Updraft: October 10, 2012 Archive

Saturday Soaker: 1st widespread rain & thunder in months; Severe risk SE MN

Posted at 5:18 PM on October 10, 2012 by Paul Huttner

1"+ rainfall model output from NAM & GFS models for metro rain Saturday

2"+ rainfall possible in SE MN & Wisconsin?

July 24th last time MSP Airport recorded 1" of rain (1.69")

Thunder threat with Saturday's system

Severe risk for southeast Minnesota Saturday including Rochester & Red Wing

Widesprerad & meaningful rains increasingly likely with Saturday's system

Season's coldest temp and hard metro freeze Friday AM

Source: Twin Cities NWS

Source: Twin Cities NWS

Headline: Real rain headed for Minnesota?

Normally an inch of rain in October wouldn't be a big deal. But this is 2012, year of the expanding drought.

The most promising looking weather system in months is aiming for Minnesota Saturday.

A potent, wrapped up low pressure system will spin northeast from the Rockies Friday and make a beeline for southern Minnesota Saturday.

The system looks favorable to tap deeper moisture from the Gulf of Mexico...something that hasn't happened over Minnesota in months.

If the models are right (and they look pretty good to my eye at this point) the system should bring rain & thunder to southern & central Minnesota late Friday night through Saturday. Rainfall totals should approach of exceed 1" in the metro.

Source: NOAA via Iowa State University

Rainfall totals in convective areas and may push 2"+ in (lucky) parts of southeast Minnesota and Wisconsin.

Source: NOAA/HPC

Saturday Severe Risk?

As the low winds up and moves into southern Minnesota, strong upper air dynamics should produce plenty of lift to generate embedded T-Storm clusters within the overall rain shield.

Source: NOAA NAM model via College of DuPage Weather Lab

South of the low, the cold front will likely generate some "discrete" supercell storms in southeast Minnesota, Wisconsin and Iowa. That could trigger some severe weather Saturday.

Source: NOAA/SPC

NOAA's Storm Prediction Center highlights the early look at Upper Midwest severe potential Saturday.

INSTABILITY...DEEP LAYER FLOW FIELDS/SHEAR AND FORCING FOR UPWARD VERTICAL MOTION WILL BECOME MOST SUPPORTIVE OF SEVERE WEATHER POTENTIAL IN THE WARM SECTOR OF A SUB-1000 MB SURFACE CYCLONE ON SATURDAY...AS IT MIGRATES ACROSS THE MID MISSOURI VALLEY...TOWARD THE GREAT LAKES REGION. EVEN WITH ONLY WEAK DESTABILIZATION...THE ENVIRONMENT NEAR A 70-90 KT SOUTHWESTERLY 500 MB JET STREAK AND 50-70 KT SOUTHERLY 850 MB JET COULD BECOME SUFFICIENT FOR A SUBSTANTIVE REGIONAL SEVERE CONVECTIVE EVENT WITH DAMAGING WIND AND PERHAPS TORNADOES.

Stay tuned as we follow upcoming model runs and tweak Saturday's forecast details. You might want to get those nice "dry" leaves up by Friday evening before they get soaked (and much heavier) this weekend.

PH