Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 200902
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
402 AM CDT Sat May 20 2017

.SHORT TERM.../Today through Tonight/
Issued at 359 AM CDT Sat May 20 2017

Large upper trough continues to impact the mid-section of the
country and is currently spinning over NE with fetch of moisture
pushing ahead of it into Iowa. This has resulted in a widespread
showers throughout the overnight hours. Associated surface low is
currently located over north central to northeast KS, with the dry
slot nosing into eastern KS. Upper low set to migrate slowly ENE
into central MN by early Sunday, with the surface low tracking
northeastward through IA and into western WI. This will allow the
dry slot to punch into much of the state through the afternoon hours
and into tonight. Therefore expect bulk of the precipitation to come
to an end early this morning as the waa wing of precip shoves north
and east through the state. May still see some spotty
showers/thunderstorms as the sfc low moves into SW IA, and with
the sfc warm front lifting northward through southern/eastern IA.
System to nearly occlude as it lifts through IA, with the dryline
shoving ENE through central/eastern IA this afternoon. May see
some additional scattered shower/storm development with that
nosing through the area. Majority of precip chances tonight to be
in the def zone region across northwest to northern IA as the
entire system continues to lift north and east.

As for temperatures cloud cover to remain across much of the CWA
today into tonight, with some breaks possible in the far south/east
as the warm front lifts northward. This should allow sfc temps to
pops up quickly in that region, otherwise remainder of the CWA will
struggle to warm much today with highs only in the upper 40s to
upper 50s. Push of colder air into the state on the backside of the
system tonight as H85 temps actually drop below freezing. However
low clouds expected to be across the CWA so should limit the temp
drop with lows mainly in the 40s tonight.


.LONG TERM.../Sunday through Friday/
Issued at 359 AM CDT Sat May 20 2017

Sunday...
Parent upper low described in the short term slated to trek
northward, making it to the Canada/Minnesota border by 00z Mon.
00z model runs cluster well enough to where general consensus
blend reliable...with less emphasis continuing to be placed on the
NAM. Associated sfc low to be located over the Northwoods of
Wisconsin by 00z Mon.

The past few model runs have been persistent with wrap-around
stratus covering Iowa most of the day. Now seeing the whites of the
eyes of the clouds, must buy in to stratus...especially across
northern to northeastern Iowa. As advertised in yesterday morning`s
AFD, have followed through on expectation to lower max temps 5
degrees vs guidance. Now have highs in the 50s down to Creston and
Ottumwa. Still may have a degree or two to shave off and could
probably even trim a few additional degrees more across the
north/northeast given higher likelihood of denser stratus during
daytime heating. Cloud thickness depths should generally not be high
enough to warrant drizzle mention beyond perhaps the
north/northeastern tier of counties.


Monday into Tuesday...
Models showing high run-to-run consistency in dropping a
shortwave southeastward through Canada and towards the upper
Midwest. Models also showing great run-to-run consistency in
"phasing" this shortwave with the upper low from this weekend.
Accompanying sfc low should be near the IA/MN border by 21z
Mon...with attendant cold front dropping south/southwestward
through the western portion of the DMX CWA. MLCAPE values approach
1000 J/KG ahead of the boundary...which would serve as a focusing
mechanism for thunderstorm development. With dewpoints in the mid
to upper 40s and sfc temps in the mid to upper 60s, sounding
analysis confirms any storms should be elevated, effectively
confining the threat to marginal hail chances, with a low strong
wind threat. This system will propagate eastward overnight,
pushing east of the DMX CWA by 09Z-12Z Tue.


Wednesday and Beyond...
Behind the Tuesday system, ridging/thermal ridging will have been
building over the intermountain west. Long- range models showing
good agreement in placing sfc high over the Midwest by 06Z
Thursday...with the thermal ridge crashing down over Iowa Thursday
into Friday. If this solution holds, temperatures will need to be
bumped up several degrees.


&&

.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1145 PM CDT Fri May 19 2017

Widespread IFR to LIFR cigs will be over Iowa through much of
Saturday before improving late. A couple waves of showers and a
few thunderstorms through the period that may reduce vsbys at
times. A boundary will move through late afternoon and into the
evenings and bring a switch in wind direction. Drier air will
arrive with the boundary and cigs will begin to improve.


&&

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

$$

SHORT TERM...Beerends
LONG TERM...Kotenberg
AVIATION...Donavon



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