Severe Thunderstorm Warning 118, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
1240 PM CDT Fri Jun 8 2018

...Updated for 18z Aviation Discussion...

.DISCUSSION.../Today through Thursday/
Issued at 405 AM CDT Fri Jun 8 2018

The forecast period will be influenced by two pattern regimes
with our current weak flow, ridging transitioning to less active
sensible weather after Monday with a cold frontal passage as the
westerlies increase and sag southward in response to a long wave
trough advancing through the NW CONUS early next week.

Currently low end convection continues to fester across northern
Iowa, initially aided by kinematic lift with the passage of a
short wave noted in satellite imagery but now driven more by deep
moisture convergence and warm advection in generally low end
925-850mb flow above the Carroll, Des Moines to Keokuk surface
warm front. This generally low topped convection is primed for
efficient rainfall rates with weak mean winds, 3.5km+ warm cloud
depths and around 1.7” precipitable water. Areal coverage of
heavy rain has not been great, but isolated locations of Cerro
Gordo and Worth Counties have seen 2-3” rains per dual pol and
MRMS precip estimates. Most high res convection allowing models
suggest this will be steady state through sunrise and then
gradually drift off to the east and dissipate later this morning
with heavy rains remaining the primary threat. A few storms may
just reach strong to severe limits however as 3hr MUCAPEs changes
are positive across southern MN with a nose of enhanced effective
shear west to east along the IA/MN border as well.

Later today the airmass will re-charge with moderate MLCAPEs
across IA and extreme values possible from KS into the Dakotas.
There is some potential for isolated peak heating development here
today, but convergence will be weak and coverage likely isolated.
The more significant potential may originate upstream into the
night with several high res models suggesting an organized MCS
advancing south and east into or near IA from the High Plains
which could be strong to at times severe with wind the primary
threat, hail to a lesser extent. Although MLCAPEs may remain
1.5-2.5K j/kg into the night south and west, the 0-3km shear
appears too weak for any QLCS tornado potential.

As with the past several days, predictability is not great in the
later periods with forcing mechanisms generally weak. Overall the
pattern typically favors late peak heating and nocturnal peaks
driven by warm advection with morning mins and spatially more
north and east as the current warm frontal placement doesn't
change much overall through the weekend. This will change by
Monday however with the cold frontal passage coinciding with peak
heating and accompanied by stronger synoptic scale forcing as the
long wave trough begins advancing into the central and northern
Plains. For Tuesday and Wednesday high pressure will generally be
in place with only infrequent, spotty PoPs driven by subtle waves
in the faster flow which may produce lower end convection at
times.

&&

.AVIATION.../For the 18Z TAFS through 18Z Saturday afternoon/
Issued at 1240 PM CDT Fri Jun 8 2018

While official TAFs have prevailing VFR, there is low to medium
confidence with weak flow and thunderstorm chances ill-defined.
Surface boundary oriented from near CIN to southwest of DSM to
southwest of OTM has agitated cumulus with showers trying to
develop. Another boundary leftover from morning convection over
Siouxland is also pushing eastward For now, have VCSH at most
terminals for a few hours later this afternoon or early this
evening, though amendments may be needed if storms will impact a
terminal. Another round of storms may move out of South
Dakota/Nebraska across the area after 6z through early tomorrow
morning, but low confidence in timing and impacts so just have
VCSH to avoid prolonged VCTS period.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

DISCUSSION...Small
AVIATION...Ansorge

Hazardous Weather Outlook
National Weather Service Des Moines IA
422 AM CDT Fri Jun 8 2018

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-090930-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene-
Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper-
Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-
Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-
Appanoose-Davis-
422 AM CDT Fri Jun 8 2018

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Scattered thunderstorms are possible today primarily northeast and
east. More widespread thunderstorms are possible tonight. A few
storms could be strong to possibly severe, with damaging winds and
hail the main threats.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Strong thunderstorms, a few of which may become severe, are
possible Saturday. The main threats with these storms are hail and
damaging winds.

Another round of thunderstorms is possible Sunday night through
Monday, but the threat and location for potential severe weather
remains uncertain.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may possibly be needed today and tomorrow.

Kotenberg

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
935 AM CDT FRI JUN 8 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0935 AM     HEAVY RAIN       GRAFTON                 43.33N 93.07W
06/08/2018  E3.18 INCH       WORTH              IA   PUBLIC

&&

AK

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
1036 AM CDT FRI JUN 8 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1020 AM     FLASH FLOOD      3 WSW MANLY             43.27N 93.26W
06/08/2018                   WORTH              IA   LAW ENFORCEMENT

            SEVERAL COUNTY GRAVEL ROADS ARE CLOSED
            AROUND THE TOWN OF MANLY WITH ONE ROAD
            WASHED OUT SOUTH OF HIGHWAY 9 ON MALLARD
            AVENUE.

&&

ANSORGE

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE DES MOINES IA
1108 AM CDT FRI JUN 8 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0935 AM     HEAVY RAIN       GRAFTON                 43.33N 93.07W
06/08/2018  E3.18 INCH       WORTH              IA   PUBLIC

0851 AM     HEAVY RAIN       1 ESE MASON CITY        43.15N 93.18W
06/08/2018  E4.70 INCH       CERRO GORDO        IA   PUBLIC

            THIS IS AN UPDATED TOTAL FROM A 615A STORM
            REPORT, WHICH HAD 3.75".

0850 AM     HEAVY RAIN       MANLY                   43.29N 93.20W
06/08/2018  E5.00 INCH       WORTH              IA   PUBLIC

            VIA SOCIAL MEDIA.

0840 AM     HEAVY RAIN       4 WSW PLYMOUTH          43.22N 93.20W
06/08/2018  M3.65 INCH       CERRO GORDO        IA   AMATEUR RADIO

            3.65 INCHES FROM 3:20A TO 8:25A; 24 HOUR
            RAIN TOTAL AS OF 8:25A IS 4.06 INCHES.

0800 AM     HEAVY RAIN       MESERVEY                42.91N 93.48W
06/08/2018  E3.50 INCH       CERRO GORDO        IA   PUBLIC

0700 AM     HEAVY RAIN       1 NNE MASON CITY        43.17N 93.19W
06/08/2018  E2.45 INCH       CERRO GORDO        IA   CO-OP OBSERVER

            24 HOUR TOTAL.

0700 AM     HEAVY RAIN       SWALEDALE               42.98N 93.32W
06/08/2018  E3.05 INCH       CERRO GORDO        IA   COCORAHS

0615 AM     HEAVY RAIN       1 ESE MASON CITY        43.15N 93.19W
06/08/2018  E3.75 INCH       CERRO GORDO        IA   PUBLIC

            VIA SOCIAL MEDIA.

0432 AM     HEAVY RAIN       4 SSE CLEAR LAKE        43.09N 93.34W
06/08/2018  E2.95 INCH       CERRO GORDO        IA   PUBLIC

            HOME WEATHER STATION.

0431 AM     HEAVY RAIN       2 WSW SWALEDALE         42.97N 93.34W
06/08/2018  M3.01 INCH       CERRO GORDO        IA   PUBLIC

            HOME WEATHER STATION.

0420 AM     HEAVY RAIN       GRAFTON                 43.33N 93.08W
06/08/2018  M2.34 INCH       WORTH              IA   PUBLIC

            HOME WEATHER STATION.

0330 AM     HEAVY RAIN       MASON CITY              43.17N 93.19W
06/08/2018  M2.13 INCH       CERRO GORDO        IA   MESONET

            RIVER GAUGE ALONG WINNEBAGO RIVER.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
1143 AM CDT FRI JUN 8 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1142 AM     HEAVY RAIN       MASON CITY              43.15N 93.20W
06/08/2018  E5.60 INCH       CERRO GORDO        IA   BROADCAST MEDIA

            FROM KIMT-TV STUDIO.

&&

AK

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
138 PM CDT FRI JUN 8 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0700 AM     HEAVY RAIN       1 SW NORTHWOOD          43.44N 93.23W
06/08/2018  E2.17 INCH       WORTH              IA   CO-OP OBSERVER

&&

AK