[tornadotony]

This reminds me of a lot of bustola systems from last summer, so I will proceed with greatest caution from this point on in this thread.

The models are depicting the potential for a significant severe weather event tomorrow afternoon and tomorrow night. A strong shortwave disturbance will ride around the ridge that is parked over the central US into the MN/WI region tomorrow afternoon, providing 50-60kt of deep-layer shear. At the surface, a boundary will be in place, with an extremely unstable atmosphere (MLCAPE likely pushing 4000J/kg). In addition to the extreme instability, low-level shear will be quite high, with 0-1km SRH of 200-300m**2s**-2 suggested.

The well-known issue with these setups is that they are often accompanied by a very strong EML and accompanying thermonuclear cap and SBCINH. The NAM removes the CINH and shows strong convective initiation in the afternoon. The GFS does not. This setup will be accompanied by very strong forcing, which will assist in any convective initiation, but will also help cells to line out after a couple hours. However, any supercells that do form and sustain will be very dangerous, with the potential for extremely large hail, damaging winds, and perhaps a strong tornado.

Finally, I'll throw in MPX's AFD, which is quite strongly worded and would suggest the probability of a moderate risk tomorrow.

Quote

000
FXUS63 KMPX 121937
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
237 PM CDT SUN AUG 12 2007

.DISCUSSION...
POTENTIALLY SIGNIFICANT SEVERE WEATHER EVENT LOOKS TO UNFOLD
TOMORROW EVENING/NIGHT...WHICH HAS THE BULK OF OUR ATTENTION FOR
THIS FORECAST PACKAGE.

AT PRESENT...SURFACE HIGH STRETCHED ACROSS THE UPPER
MIDWEST...CENTERED OVER EASTERN NORTH DAKOTA...NORTHERN
MINNESOTA...AND SOUTHERN MANITOBA. LARGE CIRRUS SHIELD FROM
EARLY MORNING CONVECTION IN NORTH DAKOTA IS ENGULFING MOST OF THE
AREA. THIS SHOULD KEEP TEMPERATURES FROM FALLING TOO MUCH
TONIGHT...DESPITE THE RELATIVELY DRY AIRMASS PRESENT BENEATH THE
SURFACE HIGH.

WARM ADVECTION WILL ENSUE ON THE BACKSIDE OF THE HIGH AS IT SLIDES
SOUTHEASTWARD OVERNIGHT. THIS WILL ALLOW FOR SOME SCATTERED STORM
DEVELOPMENT ACROSS WESTERN MINNESOTA LATE TONIGHT. VERY LITTLE
CHANGE WAS MADE TO THE POP/WX GRIDS DURING THE TONIGHT TIME FRAME.

MAJOR CHANGES MADE TO THE POP/WX/QPF FORECAST DURING THE
AFTERNOON/EVENING TIME FRAME FOR MONDAY. OUR EXPECTATION IS THAT
AN MCS WILL DEVELOP LATER TONIGHT/TOMORROW MORNING ACROSS EASTERN
NORTH DAKOTA...ON THE NORTH SIDE OF THE 700 MB CAP/WARM FRONT...IN
RESPONSE TO INCREASING WARM ADVECTION NORTH OF THE SURFACE
LOW...AND FORCING IN THE NOSE OF A WEAK LOW LEVEL JET NEAR THE
WESTERN MINNESOTA BORDER. ORIENTATION OF THE THICKNESS LINES
SHOULD FAVOR AN EAST-SOUTHEASTWARD PROPAGATION...WHICH COULD
RESULT IN ITS SOUTHERN EDGE BRUSHING THE NORTHERN PORTION OF THE
FORECAST AREA.

OUR GREATEST TIME FRAME OF CONCERN...HOWEVER...BEGINS MID
AFTERNOON TOMORROW. DEEPENING SURFACE LOW SHOULD MOVE INTO WEST
CENTRAL MINNESOTA /NEAR AXN/ BY MID/LATE AFTERNOON...WITH THE
ATTENDANT WARM FRONT STRETCHING ROUGHLY ALONG THE INTERSTATE 94
CORRIDOR. THIS PLACEMENT MAY NOT BE FAR ENOUGH SOUTH...ESPECIALLY
IF THE EARLY MORNING CONVECTION IS STRONG ENOUGH TO PUSH IT
FARTHER SOUTH. POTENT VORT MAX WILL RIDE ALONG THE BOUNDARY ACROSS
THE NORTHERN PART OF THE FORECAST AREA...AND ALONG WITH A 40 KT
LOW LEVEL JET AND A COUPLED UPPER JET STRUCTURE...SHOULD PROVIDE
PLENTY OF FORCING FOR STORMS LATE IN THE DAY. WE ARE BEING QUITE
BRAVE...KEEPING MUCH OF OUR SOUTHWESTERN FORECAST AREA DRY...BUT
WITH 700 MB TEMPERATURES AT 14C OR GREATER...WE SEE LITTLE CHANCE
OF THE WARM SECTOR CONVECTING. DEEP LAYER SHEAR VALUES IN THE 50
TO 60 KT RANGE ACROSS ROUGHLY THE NORTHERN THIRD OF THE FORECAST
AREA IS CERTAINLY SUPPORTIVE OF SUPERCELLS...ESPECIALLY IN THE
PRESENCE OF SBCAPE VALUES IN EXCESS OF 3-4 KJ/KG JUST SOUTH OF THE
FRONT IN CENTRAL/SOUTHERN MINNESOTA. ALTHOUGH WE ARE CERTAIN THAT
THE CONVECTION WILL TRANSITION INTO A WIND/HAIL THREAT DURING THE
AFTERNOON AND OVERNIGHT...DUE TO THE STRENGTH OF THE
FORCING...EARLY IN THE EVENT...WE CERTAINLY SEE THE POTENTIAL FOR
TORNADOES IN THE LXL/CBG/OEO VICINITY IF DISCRETE DEVELOPMENT CAN
OCCUR...AND CLOUD COVER FROM THE NORTHERN MCS DOES NOT CONTAMINATE
THINGS TOO MUCH.

CONVECTIVE SYSTEM SHOULD MOVE SOUTHEASTWARD...MAINLY AFFECTING
EAST CENTRAL/SOUTH CENTRAL MINNESOTA...AND WEST CENTRAL WISCONSIN
DURING THE OVERNIGHT HOURS.

SURFACE HIGH WILL SLIDE IN BEHIND THE FRONTAL PASSAGE...BUT FRONT
WILL LINGER CLOSE ENOUGH TO THE SOUTHERN PART OF THE FORECAST
AREA...THAT ADDITIONAL SHOWERS/THUNDERSTORMS ARE EXPECTED IN THE
MINNESOTA RIVER VALLEY AND ALONG THE INTERSTATE 90 CORRIDOR
TUESDAY NIGHT AND WEDNESDAY...AS A VORT MAX MOVES EASTWARD ACROSS
IOWA.

WEAK UPPER RIDGING BUILDS INTO THE AREA FOR THE MIDDLE TO LATTER
PART OF THE WEAK...BUT BEGINS TO BREAK DOWN TOWARD THE WEEKEND.
ANOTHER GOOD CHANCE OF STORMS IS ON DECK FOR THE WEEKEND...AS
ZONAL UPPER LEVEL FLOW TAKES OVER...AND ANOTHER FRONT AND A SERIES
OF SHORTWAVES MOVE ACROSS THE UPPER MIDWEST.

TEMPERATURE WISE...WE SHOULD SEE TEMPERATURES RETURNING TO A
SLIGHTLY BELOW TO NEAR NORMAL LEVEL AFTER TUESDAY.

THANKS TO DLH AND FGF FOR THE COLLABORATION ON TOMORROW/S STORM
SITUATION.

&&

.AVIATION.../18Z TAF ISSUANCE/
VFR CONDITIONS ENTIRE FORECAST PERIOD. HIGH PRESSURE MOVING
ACROSS REGION FIRST PART OF PERIOD...BUT STRONG WARM ADVECTION
DEVELOPS WESTERN MN MONDAY MORNING WITH SOME RISK OF THUNDER
KAXN/KRWF. HAVE KEPT VFR CEILINGS BUT SMALL CHANCE MVFR VSBY OF
5SM KRWF.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&

$$

KAT/JPR

[sprite]

Goodness, this threat crept up on me. Severe weather no longer exists to me, these last few days I've turned into a cat-5 hurricane junky. :guitar:

[tornadotony]

KyWetter, on Aug 12 2007, 06:54 PM, said:

Goodness, this threat crept up on me. Severe weather no longer exists to me, these last few days I've turned into a cat-5 hurricane junky. :guitar:

This was such a hardcore tornado season that I've had trouble focusing in on hurricane season and am actually more excited about the second season.

[weatherwiz]

If the cap can be broken tomorrow there is going to be some explosive development. Any supercells that form and stay discrete could really pack a punch. Could see some very large hailers tomorrow

[sprite]

tornadotony, on Aug 12 2007, 07:55 PM, said:

This was such a hardcore tornado season that I've had trouble focusing in on hurricane season and am actually more excited about the second season.

I've got a bad feeling about the upcoming November through May period. I suspect this might be one of those years with even January outbreaks. :bike:

[tornadotony]

MPX must think quite highly of this event. They're a rather conservative office, but they even have a headline and special page for tomorrow.

http://www.crh.noaa.gov/crnews/display_sto...26&source=0

"Severe Weather Expected Monday Afternoon and Evening

A potentially significant severe weather event is expected to unfold Monday afternoon and evening across portions of central Minnesota and west central Wisconsin, as low pressure deepens over western Minnesota and a warm front parks itself along the I-94 corridor. Thunderstorms are expected to develop during the mid to late afternoon, mainly from Alexandria to the Twin Cities to Menomonie, and points north. Early in the event, tornadoes will be possible, but the storms are expected to transition to more of a large hail and damaging wind threat toward mid to late evening. Heavy rain and localized flooding will also be a possibility.

Residents of Minnesota and western Wisconsin are urged to stay close to a source of weather information through the day on Monday, to receive the latest information on the severe weather threats."

[tornadotony]

KyWetter, on Aug 12 2007, 07:01 PM, said:

I've got a bad feeling about the upcoming November through May period. I suspect this might be one of those years with even January outbreaks. :bike:

I do too. These sky-high GOM temps could supply a ton of moisture to any system that can tap it...

[sprite]

tornadotony, on Aug 12 2007, 08:03 PM, said:

I do too. These sky-high GOM temps could supply a ton of moisture to any system that can tap it...

Yes, the Gulf is boiling...just like in 05/06. KY saw 60-65 dewpoints on Jan. 2, 2006...and also 65-70 degree dewpoints on March 11-12, 2006. Unprecedented in my memory!

[tornadotony]

KyWetter, on Aug 12 2007, 07:08 PM, said:

Yes, the Gulf is boiling...just like in 05/06. KY saw 60-65 dewpoints on Jan. 2, 2006...and also 65-70 degree dewpoints on March 11-12, 2006. Unprecedented in my memory!

Another November 2005 would push us to 102 fatalities for the year, which would be the 3rd highest total in the last 30 years. I hope we don't see that.

[wxmann_91]

A few things I don't like:

NAM is likely overdoing a (spurious?) H7 jet max, H85 jet max, and thus SRH's, due to convective feedback.
Upper level winds will likely blow anvils to the SE - not an ideal vector given storm inflow is also to the SE
700mb temps are increasing thru the day, although if the H7 jet max turns out to be weaker, the advection may not be as strong

Convection I do not think will be a major problem tomorrow morning, due to the lack of a pronounced vort max, but the best juxtaposition of weak synoptic forcing and the forcing of the LLJ will be in northern MN/eastern ND.

[tornadotony]

I thought this was a tad interesting...perhaps affected by convective feedback...but still...

[Indystorm]

Wondering if these developing MCS's will ever slide southeast around that ring of fire to affect you in Schererville and me here in Elkhart. Last Thursday morning t storm here had a lightning bolt that started a fire at a house a couple miles south of me. Gonna be watching for possible hurricane development in the next ten days but this is the season for MCS's for us as well.

[tornadotony]

Indystorm, on Aug 12 2007, 08:09 PM, said:

Wondering if these developing MCS's will ever slide southeast around that ring of fire to affect you in Schererville and me here in Elkhart. Last Thursday morning t storm here had a lightning bolt that started a fire at a house a couple miles south of me. Gonna be watching for possible hurricane development in the next ten days but this is the season for MCS's for us as well.

We got hit around 3:45 this morning. Not severe, but very strong. Of course, the NWR went off for Cook County when the storms were near O'Hare. At 2:45. See the 3am club thread. :axe:

[wxmann_91]

tornadotony, on Aug 12 2007, 05:57 PM, said:

I thought this was a tad interesting...perhaps affected by convective feedback...but still...

KLVN0812...sounding.PNG

Definitely convectively contaminated. But beautiful hodograph! Nearly 1000 m^2 s^-2 SRH!! In August!

[sprite]

:whistle:

wxmann_91, on Aug 12 2007, 09:14 PM, said:

Definitely convectively contaminated. But beautiful hodograph! Nearly 1000 m^2 s^-2 SRH!! In August!

[wxmann_91]

KyWetter, on Aug 12 2007, 06:18 PM, said:

:whistle:

What's the whistle about? :D

[sprite]

tornadotony, on Aug 12 2007, 08:57 PM, said:

I thought this was a tad interesting...perhaps affected by convective feedback...but still...

KLVN0812...sounding.PNG

Jesus, talk about a textbook hodograph!

[sprite]

wxmann_91, on Aug 12 2007, 09:20 PM, said:

What's the whistle about? :D

Still a disbeliever in the mythic 1,000 SRH/4,000 J/kg combination? :devilsmiley:

[wxmann_91]

KyWetter, on Aug 12 2007, 06:24 PM, said:

Still a disbeliever in the mythic 1,000 SRH/4,000 J/kg combination? :devilsmiley:

The CAPE in that sounding is only 1500 J/kg ;)

[sprite]

wxmann_91, on Aug 12 2007, 09:28 PM, said:

The CAPE in that sounding is only 1500 J/kg ;)

Yes, true. However... :scooter: