Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 211729

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1129 AM CST Mon Jan 21 2019

Issued at 1119 AM CST Mon Jan 21 2019

The 12Z set of data continues to support temperatures near
freezing at the surface Tuesday morning, with rain indicated south
of Highway 30 aloft. That signal is enough that a winter weather
advisory is likely to be issued this afternoon for Tuesday morning
through the end of the storm.


Issued at 317 AM CST Mon Jan 21 2019

Arctic high pressure over the western Great Lakes, mainly clear
skies, and light winds have allowed temperatures to plummet to
near or below zero in eastern Iowa and northwest Illinois. The
coldest temperatures so far tonight has been Freeport at -14 F!
Luckily winds are 5 mph or less for most sites, which has kept
wind chills between -5 to -15 F.


.SHORT TERM...(Today through Tuesday Night)
ISSUED AT 317 AM CST Mon Jan 21 2019

Today and Tonight

Windy and cold today with highs in the teens and 20s. SE winds are
forecast to gust between 25-30 mph. Below zero wind chills this
morning won`t warm much through the afternoon due to the strong
winds. Tonight won`t be as cold with lows similar to daytime highs
as warm air advection continues through the night.


Issued a Winter Storm Watch for the counties along highway 20 in
Iowa and also included Jo Daviess County in Illinois. A wet 3-7
inches of snow is possible in these areas, along with a brief
period of sleet or freezing rain. Precipitation is expected to
begin Tuesday morning, becoming most widespread in the afternoon
and evening. Right now, the highest snow amounts are forecast
north of highway 20 and west of the Mississippi River, and the
best chance for a mix of precipitation is to the south of highway
20. NW winds will increase on the backside of low, gusting up to
25 mph.

The moderate to heavy precipitation will be associated with
strong 850-700mb frontogenesis NW of the surface low. Coupled
with the marginal thermal profiles, there will be a very tight
gradient in snowfall amounts on the southern edge of the rain/snow
line. And there is still time for the exact placement of this line
to shift north or south.

Later shifts may have to extend headlines to the south and east
with the potential for a mix of freezing rain and sleet, or if the
rain/snow line is expected to be further south than currently
forecast. Another factor to consider are road temperatures, which
will likely lag warming air temperatures by several hours due to
the very cold antecedent conditions. So there could be a period
of freezing rain, even for locations south of I-80 Tuesday morning
before temps reach the mid/upper 30s.

Model Analysis:

Persistent SSE winds and warm air advection at the surface will
cause temperatures to rise to near freezing all the way up to a
Galena, IL to Vinton, IA line. The max wetbulb temperature aloft may
reach even further north before dynamic cooling and column cold
air advection increase on the backside of the low. What this all
means is a very tricky precip type forecast. Snow, sleet, freezing
rain, and rain are all possible within the CWA.

The ECMWF is slightly colder than the GFS/CMC and our current
forecast. Our current forecast has more weight on the warmer
solutions. If models trend toward the ECMWF snowfall amounts would
have to be increased for about a tier of counties to the south and
east of the current Winter Storm Watch. Uttech

.LONG TERM...(Wednesday through Sunday)
ISSUED AT 317 AM CST Mon Jan 21 2019

Wednesday-Wednesday night...

Forecast is dry, however if departing storm system trends stronger/
slower as noted in some models then may need to add some snow
chances into Wednesday morning. Otherwise, high pressure builds in
during the afternoon and evening providing quiet/dry conditions and
abatement of winds. Late Wednesday night may see winds become gusty
from SW ahead of an approaching arctic front, which may also result
in steady or rising temperatures.

Thursday-Thursday night...

Concern is with dangerous cold and strong winds attendant to arctic
front. High confidence exists on both, as arctic front expected to
sweep across the area on Thursday. This front will be accompanied
by strong winds, which could be near advisory criteria at times,
with GFS soundings showing 35-40+ kts of wind sitting atop the mixed
layer and depicting 10-11+ mb/3hr pressure rises. A period of
dry/fluffy snow is possible as well with the frontal passage, with
the GFS still most aggressive with this potential. But, should the
GFS verify and snow does occur with the front then likely will be
dealing with a period of potentially high impact and hazardous travel
conditions in low visibilities for the afternoon/evening commutes.
The other hazard is dangerous cold coming in behind the front, with
confidence high on occurrence. Expect temperatures to crash after the
front, with easily our coldest morning of the season so far likely
by Friday morning. GFS is still most aggressive with the cold air
depicting 850 mb temps of -22c to -26c 12z Friday, while GFS ensemble
mean has 850 mb temps to around -23c near Quad Cities. EC and GEM
are between -10c to -20c across the area by 12z Friday. To put some
perspective on that... temps this morning across the area are generally
around 0 to -10F with 850 mb temps around -12c. So, EC and GEM would
support lows easily this cold by Friday morning, while GFS would be
record breaking and in the range of -15 to -25F for lows. Given this
persistent and strong cold signal I have continued to favor the colder
CONSALL guidance over Superblend, which is likely too warm from influence
of bias corrected models. Therefore, lows by Friday morning look more like
a blend of EC/GEM and GFS, with around -10 south to -16F north. These are
just air temps. Toss in gusty winds and we expect dangerous cold wind
chills as cold as -30 to -40F Thursday night into Friday morning! Thus,
wind chill headlines look almost a certainty.

Friday-Sunday... Active polar flow pattern will persist with region in/
near active clipper track resulting in periodic bouts of snow (mainly
typical lighter snows of 1-3 inch potential with each), with timing every
other day initially Fri/Sat then by early next week. Some challenges
exist with temperatures due to model spread on where core of arctic air
will reside. Nonetheless, consensus signal is for below to potentially much
below normal temperatures during this period, and therefore continued to
favor the CONSALL guidance over Superblend for much of the period. Likely
in this pattern to also continue dealing with dangerous wind chills at times,
and gusty winds leading to some blowing/drifting snow potential in
open areas.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
ISSUED AT 1119 AM CST Mon Jan 21 2019

Cold high pressure is moving east of the region today, with a
storm moving over the area during the afternoon Tuesday. This will
mean southeast to south winds at 15 to 25 kts through tomorrow
morning, with a transition to northwest Tuesday night. Conditions
will be VFR with only high clouds through this evening, followed
by lowering cigs to IFR Tuesday morning with freezing
rain/sleet/snow likely at all sites.

Low level wind shear is expected at all sites, from surface to
2000 ft AGL, as winds blow from the south to southwest aloft at 40
to 50 kts.


IA...Winter Storm Watch from Tuesday morning through late Tuesday
     night for Buchanan-Delaware-Dubuque.

IL...Winter Storm Watch from Tuesday morning through late Tuesday
     night for Jo Daviess.



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