settles across the region Thursday and Friday 
with relatively light surface winds. Little mixing is expected in 
this environment, so highs slide to below-normal both days. And 
overnight lows both Thursday night and Friday night may slip well 
into the 30s for much of our area, signaling frost or freeze 
potential.

Models continue to indicate shortwave dropping southeast Friday 
morning, but have become bearish on precipitation. Thus will keep 
this period dry.

Saturday through Monday:

Mid level heights rise in the Plains on Saturday, ahead of shortwave 
scheduled to arrive Saturday night or Sunday. Timing and strength 
differences between models leave confidence low for timing of 
potential precipitation into the region, but a majority of model 
output shows rain at some point between Saturday night and Sunday 
night. Until there is more clarity, will maintain small rain chances 
during all those periods.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1153 AM CDT Tue Oct 19 2021

Current satellite showing clear skies over the region. LLWS threat
will be an issue at all terminals overnight. As for KOFK, a storm
system moving through the region tonight will be the focus for 
TSRA activity mainly over SD tonight with a chance a few storms 
may penetrate into northeast NE. As of now though, do not believe 
any storms will push far enough south to affect KOFK. However, 
appears that MVFR cigs will move into KOFK toward 12z and prevail 
the remainder of the morning. 

&&

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

$$

DISCUSSION...Dergan
AVIATION...DEE