National Weather Service Raw Text Product

007 
FXUS63 KDMX 010537
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1137 PM CST Thu Nov 30 2023

...Updated for the 06z Aviation Discussion...

.DISCUSSION.../Tonight through Thursday/
Issued at 249 PM CST Thu Nov 30 2023

Key Messages:

- Round 1: A wintry mix overnight into Friday morning with 
light accumulations mainly along and south of I-80
- Round 2: Light rain and snow Friday afternoon and evening once 
again mainly along and south of I-80 with little accumulation
- Round 3: Light rain and snow manly east of I-35 on Saturday night 
with little accumulation

Discussion:

We are entering an active period of wintry weather over the next 
couple days. While three separate rounds of precipitation are 
forecast, each will only result in light accumulation.

Round One: A low is lifting out of the southern plains and into the 
central US this afternoon. By this evening the northern side of 
the low will approach southern Iowa with precipitation expanding 
across southern Iowa overnight. Models are in good agreement with 
timing as precipitation arrives after midnight and departs by late
morning. Precipitation type gets a little messier with soundings 
indicating variations in ice introduction, surface temperature, 
and depth of the warm layer. With much of the lower portion of the
column near freezing, small fluctuations will be impactful for 
precipitation type. The NAM remains most aggressive on freezing 
rain with coldest surface temperatures. GFS and Euro suites 
include better ice introduction, but with surface temperatures 
near freezing, it will be a thin line on rain and snow. As this 
system fights dry air north, expect that the northern cut off 
could be rather sharp from dry to the wintry mix. Better chances 
to any ice accumulations would be far south with rain and snow 
along and south of the I-80 corridor, trending towards all rain 
towards the southeast. 

Round Two: As round one exits east midday Friday, a weak embedded 
shortwave will follow quickly on its heels bringing another quick 
shot at wintry precipitation on Friday late afternoon and evening. 
With less available moisture and a little less forcing, QPF with 
this round is lighter. With warmer daytime temperatures, this 
round is expected as mostly rain, with some snow mixing in 
especially into the evening. Primary uncertainty with this round 
is timing of the second round, as some of the CAMs maintain 
distinct waves while the HRRR has trended towards a more seamless
transition from round one to two. There is also some question as 
to snow accumulations. With the column remains deeply saturated 
thorugh the DGZ, near surface temperatures hover right at freezing
in soundings from Lamoni to Ottumwa. Given good saturation to the
surface, expect little wetbulb influence to cool the column and 
push things one way or the other.

Round Three: After a lull, the parent trough axis passes across the 
area Saturday evening and overnight. Precipitation here reaches 
further north, but recent model runs have pulled the system 
further east with main QPF along and east of the I-35 corridor. 
The primary precipitation type here will be rain, however some 
light snow may mix in overnight Saturday as the column cools and 
ice introduction increases. Any accumulations with this final 
round would be very light, a dusting or so.

Into next week a quick moving shortwave swings across the area on 
Tuesday, delivering another shot at at wintry precipitation. This 
will be followed by a warming trend to finish out the week with 
above average temperatures.

&&

.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1134 PM CST Thu Nov 30 2023

Conditions will continue to deteriorate near KOTM overnight with
lowering cigs and increasing chances for a wintry mix of
precipitation. Conditions will reach IFR at times at KOTM. Light
precipitation may reach KDSM/KALO during the period but there also
may be a period with MVFR cigs on Friday. KFOD and KMCW should
remain VFR. Generally northeast winds during the period, could
become gusty at times south.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon CST Friday for IAZ062-073>075-
082>086-092>097.

&&

$$

DISCUSSION...Hagenhoff
AVIATION...Donavon