Another multi-day outbreak (April 17-18)

[CrazyC83]

Not much change at 1730Z. It appears to be a complicated setup that could be all or nothing. High bust potential (more typical for June outbreaks) but also high boom potential.

[TwisterFanatic]

If that front draped across Oklahoma shoots north tonight and tomorrow morning, all hell could break loose.

[Ntxw]

If that front draped across Oklahoma shoots north tonight and tomorrow morning, all hell could break loose.

I'm going with the Euro on this that the front will lift to Kansas/Northern Oklahoma. Areas immediately south of that warm front needs to watch for long tracked tornadoes coming from the triple point. Also the northern fringes of the dry line should get interesting as well. One fly in the ointment that could muddle everything is if there is early convection in the day which could waste the instability somewhat.

[TwisterFanatic]

If that front draped across Oklahoma shoots north tonight and tomorrow morning, all hell could break loose.

I'm going with the Euro on this that the front will lift to Kansas/Northern Oklahoma. Areas immediately south of that warm front needs to watch for long tracked tornadoes coming from the triple point. Also the northern fringes of the dry line should get interesting as well. One fly in the ointment that could muddle everything is if there is early convection in the day which could waste the instability somewhat.

Yep.

[CrazyC83]

Based on that last point, I don't see any basis to go up to High Risk on the 0600Z. Maybe later if the convective return isn't an issue...

[Cyclenall]

One fly in the ointment that could muddle everything is if there is early convection in the day which could waste the instability somewhat.

TBH I'm not that concerned with that issue for this, I'm just content that there is no cap because I believe that would have been more problematic. Apparently instability will be very high for this one so it wouldn't make or break everything. Its even possible the early convection could be severe or significant.

Based on that last point, I don't see any basis to go up to High Risk on the 0600Z. Maybe later if the convective return isn't an issue...

A bunch of outbreaks had early morning convection or even late morning so I don't think that aspect would prevent a High Risk upgrade. I was thinking what would cause this MOD to go to HIGH and other than the shear, what could it be? Total model agreement on low ejection and placement?

[Ntxw]

TBH I'm not that concerned with that issue for this, I'm just content that there is no cap because I believe that would have been more problematic. Apparently instability will be very high for this one so it wouldn't make or break everything. Its even possible the early convection could be severe or significant.

A bunch of outbreaks had early morning convection or even late morning so I don't think that aspect would prevent a High Risk upgrade. I was thinking what would cause this MOD to go to HIGH and other than the shear, what could it be? Total model agreement on low ejection and placement?

The problem with early convection is the outflows that essentially flex the front southward. We do not want a further south front, we want a retreating front (warm front). Earlier frontal passage (think NAM) reduces the storms being able to tap into the max heating of the day thus severe linear mode along the cold front is more likely than super cells riding that warm front with long track tornadoes.

A high risk requires very high probabilities and for the margin of error to be larger than typical for confidence. This situation has things that can go wrong (from a standpoint if you're chasing for an outbreak) which puts confidence much lower than your typical high risk scenario. They are also quite often associated with a full negative trough ejecting horizontally out from the Rockies, we are looking at slightly positive to neutral tilt.

This is speaking for the current risk zones of the southern plains, places further east/northeast is a different animal. Watch the warm front, if it progresses well north it we may get a outbreak of it.

[EF-5bigj]

Well it is more favorable for long tracked violent tornadoes then the last event. Will they upgrade it to high risk?

[TwisterFanatic]

Looking at the 0z model package, seems as if the NAM is now the outlier on keeping the warm front south.

[cycloneye]

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT WED APR 17 2013

VALID 171200Z - 181200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF NORTH TX AND OK
TO EASTERN KS/SOUTHWEST MO...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SOUTHERN PLAINS TO THE
LOWER MO VALLEY/MIDWEST...

...SYNOPSIS...
A PROMINENT/NEUTRAL TO SLIGHT POSITIVE-TILT UPPER TROUGH OVER THE
WESTERN CONUS WILL CONTINUE EASTWARD TODAY FROM THE GREAT BASIN/
ROCKIES TO THE HIGH PLAINS...WITH PHASED POLAR/SUBTROPICAL JETS
INCREASINGLY INFLUENCING THE CENTRAL/SOUTHERN PLAINS INTO THIS
AFTERNOON/TONIGHT. SURFACE CYCLOGENESIS IS EXPECTED ACROSS THE
SOUTHERN HIGH PLAINS...WITH AN EASTWARD MIXING DRYLINE ACROSS
NORTHWEST/WEST-CENTRAL TX. NORTHEASTWARD FROM THE SURFACE LOW...A
SURFACE FRONTAL ZONE WILL ONLY MOVE SLOWLY ACROSS OK/NORTHWEST TX
THROUGH THE AFTERNOON...WITH A MUCH MORE AGGRESSIVE NORTHWARD PUSH
AS A WARM FRONT ACROSS THE LOWER MO VALLEY/MIDWEST THROUGH TONIGHT
IN RESPONSE TO LATE PERIOD SURFACE CYCLOGENESIS.

...SOUTHERN PLAINS TO LOWER MO VALLEY/MIDWEST...
WELL-ABOVE TYPICAL GUIDANCE SPREAD CONTINUES INTO THE DAY 1
PERIOD...ACCENTUATED BY A MUCH MORE NORTHWARD AND SEEMINGLY LESS
LIKELY SOLUTION OF THE 00Z GFS AS COMPARED TO THE 00Z NAM/12Z ECMWF.
AMONG OTHER UNCERTAINTIES...THIS IS A FACTOR FOR ONLY MODEST
CONFIDENCE IN SPECIFIC DETAILS LATER TODAY. EVEN SO...POTENTIALLY
WIDESPREAD/MULTI-FACETED SEVERE WEATHER IS LIKELY ESPECIALLY INTO
THIS AFTERNOON/EVENING.

INITIALLY...ELEVATED STRONG/POTENTIALLY SEVERE TSTMS CAPABLE OF HAIL
WILL LIKELY BE ONGOING THIS MORNING ACROSS PORTIONS OF THE
LOWER/MIDDLE MO VALLEY AND ADJACENT MIDWEST. THIS WILL BE IN
ASSOCIATION WITH A STRONG LOW LEVEL JET/WARM ADVECTION REGIME.

FARTHER SOUTH...A MORE WIDESPREAD/SURFACE BASED TSTM THREAT WILL
LIKELY EVOLVE AS EARLY AS THIS AFTERNOON...BUT ESPECIALLY INTO THIS
EVENING/TONIGHT ACROSS THE SOUTHERN PLAINS TO THE LOWER MO VALLEY IN
GENERAL VICINITY OF AFOREMENTIONED FRONTAL ZONE. WHILE NOT
NECESSARILY LIKELY...THERE MAY BE SOME POSSIBILITY THAT TSTMS
DEVELOP RELATIVELY EARLY IN THE AFTERNOON ACROSS PORTIONS OF NORTH
TX INTO EASTERN OK AND PERHAPS EVEN THE OZARKS...AND POTENTIALLY
BECOME SURFACE BASED WITHIN AN INCREASINGLY MOIST/UNINHIBITED
BOUNDARY LAYER. SHOULD THIS OCCUR...DISCRETE SUPERCELLS CAPABLE OF
LARGE HAIL/TORNADOES WOULD BE POSSIBLE.

SURFACE BASED DEVELOPMENT DOES SEEM MORE PROBABLE NEAR THE TRIPLE
POINT VICINITY OF DRYLINE/COMPOSITE FRONT...UNDER THE INFLUENCE OF A
BIT STRONGER HEATING/MASS CONVERGENCE. THIS WOULD BE ACROSS PARTS OF
NORTH-CENTRAL/NORTHWEST TX INTO SOUTHWEST/SOUTH-CENTRAL OK.
ESPECIALLY GIVEN AN INTENSIFYING LOW LEVEL JET TOWARD/AFTER
DARK...POTENTIAL WOULD EXIST FOR LARGE HAIL AND PERHAPS A FEW STRONG
TORNADOES ACROSS THIS REGION.

OTHERWISE...STORMS ARE EXPECTED TO INCREASE AFTER DARK IN VICINITY
OF THE SOUTH-SOUTHWEST TO NORTH-NORTHEAST ORIENTED FRONTAL ZONE
ACROSS OK INTO THE LOWER MO VALLEY AND EVENTUALLY MIDDLE MS VALLEY
MIDWEST. SOME POTENTIAL FOR SURFACE BASED TSTMS/SUPERCELLS AND
ASSOCIATED DAMAGING WIND/TORNADO POTENTIAL WILL EXIST MAINLY THROUGH
THE EVENING IMMEDIATELY NEAR THE FRONT...BUT THERE WILL LIKELY BE A
TENDENCY FOR UPDRAFTS TO BE UNDERCUT BY THE NOCTURNALLY
SOUTH/SOUTHEASTWARD-ACCELERATING COLD FRONT. AS SUCH...LARGE HAIL
MAY BECOME THE MOST PROBABLE/MORE WIDESPREAD CONCERN ACROSS THE
REGION.

...TN VALLEY TO CENTRAL/SOUTHERN APPALACHIANS...
AT LEAST ISOLATED TO WIDELY SCATTERED TSTMS ARE EXPECTED TO
DIURNALLY INCREASE THIS AFTERNOON ACROSS THE REGION. WHILE FORCING
ON THE LARGE SCALE WILL BE MODEST AND MID-LEVEL LAPSE RATES/VERTICAL
SHEAR WILL BE WEAK...STEEPENING LOW LEVEL LAPSE RATES DURING THE
AFTERNOON MAY CONTRIBUTE TO SOME POTENTIAL FOR EPISODIC BOUTS OF
LOCALLY DAMAGING WINDS/HAIL.

..GUYER/MOSIER.. 04/17/2013

[Ntxw]

As far as frontal position goes the lonely NAM is proving to be correct this morning. It is not along the KS/OK border and western Oklahoma is under northerly flow behind the front, no more retreating of it there. Far eastern Oklahoma, adjacent Arkansas and Missouri will however see the warm front advance. The dry line will likely be displaced and cutoff to the south. Best storms will likely form and jumble along the warm front line sw to ne.

[cycloneye]

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0738 AM CDT WED APR 17 2013

VALID 171300Z - 181200Z

...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING OVER
MUCH OF OK...SOUTHEAST KS...WESTERN NORTH TX...AND FAR WESTERN MO...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SOUTHERN PLAINS INTO
THE MID MS VALLEY...

...FOCUSED AREA OF SIGNIFICANT SEVERE THUNDERSTORM AND TORNADO
POTENTIAL IS EXPECTED TODAY...

...OK/WESTERN NORTH TX/SOUTHEAST KS...
THE MORNING SURFACE ANALYSIS SHOWS A WARM FRONT EXTENDING FROM
SOUTHWEST TO NORTHEAST OK. THIS BOUNDARY IS RAPIDLY RETREATING
NORTHWARD AND IS EXPECTED TO LIE ROUGHLY FROM WEST-CENTRAL OK INTO
SOUTHEAST KS BY MID AFTERNOON. RICH LOW LEVEL MOISTURE SOUTH OF THE
BOUNDARY WILL COMBINE WITH AMPLE DAYTIME HEATING TO YIELD AFTERNOON
MLCAPE VALUES OF 3000+ J/KG OVER MOST OF THE SOUTHEAST HALF OF OK
AND SOUTHEAST KS.

VARIOUS MODEL SOLUTIONS CONTINUE TO STRUGGLE WITH SHORT-TERM DETAILS
OF CONVECTIVE POTENTIAL. THIS APPEARS TO BE DUE TO HANDLING OF
SUBTROPICAL SHORTWAVE SEEN IN WATER VAPOR IMAGERY OVER SOUTHERN NM.
LARGE SCALE FORCING FOR ASCENT WILL OVERSPREAD OK THROUGHOUT THE DAY
IN ADVANCE OF THIS SYSTEM...BUT IT APPEARS THAT 700MB TEMPERATURES
APPROACHING 10C WILL SUPPRESS SIGNIFICANT CONVECTION OVER
WESTERN/CENTRAL OK UNTIL THIS AFTERNOON WHEN PERSISTENT LIFT AND
STRONG HEATING WILL WEAKEN THE CAP IN VICINITY OF THE DRYLINE.

PRESENT INDICATIONS ARE THAT ISOLATED THUNDERSTORMS WILL DEVELOP BY
LATE AFTERNOON ALONG THE DRYLINE IN SOUTHWEST OK AND WESTERN NORTH
TX...AND ALONG THE STALLED BOUNDARY EXTENDING ACROSS NORTH CENTRAL
OK INTO SOUTHEAST KS. VERTICAL SHEAR PROFILES WILL BE QUITE STRONG
THROUGHOUT THIS AREA WITH 0-3KM SRH VALUES EXCEEDING 300 M2/S2 AND
STRONG EFFECTIVE SHEAR. DISCRETE SUPERCELL STORMS ARE EXPECTED WITH
A RESULTANT RISK OF VERY LARGE HAIL AND A FEW STRONG TORNADOES.
THESE STORMS ARE EXPECTED TO TRACK NORTHEASTWARD ALONG AND SOUTH OF
THE SURFACE BOUNDARY INTO NORTHEAST OK AND EVENTUALLY WESTERN MO
THIS EVENING.

...MO/IL...
STRENGTHENING SOUTHERLY LOW LEVEL WINDS ARE FORECAST ACROSS MUCH OF
MO/IL TODAY...WITH MODERATE CAPE VALUES ALREADY IN PLACE. OTHER
THAN LOW LEVEL WARM ADVECTION...LARGE SCALE FORCING MECHANISMS ARE
SUBTLE. NEVERTHELESS...STEEP MID LEVEL LAPSE RATES AND SUFFICIENT
EFFECTIVE SHEAR WILL POSE A CONDITIONAL RISK OF HAIL IN THOSE STORMS
THAT CAN DEVELOP TODAY.

...MO/KS/OK/NORTH TX OVERNIGHT...
THE MAIN UPPER TROUGH IS EXPECTED TO SWING EASTWARD INTO THE PLAINS
LATE TONIGHT...RESULTING IN A LARGE SQUALL LINE AFFECTING EASTERN
KS...CENTRAL/EASTERN OK...WESTERN MO...AND NORTH TX. IT APPEARS
LIKELY THAT THESE STORMS WILL POSE A RISK OF RATHER WIDESPREAD
DAMAGING WINDS THROUGH 12Z.

...TN VALLEY TO CENTRAL/SOUTHERN APPALACHIANS...
AT LEAST ISOLATED TO WIDELY SCATTERED TSTMS ARE EXPECTED TO
DIURNALLY INCREASE THIS AFTERNOON ACROSS THE REGION. WHILE FORCING
ON THE LARGE SCALE WILL BE MODEST AND MID-LEVEL LAPSE RATES/
VERTICAL SHEAR WILL BE WEAK...STEEPENING LOW LEVEL LAPSE RATES
DURING THE AFTERNOON MAY CONTRIBUTE TO SOME POTENTIAL FOR EPISODIC
BOUTS OF LOCALLY DAMAGING WINDS/HAIL.

..HART/GARNER.. 04/17/2013

[wx247]

New outlook has expanded the significant tornado potential:

[CrazyC83]

ZCZC SPCPWOSPC ALL
WOUS40 KWNS 171132
KSZ000-MOZ000-OKZ000-TXZ000-171800-

PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0632 AM CDT WED APR 17 2013

...SEVERE THUNDERSTORMS ARE EXPECTED OVER PARTS OF THE
SOUTHERN/CENTRAL PLAINS LATER TODAY AND TONIGHT...

THE NWS STORM PREDICTION CENTER IN NORMAN OK IS FORECASTING THE
DEVELOPMENT OF TORNADOES...LARGE HAIL AND DAMAGING WINDS OVER PARTS
OF THE SOUTHERN/CENTRAL PLAINS LATER TODAY AND TONIGHT.

THE AREAS MOST LIKELY TO EXPERIENCE THIS ACTIVITY INCLUDE

SOUTHEASTERN KANSAS
FAR WESTERN MISSOURI
MUCH OF OKLAHOMA
FAR NORTHERN TEXAS

ELSEWHERE...SEVERE STORMS ARE ALSO POSSIBLE FROM CENTRAL TEXAS INTO
ILLINOIS.

WARM MOIST AND UNSTABLE AIR AT THE SURFACE WILL ADVANCE NORTHWARD
INTO OKLAHOMA...MISSOURI...AND KANSAS LATER THIS AFTERNOON AS
SOUTHERLY WINDS STRENGTHEN IN ADVANCE OF AN UPPER DISTURBANCE OVER
THE WESTERN UNITED STATES. SCATTERED TO NUMEROUS THUNDERSTORMS WILL
FORM THIS AFTERNOON AND NIGHT ALONG THE LEADING EDGE OF THIS
UNSTABLE AIRMASS FROM CENTRAL OKLAHOMA INTO EASTERN KANSAS AND
WESTERN MISSOURI. THESE STORMS WILL BE CAPABLE OF PRODUCING VERY
LARGE HAIL...DAMAGING WINDS...AND A COUPLE OF TORNADOES. FARTHER
SOUTH OVER SOUTHERN PORTIONS OF OKLAHOMA AND NORTHERN
TEXAS...ISOLATED THUNDERSTORM DEVELOPMENT IS EXPECTED TO OCCUR
DURING THE LATE AFTERNOON AND EVENING. THE COMBINATION OF STRONG
INSTABILITY AND INCREASING WINDS ALOFT WILL RESULT IN A THREAT FOR
VERY LARGE HAIL AND A FEW TORNADOES...SOME OF WHICH MAY BE STRONG.
DURING THE OVERNIGHT...STORMS ACROSS THE ENTIRE REGION WILL MERGE
INTO A SQUALL LINE WITH A CONTINUED THREAT FOR DAMAGING WINDS AND
ISOLATED TORNADOES.

STATE AND LOCAL EMERGENCY MANAGERS ARE MONITORING THIS DEVELOPING
SITUATION. THOSE IN THE THREATENED AREA ARE URGED TO REVIEW SEVERE
WEATHER SAFETY RULES AND TO LISTEN TO RADIO...TELEVISION...AND NOAA
WEATHER RADIO FOR POSSIBLE WATCHES...WARNINGS...AND STATEMENTS LATER
TODAY.

..GARNER/HART.. 04/17/2013

$$

[CrazyC83]

Meet the new look watches! Probs 60/40.

SEL4

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 114
NWS STORM PREDICTION CENTER NORMAN OK
1110 AM CDT WED APR 17 2013

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* TORNADO WATCH FOR PORTIONS OF
WEST CENTRAL ILLINOIS
EXTREME EASTERN KANSAS
WESTERN AND CENTRAL MISSOURI

* EFFECTIVE THIS WEDNESDAY MORNING THROUGH THIS EVENING FROM 1110 AM
UNTIL 1000 PM CDT.

* PRIMARY THREATS INCLUDE...
SEVERAL INTENSE TORNADOES POSSIBLE
SEVERAL LARGE HAIL EVENTS WITH A FEW VERY LARGE HAIL EVENTS TO
2.5 INCHES IN DIAMETER POSSIBLE
SEVERAL DAMAGING WIND GUSTS TO 70 MPH POSSIBLE

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 110 STATUTE
MILES EAST AND WEST OF A LINE FROM 65 MILES NORTH NORTHEAST OF
COLUMBIA MISSOURI TO 25 MILES SOUTH OF MONETT MISSOURI. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU4).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 113...

DISCUSSION...THUNDERSTORM DEVELOPMENT IS EXPECTED TO RAPIDLY
INCREASE IN COVERAGE THIS AFTERNOON...POSSIBLY INCLUDING AN EVOLVING
MESOSCALE CONVECTIVE SYSTEM...IN ADDITION TO DISCRETE SUPERCELLS.
THE ENVIRONMENT...PARTICULARLY ACROSS PARTS OF WESTERN INTO CENTRAL
MISSOURI MAY BECOME INCREASINGLY CONDUCIVE TO A STRONG TORNADO OR
TWO...IN ADDITION TO THE RISK FOR LARGE HAIL AND DAMAGING WIND
GUSTS.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
500. MEAN STORM MOTION VECTOR 23035.


...KERR

[wx247]

Here we go again... new watch wording is interesting.

Of greater concern to me (since I live in the watch) is very lengthy duration. This is longer than normal.

[CrazyC83]

Here we go again... new watch wording is interesting.

Of greater concern to me (since I live in the watch) is very lengthy duration. This is longer than normal.

Not to mention on the southwest corner, and a higher-number, possibly PDS, watch is likely to be issued for Oklahoma this afternoon.

[CrazyC83]

1630Z is delayed a bit - upgrade to High Risk being discussed? Usually when they are delayed there are internal discussions and disagreements. Personally, I would hold off...but mention upgrade possible at 2000Z.

[wx247]

1630Z is delayed a bit - upgrade to High Risk being discussed? Usually when they are delayed there are internal discussions and disagreements. Personally, I would hold off...but mention upgrade possible at 2000Z.

I don't see a high risk forthcoming, but an expanded and more aggressive moderate one is likely.

[CrazyC83]

1630Z: little change in categories in the main threat area, secondary Slight Risk area in TN/KY