Significant Severe Weather Outbreak Possible 04/26-30/2014

[TropicalAnalystwx13]

Model guidance is converging on a potentially significant severe weather and tornado outbreak across the central Plains this weekend as a shortwave ejects into the region. With a strong mid-level jet streak expected to aid in a negative tilt of the trough, an abundance of moisture should be influxed from the Gulf of Mexico. Dewpoints may exceed 60F across most of Oklahoma by Saturday evening. In addition, a strengthening 850mb jet of 30-40 knots should provide plenty of shear for rotating storms. It's important to keep in mind that while the LLJ is typically stronger than this with significant severe weather events (I'm talking high risk days), a high amount of wind shear isn't needed when you have extreme instability (GFS is painting 3500-4500 j/kg along the dryline in western Oklahoma).

The SPC Day 4-8 outlook discussion is about as bullish as I've ever seen.

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0345 AM CDT TUE APR 22 2014

VALID 251200Z - 301200Z

...DISCUSSION...
...SIGNIFICANT MULTI-DAY SEVERE EVENT EXPECTED ACROSS THE SOUTH
CENTRAL U.S. SATURDAY AND SUNDAY...STRONG TORNADOES ARE POSSIBLE...

22/00Z ECMWF IS EXHIBITING REASONABLE RUN-TO-RUN CONSISTENCY OVER
THE LAST FEW DAYS WITH THE GFS NOW TRENDING TOWARD ECMWF SOLUTIONS.
THIS FORECAST IS HEAVILY WEIGHTED TOWARD THE ECMWF.

EARLIER CONCERNS REGARDING A POLAR FRONT UNDERCUTTING STRONG SWLY
FLOW ALOFT OVER THE SRN PLAINS ARE LESSENING. WHILE UPPER BLOCK
OVER CNTRL CANADA WILL ULTIMATELY FORCE A DOMINANT SFC ANTICYCLONE
INTO THE MIDDLE OF THE CONUS...IT APPEARS THE LEADING EDGE OF THIS
AIR MASS SHOULD STRUGGLE TO ADVANCE MUCH SOUTH OF I-70 OVER KS/MO
THIS WEEKEND.

STRONG MID-LEVEL SPEED MAX IS FORECAST TO DIG SEWD INTO THE LOWER CO
RIVER VALLEY SATURDAY WITH UPPER DIFLUENCE EXPECTED ACROSS THE
PLAINS AS FAR SOUTH AS WEST TX AT 27/00Z. THIS EVOLUTION WILL ALLOW
SUBSTANTIAL MOISTURE TO ADVANCE POLEWARD ACROSS THE SRN PLAINS WHERE
PW VALUES SHOULD EASILY APPROACH 1.25 INCHES AS SFC DEW POINTS CLIMB
THROUGH THE MID-UPPER 60S ACROSS A BROAD WARM SECTOR. LATEST
THINKING IS MODERATE-EXTREME INSTABILITY SHOULD DEVELOP ALONG ERN
PLUME OF STEEP LAPSE RATES FROM WCNTRL TX...NWD INTO SCNTRL KS
SATURDAY WHERE MUCAPE COULD APPROACH 4000 J/KG. IF THERMODYNAMIC
ENVIRONMENT EVOLVES AS LATEST GUIDANCE SUGGESTS THEN POTENTIALLY
SIGNIFICANT SUPERCELL DEVELOPMENT WITH VERY LARGE HAIL AND TORNADOES
CAN BE EXPECTED. CONVECTION SHOULD INITIATE ALONG DRYLINE FROM SWRN
TX...NWD INTO WRN KS SATURDAY THEN REDEVELOP AGAIN SUNDAY FROM SERN
KS...SWD INTO CNTRL TX AS MID-LEVEL SPEED MAX EJECTS INTO THE SRN
PLAINS. SEVERE TSTMS SHOULD SPREAD INTO THE MS VALLEY BY EARLY
MONDAY. ORGANIZED SEVERE MAY CONTINUE INTO THE DAY7 PERIOD BUT
SUBSTANTIAL CONVECTION DURING THE DAY5-6 TIME FRAME COULD
POTENTIALLY DISRUPT THERMODYNAMIC ENVIRONMENT...THUS CONFIDENCE IS
NOT AS HIGH.

..DARROW.. 04/22/2014

[EF-5bigj]

I'll be watching this I have friends in those areas.

[TropicalAnalystwx13]

I went with 4/26-27/2014 in the thread topic because that's what has the most confidence at this point, but today's model runs suggest a significant severe weather and tornado risk will progress into Dixie Alley by Monday and Tuesday. Everybody needs to be watching this one. The setup on the 12z ECMWF was incredible; high risk material if it pans out.

CIPS analogs for this weekend:

- April 26, 1991
- May 3-4, 1999
- March 12, 2006
- May 24, 2011
- April 14, 2012

Google those days if you're interested.

[EF-5bigj]

Well Dixie Alley is very prone to over compensating tornado wise it takes very little it seems in MS and Alabama to get a strong or violent tornado. I've actually been watching videos of the 4/27/2011 super outbreak to see how southern tornadoes move and how the storms look they tend to be moving at high speeds and I'll be honest its hard to see one coming around were I live. Tree's,hills ect.

[RL3AO]

Obviously its 5 days out, but 12z GFS was showing absurd helicity near Dodge city.

[EF-5bigj]

Well ill be watching that two I have some high school friends in the dodge city area. My local weather has not mentioned anything about the coming weekend yet.

[RL3AO]

Just one run of the GFS, but its interesting to note that some warm air at 850-700 advects in after 21z. Everything looks ready to go at 21z, but then some capping builds in. Will have to watch that over the next couple days.

[cycloneye]

The latest update.



DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0351 AM CDT WED APR 23 2014

VALID 261200Z - 011200Z

...DISCUSSION...
..SIGNIFICANT MULTI-DAY SEVERE EVENT EXPECTED ACROSS PORTIONS OF THE
CENTRAL AND SOUTHERN PLAINS SATURDAY AND SUNDAY AND ACROSS THE MS
VALLEY AND MID SOUTH ON MONDAY...STRONG TORNADOES ARE POSSIBLE...

MEDIUM RANGE FORECAST CONTINUES TO BE HEAVILY WEIGHTED TOWARD THE
ECMWF DUE TO RUN-TO-RUN CONSISTENCY REGARDING THE 500MB EVOLUTION OF
WRN U.S. TROUGH. CONCERNS REGARDING POLAR FRONT UNDERCUTTING STRONG
SWLY FLOW ALOFT HAVE ABATED THIS MORNING. LATEST GUIDANCE DEEPENS
LEE CYCLONE OVER SERN CO SATURDAY AFTERNOON WITH SUBSEQUENT MOVEMENT
INTO WRN KS ON SUNDAY. INTENSE 500MB SPEED MAX APPROACHING 90KT
SHOULD ROUND THE BASE OF THE TROUGH ALONG THE AZ/MEXICAN BORDER THEN
EJECT INTO SWRN KS EARLY SUNDAY. AS A RESULT SFC LOW IS NOT
EXPECTED TO ADVANCE APPRECIABLY EWD UNTIL LATER MONDAY AS SECONDARY
MID-LEVEL SPEED MAX DEVELOPS FROM NORTH TX INTO THE LOWER OH RIVER
VALLEY.

MODERATE TO EXTREME INSTABILITY SHOULD DEVELOP EAST OF THE DRYLINE
SATURDAY AFTERNOON ALONG ERN PLUME OF STEEP LAPSE RATES. STRONGLY
DIFLUENT FLOW ALOFT SHOULD ENCOURAGE VIGOROUS SUPERCELL DEVELOPMENT
FROM PORTIONS OF WCNTRL TX...NWD INTO KS. VERY LARGE HAIL AND
TORNADOES CAN BE EXPECTED WITH THIS ACTIVITY.

IT/S NOT ENTIRELY CLEAR HOW FAR EAST THE DRYLINE WILL MIX SUNDAY AS
LOWEST PRESSURES WILL REMAIN FOCUSED ACROSS THE HIGH PLAINS OF WRN
KS. MODELS MIX DRYLINE EAST OF I-35 CORRIDOR ACROSS OK BY 18Z
SUNDAY BUT THE DAY5 FORECAST WILL ACCOUNT FOR DRYLINE NOT MIXING
ACROSS THE PLAINS AS FAST AS MODELS CURRENTLY DEPICT. AS A
RESULT...SUBSTANTIAL MID-LEVEL FLOW SHOULD OVERSPREAD THE
MOIST/BUOYANT WARM SECTOR AND ANOTHER DIURNALLY-INITIATED ROUND OF
POTENTIALLY TORNADIC SUPERCELLS COULD EVOLVE.

LATER MONDAY IT APPEARS THE SFC FRONT/DRYLINE SHOULD ADVANCE INTO
THE MS VALLEY. SCATTERED-NUMEROUS SUPERCELLS SHOULD EVOLVE AHEAD OF
THE FRONT FROM LA...NWD INTO MO AND POSSIBLY AS FAR EAST AS MIDDLE
TN. TORNADOES AND LARGE HAIL REMAIN POSSIBLE WITH WARM-SECTOR
CONVECTION.

..DARROW.. 04/23/2014

[RL3AO]

Right now I'm still thinking Kansas is looking the best for tornadic potential.

[Cyclenall]

Model guidance is converging on a potentially significant severe weather and tornado outbreak across the central Plains this weekend as a shortwave ejects into the region. With a strong mid-level jet streak expected to aid in a negative tilt of the trough, an abundance of moisture should be influxed from the Gulf of Mexico. Dewpoints may exceed 60F across most of Oklahoma by Saturday evening. In addition, a strengthening 850mb jet of 30-40 knots should provide plenty of shear for rotating storms. It's important to keep in mind that while the LLJ is typically stronger than this with significant severe weather events (I'm talking high risk days), a high amount of wind shear isn't needed when you have extreme instability (GFS is painting 3500-4500 j/kg along the dryline in western Oklahoma).

The SPC Day 4-8 outlook discussion is about as bullish as I've ever seen.

The Day 4-8 outlook is the most bullish I've seen in the last 1.75 years at least, I forget what was said in the headers during the big events of 2012 but I think April 14, 2012 might have had similar talk far out when D7 was put out first. I was pleasantly surprised to see this after the snore-fest this Spring is up to now.

I went with 4/26-27/2014 in the thread topic because that's what has the most confidence at this point, but today's model runs suggest a significant severe weather and tornado risk will progress into Dixie Alley by Monday and Tuesday. Everybody needs to be watching this one. The setup on the 12z ECMWF was incredible; high risk material if it pans out.

CIPS analogs for this weekend:

- April 26, 1991
- May 3-4, 1999
- March 12, 2006
- May 24, 2011
- April 14, 2012

Google those days if you're interested.

I'm I dreaming? That is the most insane set of analogs I've seen!! Those analogs are all events I would consider top producers and were all extremely memorable. Easily the best set of 'logs and only 3 events are missing from keeping it to be the most extreme possible. Yes everyone should be watching because there is a high chance something crazy will occur somewhere.

I've actually been watching videos of the 4/27/2011 super outbreak to see how southern tornadoes move and how the storms look they tend to be moving at high speeds and I'll be honest its hard to see one coming around were I live. Tree's,hills ect.

I think of high speed moving supercells with tornadoes on them usually happening in the early Spring or Fall. The wind shear and low-level movement tend to be racing so that's the cause. Those late May events last year were slow to very slow (Bennington KS).

The latest update.

This image is a keeper, a tornado outbreak sequence type. Haven't seen this yet in 2014.

[WeatherGuesser]

In the Day 6 area as of now. I can only hope the system burns most of the energy out before it gets here.

Rain yes, severe no.

I've also seen a graphic (HPS I think), showing 4+" of rain over three days right over much of the Ohio River. The fields are just getting dry enough for the farmers to work and that will throw another setback at them.

[TheProfessor]

I'm supposed to be going to OU for a tour this weekend but as of right now the chances look slim because the last thing my parents want to do is get caught traveling back on I-35 and getting caught by a Super cell.
And April 26,1991 was the Andover tornado right? If so The CIPS analogs do include some very powerful tornadoes.

[Janie2006]

I've got my eyes peeled for this one. Well, not literally because that would be extremely painful.

I don't like how this is shaping up. Dixie Alley tornadoes can be all kinds of crazy, especially along the Hattiesburg-Meridian-Tuscaloosa-Birmingham corridor. I remember one tornado in the 90s that literally flattened Lauderdale county. A community called Zero was reduced to, well, zero. Meridian dodged a bullet on that storm.

[TropicalAnalystwx13]

Models have been varying a lot with regards to the weekend today. The 0z-12z GFS runs brought in timing issues, with the trough hanging back a little longer than yesterday's guidance. If that were to occur, mid-level flow would be weaker and there would not be as much forcing to break the cap and initiate storms. However, the 18z GFS eliminated this issue...

What the 18z GFS didn't waver to is directional shear issues on Sunday. Both 500mb and 850mb winds are nearly directly out of the SW (maybe the LLJ is more SSW), suggesting that instead of isolated supercells like on Saturday, multicell structures and line segments capable of producing damaging winds would be the dominant threat.

Monday looks like a bad day across Dixie Alley (especially Mississippi) if model guidance doesn't change. As the storm moves east, it continues to draw an abundance of moisture (2m dewpoints of 70F?!) and shear continues to be strong. SBCAPE increases to 3000j/kg by 0z Tuesday on the 18z GFS. Similar to Sunday, 850mb winds are more out of the south-southwest instead of the south like on Saturday, but past experience with outbreaks in this area suggests that this kind of setup is actually equally as favorable as southerly 850mb winds. April 27, 2011 had a SSW low-level jet.

[EF-5bigj]

Dixie Alley outbreaks have unique traits we have no lack of moisture down here and we tend to strong LLJ. If there is strong wind sheer then the south will be in trouble our supercells if discrete tend to spin like tops and there is no CAP down here really. Yeah that corridor seems to have a history of violent,long track tornadoes. The most vivid example of that besides the obvious Tuskaloosa tornado was the Limestone county EF-5. Which I've rewatched the coverage of that one it was a monster sadly one of the forgotten EF-5's...

[RL3AO]

12z Euro slowed down a bit. Starting to think Sunday will be more the player.

[TropicalAnalystwx13]

12z Euro slowed down a bit. Starting to think Sunday will be more the player.

Out of all three days (Sat-Mon), Monday looks the most volatile to me. Saturday has a high ceiling if the trough ejects a little faster than models are indicating (like what we saw on yesterday's runs), and a high bust potential if the trough slows down (would mean less forcing/stronger cap). Sunday looks like the tamest day to me; the system fully ejects into the Plains, but shear is unidirectional, leading to messy storm mode.

[TwisterFanatic]

Wording from Tulsa NWS you see VERY seldom.

A MORE SIGNIFICANT RISK OF SEVERE WEATHER WILL COME WHEN THE NEXT
SYSTEM MOVES INTO THE PLAINS OVER THE WEEKEND. THE GREATEST RISK
OF SEVERE WEATHER WILL BE ON SUNDAY... INCLUDING THE POTENTIAL FOR
VERY LARGE HAIL... DAMAGING WINDS AND STRONG TORNADOES.

you'll see them use isolated tornadoes at times, but to see them using strong tornadoes is a eye opener.

[CrazyC83]

I agree, Saturday looks like a high bust potential day.

What about Tuesday in the Southeast, does it stabilize or can we get another day out of it?

[WeatherGuesser]

MESOSCALE DISCUSSION 0393
NWS STORM PREDICTION CENTER NORMAN OK
1242 PM CDT THU APR 24 2014

AREAS AFFECTED...PORTIONS OF CNTRL/SRN MO...FAR SERN KS

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 241742Z - 241915Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...THUNDERSTORMS MAY CONTINUE TO STRENGTHEN AS THEY ADVANCE
EWD ACROSS MO AND FAR SERN KS...POTENTIALLY REQUIRING WW ISSUANCE.

DISCUSSION...CONVECTION CONTINUES TO INTENSIFY AND ORGANIZE IN
ADVANCE OF A STRONG PV MAX CROSSING OK/KS. THE AIR MASS AHEAD OF AN
ASSOCIATED SFC FRONT WILL CONTINUE TO DESTABILIZE AS SLY/SWLY SFC
WINDS SUPPORT THE INFLUX OF MIDDLE/UPPER 50S DEWPOINTS. STEEP
MID-LEVEL LAPSE RATES SAMPLED BY UPSTREAM 12Z OUN/LMN RAOB AND 12Z
SGF RAOB WILL SUPPORT ROBUST UPDRAFTS AND SVR HAIL...ESPECIALLY
GIVEN 40-50 KT OF MID-LEVEL SWLYS SAMPLED BY EAX/SGF VWP DATA. DMGG
WIND GUSTS WILL BECOME OF INCREASING CONCERN IF CONVECTION CAN
SUSTAIN A QUASI-LINEAR MODE ORGANIZATION.

..COHEN/CORFIDI.. 04/24/2014


ATTN...WFO...LSX...SGF...EAX...


May be starting today instead of the 26th.

I'm so tired of all the damage and destruction from these things.