FXUS63 KDMX 191917

AFDDMX



Area Forecast Discussion

National Weather Service Des Moines IA

217 PM CDT Tue Aug 19 2025



.KEY MESSAGES...



- Areas of fog, possibly dense, returns tonight, mainly north.

  Visibilities under 1 mile possible.



- Nonzero chance for showers across the south Wednesday.



- Next best window for storms is late Friday, mainly south (~30%

  chance of precipitation).



&&



.DISCUSSION...

Issued at 212 PM CDT Tue Aug 19 2025



High pressure has set in behind the departing cold front from 

yesterday, which will hold mild and calm weather for today and 

tomorrow. We'll be able to mix out efficiently this afternoon thanks 

to the dry air provided by the high. A subtle synoptic feature will 

graze northeast Iowa this evening and profile lapse rates are steep 

enough to give a chance of at least some showers; the depth of 

saturation is too shallow for more upscale growth. Thanks to the 

light winds, fog will again be possible in the morning hours, 

especially in the northern half of the state. The LAV guidance 

highlights this well with visibilities for MCW and ALO dropping 

below 3 statute miles in the early morning.



The weather will remain relatively unchanged for much of the work 

week. With the upper-level ridge parked in the High Plains, the 

thermal ridge will just graze western Iowa, keeping highs in the 

upper 80s to near 90 degrees. High pressure will sit over the 

eastern half of the state, this being beneath northwest flow. Highs 

in this portion of the state will be closer to the 80 degree mark, 

with a least patchy fog in play through Thursday morning. More 

convectively-driven showers will be possible Wednesday afternoon 

around peak mixing.



The ridge will attempt to pivot over on Friday, but will be 

interrupted by a deepening trough seen over the PNW today. This 

trough will develop a closed low, increasing height falls and wind 

speeds in the region. It will stack in southern Canada by Friday, 

subjecting Iowa to the effects of its cold front. The consensus seen 

right now by models is the front being somewhere in central Iowa 

late Friday afternoon. F vector convergence is stronger in the 

southern/southwest part of the CWA, making this the more likely spot 

for convection. On the synoptic scale, the upper-level jet will drop 

down into the state, increasing divergence and bulk shear. LLJ 

support will be cut off after Thursday night due to high pressure in 

the Central Plains, reducing the amount of low-level moisture and 

concentrating the shear in the mid and upper levels. 0-6km bulk 

shear vectors will start orthogonal to the front and over 25kts and 

MUCAPE values will be around 1500 J/kg. There could be some 

supercells initially, but due to the speed and evolution of the 

front, they would quickly congeal into a line. Threats will start as 

large hail and damaging winds, then become solely a wind threat. The 

low-level shear is weak (<10kts) which lowers the confidence in any 

tornado threat (due mostly by the lack of a LLJ). The CSU MLP has a 

<15% outlook across the state, which works well given the 

uncertainty of available moisture. Rainfall amounts will stay under 

an inch.



Behind the front, a big pattern change is in store starting this 

weekend. The upper level closed low is slow to leave the Great Lakes 

region, locking Iowa in northwest/northern flow through at least the 

middle of next week. Highs will be in the 70s and the main moisture 

axis remains south of the state.



&&



.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...

Issued at 1231 PM CDT Tue Aug 19 2025



Pockets of MVFR cigs will quickly lift in the next hour. Light

and variable winds through the TAF period, and predominantly

northerly. Have trended more aggressive in fog potential as

guidance bring IFR cigs to northern sites tonight. Additional

MVFR cumulusformation possible in the morning hours tomorrow,

but left as few of SCT.



&&



.DMX WATCHES/WARNINGS/ADVISORIES...

None.



&&



$$



DISCUSSION...Jimenez

AVIATION...Jimenez