Severe Thunderstorm Warning 135, NWS Quad Cities, IA

Area Forecast Discussion
National Weather Service Quad Cities IA IL
603 PM CDT Mon Oct 8 2018

...00z AVIATION UPDATE...

.SYNOPSIS...
Issued at 330 PM CDT Mon Oct 8 2018

Latest sfc analysis was indicating that the main quasi-stationary
front was north of the DVN CWA from southeastern NE and up acrs
central WI, thu most of the area in the warm moist-sector. But the
main western L/W trof and east coast inter-phase has shifted the main
rain conveyor to the west up acrs the plains and into MN for
tonight and part of Tue. But then a large chunk of the trof still
appears to be on track to eject out and sweep acrs the region by
later Wed. This process to bring the passing rain conveyor acrs the
area Tue night into the first half of Wed, before finally some
progression to the pattern sweeps the rain east by Wed night for
some reprieve. But more heavy rain acrs the area Tue night into Wed
will still look to aggravate ongoing flooding situations.

&&

.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 330 PM CDT Mon Oct 8 2018

Tonight and Tuesday...Isolated to sctrd showers and storms late this
afternoon and evening, with localized heavy down pours fed by PWATs
of 1.4 to 1.7 inches along and west of the MS RVR. Enough afternoon
CAPE build up and shear that a few more enhanced cells may have to
be watched for gusty winds, besides the locally heavy rain and
ponding. With an increasing southwesterly 30-40 KT LLJ tonight,
expect some coverage increase in the shower and storm clusters
especially west of the MS RVR. Thus with the super-saturated grounds,
will keep the flash flood watch going through early Tue afternoon,
and following shifts may have to assess the need to expand it in
both time and space into Wed for the next main incoming precip
window. Expect the coverage to temporarily wane some diurnally on Tue
with a bit of a LLJ weakening through midday. In general, new
rainfall amounts of 0.25 to 0.50 of an inch along and west of the MS
RVR through 00z Wed, with locally higher amounts of an inch or more
possible under passing heavier storms cells. If cloud break some
along with precip decrease, one more unseasonably warm and humid day
with upper 70s to lower 80s on tap for Tue.

.LONG TERM...(Tuesday Night through next Monday)
ISSUED AT 330 PM CDT Mon Oct 8 2018

Tuesday night into Wed...with increasingly negatively tilted upper
trof lifts out, combining with an incoming warm moist conveyor with
PWAT's of 1.6 to 1.9 inches, the stage will be set for a stream of
showers and storms along the incoming front almost squall line-like,
but new timing under such synoptic amplification, has this occurring
well after midnight and into Wed morning. But before then, sctrd
clusters will increase acrs the evening and overnight progress ahead
of the main frontally scooped line of storms. All these various
convective rounds will have the potential to produce heavy rain, and
see widespread 1-2 inches from 00z-18z Wed, with locally higher
amounts of 3 inches possible, and that's even taking into account a
bit more progression to the system. Thus, river flooding and flash
flood potential will have to be revisited and adjusted. Shear
profiles not as strong as previous model runs, but still enough to
support strong to severe storms with damaging winds the primary
threat. With such soil saturation, even somewhat sub-severe wind
gusts may be able to push some trees and roots over. Meso-vortice
tornadoes also possible on the squall line late Tue night west of
the MS RVR. The main FROPA is now generally to push east of the MS
RVR by early Wed afternoon, with falling temps west of the MS RVR.
Most showers to be east out of the CWA by mid Wed afternoon, unless
the front slows even further.

Thursday and Friday...Cool blustery but at least dry Thu on tap with
highs in the 40s and 50s, and Friday morning lows in the low to mid
30s in much of the area with frost likely. The latest medium range
guidance now shunts any kind of overrunning clipper system on Friday
mainly west and south of the area by the strength of the ridge, and
decays it.

Saturday through next Monday...Longer range indications suggest the
weekend to be cool under passing upper troffiness, but the latest
medium range models continue to very greatly for low confidence on
an overrunning cold rain event from late Saturday into Sunday. The
latest GFS has now shunted most of it to the south of the area,
while the 12z ECMWF hits the CWA with a half inch to an inch of much
un-needed rains. A period to watch, and with the previous GFS
targeting the area, will have to continue high POPS for that far out
and watch model trends. When what ever rain or precip system exits
late in the weekend, some cold post-system signals that suggest a
freeze possible by next Monday or Tuesday mornings.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
ISSUED AT 601 PM CDT Mon Oct 8 2018

Periodic chances of showers & storms will increase at KCID/KDBQ this
evening, and have handled w/ mentions of VCTS due to low confidence
on exact timing. While VFR conditions are primarily expected, brief
drops to MVFR cigs & visibilities will be possible in
shower/storm cores. Additionally, models depict a 40-45 kt LLJ
developing around 2000 ft AGL after midnight across the region, so
have included LLWS at all terminals from midnight through 09/13z.
There will be a brief respite in showers & storms Tuesday morning
before chances increase again late in the period.

&&

.HYDROLOGY...
Issued at 317 PM CDT Mon Oct 8 2018

Forecasts for heavy rain in central Iowa to northeast Iowa are
continuing, and have not changed much. However, as this event
falls into the 48hr QPF that is used to produce river forecasts.
With moderate to heavy rain amounts falling last night, especially
over northeast Iowa the new rain is combining with the QPF to
produce crests that are much higher than issued yesterday. This is
due to the process, not because the heavy rain isn't already
forecast.

For our rivers, the Cedar River is now forecast to see greatly
increasing flows by day 2, resulting in a steady rise to 19.7
feet at Cedar Rapids, which is major. The category of major is
highly confident, though the exact crest value may change as the
we see the rain accumulate / run off.

The same is confidence on a significant rise is true for routed water
on the Wapsipinicon, Des Moines, Skunk, and Iowa basins. For the
Iowa, outflow from Coralville Dam is around 10-11Kcfs. This
helping rise Iowa City back to minor flood today, and with some
COE variation, it will rise and fall over flood stage the next
several days. Just downstream, the English River, which has had
it's stage and flow confirmed, is near crest, about 2 feet over
major flood status. This is combining with the Iowa River, to
bring a continued rise well above major flood near Lone Tree. That
Lone Tree major flood status should not drop much for the next
5-6 days. This will continue to bring major flooding down through
the lower Iowa basin this week.

With all tributaries seeing high level, rises, and in many case
major river flooding, and even the upstream portions of the
Mississippi upstream seeing heavy rainfall tonight through
Tuesday night, the big river will see some very significant rises
as well. For now, though minor flooding may be possible from
Dubuque through Bellevue, the portions most likely to flood are
from Camanche downstream. With the major flooding on the
Wapsipinicon and Rock, with high water from the Turkey and
Maquoketa, the main stem Mississippi is forecast to reach major
flood status from Rock Island, downstream. This resulted in
increase flood forecasts downstream where sites were already
forecast to reach major flood as well.

ERVIN

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flash Flood Watch through Tuesday afternoon for Benton-Buchanan-
     Cedar-Delaware-Dubuque-Iowa-Jefferson-Johnson-Jones-Keokuk-
     Linn-Washington.

IL...NONE.
MO...NONE.
&&

SYNOPSIS...12
SHORT TERM...12
LONG TERM...12
AVIATION...Speck
HYDROLOGY...Ervin

Hazardous Weather Outlook
National Weather Service Quad Cities IA IL
443 PM CDT Mon Oct 8 2018

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-091000-
Buchanan-Delaware-Dubuque-Benton-Linn-Jones-Jackson-Iowa-Johnson-
Cedar-Clinton-Muscatine-Scott-Keokuk-Washington-Louisa-Jefferson-
Henry IA-Des Moines-Van Buren-Lee-Jo Daviess-Stephenson-Carroll-
Whiteside-Rock Island-Henry IL-Bureau-Putnam-Mercer-Henderson-
Warren-Hancock-McDonough-Scotland-Clark-
443 PM CDT Mon Oct 8 2018

This Hazardous Weather Outlook is for portions of north central
Illinois...northwest Illinois...west central Illinois...east
central Iowa...northeast Iowa...southeast Iowa and northeast
Missouri.

.DAY ONE...TONIGHT

Isolated to scattered showers and thunderstorms this evening may
increase in coverage overnight especially west of the Mississippi
River. The primary threat is expected to be heavy rainfall, which
could lead to flash flooding mainly west of a line from Dubuque,
Iowa to Fairfield, Iowa. A Flash Flood Watch remains in affect for
these areas through early Tuesday afternoon. Besides the flooding
threat, an isolated severe storm is also possible in this same
general area this evening and overnight. The primary threat is
damaging winds, with an isolated tornado possible.

Area rivers are experiencing flooding. Please see the latest
Flood Statements and Flood Warnings for details.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

Heavy rainfall is possible over portions of eastern Iowa on Tuesday,
and over the entire outlook area Tuesday night into Wednesday
morning ahead of a strong cold front. An additional 1 to 2 inches
of rainfall and locally higher amounts during this time on
saturated grounds, will aggravate ongoing flooding situations or
create new ones. A Flash Flood Watch may eventually be needed for
Tuesday night into Wednesday.

A few severe storms are also possible Tuesday evening and
overnight, and the Storm Prediction Center has placed much of the
area in a slight risk for severe weather. The primary threat is
damaging winds, with an isolated tornado possible.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is possible for portions of the outlook area
tonight, and again by Tuesday evening. Reports of any flash
flooding would also be appreciated.

12

Special Weather Statement
National Weather Service Quad Cities IA/IL
745 PM CDT MON OCT 8 2018

IAC011-019-055-113-090215-
Buchanan-Benton-Delaware-Linn-
745 PM CDT MON OCT 8 2018

...SHOWERS & THUNDERSTORMS PRODUCING HEAVY RAIN WILL AFFECT
BUCHANAN... BENTON...WESTERN DELAWARE AND LINN COUNTIES UNTIL 915 PM
CDT...

At 741 PM CDT, radar indicated showers & thunderstorms with heavy
rain centered near Urbana, or near Vinton, moving northeast at 40
mph.

Minor flooding of area creeks and streams is possible.
Minor flooding of streets and creeks in urban areas is possible.

Locations impacted include...
Cedar Rapids, Independence, Vinton, Manchester, Marion, Hiawatha,
Robins, Jesup, Center Point, Fairfax, Atkins, Urbana, Dysart, Central
City, Fairbank, Palo, Shellsburg, Newhall, Edgewood and Winthrop.

This includes Interstate 380 between mile markers 17 and 55.

Minor flooding is possible. If you are driving and encounter a
flooded roadway, Turn around, don't drown. Most flood deaths occur
in vehicles.

A Flash Flood Watch remains in effect for the area until midday
Tuesday.

LAT...LON 4193 9155 4194 9229 4204 9230 4230 9230
      4230 9206 4247 9206 4247 9208 4264 9208
      4264 9129
TIME...MOT...LOC 0041Z 212DEG 36KT 4218 9191

Speck

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