Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 240544

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1244 AM CDT Sat Mar 24 2018


Issued at 330 PM CDT Fri Mar 23 2018

The latest MSAS analysis was indicating this weekend`s developing
storm system rolling east into far northwestern KS ATTM, with
pressure fall pattern suggesting a path in between the further south
12z ECMWF and the 12z GFS through Sat morning. But if it deviates,
it may look to go closer to the Euro looking at latest trends. Will
fine tune tonight`s/Sat winter headlines, and quick look at another
decent precip maker for Monday into Tuesday.


.SHORT TERM...(This Evening through Saturday)
ISSUED AT 330 PM CDT Fri Mar 23 2018

Tonight into Saturday...ensemble trends in handling both the LLVL
and up the mid level low has trended a bit south with the 12z runs,
making for some concern for a quicker switch over to both incoming
and developing precip shields along and north of I80 later this
evening, and a bit further jog in eventual higher snowfall storm
total amounts from tonight and especially Saturday. Ongoing
headlines generally on target, but will make adjustments further
south in upgrading the southern advisory counties to a warning(they
may have quite a snow gradient from south to north with more
widespread warning criteria in the north). Will expand the advisory
a tier south as well west of the MS RVR. Will push back start time
to 03z with latest thinking for all headline groups, but that may be
a bit early for the southwest couple tiers of warning/advisory
counties. Strong forcing/high omegas embedded in increasing
saturation vertical profiles with PWAT feeds reaching 1 inch or more
by late tonight into Saturday. See one round of enhanced snow
accumulation along a general swath of more organized lift from near
Independence IA, southeastward to north of Davenport/Clinton IA, and
to Princeton IL late tonight after midnight to after sunrise Sat
morning...highest snow accums for 6 hours during this window from
Dubuque on along westward and southwest of the Hwy 20 corridor
including Monticello and Vinton IA. The other prime forcing wing
pushing east along the I-80 corridor ahead of the main mid level
wave from mid Sat morning into early afternoon.

A complex scenario with low confidence still, where enhanced F-gen
bands set up, and convergent H85 MB jet axis swaths take place late
tonight into Sat morning. Because of this, will have a rather broad
winter storm warning coverage area, but expect quite a bit of storm
total snow variances in the headlines, especially taking into
account bouts of winter mix transition precip of sleet, rain-snow
mix, brief bouts if freezing rain, and mild ground/pavement temps
eating away at true snowfall amounts. The heavy wet snow will
sublimate and compact as well. extended periods of sleet along the
I80 corridor just before dawn to after sunrise may also take away
from higher snow amounts in these areas, but hen expect a dynamical
cooling column to all wet snow again by mid morning, with robust
positive omegas reaching into the dendritic growth zone for 1-2 inch
snowfall rates at times. Some elevated instability bleeding in from
the south may even foster a few bouts of thundersnow on southern
flank of snow band/bands after midnight into early Sat morning...
making for localized snow amount enhancements.  Taking into account
many variables that come with a system of this magnitude this time
of year, in general will go with snowfall amounts of 7-10 inches
along and north of a line from Williamsburg IA, to the Quad cities,
and east of Kewanee-Princeton IL areas by late Sat afternoon.
Localized higher amounts of a foot or more possible especially
northwest of Cedar Rapids to south of Dubuque...possibly to Clinton.
But again hard to pinpoint these kind of details until we see where
the actual heavy bands set up late tonight into Saturday.

Expect a rather sharp gradient to a tier or two of counties south of
I80, where rain may occur longer or longer transition mixed precip
occurs. The south may get its snow accums not until midday Sat or
into the afternoon if it stays cool aloft dynamically long enough.
Otherwise, the southern third of the CWA to get anywhere from 0.50
of an inch of rain, to 1.5 inches before it turns to a wet snow-rain
mix or all wet snow later Sat. But will also be fighting diurnal
processes at this time for much of any snow accumulation in the

Back to tonight, instability plume of mid layer 200-400+ MUCAPES may
foster at least some isolated embedded thunder south of I80 mainly
from after Midnight into early Sat morning. Profiles may support at
least small hail wiht these cells, which may be hard to discern from
sleet. The rainfall may produce minor rises on some area rivers and
streams, but currently they are down in levels with a dry-unfrozen
ground surrounding them which may limit higher run-off potential.

.LONG TERM...(Saturday Night through next Friday)
ISSUED AT 330 PM CDT Fri Mar 23 2018

The highlights of the long term forecast period include a return to
southwest flow and precipitation chances Monday into Tuesday, along
with a warming trend early next week.

Saturday evening, expect some lingering rain/snow in the far south.
Have adjusted overnight lows down across the snow cover, especially
in the north. Sunday will be chilly and dry with highs in the upper
30s/low 40s.

Monday/Tuesday: Expect broad southwest flow aloft with a frontal
boundary slowing making its way through the region. Cannot rule out
some light wintry mix Monday morning, but precipitation type is
expected to be predominately rain. Isolated thunderstorms are a good
bet, although overall parameters do not appear favorable for severe
storms. Tuesday is expected to be the warmest day of the week, with
highs from the upper 40s northwest, to around 60 degrees in the

Wednesday through Friday: Expect near normal temperatures with
relatively low chances of additional precipitation.


.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1235 AM CDT Sat Mar 24 2018

Dynamic early spring storm to bring bouts of moderate to heavy
precipitation to the TAF sites into Saturday afternoon, with conditions
lowering to widespread MVFR/IFR with areas of LIFR/VLIFR. Expect
predominately snow at DBQ/CID/MLI with pockets of embedded thunder
and significant accumulations of 6-12+ inches. BRL will be mainly
rain/showers with some sleet through daybreak then expect with more
vigorous lift should see the precipitation change over to sleet/snow
with some accumulations. Expect the snow to gradually diminish
from north to south from mid afternoon into early evening. Have
gone with improvement to VFR over the last 3-6 hours of the TAF
cycle. Winds will remain strong from easterly at 20-30 kts through
much of the TAF cycle. Have low level wind shear with winds still
from ESE around 50-55 kts near 2kft agl overnight through Saturday AM.


IA...Winter Storm Warning until 7 PM CDT this evening for Benton-

     Winter Weather Advisory until 7 PM CDT this evening for Keokuk-

IL...Winter Storm Warning until 7 PM CDT this evening for Bureau-
     Carroll-Henry IL-Jo Daviess-Putnam-Rock Island-Whiteside.

     Winter Weather Advisory until 7 PM CDT this evening for Mercer-



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