Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 242050 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Quad Cities IA IL
350 PM CDT Sat Mar 24 2018

Issued at 337 PM CDT Sat Mar 24 2018

Axis of heavy wet snow across eastern IA into north central IL
has been slowly contracting, especially on the northern edge this
afternoon. Snowfall totals as of 3 pm have reached as high as 16
inches over north central IA, while eastern IA has had a few reports
in the 10 to 12 inch range. Warmer air on the southern edge of the
system has resulted in more of a mixed precipitation mode so far
today across the southern third of the forecast area. The upper
level low was evident on satellite imagery over central IA,
sliding toward southeast IA, while the surface low was well to the
south over SE MO. A tight pressure gradient around the surface
low was resulting in strong winds of 20 to 30 mph, slightly lower
than earlier today when a few gusts were above 40 mph.
Temperatures were mainly close to freezing in the axis of snow,
while warmer readings in the mid 30s were occurring northeast and
southeast of the precipiation.


.SHORT TERM...(Tonight)
ISSUED AT 337 PM CDT Sat Mar 24 2018

Major early spring snow storm will be winding down this evening.
Winter Storm Warnings will remain in place for eastern IA into
west central IL, flanked by a row of counties in a Winter Weather
Advisory until 03z. At the current rate, it looks like we will be
able to cancel the warning along the northern counties, along
highway 20 much earlier. Further south, at least light snow should
be continuing into early evening, but may be able to cancel much
of the headlines ahead of the current 03z expiration.

Current radar trends and short term models support the
current axis of moderate to heavy snow constricting in coverage
and slowly drifting south to southeast late this afternoon into
this evening. A narrow axis of an additional 1 to 2 inches will be
possible in this band along and north of the I-80 corridor.As
the upper low pivots southeast, an axis of light snow over central
IA will rotate into southeast IA and at least part of far
northeast MO late this afternoon and may bring light
accumulations. Outside the precipitation, much of southeast IA is
reporting light fog, but do not expect this to become much of an
issue or worthy of inclusion in the forecast at this time. Winds
will continue to slowly decrease and become less of a drifting
snow impact by sunset.

Overnight, an upper level shortwave ridge builds into the area
following the departing low. Will keep a gradual north to south
clearing trend mentioned toward morning, but confidence is low on
the timing. Temperatures will be heavily impacted by the fresh
snow cover and have lower 20s over eastern IA into north central
IL, with a 25 to 30 range further northeast and lower 30s across
the far south.

.LONG TERM...(Sunday through Saturday)
ISSUED AT 337 PM CDT Sat Mar 24 2018

The overall weather pattern suggests temperatures around or above
normal next week. Another significant storm system will impact
the Midwest Monday into Tuesday.

Assessment...high confidence

Quiet and dry conditions will be seen Sunday as high pressure moves
into the Great Lakes. Temperatures will average below normal over
the snow cover.

Sunday night into Monday morning
Assessment...low confidence

Dry easterly flow will continue across the area as the high moves
into the eastern Great Lakes as the storm system approaches from the
Plains. The main question is when will the moisture surging north
saturate the atmosphere and induce precipitation.

Right now the GFS, CMC, and ECMWF have Sunday night dry with
precipitation moving in mid to late Monday morning. The WRF is the
only model bringing in precipitation, potentially in the form of
sleet and freezing rain, before sunrise Monday in the far southwest
and west areas.

The model consensus right now has slight chance pops generally west
of a line from Iowa City, IA to Kahoka, MO.

For Monday morning, the model consensus has slight chance to chance
pops south of a line from Independence, IA to Galva, IL for sleet
and freezing rain. However, if the ECMWF, CMC, and GFS are correct
precipitation would not begin until late morning and would increase
the probability of it being rain.

Monday afternoon into Monday night
Assessment...high confidence on precipitation occurring

The first part of the next storm system will move through the area.
A significant surge of warm, moist air will be seen which will keep
precipitation in the form of all rain. A layer of unstable air aloft
should result in some embedded thunderstorms.

There are still questions regarding how much rain will occur.
Embedded thunderstorms will result in locally heavier rainfall
amounts. If the suggested trend of the global models continues, the
axis of the heaviest rainfall would fall roughly along the I-55
corridor across Illinois.

Assessment...medium to high confidence on precipitation occurring

The main surface low associated with the storm system will move
through the Midwest. The model consensus has chance to categorical
pops with the highest pops along and east of the Mississippi. A
layer of unstable air aloft will bring the risk of embedded
thunderstorms to areas mainly along and east of the Mississippi. The
heaviest rainfall still looks to occur in the I-55 corridor across

Tuesday night on...

Several weak disturbances will be moving through in the flow aloft.
If the weak forcing has sufficient moisture to work with, spotty
precipitation will be possible.

Tuesday night
Assessment...medium confidence

Right now the model consensus has slight chance to chance pops for
lingering rain Tuesday night for the departing system.

Wednesday through Thursday
Assessment...medium confidence

The model consensus has mainly dry conditions. There is a weak
disturbance moving through Wednesday evening that may or may not
produce precipitation.

Thursday night through Friday night
Assessment...low to medium confidence

Another weak disturbance moves through the area Thursday night. The
model consensus has slight chance pops for a rain/snow mix.

Assessment...low to medium confidence

Another weak disturbance will move through the Midwest on Saturday.
The model consensus has slight chance to chance pops for snow
changing to rain.


.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
ISSUED AT 1245 PM CDT Sat Mar 24 2018

Strong winter storm system moving through the region this
afternoon will result in widespread IFR to LIFR conditions due to
low visibilities in heavy snow and low ceilings. CID and MLI will
be most heavily impacted by this storm. Strong and gusty east
winds will remain at 20 to 30 kts will continue through the
afternoon, then diminish significantly by evening. The snow will
end from NW to SE this evening, with conditions trending toward
VFR, but the timing of this is low confidence. VFR conditions are
then expected from late tonight through Sunday morning.


IA...Winter Storm Warning until 10 PM CDT this evening for Benton-

     Winter Weather Advisory until 10 PM CDT this evening for Keokuk-

IL...Winter Storm Warning until 10 PM CDT this evening for Bureau-
     Henry IL-Putnam-Rock Island-Whiteside.

     Winter Weather Advisory until 10 PM CDT this evening for Mercer.



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