Updraft: August 14, 2012 Archive

Near 90 & severe risk Wednesday? More on rare Duluth waterspout - "land-spout" tornado

Posted at 5:25 PM on August 14, 2012 by Paul Huttner (1 Comments)
Filed under: Tornadoes

Updated for Wednesday severe risk:

The latest indications are a developing warm front will spark a few (mainly non-severe) scattered showers & T-Storms overnight into early Wednesday morning.

-Latest Twin Cities radar loop

As the front clears, most of southern Minnesota should bust out into a sunnier, warmer air mass by midday Wednesday. If we get enough sun with our warmer southerly flow, temps may push 90 in some towns in southern Minnesota, and possibly in the metro by around 4-5 pm.

Source: Iowa State University

The strongest cool front of the summer will cut into the warmer more unstable air mass Wednesday evening. Look for a line of T-Storms to develop in northern Minnesota and work south Wednesday night.

SPC thinks (and I agree) that the best chance for severe storms will be Wednesday evening and night. A "bow echo" capable of large hail and damaging winds may from and race southeast Wednesday night.

Source: NOAA/SPC

Here's the severe weather "geek speak" from NOAA's Storm Prediction Center in Norman Oklahoma.

...UPPER MIDWEST...

TSTM DEVELOPMENT IS EXPECTED DURING THE AFTN AHEAD OF THE COLD FRONT AS HEIGHT FALLS OVERSPREAD THE AREA. THE COMBINATION OF A MODEST RETURN OF LOW-LEVEL MOISTURE AND STEEPENING LAPSE RATES SHOULD RESULT IN A MODERATELY UNSTABLE AIR MASS. TSTMS MAY INITIALLY DEVELOP OVER NRN MN...DEVELOPING SWD WITH TIME AND POSSIBLY CONTINUE INTO THE OVERNIGHT HOURS AS AN MCS.

LARGE HAIL AND DAMAGING WIND GUSTS WILL BE POSSIBLE GIVEN MODERATE INSTABILITY AND STRENGTHENING FLOW ALOFT RESULTING IN 40-45 KTS OF DEEP-LAYER SHEAR. TSTMS MAY DEVELOP INTO A MORE LINEAR STRUCTURE DURING THE EVENING WITH BOWING SEGMENTS POSSIBLE AS WINDS ALOFT BECOME MORE PERPENDICULAR TO THE CONVECTIVE LINE...ESPECIALLY OVER SRN PORTIONS OF THE SLIGHT RISK AREA.

Stay tuned!

-0.3 degrees temps vs. average so far at MSP Airport in August

1st cooler than average month since May 2011 (14 months ago)

Mixed sun & 80s ahead for most of Minnesota today

Showers increase from west to east today & tonight

Slight risk for a few severe T-Storms Wednesday in MInnesota

Rare "Land-Spout" type tornado occurred in Duluth last Thursday

Only the 2nd tornado in history recorded inside Duluth city limits

Twin Cities quick look forecast:

Source: Twin Cities NWS

Changes Brewing:

A fantastic Tuesday morning in MInnesota will give way to some significant weather changes over the next 48 hours.

Approaching low pressure is triggering some scattered showers in the eastern Dakoats today. The showers will gradualy spread east into western Minnesota today, and a few T-Storms may pop tonight as a developing warm front moves in.

Source: Twin Cities NWS

Severe risk Wednesday:

As the low pulls into Minnesota Wednesday, warmer more unstable air will slide north.

SPC has slapped a slight risk for severe weather across most of Minnesota Wednesday. Severe weather parameters favor a developing suqall line late Wednesday in western Minnesota that will rumble east by Wednesday evening into the metro.

Source: NOAA/SPC

Some key points form the SPC "Convective Outlook"

SCATTERED TSTMS SHOULD DEVELOP/INCREASE BY MID/LATE AFTERNOON WEDNESDAY AND ESPECIALLY INTO WEDNESDAY NIGHT NEAR THE ADVANCING COLD FRONT. THIS SEEMS MOST LIKELY TO OCCUR ACROSS MUCH OF MN AND ADJACENT PORTIONS OF EASTERN SD/NORTHEAST NEB/NORTHWEST IA.

AIDED BY STRENGTHENING MID/HIGH LEVEL WESTERLIES...MODERATELY STRONG VERTICAL SHEAR WILL ALLOW FOR ORGANIZED/SUSTAINED STORM STRUCTURES CAPABLE OF DAMAGING WINDS AND SEVERE HAIL. STORMS MAY CONGEAL/SPREAD EAST-SOUTHEASTWARD THROUGH THE NIGHT...PERHAPS AS AN MCS...TOWARD THE UPPER MS RIVER VALLEY/LAKE SUPERIOR VICINITY.

The primary threats appear to be damaging straight line winds and hail. Any potential tornado threat appears low.

Rare "Land-Spout" style tornado in Duluth last week:

The Duluth NWS has more analysis on the rare waterspout-tornado that swirled across Lake Superior and Park Point last Thursday.

Source: Duluth NWS

It turns out the twister was likely a non-supercell "land-spout" type tornado. Land-spouts differ from classic supercell tornadoes beacuse they develop from the ground up, instead of descending from the cloud base.

Waterspout appears to have developed near an inflection point along leading edge of strong surge of northeast winds (marine cold front)

From pictures, appears to be a bottom-up generation
process resulting from pre-existing vertical vorticity
along the boundary, which was concentrated and
stretched when updraft developed above it (classic
land-spout type process, but over water)

Non-supercell generation/maintenance processes
were likely enhanced by very warm Lake Superior
water temps near 70F (eyewitnesses stated it
appeared to weaken while crossing MN point)

Source: Duluth NWS

This event appears similar to the heat spawned "dust devil" type funnels that skip across the Arizona desert in spring and summer. These EF0 vorticies can cause minor damage, and have been known to rip off more than a few "car ports" in Tucson and Phoenix.

It turns out this is just the 2nd tornado ever to cross into the city limts of Duluth, and the first tornado in Duluth in 54 years!

Again more from the Duluth NWS.

This was not the first tornado to touch down within the Duluth City limits.

On May 26, 1958 at 3:35 pm a tornado touched down in the Duluth Heights neighborhood then traveled northeast for 6.9 miles before lifting just south of Arnold Road.

There were no injuries reported.

Below is a map of the 1958 tornado path. Click on it for a larger image.

Source: Duluth NWS

PH

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