FXUS63 KDVN 161711

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1111 AM CST Sun Dec 16 2018


Issued at 305 AM CST Sun Dec 16 2018

Shortwave is quickly traversing the Upper Midwest early this
morning, with GOES-16 water vapor imagery channels revealing
nice compact PV anomaly passing north of the MN Arrowhead.
This is generating nothing more than a progressive band of high
level cloudiness due to a parched troposphere. Quickly on the
heels of this system is another shortwave diving E/SE from MT
into SD, and accompanied by another batch of high level clouds.
At the surface, a weak high pressure ridge was bisecting the cwa
from northeast to southwest. Radiational cooling beneath strong
low level inversion was leading to patchy fog and temps bottoming
out into the lower to mid 20s within the ridge axis and surrounding
drainage sites. Meanwhile, across the west/southwest temps were
being held up in the upper 20s to around 30 due to light S/SW wind
and high cloudiness.


.SHORT TERM...(Today and Tonight)
ISSUED AT 305 AM CST Sun Dec 16 2018

Weak surface cold front attendant to lead Upper Midwest shortwave
will pass through today. But, with dry airmass it will be
accompanied by little fanfare aside from a wind shift from the NW
and a bout of some high clouds early with the passing shortwave.
Then will see some more high clouds later this morning and afternoon
with shortwave diving E/SE into the MO Valley. Neither round of
high cloudiness looks too menacing and impactful on high temps at
this juncture. Good solar insolation, weak and lagging cold
advection, and deeper mixing post-frontal will lead to another
unseasonably mild day, with highs generally from the mid 40s to
around 50 degrees. Coolest readings anticipated over portions of
far northeast Iowa with eventual low level trajectory/advection
off residual snow cover.

Tonight will feature mainly clear skies as a ridge of high pressure
builds toward the region. Guidance blend looks reasonable with
lows mainly in the mid to upper 20s. A few lows in the lower 20s
would be possible in the far west if surface winds were to
decouple being in closer proximity to ridge axis from central MN
through central IA. Most if not all of the area however, should
remain in cyclonic flow with NW winds 5-10 kts providing
sufficient BL mixing to give a break from the stretch of frosty

.LONG TERM...(Monday through next Saturday)
ISSUED AT 305 AM CST Sun Dec 16 2018

Monday and Tuesday...Passing sfc and upper ridging will make for a
generally fair wx period to start to work week off with. Continued
milder than normal temp regime ongoing as well, even with a bit of a
cool down on Monday with brunt of sfc ridge passage. Return flow
warming behind that feature to help boost Tue high temps back into
the mid to upper 40s, with even a 50 possible if adequate insolation
can hold on for much of the day. As the next mid week weather maker
tries to phase and take shape acrs the plains, the challenge will be
the extent of ongoing warm-moist conveyor from the south can top-
down saturate ahead of the incoming trof for precip chances by late
Tue night. Of more of a trick may be the extent of deepening LLVL
saturation that may be able to produce drizzle, as most model fcst
soundings suggest adequate depth of saturation for more organized
precip may not occur until later in the day Wednesday. The NAM of
course is the most aggressive in saturating the LLVL's and produces
drizzle or light rain by late Tue night, which may be trouble in the
northern CWA north of Hwy 30 if sfc temps dip below freezing.
Otherwise, ongoing southerly flow and warm sector effects such as
increasing sfc DPTs/WBZ's will keep ambient temps acrs the rest of
the CWA at or above freezing into Wed morning. With adequate
saturation concerns, will keep the fcst dry for now through 12z Wed.

Wednesday...Bulk of the latest run 00z medium range models continue
to try and phase incoming upper wave and jet energy into a deep long
wave trof along and west of the MS RVR Valley by Thu. Ongoing
moisture advection and increasing lift just ahead of the axis of
this process will induce increasing chances of precip as Wed
progresses, and especially by Wed night if current model timing and
saturation is correct. The 00z GFS is more progressive with precip
becoming widespread by late Wed morning, while the new ECMWF delays
more of a widespread onset by late Wed afternoon and especially
during the evening. Both models have mild enough vertical thermal
profiles for the precip to be rain/showers for much of the day into
the night, although the GFS with precip occurring in the north Wed
morning and sfc temps lingering in the lower 30s suggests some light
freezing rain possible toward Hwy 20 for a few hours. But with
increasing WBZ's and WAA this(light icing potential) may be marginal
even in the north.

Bulk of the models generally suggest mainly light rainfall amounts
into Wed night/early Thu morning. Then, depending on the model and
handling of trof axis progression to allow a switch over to a
cooling conveyor from the north/northwest, the watch will be on for
a change over from rain over to wet snow on the northern and western
fringe of the precip shield late Wed night into Thu morning. Again,
the more progressive GFS targets the central into eastern CWA late
Wed night and through mid Thu morning with this switch over and some
light slushy snow accums possible by Thu especially along and east
of the MS RVR. The ECMWF delays to more during the day Thu.

Thursday through Saturday...Continuing with the precip switch over
potential on the back side of the system this period, the latest
suite of medium range models really ramp up a closed upper low and
deep trof along and east of the MS RVR Valley to the Appalachians at
the end of the week. The GFS walks out the rain/snow or all wet snow
east out of the CWA by Thu afternoon, then continues to spiral
wintry precip acrs central and eastern Il just east of the local
area into Friday. The slower 00z ECMWF lingers rain/snow or all wet
snow acrs the central into eastern CWA through Thu evening, with at
least some light snow accums possible again along and east of the MS
RVR before it slips east later Thu night. But sfc temps and diurnal
effects during the day Thu may be marginal to allow for much snow
accums if the Euro's timing is correct. With still much uncertainty
at this time for a system later in the week, will just advertise
POPs for both snow and rain Wed night into Thu. In the wake of
whatever system that can form and then pull eastward, post-system
cool draw from the north should bring about a temp regime back
closer to normal for the end of the week and into the start of next
weekend. ..12..


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
ISSUED AT 1109 AM CST Sun Dec 16 2018

Quiet VFR weather will continue through Monday, with northwest
winds around 5 to 10 kts and bouts of high level cirrus. Winds
overnight should remain high enough to limit fog formation.




Back to Main Forecast Discussion Page