Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 100851
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
351 AM CDT Thu Aug 10 2017

.SHORT TERM.../Today through Tonight/
Issued at 349 AM CDT Thu Aug 10 2017

A vigorous short wave trough is passing just north of Iowa today.
The trough has a couple strong short fragments moving through the
base of the system with the first leading to isolated thunderstorm
development over the northeast forecast area early this morning.
The second fragment will help drag a boundary into the state this
afternoon and should lead to additional thunderstorm development
mainly south of Interstate 80 this afternoon and evening.

The current activity is expected to move east of the area over by 6
am. A ribbon of destabilization is forecast to develop ahead of the
approaching boundary with CAPE values exceeding 2000 J/kg in a few
areas. Deep mixing is expected to occur by this afternoon over
southern Iowa leading to high temperatures into the mid 80s and with
dew point values in the low to mid 60s, will result in LCL heights
of 5 kft or greater. Scattered thunderstorms are expected to develop
during peak heating. Any severe weather threat will be relegated to
isolated damaging wind/microburst or large hail potential.

Cooler weather will settle into Iowa overnight as the flow becomes
northerly. Temperatures are again expected to fall to near dew
points and this could lead to patchy fog development, particularly
over the northeast.


.LONG TERM.../Friday through Wednesday/
Issued at 349 AM CDT Thu Aug 10 2017

Bottom Line up Front...
Fairly inactive long term forecast pattern continues. Slight chances
for precip on Monday, but rainfall amounts should be minimal at
best. Temperatures likely to be below normal through the middle of
next week.

Friday through Monday...
Friday begins with high pressure crossing into northern
Minnesota... placing Iowa into northerly flow at the sfc. The past
few nights, models have been advertising an upper low pushing SE
through Canada and into the upper Midwest by Saturday. However,
trends have been to strengthen the sfc high and weaken the upper
low, ultimately delaying its progression into the upper Midwest
and keeping Iowa in dry NE flow into early Sunday.

By Sunday afternoon, the GFS pushes the high into northwestern
Wisconsin, ushering in easterly flow with a slight southerly
component, through 850mb. In the mid to upper levels, models
stretch and flatten the upper low and push it through northern
Iowa near peak heating. There is decent mid-level Q-vector
convergence to support lift. However, there is not enough of a
southerly component to advect abundant moisture into Iowa as sfc
dwpt depressions exceed 20 degrees. In the end, while POPs
currently exist in northern Iowa, it is hard to justify anything
beyond virga to a few hundredths of an inch, as everything should
remain fairly elevated.

Tuesday and beyond...
Aloft, broad anticyclonic flow is slated to reside over eastern
Texas and the Hudson Bay low should be in its place. This
combination will lead to westerlyish flow for Iowa. At the sfc,
the sfc high from this weekend continues to slowly propagate
eastward...making it into the Ohio Valley region by Wedensday.
This will place Iowa into southerly flow/WAA near the sfc. 850mb
temperatures go from around +10C during the weekend to around +15C
by mid-week, which is where they were at during the day
yesterday...yielding temperatures into the low to mid 80s.

By Thursday, the anticyclonic flow in Texas may wobble far enough
eastward to allow moisture and subsequent storm chances to make
it into Iowa. However, the position of the anticyclone is really
tough to pin down this far out, so do not want to get to "excited"
at this time about any noteworthy rain chances in Iowa.


&&

.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1146 PM CDT Wed Aug 9 2017

Isolated showers and thunderstorms will pass through northern into
central Iowa overnight ahead of advancing cold front. Additional
isolated activity is expected on Thursday, mainly in the afternoon
in southern Iowa. However, most locations will remain dry with
widespread VFR conditions with ceilings mid and high level. Any
restrictions to visibilities will be in and around shower activity
from the falling rain. Surface winds will be south to southwest
overnight becoming westerly on Thursday.


&&

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

$$

SHORT TERM...Donavon
LONG TERM...Kotenberg
AVIATION...Cogil



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