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fxus63 kdvn 172316 
afddvn

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
616 PM CDT sun may 17 2020

..aviation update...

Synopsis...
issued at 350 PM CDT sun may 17 2020

As expected a lifting warm front and approaching upper level low
brought some heavy rain to portions of the area, with some
areas picking up 1-2 inch rain amounts over the past 12-18+ hrs.
The heaviest amounts seemed to be mostly concentrated along and
east of the Mississippi River. This resulted in not only an
increase in flooding on the Rock River, but also new flooding on
portions of the la moine and green rivers. Early this afternoon
GOES-16 satellite imagery nicely depicts the whirling dervish
moving eastbound from central Iowa. At the surface, an occluded
front was draped between the Hwy 20 and Hwy 30 corridors and
is connected by low pressure near Marshalltown, Iowa and south of
Rochelle, Illinois. Radar shows the plume of showers and some storms
streaming up across Illinois with the back edge just grazing portions
of Bureau and Putnam counties, as the mid level dry slot continues
to work across the area.

&&

Short term...(this evening through monday)
issued at 350 PM CDT sun may 17 2020

The vertically stacked extra-tropical cyclone moving east from
central Iowa will track towards central Illinois over the next
24 hours. The system will then really slow and sag slowly south
toward the MO bootheel beyond into Tuesday, as an Omega block
forms as ridging amplifies through the plains ahead of a digging
SW Continental U.S. Upper low. What this will mean is a continuation of
cloudiness and shower chances as spokes of energy rotate around
the low. Temperatures will remain a bit below average as well, and
the addition of a north wind gusty at times will make it feel
rather cool at times.

Long term...(monday night through sunday)
issued at 350 PM CDT sun may 17 2020

Key messages:

1. Light rain chances linger across the eastern counties of the County Warning Area
into Tuesday with amounts under a tenth of an inch.

2. Tuesday night through Friday morning, dry conditions are expected
with a warming trend.

3. Active weather is forecast again Friday into next weekend.

Discussion:

Monday night, lingering rain will end toward late evening and
overnight with little if any additional accumulation. Temperatures
will settle into the upper 40s and low 50s.

Tuesday, the eastern and southeast parts of the County Warning Area have slight/low
chances for showers as the upper low slowly exiting to the southeast
brings some upper level energy over the area. Highs will be in the
mid and upper 60s.

Tuesday night through Friday morning, dry conditions with partly to
mostly cloudy skies are anticipated as a ridge of high pressure
builds into the region. A gradual warmup is also expected, with
highs in the low to mid 70s Wednesday and Thursday, climbing into
the low to mid 80s Saturday and Sunday. With the warmup late week
and next weekend, humidity levels and storm chances will also
increase. It should be noted that if the upper level low lingers
longer into Tuesday night or Wednesday, clouds and precip chances
may need to be increased accordingly.

&&

Aviation...(for the 00z tafs through 00z Monday evening)
issued at 614 PM CDT sun may 17 2020

The main rain event has ended for the area, but light showers will
pinwheel back southwest over the area through Monday. This will
result in lowering cigs this evening from VFR to MVFR and possibly
IFR through Monday as the upper low spins overhead. Visibility
will remain good outside of showers, and this will be handled by
updates if it appears to affect a site more than a half hour.

Ervin

&&

Hydrology...
issued at 350 PM CDT sun may 17 2020

More widespread moderate and heavy rainfall of 1 to 2 inches last
night and this morning in many locations across northern Illinois,
is producing new rises and significant increases in expected crests on
several Illinois tributaries. The hardest hit seems to be the Rock River
basin, with enhanced run-off producing higher and quicker crests
through mid week. Of biggest impact will be a big jump of over a
foot on the rock at Moline with it going above the major flood
category and hitting around 15 feet by Wednesday. Joslin has been
adjusted up with a crest just under the 16.5 feet major flood stage by
Wednesday. And the run-off will likley push como above flood by
Monday morning. On the Green River near Geneseo, confidence has
increased on it reaching flood stage, and so a Flood Warning has
been issued late this afternoon. Further to the south, 1 to 2
inches of rain on the already soaked la moine river basin in west
central Illinois will surge the crest near Colmar to just over
moderate flood stage on Monday.

On the Mississippi, will have to watch for localized stream/
tributary input as well as back-flow effects from the Rock River at
ld15 in the Quad Cities, but overall any broad rises are expected to
stay below action stage along the entire stretch of the mainstem.
Routing some flow eventually from northern Iowa will bring some
withing banks rises down portions of the Cedar and Iowa rivers, but
again action stages not expected to be attained.

&&

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

$$

Synopsis...McClure

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