Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 191728

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1228 PM CDT Mon Mar 19 2018


Issued at 337 AM CDT Mon Mar 19 2018

A tightly packed spring storm system is found over south central KS
early this morning, with bands of rain and thunderstorms over much of
the central plains from Nebraska southward to northeast TX.   The
local area remains in a area dominated by subsidence on the
periphery of surface high pressure over southern Canada. The
pressure gradient developing between the two systems has already
helped switch winds to east to northeast over the CWA, which is
helping keep fog formation at a minimum tonight.


.SHORT TERM...(Today and Tonight)
ISSUED AT 337 AM CDT Mon Mar 19 2018

The low pressure to the southwest is expected to move east over
southern Missouri today. As this happens, the increasing pressure
gradient will drive increasing winds through the day. These winds
will pull dry air over the area, helping keep the rain from the low
pressure to the south of our counties, but will certainly keep today
from going down as a nice spring day.  The dry air should also help
filtered sunshine going in the northeast 1/2 to 2/3rds of the area,
which should offset some of the low level cold advection. The result
will be upper 40 highs north, with a narrow axis of lower to mid 50s
central to near 50 south. This cool, warmer, cool break down is due
to the cold advection north impact, with lesser CAA and sun found
central, and even less CAA, but more cloud cover south. In any case,
if you can get out of the wind, which will increase to 15 to 25 mph
by afternoon from the northeast, it won`t be too bad of a day.

The afternoon winds, with filtered sun, is expected to bring a
enhanced risk for grass fires spreading out of control today through
6 PM. I will address this in the HWO today, though it falls well
short of any fire headline criteria.

Tonight, with mid and high cloud cover continuing to be over the
region, and northeast winds pumping through the night, lows should
fall to the upper 20s to lower 30s. Wind chills will be in the lower
to upper teens.  (at least it`s not snowing)


.LONG TERM...(Tuesday through Sunday)
ISSUED AT 337 AM CDT Mon Mar 19 2018

Tuesday and Wednesday

No significant changes for midweek.

A longwave trough will deepen over the eastern third of the U.S.
leading to colder weather (highs in the 30s and 40s) for the Upper
Mississippi Valley. On the western periphery of the longwave trough,
models have a weakening disturbance approaching E Iowa/NW Illinois
on Tuesday. Guidance suggests the better chance for light rain and
snow showers is over central and western Iowa. Locally, have slight
chances over far western sections of the forecast area.


Now both the ECMWF and GFS have isentropically forced light rain
mainly over the southwest and south. Our latest forecast has
20-30% PoPs, but may have to increase these in later updates.

Friday and Saturday

Active pattern setting up for the end of the week into the weekend.
Strong, deep layer warm air advection, a closed off 850mb low
tracking through eastern Iowa and northern Illinois, and a period
of strong low level frontogenesis may lead to widespread
precipitation. The most likely timing is Friday afternoon into
Saturday morning. Convection is also possible due to elevated
instability. Right now, have slight thunder chances along and
south of highway 34 (west of Galesburg, IL). There will likely be
a QPF band of 1" or more oriented in a WNW to ESE swath across
the Midwest into the Ohio Valley. It is just too early to know
exactly where it will focus.

West-southwest mid-level flow across the Central Rockies on
Friday will induce lee-side cyclogenesis over eastern Colorado and
western Kansas on the northern edge of a downslope enhanced
thermal ridge. ECMWF 850mb temperatures are as warm as 18 C into
northern Kansas. The northward advection of this thermal ridge is
important because it will influence the final placement of the
baroclinic zone and track of the surface and 850mb lows.

Model Trends and Confidence:

The ECMWF takes a 995mb surface low through northern Missouri into
central Illinois Friday night into Saturday morning, which is a
compromise between the further north CMC and further south GFS.
Our current forecast for Saturday is a model blend with mid 40s
north to upper 50s south. However, model spread is incredibly
high. The GFS has 30s area-wide. On the other extreme, the CMC
has 60s and 70s area-wide. The ECMWF is in between with 30s
along/north of I-80 and 60s far south. The model blend will likely
trend toward a tighter north-to-south temperature gradient with
time. Confidence is too low to stray from the blended approach at
this lead time.

As mentioned, there is a lot of forecast uncertainty with this
system -- higher than normal. The ECMWF would suggest a snowstorm
across the north (favored NE section toward Freeport), but any
shift further north of the ECMWF solution would mean more rain
than snow in this same area. The GFS is likely too far south with
the cold air and heaviest QPF due to convective feedback issues,
placing a bullseye of heavy rain in central Illinois. And finally,
the CMC is crazy warm, mainly in the 70s across the forecast area
with only light QPF. At this time, have greatest confidence in
the ECMWF because it has been the most consistent from run to run.
But again, if it shifts any further north, the threat for a
snowstorm in the northern forecast area would decrease
significantly. Stay tuned to the forecast because changes are
likely for the next several days.


No changes made to the model blend forecast. There is a chance for
light rain and snow Sunday afternoon and night, but this system
looks relatively weak. Uttech


.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
ISSUED AT 1224 PM CDT Mon Mar 19 2018

VFR conditions expected through the period with easterly winds.
Some gusty winds are expected today that could affect general
aviation at airports without east/west runways.




LONG TERM...Uttech
AVIATION...Gibbs is the U.S. government's official web portal to all federal, state and local government web resources and services.