154
FXUS63 KDMX 031932
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
232 PM CDT Fri May 3 2024

.KEY MESSAGES...
- Storms and showers arriving after midnight tonight near and
  east of Highway 71 - severe risk is small hail, gusty winds
  possible
- Stormy weather returns later Monday into Monday night with severe
  weather possible, perhaps redeveloping later Tuesday
- More clouds than sunshine, fleeting showers, and trending
  towards seasonal levels mid to late next week

&&

.DISCUSSION...
Issued at 232 PM CDT Fri May 3 2024

Morning fog was rather impressive from visible satellite this
morning highlighting the numerous river valleys across portions of
Iowa. This fog was able to fully dissipate between 9 and 10am. Now,
upper level water vapor imagery shows a parent upper low that is
spinning into the Manitoba province. Dropping through the
Intermountain West into the northern/central Rockies around this
parent upper low is the shortwave trough that will bring
thunderstorms into Iowa late this evening and our forecast area
after midnight. An area of instability up to around 500 J/kg of
MUCAPE is expected ahead of a cold front along with steep mid-level
lapse rates and sufficient shear for storm organization. Forecast
soundings show storms will be elevated in nature and thus pose a
risk of primarily small to around 1" hail with isolated gusty winds
possible. Convective allowing models show a few healthy updraft
helicity tracks entering western Iowa, but their strength quickly
wanes as they move toward central Iowa. Further, even the more
aggressive WRF-ARW and FV3 are showing wind gust potential topping
out between 30 to 40 knots. Overall, the marginal risks by the Storm
Prediction Center on day 1 into day 2 seems to handle this risk
well. Rainfall amounts look to be highest over western into portions
of central Iowa, mainly east of I-35 with 12z HREF localized
probability matched mean values of half an inch with small areas of
1.25 to 2 inches possible. The water issues over our southeastern
forecast area - namely Monroe and parts of Appanoose and Wayne
counties including the Cedar Creek basin - may then be spared from a
return of water problems. These storms will be over eastern Iowa
around midday leaving behind breezy winds from the north-northwest,
decreasing clouds, and highs in the 60s in most central Iowa cities.

With a clear sky over much of central Iowa, decreasing winds, and
the rainfall from Saturday morning, we are looking to be set up for
another round of dense fog. However, drier air will be pulled into
Iowa and brings into question whether this will negate the other
favorable factors. After any fog dissipates Sunday morning, weak
ridging will pass overhead and a southern stream wave continues to
trend south of the state with the latest NBM PoPs staying south of
Iowa. At the same time, a potent shortwave trough over the western
CONUS will move eastward toward the region and take on a negative
tilt as it lifts northeastward into our region Monday into Monday
night. Low level kinematics will be favorable at 40 to 50 knot
Monday night in the region with resulting deep layer shear looking
healthy for organized convection. This wind field will draw moister
air into the region with low 60 surface dewpoints making their way
to near if not into at least southern Iowa later Monday. MUCAPE
values will be over 1000 J/kg and mid-level lapse rates rates will
be steep around sunset Monday, but both are forecast to diminish
into the evening to some degree. Forecast sounding continue to show
an elevated warm layer that may keep storms elevated; however, given
the strong kinematic fields in the 0-3km layer, cannot rule out a
tornado risk with any line of storms if the orientation can become
favorable to the low level shear vector. So, at a minimum, at least
strong storms look favored, especially over the western half of the
state Monday night, with severe weather possible. Like yesterday,
SPC maintains probabilities largely southwest of our area on Monday
and southeast of our area on Tuesday. Latest Colorado State`s
machine learning random forest outlook and CIPS Experimental Analog-
Based Severe Probability Guidance continues to paint 5 to 15%
probabilities of severe over more of central Iowa each day lending
credence to the idea of some strong to if not severe storms in
portions of our forecast area.

The strong to severe storm risk may persist Tuesday afternoon given
the SPC, CIPS, and CSU mentioned above, but if things speed up then
this may all be pushed off to the east on Tuesday. Wednesday through
Friday has broad brushed PoPs in our current forecast as the
shortwave trough that will bring our storms chances the first two
days of next week will lift up and meander over the Montana and
western Dakotas area. This will keep weak shortwaves passing over
the state and thus keep varying degrees of clouds, fleeting showers,
and temperatures trending closer to normal in the 60s by late next
week. Severe weather Wednesday through Friday looks unlikely as the
instability will be away from the state.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1234 PM CDT Fri May 3 2024

VFR conditions will prevail through this evening at the
terminals. Thereafter, an area of showers and thunderstorms will
move into the state from Nebraska. Have introduced a few hour
period of TSRA at DSM and VCTS at FOD where confidence is
highest in thunder occurrence. Other sites have just maintained
SHRA, or VCSH as the rain departs. Thunder as well as impacts to
ceilings and visibility will need to be further assessed in
updates. After the rain and storms depart, winds from the
north-northwest will turn breezy.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Ansorge
AVIATION...Ansorge