Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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812
FXUS63 KDVN 231739
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1239 PM CDT THU JUN 23 2016

...AVIATION UPDATE...

.UPDATE...
Issued at 520 AM CDT Thu Jun 23 2016

Have issued a dense fog advisory for our NW IL counties along and
north of I-80 through 14z, where visibilities are a quarter mile
or less. Dense fog is beginning to dissipate in eastern IA
(especially NW of a CID to DBQ line) with a weak boundary of drier
air and NW winds advancing S-SE across the area and this trend
should continue. More extensive low clouds in the northern flow
over WI into NW IL and far eastern IA will prolong the fog for a
few more hours in NW IL. Over far eastern IA, webcams continue to
indicate the patchy nature of the fog and have a special weather
statement out to cover this hazard.

&&

.SYNOPSIS...
Issued at 335 AM CDT Thu Jun 23 2016

Severe storms over NW IL last evening have since pushed well east
into a severe MCS over Indiana and the Ohio Valley region. In its
wake, MSAS pressure fields show a cluster of weak lows over WI, IL
and NW IN and upstream high pressure over ND. Lingering low level
moisture, as evident by dewpoints from the mid 60s to mid 70s,
combined with nearly calm winds and initially clear skies, has lead
to widespread fog and patchy dense fog over eastern IA and NW IL
since midnight.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 335 AM CDT Thu Jun 23 2016

Initial concern is the dense fog taking shape over the area early
this morning. Remainder of the short term will feature much quieter
conditions as high pressure over the Dakotas pushes eastward.

Weak 3 hour pressure rises over MN into NW IA and light NW winds
over central IA should begin to drive and airmass with dewpoints in
the 50s to lower 60s into at least the far NW and west toward
sunrise, reducing the potential for dense fog there. Elsewhere
however, with several more hours of darkness and nearly calm winds
there will continue to be pockets of dense fog, assisted by moist
ground conditions from yesterday`s heavy rainfall. Have already
added widespread fog and patchy dense fog to the forecast through
sunrise and have a special weather statement out to cover the
areas with visibilities well below a quarter mile, which are most
widespread from the MS river into east central IA on area surface
observations. However, with most area webcams not showing much
fog so far, will hold off on an advisory.

Today: Isolated weak showers may brush the far NE during peak
heating with scattered to broken cumulus or stratocumulus over at
least the NE half of the forecast area. Developing NW winds as the
high builds eastward will gradually bring in drier air for
noticeably less humid conditions. Kept highs from the mid 70s
north to mid and possibly upper 80s in the far south, where there
will be more sunshine and surface conditions are drier.

Tonight: The surface high migrates eastward resulting in light
surface winds. This may set the stage for at least patchy fog, as
suggested by guidance. However, with drier air and a developing
light easterly low level flow out of the great lakes toward morning,
this does not look likely and will leave mention out for now. High
level moisture may produce high clouds over especially the sw,
limiting mins to the lower 60s, while the highway 20 corridor should
at least dip into the upper 50s.

.LONG TERM...(Friday THROUGH Wednesday)
ISSUED AT 335 AM CDT Thu Jun 23 2016

Main forecast concern in the long term is a cold front that is
forecast to move through the area on Saturday into Sunday.  While
this sfc boundary will appear to be a front, the main body of cooler
and drier air will advect into the area Sunday afternoon and evening
as the upper level trof advances to the east.  The cold front on
Saturday will be during peak heating of the afternoon and could lead
to thunderstorm development.

Friday, a quick cool down and dry down across the area will will
lead to pleasant highs and comfortable air before the flow turns
south to southwest again as a shortwave moves through the flow.  A
quiet start to the weekend is forecast.

Saturday and Sunday...llvl moisture advects back into the area as
temperatures warm into the 80s again.  The GEM and the ECMWF are
bullish on QPF during the afternoon in the form of airmass
thunderstorms.  With H7 temps and a llvl cap in place, convection
will not be likely until later in the day Saturday as the upper
level wave approaches the area.  No discernible upper level jet is
forecast, so for the most part there will be CAPE and little shear.
Multicell, cold pool dominated convection is expected from this
boundary and wave.  At this time it is too soon to tell if there
will be severe weather.  If the shear doesn`t increase, then I think
its safe to say that organized severe convection is unlikely.

Into next week, the flow turns more NW as cooler and drier air is in
place across the region through the end of next week.  I have
slightly higher confidence in this current forecast as both the
ECMWF and GFS are in agreement with a cool down and the large scale
flow.  Granted, this could change.  At this point though, it looks
as though this upcoming week should be rather gorgeous.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z Friday AFTERNOON)
ISSUED AT 1234 PM CDT Thu Jun 23 2016

VFR conditions across eastern Iowa and most of northern Illinois
will continue through 00z/24. MVFR clouds across northern Iowa and
Minnesota/Wisconsin are not being handled very well by the models.
Based on the overall flow, these clouds will probably move into
eastern Iowa and the remainder of northern Illinois after 00z/24.
Thus after 00z/24 conditions will slowly deteriorate to MVFR. If
fog develops, which is suggested by the models, then IFR/LIFR
conditions may be possible before sunrise Friday.

&&

.HYDROLOGY...
Issued at 304 PM CDT Wed Jun 22 2016

Continue to watch the potential for river flooding due to the heavy
rains from early this morning. Have been getting a better idea of
the basin average rainfalls so confidence is increasing in the
forecasts downstream. However, there are some small feeder
tributaries that continue to rise so there remains some uncertainty.
The Cedar River at Conesville has either reached its crest or is
nearing it but there remains a lot of water coming down the channel
so the river will remain high even after it drops below flood stage.
From the confluence of the Iowa and Cedar Rivers and downstream, the
current data has lowered the forecasts a bit, thinking the runoff is
lower due to the ongoing dry conditions to this point and the crops
being able to take in some of the water. Will continue to watch
closely, but will continue the flood watch for these locations until
confidence to upgrade or cancel occurs.

&&

.DVN Watches/Warnings/Advisories...
IA...None.
IL...None.
MO...None.
&&

$$

UPDATE...Sheets
SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...Gibbs
AVIATION...08
HYDROLOGY...Brooks



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