Flash Flood Warning 54, NWS Quad Cities, IA

Area Forecast Discussion
National Weather Service Quad Cities IA IL
644 PM CDT Thu Sep 12 2019

...00z AVIATION UPDATE...

.SYNOPSIS...
Issued at 158 PM CDT Thu Sep 12 2019

A warm front has lifted to the northern counties as in the wake of a
small cluster of storms heating is now taking place over nearly all
of the CWA. A small supercell developed in eastern Carroll county
earlier, but has moved east and no new cells are forming, indicating
some warm sector capping is taking place.  In addition, ahead of the
front, mid level lapse rates are very weak, thus convection may be
limited until the front arrives later this afternoon, though shear
is plentiful at low levels, resulting in a low threat for storms,
but any storm will need to be watched closely. We are sending up a
19Z upper air balloon to monitor the instability in the warm
sector.

&&

.SHORT TERM...(This Evening through Friday)
ISSUED AT 158 PM CDT Thu Sep 12 2019

The front will sweep through the area tonight, and with high CAPE
values in excess of 3000, we're still looking for potentially a
strong to severe line of storms, moving west to east, and bringing
winds of 50 to 70 mph, brief torrential rain, and rain amounts of
0.25 to 1.00. I am not thinking we will see any significant training
cells, with a progressive cold front shifting activity east.  It
remains limited ahead of the cold front by the weak mid level lapse
rates, thus, if the cold pool races ahead of the line, it may
rapidly decay into small storm clusters, and if they slow, they may
again strengthen as the front arrives from the west once again.
This could be a very odd evening, where storms transition from
intense to weak or decayed, only to refire to near severe again
farther east.

Lows tonight will advect down to the upper 50s west, as skies clear
behind the storms, while they hold in the upper 60s east under
clouds and higher dewpoints. Friday looks much cooler, with clear
skies possibly clouding up with cumulus during the day.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 158 PM CDT Thu Sep 12 2019

Temperatures will continue to average above normal through the
middle of next week. There are potential big changes coming late
next week.

Thursday night and Saturday
Assessment...high confidence

Quiet and dry conditions will be seen as high pressure quickly moves
through the area. Temperatures will average above normal for
Saturday.

Saturday night and Sunday
Assessment...low confidence

The models continue to show an upper level disturbance moving
through the area and generating showers and storms. However the
previous high is not far removed from the area so there are
questions regarding moisture availability.

The model consensus has chance to likely pops Saturday night with
slight chance pops Sunday morning. These pops may or may not go
lower over the next 48 hours.

Sunday night on...

Sunday night through Monday night
Assessment...high confidence

Quiet and dry conditions will be seen as high pressure moves through
the Midwest.

Tuesday through Wednesday
Assessment...low to medium confidence

Return flow will bring some moisture into the area. This moisture
combined with above normal temperatures may allow diurnal convection
to develop both Tuesday and Wednesday afternoon. Any convection that
does develop would dissipate with sunset leaving mainly dry
conditions Tuesday night and Wednesday morning.

The model consensus continues to suggest this scenario with slight
chance pops both Tuesday and Wednesday afternoon. Attention then
turns to the second half of the week.

Wednesday night and Thursday
Assessment...low to medium confidence

A couple of the global models are advertising another cold front
moving through the Midwest while another has no front. The models
advertising the cold front suggest a Thursday passage for timing.
The ECMWF and CMC global suggest a strong front while the GFS has no
front. If the strong front occurs temperatures well below normal
would be seen behind the front.

Right now the model consensus has slight chance pops Wednesday night
with slight chance to chance pops on Thursday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
ISSUED AT 639 PM CDT Thu Sep 12 2019

Showers and thunderstorms expected this evening at the terminals
ahead of a passing cold front. Conditions will be MVFR to IFR
in the precipitation. Strong, gusty winds are the main threat
with the storms. Overnight gusty westerly winds and return to
VFR conditions post-frontal. Some concerns on low clouds and
MVFR CIGs developing down into the northern sites later tonight
into Friday morning. For now though have only hinted with a
scattered deck with MVFR bases at CID and DBQ. Winds remain gusty
from the west at 15-25+ kts on Friday.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flash Flood Watch until 1 AM CDT Friday for Buchanan-Delaware-
     Dubuque.

IL...Flash Flood Watch until 1 AM CDT Friday for Jo Daviess-
     Stephenson.

MO...NONE.
&&

SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...08
AVIATION...McClure

Hazardous Weather Outlook
National Weather Service Quad Cities IA IL
426 AM CDT Thu Sep 12 2019

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-130930-
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-
426 AM CDT Thu Sep 12 2019

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...TODAY AND TONIGHT

This afternoon and evening: The Storm Prediction Center has a
slight risk for severe thunderstorms across the entire outlook
area. A strong cold front will sweep a line of thunderstorms,
some possibly severe, across the outlook area. The main risk will
be damaging winds and possible large hail. However, a stalled
boundary in eastern Iowa may serve as a focus for discrete
supercells which may produce tornadoes. This risk is greatest
north of Interstate 80 in eastern Iowa.

In addition: due to the intense rainfall rates that will accompany
these storms, there is the potential for flash flooding especially
along the Highway 20 corridor in Iowa and Illinois. This area has
received several inches of rain in the past week and is the most
vulnerable to flash flooding. A flash flood watch is in effect
through this evening for that area.

Heat index values in the lower to mid 90s can be expected this
afternoon mainly along and south of Interstate 80.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

Friday: West winds will gust up to 35 mph especially north of
Interstate 80.

Saturday night: Scattered thunderstorms are expected to develop
as a warm front returns to the area. The Storm Prediction Center
has a marginal risk for severe storms in eastern Iowa, northwest
of a Dubuque to Sigourney line.

.SPOTTER INFORMATION STATEMENT...

Spotter and amateur radio activation may be needed this afternoon
and evening.

Haase

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