Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 141701
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1201 PM CDT Sat Apr 14 2018

...AVIATION UPDATE...

.UPDATE...
Issued at 1004 AM CDT Sat Apr 14 2018

Winds have spread south a bit farther with respect to sustained
winds over 30 mph and gusts to 45, so I`ve updated to place the
Scott/Muscatine/Rock Island county areas into the wind advisory.
No other headline changes at this time. ERVIN

UPDATE Issued at 853 AM CDT Sat Apr 14 2018

I have updated to drop the front all the way through our far
southern counties. This is based on obs and radar trends showing
showers forming just south of the CWA line. So, what that will
mean is all areas today will see near steady temperatures, with no
diurnal rise. For the north, that means strong winds and mid 30s,
for the central areas, upper 30s to near 40 and moderately strong
winds, and the south lower 40s with only 15 to 25 mph winds.

Rain showers will begin to spread into the CWA from southwest to
northeast in the next hour, in a slow process, is it follows the
strong difluent just east of the upper low in western Iowa. In the
mean time, we`ve got areas of drizzle going, and too keep it
simple, I`ve left the pops and weather alone for now as they
advertise a wet day.

&&

.SYNOPSIS...
Issued at 330 AM CDT Sat Apr 14 2018

Impressive early spring storm system continues to impact the central
CONUS with a variety of weather. At the surface, a double barrel low
was situated from southeast NE to north central MO. A tightening
pressure gradient between these pair of lows and high pressure
building into Ontario was leading to strong northeast winds north of
the surface boundary as it exits the far southern counties. Temps
depict the front, ranging from 34 degrees at Dubuque and Independence
to 61 at Keokuk at 3 am. Will see periods of rain/drizzle and
perhaps isolated storms today as the system approaches. But, then
tonight through Sunday as the storm slowly pulls away and the cold
air deepens will see the precipitation change over to a light
wintry mix and then all snow with some accumulations especially
over the northwest third to half of cwa.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Sat Apr 14 2018

Today...Large slow moving cyclone center to only make it into
southwest IA by this evening. Second round of elevated showers and
some thunderstorms to develop to the lee of it, and spread acrs the
CWA from the west-southwest as the day progresses. This activity may
be more widespread and affect more of the area than what happened on
Friday which was dry slot impacted. Until these showers arrive,
expect brisk winds and drizzle. Very strong pressure gradient
northeast of low center, driving higher end wind advisory criteria
and the headline has already been issued for that parameter for
today. Gusts may approach 50+ MPH with gravity wave enhancement and
localized mix-down of high winds just aloft by the showers/storms.
Some storms may be able to produce hail as well. Where more
widespread shower and storm clusters occur, there will be the
potential of at least moderate rainfall amounts of a half inch to
over three quarters of an inch by late this afternoon. Temps
continue to be a large challenge with sharp gradient to the south of
I80 toward west-east boundary undulating in place acrs the far
southern CWA. Areas in the north to be held in the 30s all day with
rain and winds making for raw conditions.

Tonight...Brisk northeasterly boundary layer flow, as well as some
cooling aloft may produce a wintry mix sounding in the northern CWA
toward the HWY 20 corridor by mid evening. Feel the models,
especially the NAM, are still too bullish on freezing rain/icing
development taking into account mild ground temps. See more in the
way of rain changing over the rain-sleet mix, and then top-down
cooling into mainly all snow parameters from west-to-east as the
night progresses. But with brisk northeast wind fetch at the sfc and
potential lower wet bulb zero feed, will still advertise some light
freezing rain and glaze, but icing to be light and mainly on
elevated surfaces. Will go with an Winter Weather advisory along the
HWY 20 corridor from Dubuque on westward, starting mid evening for a
wintry mix making for possible slick spots. Will continue it on
Sunday as the mix transitions into all snow with 1-3 inches of
accumulation possibly by Sunday afternoon. Other areas to have
organized rain move out, with dry slot producing either drizzle or
areas of no precip at all.

.LONG TERM...(Sunday through next Friday)
ISSUED AT 330 AM CDT Sat Apr 14 2018

Sunday...expect a mainly def zone band of snow moving in from the
west, starting late tonight, and progressing acrs most of the CWA
into Sunday afternoon. With marginal sfc temps and occurring during
the day, most areas to get an inch or less mainly on grassy/elevated
surfaces. But do expect some areas north of a line from Iowa City,
to Clinton IA, and to Mt Carroll to get 1-2+ inches by late Sunday
afternoon. Areas northwest of Cedar Rapids and Dubuque, some
localized amounts up to 3 inches. Again, portions of these areas in
a winter weather advisory through Sunday evening for these higher
snow amounts following the wintry mix of Sat night. Brisk winds
mixing in with the winter precip also complicating matters. Because
of this, additional fcst shifts will have to assess whether to expand
the Advisory east and south depending on developing conditions
supportive of slick surfaces or travel impacts like strong wind
reduced visibilties. Temps really held down well below normal for
Sunday highs...winter-like 30s. Just light snow or flurries in
blustery winds for Sunday night as we get finally on the back side
of the large slow-rolling low complex.

Quick look at the longer range...another vigorous but more
progressive wave to be a precip and wind maker by Wednesday. Below
normal temp regime continues for much of the coming week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
ISSUED AT 1156 AM CDT Sat Apr 14 2018

A slow moving intense storm system will move east across the area
through Sunday night. A prolonged periods of windy, low IFR to
very low IFR conditions will be expected, as rain showers today,
change to snow tonight and last through Sunday. Winds today will
be 25 to 40 kts from the northeast, but will shift to north
tonight, and decrease to 15 to 30 kts. Snow is unlikely to
accumulate southeast of Cedar Rapids to Dubuque, but elevated
surfaces, including unheated aircraft may see wet snow
accumulations after dark tonight. Runways may be slushy at times
tonight and early Sunday. The snow during the day Sunday is
unlikely to accumulate.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Wind Advisory until 7 PM CDT this evening for Benton-Buchanan-
     Cedar-Clinton-Delaware-Dubuque-Iowa-Jackson-Johnson-Jones-
     Linn-Muscatine-Scott.

     Winter Weather Advisory from 10 PM this evening to 7 PM CDT
     Sunday for Buchanan-Delaware-Dubuque.

IL...Wind Advisory until 7 PM CDT this evening for Carroll-Jo Daviess-
     Rock Island-Stephenson-Whiteside.

MO...NONE.
&&

$$

UPDATE...Ervin
SYNOPSIS...McClure
SHORT TERM...12
LONG TERM...12
AVIATION...Ervin



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