Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 270840

Area Forecast Discussion
National Weather Service Des Moines IA
340 AM CDT Thu Jul 27 2017

.SHORT TERM.../Today through Tonight/
Issued at 326 AM CDT Thu Jul 27 2017

Rain associated with a frontal boundary that moved south through the
state Wednesday has now moved east/southeast of the area. Clouds
have been clearing from north to south with northerly winds bringing
in drier air. A large area of high pressure in place at the surface
across the Dakotas/Minnesota with this area of high pressure
expected to build into Iowa today into tonight. Cooler air will
continue to filter into the state aloft as well, with much cooler
temperatures expected today as H85 temps drop into the low to mid
teens Celsius. Therefore have highs around 80 into the mid 80s. May
have some afternoon CU bubble up especially across the southern half
of the state where drier air has not pushed completely in yet,
otherwise through mainly clear skies expected into tonight. Went
with coolest temps overnight tonight in the far northwest closest to
the center of the sfc high. Some possibility of fog late tonight
again with the sfc high moving in, however also feel that drier air
could preclude development. Therefore left any mention out of the
grids for now.

.LONG TERM.../Friday through Wednesday/
Issued at 326 AM CDT Thu Jul 27 2017

Bottom Line up Front...

This continues to look to be one of the more quiet long-term fcst
periods in quite a while. Near-normal temperatures and no
appreciable weather hazards to speak of beyond the lightning
produced via a slight possibility of a few very isolated/"hit-or-
miss" non-severe thunderstorms each afternoon/evening after Sunday.

Friday through Sunday Morning...

The extensive ridge that will effectively encompass the western
CONUS will begin to settle in near the Oklahoma panhandle. Across
the eastern CONUS, a deep cut-off low/trough will be present over
the Atlantic region. Meanwhile, during the next several days, a 1020
mb sfc high will propagate through Minnesota and into the Northwoods
of Wisconsin. The proximity of the high to Iowa will keep winds very
light...less than 10 kts... into next week. More importantly, this
synoptic setup will serve to keep Iowa into NW to NE flow above 850
mb through the weekend. Resultingly, 850mb temps look to dip down to
the +12C to +15C range...which is around 0 to -1 std dev for this
time of year... suggesting near to slightly below normal temps
through the weekend. Through the past 72 hours, the temp trends have
been slightly downward, so erring on slightly cooler side of

Sunday PM and Beyond...

Long-range models are slowly beginning to cluster around a slightly
slower progression of the sfc high which should be centered
somewhere near the WI/IL border by Sunday PM. This slower
progression has pointed towards persistence into early next week, so
have begun to nudge temps closer to persistence versus the warm-up
that would occur with the increased return flow from the high
being further to our south and east.

Could see a few isolated, weak storms manifest during peak heating
across our north/northwest. However, instability and moisture will
generally be limited. With the high so close to Iowa, shear and a
solid focusing mechanism will be very hard to come by. It will also
be tough to get anything sfc-based, beyond elevated convection. It
may not be until the end of next week until appreciable widespread
precip chances return...which may even be an optimistic at that.


.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1156 PM CDT Wed Jul 26 2017

Main challenges this forecast period are low clouds and fog
through early Thursday morning. At the start of the TAF period,
any remaining showers should be out of the terminals. Otherwise,
areas of stratus and fog prevail from northeast Iowa to west
central Iowa bringing MVFR ceilings and/or visibilities to these
terminals. Did trim back the fog over the northwest as drier air
may be arriving a tad sooner than expected. While fog will
dissipate shortly after sunrise, low clouds are expected to
persist at KDSM and KOTM into mid- morning as a cold front moves
away from the state. After the low clouds lift and scatter, VFR
conditions will prevail.





SHORT TERM...Beerends
LONG TERM...Kotenberg
AVIATION...Ansorge is the U.S. government's official web portal to all federal, state and local government web resources and services.