Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 201711

Area Forecast Discussion
National Weather Service Des Moines IA
1209 PM CDT Fri Apr 20 2018

.SHORT TERM.../Today through Tonight/
Issued at 405 AM CDT Fri Apr 20 2018

The primary concern through this period will be the evolution of
the long wave trough currently approaching the Rockies, but even
so its Iowa sensible weather impacts will be minimal. For today
high cloudiness will increase but departing surface high pressure
and weak warm advection should be sufficient to nudge temperatures
several degrees above persistence.

By tonight the system should track to our south with forcing
increasing there which will also brush southern Iowa. Moisture
will be limited however with a ribbon of drier SE flow aloft into
the state. Below that moisture will be low as well with soundings
showing plenty of dry air below 3km. A few models are suggesting
moisture may just deepen enough across northern Iowa later tonight
so have a brief period of token slight light rain chances and
possibly flurries/light snow far north if evaporative cooling is
sufficient to drop temps to the wet bulb. Otherwise the best
phasing of lift and moisture will stay to our south essentially
leading to continued dry conditions into the weekend. Temperatures
will continue to gradually moderate, especially north as the snow
pack continues to erode, but readings will still be just below
normal even though they seem comparably better.

.LONG TERM.../Saturday through Thursday/
Issued at 405 AM CDT Fri Apr 20 2018

The only precip window in this period will be Tuesday into
Wednesday with generally dry conditions and a somewhat inactive
pattern with our flow fairly weak and the jet now to our north for
the most part. This pattern will keep our temperatures normal or
below with little hope of return flow of any significance. The
system to our south Saturday will exit into Sunday with weak flow
and little forcing or moisture until early next week. A system
will mature somewhat as it crosses the High Plains into the
Missouri Valley Tuesday. There are some differences in strength
and timing, but both the GFS and ECMWF suggest a period of forcing
and deeper moisture phasing for some precip. The moisture return
magnitude will be weak however so this should generally be light
to at best moderate precip.

High pressure will then follow this system to end the period
keeping the forecast dry again with NW flow increasing somewhat.
This pattern will keep temperatures near normal at best.


.AVIATION.../For the 18Z TAFS through 18Z Saturday afternoon/
Issued at 1209 PM CDT Fri Apr 20 2018

VFR cigs are expected with light easterly wind that will increase to
10kts aft 21/15Z.  There may be a sprinkle across northern TAF`s as
upper level moisture increases late afternoon and evening but low
levels will be dry so a a sprinkle at best is all that is possible.





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