Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 261120

Area Forecast Discussion
National Weather Service Des Moines IA
620 AM CDT Fri May 26 2017

.SHORT TERM.../Today through Tonight/
Issued at 330 AM CDT Fri May 26 2017

08z analysis shows a convective complex moving eastward over
northeast Kansas and far southeast Nebraska. Most of the
thunderstorms were confined to the I-70 corridor and areas south
while a struggling area of showers were found on the northern end of
this complex. These storms are in response to a shortwave trough
that will move over Iowa today. This will bring scattered showers
and storms this morning into early this afternoon to areas
along/south of Highway 30 in Iowa. Storms will be elevated with
limited instability to work with so not expecting anything to reach
severe limits this morning. Used a blend of hi-res models (HRRR, Hi-
Res WRF ARW/NMM cores, RAP) to get higher PoP from initial guidance.

As the storms move off to the east, clouds will clear with sunshine
returning to western parts of the CWA by late this morning and to
eastern parts of the CWA by later this afternoon. Trended today`s
high temperatures near or slightly on the warmer side of consensus
MOS while continuing to have the lower high temperatures over the
eastern part of central Iowa.

Clouds will begin to return after midnight tonight as the next
shortwave approaches with rainfall generally holding off until after
sunrise Saturday. For tonight`s low, generally adjusted lows a
degree or two downward from initial guidance.

.LONG TERM.../Saturday through Thursday/
Issued at 330 AM CDT Fri May 26 2017

Saturday through Sunday Night : Confidence Medium

Early in the period there will be several fronts/waves that pass
through the region...with active weather expected at least through
Saturday night...then quieter conditions on Sunday.  Though the
models are trending toward a more common solution for the weekend
forecast...there are still some differences that may not fully be
resolved beyond 12 hours due to minor variations in wave timing
and evolution of eventual convection. By 12z Saturday both the GFS
and Euro model are projecting a low south of the state in Missouri
with increasing convection. However the similarities end there.
The GFS develops an MCS over northern Missouri and tracks it east
along a nose of thetae advection/warm front just south of the IA
MO border. Meanwhile the Euro trends in the same direction over
Missouri but also has an enhanced area of convective development
farther northwest driven by an H850/H500 wave couplet tracking
over Iowa. CAMS models are slower to break out convection Saturday
with afternoon/evening periods more predominant with everything
shifted farther northwest into Nebraska. Due to the uncertainty a
blended approach will be maintained with higher PoP over the
north during the day and also another area hugging the IA MO
border where the synoptic scale models are maintaining better
large scale forcing for convective development. Overall the better
chances for thunder should be in the south where greater instability
is forecast and 0-6km bulk shear is stronger. We are outlooked
over the south half for marginal with a slight risk just south of
the border. The bulk wind shear supports some potential for
stronger storms over the south...mainly hail with some wind threat.
Prior to convection... sufficient heating should allow for afternoon
highs to reach the upper 70s east/southeast with lower to mid 70s
west. The upper level support should move east overnight into
Sunday with lessening precipitation chances for the remainder of
Sunday. With continued mild H850 temperatures and some mixing...
afternoon highs will once again recover into the mid to upper 70s
south...lower 70s north. Both the GFS/Euro drop a cool front south
through the region Sunday night...resulting in a shift toward
cooler temperatures heading into Memorial Day and beyond.

Monday through Thursday:  Confidence Low to Medium

As the cool front drops south Sunday night...a stronger and
expansive H500 upper level low will overspread much of the Great
Lakes...southern and eastern Canada and the eastern Central
Plains. The resulting cooler system aloft with cyclonic flow/more
clouds/and a number of embedded short wave troughs migrating
through the western side of the upper level low...will cause
periods of showers from Minnesota east to Wisconsin and possibly
south into Iowa as well. The daytime periods would be most favored
due to daytime heating...and the north/northeast would be more
favored due to closer proximity of the upper level system. Confidence
remains rather low beyond Monday as to how far south the precipitation
may develop. Late Thursday there may be a better organized system
approaching from the south increasing chances for showers over
southern Iowa. Though there are chances for rain from Tuesday into
Thursday in the current forecast...though more evaluation is
needed. For now...there appear to be no significant events concerning
either heavy rainfall or convection. Highs through the period will
settle into a 60s to 70s range with lows in the 40s/50s Tuesday
and Wednesday rising to the 50s by Thursday.


.AVIATION.../For the 12Z TAFS through 12Z Saturday morning/
Issued at 620 AM CDT Fri May 26 2017

Showers with a few embedded thunderstorms will move over
southern Iowa this morning and early afternoon. Observations so
far have indicated ceilings have remained in VFR by a few to
several thousand feet as the precipitation passes. Otherwise,
clouds will clear from west to east today and winds from the
southeast this morning will become from the northwest throughout
the day. May also have to monitor for possible low stratus and
fog development late in the TAF period over eastern Iowa, but only
have a SCT ceilings and MVFR visibilities at this point at those




SHORT TERM...Ansorge
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