Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 251047

Area Forecast Discussion
National Weather Service Des Moines IA
547 AM CDT Mon Mar 25 2019

...Updated for 12z Aviation Discussion...

.DISCUSSION.../Today through Sunday/
Issued at 314 AM CDT Mon Mar 25 2019

.Overview: Temperatures will rise into the 60s by the middle part
of this week with gusty winds expected on Wednesday. Rain chances,
including thunderstorms, will increase Wednesday night into
Thursday with precipitation lingering into Saturday. Some of the
rain may change to snow Friday night with cooler weather expected
next weekend.

.Details: Upper level low pressure system the talk of the discussion
the last few nights is slowly moving into west central Illinois
early this morning. Still a few light showers or areas of drizzle
over south central Iowa early this morning, but those will quickly
end. GOES-East Nighttime Microphysics RGB shows a plethora of low
clouds over Iowa with some clear spots over northern Iowa. These
clouds will stay with us a good part of the day, especially over
western Iowa as the flow aloft becomes from the northwest with
surface high pressure swinging through the region today into
tonight. As the surface high moves off to the east and upper level
ridging builds over the central US on Tuesday, surface and low level
winds will become from the southwest. Southwest flow and warm air
advection will strengthen on Wednesday resulting in a warm, windy
day. Boundary layer still looks to mix to around 1km, but wind gusts
potential is more muted than last night by about 5 knots or so. With
850mb temperatures of 6 to 8C expected by Wednesday afternoon,
expect temperatures solidly in the 60s across central Iowa with
areas in western Iowa topping 70 degrees. For the Des Moines metro,
spread of guidance ranges from 60 to 75 with current forecast above
the IQR and near the upper end of reasonable guidance. Have trended
the forecast dry on Wednesday despite some theta-e advection and
modest Q-vector convergence passing through the state. At this time,
CMC is the most robust with any rain with the GFS giving token
amounts at best over far southern Iowa. Better chances for rain and
thunderstorms will be going forward from Wednesday night into
Thursday as a cold front moves into the area from the north. Shear
is sufficient for thunderstorms along with large scale forcing, but
instability is weaker compared to the last several runs. This
appears to stem from a faster arrival of the front compared to
past runs with the front stalling over southern Iowa if not
northern Missouri. Where this front ends up will also dictate how
warm Thursday will be with 60s expected south of the front and
possibly over southern Iowa.

As low pressure moves out from the southern Plains toward Missouri,
there will be additional rain chances Friday into a good chunk of
Saturday. Colder air Friday night will allow the rain to change to
snow over part of the state. With surfaces warming earlier in the
week, this will help to offset any accumulations, though some light
accumulations may still be possible. All this liquid is not needed
with soils still saturated across the state and rivers already
swollen if not in flood. Current 00z GFS/CMC/ECMWF consensus would
have the higher amounts over southern Iowa that could eclipse an
inch. Surface high pressure is expected to pass over the region
Saturday night into Sunday providing drier weather with temperatures
slightly below normal.


.AVIATION.../For the 12Z TAFS through 12Z Tuesday morning/
Issued at 547 AM CDT Mon Mar 25 2019

Clouds with pocket of clear sky prevail over the state this
morning. Where there are clouds, ceilings ranging from VFR or
MVFR over northern Iowa to IFR over southern Iowa. Overall,
anticipate ceilings improving into VFR late today or no later than
this evening. In between, there will primarily be MVFR ceilings
with brief periods where the sky may become clear or ceilings lift
into VFR before returning to restrictions.




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