Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 111206

Area Forecast Discussion
National Weather Service Quad Cities IA IL
606 AM CST Thu Jan 11 2018


Issued at 330 AM CST Thu Jan 11 2018

As of 330 AM, an impressive, compact mid-level vorticity max
really stood out over far north-central Oklahoma on GOES-16 WV
imagery. This feature is forecast to reach E Iowa/NW Illinois
later today bringing wintry precip to the area.

Locally, temps were extremely mild for a January night - in the
40s and 50s, and scattered light rain showers where developing.


.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CST Thu Jan 11 2018

The main message today is the potential for icy roads from a
wintry mix of precip melting initially and then freezing as
temperatures fall from the 50s and 40s to the 20s and 10s.

A Winter Weather Advisory was issued for the entire CWA to
highlight the potential for icy roads later today. Please refer to
the advisory for location specifics on precip types, amounts, and
timing. The advisory is in effect until midnight, however; any
roads, sidewalks, etc. that become icy will likely not improve
through the night. In fact, the precip will be done by evening,
put the advisory out through midnight for those considering
evening/early nighttime travel.

A strong cold front with a rapid temperature drop of 20 degrees
in 3 hours is expected today. Most locations will fall from the
50s and 40s to the 20s and 10s. The cold front will reach the
western CWA during the mid morning hours, should be near the
Mississippi around midday and reach the far east by the mid
afternoon. Temps will continue to plunge through the evening and
overnight, bottoming out in the single digits west of the
Mississippi River and teens elsewhere for a less than 24 hour drop
of 30-40 degrees.

Model Trends:

Now that we are within 24 hours of this event, hi-res guidance
(RAP/HRRR/NMM/NAM) have focused in on a compact 500mb vorticity
max, currently over north-central Oklahoma per GOES imagery, to
provide large scale ascent for wintry precip to occur on the cold
side of the sfc front. As the mid-level forcing moves through from
late morning through the late afternoon, moderate pockets of
mixed precip - mainly in the form of sleet are possible due to
banded zones of forcing from 850-700mb frontogenesis and steep
mid-level lapse rates and low MUCAPE. Trends in recent guidance
favor the briefly moderate precip to occur over the central and NE
sections of the CWA.

Potential Impacts:

Sleet, snow, or freezing rain accumulations are expected to be
relatively minor. But since pavements temps are above freezing,
the melting and then eventual freezing of the water into ice is
the primary concern with this event as temps quickly dive into the
20s and 10s. There will also be a fair amount of wind with NW
gusts up to 35 mph potentially adding visibility restrictions at
times. Uttech

.LONG TERM...(Friday through Wednesday)
ISSUED AT 330 AM CST Thu Jan 11 2018

Arctic air will dominate the entire extended forecast, which is
thankfully far more straightforward compared to the last several
days. The air mass at hand will be already established into the
entire CWA by tonight, so Friday`s weather will undoubtedly be dry
and cold. The highs and lows through Sunday will be somewhat buoyed
by a lack of deep snow cover. The northwest 1/3 of the CWA may see
slightly cooler temperatures that our forecast should the ground be
white, but the current sleet favored potential just doesn`t
guarantee that radiational impact.

That all changes Sunday afternoon and night, as a model forecasted
classic clipper plunges into the Midwest ahead of an impressive
+1045 to +1050mb surface high. That`s roughly the same high pressure
strength as we saw a week ago with -20 low temps. So, with growing
confidence, we should see a snow event Sunday PM. The current model
data supports very good dendritic growth, and SLRs are looking to be
on the order of 20 to 30:1. Therefore, it can be figured that this
clipper`s QPF of 0.10 to 0.25 will be a good snow producer, and a
likely headline. Like many clippers, winds will be light during the
snow, but will increase behind. With such a strong high pressure
progressing into the Plains Monday, winds could be quite strong
later Sunday night into Monday, and with powdery snow on the
ground, we`ll have to watch for blowing/drifting snow impacts, as
well as wind chill advisory impacts. For now, I will address both
snow and wind impacts in the HWO.

The expected snow pack and bitterly cold air will give us a good
chance at well below zero lows again by Monday night through Tuesday
night. By Thursday, moderating temperatures are forecast by the
blended data, but at this point we`re not talking about big melt
down like what just occurred. Highs in the lower 30s are possible by



.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
ISSUED AT 606 AM CST Thu Jan 11 2018

MVFR should prevail through much of this TAF cycle. Brief periods of
IFR are possible during steadiest precip and gusty NW winds of 20-30
kts this afternoon.

Strong cold front to abruptly switch sfc winds from SSW to NW this
morning. A wintry mix of precip is also expected at all sites today.
It will transiting from rain to freezing rain to sleet, and could
end as snow at KCID/KDBQ. Accumulations will be minor, generally
under 1 inch of combined sleet and snow, and less than a tenth of
ice accumulation. Primary concern is for water to freeze on pavement
as temps fall into the 20s and 10s behind the front. Uttech


IA...Winter Weather Advisory from noon today to midnight CST tonight
     for Cedar-Clinton-Des Moines-Dubuque-Henry IA-Jackson-Jones-
     Lee-Louisa-Muscatine-Scott-Van Buren.

     Winter Weather Advisory until midnight CST tonight for Benton-

IL...Winter Weather Advisory from noon today to midnight CST tonight
     for Carroll-Henderson-Jo Daviess-Mercer-Rock Island-

     Winter Weather Advisory from 3 PM this afternoon to midnight CST
     tonight for Bureau-Hancock-Henry IL-McDonough-Putnam-Warren.

MO...Winter Weather Advisory from noon today to midnight CST tonight
     for Clark-Scotland.



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