625 
FXUS63 KDMX 180420
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1020 PM CST Sun Dec 17 2023

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

.DISCUSSION.../Tonight through Sunday/
Issued at 251 PM CST Sun Dec 17 2023

Key Messages:

- Gusty winds expected overnight and into early tomorrow morning
- Few snow showers/flurries possible northeast overnight (10-20%)
- Cooler tomorrow, then warming back up through Tues and rest of
  the week
- Precipitation returns again late next week

Stratus continues to produce overcast conditions throughout much of 
the area this afternoon with only some clearing over the 
southwestern portions of Iowa. However, the stratus will erode away 
as a weak boundary in northwestern Iowa continues to track southeast 
into the state, albeit with high clouds moving in instead. This will 
be the first of two waves dropping into Iowa tonight, both of which 
causing a ramp up in winds and wind gusts. There will be a modest 
bump in wind with the first wave with wind speeds of 10 to 15 mph 
and gusts up to 25. 

Later tonight, a more amplified wave will drop out of Canada into 
the upper Mississippi River valley region, bringing relatively 
strong winds overnight into early tomorrow morning. This system will 
have strong gradient winds with associated cold air advection 
helping to mix down the 40 to 50 kt low level flow. HREF 
probabilities reflect this, showing roughly a 70 to 80% chance of 
winds greater than 40 mph in northern Iowa and a slightly lower 
chance of about 30 to 40% chance for winds greater than 45 mph, 
which would be exceeding advisory criteria. Therefore, given the 
favorable synoptic setup and the possibility for winds to 
overachieve guidance tonight, have issued a Wind Advisory in 
collaboration with neighbors to my north and east tonight into early 
tomorrow morning. The peak winds will likely be between midnight and 
6 am, so make sure you take some time tonight to tie down any loose 
plastic snowmen or reindeer that could go flying around overnight! 

In addition to the winds, cooler temperatures and a few isolated 
snow showers are expected as this system passes through. The cold 
temperatures and winds will be the more area-wide impact, while the 
snow showers will be contained to the far northeastern portion of 
the area, if that. Moisture availability over our service area is 
quite poor, with a very shallow layer of saturation in the dendritic 
growth zone for a few hours tomorrow morning. However, with the 
strong flow and instability present, short range guidance continues 
to show signs of convective snow showers, which may be able to 
produce snowfall rates capable of overcoming the dry layer. That 
being said, with minimal moisture present, anything more than a few 
flurries or a brief dusting is unlikely.

Winds diminish through Monday afternoon and evening as surface high 
pressure passes overhead, keeping skies clear. Winds then pick up 
again on Tuesday as low pressure produces tightening pressure 
gradients overhead. This will be more of a warm air advection regime 
and doesn’t look to quite reach advisory criteria. However, the WAA 
will help to boost temperatures back into the 40s on Tuesday. This 
southerly flow continues through the rest of the work week as a 
zonal upper level pattern sets up. The next change in weather 
conditions comes at the end of the week, as another shortwave makes 
its way through the state and brings more chances for precipitation. 
Fortunately, (or unfortunately, depending on who you ask) 
temperatures will remain unseasonably warm, causing this 
precipitation to fall as rain instead of snow. The rest of the 
holiday weekend seems active in the long range guidance, but of 
course its still too far out to get attached to any one solution. 

&&

.AVIATION.../For the 06Z TAFS through 06Z Monday night/
Issued at 1020 PM CST Sun Dec 17 2023

Main concern wind. Stronger wind/wind gusts ramping up in southern
MN and northwest IA to impact much of area through 18-21z Monday;
diminishing first northwest (FOD) and then remainder of area by
00z. Looking for light/var aft 00z til end of period. VFR
conditions with only a small chance of a brief flurry/snow shower.
/rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 AM CST Monday for IAZ004>007-015>017-
024>028-036>039-049-050-062.

&&

$$

DISCUSSION...Dodson
AVIATION...REV