Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 230534
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1134 PM CST Thu Feb 22 2018

...AVIATION UPDATE...

.UPDATE...
Issued at 745 PM CST Thu Feb 22 2018

I have issued a small winter weather advisory for our Iowa Highway
20 counties through 6 AM. The forecast for rising temps appears to
be correct, but not until after Midnight, thus the light
rain/light sleet/light drizzle is possibly freezing on contact to
untreated roads in the far northwest. The Iowa 511 website reports
patchy snow or ice in that area, and with air temperatures near
32 there, that probably will not improve until later tonight, and
an advisory seems the best approach to cover the light glaze on
untreated roads there.

&&

.SYNOPSIS...
Issued at 315 PM CST Thu Feb 22 2018

Warm air advection and low level moisture transport was producing
stratus and patchy fog. Mid afternoon temperatures have risen into
the mid to upper 30s. 3 hr pressure falls of 4 mb was noted across
the dvn cwa.

Synoptically, a deep upper level trough was anchored in the
western United States with a fast southwest flow aloft over the
Midwest.

&&

.SHORT TERM...(This Evening through Friday)
ISSUED AT 315 PM CST Thu Feb 22 2018

Forecast focus on light rain tonight.

Tonight: Weak wave ejecting out of the main trough will provide
forcing, and along with increasing moisture, will spread light
rain into our western cwa by early to mid evening, with this rain
then pushing across the remainder of the cwa by around midnight.
The rain is expected to continue for most of the night, but then
end from west to east late tonight. By sunrise the rain should
essentially have exited the dvn cwa, as this wave lifts off to the
northeast of the area. This forecast is heavily based on the
HRRR/NAMNEST. Rainfall amounts should generally be in the range of
one-tenth to one-quarter of an inch. However, this amount of rain
should not have additional impact on rivers. I have also added
patchy fog in the grids. Lows should bottom out in the lower to
mid 30s.

Friday: A dry day but plenty of clouds for much of the day. There
may be some partial clearing in the north during the afternoon.
Highs will be in the upper 30s to mid 40s.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 315 PM CST Thu Feb 22 2018

Main forecast concern for the long term is the system at the
beginning of the period.  A wintry mix will give way to rain and
thunderstorms on Saturday.  Once this system moves out of the area,
temperature will begin to warm to above average.

Friday night into Saturday, the main H5 trof is forecast to swing
through the area.  A response in the low levels will lead to H85 WAA
during the day on Saturday.  Depending on the model, the warm sector
and triple point either travels through the CWA or just to the south
of the CWA.  Regardless, overall temperatures will warm above
freezing across the area, melting any frozen precip that has fallen.
Main concerns turns to where the warm sector is.  With a deepening
surface low, winds will be backed near the warm front.  Between 00z
Sunday and 06z Sunday the H5 trof turns negative  This will lead to
a strong wind field that shows speed and directional shear.  If
convective updrafts can form in the warm sector and then approach
the warm front storms could rotate.  This could lead to a chance for
severe weather.  The location of the warm front and triple point
will be the limiting factors and will need to be watched by later
shifts.

Overall rainfall totals look to be light with this system. Overall
totals look to be less than half an inch. This will likely not
affect any of the current river flooding.  However, if there are
thunderstorms then rainfall amounts could be higher.  Thunderstorms
could lead to more flooding.

After this time, temperatures will warm as SW flow leads to warm air
across the area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
ISSUED AT 1129 PM CST Thu Feb 22 2018

Very low cigs and visibilities in light rain and drizzle will
continue into the night, with Cigs generally less than 500 ft and
visibility between 1/4 mile and 2 miles. Around 10Z this morning,
winds will switch to south and southwest, ushering in drier air
and ending this fog event, likely also ending rains. By mid
morning Friday, winds will become northwest and VFR weather will
return to the region.

&&

.HYDROLOGY...
Issued at 213 PM CST Thu Feb 22 2018

Flooding is ongoing in the Rock River and Wapsi River basins. With
the exception of Como, all sites are rising. With the flooding on
the Pecatonica River, Yellow Creek is also backed up and leading
to flooding. As a result an areal flood warning has been issued
for Yellow Creek. This will likely need to be continued until the
Pecatonica crests and starts to drop through the weekend.

On the Rock River, a long ice jam runs from Erie to Prophetstown.
This ice jam is leading to high water and impacts along the river.
This will continue until the jam breaks. Ice will lead to rapid
changes in the river. Those along the river should pay attention
to future forecasts.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Winter Weather Advisory until 6 AM CST Friday for Buchanan-
     Delaware-Dubuque.

IL...NONE.
MO...NONE.
&&

$$

UPDATE...Ervin
SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Gibbs
AVIATION...Ervin
HYDROLOGY...Gibbs


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