Severe Outbreak for May 18-19-20-21 (Watches-Warnings)

[cycloneye]

Let's see what this outbreak brings.

Moderate Risk for May 18


DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT FRI MAY 17 2013

VALID 181200Z - 191200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF NWRN KS/SWRN
NEB...

...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM
EXTREME NWRN TX INTO SERN ND/NWRN MN...

...PLAINS...

LATEST MODEL GUIDANCE IS IN GENERAL AGREEMENT REGARDING THE
EVOLUTION OF UPPER TROUGH AS IT PROGRESSES ACROSS THE WRN U.S. INTO
THE HIGH PLAINS LATE IN THE PERIOD. OF PARTICULAR CONCERN IS THE
EXPECTED INCREASE IN MID LEVEL FLOW INTO THE HIGH PLAINS ATOP AN
INCREASINGLY MOIST/BUOYANT AIRMASS. LATEST SATELLITE IMAGERY
DEPICTS EXTENSIVE LOW CLOUDS ACROSS OK WITH A DECIDEDLY ELY LOW
LEVEL COMPONENT WITHIN THE BOUNDARY LAYER. THIS CLOUDINESS WILL BE
STUBBORN TO ERODE DURING THE DAY1 PERIOD AND IN THE ABSENCE OF
MEANINGFUL THUNDERSTORM ACTIVITY ACROSS THE SRN/CNTRL PLAINS THROUGH
SATURDAY MORNING ABUNDANT LOW LEVEL MOISTURE SHOULD RAPIDLY RETURN
ACROSS KS INTO NEB SATURDAY.

LATEST THINKING IS WARM ADVECTION MAY DRIVE A BOUT OF EARLY MORNING
CONVECTION ACROSS PARTS OF THE ERN DAKOTAS BENEATH MODEST LLJ.
WHILE THIS ACTIVITY MAY PRODUCE SOME HAIL...IT SHOULD SPREAD EWD
INTO THE UPPER MS VALLEY DURING THE MID DAY HOURS AS A WEAK BRANCH
OF THE LLJ FOCUSES INTO THIS REGION.

LATEST SHORT RANGE MODEL GUIDANCE INSISTS STRONG HEATING WILL OCCUR
ACROSS SERN CO INTO NWRN TX. THIS SHOULD ALLOW DRYLINE TO MIX TO A
POSITION NEAR THE OK BORDER...ARCING NWWD TO A SFC LOW OVER WRN KS
BY 19/00Z. WITH SFC DEW POINTS EXPECTED TO RISE WELL INTO THE
MID-UPPER 60S EAST OF THE DRYLINE...EXTREME INSTABILITY MAY DEVELOP
ALONG A CORRIDOR FROM WRN OK INTO NWRN KS WHERE SBCAPE COULD EXCEED
4000 J/KG. AS TEMPERATURES WARM INTO THE LOWER 90S ACROSS THE TX
PANHANDLE INTO SWRN KS INHIBITION WILL BE NEGATED AND DISCRETE
SUPERCELL STRUCTURES ARE EXPECTED TO DEVELOP. HAVE INCREASED THE
SEVERE PROBS ACROSS PORTIONS OF KS/NEB AS THIS PORTION OF THE CNTRL
PLAINS SHOULD EXPERIENCE STRONGER DEEP LAYER SHEAR...POTENTIALLY
SUPPORTIVE OF TORNADOES. LATEST 12Z NAM FORECAST SOUNDINGS STRONGLY
SUPPORT SUPERCELLS ACROSS THE MDT RISK REGION WITH SBCAPE IN EXCESS
OF 4000 J/KG WITH SFC-6KM SHEAR ON THE ORDER OF 40KT.
ADDITIONALLY...VERY LARGE HAIL MAY ACCOMPANY ANY SUPERCELLS THAT
DEVELOP SATURDAY. LATEST FORECAST HAIL ALGORITHMS SUGGEST HAIL
COULD EASILY EXCEED BASEBALL SIZE WITH ORGANIZED ACTIVITY.

SOMEWHAT WEAKER DEEP LAYER FLOW ACROSS THE SRN PLAINS MAY LIMIT
OVERALL SEVERE THREAT AND FOR THIS REASON HAVE ONLY EXTENDED 15
PERCENT THREAT INTO PORTIONS OF NWRN TX.

...TN VALLEY/CNTRL GULF STATES...

WEAKENING UPPER TROUGH WILL TRANSLATE INTO THE MIDDLE TN VALLEY/NRN
GULF STATES SATURDAY. MODEST NWLY FLOW ALONG BACKSIDE OF THIS
FEATURE MAY PROVIDE ENOUGH SHEAR FOR ORGANIZED MULTI-CELL UPDRAFTS
CAPABLE OF PRODUCING SOME HAIL/WIND. THIS ACTIVITY SHOULD BE
MODULATED BY DIURNAL HEATING AND SHOULD WEAKEN WITH AFTER SUNSET.

..DARROW.. 05/17/2013

[cycloneye]

DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0240 PM CDT FRI MAY 17 2013

VALID 172000Z - 181200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF TX...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN
PLAINS...

...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE CNTRL GULF
STATES...

CORRECTED FOR SIG HAIL LINE

...TX...

HAVE OPTED TO INTRODUCE 10 PERCENT SIG HAIL THREAT TO PORTIONS OF TX
AND EXPAND THE CATEGORICAL SLGT NORTH AND EAST TOWARD THE WRN PARTS
OF NCNTRL TX.

LATEST HIGH RES MODEL GUIDANCE HAS TRENDED TOWARD SCATTERED TSTM
DEVELOPMENT ALONG THE DRYLINE FROM EAST OF SJT TO NW OF MWL OVER THE
NEXT FEW HOURS. LATEST VIS IMAGERY SUPPORTS THIS EVOLUTION WITH
DEEPENING CU FIELD OVER MCCULLOCH COUNTY AND NEW CU OVER SHACKELFORD
COUNTY NE OF ABI. WITH SFC TEMPERATURES AROUND 103F AT BOTH ABI AND
SJT...AND WITH DEW POINTS NEAR 70 EAST OF THE DRYLINE...IT APPEARS
TSTMS WILL DEVELOP SHORTLY. EXTREME SBCAPE...ON THE ORDER OF 4000
J/KG...AND MODEST DEEP LAYER SHEAR SUGGEST VERY LARGE HAIL MAY
ACCOMPANY THESE STORMS. ADDITIONALLY...STRONG DOWNBURSTS COULD BE
OBSERVED GIVEN THE TEMP/DEW POINT SPREADS.

[CrazyC83]

Looks quite ominous to say the least. Luckily farther north than Wednesday's outbreak, but this could be much more widespread. Sunday and Monday look bigger, and it might go as long as Wednesday or Thursday...

[Cyclenall]

Every day since this last Wednesday this week has had at least 1 tornado, the active tornado pattern begins. These days have massive potential to over-perform and make up for lost time (you know the word by now ). I don't want the tornadoes to occur at night though, I'm getting tired of that now plus it puts more lives in danger.

Ground zero tomorrow looks to be south-central Kansas and specifically Pratt county. 0-3km EHI is over 20 there which is . Amazing potential for tornadoes and extremely large hail, me thinks between cantaloupe and small watermelon size is within reach.

[cheezyWXguy]

Every day since this last Wednesday this week has had at least 1 tornado, the active tornado pattern begins. These days have massive potential to over-perform and make up for lost time (you know the word by now ). I don't want the tornadoes to occur at night though, I'm getting tired of that now plus it puts more lives in danger.

Ground zero tomorrow looks to be south-central Kansas and specifically Pratt county. 0-3km EHI is over 20 there which is . Amazing potential for tornadoes and extremely large hail, me thinks between cantaloupe and small watermelon size is within reach.

Are...are you serious? How often in the past has watermelon sized hail ever fallen?

[CrazyC83]

Tomorrow may not be the greatest tornado day, since shear isn't terribly high. However, EXTREMELY large hail is likely (size of softballs or larger), along with some tornadoes (a strong tornado or two cannot be ruled out).

IMO, the initial D1 should be 60H hail, 10H tornado, 30 wind

[Cyclenall]

Are...are you serious? How often in the past has watermelon sized hail ever fallen?

Extremely rare, but if there is a day it happens its tomorrow with parameters like that. Obviously the highest end potential would be record territory but something a little bigger than softballs is what I'm getting at. The NWS offices' text is just referring to softball size for now.

[TropicalAnalystwx13]

NOW TO THE TORNADO THREAT -- THERE IS REASON FOR GREAT
CONCERN ABOUT THE POSSIBILITY FOR LONG-LIVED, SIGNIFICANT TORNADOES
IN AN ENVIRONMENT THAT IS CHARACTERIZED BY SURFACE-BASED CAPE IN THE
3500-4500 J/KG RANGE ALONG WITH 0-1KM AGL HELICITY RAMPING UP TO THE
300-400 J/KG RANGE AS WELL (THANKS TO THE DYNAMIC LOW LEVEL JET THAT
DEVELOPS JUST AFTER SUNSET). THIS IS A TREMENDOUS AMOUNT OF
POTENTIAL ENERGY BOTH FROM KINEMATICS AND THERMODYNAMICS TO SUPPORT
EXTREMELY STRONG LOW LEVEL ROTATION IN SUPERCELL
THUNDERSTORMS...INCLUDING LONG-LIVED AND STRONG TORNADOES THAT
THRIVE DURING THE POST-SUNSET HOURS. THERE MAY ONLY BE ONE OR TWO
STORMS THAT THRIVE AFTER SUNSET...BUT THE DAMAGE POTENTIAL COULD BE
GREAT FROM JUST ONE ISOLATED SUPERCELL STORM. EVENTUALLY DURING THE
03-06Z TIME FRAME...THE NOCTURNAL BOUNDARY LAYER COOLING WILL BE
SUFFICIENT ENOUGH TO LESSEN THE TORNADO THREAT...AND SUPERCELL
STORMS MAY DISSOLVE ALL TOGETHER BY 05 OR 06Z AS THE STORMS MOVE
TOWARD CENTRAL OR SOUTH-CENTRAL KANSAS. - Dodge City, KS NWS

[cycloneye]

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0803 PM CDT FRI MAY 17 2013

VALID 180100Z - 181200Z

...THERE IS A SLGT RISK OF SVR TSTMS CNTRL AL...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN
PLAINS...

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS OF CNTRL AND N-CNTRL
TX...

...NERN WY EASTWARD INTO ERN SD...
SEVERAL CLUSTERS OF STRONG-SEVERE STORMS LOCATED TO THE N-NW-W OF
THE BLACK HILLS AND OVER THE NEB SANDHILLS AND ADJACENT SD THIS
EVENING WILL CONTINUE TO POSE A MAINLY LARGE HAIL/SEVERE WIND GUST
THREAT THIS EVENING. THE 00Z/18 RAP RAOB EXHIBITED A MORE THAN
ADEQUATE DEEP LAYER SHEAR PROFILE FOR STORM ORGANIZATION...INCLUDING
BOWING SEGMENTS AND SUPERCELLS. AS A SURFACE LOW DEVELOPS EWD
TONIGHT FROM NERN WY INTO WRN SD ...AN INTENSIFYING LLJ/WAA OVER THE
CNTRL-NRN PLAINS WILL BECOME MORE FAVORABLE FOR UPSCALE GROWTH FOR
EXISTING CONVECTION. SUBJECTIVE SURFACE MESOANALYSIS PLACES A
FRONTAL ZONE DRAPED EWD ACROSS SRN SD INTO NRN IA. AS A
WELL-DEFINED MCV LOCATED S-CNTRL SD TRACKS EWD ALONG THIS
BOUNDARY...A PERSISTENT THREAT FOR LARGE HAIL/DMGG WIND GUSTS WILL
PROBABLY CONTINUE INTO THE OVERNIGHT IN AREAS DOWNSTREAM ACROSS
PORTIONS OF NRN NEB AND SD.

...PARTS OF AL/MS...
REMNANT MID LEVEL CIRCULATION LOCATED OVER THE LOWER OH/TN VALLEYS
WILL CONTINUE TO FOCUS A BELT OF STRONGER LOW LEVEL FLOW FROM THE
CNTRL GULF COAST THROUGH MUCH OF AL. A STREAMLINE ANALYSIS SHOWS
LOW LEVEL DIFFLUENCE OVER THE LOWER MS VALLEY...SUGGESTIVE OF ANY
REGENERATIVE ACTIVITY WILL FAVOR THE AL/MS BORDER AND LOCALES E.
THE 00Z/18 BMX RAOB SHOWED A RATHER MOIST PROFILE /PW 1.75 IN./
CO-LOCATED WITH A SUFFICIENTLY ENLARGED HODOGRAPH THAT WILL PROBABLY
CONTINUE TO SUPPORT STORM ORGANIZATION...CAPABLE PRIMARILY OF A
LOCALLY DMGG WIND THREAT.

...PORTION OF N-CNTRL AND CNTRL TX...
RADAR MOSAIC SHOWS A FEW DISCRETE SUPERCELLS OVER WRN N-CNTRL TX AND
CNTRL TX EARLY THIS EVENING. DESPITE A LESS THAN IDEAL SETUP FOR
STORM PERSISTENCE OWING MAINLY TO LITTLE IF ANY LARGE SCALE SUPPORT
ALOFT...A VERY STEEP RATE ENVIRONMENT SAMPLED BY THE 00Z/18 FWD/MAF
RAOBS WITHIN A MOISTURE RICH LOW LEVEL ENVIRONMENT WILL BE FAVORABLE
FOR AT LEAST A SHORT-TERM THREAT FOR LARGE TO VERY LARGE HAIL.
NOCTURNAL COOLING AND INCREASING CINH WILL GRADUALLY ACT TO WEAKEN
THE STORMS AS NEAR-SURFACE INFLOW PARCELS BECOME LESS ABLE TO REACH
THE LFC. UNTIL THEN...A BRIEF WINDOW FOR LOW LEVEL MESOCYCLONES TO
PRODUCE A TORNADO MAY BE REALIZED.

..SMITH.. 05/18/2013

[RL3AO]

Had a lonely supercell pop up in SW Minnesota today which spun up a quick tornado. I was quite surprised to see a tornado warning crawling on the bottom of the tv.

[cycloneye]

MESOSCALE DISCUSSION 0673
NWS STORM PREDICTION CENTER NORMAN OK
0728 PM CDT FRI MAY 17 2013

AREAS AFFECTED...NE WYOMING..SE MONTANA...WRN AND CENTRAL SOUTH
DAKOTA

CONCERNING...SEVERE THUNDERSTORM WATCH 167...

VALID 180028Z - 180200Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 167
CONTINUES.

SUMMARY...TSTMS ARE EXPECTED TO PERSIST FOR THE NEXT FEW HOURS
ACROSS PORTIONS OF WRN SOUTH DAKOTA AND ERN WYOMING...WITH LARGE
HAIL AND ISOLATED DAMAGING WINDS THE PRIMARY CONCERNS.
ADDITIONALLY...A NEW WW MAY BE REQUIRED DOWNSTREAM OF WW167 ACROSS
PORTIONS OF CENTRAL SOUTH DAKOTA WITHIN THE HOUR.

DISCUSSION...AT 00 UTC...A CLUSTER OF TSTMS WAS ONGOING ACROSS
PORTIONS OF SWRN SOUTH DAKOTA AND NWRN NEBRASKA. THESE TSTMS WERE
MOVING ENE AND LOCATED IN AN ENVIRONMENT CHARACTERIZED BY DEEP-LAYER
SHEAR AOA 35 KTS AND MLCAPE VALUES AROUND 1000 J/KG. THIS
ENVIRONMENT SHOULD PERSIST THROUGH THE NEXT FEW HOURS AND SUPPORT AN
ONGOING SVR THREAT. FARTHER E...THE ENVIRONMENT APPEARS TO BE
CONDUCIVE FOR THE MAINTENANCE OF THE ONGOING TSTMS AS THEY MOVE ENE
OUT OF WW167. FURTHERMORE...RECENT RADAR TRENDS SUGGEST THE
POSSIBILITY OF A DEVELOPING MCV ACROSS BENNETT AND JACKSON COUNTIES
IN SOUTH DAKOTA WHICH SHOULD HELP MAINTAIN TSTM INTENSITY...AT LEAST
IN THE SHORT TERM. THIS WOULD SUGGEST THE NEED FOR A NEW WW
DOWNSTREAM OF WW167. THE PRIMARY CONCERN WITH ANY NEW WATCH WOULD
CONTINUE TO BE LARGE HAIL AND ISOLATED DAMAGING WIND GUSTS.

TO THE NW...ACROSS NE WYOMING AND WEST-CENTRAL SOUTH DAKOTA...TSTMS
ARE EXPECTED TO PERSIST FOR THE NEXT FEW HOURS. ALTHOUGH THE
ENVIRONMENT IS NOT AS FAVORABLE HERE AS TO THE SOUTHEAST...IT SHOULD
REMAIN CONDUCIVE FOR THE CONTINUATION OF AN ISOLATED SVR
THREAT...WITH LARGE HAIL AND ISOLATE DAMAGING WIND GUSTS THE PRIMARY
CONCERNS.

..MARSH/GUYER.. 05/18/2013

[cycloneye]

This is Dr Greg Forbes Torcon update:

Saturday, May 18

Start of a severe weather outbreak. Scattered severe thunderstorms and tornadoes in north-
central OK, west and central KS, west and central NE, central and east SD, southeast ND,
west-central and northwest MN.

TOR:CON -
KS northwest - 5
KS southwest, central - 4
MN west-central, northwest - 2
ND southeast - 2
NE southwest - 5
NE northwest - 3
NE central - 4
OK northwest - 4
OK southwest - 2 or less
SD south-central - 3
SD north-central, northeast - 2 to 3
TX northwest near Abilene, Wichita Falls - 2 or less
other areas - less than 2

Sunday, May 19

Severe weather and tornado outbreak. Severe thunderstorms and tornadoes in east half NE, IA,
north and west MO, east half KS, central and northeast OK, extreme north-central TX near Wichita
Falls-Gainesville, extreme east SD, central and south MN, west and north-central WI.

TOR:CON -
IA west, central - 7
IA east - 4 to 5
KS east - 6
MN south - 4 to 5
MN central - 3
NE east - 4 to 5
OK north-central, northeast - 5
OK south-central - 3 or less
SD east - 4 to 5
TX north-central near Wichita Falls, Gainesville - 3 or less
WI west, north-central - 3
other areas - less than 2

Sunday night/overnight: The severe thunderstorm threat will likely continue overnight in the east half of OK, northwest
AR, west, central, and northeast MO, IA, north and west-central IL, south MN, south and west-
central WI. TOR:CON - 3 after midnight in these areas

Monday, May 20

Severe weather outbreak continues. Severe thunderstorms and tornadoes in southeast MN, central
and south WI, eastern upper peninsula MI, lower peninsula MI, northwest OH, north and central
IN, north and central IL, east IA, northeast, central, southwest MO, southeast KS, northeast
and central OK.

The severe threat continues overnight
in east IA, north IL, northeast OK, northwest AR, MO including southeast after midnight.

TOR:CON -
IA east - 4
IL north - 5
IL south - 3
IN north - 4
KS southeast - 4
MI lower - 4
MI eastern upper - 3
MN southeast - 3
MO northeast, central, south - 4
OH extreme northwest - 3
OK central, northeast - 5
WI central - 3 to 4
WI south - 4 to 5
other areas - less than 2

[CrazyC83]

Key questions:

* For Saturday, I don't see a High Risk at this point. But how high will they go with threats, especially the tornado threat? 10H or 15H seem most likely. The Moderate Risk would surely be for hail as well if not tornadoes.

* Moderate Risk for Day 2 is likely IMO, and Day 3 (Monday) maybe as well?

[TwisterFanatic]

Day 1 - Saturday - 10% Hatched Tornado Area



DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CDT SAT MAY 18 2013

VALID 181200Z - 191200Z

...THERE IS A MDT RISK OF SVR TSTMS FOR PARTS OF WRN OK AND WRN
KS...

...THERE IS A SLGT RISK OF SVR TSTMS FOR A LARGE PORTION OF THE
PLAINS STATES...

...AN ACTIVE SEVERE WEATHER DAY IS EXPECTED OVER A LARGE PORTION OF
THE PLAINS. LARGE DESTRUCTIVE HAIL AND THE POSSIBILITY FOR A FEW
STRONG TORNADOES ARE THE MAIN THREATS...

...SYNOPSIS...
INCREASING CYCLONIC MID-UPPER FLOW WILL OVERSPREAD MUCH OF THE
PLAINS THROUGH THE DAY 1 PERIOD DOWNSTREAM OF AN APPROACHING LARGER
SCALE WRN U.S. TROUGH. THE PRIMARY UPPER TROUGH AXIS WILL MOVE FROM
THE GREAT BASIN TO THE CNTRL ROCKIES-SRN HIGH PLAINS BY SUNDAY
MORNING. AN ELONGATED LEE TROUGH WILL CONSOLIDATE INTO A LOW
FORECAST INVOF THE ERN CO/WRN KS BORDER BY 00Z/19. A MOISTURE RICH
RESERVOIR OVER THE SRN PLAINS WILL CONTINUE TO BE DRAWN NWWD INTO
PORTIONS OF THE CNTRL HIGH PLAINS E OF A SHARPENING DRYLINE BY
AFTERNOON. SEVERE STORMS ARE EXPECTED TO DEVELOP DURING THE
AFTERNOON-EVENING HOURS WITH SOME OF THESE STORMS CONTINUING WELL
AFTER DARK.

...PLAINS...
FRIDAY EVENING WATER VAPOR IMAGERY SHOWS A LEAD SHORTWAVE TROUGH
OVER SRN NM AND THIS FEATURE IS FORECAST TO MOVE INTO CNTRL KS-OK BY
EARLY-MID AFTERNOON. DESPITE IMPLIED SUBSIDENCE IN ITS WAKE...THE
APPROACH OF THE LARGER SCALE TROUGH AND ASSOCIATED HEIGHT FALLS
/FORCING FOR ASCENT/ WILL OVERSPREAD THE HIGH PLAINS DURING THE
AFTERNOON-EVENING. BENEATH THE STOUT EML...HIGH QUALITY BOUNDARY
LAYER MOISTURE SAMPLED BY RAOBS OVER THE SRN PLAINS FRIDAY EVENING
/15-16 G/KG 100MB MEAN MIXING RATIO/...WILL LEAD TO DEWPOINTS
RANGING FROM THE LOWER 60S OVER THE DAKOTAS TO THE UPPER 60S AND
LOWER 70S FARTHER S OVER OK/KS BY MID AFTERNOON. STRONG DIABATIC
HEATING ALONG THE DRYLINE WILL CONSIDERABLY WEAKEN AN INITIALLY
STOUT CAP BY MID-LATE AFTERNOON. VERY STEEP MID LEVEL LAPSE RATES
IN EXCESS OF 8-9 DEG C/KM IN COMBINATION WITH THIS RICH MOISTURE
WILL CONTRIBUTE TO MODERATE INSTABILITY OVER PARTS OF THE NRN PLAINS
TO EXTREME INSTABILITY /4000-5000 J/KG MLCAPE/ OVER PARTS OF KS INTO
NWRN TX.

ONCE THE CAP IS ERODED IN POCKETS ALONG THE DRYLINE...EXPLOSIVE
UPDRAFTS WILL RAPIDLY BECOME SEVERE AND INITIALLY FAVOR LARGE TO
VERY LARGE HAIL AND DMGG WINDS. SUFFICIENT DEEP LAYER SHEAR
/RANGING FROM AROUND 30 KT FROM NWRN TX TO WELL INTO THE SUPERCELL
RANGE FROM KS NWD/ WILL PROMOTE DISCRETE SUPERCELLS AS THE EARLY
CONVECTIVE MODE. BY THE 00Z-04Z PERIOD...STRONGER LOW LEVEL MASS
RESPONSE IN THE FORM OF A STRENGTHENING LLJ E AND SE OF THE KS/CO
LOW OVER PARTS OF WRN KS AND WRN OK...WILL ACT TO ENLARGE HODOGRAPHS
/200-500 M2/S2 EFFECTIVE SRH/ DURING THIS TIMEFRAME. AS A
RESULT...SUPERCELL TORNADO POTENTIAL APPEARS HIGHEST DURING THE
EVENING WITH PERHAPS A STRONG TORNADO OR TWO OCCURRING. UPSCALE
GROWTH MAY EVENTUALLY OCCUR WITH ANY PERSISTENT OR REGENERATIVE
CLUSTER OF SUPERCELLS WITH A LINGERING OVERNIGHT THREAT FOR A FEW
TORNADOES AND DMGG WINDS.

...SRN APPALACHIANS...
A WEAKENING MID LEVEL TROUGH OVER THE SRN APPALACHIANS VICINITY WILL
LIKELY PROVIDE AN IMPETUS FOR DIURNALLY-DRIVEN STORMS AS SURFACE
HEATING LEADS TO THE POSSIBILITY FOR A FEW STRONG STORMS CAPABLE OF
LOCALLY DMGG WIND. THIS ACTIVITY WILL LIKELY WANE IN INTENSITY BY
THE EVENING AS THE BOUNDARY LAYER STABILIZES.

[TwisterFanatic]

Day 2 - Sunday



DAY 2 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0111 AM CDT SAT MAY 18 2013

VALID 191200Z - 201200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF ECNTRL OK...ERN
KS AND WRN MO...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE GREAT
PLAINS AND LOWER TO MID MO VALLEY...

CORRECTED TO MAKE MINOR WORDING CHANGES

...REGIONAL SEVERE WEATHER OUTBREAK POSSIBLE ACROSS PARTS OF THE SRN
PLAINS...CNTRL PLAINS AND LOWER MO VALLEY...

...SRN AND CNTRL PLAINS/LOWER MO VALLEY...
A NEGATIVELY-TILTED UPPER-LEVEL TROUGH WILL TRANSLATE EWD INTO THE
SRN AND CNTRL PLAINS ON SUNDAY AS A MID-LEVEL JET MOVES EWD THROUGH
THE CENTER OF THE TROUGH. AT THE SFC...A LOW IS FORECAST TO DEEPEN
AND MOVE NEWD FROM CNTRL KS INTO ERN NEB AS A COLD FRONT ADVANCES
SEWD ACROSS ECNTRL KS AND CNTRL OK. SFC DEWPOINTS TO THE EAST OF THE
FRONT SHOULD BE IN THE MID TO UPPER 60S F WITH MODERATE TO STRONG
DESTABILIZATION LIKELY ACROSS THE MODERATE RISK AREA BY MID TO LATE
AFTERNOON. FORECAST SOUNDINGS AROUND MIDDAY SHOW A CAPPING INVERSION
IN PLACE ACROSS MUCH OF THE WARM SECTOR. THE MODELS WEAKEN THE CAP
BY 21Z ALLOWING FOR CONVECTIVE INITIATION ALONG AND AHEAD OF THE
FRONT. STORMS SHOULD FIRST INITIATE IN NRN AND CNTRL KS...QUICKLY
EXPANDING SWD INTO NRN AND CNTRL OK. AS STORM COVERAGE INCREASES
DURING THE EARLY EVENING...A SEVERE PRODUCING MCS MAY ORGANIZE
ACROSS ERN KS AND ECNTRL OK...MOVING ESEWD ACROSS THE MODERATE RISK
AREA.

FORECAST SOUNDINGS BY 21Z SUNDAY AT TULSA...OKLAHOMA CITY AND KANSAS
CITY SHOW STRONG INSTABILITY WITH MLCAPE VALUES OF 2500 TO 3500
J/KG. DEEP LAYER SHEAR IS FORECAST TO INCREASE DURING THE LATE
AFTERNOON ACROSS THE MODERATE RISK AREA AS A MID-LEVEL JET MOVES
INTO THE REGION FROM THE WEST. THIS COMBINED WITH 850 TO 500 MB
LAPSE RATES EXCEEDING 8.0 C/KM SHOULD BE VERY FAVORABLE FOR
SUPERCELLS WITH LARGE HAIL. HAILSTONES OF GREATER THAN 2 INCHES IN
DIAMETER WILL BE POSSIBLE WITH THE MORE INTENSE SUPERCELLS. IN
ADDITION...A LOW-LEVEL JET IS FORECAST TO BECOME FOCUSED BY EARLY
SUNDAY EVENING FROM SW MO SWWD INTO ECNTRL OK. SUPERCELLS ON THE WRN
EDGE OF THE LOW-LEVEL JET WILL HAVE A CHANCE TO BECOME TORNADIC WITH
A CLUSTER OF TORNADOES POSSIBLE ACROSS THE MODERATE RISK AREA. THE
GREATEST CHANCE FOR STRONG TORNADOES SHOULD EXIST ACROSS ECNTRL OK
AND SE KS WHERE 0-3 KM STORM RELATIVE HELICITIES ARE FORECAST TO
REACH 400 M2/S2 IN THE 00Z TO 03Z TIMEFRAME. DUE TO THE STRONG DEEP
LAYER SHEAR...CELLS SHOULD REMAIN DISCRETE DURING MUCH OF THE EVENT.
SUPERCELLS COULD ALSO PRODUCE SWATHS OF WIND DAMAGE. THE WIND DAMAGE
THREAT COULD BECOME ENHANCED DURING THE EVENING IF A LINEAR MCS CAN
ORGANIZE.

...MID-MO VALLEY/NRN PLAINS/UPPER MS VALLEY...
SOUTH TO SOUTHWEST FLOW WILL BE IN PLACE ACROSS THE NCNTRL U.S.
SUNDAY AS AN UPPER-LEVEL TROUGH MOVES INTO THE SRN AND CNTRL PLAINS.
AT THE SFC...A LOW IS FORECAST TO DEEPEN AND MOVE NEWD INTO THE
MID-MO VALLEY DURING THE DAY. A MODERATELY UNSTABLE AIRMASS SHOULD
BE IN PLACE BY MID AFTERNOON TO THE EAST AND NORTHEAST OF THE LOW
ACROSS ERN NEB...SERN SD...IA AND SRN MN WHERE SFC DEWPOINTS MAY
REACH THE LOWER TO MID 60S F. THE AIRMASS SHOULD BE UNCAPPED ACROSS
MUCH OF THE REGION ALLOWING FOR CONVECTIVE INITIATION TO TAKE PLACE
EARLY IN THE DAY. THUNDERSTORMS COULD BE ONGOING DURING THE MORNING
ACROSS IA AND MN ALONG WRN EDGE OF THE LOW-LEVEL JET WITH ADDITIONAL
THUNDERSTORM DEVELOPMENT TAKING PLACE BENEATH THE UPPER-LEVEL LOW
EARLY SUNDAY AFTERNOON. SEVERAL CLUSTERS OF ORGANIZED THUNDERSTORMS
APPEAR LIKELY TO PERSIST THROUGH THE AFTERNOON WITH MCS DEVELOPMENT
POSSIBLE ACROSS PARTS OF THE REGION BY EVENING.

FORECAST SOUNDINGS AT OMAHA AND DES MOINES AT 21Z SHOW MODERATE
INSTABILITY WITH MLCAPE VALUES IN THE 2000 TO 3000 J/KG RANGE. THIS
COMBINED WITH 30 TO 40 KT OF 0-6 KM SHEAR SHOULD SUPPORT SUPERCELL
DEVELOPMENT WITH A THREAT FOR LARGE HAIL. HAILSTONES OF GREATER THAN
2 INCHES IN DIAMETER WILL BE POSSIBLE WITH THE MORE DOMINANT
SUPERCELLS MAINLY IN SE NEB AND SRN IA WHERE INSTABILITY IS FORECAST
TO BE THE GREATER THAN IN AREAS TO THE NORTH. A FEW TORNADOES MAY
ALSO OCCUR WITH THE MORE INTENSE SUPERCELLS AS THE LOW-LEVEL JET
STRENGTHENS EARLY SUNDAY EVENING. WIND DAMAGE WILL BE POSSIBLE WITH
SUPERCELLS AND BOWING LINE-SEGMENTS ESPECIALLY IF AN MCS CAN
ORGANIZE DURING THE EARLY EVENING.

...TN VALLEY/CNTRL AND ERN GULF COAST STATES...
AN UPPER-LEVEL TROUGH IS FORECAST TO MOVE SEWD ACROSS THE ERN GULF
COAST STATES SUNDAY AFTERNOON. THUNDERSTORMS SHOULD DEVELOP ALONG
AND AHEAD OF THE TROUGH AXIS AS SFC TEMPS WARM. FORECAST SOUNDINGS
FROM MIDDLE TN SEWD ACROSS NCNTRL AL INTO WRN GA AT 21Z SUNDAY SHOW
MLCAPE VALUES IN THE 1500 TO 2500 J/KG RANGE WITH STEEP LOW-LEVEL
LAPSE RATES. THIS COULD BE ENOUGH FOR A MARGINAL WIND DAMAGE THREAT
WITH MULTICELL STORMS THAT DEVELOP DURING THE AFTERNOON.

..BROYLES.. 05/18/2013

[TwisterFanatic]

Day 3 - Monday - 30% Hatched Probs



DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0231 AM CDT SAT MAY 18 2013

VALID 201200Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN
PLAINS...CNTRL PLAINS...MID MS VALLEY...UPPER MS VALLEY AND GREAT
LAKES REGION...

...REGIONAL SEVERE WEATHER EPISODE POSSIBLE ACROSS PARTS OF THE SRN
AND CNTRL PLAINS INTO THE OZARKS MONDAY AFTERNOON AND EVENING...

...SRN AND CNTRL PLAINS/OZARK PLATEAU...
AN UPPER-LEVEL LOW WILL REMAIN IN PLACE ACROSS THE NRN AND CNTRL
PLAINS ON MONDAY WITH SOUTHWEST FLOW LOCATED FROM THE SRN PLAINS
INTO THE MID MS VALLEY. AT THE SFC...A LOW IS FORECAST TO MOVE NEWD
ACROSS THE SRN PLAINS WITH DEWPOINTS SOUTH AND EAST OF THE LOW IN
THE MID TO UPPER 60S F. A CAPPING INVERSION IN PLACE FOR MUCH OF THE
DAY...SHOULD WEAKEN BY LATE AFTERNOON ALLOWING FOR ROBUST CONVECTIVE
INITIATION. MODEL FORECASTS DEVELOP SEVERAL CLUSTERS OF
THUNDERSTORMS LATE MONDAY AFTERNOON FROM THE SFC LOW NEAR THE RED
RIVER NEWD INTO CNTRL AND ERN OK. THE MODELS APPEAR TO ORGANIZE AN
MCS ACROSS THE SRN PLAINS AND MOVE THIS CONVECTIVE SYSTEM NEWD INTO
THE OZARKS DURING THE EVENING.

FORECAST SOUNDINGS IN SRN OK AND NEAR THE RED RIVER IN NORTH TX AT
00Z/TUE SHOW IMPRESSIVE THERMODYNAMIC AND SHEAR PROFILES WITH MLCAPE
VALUES OF 2500 TO 3500 J/KG AND 0-6 KM SHEAR VALUES OF 45 TO 55 KT.
THIS ENVIRONMENT SHOULD BE FAVORABLE FOR SUPERCELLS WITH LARGE HAIL.
HAILSTONES OF GREATER THAN 2 INCHES IN DIAMETER WILL BE POSSIBLE
WITH THE MORE DOMINANT SUPERCELLS. IN ADDITION...LOW-LEVEL
HODOGRAPHS ALSO LOOK IMPRESSIVE WITH 0-3 KM STORM RELATIVE
HELICITIES IN THE 400 TO 50O M2/S2 RANGE BY EARLY MONDAY EVENING.
THIS SUGGESTS TORNADIC SUPERCELLS WILL BE POSSIBLE WITH A POTENTIAL
FOR STRONG TORNADOES. IF MESOSCALE CONDITIONS COME TOGETHER AS THE
MODELS SUGGEST...THEN A CLUSTER OF TORNADOES COULD OCCUR ACROSS
PARTS OF THE SRN PLAINS LATE MONDAY AFTERNOON INTO THE EVENING. WIND
DAMAGE WILL ALSO BE POSSIBLE WITH SUPERCELLS AND BOWING
LINE-SEGMENTS. THE MAIN CONCERN ABOUT FORECASTING A SIGNIFICANT
EVENT THIS FAR OUT...IS THAT MULTIPLE DAYS OF THUNDERSTORMS BETWEEN
NOW AND MONDAY WILL LIKELY ALTER THE OUTCOME AND THAT THE SCENARIO
WILL BE DIFFERENT THAN WHAT IS CURRENTLY PRESENTED BY THE MODELS.

...MID TO UPPER MS VALLEY/GREAT LAKES...
AN UPPER-LEVEL LOW IS FORECAST TO REMAIN IN PLACE ACROSS THE NRN AND
CNTRL PLAINS ON MONDAY AS A SHORTWAVE TROUGH ROTATES AROUND THE ERN
SIDE OF THE UPPER-LEVEL LOW. THE SHORTWAVE TROUGH AND AN ASSOCIATED
MID-LEVEL JET WILL HELP FOCUS CONVECTIVE DEVELOPMENT ACROSS THE MID
TO UPPER MS VALLEY AND GREAT LAKES REGION MONDAY AFTERNOON. SFC
DEWPOINTS ARE FORECAST TO BE IN THE LOWER TO MID 60S F ACROSS A
BROAD CORRIDOR FROM THE MID MS VALLEY EXTENDING NEWD INTO THE LOWER
OH VALLEY WHERE THE MODELS DEVELOP MODERATE INSTABILITY BY
AFTERNOON. THIS COMBINED WITH MODERATE DEEP LAYER SHEAR
PROFILES...ENHANCED BY THE MID-LEVEL JET...SHOULD SUPPORT SEVERE
THUNDERSTORM DEVELOPMENT. THE SEVERE THREAT SHOULD DEVELOP ACROSS A
BROAD AREA WHERE MESOSCALE FEATURES AND THE MAGNITUDE OF INSTABILITY
WILL BECOME IMPORTANT FOR SEVERE THREAT COVERAGE. WIND DAMAGE AND
LARGE HAIL APPEAR TO BE THE GREATEST THREATS AT THIS TIME BUT MUCH
UNCERTAINTY EXISTS CONCERNING HOW THE EVENT WILL PLAY OUT.

..BROYLES.. 05/18/2013

[cycloneye]

Large hail looks to be be the biggest threat today, along with the possibility of tornadoes. Capping may somewhat limit storm coverage, and initiation will likely wait until pretty late in the day, but by evening any supercells that develop will be very dangerous. Sunday and Monday look like even better setups for tornadoes.

[CrazyC83]

Indeed hail is today's #1 threat. IMO, a 60H hail area should have been added. Some of them could be bigger than softballs...

That said, despite the shear being not ideal, the instability could allow for some tornadoes, one or two could easily be intense.

[somethingfunny]

I think I will take a drive up to Oklahoma tomorrow.

[cycloneye]

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0754 AM CDT SAT MAY 18 2013

VALID 181300Z - 191200Z

...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING OVER
PORTIONS OF SOUTHWEST NEB...WESTERN KS...AND WESTERN OK...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS MUCH OF THE GREAT PLAINS
AND UPPER MIDWEST...

...ACTIVE SEVERE WEATHER EVENT EXPECTED ACROSS PARTS OF NEB/KS/OK
LATER THIS AFTERNOON AND EVENING...

...NEB/KS/OK...
MORNING WATER VAPOR LOOPS SHOW A BROAD UPPER TROUGH OVER THE WESTERN
STATES...WITH SEVERAL SHORTWAVE TROUGHS EMBEDDED IN THE CYCLONIC
FLOW. ONE SHORTWAVE TROUGH CURRENTLY OVER WESTERN AZ IS EXPECTED TO
EMERGE INTO THE CENTRAL PLAINS THIS EVENING...PROVIDING THE FOCUS
FOR SEVERE THUNDERSTORM DEVELOPMENT. AHEAD OF THE
TROUGH...SOUTHERLY LOW LEVEL WINDS WILL MAINTAIN AMPLE MOISTURE
ACROSS THE PLAINS WITH 60S TO LOWER 70S DEWPOINTS EXPECTED FROM
CENTRAL/WESTERN KS INTO OK AND NORTH TX. THE DRYLINE IS FORECAST TO
BECOME ESTABLISHED FROM WESTERN OK INTO THE EXTREME EASTERN TX
PANHANDLE BY MID/LATE AFTERNOON. STRONG HEATING AND DEEP MIXING
BEHIND THE DRYLINE COUPLED WITH WEAK BUT SUSTAINED LARGE SCALE
ASCENT ASSOCIATED WITH THE WESTERN TROUGH WILL EVENTUALLY ERODE THE
CAP. RAPID THUNDERSTORM DEVELOPMENT WILL BEGIN OVER WESTERN KS BY
20Z...WITH ACTIVITY DEVELOPING SOUTHWARD ALONG THE OK/TX PANHANDLE
BORDER BY LATE AFTERNOON. FAVORABLE EFFECTIVE SHEAR AND VERY HIGH
CAPE VALUES /MLCAPE OF 3500+ J/KG/ WILL PROMOTE SUPERCELLS CAPABLE
OF VERY LARGE HAIL. LCL HEIGHTS AND LOW LEVEL SHEAR ARE NOT
FORECAST TO BE PARTICULARLY FAVORABLE FOR TORNADOES...BUT DEGREE OF
INSTABILITY MAY COMPENSATE FOR NEGATIVE FACTORS SO HAVE MAINTAINED
RISK OF ISOLATED STRONG TORNADOES ACROSS MUCH OF THE MODERATE RISK
AREA. THUNDERSTORMS ARE LIKELY TO GROW UPSCALE THROUGH THE EVENING
AS A BROKEN LINE MOVES EASTWARD INTO CENTRAL KS AND NORTH-CENTRAL OK
WITH AN INCREASED RISK OF DAMAGING WINDS.

...TX...
SEVERAL MODEL SOLUTIONS INDICATE THAT AT LEAST WIDELY SCATTERED
THUNDERSTORMS WILL DEVELOP BY LATE AFTERNOON ALONG THE
DRYLINE...PERHAPS AS FAR SOUTH AS DYS/BWD. FORCING WILL BE WEAK BUT
STRONGER THAN YESTERDAY. ANY STORM THAT FORMS ALONG THE CORRIDOR
WILL LIKELY BECOME SUPERCELLULAR WITH A RISK OF VERY LARGE HAIL AND
DAMAGING WINDS.

...SD/ND/MN/IA...
MULTIPLE CLUSTERS OF THUNDERSTORMS ARE ONGOING THIS MORNING OVER
EASTERN SD INTO MN/WI. SOME INTENSIFICATION IS POSSIBLE ALONG THE
LEADING EDGE OF THIS ACTIVITY LATER THIS MORNING...BUT THE PRIMARY
SEVERE THREAT WILL LIKELY OCCUR LATE THIS AFTERNOON AND EVENING AS
NEW STORMS FORM OVER NEB/SD AND SPREAD EAST-NORTHEASTWARD. DETAILS
OF CONVECTIVE EVOLUTION ARE UNCLEAR AT THIS TIME DUE TO ONGOING
STORMS...BUT IT APPEARS THAT HAIL AND DAMAGING WINDS WILL BE
POSSIBLE WITH STRONGER STORMS ACROSS MUCH OF THE NORTHERN PLAINS AND
UPPER MIDWEST LATER TODAY.

...SOUTHEAST STATES...
A REMNANT UPPER TROUGH REMAINS OVER THE TN VALLEY AND SOUTHEAST
STATES TODAY. THIS WILL LEAD TO ANOTHER DAY OF SCATTERED
THUNDERSTORMS OVER A RELATIVELY LARGE AREA. IT APPEARS THE CORRIDOR
MOST LIKELY TO SEE A FEW STRONG STORMS WILL BE FROM CENTRAL AL INTO
SOUTHWEST GA AND NORTH FL WHERE STRONG HEATING/DESTABILIZATION WILL
OCCUR. STORMS CURRENTLY OVER CENTRAL AL ARE EXPECTED TO SPREAD
SOUTHEASTWARD ACROSS THIS REGION POSING A RISK OF LOCALLY DAMAGING
WINDS AND HAIL.

..HART/LEITMAN.. 05/18/2013