Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 152349

Area Forecast Discussion
National Weather Service Des Moines IA
649 PM CDT Sun Apr 15 2018

.SHORT TERM.../Tonight/
Issued at 349 PM CDT Sun Apr 15 2018

Large area of low pressure has move east and is centered over the
mid Ohio valley. Broad cyclonic flow extends well west into
Minnesota and Iowa. The water vapor imagery continues to show warm
conveyor moisture lifting north from the gulf with a portion
still wrapping around through the cyclonic flow. This has helped
keep bands of light to sometimes moderate snow going today though
some shearing is starting to show up with the moisture connection
into Iowa being cutoff. Despite the areas of snow today, solar
radiation passing through the clouds has allowed road temperatures
to warm into the 40s to low 50s across much of central Iowa. The
warm road temperatures have resulted in vastly improved road
conditions across the state. Still some blowing of snow causing
partially snow covered roads, especially in the west bound and
south bound lanes with northern Iowa being most impacted.

Snow will continue to diminish into the evening with little to no
expected accumulations expected. The winter weather advisory will
expire at 4 pm. There will likely still be some travel impacts
beyond the advisory times due to some low level blowing snow over
roadways and some refreezing into the this evening with the loss of
the solar radiation. The wind will remain breezy overnight from the
northwest. Temperatures will be near record lows in the upper teens
to mid 20s. The wind and clouds likely will keep most locations from
surpassing their records but regardless, it is cold for mid April.

.LONG TERM.../Monday through Sunday/
Issued at 349 PM CDT Sun Apr 15 2018

Winds from the northwest will remain brisk on Monday as the
strong area of low pressure that brought our wintry weekend
weather moves into the Northeast. In addition, clouds will
gradually clear from west to east, though may linger much of the
day over the northeastern portion of the forecast area. After a
very cold start to the day, temperatures will struggle into the
30s over northern and central Iowa and low 40s over southern Iowa.
These temperatures are 20 to 25 degrees below normal for mid-
April. Monday night will be yet another very cold night with near
record lows possible in some places. Compared to Sunday night,
skies will be clear and winds will be lighter helping to drop
temperatures despite weakening cold air advection.

Mid-level ridging will pass over the state allowing for some
sunshine initially on Tuesday. However, the next shortwave trough
will be moving across the Rockies with surface low pressure
entering western Kansas late Tuesday. GFS is faster than the
NAM/EC/CMC so slowed down PoPs in the east Tuesday night.
Differences in low pressure track despite being slight (central
Iowa compared to near the Missouri border), surface temperatures
around freezing, and a warm nose of air aloft make for a
challenging forecast. Initially, there will be good ice
introduction, but this is lost over parts of northern Iowa later
Tuesday night into Wednesday morning. Soundings show the warm nose
aloft that will aid in melting hydrometeors and with boundary
layer temperatures near freezing, likely looking at some freezing
rain (or drizzle if no ice introduction) over parts of northern
Iowa. As colder air begins to wrap into the system as
strengthening winds become from the northwest on Wednesday, will
see a transition to mainly snow north, rain/snow mix central and
all rain likely south before ending Wednesday night. A potential
for moderate snow exists over northern Iowa. Cross sections from
the NAM show potential for a corridor of strong omega within the
dendritic growth zone from mid-morning into the afternoon over
northern Iowa. The GFS isn`t as focused with a broad area of
strong omega. If the NAM were to verify, will see dynamic cooling
currently not accounted for in the forecast and less ice. Overall,
there is general agreement amongst models in a heavier area of
QPF north of the low pressure somewhere over northern Iowa or
southern Minnesota. Felt confident enough to incorporate WPC QPF
with Superblend to start upping amounts. However, placement of the
area of higher QPF will be refined in the coming days along with
precipitation types.

High pressure will cross the area on Thursday resulting in
relatively quiet weather. However, the next upper level low pressure
will be moving east of the Southwest US by Friday morning. Similar
to previous forecast, low pressure will track south of the state
Friday night into early Sunday, which will still be able to
spread a mix of rain or snow into the state.


.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 648 PM CDT Sun Apr 15 2018

Clouds will persist across Iowa into the evening but confidence in
whether individual site ceilings will be MVFR or VFR is medium at
best as these conditions are quite variable in time and space at
the movement. Occasional flurries will continue, but infrequent
bursts of snow may also drop conditions to MVFR or even IFR
briefly adding to lower confidence. Clouds should persist in the
broad cyclonic low level flow into Monday as well, but confidence
between VFR or MVFR conditions will stay no better than medium.





SHORT TERM...Donavon
LONG TERM...Ansorge
AVIATION...Small is the U.S. government's official web portal to all federal, state and local government web resources and services.