Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 151135

Area Forecast Discussion
National Weather Service Quad Cities IA IL
635 AM CDT Sun Apr 15 2018


Issued at 555 AM CDT Sun Apr 15 2018

Latest model guidance more robust with saturation and omegas
within dendritic zone across portions of the southwest cwa,
and radar/observational trends appear to be bearing this out
with band of heavier snow rotating in along/southwest of Vinton
to Washington corridor. Given this and obs depicting freezing
drizzle and road reports partially covered to our southwest,
I have added a handful of additional counties into the advisory
including cities of Iowa City, Marengo, Tipton, Washington and
Fairfield. Expect this area may have best chance of higher amounts
with system around 2" or little more. Lift and saturation in
the dendritic zone weaken toward the Mississippi River into NW IL,
so it would appear lesser amounts remains the trend heading east/


Issued at 321 AM CDT Sun Apr 15 2018

Strong, stacked low pressure system over the Midwest continues to
track slowly eastward. Regional radar shows much of the cwa in
between main forcing, with one ribbon of widespread precip
migrating through eastern IL within upper level diffluence and
proximity to low level moist conveyor with secondary swath /mainly
snow/ from MN through central IA in deformation NW of mid/upper
level circulation. Still some light precip being noted across
portions of the cwa mainly drizzle or very light rain, with some
light icing occurring along the Hwy 20 corridor on elevated
surfaces with temps at or below freezing. Thermal structure
continues cooling into western cwa and therefore seeing any light
precip transitioning to snow. This low pressure system will
continue to track toward the Great Lakes and Ohio Valley over next
24 hours. This will continue to bring precipitation to the region
trending toward snow on Ptype with deepening cold air on backside,
with some accums likely over portions of the cwa especially on
grassy and elevated surfaces.


.SHORT TERM...(Today and Tonight)
ISSUED AT 321 AM CDT Sun Apr 15 2018

Patchy light precip to start the day, as initially area remains in
between forcing mechanisms. Ptype will be a bit messy until better
forcing and thermal structure cools sufficiently to support
mainly snow, which should gradually occur from west to east today.
In the interim, mainly drizzle/light rain east with a mix of
sleet or brief snow in any more robust intensity. Meanwhile, west
will be mainly very fine snow and possibly drizzle/freezing
drizzle. Evolving will be deformation wrapping into cwa later
today into tonight on backside of mid/upper level low. This should
promote some better intensity and sufficiently cold for snow
especially west of the Mississippi River, although may continue
to have Ptype issues east of the Mississippi River into the afternoon.

Main hazard for much of the winter weather advisory initially will
be light freezing drizzle/very light freezing rain with minor
glaze especially on elevated surfaces, but some roadways may also
see slick conditions on the Hwy 20 corridor with pavement temps
around or just below freezing. With temps slipping down around 32F
to Cedar Rapids and Monticello, I have added another tier north
of Hwy 30 into the winter wx advisory. Eventually expect to see
precip transition over to snow today lingering for a while tonight
before tapering off. Anticipate some snow accumulations up to an
inch or two mainly north/west of Quad Cities and mostly on
grassy/elevated surfaces, with main exception being the advisory
areas where temps support some roads possibly becoming snow covered.
In addition, gusty winds will aid in periods of reduced
visibilities in the snowfall. Confidence on snow accums is low
though as concerns exist with trends of slower low movement,
weakening deformation, Ptype challenges especially east of the
Mississippi, and marginal surface temps largely outside of the
advisory areas.

Temps today will budge very little due to clouds, bouts of precip
and northeast winds. Kept most areas in the 30s with potential to
brush 40 in parts of the far south/east. Tonight will see temps
drop into the 20s areawide.

.LONG TERM...(Monday through Saturday)
ISSUED AT 321 AM CDT Sun Apr 15 2018

Monday...This day to be a chilly blustery day in lingering backside
of slow-rolling backside of GRT LKS cyclone complex.  Mostly cloudy
with northwest winds of 15 to 25 MPH and gusts over 30 MPH, making
for wind chills in the teens through late morning. Despite steep
LLVL lapse rates driving deep mixing and the winds, most temps
probably not to make it out of the 30s in most of the fcst
area...maybe the low 40s in the south. Channeled satellite vort lobe
to wring out sctrd flurries or even light snow showers through at
least early afternoon. As omega block upper ridge lobe settles east
acrs the plains/MO RVR Valley, some cloud and wind decrease later
Monday night will allow for temps to crash well down into the 20s
into early Tue morning...good thing the growing season is so far
behind, otherwise freeze headlines would normally be needed for this
time of year.

Tuesday and Wednesday...The latest 00z run medium range models eject
a strong wave out of the western CONUS upper TROF, and it will look
to undercut omega block ridge and slice it`s way eastward somewhere
acrs the mid to upper MS RVR valley this period. The latest suite of
medium range models suggest both SFC and upper lows to progress
eastward acrs IA generally from late Tue night through late Wed
night. They are however, varying still on speed and north-south
pathway placement. The 00z GFS and NAM seem a bit fast with strength
of the lee-side ridge this wave will have to battle, and they spread
a lead wing of precip into the northern half of the CWA after 06z
Wed. With brisk pre-system east flow and cool/low wet bulb fetch
north of any developing warm front, the NAM and GFS advertise a
wintry mix of sleet and freezing rain north of I80 late Tue night
into Wed morning. The NAM even advertises elevated instability
feed/MUCAPES of 200-400+ J/KG making for thunderstorms possible late
Tue night into Wed morning acrs the southwest half or more of the
DVN CWA. Strong sfc winds wrapping around the developing low
pressure may approach advisory levels again in some portions of the
area. During the day Wed, precip should change over to all regular
rain/showers, then as the system passes, wrap around DEF zone type
snows possible move in acrs at least the northern third to half of
the CWA later Wed afternoon and evening with strong dynamical/top-
down cooling post-wave  profiles. The 00z ECMWF is slower, with lead
WAA wing of precip not arriving acrs the north until after 12z Wed,
allowing for some sfc temp recovery and less of a freezing rain
threat. But even the Euro suggests post wave accumulating snows of
at least 1-2 inches wrapping in north of I80 Wed night. The model
still need time to resolve this wave in the runs over the next 24-36

Thursday through next Saturday...After whatever mid week low
pressure system can roll through and affect the region, a blocked
pattern will look to evolve acrs much of the CONUS this late week
period. The new ECMWF even suggests a type of Rex Block and keeps
the CWA mainly dry with moderating temps back closer to normal
through Sat. The 00z GFS progresses another large closed low out of
the blocked pattern acrs the mid CONUS, with it`s northern flank
precip bands making into the local area by Sat. Enhanced northeast
cooling flow into this system may once again make for precip type
forecast headaches/wintry mix potential a week from now, if the
current run GFS has it`s way. ..12..


.AVIATION...(For the 12Z TAFS through 12Z Monday Morning)
ISSUED AT 630 AM CDT Sun Apr 15 2018

Generally MVFR to IFR conditions expected through the TAF period,
as an upper level low pressure system moves slowly over the
region. This system will bring periods of a light wintry mix
changing to snow today, with a glaze of ice and snow accumulations
of 1 to 3 inches north/west of the Quad Cities. Bouts of light
snow will taper off to mostly flurries later tonight lingering
into Monday. Gusty northeast winds 15-30 kts will shift to northwest
by tonight.


IA...Winter Weather Advisory until 7 PM CDT this evening for Benton-

IL...Winter Weather Advisory until 7 PM CDT this evening for Jo



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