Damaging Winds and Heavy Rain in Iowa, June 9 to 10, 2020

Area Forecast Discussion
National Weather Service Des Moines IA
430 AM CDT Tue Jun 9 2020

.DISCUSSION.../Today through Monday/
Issued at 350 AM CDT Tue Jun 9 2020

The main focus on this forecast package is the next 36 hours. Iowa
will get hit with a double whammy beginning this morning. As has
been discussed previously, the remnants of Cristobal will eject
out of the Southern Plain and into the western Great Lakes region
by late tonight. Model soundings are a little slower to saturate
this morning but not by much. Deep saturation will occur by 8 to
10 AM across much of central and southern Iowa with moderate to
heavy rainfall occurring near the I-35 corridor and eastward. A
moderate risk of excessive rainfall has been issued by WPC for the
northern half of the state into the northeast part of Iowa. Model
soundings continue to have PWATs of 2 to 2.5 inches from late
morning through the afternoon. The heaviest rain will fall where
the strongest storms develop...mainly across our eastern forecast
area and locations east. The severe threat with Cristobal for us
will be marginal but further to the east/southeast the shear will
be better and storms in those areas ma produce strong wind and
possibly a tornado.

After midnight, the remnants of Cristobal will have shifted north
and east and other than lingering rain across our northeast, much
of the rain threat from that system will have ended. However...the
double whammy comes tonight as a strong shortwave lifts out of the
central and southern Plains. A surface low will develop somewhere
over eastern KS/NE and lift across southern Iowa into Illinois by
Wednesday afternoon. Stronger instability and shear lift into far
southwest Iowa later this evening. A second round of heavy rain
will spread across the region from west to east and hi-res models
develop a line of storms across southwest Iowa in the warm
advection wing of this system. Some of these storms are expected
to become super cellular and if they do, large hail, damaging wind
and a tornado or two can all be possible...at least initially. As
the low moves east, the strongest shear moves into Missouri but
southern Iowa will still have a potential for strong storms
through midnight. One other issue late this afternoon and tonight
will be a potential for strong winds across the west as Cristobal
pulls out and the next low moves in. A strong pressure gradient
will develop over this area. Soundings show potential wind gusts
around 40 kts. A wind advisory may be needed for southwest and
western Iowa tonight but with everything else that will go on
before tonight, I opted to hold off on wind headlines given the
heavy rain/flash flood threat and the severe threat after that.

This second system pulls out by mid day Wednesday and while cooler
air settles in, the pattern dries out and an upper ridge builds
into the Plains through the weekend. The GFS want to push a couple
of weak waves through the flow over Iowa giving us a chance for
showers Friday night through Saturday but this appears to be
inconsequential. After the weekend, models vary on the handling of
the upper ridge with the GFS having a large Canadian system
pushing the ridge axis east and attempting to flatten the ridge.
The Euro is further west with the upper low thus keeping any
precip potential further west of Iowa. Even if the GFS were
correct, most of the precip moves off to our north and west but we
do get clipped on Monday /Tuesday with some light precip across
these areas. Temps gradually warm Thursday but with the flattening
ridge over the weekend, highs will be slightly cooler...in the mid
70s to lower 80s.

&&

.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1148 PM CDT Mon Jun 8 2020

VFR conditions for much of the rest of the night will decline
into MVFR shortly after sunrise Tuesday. As moderate to heavy
rainfall moves northward into the state ahead of what is currently
Tropical Depression Cristobal, periods of IFR restrictions are
expected. Thunder will be limited and just have vicinity
mentioned mainly late morning or afternoon. As round one of rain
exits Tuesday afternoon and evening, there will be a break and
perhaps even VFR conditions at DSM or OTM Tuesday evening.
However, round two with showers and thunderstorms is expected
later Tuesday night, which may impact the terminals toward or
after 6z Wednesday.

&&

.HYDROLOGY...
Issued at 350 AM CDT Tue Jun 9 2020

Widespread 2 to 3 inch rainfall amounts are forecast across
eastern Iowa with the two systems to impact Iowa through
Wednesday. The excessive rainfall outlook has been upgraded to
moderate for northern and northeastern Iowa as expected and based
on the further west track of the heavier rainfall the flash flood
watch was expanded to include the western three counties across
the northern end of the watch. Winnebago, Hancock and Wright
counties are now included in the watch.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 7 AM CDT this morning through Wednesday
morning for IAZ006-007-016-017-025>028-036>039-047>050-059>062-
072>075-083>086-094>097.

&&

DISCUSSION...FAB
AVIATION...Ansorge
HYDROLOGY...FAB

Hazardous Weather Outlook
National Weather Service Des Moines IA
433 AM CDT Tue Jun 9 2020

IAZ070-081-092-093-101100-
Cass-Adams-Taylor-Ringgold-
433 AM CDT Tue Jun 9 2020

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

There is a slight risk of severe storms this evening across the
area. Main threat is damaging winds and large hail. An isolated
tornado is also possible.

Strong northwest winds are expected late tonight with gusts of 35
to 45 mph.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Strong northwest winds will persist into Wednesday with gusts of
35 to 45 mph.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening.

IAZ004-005-015-023-024-033>035-044>046-057-058-071-082-101100-
Emmet-Kossuth-Palo Alto-Pocahontas-Humboldt-Sac-Calhoun-Webster-
Crawford-Carroll-Greene-Audubon-Guthrie-Adair-Union-
433 AM CDT Tue Jun 9 2020

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

A few thunderstorms are expected today into tonight. A strong to
severe storm cannot be ruled out, but the threat of widespread
severe weather is low at this time.

Strong northwest winds are expected late tonight with gusts of 35
to 45 mph.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Strong northwest winds will persist into Wednesday with gusts of
35 to 45 mph.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not needed at this time.

IAZ006-007-016-017-025>028-036>039-047>050-059>062-072>075-
083>086-094>097-101100-
Winnebago-Worth-Hancock-Cerro Gordo-Wright-Franklin-Butler-Bremer-
Hamilton-Hardin-Grundy-Black Hawk-Boone-Story-Marshall-Tama-
Dallas-Polk-Jasper-Poweshiek-Madison-Warren-Marion-Mahaska-Clarke-
Lucas-Monroe-Wapello-Decatur-Wayne-Appanoose-Davis-
433 AM CDT Tue Jun 9 2020

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

A Flash Flood Watch is in effect for the area. Please refer to
the National Weather Service website at weather.gov/desmoines for
further details.

In addition to heavy rainfall, a few thunderstorms are possible
today into tonight. A strong to severe storm cannot be ruled out,
but the threat of widespread severe weather is low at this time.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Strong northwest winds will persist into Wednesday with gusts of
35 to 45 mph.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not needed at this time.