Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 180803

Area Forecast Discussion
National Weather Service Quad Cities IA IL
303 AM CDT Thu May 18 2017

Issued at 300 AM CDT Thu May 18 2017

At 300 AM CDT, surface low pressure was centered in western
Wisconsin, with a cold front trailing into central Iowa. Severe
storms had pushed east of the area, with lingering showers
skirting Highway 20 and points north. A southwest breeze held
temperatures up in the 60s to low 70s.


.SHORT TERM...(Today and Tonight)
ISSUED AT 300 AM CDT Thu May 18 2017

The main forecast issue in the short term period is the potential
for isolated strong to severe storms late tonight.

In the near term, light showers may continue to fester in the far
north through late morning. Otherwise, expect a northwest wind
developing behind a cold front that will push through the forecast
area today. The temperature contrast will be rather large from
northwest to southeast, with highs in the upper 50s near
Independence, to around 80 degrees in the Macomb area.

For tonight, several CAMS depict a thunderstorm complex pushing
through Missouri overnight and the northern fringe lifting into
the forecast area after midnight. Areas along and south of Highway
34 from Fairfield to Galesburg are outlooked in the marginal risk
area. Steep mid-level lapse rates would favor marginally severe
hail. Lows tonight will be much cooler, settling in the 40s to low

.LONG TERM...(Friday through Wednesday)
ISSUED AT 300 AM CDT Thu May 18 2017

There is a persistent signal indicating temperatures mainly below
normal for the weekend and much of next week with a fairly active
weather pattern. Precipitation has the potential to average above

Friday, the first of a two part storm system will move through the
area. The 00z model suite has sped up the arrival of the rain
whereas the Dprog/dt trend had been slower. Interestingly, the winds
aloft supplying the moisture flow are not overly strong so the rain
might arrive somewhat slower than what the models depict depending
upon the depth of the dry air over the area.

Regardless, rain will overspread the area from southwest to
northeast during the day Friday. A layer of unstable air aloft is
expected to allow embedded thunderstorms to develop as the overall
forcing increases during the day. The stronger storms would be
capable of producing small hail.

Friday night through Saturday evening the second, and stronger part
of the storm system will move through the area. There are
disagreements among the models regarding the track of this system.
The ECMWF/GFS/CMC global take the low across Iowa but anywhere from
central/western, ECMWF/GFS respectively, to eastern Iowa, CMC
global. The WRF takes the low from northern Missouri to southern
Lake Michigan, much further east. Where the low tracks will be
important as a further west scenario increases the probability of
getting into the warm sector and thus the potential for storms.

Based on what the internal signals from the models are suggesting,
the following scenario appears reasonable.

Friday night: areal coverage of the rain will increase again as
moisture moves into the area and the overall forcing increases. A
layer of unstable air aloft will allow embedded thunderstorms to
develop. The stronger storms will be capable of producing hail that
may approach severe limits.

Saturday/Saturday night: going with a modified consensus, the
surface low would track across eastern Iowa; probably closer to the
Quad Cities than Cedar Rapids based on Dprog/dt trends. Such a track
would bring the warm sector into the eastern half of the area during
its passage. If this scenario is realized, there would be a
potential for developing severe storms with the afternoon/evening
time frame being favored.

Regardless, the best chances for rain would be during the day
Saturday. Rain will quickly end from west to east Saturday evening
as the dry punch aloft and associated cold front moves through the

Sunday on...

Quiet and cool conditions will be seen Sunday through Monday across
the area as high pressure moves through the Midwest. Temperatures
will average below normal.

Monday night through Tuesday night the next storm system moves
through the Midwest. The models disagree on the overall timing and
track of the system but generally agree upon moving the storm from
the southern Plains northeast to Michigan. The model consensus has
chance to likely pops Monday night and chance pops Tuesday/Tuesday

Depending upon the track and timing of the storm system, Wednesday
could end up being dry. Right now the model consensus has slight
chance to chance pops across the eastern half of the area for a
slower departure.


.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
ISSUED AT 1148 PM CDT Wed May 17 2017

A surface low pressure system moving from MN to the Great Lakes
will provide breezy conditions tonight into Thursday. There is low
confidence in the potential for an MVFR stratus deck developing
late tonight and lingering into Thursday morning, which is
included at CID and DBQ. Once any stratus lifts, VFR conditions
will prevail. Winds will veer to the west Thursday and diminish
to less than 12 kts by late day.




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