024 
FXUS63 KOAX 291745
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1245 PM CDT Wed Sep 29 2021

...Updated Aviation Forecast Discussion...

.DISCUSSION...
Issued at 400 AM CDT Wed Sep 29 2021

As of 4 AM, temperatures are relatively mild under increasing 
cloud cover. Most locations are in the mid to upper 60s, with some
50s in western Iowa where clouds have been a bit more sparse this
morning.

Persistence should be thrown out for today as change is already
upon us. After two days of record autumnal heat, high temps will 
be perceptibly cooler under the increased cloud cover. There are 
already some showers in Nebraska's panhandle in response to the 
ejecting shortwave. Have slowed and reduced POPs a bit for today,
with the best chances in northeast Nebraska. Those chances will 
grow in that area until peaking near 80% after midnight. Severe 
weather isn't expected - shear is lacking - but lightning thunder 
and some 40-50 mph gusts are possible. 

Our biggest concern is the marginal threat of heavy rains, as
reflected in WPC's Day 1 and Day 2 ERO. Precipitable water values
will be peaking at 1.5" or so, which would be in the 98th
percentile in late September. Current QPF forecast suggests 1-2"
for much of eastern Nebraska... with 0.5 to 1.0" for western Iowa
and the Omaha metro. It'll help drought conditions, but is too
late for those harvesting. 

The rain and associated front's progress east is impeded by a bit
of a blocking ridge so those rains will be slow to exit the CWA 
on Thursday night. 

More rain is possible on Friday with more energy ejecting NNE, 
though better chances are forecast southeast of this area. 

Saturday brings better chances with what looks like another 
cut-off low sweeping out of the Four Corners area. POPs top out 
at 60% south of I-80 with that system. 

Through it all, temps will be markedly cooler than they have been.
Today will be a bit of a transition day from the record heat of
the past two days to regular 70s and even 60s for the remainder of
the forecast. Expect highs from the lower to mid 80s today. 

The rest of the forecast is cooler with the instability keeping 
plenty of clouds around, rain chances pocked across the forecast,
and regular NNW winds. Those NNW winds become increasingly common
this time of the year. Eppley's wind rose climatology shows NNW 
winds are recorded about 18% of the time in September, 24% of the 
time in October. Their climatological peak is in January when 
about 1/3 of all winds recorded out of the NNW.

Sweater weather approaches! 

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1233 PM CDT Wed Sep 29 2021

Rain and thunderstorm activity should continue to affect 
northeast Nebraska through at least 22Z today. Precipitation 
should then decrease in coverage between 22Z today and 05Z 
Thursday, before gradually increasing again after 05Z. Widespread
thunderstorm activity is possible between 08z and 15Z Thursday. 
Storms are almost certain to affect the TAF sites (KOMA, KOFK & 
KLNK) during this period, but confidence in the exact timing 
remains low. Therefore the TAFs don't include thunderstorm 
activity at this time. Expect storms to be added to the TAFs as 
confidence increases.

Mixed cloud bases are expected over the region through 08Z 
Thursday, with VFR conditions away from rainfall and MVFR 
conditions in the vicinity of any storms or rain showers. MVFR 
conditions should become the prevailing state across the region
between 08z and 15Z Thursday. Winds should remain light over the 
region, with southeast winds gradually transitioning to north 
winds between 06Z and 15Z Thursday.

&&

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

$$

DISCUSSION...Nicolaisen
AVIATION...Albright