National Weather Service Raw Text Product

Displaying AFOS PIL: AFDDMX Received: 2018-02-09 23:35 UTC

FXUS63 KDMX 092335

Area Forecast Discussion
National Weather Service Des Moines IA
535 PM CST Fri Feb 9 2018

.SHORT TERM.../Tonight through Saturday/
Issued at 304 PM CST Fri Feb 9 2018

Next round of snow expected for mainly southern Iowa tonight. 
Forcing ahead of the next shortwave to impact Iowa will increase and 
shift across the state from mid to late evening through about 12Z in 
the southeast.  The strongest forcing will be in a fairly narrow 
band across southern Iowa...likely across the highway 34 corridor 
but strong mid-level forcing will exist all the way to the I-80 
corridor.  High-res models were initially pegging the highway 34 
corridor but through the day were gradually shifting north and 
coming more in line with the NAM.  I still believe the NAM is too 
far north bringing the higher qpf a little north of the I-80 
corridor and given that the qpf for the GFS, RAP and the HRRR was 
about a tenth of an inch less overall...some tweaks/blends were made 
to the qpf in both amount and location taking the other models into 
consideration. Snowfall amounts will be somewhat tricky since this 
strong forcing is mainly mid level but the moisture is deeper and 
the forcing does tap into it and it is within the better dendritic 
growth zone of -10 to -20 degrees C. Putting it all together gives 
us an expected snowfall of around 3 inches near the I-80 corridor 
with 4 inches or so around the highway 34 corridor.  A winter 
weather advisory will be issued for this area to coincide with when 
the better forcing moves in.

By the 12-15Z timeframe the forcing is exiting to the east and while 
some light snow may continue towards mid morning Saturday, the bulk 
of the accumulating snow for our forecast area should be done just 
after 12Z.  The remainder of Saturday should be dry ahead of the 
next system to impact the state but clouds will remain over the 
state and it will cold.  

.LONG TERM.../Saturday night through Friday/
Issued at 304 PM CST Fri Feb 9 2018

The next and last in a series of systems to affect the state will
arrive on Saturday night. Surface features will be well south of
the state with almost all forcing residing in the mid levels
associated with the passing shortwave. The increased forcing will
quickly saturate the atmosphere during the evening with snow 
spreading northward to around the Highway 92 corridor by midnight.
The snow area will extend a bit farther north across the eastern 
CWA reaching the I80 corridor near Grinnell. With the forcing
persisting overnight, anticipate light snow to continue until
shortly after daybreak in the far southeast before subsidence and
drier air arrive. With the snow ending Sunday morning in the
southeast, quiet weather is expected the remainder of the day
across central Iowa albeit rather cold with a canadian airmass in
place along with extensive snow cover.  

Much of the upcoming week will see quiet weather as system drops
down the west coast and becomes cutoff. There will be some
moderation by midweek as the upper flow flattens somewhat across
the CONUS, however this reprieve from the colder weather appears
short lived as additional polar will be poised to arrive by the
end of the next work week. 


.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 532 PM CST Fri Feb 9 2018

Area of snow and MVFR cigs area expected to impact southern IA
including the KDSM/KOTM areas overnight. Visibilities may drop to
IFR or below at times. The snow will end late tonight into
Saturday morning and conditions will return to VFR. Little to no 
impact at other sites with VFR conditions expected to persist.
Northerly winds at less than 12kts will continue through Saturday.


Winter Weather Advisory from 9 PM this evening to 7 AM CST 
Saturday for IAZ057>062-070>075-081>086-092>097.