Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 182336
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
636 PM CDT Thu May 18 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 255 PM CDT Thu May 18 2017

Cold front extended from lower MI to central IL and then to low
pressure situated in the se corner of CO. Classic severe weather
set-up in the Plains with a dry line in west TX with temperatures
around 90 and dewpoints in the teens to the west, and readings
near 90 with dewpoints near 70 east of the dry line. GOES-16
showed supercells rapidly developing west of Wichita Falls and
Lawton moving northeast. In the meantime, a snowstorm was
occurringin CO and WY.

In the dvn cwa, northerly winds were bringing clouds and cooler
temperatures to our northern cwa while it was milder in the south
with a west wind, and plenty of sunshine. 2 pm temperatures
ranged from 61 at Independence to 82 at Macomb.

&&

.SHORT TERM...(This Evening through Friday)
ISSUED AT 255 PM CDT Thu May 18 2017

Forecast focus on showers and thunderstorms returning.

Numerous tornadic supercells will be firing across the central/southern
Plains and into western MO through this evening. These will
eventually congeal into clusters/lines and then spread towards the
dvn cwa. The ESRL HRRR and NAMNEST indicate these storms to gradually
weaken and stratify out as they get into our sw cwa well after
midnight. However, an isolated elevated severe hailer (around 1 inch)
is possible in our far south where SPC has a marginal risk. There
is at least moderate shear but instability is minimal. These
showers and embedded storms will then continue spreading northeast
over the remainder of the cwa Friday morning. On Friday afternoon,
any scattered showers and isolated storms should gradually
diminish and many areas may end up dry, as the forcing weakens.
Rainfall amounts averaging around 1/2 inch is expected.

Lows tonight will range from the lower 40s along Highway 20 to the
mid 50s in extreme northeast MO. Highs on Friday should range from
the lower 50s along Highway 20 to the mid 60s in extreme northeast MO.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 255 PM CDT Thu May 18 2017

Complex long term scenario, with a slight chance of severe
weather and decent rainfall early this weekend, along with a drop
in temperatures expected by next week.

Friday night into Saturday...Model consensus is in good agreement of
showers and thunderstorms across the entire CWA beginning during the
Friday night period. Modest instability and shear will also be
present, which may help support hail in the stronger storms.

Compared to previous runs, all models seem to be converging on the
track of the surface low, with a general track from southern Iowa to
northeast Iowa during the day. Handling of the warm sector, however,
is still subpar likely due to forecast precipitation coverage. The
GFS continues to favor a more northern intrusion of the warm sector
into our southeastern counties, while others such as the Canadian
keep it and associated precipitation south into central Illinois.
The Storm Prediction Center has placed our counties along and
east of the Mississippi in a marginal risk of severe weather at
this time, and will therefore continue to monitor this low
confidence situation.

Saturday night through Monday afternoon...Showers and thunderstorms
will exit the region Saturday night, giving way to a mix of clouds
and sunshine for Sunday and much of Monday as high pressure builds
across the central Great Plains and lower Mississippi Valley.
Temperatures for Sunday will be below normal as cooler air advects
behind the departing low, with highs expected to climb into the
upper 60s. By Monday we will return to normal as highs climb into
the lower 70s.

Monday night on...Our next system will impact the CWA Monday night,
with showers and thunderstorms expected through the day Tuesday.
It`s too early to gage if severe weather will be possible, but at
this time forecast instability is low across the region.

Further out, most models suggest drier weather making its way
into the region by Wednesday and continuing through at least
Thursday evening. The GFS is the only outlier with an upper level
shortwave moving into the area on Thursday. Look for temperatures
to average below to near normal.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
ISSUED AT 637 PM CDT Thu May 18 2017

A reinforcing cold front making its way southeast through eastern
Iowa was providing a wind shift to more northerly surface winds
and a trailing stratocu deck likely to remain just above MVFR
thresholds this evening. Winds will veer to the northeast and
strengthen overnight as a storm system strengthens in the plains.
Elevated showers and thunderstorms are expected late tonight and early
Friday morning, which will dissipate to showers by mid morning.
This is expected to be followed by lowering ceilings and possible
light fog as cooler air moves in from the east-northeast during
the day. Will keep conditions MVFR for now, thinking the models
may be too pessimistic with their widespread sub 1000 ft, IFR,
ceilings over the region in the afternoon.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Speck
AVIATION...Sheets



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