Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 220430

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1130 PM CDT Wed Mar 21 2018


Issued at 343 PM CDT Wed Mar 21 2018

18Z surface data has high pressure from the upper Midwest into the
southern Plains. Dew points were in the teens and 20s from the upper
Midwest into the Ohio Valley with 30s in the Plains.


.SHORT TERM...(This Evening through Thursday)
ISSUED AT 343 PM CDT Wed Mar 21 2018

Late this afternoon through tonight
Assessment...high confidence

Quiet and dry conditions will be seen from late this afternoon
through tonight as high pressure moves into the Great Lakes.

Assessment...medium confidence

A weak upper level disturbance will move through the far southwest
and south areas during the day. The initially dry atmosphere may
allow a rain/snow mix or all snow to occur initially before changing
to all rain. The possibility does exist that precipitation may not
begin until late morning. If that occurs, the probability increases
that all rain would be seen.

.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 343 PM CDT Wed Mar 21 2018

A significant system will impact the Midwest Friday into Saturday.

Thursday night Friday morning
Assessment...high confidence

Lingering light rain will end Thursday evening in the far south
leaving quiet and dry conditions the remainder of Thursday night
into Friday morning. Attention then turns to the next storm system.

Friday afternoon through Saturday
Assessment...low confidence

A significant storm system will affect the area Friday afternoon
through Saturday. The probability of wet accumulating snow is
increasing but amounts are still in question due to uncertainty in
the storm track. Winter headlines for this storm system are possible
in the next 24-36 hours.

Initially, the dry easterly flow will hold off the precipitation.
However, by late Friday afternoon rain will have broken out across
all but the far northeast. The best chances for rain are generally
west of a line from Independence, IA Galesburg, IL.

Friday night rain will continue during the early evening with
possibly a few rumbles of thunder south of an Ottumwa, IA to
Galesburg, IL line. By mid to late evening and continuing overnight,
the rain will mix with and change over to all snow generally north
of a line from Belle Plaine, IA to Princeton, IL. A narrow
transition zone of a rain/snow mix looks to occur around and just
south of I-80. South of a Williamsburg, IA to Kewanee, IL line a
cold rain will continue through sunrise Saturday.

As colder air gets pulled further south Saturday morning, the
rain/snow mix line will push down to an Ottumwa, IA to Galesburg, IL
line. The I-80 corridor on north will see all snow while a cold rain
continues across the far south.

A slight warming of air temperatures Saturday afternoon is expected
to turn the precipitation back over to all rain.

IMPORTANT NOTE...Any slight change in the storm track or the amount
of cold air present will result in significant changes to
precipitation type and potential snowfall amounts. The energy that
will develop this storm system is just now approaching the west
coast. Once the system is sampled by the more dense land observing
networks, the models will likely shift the storm track.

As for snow amounts, the storm track and thermal profiles of the
atmosphere will be very important. Overall forcing will be quite
strong Friday night into Saturday morning so the probability is high
that a significant band of accumulating snow will develop. Where
this band sets up may not be fully known until Friday night.

Additionally, area roads will have absorbed a considerable amount of
heat prior to the rain and eventual snow. This heat will need to be
dissipated before accumulation occurs on roads. Accumulation on
grassy and elevated surfaces is expected.

Right now the best potential for accumulating snow is generally
north of a Belle Plaine, IA to Kewanee, IL line. Accumulations here
may be 3 to 6 inches. The strength of the forcing does suggest the
potential for a narrower band of higher amounts. Little if any snow
is expected south of an Ottumwa, IA to Galesburg, IL line.

Saturday night night on...

The models are suggesting the potential for more active weather
next week.

Saturday night through Sunday night
Assessment...high confidence

Quiet and dry conditions will be seen as high pressure moves through
the Midwest.

Monday through Tuesday night
Assessment...low confidence

The global models are advertising another storm system moving
through the Midwest. However, each model has differences in timing
and the storm track. Some of the timing differences can be
attributed to the strength of the high on the east coast. In spite
of these differences, the models are giving the best chances of
precipitation Monday night into Tuesday.

Right now the model consensus has slight chance to chance pops
Monday, categorical pops Monday night, likely to categorical pops
Tuesday, and slight chance to chance pops Tuesday night.

Assessment...medium to high confidence

The current model consensus has quiet and dry conditions for
Wednesday with high pressure building into the Midwest.


.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
ISSUED AT 1119 PM CDT Wed Mar 21 2018

VFR conditions to remain dominant through the TAF period. Can`t
rule out some patchy MVFR fog around daybreak, but believe this
would mainly occur outside of TAF sites focused in river valleys
and other low lying areas. Otherwise, expect an increase in mid
clouds by mid morning through Thursday afternoon with virga and
sprinkles in developing warm advection mainly at CID and BRL. Winds
are expected to remain light through the period, predominately
from a northerly direction into Thursday AM before becoming variable.




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