Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 212142

Area Forecast Discussion
National Weather Service Quad Cities IA IL
342 PM CST Wed Feb 21 2018

Issued at 330 PM CST Wed Feb 21 2018

Large area of high pressure acrs the upper Midwest will continue to
slide eastward toward the GRT LKS, while steering southwesterlies
aloft with embedded waves, organize from the desert southwest, to
the eastern GRT LKS. Thus a couple of precip events will roll up
acrs portions of the area from late tonight, through Friday...and a
wetter system/larger wave possibly impacting the region on


.SHORT TERM...(This Evening through Thursday)
ISSUED AT 330 PM CST Wed Feb 21 2018

Tonight...High clouds will thicken and lower overnight into Thu
morning, before an embedded vort max now located over the
southwestern plains, ripples up toward the southern and southwestern
CWA by late tonight. Some initial precip fields(mainly aloft/virga
form) are already organizing acrs OK into KS. Lift and column
saturation will have to increase for precip to reach the sfc, but
most models do so in the far southern CWA by 10z to 12z or so. Fcst
soundings initially support mainly snow with some ice pellets as this
precip arrives, but building warm wedge aloft turn it into mainly
freezing rain by 11-13z Thu morning along and south of the Hwy 34
corridor. Away from this incoming precip...dry conditions with non-
diurnal lows in the upper teens to lower 20s, and mid 20s south of

Thursday...the wintry mix precip wing will look to build
northward Thursday morning up toward the I80 corridor, with it
primarily being freezing rain mixed with some sleet. The sleet,
and even some snow mix will take away from the ice glaze
accumulation possible, but still getting up to 0.05 of an inch in
these southern areas, with up to a tenth of an inch possible
especially west of the MS RVR. Since this wintry mix happening
around the morning commute, will issue a Winter Weather Advisory
from 10z through 18z for areas roughly south of a Fairfield IA, to
Monmouth IL line. Sfc temps should improve above freezing in
those areas after 18z, limiting the freezing rain impacts. Will
break out a corridor from Keokuk County, to Louisa Co. in Iowa
with a later start time of 15z, with some possible lingering
freezing rain or freezing drizzle into the early afternoon/20z.
Expect the afternoon precip to wane along with improving sfc temps
to limit much freezing potentail in the afternoon. But will still
have to watch the northwestern CWA, Iowa City to Cedar Rapids and
to Independence IA for lingering freezing drizzle or very light
freezing rain during the afternoon for headline expansion if need
be. Highs up in the 30s and above freezing most areas by Thu mid
afternoon, except possibly the far northwest where sfc temps may
hover around 32 degrees. the precip should wave and end, besides
spotty drizzle along and south of I80 during the afternoon. Some
patchy fog possible in the north Thu afternoon, but will not add
it to the grids for now. ..12..

.LONG TERM...(Thursday Night through next Wednesday)
ISSUED AT 330 PM CST Wed Feb 21 2018

Active weather period to continue through the weekend across the
area.  Overall chances for mixed precip types look possible for all
events, especially overnight.  During the daytime hours, temperature
warm area wide leading to melting of frozen precip and rain across
the area.

First event will be ongoing at 00z as a shortwave trof moves into
the area.  At the same time, a response in the H85 wind fields will
lead to rising motion and warmer air moving to the area.  This
forcing will lead to rain across the area.  Higher resolution
guidance suggests that there could be split in the QPF between the
north and south CWA.  Looking at thermo fields, fzra looks possible
later in the overnight.  Overall impacts look to be low as
accumulating ice will be difficult as temps will be close to
freezing.   That said, a winter weather advisory could very well be
needed across the far north as warming temps don`t occur until later
Friday morning.

A slight reprieve from the precipitation is expected Friday before a
strong wave moves through the area.  This wave is the last system to
affect the area in the long term forecast.  12Z GFS has this closed
H5 flow swinging negative across the CWA during the day on Saturday.
A surface low is forecast to move across the CWA.  Strong H85 WAA
will usher in warm temperatures for Saturday.  Surface winds will be
out of the east and will likely limit the overall north movement of
a warm front.  Shear is high for this system during the day as
backed surface winds rapidly turn southerly and up to 50 kts at H85.
If convection can form then there may be a chance for strong
thunderstorms.  This will need to be watched by later shifts.  As
far as ptype goes snow transitioning to fzra then rain will occur
from south to north Saturday morning.  Little no snow and ice
accumulation is expected.

Past Saturday, forecast turns to temperatures above average into the
40s most days.  Hopefully this will aid in melting soil and allowing
any water left from the previous event to soak into the ground.


.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 1128 AM CST Wed Feb 21 2018

VFR conditions for most of the TAF cycle with overrunning high
clouds over departing high pressure ridge. North winds of 8-12
KTs becoming northeast overnight. CIGs will lower from the south
late tonight and especially Thu morning, as a precip-making
system pushes toward the area. This system may eventually produce
a wintry mix of freezing rain and snow along and west of the MS
RVR by mid Thu morning, first impacting the BRL site by around 14
or 15z.   ..12..


Issued at 330 PM CST Wed Feb 21 2018

Chance for precip will continue through Saturday.  At this time, it
appears that overall additional rainfall would not affect ongoing
flooding.  If there are thunderstorms on Saturday then current
flooding could be affected.  Overall, many runoff sites have crested
today or no longer have flooding occurring.  The Rock and Wapsi
Rivers continue to have ice affecting the rivers.  Both of these
rivers are expected to experience impacts of moderate to major
flooding.  For more information on these sites, refer to current
flood statements.


IA...Winter Weather Advisory from 4 AM to noon CST Thursday for Des
     Moines-Henry IA-Jefferson-Lee-Van Buren.

     Winter Weather Advisory from 9 AM to 2 PM CST Thursday for

IL...Winter Weather Advisory from 4 AM to noon CST Thursday for

MO...Winter Weather Advisory from 4 AM to noon CST Thursday for Clark-



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