Scattered showers today; Severe repeat unlikely; Anatomy of an outbreak

You may need your umbrella today, but hopefully your weather radio won’t be blaring away like last night.

A cool front has slipped through the metro overnight. The front will stall today from near the Twin Cities south into Iowa and be the focal point for scattered showers and a few thunderstorms. Unlike Tuesday evening, it looks like most of the storms should remain below severe limits in Minnesota today.

Look for scattered showers and a few thunderstorms to ride north along the front today. The storms may contain small hail at times, along with lightning and downpours. Thankfully, severe weather parameters are much lower today across Minnesota.

-Latest Twin Cities radar loop

SPC paints the severe weather risk area mostly south of Minnesota today, as a wave of low pressure spins in the central Midwest.

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Temperatures should also be cooler than Tuesday under more clouds and scattered showers. Look for highs generally in the 70s.

NWS storm survey teams in St. Michael today:

The Twin Cities NWS has teams in the field today near St. Michael to asses Tuesday evening’s (likely) tornado damage. Here’s the wording from NWS.

…NWS Storm Damage Survey to be Conducted Today…

An NWS storm survey team will review the damage today likely associated with a tornado near the St. Michael area in far eastern Wright County on Tuesday evening. It is yet to be determined if other areas associated with this storm into southeastern Sherburne and far western Anoka Counties need to also be surveyed. In addition, other supercell thunderstorms which had strong rotation and had reports of wall and funnel clouds may also need to be assessed upon further review and coordination with emergency officials on Wednesday.

Ingredients came together:

All the severe weather ingredients came together last night for a few critical hours in and close to the Twin Cities. A powerful warm front surged north with plenty of heat and temperatures in the 90s south of the front. Dew points surged into the low 70s in the Twin Cites just as storms developed Tuesday evening, adding fuel to the storms.

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Twin Cities NWS explains the set up Tuesday evening.

“A severe weather event with primarily large hail unfolded across central and eastern Minnesota on Tuesday evening. Warmth and moisture to the highest levels observed so far in the Twin Cities during 2011, surged northward ahead of an approaching surface low pressure (Figure 1). Afternoon temperatures reached the upper 70s to lower to mid 90s across much of the area.

Dew points accelerated into the mid 60s and lower 70s by late afternoon. Such high warmth and moisture created strong to extreme instability in the atmosphere. The values of the lowest 100mb mixed-layer CAPE, as shown in Figure 2, were a high 4,500 J/kg and were actually even larger in the hours prior. The lack of convective inhibition at this time allowed storms to further blossom from 6 to 8 pm, which is the period that the storms entered the Twin Cities metro area.

The deep instability, including well above the freezing level in the atmosphere, led to much of the hail being golf ball size or larger. This was even the case at the NWS Forecast Office in Chanhassen (see below), where hail just over two inches in diameter occurred at the edge of a storm core. Atmospheric wind shear was supportive for supercells. Turning wind direction in the low-levels (Figure 3) further offered tornado potential in some storms. This was realized within a corridor immediately ahead of the focusing feature: a cold front/dry-line. Indeed there were multiple storms that developed with rotating wall clouds and/or funnels along this boundary, with at least one of these likely having produced a tornado near St. Michael.”

“Hailers”

The atmosphere was ripe for producing big hail Tuesday night. Updrafts around 100 mph were likely with the storms, and temperatures as cold as -30C supported large hail growth high in the storms last night.

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Twin Cities NWS upper air sounding last night shows large hail potential.

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NWS hail tracker show where large hail fell last night.

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Hail from Twin Cities NWS office that fell in Chanhassen.

A slew of warnings:

The warnings came fast and furious Tuesday evening.

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Twin Cities NWS warnings issued Tuesday evening.

Welcome to severe weather 2011. We got off pretty lucky Tuesday night. We came very close to an “urban tornado” last night in Hennepin County.

If the storms in the metro had a little more rotation, we could have had a tornado that tracked from Eden Prairie through Edina, right over Lake Calhoun through downtown Minneapolis toward a packed Target Field.

Though we got plenty of large hail and funnel clouds, we were fortunate to dodge the tornado bullet in the metro.

PH

  • gordonjh

    I don’t understand why, as the television news people had several “watch” areas suddenly everything changed to a “WARNING” even though there was no tornado ON THE GROUND. It has been pounded into people the difference between “favorable conditions to create tornados” -a WATCH and that a WARNING means that there was an active tornado on the ground throughout the Minneapolis area.

    Doesn’t sounding sirens and declaring a WARNING even with no tornado on the ground go against years of training about the difference between a WATCH and a WARNING?