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fxus63 kdvn 171002 
afddvn

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
402 am CST sun Dec 17 2017

Synopsis...
issued at 349 am CST sun Dec 17 2017

Low clouds and patchy fog has advected and/or developed into areas
near the Hwy 20 corridor early this am. Temps in these areas
are at or below freezing and watching closely the potential for a
few slick spots. Not seeing any suggestion of light precip via
dual-pol data, nor revealing any reports per inquiry of sheriffs
offices at this time. Otherwise, high cloudiness continues to
overspread the County Warning Area and thicken ahead of approaching storm system
from the Southern Plains. Attendant to this system is a fairly
large shield of rain from la through Arkansas wrapping back into an
mid/upper level circulation over Kansas. This system will lift over
the area today and bring only light precip to portions of the
area, as the system is shown to weaken while the brunt of
moisture advection is shunted to our south/east with veering of
the low level jet.

&&

Short term...(today and tonight)
issued at 349 am CST sun Dec 17 2017

Patchy to areas of fog will persist until mid am across northern
portions of the County Warning Area. Will continue to monitor for any dense
fog and slick spots on roadways. Otherwise, aforementioned
shortwave trough will lift northeastward across the region today
and bring light precip to the cwa, beginning around mid am south
then proceeding to advance east/NE while weakening through the
afternoon. This should fall mainly as rain, but can't totally rule
out some sleet or even a few snowflakes mixed at the onset with
the dry air. The bulk of any measurable rain is anticipated south
of Dubuque to Cedar Rapids line and mostly a trace to a few
hundredths of an inch, with portions of southeast Iowa and northeast
MO most favored for the higher accumulation. Due to the cloud
cover and eventual light precip in some areas, highs today should
be held down mainly in the upper 30s to middle 40s.

After this shortwave passes by early this evening, model soundings
and time-height sections show considerable low level moisture
lingering into Monday morning. Some weak isentropic lift is
shown this evening, which will bring potential for drizzle with
drying aloft, with best potential continuing to remain mainly
southeast of Dubuque to Cedar Rapids line where also aided
potentially by subtle weak surface trough and attendant convergence.
Overnight, not seeing much signal for any lift with either weak
ridging or flattening of flow aloft. But, with subtle weak wind
shift or trough axis in vicinity may continue to see some patchy
drizzle in aforementioned areas, or roughly southeast 1/2 of County Warning Area.
Thermally very little advection noted tonight as winds quite weak,
thus have nudged up mins tonight. Most areas that are favored for
drizzle tonight will likely remain above freezing. But, if some
drizzle were to develop north/west of Quad Cities overnight then
these areas would be near to below freezing for some risk of slick
spots. And if this occurs it could linger into the Monday am
commute. However, there is low confidence on this occurring at this
time. Aside from drizzle potential mainly this evening, there will
also be potential for fog some perhaps dense given light wind and
abundant moisture.



Long term...(monday through saturday)
issued at 349 am CST sun Dec 17 2017

Monday afternoon and Tuesday

Southwest winds will help to mix out or thin the low stratus through
the afternoon and evening from west to east. Otherwise, for Monday
and Tuesday, zonal mid-level flow will result in mild and dry
weather with highs near 40 f far north to the lower 50s far south.

Wednesday

A weak cold front, that will stall out across east Iowa/northwest Illinois,
will bring cooler air into the region on NE/east-northeast winds. Forecast
highs are in the mid 30s NE to the mid 40s SW. It's a dry front, so
no precip is expected through mid week.

Thursday and Friday

Models are in agreement developing a low in the Midwest along an
850mb baroclinic zone late this upcoming week. However, the model
trends over the past 24 hours have reversed and now take the sfc low
further to the northwest. Due to the model inconsistencies from run to run,
forecast confidence is low.

The GFS/European model (ecmwf) ensemble means and the European model (ecmwf)/CMC deterministic
solutions all track the sfc low either near or over east Iowa/northwest
Illinois which is not favorable for more than very minor snow
accumulations on the backside of the low. The deterministic GFS is
the outlier taking the sfc low further southeast which would bring
accumulating snow to approximately the northwest half of the County Warning Area Thursday
night into Friday morning.

The key messages are:

1) at this time, the most likely area for accumulating snow of more
than a few inches is northwest and north of our County Warning Area.

2) to message the low forecast confidence Thursday night, the
current forecast has a rain/snow mix to rain transition from northwest to
southeast through the County Warning Area. Did not want to go with likely or definite snow
as the model blend suggested because that would message high
confidence in wintry precip which is not the case based on the
latest suite of model data.

3) a lot can change over the next ~3 days regarding the sfc low
track and even the evolution of the upper wave and sfc cyclone, so
it's important to keep up with the forecast.

Saturday

Near to below normal temps are likely as cold air advection ensues
behind the late week sfc low. Uttech

&&

Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1107 PM CST Sat Dec 16 2017

Low stratus with IFR to low MVFR ceilings in moist northeasterly
fetch will advect into dbq terminal and likely to sag down in
vicinity of Cid toward 12z. Some fog is also likely to accompany
the stratus. While some of the guidance is showing potential for
dense fog and LIFR/vlifr visibility mostly at dbq, existence of
stratus and enough northeast fetch lends to lower confidence and
have kept visibility restriction in line with ceiling forecast.
Went for improvement to VFR at dbq and Cid by mid morning through
midday, as low level flows shifts from east/southeast and advects
in slightly drier air. Storm system lifting up across the area
by late morning through afternoon will bring areas of light rain
and sprinkles. This light precipitation should diminish by evening.
Moistening of low levels due to the light rain and advection
processes will likely lead to development of IFR to MVFR conditions
in low clouds and fog Sunday evening.

&&

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

$$

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