Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 302011
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
311 PM CDT Thu Mar 30 2017

.SHORT TERM.../Tonight through Friday/
Issued at 311 PM CDT Thu Mar 30 2017

20z visible satellite imagery clearly shows mid-level low pressure
over far western Missouri. Stratus clouds cover the state with areas
of drizzle over central and south central Iowa. Showers have been
confined to eastern Iowa with the most concentration of showers over
the southeast closer to the surface low. Soundings across central
Iowa show that low level moisture will persist overnight and into
tomorrow morning. May still have some areas of drizzle into this
evening, but overall should be drying out beneath the clouds. With
plentiful clouds, kept overnight lows near initial guidance, which
was generally on the warmer side of MOS guidance.

As the low pressure moves into the Ohio Valley, subsidence and drier
air mixing down into the atmospheric column will allow for some
filtered sunshine, mainly over north central and northwestern Iowa.
There may be some peeks of sunshine later in the afternoon over
central and southern Iowa, but confidence is not as high in those
locations given the persistence of the cloud cover and not as much
dry air. Despite the clouds, temperatures should be able to attain
higher values than today, but will still be below normal for the end
of March as weak ridging passes overhead.

.LONG TERM.../Friday night through Thursday/
Issued at 311 PM CDT Thu Mar 30 2017

Friday Night through Sunday Night.  Confidence Medium to High.

Main challenges remain the same over the next several days.  With
weak ridge of high pressure across the area late Friday afternoon
and H850 trough now forecast to settle over northern Missouri...we
should see some brief breaks in overcast...though short lived.
Pattern for now anyway not very supportive of clear/sunny skies. As
the high builds east Friday night...weak warm air advection and
moisture return will allow for mid level clouds to expand into Iowa
bringing mostly cloudy conditions by Saturday morning. There may
again be some breaks in the clouds but mainly over the east/
southeast as Great Lakes high may assist in keeping slightly drier
low level RH in that area a bit longer.  This mornings 12z GFS is
also backing off on precipitation onset through most of Saturday.
With an inverted trough and weak warm front developing over the area
on Sunday...periods of showers are likely in the morning and again
in the afternoon/evening. By Sunday afternoon steepening mid level
lapse rates may promote some thunder over the south with isolated to
scattered in coverage. With the weekend event...another quarter to
three quarters of an inch of rain will be possible with the majority
of the area in the .25 to .50 range.  Highs Saturday into Sunday
will likely show some warming as east southeast winds return to the
area.

Monday through Thursday.  Confidence Low.

The GFS shows Monday looking better today...with the GFS now
bringing high pressure/subsidence/and sunshine back into the region
for most of the day. With sufficient mixing even with northwest flow
and H850 temperatures 3 to 5C over the area...highs would easily
reach the mid to upper 50s northeast to the mid 60s in the south in
this scenario. That being said...todays 12z Euro is less optimistic
about much clearing on Monday and now indicating slightly cooler
afternoon H850 temperatures as well. Will not stray too far from
guidance at this point due to continued uncertainties.

Todays 12z GFS is also now nearly 24 hours faster with the midweek
storm next week compared to yesterday.  The 12z Euro is also faster
with the eastward progression of the system...though not quite as
fast as the GFS.  With significant changes from yesterday...
confidence today has dropped for midweek.  The slower solution
yesterday would have allowed for greater moisture return and
potentially stronger storms to develop farther north into the
Central Plains. Todays model packages are more suggestive of the
moisture return becoming more fully realized east of the area due to
some latency of moisture return following the departing storm on
Sunday night. None the less a round of showers and possible
thunderstorms is anticipated...though timing is in question. This
will also have some impact on temperatures as there are some
differences from model to model and run to run regarding warm sector
placement/highs and mins.  The current window of preferred higher
PoP will be from Tuesday through Wednesday afternoon. For now will
leave out mention of thunder though late Tuesday into Tuesday night
would be the most favored time for any convection at this point and
mainly over the south half of the forecast area.  Highs through the
period are likely to be mild in the 50s Tuesday/Wednesday with some
uncertainties by Thursday.  The Euro is looking rather chilly by
Thursday with the arrival of a Saskatchewan shortwave and brief push
of colder Canadian air.  Conversely...the GFS never recognizes any
separation between the Wednesday and second wave Thursday resulting
in cold air advection arriving concurrently with the midweek storm.
With the high amplitude pattern still in place and plenty of energy
around...will need a few days to nail down any details for next
week as models continue to struggle.

&&

.AVIATION.../For the 18Z TAFS through 18Z Friday afternoon/
Issued at 1245 PM CDT Thu Mar 30 2017

Stratus clouds prevail over the state as low pressure spins near
the Kansas/Missouri border with elevated clouds circulating around
this low. IFR/LIFR ceilings will continue over southern Iowa with
some drizzle at times while IFR and low MVFR ceilings will be
over northern Iowa through this afternoon. Showers have been
quite limited and only have a mention at KALO and KOTM at this
time. Overnight, IFR and low MVFR ceilings will persist and last
into Friday morning. Drier air will finally begin to push into the
state later tomorrow morning, which should finally allow for
ceilings to begin to lift over the northern TAF sites toward the
end of the TAF period.


&&

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

$$

SHORT TERM...Ansorge
LONG TERM...REV
AVIATION...Ansorge


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