Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 222321

Area Forecast Discussion
National Weather Service Quad Cities IA IL
621 PM CDT Thu Mar 22 2018


Issued at 330 PM CDT Thu Mar 22 2018

High pressure located across the Mississippi River valley today
led to quiet weather across most of the area. Light variable
winds were reported across the area. To our southwest, warmer
temperatures were beginning to creep into western IA. Aloft, a
warm advection led to the development of isolated rain showers
across NE MO and SE IA.


.SHORT TERM...(This Evening through Friday)
ISSUED AT 330 PM CDT Thu Mar 22 2018

Majority of short term period is quiet as a storm system
approaches the area late in the period. An open wave is expected
to approach the area. Through the short term, midlevel ridging
should keep precip off until late in the period. Latest forecast
has slowed down precip onset. Another limiting factor for precip
onset would be a dry easterly wind. This should keep the low
levels dry. Once saturation occurs in the lower levels, then
precip would start at that time. There will likely be a time
tomorrow afternoon where radar depicts precipitation that is not
hitting the ground. Thermal profiles are warm enough for all rain
through 00z Friday.

.LONG TERM...(Friday Night through next Thursday)
ISSUED AT 330 PM CDT Thu Mar 22 2018

Friday night and Saturday...Dealing with the challenging early
spring storm system, with the wave now moving on the west coast
shore. Hopefully will get better sampled this evening, and will keep
the watch going as is for now, except add Stephenson Co in NW IL
with the potential for at least higher end advisory snows in the
southwest part of that county. The 12z ECWMF has trended further
south with the developing sfc low than the 12z GFS/GEM, with the low
acrs far east central MO at 12z Sat, as opposed to the GFS/GEM east-
northeast of Kansas City at that time. The Euro would mean a quicker
transition to snow and further south, with possibly the I80
corridor being the heavy swath of snow accums, as opposed to further
north and northeast like previous runs suggested. But with ongoing
uncertainty and watch ongoing, will take an ensemble blend of
forcing, saturation and thermal profiles for the latest thinking
which ends up not all that different from the previous package.

Unseasonable PWAT feed of 0.70 to around 1 inch still on track, with
robust but open and progressive upper short wave wave dropping east-
southeast right acrs the DVN CWA by Sat morning. Strong 15 to 20
upward omegas induced by this feature with deepening saturation will
make for a proficient precip maker, but snow transition zone and
amounts still somewhat up in the air. For now will have the
northeastern flank of the incoming rain wing start to dynamically
cool to rain-snow mix acrs the western Hwy 20 corridor into NW IL
around 02z-03z Friday evening, migrating down to I80 not til well
after midnight. The fcst soundings more supportive of the
transition zone being more a rain-snow mix with a touch of sleet,
going to all wet opposed to the NAM which wants to break
out ice-accumulating freezing rain from Cedar Rapids down to east of
the Quad Cities after midnight. Sfc temps and lower boundary layer
make for a low freezing rain impact, and may eat away at true snow
accumulation totals.  The extent of lift and saturation, with
elevated F-gen band or bands suggest the previous shifts mention of
1-2 inch per hour snowfall rates in max lift window, which is 2-3 AM
through mid Sat morning, it`s just how far north or south these
enhanced bands set up. Ensemble swaths suggest bands form near
Independence IA, southeastward to Anamosa IA and south Clinton, with
Sat morning bands setting up from Dubuque to Princeton IL.

Increasing east-to-southeast sfc winds to 15 to 25 MPH sustained and
gusts up to 38 MPH to complicate things/sharply reduced visibilties
late Friday night and Saturday morning, but wet nature to snow
should limit it to shallow drifting. For times sake, all in all will
advertise storm snow totals of 5-8+ inches along and north of a line
from Cedar Rapids-Davenport-Princeton IL line, with sharp gradient
to the south of I80. Areas from Sigourney IA, to Monmouth may only
get a few tenths Sat morning. The GFS does break out a band of
localized heavy wet snow of 2-4+ inches under the passing upper
wave acrs Southeast IA into western IL during late Sat morning into
early afternoon (much like what happened last Sat), but these
details to hard to pinpoint at this point. Some concern that with
warm ground and low LSR`s, that advertised snow amounts may be on
the high end.

South of the snow band/south of I80, locally moderate to heavy
rainfall of 0.75 to over an inch possible by midday Saturday. Lift
and an elevated instability plume of 100-250+ MUCAPES sweeping up
acrs the south half of the CWA as Fri night progresses supports some
embedded elevated thunder. The stronger cells capable of producing
at least small hail, if not a half inch. There may be enough
northward instability migration to interact with the snow
bands...thunder snow late Friday night?

The rest of the long range...Another low and frontal boundary to
roll up through the region Monday into Tuesday, with much milder
profiles to support all rain/showers, and even some thunder again
especially Monday night. Convergence, moisture feed and synoptic
scale set-up support the potentail for more locally heavy rain in
lee of the sfc wave and frontal intrusion...possibly of over an inch
by Tuesday morning. Latest thinking/feature placement has the IL
side of the river more favorable for significant rainfall through Tue.
Progressing northern plains upper trof will hopefully shunt the rain
convergent focal point frontal system along and south of the DVN CWA
by Wednesday, with cooling an drying trends locally into next
Thursday.   ..12..


.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
ISSUED AT 616 PM CDT Thu Mar 22 2018

VFR conditions expected to dominate the TAF cycle, with clouds decreasing
tonight before increasing again on Friday ahead of a developing storm
system. The clouds will eventually produce some light rain especially
from CID to BRL, and possibly to MLI by late in the TAF cycle. Light
winds will turn easterly tonight then increase to 10-20 kts and gusty
on Friday.


IA...Winter Storm Watch from Friday evening through Saturday
     afternoon for Benton-Buchanan-Cedar-Clinton-Delaware-

     Winter Storm Watch from Friday evening through Saturday
     afternoon for Johnson-Muscatine.

IL...Winter Storm Watch from Friday evening through Saturday
     afternoon for Bureau-Carroll-Henry IL-Jo Daviess-Putnam-
     Rock Island-Stephenson-Whiteside.



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