Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 182042

Area Forecast Discussion
National Weather Service Des Moines IA
342 PM CDT Wed Apr 18 2018

.SHORT TERM.../Tonight through Thursday/
Issued at 317 PM CDT Wed Apr 18 2018

The primary forecast challenge is residual impacts from the late season
winter storm.

Tonight...Forecast Confidence: Medium/High

GOES-16 satellite imagery continues to show a potent upper level system
moving across the upper Midwest. Recent radar mosaic from 3pm this
afternoon continues to depict areas of light to moderate snow rotating
across the CWA from NW to SE.  Visibilities have come up from earlier
in the ranging from 1 to 5 miles in snow. Getting plenty of
reports of moderate to heavy snow across the upper third of Iowa -
ranging from 5 to 10 inches. Highest totals were generally along and
north of US 18. Snow totals were lower than expected further south
/e.g. Waterloo/...mainly due to a pronounced dry slot that moved
through the area...and kept p-type more light freezing rain and drizzle
rather than snow.

Additionally...seeing areas of convective snow showers develop this
afternoon due to steep low level lapse rates and areas of modest
instability /SBCAPE ~ 100 J/kg/ within the PBL.  So although the
strongest synoptic scale forcing and lift has moved east of the CWA,
will continue to see at least occassional snow showers through this
evening. Additional snow accumuations should be rather light...up to 2
inches in the north and perhaps an inch south.

Based on webcams and road reports...have decided to cancel the Winter
Weather Advisory for the counties along I-80.  Kept the Advisory and
Warning further north for now...due to ongoing snow and continued
partially covered roadways.  However, would not be surprised if this
could be canceled early later this evening.

Otherwise...expdecting mostly cloudy and cold conditions overnight with
lows in the 20s.

LONG TERM.../Thursday night through Wednesday/
Issued at 317 PM CDT Wed Apr 18 2018

Thursday through Wednesday...500 mb heights rise late this week
over the upper midwest as an upper ridge builds across the area.
The next upper low was moving onshore in the Pacific Northwest
this afternoon. It should emerge from the Central Rockies early
this weekend. By that point, it will disconnected from the
westerlies which will be well to the north. As a result, the
models slowly drift the upper low into the Southern Plains late
this weekend. Meanwhile, both the 12Z GFS/ECMWF bring a northern
stream shortwave across the northern plains into the upper midwest
Tuesday/Wednesday which should result in a Pacific cold frontal
passage Tuesday night or Wednesday. With the upper low to the
south, moisture return should be reduced thus lower precipitation
chances look good.

At the surface, a slow moving high pressure system will move across
the region Thursday through the weekend. The sensible weather will
be a several day dry period with moderating temperatures and
relatively low surface winds. Temperatures may exceed normal
temperatures by next Monday which will help dry things out. High
temperature climo is in the lower to middle 60s by early next week.
We should see slightly cooler temperatures but still much warmer
than recent temperatures by the end of the period.


.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1240 PM CDT Wed Apr 18 2018

Late season winter storm will continue to impact terminals through
early evening. IFR to LIFR conditions will continue across
KMCW/KALO/KFOD in the area of heaviest snow.  KDSM/KOTM will see
lighter -RA/SN...but still IFR to MVFR CIGS and VSBYs due to fog
and possible drizzle. Pcpn will end around 03z although will
likely see a continuation of low stratus and MVFR and IFR CIGs for
much of the overnight. Improving conditions expected to early
Thursday...trending to VFR towards morning. Winds will continue to
shift from N/NE to NW.


Winter Weather Advisory until 1 AM CDT Thursday for IAZ047>050.

Winter Storm Warning until 7 PM CDT this evening for IAZ004-005-

Winter Storm Warning until 1 AM CDT Thursday for IAZ006-007-016-

Winter Weather Advisory until 7 PM CDT this evening for



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