How Iowa forecasters tracked Thursday’s devastating tornadoes

The skies turned menacing across central Iowa last night.

NWS tornado survey teams are still in the field as of this post, but at least 5 tornadoes and probably several more skipped across counties east of Des Moines.

Tornado damage is significant. But thanks to several timely tornado warnings, there were no deaths and only minor injuries. Warning lead time by the Des Moines NWS for the most devastating twisters seems to have ranged between 17 and 30 minutes. That’s an amazing performance anytime, especially when dealing with multiple tornadic supercells at once.

That said some of the earliest tornadoes to form offered less lead time. That’s typical in the early stages of a tornado outbreak, as tornadoes are often the first severe weather phenomenon to form as powerful storm updrafts accelerate skyward.

Tick-tock

Local NWS offices transmit severe weather information on multiple platforms. Here’s a tick-tock of events yesterday that suggest the Des Moines NWS reacted at a high level, and probably saved many lives with timely warnings.

9:58 am

At 9:58 am the Des Moines NWS send out this tweet highlighting the threat for severe weather Thursday afternoon. The graphic says “a tornado is possible!”

2:50 PM

The Des Moines NWS office issues a tornado warning that includes

BULLETIN – EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE DES MOINES IA
250 PM CDT THU JUL 19 2018

THE NATIONAL WEATHER SERVICE IN DES MOINES HAS ISSUED A

* TORNADO WARNING FOR…
NORTHEASTERN POLK COUNTY IN CENTRAL IOWA…
SOUTHWESTERN MARSHALL COUNTY IN CENTRAL IOWA…
NORTHWESTERN JASPER COUNTY IN CENTRAL IOWA…

* UNTIL 315 PM CDT.

* AT 250 PM CDT, A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO
WAS LOCATED NEAR BONDURANT, OR 7 MILES NORTH OF ALTOONA, MOVING
EAST AT 30 MPH.

HAZARD…TORNADO.

SOURCE…WEATHER SPOTTERS REPORTED FUNNEL CLOUD.

2:58 pm

There are several reports of a tornado on the ground near Bondurant.

1958 4 NNE BONDURANT POLK IA 4174 9344 SEVERAL REPORTS OF THIS TORNADO. (DMX)

3:10 pm

Des Moines NWS transmits the tornado watch issued by NOAA’s Storm Prediction Center.

3:19 pm

NWS Des Moines has issued multiple tornado warnings. Tornadoes have been sighted and are on the ground.

3:22 pm

NWS Des Moines issues a tornado warning that includes Marshalltown, Iowa. The warning projects the tornado will be near Marshalltown around 3:45 pm.

BULLETIN – EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE DES MOINES IA
322 PM CDT THU JUL 19 2018

THE NATIONAL WEATHER SERVICE IN DES MOINES HAS ISSUED A

* TORNADO WARNING FOR…
SOUTHEASTERN STORY COUNTY IN CENTRAL IOWA…
SOUTHERN MARSHALL COUNTY IN CENTRAL IOWA…

* UNTIL 400 PM CDT.

* AT 322 PM CDT, A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO
WAS LOCATED 7 MILES NORTHWEST OF BAXTER, OR 13 MILES SOUTHEAST OF
NEVADA, MOVING EAST AT 55 MPH.

HAZARD…TORNADO.

SOURCE…RADAR INDICATED ROTATION.

IMPACT…FLYING DEBRIS WILL BE DANGEROUS TO THOSE CAUGHT WITHOUT
SHELTER. MOBILE HOMES WILL BE DAMAGED OR DESTROYED.
DAMAGE TO ROOFS, WINDOWS, AND VEHICLES WILL OCCUR. TREE
DAMAGE IS LIKELY.

* THIS DANGEROUS STORM WILL BE NEAR…
STATE CENTER AROUND 330 PM CDT.
MARSHALLTOWN AROUND 345 PM CDT.

3:50 pm

NWS storm reports indicate widespread damage in and near Marshalltown.

2150 MARSHALLTOWN MARSHALL IA 4204 9291 MARSHALLTOWN COURTHOUSE LOST CLOCK TOWER. TREES DOWN ALL OVER TOWN.

2155 2 NW MARSHALLTOWN MARSHALL IA 4205 9294 REPORTS OF CATASTROPHIC DAMAGE … INCLUDING VEHICLES MISSING … VEHICLES OVERTURNED … TOPS OF BUILDINGS GONE … TREES DOWN … POWER LINES … GAS LINES … ETC

Ample lead time

Overall it looks like most of the tornado warnings were issued with 17 to 30 minutes of lead time. That’s a pretty remarkable and effective advance warning for tornadoes. Local residents had plenty of time to seek safe shelter.

Overall it appear to be a good night for forecasters at the Des Moines NWS office.