National Weather Service Raw Text Product

387 
FXUS63 KOAX 181732
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1132 AM CST Fri Dec 18 2020

...Updated Aviation Forecast Discussion...

.DISCUSSION...
Issued at 300 AM CST Fri Dec 18 2020

The primary forecast concerns are potential for some light rain 
or light snow this afternoon and evening, then possible system 
that could bring precipitation to parts of the region Tuesday 
night and Wednesday of next week. 

A fairly strong mid tropospheric trough located to our west will
be moving through the nations mid section today and tonight, with
at least some models showing potential for precipitation. 500 mb
chart from last evening showed 12 hour height falls of 50 meters
or more from MT down into AZ and southern CA. Extensive high
clouds had spread over most of the forecast area with some mid 
level cloudiness as well. Forcing for ascent will increase but 
depending on which model you look at, there is some question if 
the amount of moisture and lift will be enough for saturation. 
Some recent runs of the RAP13, HRRR and even the 00Z GFS showed 
that some light rain could develop in northeast NE this afternoon,
then spread east/southeast this evening. Temperatures during the 
daylight hours will probably be warm enough for just rain, with a 
mix very early in the evening and then just light snow before 
chances exit the area. Will keep POPs mainly from 20 to 40 
percent. These are all behind the weak cold front that will be 
pushing through the region. Southerly winds will shift to the 
northwest. Expect high temperatures today to range from the upper 
30s to the upper 40s. 

The mid level trough axis will push east of the area later tonight
and we will lower POPs to less than 10 percent after midnight. 
Surface ridge axis also builds over the area by Saturday morning. 
Lows tonight should range from the mid teens to lower 20s. 

A couple of ripples will move through the region in generally
northwest mid level flow from Saturday into Monday, but little or
no precipitation is expected. Temperatures will be on the cool
side for Saturday, but should moderate Sunday and then even more 
on Monday. Highs Monday should reach the mid 40s to mid 50s. 

From Tuesday into Thursday, we will see some fairly big changes 
in the pattern as mid tropospheric trough amplifies and moves 
through the region. Temperatures should still be mild on Tuesday 
with highs in the 40s and 50s, but this will be replaced with 
highs only in the 20s by Thursday. There are signals that during 
this transition that we could see some precipitation. The 00Z 
ECMWF was the most bullish with rain/snow, especially Tuesday 
night into Wednesday. There is still a fairly high amount of model
spread in those periods, but we felt at least a small chance of 
snow was needed for the forecast in northeast NE Tuesday night. We
expect better model agreement as we get into early next week and
may add more chances for snow Wednesday if trends remain the same.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1124 AM CST Fri Dec 18 2020

High-level clouds continue to float over the general region, with
the main concern for the TAF period being a weak frontal passage
that is expected to turn winds northwesterly this afternoon and 
some MVFR ceilings that short term models show accompanying it.
Behind the front, winds could gust to around 20 knots around the
KOFK area but could reach the KOMA and KLNK sites. Clouds are
expected to move out of the area over the course of the overnight
hours and should give us a sunny end to the TAF period.

&&

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

$$

DISCUSSION...Miller
AVIATION...Petersen