Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 210430

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1130 PM CDT Sat May 20 2017


Issued at 330 PM CDT Sat May 20 2017

Latest analysis was indicating occluded sfc low currently acrs west
central IA, with associated warm front pushing up the southern third
of the DVN CWA not all that far south of the I80 corridor. Large
temp contrast from north to south around the frontal system.  Most of
the organized rains have pushed to the north, with just some
lingering drizzle and fog in pre-warm front llvl moisture
convergence zone. A more organized warm sector still further to the
south acrs the southern tier of DVN CWA counties an into
northeastern MO where llvl based CAPES have grown to 500+ J/KG.
After isolated to sctrd shower/ thunderstorm chances with this
system this evening, then cool, breezy but mainly dry to end the
weekend. Then portion of northern CONUS upper troffiness to dig back
southeastward for the next shower/storm chances later Monday into
Tuesday. Near normal highs Monday ahead of this system, then below
normal into mid next week.


.SHORT TERM...(This Evening through Sunday)
ISSUED AT 330 PM CDT Sat May 20 2017

The main upstream cyclone will look to roll north into southern
MN tonight. As it does, it will try and drag the sfc low and warm
front occlusion through the area and through the evening. This
process will have to battle pre-frontal rain cooled and worked
over airmass, but if the low has the push the models indicate it
will, it should be just north and northeast of the CWA by midnight
to 3 AM CDT or so. Thus could be a scenario where temps continue
to rise into the evening with 24 hr highs occurring after 00z. But
more of a challenge/fcst concern, is if isolated to sctrd showers
and thunderstorms can fire over the next few hours as dry slot
and warm front push northeastward through the area. Feel that they
will and adjust POPS for coverage using scattered and isolated
wording late this afternoon and into the evening. Looking at
various forcing wings and the negatively tilted cyclone itself,
sctrd storms along an arch oriented from southeast-to-northwest
will sweep acrs the CWA though 10 PM, and look to exit the far
east toward midnight. Airmass recovery with warm frontal push and
approach, eastern edge of dry slot effect, and omega/lift max
suggest more activity taking off after 6 to 7 PM this evening, but
will have to watch the south after 5 PM as well.

As for storm strength, instability will look to remain rather
marginal and if activity holds off until after 6 PM initiation, time
of day not all that favorable as well. But both llvl and bulk shear
profiles are adequate to support strong storms, so can`t totally
rule out an isolated storm capable of producing hail and a strong
wind gust especially east of the MS RVR. LLVL west to southwest post-
wave flow will cool advect by early Sunday morning for a return to
40s and lower 50s for overnight lows.

Sunday...Wrap-around filling northwestern GRT LKS cyclone to make
for a mostly cloudy, breezy and below normal temp-day for Sunday.
will keep the forecast dry for now, but suppose a low chance for
isolated instability showers in the north Sunday afternoon. Highs
Sunday in the 50s to low 60s will be well below normal.     ..12..

.LONG TERM...(Sunday Night through next Saturday)
ISSUED AT 330 PM CDT Sat May 20 2017

Sunday Night, Skies will be mainly clear. It will be chilly with
overnight low temperatures dropping into the mid 40s.

Monday and Tuesday, 12Z Saturday runs of GFS/ECMWF/GEM are in good
agreement in keeping skies mainly dry for most of the day on Monday.
The models then prog an upper level shortwave to rotate around a
closed 500 millibar low centered over the upper Great Lakes, and
dive this wave south into the upper mid-west. A cold front
associated with this shortwave will slowly move through the area
Monday evening and Tuesday bringing with it a chance of showers.
There could also be thunderstorms with this frontal passage as day
time heating and upper level dynamics combine to destabilize the
atmosphere. The threat of severe weather can not be determined at
this time. Temperatures on Monday will be the warmest of the week
with highs in the mid 70s and lows in the 50s. Once the cold front
moves through on Tuesday, temperatures will drop to at least 10
degrees below normal with highs only in the 60s and lows in the 40s.

Wednesday through Friday, Models develop a longwave upper level
ridge west of the region with its axis extending from the desert
southwest to near Minnesota. With the upper Mississippi Valley being
on the east, subsidence, side of this ridge it will be mainly dry
with cool temperatures. On Wednesday, a few scattered showers are
possible in the cyclonic flow wrapping around the back side of the
upper low over the Great Lakes. Temperatures will continue to be
well below normal with highs in the 60s and lows in the 40s.

Next Saturday, A 500 millibar shortwave will approach from the west
and pass over the region bringing the next chance of showers and
thunderstorms next weekend. High temperatures should be closer to
normal with highs in the 70s.


.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
ISSUED AT 1127 PM CDT Sat May 20 2017

The transition to mainly VFR conditions is nearly complete as of
05Z this evening as dry mid level air works around the departing
storm system. Wrap around low clouds will arrive from west to east
Sunday morning, but the period of fog and drizzle appears to be
over now, and visibilities should be 6 miles or better through the
period. The MVFR clouds sunday morning will persist through late
morning to early afternoon, before lifting to VFR the remainder of
the day and evening hours.


Issued at 921 PM CDT Sat May 20 2017

There is no change in active watches and flood warnings tonight,
but the latest Mississippi River forecasts are showing some rises
to near or above flood stage now on multiple sites around a week
from now. I`d like to see this trend continue into the morning
forecast runs before issuing official watches or warnings on this.
In any case, the big river will be rising this next week, and
we`ll need to keep an eye on all Mississippi river sites rising
to minor flood potential by late next week.




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