Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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093
FXUS63 KDVN 230943
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
343 AM CST Fri Feb 23 2018

.SYNOPSIS...
Issued at 315 AM CST Fri Feb 23 2018

As of 300 PM: All airport observing sites were above freezing.
However, several mesonet sites were at 32-33 F across northern
Buchanan and far northern Delaware Counties. So there remains a
threat for slippery patches on untreated roads and sidewalks.

Light rain and drizzle, coinciding with a broad and weak area of
low pressure, was impacting all but the southwest third of the
forecast area. There have also been areas of fog overnight with
visibilities occasionally below 1/2 mile. Visibilities will
improve as winds turn to the southwest.

&&

.SHORT TERM...(Today) ISSUED AT 315 AM CST Fri Feb 23 2018

A Winter Weather Advisory remains in effect for Buchanan and
Delaware Counties until 6 AM for the possibility of a light
glazing of ice on untreated surfaces. The threat is for locations
mainly north of highway 20. Iowa DOT road conditions and pavement
temperatures indicate the better chances for ice are north of the
Quad Cities forecast area, but will keep Buchanan and Delaware in
the advisory due to pockets of 32 F degree observations.

Dubuque County was removed from the advisory because temperatures
had warmed into the mid 30s county-wide.

The rest of today will be quiet as the 700-500mb ascent zone
driving the light rain quickly exits into Wisconsin and E
Illinois. Highs will be in the 30s and 40s. Uttech

.LONG TERM...(Friday Night through Thursday) ISSUED AT 315 AM CST
Fri Feb 23 2018

Main forecast challenge is the system early in the period. The upper
level trough out west will lift east-northeast, sending a strong
shortwave and surface low through the Midwest Saturday. Warm
advection and moisture return ahead of this will bring a threat of
mixed wintry precipitation late tonight into early Saturday morning.
Models have suggested a delayed onset from the previous forecast and
are also trending drier, which is reasonable taking into account the
strengthening, dry low level easterly flow late tonight at the onset
of the warm advection aloft. Thus, only anticipating light
precipitation, with perhaps a glazing of ice in the far south or
snow accumulation of less than a quarter inch.

Temperatures will slowly rise through the day with showers becoming
more numerous by afternoon as developing surface low approaches from
the southwest. Models disagree on the path of the main surface low,
either through the forecast area, or to the south Saturday afternoon
into Saturday evening , which will be critical for temperatures and
thunderstorm threat. The late day timing of both the surface low and
strong upper forcing appears too late in the day to tap into diurnal
instability, lending low confidence in any threat of strong storms,
given the amount of low level shear. Will continue a mention of at
least isolated thunderstorms with a compromise blend of model high
temperatures from the mid 30s north to around 50 south. If the more
northern tracks verify, the far south could and up well with highs
well into the mid 50s. The fast movement of the system and
likelihood of moisture focusing on the established rainfall axis
from southern MO into the Ohio River suggests total QPF less
than a quarter inch in most areas.

Dry weather and above to much above normal temperatures follow for
Sunday through Tuesday under a zonal, then reestablishing southwest
flow aloft. Relatively high pops are in place Wed into Thu where
models are in rough agreement with another low pressure system
lifting through the forecast 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 315 AM CST Fri Feb 23 2018

Flooding due to runoff from heavy rainfall earlier continues along
portions of the Pecatonica, Rock, and Wapsipinicon Rivers. Major
flooding is occurring on the Rock River at Moline and Joslin, where
stages were still rising early this morning. An ice jam is affecting
the river from roughly Erie to Prophetstown, contributing to the
high water and impacts along the river. Until this ice moves further
downstream, rapid changes in river levels can be expected. Further
upstream, the flood crest has passed at Como, where moderate
flooding was occurring and river levels have been slowly receding
since Wednesday night.

On the Pecatonica River, moderate flooding is occurring and the
river is forecast to crest with major flooding this weekend. Water
continues to back up and cause flooding along Yellow Creek and an
Areal Flood Warning remains in effect for this impact. This flooding
will continue until the Pecatonica begins to recede early next week.

On the Wapsipinicon River near Dewitt, the river crested Thursday
and levels are forecast to continue to fall. Moderate flooding is
occurring this morning and the river is forecast to drop below flood
stage this afternoon.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Winter Weather Advisory until 6 AM CST early this morning for
     Buchanan-Delaware.

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

$$

SYNOPSIS...Uttech
SHORT TERM...Uttech
LONG TERM...Sheets
AVIATION...Ervin
HYDROLOGY...Sheets



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