Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kdvn 101122 

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
522 am CST Tue Dec 10 2019

..aviation update...

issued at 315 am CST Tue Dec 10 2019

What a difference a day makes! Yesterday's calm winds, fog, and 40s
are replaced by strong west winds, clearing skies, and single digits
and teens temperatures. Wind chills are in the -10 range northwest
to around zero southeast. Today will be a winter day.


Short term...(today through wednesday)
issued at 315 am CST Tue Dec 10 2019

Today will see cold temperatures dominate the forecast, as high
remain in the teens north to upper 20s south. Some passing cloud
cover is likely, which will hold temperatures down, especially in
the central and north at times. Winds will be generally in the 10 to
15 mph range northwest, which keeps the wind chills in the lower to
mid single digits north of I-80 today, and in the lower to mid teens

Tonight through Wednesday, a weak clipper system looks to impact our
County Warning Area. Snow is expected to move through the area between midnight and
9 am Wednesday. This is a rather typical clipper, where forcing is
robust, moisture is starved and the event is short lived. Models
sounding suggest this will be supported for a few hours dendritic
growth, thus I do believe we'll see a stripe of accumulating snow,
mainly in a 50 to 80 mile wide band from Fort Dodge to the Quad
Cities. All surfaces will be well below freezing, thus, this event
should have no problem accumulating, and will advertise in the severe weather potential statement a
slick Road potential late tonight into the Wednesday am commute.
Total accumulation does look light, generally an inch or less.

Wednesday afternoon will be dry, with temperatures holding in the
20s for nearly all of the County Warning Area.


Long term...(wednesday night through monday)
issued at 315 am CST Tue Dec 10 2019

Wednesday night and Thursday...non-diurnal temp trends likely for
Wed night with 12 hour lows occurring during the evening after sunset,
before sfc return flow organizes overnight into Thu morning. This
combined with expected plume of mid level warm air advection cloud
increase from the west ahead of digging northern plains short wave
to produce rising temps into Thu morning. Low level baroclinic gradient
will adjust and tighten from the Dakotas down toward the eastern Ohio
River Valley, Hi-lighting the most probable path of developing sfc
wave development and propagation. Associated clipper lift and pre-
wave saturation will look to take shape along and north of the dvn
County Warning Area taking into account latest synoptic scale thermal projection,
suggesting bulk of any warm air advection Wing precip to occur to the north of the
County Warning Area acrs Minnesota and WI on Thu. Will trend that way with northward pop
progression but still keep low to moderate chance pops in the north
throwing a Bone to the American models which still skirt these areas
with some light snow transition to rain-snow mix or all rain as the
elevated warm nose nudges to the north. Fcst soundings suggest deep
and robust southwest flow on Thu of 50+ kts. Even limited mixing
into base of shallow inversion will make for breezy sfc winds of 10-
20 miles per hour with higher gusts. Sfc temps to zoom above normal the, with
the same conservative mix depth translating into highs in the upper
30s to near 40 degrees in the far north, to the upper 40s in the

Friday...a day starting a transition as the latest 00z model runs
and mid to upper level jet progs suggest a short wave phasing
process between streams trying to take shape over the mid to upper
MS River Valley regions of the mid Continental U.S.. Friday looks to be one more
mild day with some 40s possible despite probable cloud cover. Low
confidence that there will be enough moisture depth for some spotty
light precip to develop as Friday progresses. The blend maintains
some low pops for Friday, but think the dry 00z Gem/GFS are more on
track through 00z Sat anyway. Then the majority of 00z medium range
model runs then roll the upper trof or even mid level cyclone
development over or close enough to the local fcst area by Sat
morning. Some signs of a trowal-like moisture feed for precip to
rotate in or develop right acrs the area as Friday night into Sat
morning progresses. The latest solutions suggest the wave to
progress enough to induce enough low to mid level cold conveyor for
a rain switch over to wet snow and some accums possible by Sat
morning especially west of the MS river. A few models suggest even
headline making snow amounts possible into Sat morning especially
combined with increasing northwest sfc winds into the back of
departing wave, but it is still early for concern and confidence
regarding these details yet, but will have to watch additional
phasing and wave development in the coming model runs over the next
48 hours or so.

Saturday through Monday...will continue pops for mainly snow on Sat
to handle the potentail of whatever system that can form in or close
to the area Friday night into the start of the weekend. As this
system progresses to the east, pops may eventually be trended down
into Sunday and day 7, with the latest upper jet placement and
southward additional trof phasing favoring a more active southern
stream from the Southern Plains to Ohio River/Tennessee Valley regions. But
again this a low confidence scenario at this point with recent
phasing issues and north/south action zone lay-outs on the medium
range model/ensemble outputs of the past 24-36 hours. As for temps,
cold advection draw from the north in wake of the passing wave will
look to make for below normal temps this period, especially if snow
cover can increase. ..12..


Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 520 am CST Tue Dec 10 2019

Mid clouds will stream over the area today, with VFR and cold
conditions through evening, along with northwest wins at 10 to 15
kts. Tonight, as fast moving light snow system will move through
the area between 06z and 15z Wednesday. This could bring a light
amount of snow and visibility under 5 miles.


Dvn watches/warnings/advisories...


National Weather Service Glossary of Abbreviations