Severe Thunderstorm Warning 237, NWS Des Moines, IA

670 
WWUS53 KDMX 052257
SVSDMX

Severe Weather Statement
National Weather Service Des Moines IA
557 PM CDT SUN AUG 5 2018

IAC099-157-171-052330-
/O.CON.KDMX.SV.W.0237.000000T0000Z-180805T2330Z/
Poweshiek IA-Tama IA-Jasper IA-
557 PM CDT SUN AUG 5 2018

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 630 PM CDT
FOR NORTHWESTERN POWESHIEK...SOUTH CENTRAL TAMA AND NORTHEASTERN
JASPER COUNTIES...

At 557 PM CDT, a severe thunderstorm was located near Grinnell,
moving east at 30 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...
Grinnell, Brooklyn, Rock Creek Lake, Holiday Lake and Rock Creek
State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Torrential rainfall is occurring with this storm, and may lead to
flash flooding. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 4173 9285 4185 9284 4192 9244 4172 9245
TIME...MOT...LOC 2257Z 268DEG 25KT 4179 9276 

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

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571 
WWUS53 KDMX 052306
SVSDMX

Severe Weather Statement
National Weather Service Des Moines IA
606 PM CDT SUN AUG 5 2018

IAC099-052315-
/O.CAN.KDMX.SV.W.0237.000000T0000Z-180805T2330Z/
Jasper IA-
606 PM CDT SUN AUG 5 2018

...THE SEVERE THUNDERSTORM WARNING FOR NORTHEASTERN JASPER COUNTY IS
CANCELLED...
    
The severe thunderstorm which prompted the warning has moved out of 
the warned area. Therefore, the warning has been cancelled.

LAT...LON 4172 9245 4173 9277 4186 9277 4192 9244
TIME...MOT...LOC 2305Z 268DEG 25KT 4179 9268 

$$

IAC157-171-052330-
/O.CON.KDMX.SV.W.0237.000000T0000Z-180805T2330Z/
Poweshiek IA-Tama IA-
606 PM CDT SUN AUG 5 2018

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 630 PM CDT
FOR NORTHWESTERN POWESHIEK AND SOUTH CENTRAL TAMA COUNTIES...

At 605 PM CDT, a severe thunderstorm was located near Grinnell,
moving east at 30 mph.

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

SOURCE...Radar indicated.

IMPACT...Expect damage to roofs, siding, and trees.

Locations impacted include...
Grinnell, Brooklyn and Holiday Lake. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Torrential rainfall is occurring with this storm, and may lead to
flash flooding. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 4172 9245 4173 9277 4186 9277 4192 9244
TIME...MOT...LOC 2305Z 268DEG 25KT 4179 9268 

HAIL...0.75IN
WIND...60MPH
 
$$

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487 
WWUS53 KDMX 052325
SVSDMX

Severe Weather Statement
National Weather Service Des Moines IA
625 PM CDT SUN AUG 5 2018

IAC157-171-052334-
/O.EXP.KDMX.SV.W.0237.000000T0000Z-180805T2330Z/
Poweshiek IA-Tama IA-
625 PM CDT SUN AUG 5 2018

...THE SEVERE THUNDERSTORM WARNING FOR NORTHWESTERN POWESHIEK AND
SOUTH CENTRAL TAMA COUNTIES WILL EXPIRE AT 630 PM CDT...
                
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 will be allowed to expire.  However small
hail, gusty winds and heavy rain are still possible with this
thunderstorm.

LAT...LON 4172 9245 4173 9277 4186 9277 4192 9244
TIME...MOT...LOC 2324Z 258DEG 25KT 4182 9251 

$$

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Area Forecast Discussion
National Weather Service Des Moines IA
309 PM CDT Sun Aug 5 2018

.SHORT TERM.../Tonight through Monday/
Issued at 309 PM CDT Sun Aug 5 2018

Iowa will remain beneath brisk zonal flow aloft through Monday. A
quasi-stationary synoptic boundary has set up from eastern
nebraska across northern Iowa and over to near the
Wisconsin/Illinois border. We have already seen three separate
rounds of convection across northern Iowa today as broad forcing
for vertical ascent increases ahead of a shortwave impulse
approaching from the west. These thunderstorms have reinforced the
synoptic boundary and wobbled it around some, but it appears
nearly anchored roughly along Highway 20 at this point. meanwhile
more showers and storms are approaching from central Nebraska as
evidenced by regional radar imagery. South of the boundary skies
are mostly clear and temperatures have risen well into the 90s,
with Lamoni reading 96 at this hour. However dewpoints are in the
60s and heat index values do not justify a headline.

We may or may not see a brief lull in convection across northern
Iowa behind the current round of thunderstorms, but in any event
as forcing increases this evening we will see additional, more
widespread storm development. Overnight this will be enhanced by
the nocturnal low-level jet and strong moisture transport into the
boundary, which should also cause a gradual southward shift of the
boundary and associated convection. It is difficult to tell how
far south it will get as convective outflow fights against the
inflow from the jet, but somewhere between Interstate 80 and
Highway 30 appears most likely. Have continued trend of increasing
POPs across about the northern half of the forecast area, and
bleeding them southward to account for this uncertainty. In terms
of impacts, given the degree of deep-layer shear and adequate
instability, there is certainly a risk of large hail and/or
damaging winds with the stronger updrafts, particularly from late
this afternoon into early tonight. There is also a definite threat
of heavy rain across northern Iowa, with several rounds of storms
and potential for training near the boundary, but given the
antecedent conditions flash flooding appears unlikely except
perhaps in urban areas where high rainfall rates may occur.

By Monday morning the aforementioned impulse will be passing and
the more robust/widespread convection will shift off to the east.
However, the synoptic boundary will likely still linger somewhere
over our forecast area, probably in central or possibly southern
Iowa, and will be slow to move out. This should lead to additional
thunderstorm development, particularly in the afternoon and
evening and mainly in southern Iowa, with a marginal attendant
severe weather risk.

.LONG TERM.../Monday night through Sunday/
Issued at 309 PM CDT Sun Aug 5 2018

On Monday night and Tuesday a broad 500 mb trough will move
overhead, transitioning us into more of a light northwesterly
steering flow regime. This will also finally push the boundary
south of our area, though there may still be lingering storms in
our southern counties early Monday night before this occurs. On
Tuesday we will see isolated showers and storms as the 500 mb
trough moves overhead, but these should be spotty and benign.
Otherwise, mainly dry and less hot weather will prevail through
the weekend. A weak surface trough creeping across the region will
provide low thunderstorm chances between Thursday and Friday, but
again these should be isolated and of little impact. Meanwhile
temperatures will be slow to warm in the northwesterly flow
regime, probably rising a degree or two each day from mid-week
onward.

By Friday a large 500 mb ridge will have built along the Rockies
and across the western U.S., with Iowa residing on its eastern
periphery, aiding the slow warming trend, while a modest longwave
trough extends from eastern Canada down into the southeastern
U.S. Next weekend we will see a blocking pattern develop in which
the large thermal ridge slides northeastward over the Upper
Midwest and south central Canada, causing the aforementioned
longwave trough to close off and retrograde southwestward roughly
down the Ohio River valley. Long-range models have been having a
bit of difficulty pinning down this evolution, but are coming into
better agreement today in bringing the closed 500 mb low over
Illinois/Indiana early next week. This would support a
continuation of moderate to slightly warming temperatures, but if
solutions change to the point where the low makes it westward to
Iowa then this would change things. We will be watching this over
the course of this week.

&&

.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1245 PM CDT Sun Aug 5 2018

TAF forecasts are complicated by low-confidence thunderstorm
scenario across northern Iowa for much of the period. Really any
time from mid/late afternoon today through Monday morning could
see TSRA, especially at MCW, with a somewhat lower probability at
FOD/MCW. Have covered primarily with VCTS and tried to keep this
limited to the most likely window, from this evening through
around sunrise Monday. Amendments are likely, and timing of
impacts will need to be refined in subsequent TAF issuances. At
DSM/OTM thunderstorms are possible but much lower probability so
not advertised in the TAFs at this time.

&&

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

&&

SHORT TERM...Lee
LONG TERM...Lee
AVIATION...Lee

Hazardous Weather Outlook
National Weather Service Des Moines IA
350 PM CDT Sun Aug 5 2018

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-061100-
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-
350 PM CDT Sun Aug 5 2018

This Hazardous Weather Outlook is for portions of northern and central
Iowa.

.DAY ONE...This afternoon and tonight

Scattered thunderstorms continue into tonight. There is a
marginal to slight risk of severe weather with the primary threats
being damaging wind and large hail. Locally heavy rain will also
be possible into tonight with isolated one to two inch amounts
possible.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Chances for thunderstorms linger into Monday with a few strong
storms possible in central Iowa. Otherwise, there will be
isolated and sporadic chances for storms later in the week with
the severe weather potential yet to be determined.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed tonight and possibly Monday.

IAZ081>086-092>097-061100-
Adams-Union-Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-
Wayne-Appanoose-Davis-
350 PM CDT Sun Aug 5 2018

This Hazardous Weather Outlook is for portions of southern Iowa.

.DAY ONE...This afternoon and tonight

There will be chances for thunderstorms overnight. The risk of
severe weather is low.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Chances for strong to perhaps severe storms will be possible later
Monday. Otherwise, there will be isolated and sporadic chances
for storms later in the week with the severe weather potential yet
to be determined.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed briefly Monday.

Small

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
226 PM CDT SUN AUG 5 2018

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

0933 AM     TSTM WND DMG     3 NW HAMPTON            42.77N 93.24W
08/05/2018                   FRANKLIN           IA   TRAINED SPOTTER

            TREE BRANCHES DOWN AT BEED'S LAKE STATE PARK
            CAMPGROUND.

&&

BSS

Special Weather Statement
National Weather Service Des Moines IA
236 PM CDT Sun Aug 5 2018

IAZ005-015>017-023>028-033>039-052130-
Kossuth-Palo Alto-Hancock-Cerro Gordo-Pocahontas-Humboldt-Wright-
Franklin-Butler-Bremer-Sac-Calhoun-Webster-Hamilton-Hardin-Grundy-
Black Hawk-
Including the cities of Algona, Emmetsburg, Garner, Britt,
Kanawha, Mason City, Clear Lake, Pocahontas, Laurens, Rolfe,
Fonda, Gilmore City, Humboldt, Eagle Grove, Clarion, Belmond,
Hampton, Parkersburg, Clarksville, Shell Rock, Greene, Aplington,
Allison, Dumont, Waverly, Sac City, Lake View, Odebolt,
Wall Lake, Schaller, Early, Rockwell City, Manson, Lake City,
Pomeroy, Fort Dodge, Webster City, Iowa Falls, Eldora, Ackley,
Grundy Center, Reinbeck, Conrad, Dike, Wellsburg, Waterloo,
and Cedar Falls
236 PM CDT Sun Aug 5 2018

...Strong Thunderstorms over Northern Iowa this Afternoon...

Scattered thunderstorms have slowly strengthened along and just
north of Highway 20 into midday and will continue to affect
portions of northern Iowa this afternoon. The strongest storms may
produce up to nickel sized hail, wind gusts to 50 mph and heavy
rains.

Those participating in outdoor activities, including boaters,
should be prepared to seek safe shelter if storms approach.

Small

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
345 PM CDT SUN AUG 5 2018

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

0330 PM     LIGHTNING        FORT DODGE              42.51N 94.18W
08/05/2018                   WEBSTER            IA   NEWSPAPER

            LIGHTNING STRUCK A HOUSE RESULTING IN A
            SMALL FIRE BEHIND THE FUSE BOX. FROM FORT
            DODGE MESSENGER.

&&

BSS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
402 PM CDT SUN AUG 5 2018

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

0427 AM     TSTM WND DMG     5 N MANSON              42.60N 94.54W
08/05/2018                   POCAHONTAS         IA   TRAINED SPOTTER

            LARGE TREE LIMBS DOWN. SHINGLES OFF ROOFS.
            TIME ESTIMATED BY RADAR.

&&

BSS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
410 PM CDT SUN AUG 5 2018

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

0450 AM     TSTM WND GST     FORT DODGE              42.51N 94.18W
08/05/2018  E60 MPH          WEBSTER            IA   TRAINED SPOTTER

            ESTIMATED 60+ MPH WINDS NEAR JOHN F KENNEDY
            PARK. TIME ESTIMATED.

&&

BSS

Special Weather Statement
National Weather Service Des Moines IA
531 PM CDT SUN AUG 5 2018

IAZ049-050-061-062-052330-
Tama IA-Poweshiek IA-Jasper IA-Marshall IA-
531 PM CDT SUN AUG 5 2018

...Isolated Strong Storms Developing...

At 529 PM CDT, Doppler radar was tracking a pair of strong
thunderstorm near Rock Creek Lake, or near Newton, and another near
Tama moving east at 40 mph.

Dime size hail and winds in excess of 40 mph will be possible with
these storms.

Locations impacted include...
Newton, Grinnell, Tama, Brooklyn, Rock Creek Lake, Victor, Kellogg,
Gilman, Holiday Lake, Malcom, Chelsea, Laurel, Oakland Acres,
Hartwick, Vining, Grinnell Regional Airport and Rock Creek State
Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4170 9305 4181 9306 4196 9276 4200 9230
      4170 9230
TIME...MOT...LOC 2229Z 264DEG 33KT 4174 9294

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