Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 200837

Area Forecast Discussion
National Weather Service Quad Cities IA IL
337 AM CDT Sat May 20 2017

Issued at 324 AM CDT Sat May 20 2017

As of 3 AM, a 1006 mb sfc low was positioned over NE Kansas. To the
east of the low, a large MCS stretched from near Quincy, Illinois
all the way through central Missouri and into northern Arkansas.
Over E Iowa/NW Illinois, it was cool in the 40s with steady ENE
winds of 10-20 mph. Most areas were dry with the exception of
some patchy drizzle or brief light showers. There was one heavier
batch of showers and isolated thunderstorms approaching SE Clark,
and southern Hancock and McDonough Counties from the south.

The SPC mesoanalysis had approximately 1000 J/kg of MUCAPE across
the southern tier of counties, so occasional lightning strikes
are possible early this morning in this area.


.SHORT TERM...(Today and Tonight)
ISSUED AT 324 AM CDT Sat May 20 2017

This Morning:

The northern stratiform part of a large MCS will move through much
of the forecast area from SW to NE (PoPs are 70-90%). Instability
will be present, but it will be elevated. Have at least slight
chances for thunder as this precipitation shield moves through the
CWA. Locations to the south and southeast of the Quad Cities have
the best chance for thunder. The showers and isolated storms are
forecast to quickly dissipate and move out of the CWA between 9 to
11 AM.

This Afternoon and Tonight:

A deep mid and upper-level trough will become negatively tilted
as it moves through the Midwest. This is the same trough that
brought heavy snow to parts of the central and northern Rockies
the past few days. The attendant sfc and 850mb lows are forecast
to follow along a tight baroclinic zone from Kansas northeastward
into Iowa and Minnesota.

The latest outlook from the Storm Prediction center has a marginal
risk for severe storms along and east of a line from SE
Stephenson County to Le Claire to Macomb. A sfc warm front is
expected to lift northward today causing temps to reach the 70s
and pushing dewpoints into the 60s. Although, the HRRR/NAM/ECMWF
favor the strong and severe storms to form well east of the CWA,
across parts of Indiana and Kentucky, where the higher instability
pools ahead of the remnant MCS outflow boundary.

The GFS is much higher with SBCAPE over E Iowa/NW Illinois this
afternoon but is the outlier in this regard. That said, there is
still a chance for thunderstorms along and ahead of an approaching
cold front and under a mid-level dry slot. However, thinking
areal coverage will be on the low-side, meaning many locations
will receive little or no additional rain. The more sun we get in
the dry slot, the better chance for scattered showers and
thunderstorms to form during the mid afternoon into the evening.
Rain chances end overnight and temps fall into the mid 40s to near
50 F. Uttech

.LONG TERM...(Sunday through Friday)
ISSUED AT 324 AM CDT Sat May 20 2017

Active pattern will continue through the extended period.  Forecast
confidence is initially high as models generally agree on the
behavior of the current upper low into Monday.  By mid-week however,
models increasingly disagree on evolution of the long wave trough
over the eastern US.  Have favored a model blend this morning,
leaning heavily on the GFS and ECMWF.

Sunday will be dry under the wrap-around from the exiting low to the
north.  Respite from the rain will come to an late Monday as a
strong short wave drops into the plains and pushes an associated
cold front into the area.  With the upper trough deepening aloft and
the energy continuing to circulate around the sluggish upper low,
front will be slow to clear the area, and expect to see several
periods of rain and possibly thunder late Monday through Tuesday.

Surface ridge is progged to be over the area Thursday which should
result in a dry day before rain chances return next weekend.


.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1147 PM CDT Fri May 19 2017

IFR conditions will be the rule overnight through much of
Saturday. Initial MVFR ceilings are likely to lower to IFR at all
sites by 3 am with waves of light rain or drizzle moving through
early in the period and then again toward sunrise. There is a low
potential for thunderstorms, which has been limited to the BRL
site in the forecast. A low pressure system advancing from KS into
IA will to lift a warm front into the region during the day
Saturday, veering gusty east winds to the southeast by afternoon.
This front may also trigger thunderstorms, which are included
with PROB30 groups at MLI and BRL. There will likely be some
improvement toward evening, but forecast confidence in the timing
of this trend is low. For now, have a transition to MVFR at BRL,
MLI and CID by Saturday evening.


Issued at 324 AM CDT Sat May 20 2017

The English River near Kalona has crested just below flood stage and
the warning will be cancelled shortly.

Flooding is forecast along the Iowa River at Marengo and Oakville by
early next week and flood watches are in effect for these points.
Depending on where and how much rainfall falls today, the watches
will either be upgraded to a warning or canceled.

On the Mississippi River, levels are generally forecast to rise
during the next week due to both routed water and tributary inputs.
Burlington is hovering just below flood stage will likely return to
flood stage by Monday so a flood warning remains in effect.




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