Thanksgiving Week Severe Weather

[msp]

someone had to...

CF with a strong temp gradient will be dragged through the south midweek. possible severe event?

SPC not too bullish:

THEREAFTER...TSTMS WILL REMAIN POSSIBLE ACROSS PORTIONS OF THE TN

VALLEY/ARKLATEX AND GULF COAST STATES ON DAYS 5/6...GENERALLY ALONG

A DECELERATING COLD FRONT. HOWEVER...A PARTICULARLY

WIDESPREAD/ORGANIZED SEVERE WEATHER EPISODE IS NOT CURRENTLY

EXPECTED.

go.

[Thundersnow12]

The moisture will be there for it, upper 50's near 60 forecasted last I saw, even better juice further south. I also saw that SPC had a discussion out for D4. looks like some serious mid-level winds.

WITH ONE SUCH SHORTWAVE TROUGH EXPECTED TO CROSS THE UPPER MIDWEST

ON DAY 4/MONDAY...THIS SCENARIO COULD SUPPORT SOME RELATIVELY

LOW-TOPPED/FAST MOVING TSTMS ACROSS PORTIONS OF THE MIDWEST/WESTERN

GREAT LAKES ALONG/AHEAD OF A COLD FRONT. THE PRIMARY UNCERTAINTY

WILL BE REGARDING LIMITED MOISTURE/BUOYANCY GIVEN LITTLE OPPORTUNITY

FOR CONSEQUENTIAL MOISTURE RETURN. NONETHELESS...SOME STRONG/SEVERE

TSTMS CANNOT BE RULED OUT DAY 4/MONDAY ACROSS THE MIDWEST/GREAT

LAKES REGION WITHIN A STRONGLY FORCED/SHEARED REGIME.

[msp]

yeah, i guess we'll include monday too given i left the title open for the whole week

WITH ONE SUCH SHORTWAVE TROUGH EXPECTED TO CROSS THE UPPER MIDWEST

ON DAY 4/MONDAY...THIS SCENARIO COULD SUPPORT SOME RELATIVELY

LOW-TOPPED/FAST MOVING TSTMS ACROSS PORTIONS OF THE MIDWEST/WESTERN

GREAT LAKES ALONG/AHEAD OF A COLD FRONT. THE PRIMARY UNCERTAINTY

WILL BE REGARDING LIMITED MOISTURE/BUOYANCY GIVEN LITTLE OPPORTUNITY

FOR CONSEQUENTIAL MOISTURE RETURN. NONETHELESS...SOME STRONG/SEVERE

TSTMS CANNOT BE RULED OUT DAY 4/MONDAY ACROSS THE MIDWEST/GREAT

LAKES REGION WITHIN A STRONGLY FORCED/SHEARED REGIME.

[Srain]

I think we have a decent shot next week. I've seen this type pattern before and it often yeilds a punch. Thanks Mike for starting the thread. Our first in our new home.

[baroclinic_instability]

Seems to be two events worth noting for potential. The mid level speed max coming Monday night and then the main trough coming Wed/Thurs across the southern OH Valley. Wow this is a tough one in determining convective potential...let me process this before I bother saying anything lol.

[patrick7032]

Seems to be two events worth noting for potential. The mid level speed max coming Monday night and then the main trough coming Wed/Thurs across the southern OH Valley. Wow this is a tough one in determining convective potential...let me process this before I bother saying anything lol.

With incoming jets at all levels 300 j/kg will get severe warnings to be issued I bet. The maps show only 100 j/kg or so, but Bufkit shows more. All the soundings were basically the same. We'll have good low level moisture for this time of year. I wouldn't be surprised if they put a see text out at some point.

[csnavywx]

With incoming jets at all levels 300 j/kg will get severe warnings to be issued I bet. The maps show only 100 j/kg or so, but Bufkit shows more. All the soundings were basically the same. We'll have good low level moisture for this time of year. I wouldn't be surprised if they put a see text out at some point.

Going to be a little tough to get sustained updrafts given the amount of shear vs CAPE. BRNs likely on the low side. My guess is that they'll behave somewhat similar to the Octobomb storms. They go up for 10-15 or so minutes, then get decapitated by the shear. Also, this CAPE is more elevated in nature, so it's going to be tougher to transfer momentum to the surface given the weaker low-level lapse rates.

Having said that, a few stronger storms this late in the season is nothing to complain about!

Edit: Haha, yeah I just saw the BUFKIT output of 1.63 for the BRN, sheez...

[patrick7032]

Going to be a little tough to get sustained updrafts given the amount of shear vs CAPE. BRNs likely on the low side. My guess is that they'll behave somewhat similar to the Octobomb storms. They go up for 10-15 or so minutes, then get decapitated by the shear. Also, this CAPE is more elevated in nature, so it's going to be tougher to transfer momentum to the surface given the weaker low-level lapse rates.

Having said that, a few stronger storms this late in the season is nothing to complain about!

Edit: Haha, yeah I just saw the BUFKIT output of 1.63 for the BRN, sheez...

True....one thing to watch though is the models undergoing the low-level instability. With 12C at 850 it will be warmer than 15C at the surface, even if you only mix up to 900. A week ago I believe here at DTW we had similar 850 temps and were around 70. I'm not expecting that but I think low to may mid 60s may be possible, which may give a little more cape, but from my standpoint I won't be chasing so if I get storms around I'll be having fun with TS obs.

[patrick7032]

True....one thing to watch though is the models undergoing the low-level instability. With 12C at 850 it will be warmer than 15C at the surface, even if you only mix up to 900. A week ago I believe here at DTW we had similar 850 temps and were around 70. I'm not expecting that but I think low to maybe mid 60s may be possible, which may give a little more cape, but from my standpoint

I won't be chasing so if I get storms around I'll be having fun with TS obs.

[patrick7032]

Has anyone been having problems with the server? Tried to delete the redundant post and it won't let me.

[patrick7032]

GRR also agrees with this. Excerpt is below.

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE GRAND RAPIDS MI

347 PM EST FRI NOV 19 2010

.LONG TERM...(245 PM EST FRI NOV 19 2010)

(MONDAY THROUGH HOLIDAY WEEKEND)

POTENTIAL LONG RANGE IMPACTS INCLUDE A CHANCE OF STRONG

THUNDERSTORMS ON MONDAY AND THE POTENTIAL FOR A LAKE ENHANCED SNOW

EVENT LATE NEXT WEEK.

AS PER YESTERDAY...VERY GOOD GENERAL AGREEMENT BETWEEN ECWMF/GFS/FIM

ON EVOLUTION OF LONG WAVE PATTERN THROUGH THE THANKSGIVING HOLIDAY

WEEKEND. STRONG TROF WILL DEVELOP OVER THE WEST THIS WEEKEND WITH

DOWNSTREAM RIDGE AMPLIFYING OVER THE EASTERN HALF OF THE COUNTRY.

THE TROF THEN PROGRESSES EASTWARD TO OUR REGION BY LATE IN THE WEEK.

THE BROAD IMPLICATIONS FOR OUR REGION IS THAT NEXT WEEK WILL START

OUT WITH MUCH ABOVE NORMAL TEMPERATURES AND LIKELY END WITH MUCH

BELOW NORMAL TEMPERATURES.

AGREEMENT ON SHORTWAVE TIMING MUCH BETTER THAN YESTERDAY BETWEEN 12Z

ECMWF AND GFS. FIRST IN A SERIES OF SHORTWAVES MOVES NEWD THROUGH

WISCONSIN ON MONDAY. ACCOMPANYING SFC LOW ALSO MOVES WEST OF US

WITH H85 TEMPS AT LEAST +8C DURING THE DAY. COLD FRONT PUSHES

THROUGH MONDAY NIGHT. THERE LOOKS TO BE A THREAT OF STRONG

LOW-TOPPED THUNDERSTORMS AS A MODEST AMOUNT OF CAPE...LESS THAN

500J...POTENTIALLY INTERACTS WITH STRONG WIND FIELDS. SO ADDED

THUNDER POTENTIAL TO GRIDS ON MON.

[Chicago Storm]

0z NAM:

[Stebo]

SPC's day three outlook with discussion below, has see text for IL/IN/MI areas.

SPC AC 200743

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0143 AM CST SAT NOV 20 2010

VALID 221200Z - 231200Z

...SYNOPSIS...

AS A LONGWAVE TROUGH/BROAD CYCLONIC UPPER FLOW PREVAILS OVER THE

MAJORITY OF THE CONUS ON MONDAY...AN EMBEDDED/CONSIDERABLE SHORTWAVE

TROUGH IS EXPECTED TO RACE NORTHEASTWARD FROM THE CENTRAL

ROCKIES/HIGH PLAINS TO THE UPPER GREAT LAKES VICINITY BY EARLY

TUESDAY. AS A SURFACE LOW STEADILY DEEPENS/ADVANCES NORTHEASTWARD

ACROSS THE MIDWEST/UPPER GREAT LAKES...SHOWERS/TSTMS ARE EXPECTED

ESPECIALLY ALONG A GENERALLY EASTWARD MOVING COLD FRONT.

...MIDWEST/WESTERN GREAT LAKES...

A STRONG EARLY DAY LOW LEVEL JET AND ASSOCIATED WARM

ADVECTION/MOISTURE TRANSPORT REGIME ABOVE THE SURFACE WILL

CONTRIBUTE TO THE NORTHWARD FLUX/PARTIAL RETURN OF A MODIFIED

MARITIME AIRMASS ACROSS THE MIDWEST...AHEAD OF A DEVELOPING SURFACE

LOW/EASTWARD ADVANCING COLD FRONT. ASIDE FROM THE POSSIBILITY OF

EARLY DAY ELEVATED TSTMS ACROSS THE UPPER GREAT LAKES/MAINLY LAKE MI

GENERAL VICINITY...IT IS CONCEIVABLE THAT THE PRIMARY TIMING OF WARM

SECTOR TSTMS AND ANY SEVERE THREAT MAY NOT OCCUR UNTIL THE

EVENING/PERHAPS LATE NIGHT HOURS...ROUGHLY COINCIDENT WITH THE

EXPECTED MAIN ARRIVAL OF THE PLAINS SHORTWAVE TROUGH/JET STREAK.

REGARDLESS...BUOYANCY WILL BE LIMITED THROUGHOUT THE PERIOD AMID THE

GENERAL PREVALENCE OF 50S F SURFACE DEWPOINTS.

NONETHELESS...PROVIDED WEAK BUOYANCY OF SEVERAL HUNDRED J/KG CAPE

MONDAY AFTERNOON/NIGHT...A RATHER STRONG LOW/MID TROPOSPHERIC WIND

FIELD MAY BE CONDUCIVE FOR ISOLATED TO SCATTERED LOW-TOPPED/FAST

MOVING STRONG/SEVERE TSTMS CAPABLE OF WIND DAMAGE...AT LEAST ON AN

ISOLATED BASIS.

..GUYER.. 11/20/2010

[baroclinic_instability]

SPC's day three outlook with discussion below, has see text for IL/IN/MI areas.

..GUYER.. 11/20/2010

I not only agree with his assessment, I won't be surprised if they don't bump this up to a slight across portions of east-central Indiana where CAPE will be a bit higher and the vertical shear will be plenty strong but not as insane as it is farther north. Low level winds at 50 kts and 700 hpa winds in excess of 60+ kts means momentum transport won't be an issue either.

[Stebo]

I not only agree with his assessment, I won't be surprised if they don't bump this up to a slight across portions of east-central Indiana where CAPE will be a bit higher and the vertical shear will be plenty strong but not as insane as it is farther north. Low level winds at 50 kts and 700 hpa winds in excess of 60+ kts means momentum transport won't be an issue either.

Yeah I'd say probably the whole 5% has a chance of being upgraded, especially if ~500-750 J/kg of CAPE is realized. Which both NAM and GFS are hinting at.

[IWXwx]

Hey, I like where I'm at here for severe, kinda in the bullseye for now. If we can't get a good snow out of this, might as well get some good storms.

[tornadotony]

I really think the threat for severe weather and even tornadoes is increasing for Monday across northern Illinois and southern Wisconsin.

The pattern we're seeing evolve for Monday is quite similar to January 7th, 2008. Just compare the GFS 500mb and sfc plots for Monday to the plots for 1/7/08:

GFS 500hPa T, wind, hght:

http://www.twisterda...e&archive=false

GFS sfc T, wind, pressure:

http://www.twisterda...e&archive=false

1/7/08 500hPa:

http://www.spc.noaa....7/500-oa-00.gif

1/7/08 sfc:

A few things of note:

1) Note the position of the subtropical high, the similarities in position and strength

2) Note the cold 500hPa temps in both scenarios, with H5 T of -18 to -19C

3) Note the boundary sprawling from the srn plains to the Great Lakes region, with a low center on the srn High Plains and another in the Great Lakes region indicative of a strung-out system

With bountiful moisture return by late November standards (mid-upper 50 dews), warm temps (65F+ likely in the warm sector), a shortwave trough embedded in the main system to enhance lift, and the frontal boundary in place, it would be not at all a shock to see low-topped tornadic supercells on Monday across nrn IL and srn WI.

[L.B. LaForce]

Definitely an interesting situation evolving. I went to look at the Euro models, but they no longer exist over at eastern

[cmichweather]

Definitely an interesting situation evolving. I went to look at the Euro models, but they no longer exist over at eastern

http://raleighwx.americanwx.com/models.html

[Hoosier]

I really think the threat for severe weather and even tornadoes is increasing for Monday across northern Illinois and southern Wisconsin.

The pattern we're seeing evolve for Monday is quite similar to January 7th, 2008. Just compare the GFS 500mb and sfc plots for Monday to the plots for 1/7/08:

GFS 500hPa T, wind, hght:

http://www.twisterda...e&archive=false

GFS sfc T, wind, pressure:

http://www.twisterda...e&archive=false

1/7/08 500hPa:

http://www.spc.noaa....7/500-oa-00.gif

1/7/08 sfc:

A few things of note:

1) Note the position of the subtropical high, the similarities in position and strength

2) Note the cold 500hPa temps in both scenarios, with H5 T of -18 to -19C

3) Note the boundary sprawling from the srn plains to the Great Lakes region, with a low center on the srn High Plains and another in the Great Lakes region indicative of a strung-out system

With bountiful moisture return by late November standards (mid-upper 50 dews), warm temps (65F+ likely in the warm sector), a shortwave trough embedded in the main system to enhance lift, and the frontal boundary in place, it would be not at all a shock to see low-topped tornadic supercells on Monday across nrn IL and srn WI.

Interesting. I guess my default position is to start out skeptical with severe events that far north at this time of year, but they can and do occur. I've only spent a little time looking at it, but as far as tornadic potential, it appears the winds are unidirectional especially above 850 mb. The low level shear does look pretty good though. I remember you playing up 1/7/08 and we know how that turned out...

[Jim Martin]

The last November severe weather event that I can remember is November 10, 2002. This was the day of the Van Wert, OH EF4 tornado that destroyed the movie theater in town. I hope this potential severe weather event is not as bad as 2002.

[tornadotony]

Interesting. I guess my default position is to start out skeptical with severe events that far north at this time of year, but they can and do occur. I've only spent a little time looking at it, but as far as tornadic potential, it appears the winds are unidirectional especially above 850 mb. The low level shear does look pretty good though. I remember you playing up 1/7/08 and we know how that turned out...

Yeah, we're not close enough yet to where I'm completely ready to bite, but the trends appear ominous.

[Indystorm]

Is the NAM starting to develop the idea of higher helicity vs. unidirectional shear in the affected areas from OK ne to MI for Monday evening? Will be interesting to watch trends and amount of moisture return in future runs.

http://wxcaster4.com...OS_STP_57HR.gif

[csnavywx]

I really think the threat for severe weather and even tornadoes is increasing for Monday across northern Illinois and southern Wisconsin.

The pattern we're seeing evolve for Monday is quite similar to January 7th, 2008. Just compare the GFS 500mb and sfc plots for Monday to the plots for 1/7/08:

GFS 500hPa T, wind, hght:

http://www.twisterda...e&archive=false

GFS sfc T, wind, pressure:

http://www.twisterda...e&archive=false

1/7/08 500hPa:

http://www.spc.noaa....7/500-oa-00.gif

1/7/08 sfc:

A few things of note:

1) Note the position of the subtropical high, the similarities in position and strength

2) Note the cold 500hPa temps in both scenarios, with H5 T of -18 to -19C

3) Note the boundary sprawling from the srn plains to the Great Lakes region, with a low center on the srn High Plains and another in the Great Lakes region indicative of a strung-out system

With bountiful moisture return by late November standards (mid-upper 50 dews), warm temps (65F+ likely in the warm sector), a shortwave trough embedded in the main system to enhance lift, and the frontal boundary in place, it would be not at all a shock to see low-topped tornadic supercells on Monday across nrn IL and srn WI.

BRNs (cape/shear balance) needs to be higher than 2-4 this time. This was overlooked in October and though a few storms managed to rotate or even drop a brief tornado, they were obliterated shortly after due to shear. I'd like to see them up over the traditional 10 value.

[tornadotony]

BRNs (cape/shear balance) needs to be higher than 2-4 this time. This was overlooked in October and though a few storms managed to rotate or even drop a brief tornado, they were obliterated shortly after due to shear. I'd like to see them up over the traditional 10 value.

Don't trust the models to accurately represent the low-level thermal profile in this situation. Those who did that on 1/7/08 got burned and got burned badly. The NAM and GFS are both indicating non-negligible instability while depicting sfc temps near 60. DVN and LOT are going near 65 for Monday. If that happens, CAPE will increase rather substantially, probably to pockets of 1000J/kg or greater, with much of that in the lowest levels of the atmosphere.

Also not to be overlooked is the threat that appears to be evolving in the Ozarks. The latest NAM is showing CAPE rising overnight across the Ozarks with an increasingly sheared low-level environment, just like 1/7/08.

[Hoosier]

Don't trust the models to accurately represent the low-level thermal profile in this situation. Those who did that on 1/7/08 got burned and got burned badly. The NAM and GFS are both indicating non-negligible instability while depicting sfc temps near 60. DVN and LOT are going near 65 for Monday. If that happens, CAPE will increase rather substantially, probably to pockets of 1000J/kg or greater, with much of that in the lowest levels of the atmosphere.

Also not to be overlooked is the threat that appears to be evolving in the Ozarks. The latest NAM is showing CAPE rising overnight across the Ozarks with an increasingly sheared low-level environment, just like 1/7/08.

Given relatively strong southerly flow, I think it's all but given that we see mid to upper 60's into northern IL on Monday. Clouds could be a hindrance, but the models are indicating quite a bit of dry air aloft.

[tornadotony]

Given relatively strong southerly flow, I think it's all but given that we see mid to upper 60's into northern IL on Monday. Clouds could be a hindrance, but the models are indicating quite a bit of dry air aloft.

Yeah, and with 500mb T of -17 or -18C, I struggle to see 1000J/kg CAPE being a stretch...

[baroclinic_instability]

BRNs (cape/shear balance) needs to be higher than 2-4 this time. This was overlooked in October and though a few storms managed to rotate or even drop a brief tornado, they were obliterated shortly after due to shear. I'd like to see them up over the traditional 10 value.

Don't trust the models to accurately represent the low-level thermal profile in this situation. Those who did that on 1/7/08 got burned and got burned badly. The NAM and GFS are both indicating non-negligible instability while depicting sfc temps near 60. DVN and LOT are going near 65 for Monday. If that happens, CAPE will increase rather substantially, probably to pockets of 1000J/kg or greater, with much of that in the lowest levels of the atmosphere.

Also not to be overlooked is the threat that appears to be evolving in the Ozarks. The latest NAM is showing CAPE rising overnight across the Ozarks with an increasingly sheared low-level environment, just like 1/7/08.

Undoubtedly going to be a pretty unseasonably late severe weather threat, but I don't find the wind fields all that conducive to either tornadoes and or long lived supercells. First the orientation of the front. The GFS keeps trending slightly more amplified with the low amplitude shortwave passing through the plains and into the Great Lakes Monday night. It seems the models are slightly more SW-NE oriented with the cold front in response and it seems most models are initiating convection slightly aloft along the frontal circulation. The problem is the nearly unidirectional SW flow aloft oriented perfectly parallel to the front with any early rotating storms rapidly transitioning into a line of multicell clusters of thunderstorms and heavy QPF. Low level wind fields are not conducive at all to supporting supercells for a very long time. I still think wind is the main threat, and that will be early on before transitioning into a heavy rain event.

[baroclinic_instability]

I don't know, 1000 j/kg seems a bit much considering, at this point in time, the expected layers of clouds, especially in the upper levels. The GFS jet stream configuration would put the plume of relatively thick high clouds over the suspected region of convection. November insolation won't be conducive to much boundary layer warming at all.

[tornadotony]

Undoubtedly going to be a pretty unseasonably late severe weather threat, but I don't find the wind fields all that conducive to either tornadoes and or long lived supercells. First the orientation of the front. The GFS keeps trending slightly more amplified with the low amplitude shortwave passing through the plains and into the Great Lakes Monday night. It seems the models are slightly more SW-NE oriented with the cold front in response and it seems most models are initiating convection slightly aloft along the frontal circulation. The problem is the nearly unidirectional SW flow aloft oriented perfectly parallel to the front with any early rotating storms rapidly transitioning into a line of multicell clusters of thunderstorms and heavy QPF. Low level wind fields are not conducive at all to supporting supercells for a very long time. I still think wind is the main threat, and that will be early on before transitioning into a heavy rain event.

Unidirectional flow? Check.

Flow parallel to the front? Check.

Result:

Now to be fair, a nasty, nasty line (some 70-80MPH wind gusts) did develop and propogate across nrn IL, nrn IN, srn lower MI, and nwrn OH after the supercell that produced two high-EF3 tornadoes moved over the lake...and another nasty line took shape across the Ozarks as the secondary low moved east during the overnight hours...but not after literally dozens of supercells accosted the I-44/I-55 corridors from Tulsa to Chicago...