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567 
FXUS63 KDMX 191134
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
634 AM CDT Tue Oct 19 2021

.SHORT TERM.../Today through Tonight/
Issued at 256 AM CDT Tue Oct 19 2021

.Short Term /Today through Wednesday/...

Forecast Challenges: 

 ...Extend of precip and thunder/svr chances Wednesday   
 ...Cool Down into late week 
 ...Changing evolution of weekend/early next week storm

Confidence through Wednesday:  Medium

Little impactful weather expected today.  Retreating high over the 
lower Ohio River Valley will continue drifting east today as low 
pressure over the Rockies begins to get more organized.  Weak system 
over Colorado now with a surface low with a 2 part H850 low over 
central and western Colorado.  Both aloft and at the surface, a weak 
warm front/trough is pushing north across Iowa tonight with patchy 
mid to high level clouds moving through presently. These clouds 
should be nearly east of the area by 18z with generally mostly sunny 
skies for the balance of the afternoon hours. Despite these high 
clouds, H850 temperatures are expected to warm about 3C higher this 
afternoon than Monday afternoon. Though we will not realize the 
entire warm nose in the sounding, mixing up to about 865 mb should 
help push afternoon highs well into the 70s again this afternoon; 
especially given the generally continued dry conditions across the 
region.  By tonight, the Colorado low will be tracking into eastern 
Nebraska between 00 and 06z with rather strong warm air advection 
and H850 low level jet of 35 to 40kts across southern Iowa. As the 
low tracks northeast overnight into northwest Iowa, elevated 
convection is anticipated to break out along the upper level warm 
front in northern Iowa and southern MN, southeast South Dakota. 
There may be some shower or isolated thunderstorm activity also 
flaring east into central and eastern Iowa between 06 and 12z, and 
again from 12 to 18z, though chances will remain low there. There 
remains some uncertainty as to the exact track of the low across 
northern Iowa Wednesday. Most of the models take it between US 20 
and the Iowa MN border. The proximity of the low/occluded front will 
be key to afternoon thunderstorm redevelopment. SPC has included a 
marginal risk in northwest Iowa through 12z Wednesday as lift near 
the center of the upper level low may enhance a low risk of hail. As 
we move into the late morning and afternoon, the low tracking in 
northern Iowa will have the same impact as strong mid level warm air 
advection, 500 to 1000 j/kg mucape and 40kts shear combine for a 
threat for a few rotating storms with hail. Again, with the varying 
tracks of the low, the higher risk of the elevated storms will be 
along the occluded front near the sfc low and that will need to be 
narrowed down a bit in the next 24 hours as the track of the low 
becomes more certain. There will also be an area of storms 
developing along and ahead of the cold portion of the front over 
eastern Iowa. The bulk of that activity will likely occur just east 
of our forecast area. Highs Wednesday will be cooler over the region 
with upper 60s to lower 70s east and lower 60s northwest and west as 
the cooler air sweeps into the area behind the low. Winds will also 
pick up in the afternoon with westerly winds gusting to near and 
over 30 mph from I35 and west. 

.LONG TERM.../Wednesday through Monday/
Issued at 256 AM CDT Tue Oct 19 2021

Confidence: Medium...Lowering into the Weekend

As the elongated trough/low continues to pull northeast into 
Wisconsin and northeast Iowa by 12z Thursday, wrap around moisture 
and colder air will swing through Iowa. Clouds will again fill in 
across the region Wednesday night with the advancing cold air and 
some showers/drizzle will also be possible. A secondary cool 
front or trough will be across central Iowa at 12z with clouds 
lingering for most of the day over central sections, all day in 
the southeast and through about noon over the north. H850 
temperatures drop to 5C in the southeast and remain about 3-4C in 
the north by late day. With some mixing expected, highs will be 
capped in the lower to mid 50s north and in the mid to upper 50s 
in the south. The GFS, Euro and GEM all shoot another weak short 
wave southeast into the area already on Friday. Clouds, a small 
chance for sprinkles and cool H850 temperatures will hold 
afternoon highs to near 50 north while central Iowa nears the mid 
50s and the southwest the upper 50s by days end. The bulk of the 
clouds are likely to clear northeast areas by sunset with another 
band of clouds moving into western and southern areas as some warm
air advection aloft tries to return into Saturday morning. We 
continue to monitor the chances for frost and freeze conditions 
Friday night into Saturday morning. At this time, the most likely 
areas would be the north and northeast valley areas with 
temperatures around 30 north to the lower 30s into the Iowa and 
Cedar River Valleys. 

As the weekend rolls around, the operational models begin to 
diverge. The GFS is now speeding up the southern stream low and 
pulling it rapidly north into Iowa by Sunday morning, while the Euro 
is still 24 hours slower. The GEFs, like the GFS, has rain rapidly 
expanding into Iowa by 12z Sunday as well. The GEM is also swinging 
the low more quickly north into Sunday with a broad area of warm air 
advection rain/potential thunder through the day. With differences 
becoming more stark between the Euro and the other guidance, its 
safe to say that rain will occur between Sunday into Monday, but the 
timing still needs to be addressed in more detail. With warmer air 
aloft following the push of warm air advection, highs Monday will 
begin to tick up again and should reach the mid 60s southwest, while 
areas central and north will reach the lower to mid 60s by late day 
with lingering showers. 

&&

.AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/
Issued at 634 AM CDT Tue Oct 19 2021

VFR conditions expected through the period with mid level deck
arriving aft 08z north sites. Warm air advection showers possible
aft 08z northwest and 10z east. Otherwise, winds mix to near 20kts
aft 17z today, relaxing around 00z. /rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...REV
LONG TERM...REV
AVIATION...REV