Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 210856

Area Forecast Discussion
National Weather Service Quad Cities IA IL
356 AM CDT Wed Mar 21 2018

Issued at 341 AM CDT Wed Mar 21 2018

The synoptic pattern in place remains stagnant as cyclonic flow
continue to rotate over the eastern cornbelt, as the evolving
nor`easter takes place. While high clouds are plentiful overnight
tonight, the pattern is beginning to shift slightly east, which will
bring the subsidence band over central Iowa eastward today.  Lower
clouds remain stuck over western MN, IA, and MO, and thankfully for
those who like sunshine, the flow will remain north to northeasterly
keeping this moisture west of the area.


.SHORT TERM...(Today and Tonight)
ISSUED AT 341 AM CDT Wed Mar 21 2018

Much like yesterday, the northerly flow today will inhibit much
warming, as the cold advect through the day, despite plenty of
sunshine, especially this afternoon. Mixing to around 850mb will
only result in mid 40s, so there is little risk of today`s sunshine
resulting in a warm day. Winds will once again be a notch lower than
yesterday and the day before, despite the relatively deep mixing.
Tonight, with mostly clear skies through much of the night, we
should bottom out to a low in the mid 20s northeast to lower 30s
southwest by early morning, followed by a slow increase in
temperatures and cloud cover ahead of the approaching system for


.LONG TERM...(Thursday through Tuesday)
ISSUED AT 341 AM CDT Wed Mar 21 2018


Light rain will affect parts of the southwest forecast area during
the day. Otherwise, it will be quiet with above temperatures into
the upper 40s to lower 50s.

Friday and Saturday

Main concern Friday night into Saturday is potential for
accumulating snow for parts of the forecast area. Models are in
agreement bringing a slow moving, neutrally tilted shortwave from
the Central Rockies through Iowa and Illinois. The system will
have ample moisture to work with due to unimpeded low-level
moisture advection emanating from the Gulf of Mexico. Forecast
PWATs are between 0.75 to 1 inch.

Model consensus takes the Q-vector convergence bullseye near or
right over the forecast area during the first phase of this event
(Friday night and early Saturday morning). A coupled upper jet
structure and isentropic lift will lead to a period of moderate
ascent and widespread precipitation. Initially Friday evening and
night, lower tropospheric profiles should support rain across the
area. But effects of evaporative cooling, exaggerated by a dry
easterly flow, should lead to a quick changeover to snow over the
northeast third of the CWA, with the rain to snow transition
approaching the I-80 corridor later in the night.

The heaviest QPF, of 1"+, will occur in a NW to SE oriented swath
where low-level deformation and strong frontogenetic forcing
persist into early saturday afternoon. It`s a little too early to
know exactly where this band will set up. But right now, the
ECMWF/GFS/CMC favor the southern two-thirds of the forecast area.
However, there is plenty of time for shifts in the placement.

Potential Snow Amounts and Impacts:

Generally expecting 3-6 inches of heavy wet snow for parts of the
area, but there will likely be a narrow band of greater than 6
inches. Confidence at this lead time is too low to know exactly
where this will set up. With marginal boundary layer temperatures
in the 30s and a late March sun angle, the most efficient snow
accumulation will occur where there are heavy snow rates. Due to
this fact, a tight gradient in snow amounts is likely on both the
southern and northern edges of the moderate to heavy snow.

The current forecast focuses the most significant accumulations in
the northeast section of the CWA. This is preliminary and forecast
changes can be expected through the week. If confidence on a
period of heavy wet snow and gusty east winds increases in future
updates, we would have to consider winter weather headlines for
parts of the CWA.

Sunday On

No changes were made to the model blend. Another system is forecast
to impact the region on Monday and Tuesday bringing a chance for
rain. Uttech


.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
ISSUED AT 1116 PM CDT Tue Mar 20 2018

VFR conditions will continue through the TAF cycle with decreasing
clouds on Wednesday as subsidence strengthens in wake of a storm
system departing the Ohio Valley. Northerly winds around 10 kts will
become light and variable Wednesday night, as high pressure builds in.




LONG TERM...Uttech
AVIATION...McClure is the U.S. government's official web portal to all federal, state and local government web resources and services.