Scattered storms this evening

Update 4pm:

Storm fired rapidly over Woodbury in past few minutes. Additional rapid development possible/likely in the next hour. Heavy rainfall with these storms could cause rapid local street flooding.

-Twin Cities radar loop.

SPECIAL WEATHER STATEMENT

NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN

403 PM CDT SAT JUL 23 2011

MNZ060>063-069-070-WIZ023-024-232200-

ANOKA-DAKOTA-HENNEPIN-PIERCE-RAMSEY-SCOTT-ST. CROIX-WASHINGTON-

403 PM CDT SAT JUL 23 2011

AT 357 PM CDT…RADAR INDICATED THAT THUNDERSTORMS WERE RAPIDLY

DEVELOPING NEAR ST PAUL AND ACROSS THE EAST METRO. THESE STORMS WERE MOVING EAST AT 25 MPH. MORE DEVELOPMENT IS LIKELY.

HAIL UP TO DIME SIZE AND WINDS UP TO 50 MPH ARE EXPECTED WITH THESE

STORMS.

PEOPLE IN THE TWIN CITIES METRO AREA SHOULD MONITOR THE WEATHER

SITUATION CLOSELY. LISTEN FOR POSSIBLE WARNINGS AND BE PREPARED TO

TAKE APPROPRIATE ACTION SHOULD SEVERE WEATHER THREATEN.

PRECAUTIONARY/PREPAREDNESS ACTIONS…

STAY TUNED TO NOAA WEATHER RADIO…COMMERCIAL RADIO…OR YOUR LOCAL

TELEVISION STATIONS FOR LATER STATEMENTS AND POSSIBLE WARNINGS

CONCERNING THIS WEATHER SITUATION.

Update 3:40pm:

Storms so far are favoring areas north of metro. We’re not out of the woods yet in the Twin Cities.

Stay tuned and stay aware for now…there is still the potential that storms could deveop near the metro through this evening!PH

Update 3pm:

Scattered storms are building as expected this afternoon. Some of the storms will be strong to severe as they move east southeast through this evening.

The storms fomed near St. Cloud where they have already prdoced hail reports.

MPX: Cold Spring [Stearns Co, MN] trained spotter reports HAIL of half dollar size (M1.25 INCH) at 02:51 PM CDT –

MPX: 1 E Cold Spring [Stearns Co, MN] trained spotter reports HAIL of nickel size (M0.88 INCH) at 02:43 PM CDT –

MPX: 1 S Richmond [Stearns Co, MN] emergency mngr reports HAIL of quarter size (M1.00 INCH) at 02:45 PM CDT –

MPX: St Cloud [Stearns Co, MN] trained spotter reports HAIL of penny size (M0.75 INCH) at 02:37 PM CDT –

Storm chances will run into the evening hours in the metro and western Wisconsin.

-Latest Twin Cities radar loop here

-Latest NWS weather warnings here

-Latest storm reports here

PH

****

Round #1 of our Saturday storms arrived right on schedule this morning.

Round #2 should develop this afternoon, and the “main event” could feature more severe weather than the morning storms.

Heads up: Keep an eye out for rapidly developing thunderstorms this afternoon & evening that could quickly turn severe. The most likely overall window for severe storms appears to be between 3pm and 8pm this afternoon & evening.

The system:

A cold front is cutting into the humid and unstable air mass over Minnesota today.

1 1 1 1 1 wx styy.png

Timing: It appears the most likely window for a second round of storms to develop may be between 3pm and 9pm tonight in the metro area and western Wisconsin.

Storm character: Storms may develop rapidly and quickly turn severe (and potentially tornadic) this afternoon. The storms may then evolve into a bow echo with damaging straight line winds as they move east this evening.

Expect watches and possible warnings later today. Storms will be capable of extremely heavy rain, frequent lighting, damaging winds in excess of 60-70 mph and large hail.

1 1 1 1 1 spc.PNG

SPC risk area today.

Tornado threat:

There is a risk for tornadoes with a few of the storms today. There is enough “shear” or spin in the lowest mile of the atmosphere to produce mesocyclones that can spin up tornadoes.

One local meteorologist, Andrew Revering, runs models that specifically calculate tornado probabilities for specific areas. Andy sent me these images highlighting the tornado threat over Minnesota today. You can see more of his work here at tornadotarget.com.

As you can see from the images below, the greatest threat for tornadic storms will likely be from St.Cloud southeast into the Twin Cities & western Wisconsin today.

(Click images to enlarge)

1 1 1 1 1 ehi.png

So called Energy Helicity Index (EHI) highlights most likely areas of (tornadic) wind shear at 7pm today.

1 1 1 1 1 sig tor sat.png

Significant Tornado Parameter from the Storm Prediction Center’s research

1 1 1 1 1 3km hel.png

3km Helicity, corkscrew effect in the atmosphere, can contribute to supercells and ultimately tornadoes.

If/when storms get going this afternoon we will have live team coverage on MPR News.

Keep an eye to the sky this afternoon & evening!

PH

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