Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 300451

National Weather Service Des Moines IA
1151 PM CDT Thu Sep 29 2016

...Updated Aviation Discussion...

.SHORT TERM.../This evening through Friday/
Issued at 334 PM CDT Thu Sep 29 2016

Little of concern tonight outside of possible fog redevelopment.
The Ohio Valley upper low should remain nearly stationary with
clear skies across Iowa. The broad low level cyclonic flow
continues to drawn in some lower humidities, especially east,
however the latest RAP shows somewhat higher 0-500m RH north and
west. This is also where early morning stratus and fog lingered so
have introduced some patchy fog wording there early in the morning
with clear skies and light wind.

.LONG TERM.../Friday night through Thursday/
Issued at 334 PM CDT Thu Sep 29 2016

The more likely window for sensible weather through this period
will be toward the middle of next week, although the current
Ohio Valley upper low may just brush Iowa with light precip over
the weekend. The models are in good agreement drifting the system
back to southern Lake Michigan by late Saturday. The forcing will
be neutral or subsident but increasing moisture 3km and below may
be sufficient to squeeze out some light showers east. The system
should finally depart to end the weekend as the western CONUS
trough advances. This will increase temps and moisture somewhat as
return flow begins and ridging enters Iowa. The GFS and ECMWF are
now fairly consistent and suggest deep forcing increasing west to
east Tuesday Night into Wednesday. Timing is still somewhat
suspect however with the ECMWF frontal passage much faster, so
while the best window appears to be around Wednesday have lingered
some low PoPs east into Thursday. Instability looks weak
regardless of the solution, but both deep and shallow shear are
quite high. This suggests somewhat of a weak, subtle fall QLCS
tornado threat if diurnal timing is favorable due to the high
shear values 3km and below.


.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1147 PM CDT Thu Sep 29 2016

The main concern is the incoming stratus, likely MVFR, by Friday
afternoon and into the evening. Upper low over the Great Lakes
looks to retrograde slightly northwestward toward Iowa during the
day Friday. A good fetch of low level moisture moves into eastern
Iowa during the morning and looks to impact ALO/OTM around midday
and even MCW early Friday afternoon. BUFR soundings suggest MVFR
stratus deck with some weak mixing likely to develop. The surface
pressure gradient tightens enough to keep mention of gusts during
the afternoon. Have MVFR ceilings during the end of the TAF
period as once the stratus sets in, it looks to linger for much of
the weekend.





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