Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 211112

Area Forecast Discussion
National Weather Service Quad Cities IA IL
612 AM CDT Mon May 21 2018


Issued at 325 AM CDT Mon May 21 2018

Current water vapor loop was indicating vort max embedded in band of
cyclonic southwesterlies aloft, propagating acrs the area and
driving ongoing sctrd to clusters of showers moving north-northeast.
Little in the way of lightning detected, except for in larger band
moving up in between Macomb IL and Peoria, headed toward the eastern
I-80 corridor near Princeton IL. W/V loop also was indicating the
main upper low acrs eastern SD, looking to roll acrs MN by this
evening. After the precip winds down later today, large cut-off
upper low adjusting eastward acrs the western Intermountain region
to pump up ridging acrs the MO and MS RVR Valleys, which may allow
for a mainly dry mid week period before rain chances increase again
from the west by the end of the week.


.SHORT TERM...(Today and Tonight)
ISSUED AT 325 AM CDT Mon May 21 2018

Today...Will walk out the passing vort max and associated areas of
showers as the day progresses. Shower coverage will be highest
north of I80 after 12z, as well as east of the MS RVR. A pocket of
higher MUCAPES will allow for some thunder, or at least isolated
flashes moving up mainly along and east of the MS RVR acrs northern
IL this morning. After the larger cluster of showers move out of the
area after mid morning, just expect some spotty showers to pop up
acrs the CWA in lingering cyclonic flow lift regime into the
afternoon. Until the precip winds down and decreases in coverage,
areas that manage to get hit by a larger cluster or two may get a
quarter up to a half inch of new rainfall. Most areas though,
probably 0.15 or less. Some patchy fog may develop this morning acrs
portions of southeastern IA and northeast MO in light convergent
cyclonic sfc flow as sfc wave approaches. Otherwise, banking on a
few breaks in the overcast along with some dry hours this afternoon
to attain the fcst highs...most areas in the upper 60s to low 70s
except for the far south and north.

Tonight...Will go mainly dry, but a few 00z run models including the
ECMWF develop some showers into the northwestern and northern CWA
this evening and into the overnight as the upper trof digs out of MN
and into southern WI/northeastern IL.  Weak ridging to make for
light northwest or variable sfc flow acrs the CWA by midnight. If
skies can clear enough, may have to watch for some fog development
in spots, but for now will hold off mention. Cool lows well down in
the 50s in many areas, and again how cool dependent on extent of
clearing or clear areas. Thus there may be some variance in low temp
values by 12z Tue.   ..12..

.LONG TERM...(Tuesday through next Sunday)
ISSUED AT 325 AM CDT Mon May 21 2018

After a brief respite, the unsettled pattern returns for the second
half of the week into the start of the holiday weekend before
abating yet again just in time for Memorial Day.

Weak high pressure builds down into the area on Tuesday providing a
break from the unsettled pattern of recent. The main challenge on
Tuesday will be with cloud forecast and impact on high temps. This
holds true especially across northern IL where a boundary off Lake
Michigan may surge inland and generate more widespread low clouds
with temps possibly struggling to reach 70 degrees. Further west
away from the boundary expect more solar insolation to push highs to
around 80.

A large upper low developing over the southwest CONUS is shown to
eventually open up and lift across the northern tier of states late
week. In advance... Wed/Thu... heights aloft will build overhead
resulting in near to above normal temperatures. The main track of
any ejecting lead shortwaves, and subsequent support for ascent and
focus of low level jet during this midweek (Wed/Thu) timeframe will
be largely to our west on backside of ridge. Thus, while we will
have rain chances Wed/Thu this appears likely to be more for remnant
or decaying activity and generally spotty/light, with the more
robust convection and heavier rains taking aim to our north/west.

Our better window for storms and heavier rains would appear to be
Fri/Sat, as remnant upper low traverses northern CONUS flattening
the ridge over the region. At the same time, low level jet focus
and attendant moisture advection veer into the region owing to
better prospects for convection. Any organized severe weather threat
looks low right now with lack of upper jet support. Otherwise, the
main story Fri/Sat will be the warm and humid conditions, with the
potential to see highs well into the 80s to near 90 degrees in the
presence of 850 mb temps generally between 17C and 20C. Temps though
will be very dependent on extent of convective debris/cloudiness.
Dewpoints could be pushing 70 in some areas thus making it feel
more summerlike in the humidity department ... right on cue for the
unofficial start of summer.

Sunday and Monday look to feature another bout of high pressure and
a return of dry conditions, and seasonable temps and humidity


.AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning)
ISSUED AT 605 AM CDT Mon May 21 2018

Passing showers with varying bouts of low MVFR to IFR CIGs VSBYs
will continue through late morning, before the showers wane into
the afternoon with a progressing short wave. Pockets of MVFR to
IFR fog as well, especially south of I80. Some improvement in
CIGs to all MVFR this afternoon. Light winds will become west to
northwest this evening behind a weak passing sfc low pressure. If
clouds continue to raise and thin tonight, there may be the
potential of more fog development as sfc winds go light and
variable in many areas especially after midnight.




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