Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 072333

Area Forecast Discussion
National Weather Service Des Moines IA
533 PM CST Thu Dec 7 2017

...Updated for 00z Aviation Discussion...

.SHORT TERM.../Tonight through Friday/
Issued at 300 PM CST Thu Dec 7 2017

Deep cyclonic flow continues for the eastern two-thirds of the conus
as an upper level low churns over the Hudson Bay. Numerous
shortwaves embedded within the mean flow aloft will keep our weather
fairly active and progressive through the forecast. One such wave
will push a weak front through the cwa this evening and overnight.
Stratus clouds filter in from the north behind the front, and
possibly even a few flurries over north central Iowa where some
moisture will extend up into the -12C to -15C layer. A warm up back
to near normal highs is expected tomorrow, although more widespread
cloud cover across the north may hold temperatures in the 20s
through the day along with a chance for a few lingering flurries.

.LONG TERM.../Friday night through Thursday/
Issued at 300 PM CST Thu Dec 7 2017

A more robust shortwave quickly dives south through the Upper
Mississippi region Friday night and forces another cold front
through the area. Strong pressure rises and cold air advection
behind the front will lead to the development of gusty northwest
winds. Bufkit soundings show winds of 40-45kt near the top the
mixed layer, so it shouldn`t be too difficult to achieve gusts in
excess of 30 mph at the surface. The strongest gusts are likely
north of I-80 where gusts may meet borderline wind advisory
criteria for a 2-3 hour period behind the front. In addition, most
hi-res models support the potential for light snow in our
northern zones Friday evening. A dusting to a couple tenths of an
inch of accumulation is possible for areas along and east of a
Mason City-Waterloo line, but most measurable snowfall should stay
north and east of the cwa. Dry air should limit snow chances
further to the south and west.

A leap back into the 40s and low 50s is expected Sunday as warm air
advection ramps up ahead of a shortwave dropping into the northern
Plains. However, the warm up is short lived as the wave and
attendant cold front quickly dive south. Non-diurnal temp trends
look likely for Monday with highs occurring either at midnight or
during the morning hours followed by blustery conditions with
steadily or falling temperatures. Some light snow is possible Monday
morning, but again the more favorable lift and moisture slides east
of the forecast area. Little change is expected to the prevailing
synoptic pattern through most of next week. The timing of any
perturbations in the mean flow aloft becomes quite unpredictable
toward the middle of next week as deterministic models and their
ensemble members all exhibit a high degree of spread. Given the
current pattern would not be surprised to see additional chances for
light snow and reinforcing shots of cold air, but the predictability
of such events is too low to have any confidence at this time.


.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 531 PM CST Thu Dec 7 2017

Medium confidence in VFR category TAF forecast at all sites. Have
"nuisance" flurries moving in from NW to SE across Iowa, beginning
around 08z in northern Iowa, making it to KDSM at around 13z. At
this time, it does not appear flurries will reduce vsbys below 6
SM. Big mitigating difference in tonight`s flurries is that winds
will only be in the 10 kt or less range... as opposed to the 15
to 25 kt range they were the pat few nights. CIGS should stay
above 3000ft.




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