July 27, 2016 Northern Iowa Landspout Tornadoes

Tornado Details:

Tornado - 6.0 mi WNW of Algona KOSSUTH COUNTY Date July 27, 2016 Time (CDT) 5:15pm-5:16pm EF Rating EF-0 Est. Peak Winds 60 mph Path Length 0.36 miles Max Width 15 yards Injuries/Deaths 0/0 Summary: This was a small, brief landspout tornado reported by law enforcement. No damage was reported. Location estimated based on radar. Track Map

Storm-relative velocity radar image at the time of the tornado, showing broad rotation at a beam height of 9200 ft AGL west of Algona.

Tornado - 4.8 mi W of Scarville WINNEBAGO COUNTY Date July 27, 2016 Time (CDT) 6:11pm-6:12pm EF Rating EF-0 Est. Peak Winds 60 mph Path Length 0.35 miles Max Width 20 yards Injuries/Deaths 0/0 Summary: This was a short-lived tornado that was photographed from multiple angles. No damage was reported. Track Map

Photo of the tornado in the distance (Kristi Yost via KAAL-Used with Permission) Funnel/tornado just over the hill (Krystle Roth via KAAL-Used with Permission) Reflectivity and storm-relative velocity radar image at the time of the tornado showed little evidence of a tornado.

Tornado - 3.1 miles WNW of Bode HUMBOLDT COUNTY Date July 27, 2016 Time (CDT) 6:39pm-6:41pm EF Rating EF-0 Est. Peak Winds 60 mph Path Length 0.68 miles Max Width 30 yards Injuries/Deaths 0/0 Summary: This well-defined tornado was photographed from multiple angles. Crop damage was reported along the track. Track estimated based on photos and radar. Track Map

Photo of the tornado shortly after touchdown. Note the dust swirl on the ground. (Wendy Greene-Dugan via the Attig and Hobbs Weather Page-Used with Permission) Tornado in the distance. (Mary Reis via the Attig and Hobbs Weather Page-Used with Permission) Tornado as it was roping out. (Wanette Clabaugh Bird via the Attig and Hobbs Weather Page-Used with Permission) Reflectivity and storm-relative velocity radar image at the time of the tornado, showing the new updraft going up on the west flank of the storm and lack of a circulation.

The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:

EF0 Weak 65-85 mph	EF1 Moderate 86-110 mph	EF2 Significant 111-135 mph	EF3 Severe 136-165 mph	EF4 Extreme 166-200 mph	EF5 Catastrophic 200+ mph

Storm Reports

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE DES MOINES IA
832 PM CDT WED JUL 27 2016

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

0516 PM     TORNADO          5 WNW ALGONA            43.10N 94.33W 
07/27/2016                   KOSSUTH            IA   EMERGENCY MNGR  

            SMALL AND BRIEF LANDSPOUT TORNADO TOUCHED DOWN AND HAS 
            SINCE LIFTED. NO REPORTS OF DAMAGE.

0521 PM     FUNNEL CLOUD     5 W ALGONA              43.08N 94.32W 
07/27/2016                   KOSSUTH            IA   EMERGENCY MNGR  

            STRONG ROTATION AND FUNNEL CLOUD GOING UP AND DOWN. 
            FUNNEL DESCENDING TOWARDS GROUND DURING THE REPORT CALL.

0600 PM     FUNNEL CLOUD     4 WNW SCARVILLE         43.49N 93.70W 
07/27/2016                   WINNEBAGO          IA   TRAINED SPOTTER 

            RELAYED BY THE NWS IN MINNEAPOLIS. SPOTTER IN THE TOWN OF
            KIESTER MN REPORTS SEEING A FUNNEL CLOUD SOUTH OF TOWN IN
            FAR NORTHERN WINNEBAGO COUNTY.

0612 PM     TORNADO          4 W SCARVILLE           43.47N 93.70W 
07/27/2016                   WINNEBAGO          IA   PUBLIC          

            MULTIPLE PHOTOS ON SOCIAL MEDIA SHOW FUNNEL EXTENDING 
            CLOSE TO IF NOT TOUCHING THE GROUND. ESTIMATED LOCATION 
            BASED ON PHOTOS AND RADAR.

0640 PM     FUNNEL CLOUD     2 WSW BODE              42.86N 94.32W 
07/27/2016                   HUMBOLDT           IA   TRAINED SPOTTER 

            FUNNEL AT LEAST HALF WAY TO THE GROUND. SPOTTER POSSIBLY 
            SEES DEBRIS UNDER THE FUNNEL.

0641 PM     TORNADO          2 WSW BODE              42.86N 94.33W 
07/27/2016                   HUMBOLDT           IA   LAW ENFORCEMENT 

            BRIEF TOUCHDOWN. HAS SINCE LIFTED.

What is a Landspout?

Landspouts differ in multiple ways from their supercell or squall line counterparts. Landspout tornadoes form during the development stage of thunderstorms, underneath the thunderstorm's growing updraft (oftentimes just a cumulus cloud). There may not even be any rain falling! Supercellular and squall line tornadoes form during the mature stage of the storm. Landspout tornadoes also form via a "bottom-up" process. They favor storms located along frontal boundaries (see Fig. 1), where the converging air masses produce a vertical circulation (vertical vorticity) in the atmosphere. If a thunderstorm updraft interacts with this swirling air, it can act to rapidly stretch and tighten this circulation and produce a tornado (Figs. 2-3).

These two key differences make landspouts extremely difficult to spot on radar. Thankfully, landspouts are generally weak and transient, causing little to no damage, as was the case with this event. Nonetheless, one should always exercise caution around a tornado regardless of its origin.

Nonetheless, the environments that preclude a landspout can be predicted and were recognized by the Des Moines NWS prior to the event. At 5:02pm (15 minutes before the first report), the NWS issued a special weather statement highlighting the threat for funnel clouds and possibly a brief, weak tornado. One tornado warning was issued at 5:23pm for Kossuth County when multiple reports indicated that a funnel cloud was lowering and may touch down. Tornado warnings were not issued for the Winnebago and Humboldt county landspouts. This is because the tornadoes had dissipated by the time reports of their existence reached the NWS and the chance of an additional tornado that would pose a threat to life and property was very remote.

Figure 1: Surface observations at 6pm show the weak front sagging through Iowa (change in wind direction).	Figure 2: Surface vorticity and 0-3 km MLCAPE were maximized near the tornadoes. This infers that an ample circulation (vorticity) was available and enough instability was present to stretch and tighten this spin.	Figure 3: The non-supercell tornado parameter, which takes into account multiple environmental parameters, highlighted a broad region that could favor landspouts over northern Iowa.