Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 252312
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
612 PM CDT Tue Apr 25 2017

.SHORT TERM.../Tonight through Wednesday/
Issued at 340 PM CDT Tue Apr 25 2017

Surface low pressure is centered over central Oklahoma this
afternoon with a trough extending well north through central Iowa
and Wisconsin. In Iowa, this trough extends from near Clarinda to
just west of the Des Moines metro and through Charles City.
Temperatures are in the low to mid 70s over portions of central and
southeast Iowa ahead of this boundary while low 40s are currently
over northwest Iowa. An area of low pressure will lift up
north/northeast along the trough and into Iowa. This will keep
boundary momentum eastward quite slow then will gradually wrap
around the low pressure center as it lifts northeast.

Some instability will develop in vicinity of the boundary mainly
this evening east of Interstate 35 and south of Highway 30. The
arrival of the surface low pressure will coincide with deeper layer
theta-e advection and increasing kinematic forcing from passing
short wave fragments.

The boundary will pass to the east by Wednesday. This combined with
closed upper low moving into the Northern Plains allowing for the
colder air now moving into northwest Iowa to spill further south.
Precipitation chances may linger far north and east but will
diminish throughout the day with the arrival of drier mid level air.
Possible some light drizzle occurs but nothing measurable. It will
be a blustery day with the colder temperatures and breezy northwest.
winds.

.LONG TERM.../Wednesday night through Tuesday/
Issued at 340 PM CDT Tue Apr 25 2017

Bigger changes were made to the forecast grids today as model trends
continued to show a bigger push of dry air coming in Wednesday and
Wednesday night.  As a result, pops were drastically reduced
Wednesday evening...keeping only slight chance pops across the far
Southeast in the evening.  Overnight the upper low shift North into
Canada and a shortwave pivoting around the low could bring some
precip back to the far East briefly overnight so slight chance pops
were added in that time frame from about 08z to 11Z.  Next I took a
harder look at the frost potential and ruled that out as well. First
we will have entirely too much cloud cover and while minor
adjustments were made to temps to warm them a bit due to the
clouds, the other thing detracting from frost is the wind...which
will be up between 10 and 13 mph.  If the cloud or the wind forecast
is a little off then we may see some...especially in low lying areas
but for now the presence of clouds and wind negate the frost threat.

Dry conditions will exist through most of Thursday and Thursday
night.  We will have clouds around though at this point it`s hard to
say how thick and for how long.  Every location should se periods of
sun and clouds thorugh Thursday night before clouds really roll back
in towards Friday morning.

The next upper trough moves across the Southern Plains developing a
surface low over the Southern Plains with a frontal boundary
extending up thorugh MO towards IA.  Moisture will return towards
daybreak Friday to far Southern Iowa and spread showers to that
area.  The precip should spread North through the day as the surface
low and upper level trough shift Eastward.  We will likely see light
to moderate rainfall Friday with rain continuing across the South
Friday evening.  Model trends the last couple of days has been for
the heavy rainfall and storms to shift further South and East and
that trend continued again today so the mention of heavy rainfall
will be removed from our products for now.

Saturday through Monday the next deep trough moves into the Plains
where an upper low develops in the trough slowing the progression of
this wave and producing an extended period of rainfall for Iowa.
Again, periods of moderate rainfall will be possible we are getting
a little far out to have high confidence in how much if any and
where this would fall.  Some instability works into the area late
Saturday night and Sunday as colder air works into the Northwest. We
could see some thunderstorms South and rain and snow North late
Saturday night and early Sunday morning.  Temps Sunday will be even
cooler than the 50`s we will see prior to then with highs likely to
be in the 40`s to around 50 by late afternoon.  All in all the
period will remain wet but with breaks in the precip at times.

&&

.AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/
Issued at 541 PM CDT Tue Apr 25 2017

Clouds will lower from northwest to southeast bringing MVFR and
then IFR ceilings to most terminals tonight. Showers are expected
to develop as a cold front swings through the state tonight and
there may even be some thunder at the far southeast terminals this
evening. Drier air will arrive Wednesday morning and any lingering
showers will end in the morning and IFR conditions should rise
into MVFR toward midday.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Donavon
LONG TERM...FAB
AVIATION...Ansorge



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