Severe Thunderstorm Warning 201, NWS Des Moines, IA

458 
WWUS53 KDMX 280856
SVSDMX

Severe Weather Statement
National Weather Service Des Moines IA
356 AM CDT WED JUN 28 2017

IAC049-153-280930-
/O.CON.KDMX.SV.W.0201.000000T0000Z-170628T0930Z/
Polk IA-Dallas IA-
356 AM CDT WED JUN 28 2017

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 430 AM CDT
FOR NORTHWESTERN POLK AND SOUTHEASTERN DALLAS COUNTIES...

At 356 AM CDT, a severe thunderstorm was located near Van Meter, or
near Adel, moving northeast at 40 mph.

HAZARD...60 mph wind gusts and quarter size hail. 

SOURCE...Radar indicated. 

IMPACT...Hail damage to vehicles is expected. Expect wind damage to 
         roofs, siding, and trees. 

Locations impacted include...
Des Moines, West Des Moines, Ankeny, Urbandale, Johnston, Clive,
Altoona, Waukee, Grimes, Adel, Windsor Heights, Polk City,
Saylorville, Granger, Big Creek Lake, Saylorville Lake, Valley West
Mall, Merle Hay Mall, Jordan Creek Town Center and Weh-Weh-Neh-Kee
State Park.

This includes the following highways...
 Interstate 35 between mile markers 87 and 92.
 Interstate 80 between mile markers 114 and 138.
 Interstate 235 near mile marker 1.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 4163 9399 4185 9375 4167 9350 4153 9392
TIME...MOT...LOC 0856Z 223DEG 36KT 4157 9396 

HAIL...1.00IN
WIND...60MPH
 
$$

Donavon

867 
WWUS53 KDMX 280904
SVSDMX

Severe Weather Statement
National Weather Service Des Moines IA
404 AM CDT WED JUN 28 2017

IAC049-153-280913-
/O.CAN.KDMX.SV.W.0201.000000T0000Z-170628T0930Z/
Polk IA-Dallas IA-
404 AM CDT WED JUN 28 2017

...THE SEVERE THUNDERSTORM WARNING FOR NORTHWESTERN POLK AND
SOUTHEASTERN DALLAS COUNTIES IS CANCELLED...
                
The storm which prompted the warning has weakened below severe
limits, and no longer poses an immediate threat to life or property.
Therefore the warning has been cancelled.

LAT...LON 4163 9399 4185 9375 4167 9350 4153 9392
TIME...MOT...LOC 0902Z 232DEG 38KT 4162 9388 

$$

Donavon

Area Forecast Discussion
National Weather Service Des Moines IA
1152 PM CDT Tue Jun 27 2017

.SHORT TERM.../Tonight through Wednesday/
Issued at 158 PM CDT Tue Jun 27 2017

The primary concern through the period will be convective trends
into Wednesday as an MCS is expected to develop across the High
Plains and reach Iowa during the early morning hours Wednesday.
There will be a pronounced regime change heading into this with a
return to more seasonal temperature and humidity levels in just a
short amount of time. Dewpoints may rise 20+F in 12-14 hours in
many locations.

Sharply increasing warm/theta-e advection will advance through
Iowa this evening, but initially be moisture starved with little
sensible weather. However kinematic forcing ahead the current
WY/MT short wave will work with persistent Plains return flow to
moisten our upstream airmass and feed MCS development. MUCAPEs
should be 1500-3000 j/kg into early tomorrow morning west. This
diminishes by 09z however which supports the west to east gradient
noted in the SPC Day 1 outlook and 3hr Calibrated Severe Probs
per the 09z SREF. 35-50kts of inflow per 300-305K isent surfaces
will support the MCS in some form into the night however, likely
based on shallow convergence and outflow with some suggestions
that the synoptic warm front will try to surge to northern Iowa or
farther north.

It will not take much to get re-generation by tomorrow afternoon
however with most models suggesting uncapped 2000-3000 j/kg
MLCAPEs and 35-45kt of 0-6km shear favorably oriented to the
approaching boundary for discrete cells or at least small
clusters. This will support all modes of severe weather, most
likely over central and southeast sections, and fully expect
current SPC Day 2 Slight Risk to be upgraded once confidence in
location can be better pinned down after overnight outflow shows
its hand. One interesting note is that the convection allowing
model ARW cores are less aggressive than one might expect per the
aforementioned shear and instability based on updraft helicity vs
NMM cores, which are often on the higher end anyways. Thus there
is still some uncertainty with the tornado potential versus more
likely damaging wind and hail. If local outflow does not favorably
augment 0-1 SRH the general synoptic regime, broad SW low level
flow, would seem to be less favorable for tornadoes.

.LONG TERM.../Wednesday night through Tuesday/
Issued at 158 PM CDT Tue Jun 27 2017

The potential for additional strong to severe thunderstorms
Wednesday night through Thursday is the focus of the extended
forecast.

Thunderstorm development Wednesday night will be ongoing near a
cold front extended from northeast to southwest Iowa. Ahead of
the front, an unstable airmass is expected with forecast models
progging MU CAPE values over 2500 j/kg along with a strengthening
and veering low level jet near 30-50 knots. Numerous strong to
severe thunderstorms will develop along this boundary during the
evening and overnight hours aided by the passage of a shortwave in
zonal flow aloft. Damaging winds, large hail, heavy rain and a
few tornadoes within a few hours of initiation will be possible.
The surface front looks to become parallel to the zonal flow
overnight Wednesday into Thursday morning shifting the focus for
showers and thunderstorms and heavy rain to southern Iowa.

Surface low deepens on Thursday across Kansas in response to a
deepening upper trough over the Dakotas with favorable moisture
transport over east west oriented surface boundary. Another round
of strong to severe thunderstorms will develop with shortwave
kicking ahead of a deepening upper trough. Along with heavy rain,
all modes of severe weather will be possible including tornadoes
with thunderstorm development near the front.

Thunderstorms will end west to east across the state Friday with
boundary exiting into the Mid-Mississippi Valley. The upper trough
digs over the Midwest Saturday. Northwest winds will increase
with windy conditions expected from strong mixing. A few showers
and thunderstorms will be possible over northern Iowa Saturday
afternoon and evening aided by daytime heating and another
shortwave rotating around the base of the upper low.

Next week, the pattern shifts to northwest flow aloft over Iowa
with an upper ridge building over the Rockies. Could see another
round of showers and thunderstorms on Monday before warmer and
drier weather returns.

&&

.AVIATION.../For the 06Z TAFS through 06Z Wednesday night/
Issued at 1152 PM CDT Tue Jun 27 2017

Showers and storms still expected to move through much of the
state tonight, with the activity expected across the south pushing
slower across NE than previously expected. Therefore have
adjusted timing. Should see additional activity by late afternoon
so have highlighted with VCTS or VCSH depending on greater
confidence and where better chance for thunder expected. Low level
wind shear still possible through sunrise especially across the
western sites, then gusty south to southwesterly winds expected
Wednesday.

&&

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

&&

SHORT TERM...Small
LONG TERM...Angle
AVIATION...Beerends

Hazardous Weather Outlook
National Weather Service Des Moines IA
334 PM CDT Tue Jun 27 2017

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-282045-
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-
334 PM CDT Tue Jun 27 2017

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

Strong to potentially severe thunderstorms are forecast to develop
over western portions of Iowa after midnight and will spread
eastward Wednesday morning. Large hail and damaging winds look to
be the primary threat, but an isolated tornado or two cannot be
completely ruled out. Locally heavy rain is also possible.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Thunderstorms Wednesday morning are likely to diminish in
coverage and intensity across eastern portions of Iowa after
sunrise. A second round of strong to severe storms will develop
by the afternoon over central to western Iowa. Large hail,
damaging winds and even a few isolated tornadoes are possible.

Additional strong to severe thunderstorms are forecast Thursday
night into Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is possible late tonight and likely again
Wednesday afternoon.