Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 192003

Area Forecast Discussion
National Weather Service Des Moines IA
303 PM CDT Mon Mar 19 2018

.SHORT TERM.../Tonight through Tuesday/
Issued at 256 PM CDT Mon Mar 19 2018

The main forecast concern was focused on the light snow to move into
western Iowa Tuesday.  Models continue to be in great agreement with
timing and location of the light snow Tuesday and thus no
significant changes to the ongoing forecast. Surface low currently
tracking across Missouri remains well south of the forecast area
tonight and will mainly bring some cloud cover across the south
this evening. A very weak 500mb shortwave enters western Iowa b/t
06-12z Tuesday and transitions across the state throughout the
day. Saturation begins during the same time at CRL to FOD to EST
and have high pops going past 09z through 18z Tuesday. Forcing is
within the dendritic layer, albeit weak, but should be strong
enough to overcome the shallow dry layer near the surface tomorrow
morning. As the shortwave moves east, the weak forcing diminishes
and have low confidence with much snow accumulation east of
Interstate 35. Especially with the surface temperatures warming
into the upper 30s to lower 40s toward the afternoon. There is
another vort max that stretches across western Iowa by late
Tuesday afternoon and may regenerate some snow showers over the
west to northwest during this time. Thus, kept light snow
accumulations going in the northwest b/t 18-00z tomorrow and may
need to extend pops past 00z Wednesday over the far northwest.
Particularly if there is some lingering deeper moisture and ice
introduction into the column.

.LONG TERM.../Tuesday night through Monday/
Issued at 256 PM CDT Mon Mar 19 2018

Another quick moving shortwave looks to bring rain and/or snow to
the central and southwest portions of the forecast area Thursday.
Forecast soundings portray a fairly deep dry layer below 800mb to
the surface Thursday morning. GFS is certainly stronger with the
forcing and as a result, higher with the QPF amounts. Regardless,
surface temperatures look to be warm enough to melt any snow prior
to reaching the surface and have low confidence with much

Friday into Saturday, there remains some uncertainty wrt the surface
low track across the region. Models have at least come into decent
agreement with timing of the surface low. The GFS is slightly faster
and further south than the ECMWF Saturday morning. Still, models
place the forecast area within the easterly flow and rain much of
the day. Confident to at least lower maximum temperatures a few
degrees on Saturday and leaning to the potential for slightly more
snow over central to northern Iowa. Models diverge in solutions
late in the weekend into early next week and low confidence with
any precipitation location and type Saturday night into Monday.


.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1212 PM CDT Mon Mar 19 2018

Main concern was with winds mixing throughout the afternoon and
have mention of gusts to near 20 knots for most TAF sites except
OTM were a bit more sunshine has allowed for deeper mixing and
slightly stronger gusts. Winds decouple by this evening. Have
introduced MVFR ceilings at FOD, MCW and DSM for incoming system
to produce some light snow.





SHORT TERM...Podrazik
LONG TERM...Podrazik
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