National Weather Service Raw Text Product

Displaying AFOS PIL: AFDDMX Received: 2017-12-07 23:33 UTC

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