Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 140331
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
931 PM CST Fri Jan 13 2017

.UPDATE...
Issued at 920 PM CST Fri Jan 13 2017

Watching expansive area of precipitation over portions of E KS and
W MO near to south of KC metro. Isentropic lift on 305K sfc
depicts this current precip well, and supports this lifting across
the far southern cwa after 07z through 12z. Have increased pops
and expanded northward to near Fairfield, IA to Princeton, IL axis
overnight. Overall the setup doesn`t look to dissimilar from a few
nights ago when we had convection streaming across these same
locations. What is different is moisture and magnitude of
transport nowhere near as impressive for much, if any thunder.
Nonetheless, still fairly steep mid level lapse rates within
strong mid level baroclinic zone for likelihood of scattered
showers with brief bursts of sleet and freezing rain potentially
leading to slick conditions over portions of southeast IA, northeast
MO into west central IL.

&&

.SYNOPSIS...
Issued at 315 PM CST Fri Jan 13 2017

18Z surface data had arctic high pressure over the western Great
Lakes with a frontal boundary from Texas into the Tennessee Valley.
Dew points were in the single digits above and below zero from the
northern and central Plains into the western Great Lakes. Dew points
in the teens and higher ran from the Great Lakes to the Gulf coast.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 315 PM CST Fri Jan 13 2017

Quiet and dry conditions will be seen through sunset and into the
early evening hours. The exception will be in the highway 20
corridor which might see some isolated flurries with a passing
disturbance.  Attention then turns to later tonight and Saturday.

The morning balloon data showed a large and deep layer of cold, dry
air across the area. Moisture will start surging into the area late
this evening and overnight that will slowly moisten the dry layer at
the surface.

Based on trends from the RAP model, moisture will be slow to arrive
this evening. Thus dry conditions are expected through midnight.
There will likely be returns on the radar develop this evening.
However, these returns will be clouds developing and/or virga.

After midnight, the first wave will move from Missouri into southern
Illinois. Per the RAP trends, the lower atmosphere slowly saturates.
However, there is a large area of dry air above the fairly shallow
moist layer. Additionally, the moist layer ends when temperatures
get just above freezing aloft.

Given this information, there are questions regarding the potential
for precipitation occurring late tonight and into Saturday morning.
Right now it appears that there is a low risk for a mix of sleet and
possibly freezing rain south of a line from Galesburg, IL to just
north of Memphis, MO.

The cold temperatures and the depth of the cold air at the surface
brings the possibility for the lower atmosphere to cool as
precipitation begins. If this occurs, then the precipitation could
be a mixture of sleet and snow.

If there is any ice accumulation tonight, areas south of a Macomb,
IL to Bible Grove, MO line would have the best chances of seeing a
very light glaze.

On Saturday, any lingering sleet, freezing rain, or snow in the far
southern areas will end during the morning hours followed by
temperatures climbing to around freezing. The remainder of the area
will see dry conditions.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 315 PM CST Fri Jan 13 2017

Focus remains centered on the slow moving winter storm system that
will lift through the area Monday and Tuesday. Latest model runs
demonstrate critical differences in the timing and track of the
surface low and exhibit an overall slowing trend over previous runs.
Thus forecast confidence remains low and no changes were made to the
winter storm watch headlines in place for Sunday into Monday
morning.

Overall, the ECMWF is more progressive with precipiation breaking
out in the south late Saturday night, then becomes a slower, and
more westerly outlier with the surface low tracking through central
IA Monday night into Tuesday. The GFS and Canadian are faster with
the low lifting out and also trend further east, passing over
eastern IA/NW IL Mon night, reaching into lower MI Tuesday. Will
continue with a low confidence blend for now, with the overall
signal still showing freezing rain/sleet and possible light snow at
the onset Sunday, changing the mix to all rain from south to north
with the strong warm/moist advection and passing warm sector Sunday
night through Monday morning.

Saturday night: A cold and dry low level airmass remains in place
associated with a 1034 mb plus high over southern MN/SW WI under a
weakly confluent upper flow. The ECMWF remains the most progressive
suggesting precipitation breaking out in the south by 12Z Sunday,
while the more likely scenario suggests the northward advancing
precipitation will stay to the south as the weak low level east to
northeast flow continues a feed of dry air under weak forcing. Thus
have only slight chance pops in the far south with low temperatures
in the teens to low 20s.

Little changes made to the main event Sunday and beyond with light
ice accumulations of a tenth to possibly near a quarter inch in the
far south/southwest before the changeover to all rain occurs late
Sunday night through Monday morning. Latest models suggest areas
north of I-80 may not see the mixed precipitation begin until Sunday
evening. If current model trends continue, Sunday through Sunday
evening timeframe would pose the greatest risk for ice accumulations
in the south, while the late Sunday night and Monday periods may be
at most risk for sleet and ice accumulations central and north.
This is especially true if the slower, more westerly solutions bear
out, keeping a low level feed of cold, dry air from under the
exiting ridge into the area, under the deepening warm, moist
advection aloft and stronger upper level forcing. Temperatures
climbing into the 30s and 40s from late Monday through Tuesday
should then quickly melt any accumulations.

Tuesday night and beyond looks dry with above normal temperatures
under a split flow aloft that keeps arctic air bottled up well to
the north.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
ISSUED AT 537 PM CST Fri Jan 13 2017

Main concern tonight is the potential for pockets of lower MVFR
cigs to develop at the terminals, as 925 mb winds turn e/se and
attempt to advect pockets of low clouds and cigs 1200-1800 ft agl
into the terminals from central IL. The MVFR cigs are fairly
spotty and not widespread thus making confidence lower on
occurrence. As a result, I have kept the TAFs all VFR through the
period hinting at lower cloud potential with scattered MVFR bases
mid evening into the overnight. Any MVFR cigs would appear to be
fairly short-lived as 925 mb winds turn westerly late tonight,
which would bring in drier air and shunt any lower cigs east of
the terminals. Will continue to assess ob trends and amend if needed.
E/NE winds around 5-10 kts will turn from N/NW on Saturday as
reinforcing high pressure builds into the Upper Midwest.


&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Winter Storm Watch from Sunday afternoon through Monday morning
     for Benton-Buchanan-Cedar-Clinton-Delaware-Dubuque-Iowa-
     Jackson-Johnson-Jones-Linn-Muscatine-Scott.

     Winter Storm Watch from Sunday morning through late Sunday night
     for Des Moines-Henry IA-Jefferson-Keokuk-Lee-Louisa-Van
     Buren-Washington.

IL...Winter Storm Watch from Sunday afternoon through Monday morning
     for Henry IL-Rock Island.

     Winter Storm Watch from Sunday morning through late Sunday night
     for Hancock-Henderson-McDonough-Mercer-Warren.

MO...Winter Storm Watch from Sunday morning through late Sunday night
     for Clark-Scotland.

&&

$$

UPDATE...McClure
SYNOPSIS...08
SHORT TERM...08
LONG TERM...Sheets
AVIATION...McClure



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