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Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
1025 PM CST Mon Dec 9 2019

..06z aviation update...

Update...
issued at 923 PM CST Mon Dec 9 2019

Wrap-around low clouds and flurries remain anchored over portions
of ec/NE Iowa and northwest Illinois this evening. The back edge of the
low clouds extends across southeast Minnesota into far NE Iowa, and
appears to be picking up eastward movement as the low pulls away
and flow gradually exhibiting more anticyclonic component further
west. Therefore, will continue to forecast low clouds exiting
stage right overnight. But then more clouds await upstream in the
plains attendant to warm advection/weak thermal ridging. Some of
this cloudiness may enter stage left late tonight into Tuesday am.
Looks like far west/SW areas would be most favored for the greater
cloud coverage. Overall, hourly temperatures have been running 1-2
degrees or so colder outside of the cloud cover, and with most
areas to see a period of clearing tonight I have dropped lows a
bit with a general range of 5f northwest to 15f far S. Winds will
continue to slowly subside tonight, with gusts becoming less
frequent and not as high especially as weak ridging nudges closer.
The winds combined with the cold temperatures will make it feel
even colder and more like around zero to -10 for the morning
commute tomorrow. Winter is back!

&&

Synopsis...
issued at 241 PM CST Mon Dec 9 2019

Quite a busy afternoon of weather across the area as a cold front
passed through early this afternoon. A narrow and intense band of
snow followed behind the front and was being fueled by strong low-
level frontogenetical forcing. Combined with strong northwest winds
gusting around 35 mph, this lead to brief periods of whiteout
condtions and several accidents from central to eastern Iowa. Along
with the snow, temperatures across the area were falling rapidly,
and as of 2 PM ranged from 21 in Independence, to a still mild 46 in
Keokuk. This cold will be the primary focus of the short term
period.

&&

Short term...(this evening through Tuesday night)
issued at 241 PM CST Mon Dec 9 2019

Key messages:

1) snow ending this evening with dry condtions expected through
Tuesday

2) chilly temperatures expected for the period, with wind chills
ranging from the single digits to near 10 degrees below zero tonight.

3) chance of light snow over eastern Iowa Tuesday night.

Leftover snow showers will exit the region this evening with skies
expected to clear from west to east tonight. Cold air advection will continue as
northwest winds funnel in a modified Arctic air mass across the mid
to upper Mississippi River valley. Temperatures will have no trouble
dropping into the upper single digits (north of Highway 30) to lower
and middle teens (south). With northwest winds expected to be around
10 to 15 miles per hour Tuesday morning, wind chills ranging from zero to 10
degrees below zero are expected over areas with the coldest lows.

The chilly weather will continue through Tuesday, but the good news
is the sun will be out for much of it! Afternoon highs will range
from near 20 along the Highway 20 corridor, to near 30 over west
central Illinois and northeast Missouri.

Tuesday night, deterministic guidance is in good agreement of a weak
clipper system riding the southern portion of a 500 hpa low that
will be centered just north of the Great Lakes. This looks to remain
relatively light on the quantitative precipitation forecast side as not a lot of moisture will be in
place ahead of it. Quantitative precipitation forecast of only a few hundreths will translate to
only a few tenths of an inch of snow accumulation by Wednesday
morning.

Long term...(wednesday through monday)
issued at 245 PM CST Mon Dec 9 2019

Wednesday

A band of light snow may linger across central and northeast
sections of the County Warning Area early Wednesday morning before quickly
dissipating as an area of low-level isentropic lift shifts
to the east. Minor snow accumulations of dry snow are possible
which could lead to slippery roads for the morning commute. The
favored area for a dusting or more is in the counties along and
north of I-80. Temps will be about 10 degrees below average with
upper teens north to low 30s far south.

Thursday on

The Arctic high will shift into the eastern U.S. For late this week,
which will cause surface winds to increase out of the south
leading to a warm up. High temps will respond, reaching into the
30s on Thursday and 40s on Friday.

A low tracking along the U.S./Canadian border will drag a weak front
through Thursday afternoon and Thursday night, possibly glancing
the north or northwest with light precip, mainly in the form of
snow. Little if any accumulation is anticipated at this time.

Into next weekend, forecast confidence remains low regarding
chances for snow across eastern Iowa and northwest Illinois.
Models vary quite a bit on the timing and strength of a few
shortwave troughs forecast to pass through the central U.S. Model
blend chances for precip have trended a little higher with the
afternoon update (now at 30-40%). But again, confidence is low on
the placement and strength of the aforementioned shortwaves.
Model blend temps trend colder late in this period, falling to
slightly below normal by Sunday and Monday. Uttech

&&

Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1020 PM CST Mon Dec 9 2019

Predominantly VFR conditions expected, as MVFR stratus pushes east
of dbq and mli terminals early in the period. There is a low
chance of high MVFR ceilings developing at Cid and brl on Tuesday
attendant to warm advection. Winds will slowly subside but remain
sustained above 10 kts and gust higher at times through Tuesday.
Late Tuesday and Tuesday evening winds will become light and shift
from the southwest and south.

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&

$$

Update...McClure

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