Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 242035

Area Forecast Discussion
National Weather Service Des Moines IA
335 PM CDT Mon Apr 24 2017

.SHORT TERM.../Tonight through Tuesday/
Issued at 333 PM CDT Mon Apr 24 2017

Few major concerns overnight tonight and Tuesday. Breezy conditions
will abate aft 00z for most of the area...with some mixing extending
into the early evening hours. With approaching cool front and low
pressure overnight into Tuesday morning...increased thetae advection
and frontal forcing will focus shower development across the far
west by 12z...then increasing shower coverage over the area during
the day.  With the inverted trough setting up over the western
counties by 18z...upglide lift will occur along and more so to the
west of the trough.  Have increased PoP over the northwest areas
during the daytime hours to reflect the better potential there.
Currently Bufkit soundings show little if any elevated instability
for Tuesday and with most of the lift north of the boundary into a
cooler airmass...models continue to indicate little if any
instability as well.  For now have left any mention of thunder out
of the present forecast.  Lows tonight will be quite mild once again
with persistent south winds south of the approaching boundary.
Tuesday afternoon highs will not reach todays levels...but will
still be mild over the southeast half where lower to mid 70s are
still possible.  North of the boundary mid to upper 50s will be more

.LONG TERM.../Tuesday night through Monday/
Issued at 333 PM CDT Mon Apr 24 2017

Tuesday night a deep upper trough moves out of the Rockies into the
Plains and ejects energy across the region up into the Upper
Midwest.  The surface response is the development of a low over KS
with a frontal boundary extending across roughly the I-35 corridor
at 00Z and just East of the forecast area by 12Z Wednesday.  During
this time there is some forcing along the front but broadscale
forcing and theta-e advection has shifted to the East.  There will
be pretty widespread light precip through Tuesday night.  Ahead of
the front where some instability and shear will exist, there will be
at least isolated thunderstorms mainly East of the I-35 corridor.
Not really looking at any kind of severe potential but locally heavy
rain may occur with the storms.

On Wednesday the base of the upper trough shifts East and the trough
axis is parked over the region as the surface low and frontal
boundary shifts into the Great Lakes region.  As a result we will
still have some light precip...mainly from the deformation zone
which will end by early afternoon as cooler and drier air works into
the region.

Wednesday is trending drier but the the upper trough still over us
and pivoting Northeast I kept some pops going.  Pops are likely
overdone but I stayed with the model blends for now in going with
slight chances West and chance pops East.  Some pretty cold air
moves in Wednesday night so if we have any precip...especially North
and West it will likely be a rain snow mix possibly even changing
over to snow briefly.  If we do not see precip and start to clear,
then frost is possible.  It`s worth keeping an eye on at this point
but confidence is not high enough at this point to say one solution
is favored over another.

Thursday looks like we see a break as the first systems finally
lifts off but another strong wave pushes into the Southern/Central
Plains with a surface low and boundary over KS/OK slowly lifting
into Iowa late Friday night or Saturday.  Rain chances will move
into the far South/Southwest Thursday night then spread across the
area on Friday.  The current track of the low suggests that we will
b e on the cold side of this system so again...little threat for
severe storms but across the Southeast isolated storms will be
possible with heavy rainfall again a potential.  The upper wave
develops a low around IA by Sunday and thus deepens the trough over
the area keeping rain chances going through the weekend.  Unlike
last weekend, the upcoming weekend looks to be quite wet.  The
system lifts out on Monday giving us a dry start to next week.


.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1250 PM CDT Mon Apr 24 2017

Main concern this period will be wind through 02z this
evening...then development of showers by 12z through remainder of
period. Strong gradient winds with sufficient mixing will persist
into the early evening...gradually diminishing by 02z. Along with
that a few areas may see LLWS overnight. Frontal boundary with
potential for -shra arrives into Tuesday...through remainder of
period. Better coverage along the boundary will exist at KFOD and
KMCW with lesser chances at KDSM/KALO. Have kept VCSH at southern
locations. CIGS to lower toward MVFR by 18z north sites KMCW/KFOD
as well. /rev




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