Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 221750
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1150 AM CST Wed Feb 22 2017

...18Z AVIATION UPDATE...

.UPDATE...
Issued at 1029 AM CST Wed Feb 22 2017

All the dense fog has dissipated across northwest Illinois and
thus the dense fog advisory has been cancelled. Some fog persists,
so kept a patchy fog mention in until 11 am. Stratus in
northern/central IL may still linger into early/mid afternoon,
though, with plentiful low level moisture in place below a
strengthening inversion. Overall, most of the stratus concern
should be east/south of the forecast area.

UPDATE Issued at 902 AM CST Wed Feb 22 2017

Dense fog dissipating on schedule across eastern Iowa. However,
stratus/fog is thicker across northwest Illinois. Visibilities are
coming up slightly with the latest 9 am observations, ranging from
0 to 1/2 mile. To be on the safe side, have extended the dense fog
advisory until Noon. The advisory may be able to be cancelled at
11 am, but with some guidance suggesting visibilities could stay
down until Noon and to blend nicely with neighboring offices,
have extended the advisory until Noon.

May have to watch temperatures and sky cover across northwest
Illinois as well. The stratus deck may not dissipate until Noon.

UPDATE Issued at 741 AM CST Wed Feb 22 2017

With sunrise, we are seeing the dense fog become more patchy in
nature, but with many areas still reporting 1/4 or less, I`m
inclined to keep the advisory intact through the 9 AM conclusion.

ERVIN

&&

.SYNOPSIS...
Issued at 330 AM CST Wed Feb 22 2017

The moisture never did get very far away from the area yesterday
with the weak high pressure in place, and that left the stage set
for shallow moisture return on the developing south winds this
morning. Dense fog has spread throughout most locations southeast of
Mt. Pleasant to Maquoketa to Freeport Il line as of 2 AM.
Temperatures have risen slightly since mid evening, and with
dewpoints in the upper 40s to lower 50s working in, it looks like
we`ll have a very mild start to the day, but the fog will at least
create some negative impact to the initial rise in temperatures.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CST Wed Feb 22 2017

The HRRR has a great handle on the fog, and is on board with a 8-9
AM mixing out, and with clear skies above it, that looks accurate.

Yesterday, Omaha mixed to above 850mb.  Needless to say, it we pull
that off, we`re going to destroy records by 8 to 10 degrees. It does
look like there will be a 3 to 5 hour period from late morning,
where a combination of clear skies, southwest winds around 20 mph
gusting to 28 mph will bring ideal warming conditions. This supports
highs reaching the lower to mid 70s area wide. If we take full
advantage of today`s set up, I still can`t rule out upper 70s, but
again, that`s a best case scenario, and the morning dense fog will
create enough of an unknown for me to keep from going with that.

The rise in afternoon temperatures should also correspond with a
drop in humidity values to under 35 percent in the southwest 1/2 or
so. This will create GFDI values in the very high range for several
hours, and we`ll keep addressing this fire spreading threat in the
HWO and in today`s weather graphics.
ERVIN

.LONG TERM...(Thursday through next Tuesday)
ISSUED AT 330 AM CST Wed Feb 22 2017

Thursday...Latest suite of 00z run models suggest Thu to be a post-
frontal day with boundary laying out west-to-east along and south of
the CWA. Will have to watch for at least some patchy fog in the
northern third of the CWA Thu morning, then attention turns to
increasing lift signal acrs the area from the southwest to lee of
developing upper trof. Strong isentropic signal suggest overrunning
rains to spread up and over the boundary as the day progresses and
especially during the afternoon. Will keep it stratiform rain for
now through 00z Fri, but an embedded thunderstorm possible in the
west/southwest by late afternoon. Rain more widespread acrs the
south half of the CWA Thu afternoon in and just north of developing
prime LLj convergent zone...0.10 to 0.20 tenths of an inch of rain
possible by early evening in these areas. Despite easterly llvl flow
north of the front and increasing precip chances, still a seasonably
mild day with highs in the upper 40s north, to the upper 50s/around
60 in the south.

The models continue to vary with developing llvl cyclone and ejection
path northeastward out of the southern/central plains Thu night into
Friday.  00z run SREF placement has the sfc low center deepening
close to 990 MB acrs central into north central IA by 12z, while the
00z ECMWF continues to be a southern trended with the cyclone
near Kirksville MO at that time. But even the further south Euro`s
thermal parameters support all liquid precip even in the northwest
thru Fri morning. Several medium range models suggest strong warm
moist conveyor on nose of 50 KT LLJ converging just north of the
LLVL boundary targeting the northern 2/3`s of the DVN CWA Thu
night. Again, it appears this process to fuel a
elevated/overrruning rain band embedded with thunder or even a
elevated cool season type of MCS acrs the area. The NAM suggests a
plume of 500-1000 J/KG MUCAPES to push acrs the CWA THu night from
the southwest supporting thunder chances, but they should be
rooted above strong llvl shear profiles hopefully to limit the
severe risk. But if they can tap into the upper layer of the
enhanced shear profiles, there would be at least a hail threat.
PWAT feeds of an inch or even more suggest rainfall amounts of the
same values possible under the prime convergent swaths by early
Fri morning. Thus seasonably heavy rainfall and some run-off may
produce rises on area creeks and rivers by Fri.

Friday...This day initially looks to be a dry slot/punch day from the
southwest for a part of the day, but lingering showers and even
some storms in the north and east through midday. Windy an mild
conditions in the dry slot with gusts up to at least 35 MPH, and
deep mixing in temporary WAA surging temps into the upper 50s or
even 60s acrs the east half of the FCST area. Interaction of dry
slot into warm moist tongue under strong diffluent southwesterly
cyclonic lift regime may spawn a severe weather episode/supercells
not all that far east of the CWA Fri afternoon, with southwestern
IL into NW Indiana looking like the prime axis currently.

Fri night...wrap around def zone band of precip still on track to
sweep east acrs the CWA, just some timing and thermal differences
still in the latest available medium range solutions. But the gist
is that strong in-wrapping cold conveyor should switches the rain
into wet snow with current model runs suggesting from a half inch
to 1.5 inches possible by Sat morning north of I80. The snow may
fall as northwest winds increase to 15 to 30 MPH making for reduced
VSBYS and tricky travel, but it may also occur lat Fri night and
early Sat morning. Warm ground from the recent warm spell also may
play as a snow accumulation inhibitor, unless rates can overcome
that.

Saturday and Sunday...The latest runs suggest Sat to be dry and more
seasonable, and will have to watch for a light isentropic precip
event on Sunday as return flow/lift impinges on lingering llvl
baroclinicity. The 00z ECMWF has remained more consistent with light
precip amounts and south track, while the 00z GFS has trended wetter
and further north. Somewhat moderating temps on Sunday as well.

Next Monday and Tuesday...Longer range signals suggest continued
thermal moderation into early next week, as well as a delay of the
next warm moist conveyor from the south fed precip event not til
late Mon nigh or more like Tue. The further the delay, the more
likely it will be mainly another rain event as opposed to snow or
wintry mix. Mild signal and another strong cyclone rolling acrs the
Midwest for mid next week.    ..12..

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 1145 AM CST Wed Feb 22 2017

VFR conditions to be found through most of TAF cycle at all sites.
Occasional gusts over 20 kts can be expected this afternoon at
CID/DBQ/MLI. A cold front will switch winds to the northwest by
the middle of the evening, then turn to the northeast after
midnight. Guidance does show some post frontal MVFR clouds trying
to drop south early Thursday and have included a SCT030 deck at
DBQ/CID.

&&

.CLIMATE...
ISSUED AT 330 AM CST Wed Feb 22 2017

Record Highs for today February 22...

Moline.........66 in 1922
Cedar Rapids...64 in 1984
Dubuque........61 in 1984
Burlington.....66 in 2000

&&

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

$$

UPDATE...AJ
SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...12
AVIATION...Gross
CLIMATE...Ervin



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