November 17 Severe Weather & Tornado Outbreak

[EF-5bigj]

I wonder how unstable the atmosphere will be on Sunday.

[cycloneye]

Cool graphic by SPC.

[TropicalAnalystwx13]

[WeatherGuesser]

Media chiming in:

http://news.google.com/news/story?pz=1& ... Uh3dSgpxwM

[EF-5bigj]

Good to see the media is staying ahead of it.

[CrazyC83]

I think the southern threat is being underestimated though...they may not have the extreme shear, but they will have greater instability...

[EF-5bigj]

I'm in Dixie alley and this area tends to be pretty volitile so it may ramp up in the MS,AL area more then we are seeing. It's moist here for sure and in the 60-70s right now.

[TropicalAnalystwx13]

NWS Chicago AFD:

THINGS REALLY BEGIN TO GET POTENTIALLY INTERESTING ON SUNDAY AS
STRONG SHORTWAVE BEGINS TO TAKE ON A MORE NEUTRAL AND EVENTUALLY
NEGATIVE TILT BY EVENING AS IT TRACKS INTO THE GREAT LAKES.
INGREDIENTS REALLY SEEM TO BE FALLING VERY NICELY INTO PLACE FOR A
SEVERE THUNDERSTORMS WITH A DAMAGING WIND AND TORNADO THREAT SUNDAY
ACROSS OUR CWA. POWERFUL 120KT UPPER JET IS PROGGED TO NOSE INTO
CENTRAL ILLINOIS BY 18Z SUNDAY WITH STRONG UPPER LEVEL DIVERGENCE IN
THE LEFT EXIT REGION OF THE JET LIKELY SUPPORTING STRONG LARGE SCALE
ASCENT OVER THE AREA WITH RAPIDLY DEEPENING SURFACE LOW AND STRONG
SURGING COLD FRONT LIKELY TO PROVIDE THE STRONGEST LOW LEVEL
FORCING/FOCUS FOR CONVECTIVE INITIATION SUNDAY ALONG THE FRONT.

COLD SEASON SEVERE WEATHER IN OUR AREA OFTEN FEATURE SBCAPE OF LESS
THAN 1000 J/KG...YET GUIDANCE CONTINUE TO ADVERTISE SBCAPES
APPROACHING 1500 J/KG SUNDAY AFTERNOON AS POCKET OF VERY COLD AIR
ALOFT MOVES IN WITH 700-500MB LAPSE RATES >8C/KM. THE INSTABILITY
COMBINED WITH THE TYPICALLY STRONG/EXTREME SHEAR WITH DEEP COLD
SEASON CYCLONE RAISES THE THREAT OF A POTENTIALLY DANGEROUS SEVERE
WEATHER EPISODE ACROSS THE REGION. MODEL FORECASTS SUGGEST THAT
THERE WILL BE A FAIRLY BROAD WARM SECTOR SUNDAY AFTERNOON WITH
MODERATE INSTABILITY AND MINIMAL CINH. CERTAINLY THE MOST LIKELY
SCENARIO WOULD BE FOR CONVECTION TO BE FOCUSED ALONG THE COLD FRONT
AND LIKELY GOING LINEAR FAIRLY QUICKLY AFTER INITIATION...BUT WITH
THE POTENTIAL FOR A DEVELOPING LARGE STRONGLY SHEARED AND WEAKLY
CAPPED WARM SECTOR CANNOT RULE OUT SUPERCELLS DEVELOPING AHEAD OF
CONVECTIVE LINE DUE TO LARGE SCALE ASCENT IN LEFT EXIT REGION OF JET
COUPLED WITH MODEST LOW LEVEL THETA-E ADVECTION. INITIAL DEVELOPMENT
OF CONVECTION ALONG THE COLD FRONT COULD ALSO BE SUPERCELLS
BEFORE MORPHING INTO A LINE...IN EITHER OF THESE SCENARIOS POTENTIAL
WOULD EXIST FOR TORNADIC SUPERCELLS. CLIMO SUGGESTS THAT NOVEMBER
TORNADOES IN OUR AREA ARE VERY RARE...BUT WHEN THEY OCCUR THEY ARE
FREQUENTLY STRONG. DAMAGING WIND THREAT WITH CONVECTIVE LINE LOOKS
TO BE QUITE HIGH GIVEN THE ALREADY STRONG FIELDS IN PLACE...WITH
ATTENDANT THREAT OF EMBEDDED MESOVORTEX DEVELOPMENT LEADING TO
ENHANCED WIND DAMAGE AND/OR QLCS TORNADO THREAT.

DEFINITELY WORTH NOTING THAT THERE ARE MANY MESOSCALE VARIABLE THAT
NEED TO FALL INTO PLACE JUST RIGHT TO RESULT IN SIGNIFICANT SEVERE
WEATHER OUTBREAKS. ITS CERTAINLY NOT HARD TO ENVISION MULTIPLE
SCENARIOS WHERE OUR CWA DODGES ANOTHER SEVERE WEATHER BULLET...BUT
CURRENT INDICATIONS ARE THAT A SIGNIFICANT TORNADO/DAMAGING WIND
THREAT COULD DEVELOP SUNDAY EITHER IN OR CLOSE TO OUR AREA. DESPITE
THE UNCERTAINTIES AND BUST POTENTIAL...ENOUGH INGREDIENTS APPEAR TO
BE FALLING INTO PLACE TO REALLY RATCHET UP THE "HYPE" FOR THE
POTENTIAL EVENT. A COUPLE OF THINGS TO CONSIDER ABOUT THIS EVENT IS
THAT IT WOULD BE AN "OUT OF SEASON" EVENT ON THE WEEKEND WHICH COULD
CATCH PEOPLE OFF GUARD. IN ADDITION...THE VERY STRONG WIND FIELDS
WILL RESULT IN AN EXTREMELY FAST WITH BUNKERS FORECAST RIGHT MOVING
STORM MOTION SUGGESTING THE POTENTIAL FOR STORMS TO BE MOVING AT
CLOSE TO 60KT.

[EF-5bigj]

Strong tornadoes and fast moving storms hmmm.

[TropicalAnalystwx13]

The 0z NAM is discrete cell city. Any of these discrete cells, which should be moving well over 40kt by the way, will have the potential to produce strong to intense (violent?) tornadoes.

[CrazyC83]

Tornado threat as far north as northern Ontario in that setup. In the middle of November. Unbelieveable.

[EF-5bigj]

So the tornadoes produced will be significant to violent?

[tomboudreau]

Only 25 miles east of the Moderate area. Not good. Timing is between 10 PM and 2 AM for my area. A major nighttime event.

[CrazyC83]

So the tornadoes produced will be significant to violent?

Quite likely.

[EF-5bigj]

So that would mean these tornadoes could be long track to.

[CrazyC83]

So how high does the SPC go at 06Z? I think they might be a bit conservative, strongly worded MDT with hints of HIGH later...probably 10H tornado and 45H wind.

[Cyclenall]

Tornado threat as far north as northern Ontario in that setup. In the middle of November. Unbelieveable.

I will buy you a cake if there is a strong tornado in northern Ontario tomorrow. I think you mean central ON because northern has quite a snowcover and no convection up there progged.

So that would mean these tornadoes could be long track to.

Can't comment on that but its not always the case in general. They will be incredibly fast moving which can produce devastating results (March 2, 2012).

So how high does the SPC go at 06Z? I think they might be a bit conservative, strongly worded MDT with hints of HIGH later...probably 10H tornado and 45H wind.

Don't you need higher model agreement and more moisture or CAPE?

[EF-5bigj]

The March 2,2012 tornadoes where fast moving and happened in the morning. This looks to happen in the morning and early afternoon

[CrazyC83]

Tornado threat as far north as northern Ontario in that setup. In the middle of November. Unbelieveable.

I will buy you a cake if there is a strong tornado in northern Ontario tomorrow. I think you mean central ON because northern has quite a snowcover and no convection up there progged.

So that would mean these tornadoes could be long track to.

Can't comment on that but its not always the case in general. They will be incredibly fast moving which can produce devastating results (March 2, 2012).

So how high does the SPC go at 06Z? I think they might be a bit conservative, strongly worded MDT with hints of HIGH later...probably 10H tornado and 45H wind.

Don't you need higher model agreement and more moisture or CAPE?

That model brings severe weather as far north as 46-47N latitude. Agreed it requires more model agreement and instability. Not all models bring widespread tornado action.

If I were drawing the maps, I'd leave the MDT basically where it is, expand the SLGT north and south, have a 45H wind area in the MDT, 30H surrounding it on all sides and 15 in the remainder. For tornadoes, the 10H area would run roughly in a parallelogram from Sheboygan, WI to Saginaw, MI on the northern end and from about Bowling Green, KY to Poplar Bluff, MO on the southern end (mostly the western half of the MDT area, with some in the SLGT area also included).

[CrazyC83]

BREAKING NEWS - HIGH RISK ISSUED

SPC AC 170552

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1152 PM CST SAT NOV 16 2013

VALID 171200Z - 181200Z

...THERE IS A HIGH RISK OF SVR TSTMS ACROSS PARTS OF ERN IL...IND
AND FAR SW LOWER MI...

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF IL...LOWER
MI...OH...IND...KY AND WRN TN......

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE MID TO
UPPER MS VALLEY...OH VALLEY...SRN GREAT LAKES AND TN VALLEY...

...TORNADO OUTBREAK WITH MULTIPLE SIGNIFICANT TORNADOES AND
WIDESPREAD DAMAGING WINDS EXPECTED ACROSS THE OH VALLEY AND SRN
GREAT LAKES REGION TODAY...

AN IMPRESSIVE NEGATIVELY-TILTED UPPER-LEVEL TROUGH AND POWERFUL 80
TO 100 KT MID-LEVEL JET WILL MOVE ACROSS THE NCNTRL U.S. TODAY. AT
THE SFC...A LOW WILL TRACK NEWD INTO THE UPPER MIDWEST AS A COLD
FRONT ADVANCES EWD INTO THE MID TO UPPER MS VALLEY. AHEAD OF THE
FRONT...STRONG MOISTURE ADVECTION WILL OCCUR DUE TO A WELL-DEVELOPED
AND BROAD 60 TO 75 KT LOW-LEVEL JET. AN EXTENSIVE AREA OF
THUNDERSTORMS WITH AN ISOLATED SEVERE THREAT SHOULD BE ONGOING ALONG
THE ERN EDGE OF THE LOW-LEVEL JET FROM NE AR NEWD INTO SRN IND AT
DAYBREAK WITH THIS ACTIVITY MOVING EWD AWAY FROM THE INSTABILITY
AXIS THIS MORNING. FURTHER TO THE WEST...THE LOW-LEVEL JET WILL
TRANSPORT LOW TO MID 60S F SFC DEWPOINTS INTO THE MID MS VALLEY AND
OH VALLEY RESULTING IN A CORRIDOR OF MODERATE INSTABILITY FROM NE AR
NNEWD INTO CNTRL IL BY MID MORNING. DUE TO STRONG LARGE-SCALE ASCENT
ASSOCIATED WITH THE UPPER-LEVEL TROUGH...SFC-BASED CELL INITIATION
SHOULD OCCUR AHEAD OF THE FRONT BY MID MORNING ACROSS NRN AND CNTRL
IL WITH STORM COVERAGE EXPANDING EWD INTO IND AND LOWER MI BY EARLY
AFTERNOON. ALTHOUGH CELLS MAY REMAIN DISCRETE THROUGH MUCH OF THE
AFTERNOON...THE DEVELOPMENT OF A SQUALL-LINE APPEARS LIKELY DURING
THE LATE AFTERNOON ACROSS THE OH VALLEY WITH THE LINE DEVELOPING SWD
INTO THE TN VALLEY DURING THE EARLY EVENING.

FORECAST SOUNDINGS AT URBANA IL AND INDIANAPOLIS IND IN THE 18Z TO
21Z TIMEFRAME SHOW SBCAPE NEAR 1500 J/KG...0-6 KM SHEAR AROUND 70
KT...LOW-LCL HEIGHTS AND LONG LOOPED HODOGRAPHS SUGGESTING
SUPERCELLS AND TORNADOES WILL BE LIKELY AS DISCRETE CELLS INTENSIFY.
0-3 KM STORM RELATIVE HELICITIES OF 400 TO 450 M2/S2 WILL BE
FAVORABLE FOR STRONG TORNADOES WITH SEVERAL LONG-TRACK DAMAGING
TORNADOES EXPECTED TO OCCUR FROM ERN IL ENEWD ACROSS MUCH OF WRN AND
CNTRL IND FROM LATE MORNING INTO EARLY AFTERNOON. AS CELL COVERAGE
INCREASES AHEAD OF THE FAST MOVING FRONT...A SQUALL-LINE SHOULD
ORGANIZE LATE THIS AFTERNOON. WIDESPREAD WIND DAMAGE WILL BE
ASSOCIATED WITH THE LINE ALONG WITH TORNADOES WITH ROTATING CELLS
EMBEDDED IN THE LINE. THE SEVERE THREAT SHOULD RAMP UP SOUTH OF THE
OH RIVER DURING THE LATE AFTERNOON AS CELLS INITIATE SWD ALONG THE
FRONT. THE POTENTIAL FOR WIND DAMAGE AND TORNADOES SHOULD DEVELOP AS
A FAR SOUTH AS THE TN VALLEY DURING THE EVENING AS AN EXTENSIVE LINE
OF SEVERE STORMS MOVES EWD INTO THE UPPER OH VALLEY AND CNTRL
APPALACHIAN MTNS.

SEVERAL FACTORS APPEAR TO BE COMING TOGETHER FOR A TORNADO OUTBREAK
ACROSS THE OH VALLEY. THE FIRST FACTOR IS THAT THE SYSTEM IS
NEGATIVELY-TITLED AND VERY WELL-ORGANIZED. THE SECOND IS THAT THE
LOW AND MID-LEVEL JETS WILL BECOME FAVORABLY COUPLED IN THE OH
VALLEY TODAY COINCIDING WITH AN OUTBREAK OF STORMS ACROSS THE WARM
SECTOR. THE THIRD IS THAT SUPERCELLS ARE EXPECTED TO REMAIN DISCRETE
INTO THE MID-AFTERNOON. THESE FACTORS COMBINED WITH EXTREMELY
FAVORABLE LOW-LEVEL SHEAR PROFILES JUSTIFIES THE ISSUANCE OF A HIGH
RISK ACROSS ERN IL...IND AND SW LOWER MI.

..BROYLES/BUNTING.. 11/17/2013

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