Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 220835

Area Forecast Discussion
National Weather Service Quad Cities IA IL
335 AM CDT Tue May 22 2018

Issued at 330 AM CDT Tue May 22 2018

Mid to upper moisture flow patterns on the current water vapor loop
showing passing upper trof along and north of the CWA over the upper
MS RVR Valley, while large cut-off upper low adjusts eastward acrs
NV and southern CA west of the 4-corners region. This western upper
trof will effectively amplify upper ridge axis/building thermal dome
acrs the mid CONUS over the next several days, until an ejecting
piece of wave energy tries to break it down by late week and into
the start of the weekend, for increasing precip chances by that


.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Tue May 22 2018

Today...Fog the initial issue early this morning, with varying
amounts of both lower level and high clouds currently helping limit
more of a widespread dense fog threat around light convergent sfc
flow around an inverted sfc trof aligned over the area. But Looking
at the latest Obs and several webcams, seems it is expanding acrs
the western two tiers of counties and will issue an Advisory for
those areas. Will also target the three counties of NW IL with the
dense stuff most widespread acrs Stephenson Co. The pockets of true
dense fog further east and south are not widespread enough to
warrant an advisory at this time, but will watch trends over the
next several hours through sunrise for headline expansion.

Expect morning clouds and fog to mix out and decrease by late
morning, for partly to mostly sunny skies during the afternoon. As
the passing short wave trof to the northeast digs down toward
southwest lower MI and northeast IL, a few models develop at least
some isolated showers in the north and northeastern third of the
this morning and into the midday, before the trof exits off to the
east-southeast. Low confidence in this possibility at this time and
will keep the fcst dry for today. Fcst soundings mix deep today up
to base of H85 MB broad inversion, and will lean toward the warmer
side of guidance. Widespread highs in the upper 70s to lower 80s,
except acrs the northeastern third where more low to mid 70s will

Tonight...The 00z run models really pump up upper ridge axis acrs the
MO RVR valley and towards the mid to upper MS RVR Valley through
early Wed morning. An increasing southwesterly 20-25 KT LLJ
converges an elevated THTA-E wing from acrs northwest IA, into
central and toward southeastern IA by midnight. An elevated warm air
advection(WAA)wing of showers and thunderstorms expected to develop
acrs the mid MO RVR Valley-northwest into north central IA
tonight...with the potential for some of this activity to bleed east-
southeast into the northwestern CWA late tonight after 3-4 AM CDT.
Like mentioned before, the ridge just east of this process will be
stout, and the elevated convection may have trouble maintaining as it
enters the local area/northwestern third of the DVN CWA. Will go
with slight to moderate CHC POPs for now in these areas after 1 AM
if even for a decreasing wing of showers and storms. A few models
such as the 00z run GFS even stop the precip before it enters the
CWA through 12z Wed morning, just decaying debris sliding this far
east. Some signs of more fog development late tonight in
northeastern into north central IL, possibly making it as far west
into the Freeport IL area again, but for now will hold off mention.
Lows in the 50s to around 60.    ..12..

.LONG TERM...(Wednesday through next Monday)
ISSUED AT 330 AM CDT Tue May 22 2018

Summer-like weather expected heading into... and throughout the
upcoming Memorial Day holiday weekend characterized by above
normal temperatures, humid conditions, fairly weak flow aloft and
near daily storm chances.

Overall, the pattern through the period will feature a mean upper
ridge over the central CONUS with fairly persistent low pressure
over the southwest U.S. This will set the stage for persistent
southerly surface low and above normal temperatures for much of
the period, with progged 850 mb temps of 16C-19C supportive
of highs in the mid/upper 80s to possibly near 90 in a few areas
in absence of convective debris/cloudiness. Additionally, dew
points will climb well into the 60s bringing heat index values
in the upper 80s to lower 90s late week and through the
holiday weekend. Hydration will be important for those outdoor
activities, as this looks to be the first prolonged warm spell of
the season.

Overall, rain chances for much of the period look rather spotty.
Initally Wed/Thu - mostly dry with mainly just shower chances
for potential decaying remnants of weakening convection from the
Plains, where bulk of storms expected into late week attendant to
foci of low level jets and close proximity of main track of ejecting
shortwaves on backside of upper ridge. Our best chance for showers
and thunderstorms may be Friday night into early Saturday, as
shortwave energy traverses the northern tier of states. This feature
will flatten the upper ridge, and may provide some ascent atop the
persistent moist, southerly flow for better coverage of showers and
thunderstorms. Beyond, the remainder of the holiday weekend now
appears may harbor at least small daily chances for showers and storms
of the airmass variety - largely diurnally driven. Bottom line, while
rain chances will exist almost daily throughout the next 7 days there
will be many dry hours as well.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
ISSUED AT 1230 AM CDT Tue May 22 2018

Areas of low MVR to IFR stratus north of I80 into this morning,
with patchy VFR to MVFR BKN CIGS south of I80. The bigger impact
will potentially be areas of fog, which could become locally
dense into early Tue morning where areas clear off cloud-wise,
along with light and variable wind zones. Otherwise, areas of
MVFR to IFR fog even under the cloud cover through 14z this
morning. Passing ridge will make for light west to northwest sfc
wind regime on Tuesday, and lifting CIGs to VFR or mainly clear by
late morning. A warm front will start to organize acrs the
central into northern plains this evening, changing the sfc winds
to a light east to southeast direction as the evening progresses.


IA...Dense Fog Advisory until 9 AM CDT this morning for Benton-Henry
     IA-Iowa-Jefferson-Johnson-Keokuk-Linn-Van Buren-Washington.

IL...Dense Fog Advisory until 9 AM CDT this morning for Carroll-Jo



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