Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 281132

National Weather Service Des Moines IA
632 AM CDT Wed Sep 28 2016

...Aviation Update...

.SHORT TERM.../Today/
Issued at 333 AM CDT Wed Sep 28 2016

Going forecast has seen little change with this package issuance.
The closed upper level low continues to slowly work southward,
currently centered over east-central WI and should drop into
Indiana by the afternoon. In the mean time, cloud cover has
overtaken the northeast half to two thirds of the state and should
slowly continue to spread through the day before diminishing in
the evening as the low pulls away. Do not anticipate precipitation
through the forecast area, however a few sprinkles may be possible
in the far east as a series of vort maxes move around the system.
Morning wave should remain east, late morning/early afternoon wave
has the most potential to affect the area. With confidence
relatively low, and nothing more than sprinkles possible given the
stable environment, the forecast remains dry. Limited mixing with
cloud cover should keep winds from tapping into mid 20s kt gusts,
however even mixing to around 900mb will likely result in
occasional 20 kt gusts. With cloud cover, northerly winds firmly
established and mixing to only around 900mb anticipated, dropped
highs a degree or two into the lower 60s. Afternoon mixing depth
will determine whether or not that was the right play.

.LONG TERM.../Tonight through Tuesday/
Issued at 333 AM CDT Wed Sep 28 2016

Little change to the going forecast. Main chances for precip will
come toward late in the period. In the meantime...dry conditions
and seasonable temperatures will prevail.

The forecast period will begin with the deep upper-level low
located over the southern Great Lakes region. It is progged to
drift southward, reaching the middle Ohio River valley by Thursday
morning. It will remain there through Friday night, at which time
it will begin drifting northward again toward the southern Great
Lakes by Saturday evening. As the low returns northward, forcing
and moisture will be sufficient for cloud cover to spread back
into the CWA from the east. Have some slight chance POPs across
the far eastern CWA during the day on Saturday in conjunction with
the returning upper-level low.

The best chances for precip during the long term period will be
from Monday into Tuesday (actually Wednesday but Tuesday ends the
long term period. Longwave trof comes onshore across the western
U.S. during the day on Sunday and then sends a potent shortwave
trof across the Rockies toward our CWA by Tuesday. Surface
reflection will be a frontal system east of the Rockies. Warm air
advection will initially drive the precip chances on Monday, with
the CWA in the warm sector on Tuesday. TSRA will be possible given
the instability for both the warm air advection coincident with
the advancing warm front, as well as precip in the warm sector. By
00Z Wednesday, the surface cold front will have reached the
vicinity of the Missouri River. Both instability and 0-6 km shear
values suggest the potential for severe weather. Thus, this risk
will have to be continued to monitored.


.AVIATION.../For the 12Z TAFS through 12Z Thursday morning/
Issued at 628 AM CDT Wed Sep 28 2016

Main concern through the TAF period will be timing MVFR CIGs
across the sites. Already MVFR at KMCW/KALO/KFOD and on the door
steps of KDSM/KOTM. While IFR CIGs exist in northwest Iowa, not
expected to affect KMCW/KALO. CIGs will lift during the morning
and afternoon, right around the MVFR/VFR cut off, but have all
sites seeing VFR as winds should help mix and lift. Clouds will
slowly dissipate then through the evening and overnight. Winds
will be gusty during the day, to around 20kts at times, out of
the north.




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