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April 12th/13th and 15-16th Severe Weather Thread


andyhb

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Getting ready to make the drive to OK with 'kevlon62'.

Early target call for tomorrow looks to be somewhere NW/W of OKC.

Perfect, My ground zero is the US 412 and US 60 intersection. Careful on your positioning relative to the Cimmaron River, there's only a handful of crossings. Good Luck and be safe!

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Still thinking Kansas/I-35 corrdior ICT to MKC/MCI is the biggest target. Oklahoma is much more isolated, it looks like off NAM, but lone potential monsters potential.

522569_333601473362325_100001374243871_866085_1381095653_n.jpg

That NAM suggested isolated storms that do form in OK West/SW of OKC d looks they have all the ingredients, however.

post-138-0-47417000-1334292732.gif

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I'm sitting in a Holiday Inn on the northwest side of OKC. I could have headed back to Dallas from Southwest Oklahoma but decided to just get a room through Sunday up here so I didn't have a five hour drive tomorrow morning. Winds are roaring out of the southeast tonight and you can sense something is on the way. I haven't had a chance to look at model data for Friday or Saturday yet since I just got in after driving for a few hours. I'm just hoping I have a hotel to return to tomorrow evening and once again on Saturday.

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I mean, it's not even just the unfavorable jet orientation, but the delayed forcing due to the positive tilt of the trough, the stout EML consisting of H7 temps over 7-8C, and the weak VV's progged by the NAM at 00Z.

Agree 110% even the 12z's had me concerned about convective initiation.
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SPC Day 1.

SLGHT RISK, 10% TOR, NW OK.

day1probotlk_1200_torn.gif

HOWEVER...BY THIS EVENING...GUIDANCE IS SUGGESTIVE THAT A FOCUSED

AREA OF STRENGTHENING LOWER/MID TROPOSPHERIC WARM ADVECTION...

BENEATH INCREASINGLY DIFLUENT AND DIVERGENT HIGH LEVEL FLOW...WILL

DEVELOP ACROSS PARTS OF WESTERN INTO NORTH CENTRAL OKLAHOMA...BEFORE

GRADUALLY SHIFTING NORTHEASTWARD OVERNIGHT. AS THIS OCCURS IN THE

PRESENCE OF MODERATELY LARGE BOUNDARY LAYER CAPE...AND STRONG

VERTICAL SHEAR...STRONG/SEVERE STORMS APPEAR LIKELY...INCLUDING

DISCRETE SUPERCELLS. COINCIDING WITH STRENGTHENING SOUTHERLY 850

WIND FIELDS /30-50+ KT/...WHICH WILL RESULT IN ENLARGING CLOCKWISE

CURVED LOW-LEVEL HODOGRAPHS...A FEW TORNADOES WILL BE POSSIBLE. ONE

OR TWO COULD BE STRONG...ALONG WITH THE RISK FOR VERY LARGE

HAIL...BEFORE CONVECTION GRADUALLY WEAKENS AS BOUNDARY LAYER

INSTABILITY WANES LATE THIS EVENING INTO THE OVERNIGHT HOURS.

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SPC Day 1.

SLGHT RISK, 10% TOR, NW OK.

HOWEVER...BY THIS EVENING...GUIDANCE IS SUGGESTIVE THAT A FOCUSED

AREA OF STRENGTHENING LOWER/MID TROPOSPHERIC WARM ADVECTION...

BENEATH INCREASINGLY DIFLUENT AND DIVERGENT HIGH LEVEL FLOW...WILL

DEVELOP ACROSS PARTS OF WESTERN INTO NORTH CENTRAL OKLAHOMA...BEFORE

GRADUALLY SHIFTING NORTHEASTWARD OVERNIGHT. AS THIS OCCURS IN THE

PRESENCE OF MODERATELY LARGE BOUNDARY LAYER CAPE...AND STRONG

VERTICAL SHEAR...STRONG/SEVERE STORMS APPEAR LIKELY...INCLUDING

DISCRETE SUPERCELLS. COINCIDING WITH STRENGTHENING SOUTHERLY 850

WIND FIELDS /30-50+ KT/...WHICH WILL RESULT IN ENLARGING CLOCKWISE

CURVED LOW-LEVEL HODOGRAPHS...A FEW TORNADOES WILL BE POSSIBLE. ONE

OR TWO COULD BE STRONG...ALONG WITH THE RISK FOR VERY LARGE

HAIL...BEFORE CONVECTION GRADUALLY WEAKENS AS BOUNDARY LAYER

INSTABILITY WANES LATE THIS EVENING INTO THE OVERNIGHT HOURS.

mention of possible strong tornadoes but no hatching.

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mention of possible strong tornadoes but no hatching.

Probably uncertain about the convective evolution. Maybe discrete supercells for only a short time before it becomes a big blob of an MCS.

Elevated overnight stuff firing here now.

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I'm not convinced of sfc-based initiation tomorrow, but the SPC WRF does initiate a lone supercell over NW OK tomorrow and keeps it isolated in that region between 00Z-06Z. The motion and location of that supercell more or less matches the 10% risk area from SPC.

Where you getting the SPC WRF? The place I get it didn't update.

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SPC will be going High Risk with the new day 2 outlook from OKC to Central Kansas... (Internal chat)

And it's out with this headline:

TORNADO OUTBREAK LIKELY ACROSS THE SRN AND CNTRL PLAINS NWD INTO THE

MID-MO VALLEY FROM SATURDAY AFTERNOON THROUGH SATURDAY NIGHT

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33mtlpy.jpg

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1258 AM CDT FRI APR 13 2012

VALID 141200Z - 151200Z

...THERE IS A HIGH RISK OF SVR TSTMS ACROSS PARTS OF OK AND KS...

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF NW TX...CNTRL

AND WRN OK...CNTRL AND ERN KS...SE NEB...NW MO AND FAR SW IA...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE MID-MO

VALLEY...UPPER MS VALLEY...SRN PLAINS AND CNTRL PLAINS...

TORNADO OUTBREAK LIKELY ACROSS THE SRN AND CNTRL PLAINS NWD INTO THE

MID-MO VALLEY FROM SATURDAY AFTERNOON THROUGH SATURDAY NIGHT

...SRN AND CNTRL PLAINS...

AN IMPRESSIVE UPPER-LEVEL LOW WILL MOVE EWD ACROSS FOUR CORNERS

REGION SATURDAY AS A POWERFUL 90 TO 110 KT MID-LEVEL JET EJECTS NEWD

INTO THE SRN AND CNTRL PLAINS. AHEAD OF THE SYSTEM...A CORRIDOR OF

MODERATE TO STRONG INSTABILITY IS FORECAST ACROSS ECNTRL KS...CNTRL

OK INTO NW TX. THIS COMBINED WITH STEEP MID-LEVEL LAPSE RATES AND

STRONG LOW-LEVEL SHEAR WILL BE VERY FAVORABLE FOR SEVERE STORMS AND

A TORNADO OUTBREAK WILL BE LIKELY ACROSS THE SRN AND CNTRL PLAINS

FROM LATE SATURDAY AFTERNOON LASTING THROUGH THE EVENING AND INTO

THE OVERNIGHT PERIOD.

NAM AND NAMKF FORECAST SOUNDINGS AT 00Z SATURDAY EVENING FROM SALINA

KS SWD TO AROUND OKLAHOMA CITY SHOW MLCAPE VALUES FROM 2000 TO 3000

J/KG WITH 0-6 KM SHEAR IN THE 60 TO 75 KT RANGE. IN

ADDITION...HODOGRAPHS ARE LARGE AND LOOPED WITH 0-1 KM SHEAR VALUES

IN THE 30 TO 40 KT RANGE. THIS ENVIRONMENT SHOULD BE VERY FAVORABLE

FOR SUPERCELLS AND TORNADOES. 0-3 KM STORM RELATIVE HELICITIES ARE

FORECAST TO BE AROUND 400 M2/S2 WHICH IS IDEAL FOR STRONG TORNADOES

AND A TORNADO OUTBREAK APPEARS LIKELY. THE GREATEST THREAT FOR

SIGNIFICANT TORNADOES SHOULD EXIST SATURDAY EVENING FROM SALINA SWD

TO OKLAHOMA CITY. 700 TO 500 MB LAPSE RATES AROUND 7.5 C/KM WILL

ALSO BE FAVORABLE FOR LARGE HAIL AND HAIL GREATER THAN 2 INCHES WILL

BE POSSIBLE THE MORE INTENSE SUPERCELLS. A WIND DAMAGE THREAT WILL

ALSO EXIST DUE TO THE EXPECTED INTENSE NATURE OF THE STORMS.

THE MAIN CONCERN FOR THIS FORECAST IS CONVECTIVE COVERAGE. MANY OF

THE MODELS DO NOT DEVELOP NUMEROUS THUNDERSTORMS ALONG THE DRYLINE.

IN SPITE OF THIS...THE MODELS DIMINISH THE CAP ACROSS THE SRN AND

CNTRL PLAINS LATE SATURDAY AFTERNOON SO THIS BRINGS THE MODELS INTO

QUESTION. IN ADDITION...THE MODELS DRIVE A BAND OF LARGE-SCALE

ASCENT ACROSS CNTRL KS DURING THE EARLY EVENING SUGGESTING MANY

STORMS SHOULD INITIATE WITH STORMS INITIATING SWD WITH TIME EARLY

SATURDAY EVENING AS THE LOW-LEVEL JET STRENGTHENS. THESE FACTORS

COMBINED WITH SFC DEWPOINTS IN THE LOWER TO MID 60S F AND VERY

FAVORABLE LOW-LEVEL SHEAR PROFILES SHOULD PRODUCE AND ENVIRONMENT

FAVORABLE FOR A TORNADO OUTBREAK. AFTER COLLABORATION WITH WFOS

WICHITA...NORMAN...TOPEKA...TULSA AND DODGE CITY...A HIGH RISK WILL

BE ISSUED DUE TO THE POTENTIAL FOR A HIGH-END LIFE THREATENING EVENT

ACROSS THE SRN AND CNTRL PLAINS.

...MID-MO VALLEY/UPPER MS VALLEY...

AN IMPRESSIVE UPPER-LEVEL LOW WILL MOVE ACROSS THE FOUR CORNERS

REGION SATURDAY. AT THE SFC...A LOW SHOULD MOVE ACROSS NEB WITH A

WARM FRONT EXTENDING EWD ACROSS IA. THUNDERSTORMS SHOULD BE ONGOING

ALONG THIS BOUNDARY WITH STORMS EXPANDING NWD INTO THE UPPER MS

VALLEY. SOUTH OF THE BOUNDARY...THE MODELS DEVELOP MODERATE

INSTABILITY WITH A DRYLINE LOCATED IN ECNTRL NEB. THUNDERSTORMS THAT

INITIATE ALONG THE DRYLINE AND EWD ACROSS THE WARM SECTOR WILL

LIKELY HAVE AN ENHANCED SEVERE THREAT. STRONG DEEP LAYER SHEAR AND

ENHANCED LOW-LEVEL SHEAR WILL BE FAVORABLE FOR SUPERCELLS AND

TORNADOES. A FEW STRONG TORNADOES MAY OCCUR WITH THE MORE DOMINANT

SUPERCELLS ESPECIALLY AS THE LOW-LEVEL JET STRENGTHENS SATURDAY

EVENING. ALTHOUGH A TORNADO OUTBREAK WILL BE POSSIBLE ACROSS PARTS

OF THE REGION...THE GREATEST MOISTURE RETURN SHOULD REMAIN FURTHER

TO THE SOUTH SUGGESTING THE HIGHEST TORNADO THREAT SHOULD EXIST

ACROSS SERN NEB...SW IA...NW MO AND ERN KS WHERE A MODERATE RISK IS

LOCATED.

...NW TX/WCNTRL TX...

AN IMPRESSIVE UPPER-LEVEL LOW WILL MOVE EWD ACROSS THE FOUR CORNERS

REGION AND INTO THE HIGH PLAINS SATURDAY EVENING. MODEL FORECASTS

DEVELOP THUNDERSTORMS ALONG A WELL-DEFINED DRYLINE DURING THE

EVENING FROM WRN OK SSWWD ACROSS NW TX INTO WCNTRL TX. FORECAST

SOUNDINGS SATURDAY EVENING ALONG THIS CORRIDOR SHOW MODERATE

INSTABILITY...STRONG DEEP LAYER SHEAR AND STEEP MID-LEVEL LAPSE

RATES WHICH SHOULD BE FAVORABLE FOR SUPERCELLS WITH LARGE HAIL.

SUPERCELLS SHOULD BE CAPABLE OF PRODUCING 2 INCH OR GREATER HAIL DUE

TO THE THERMODYNAMIC PROFILE. STRENGTHENING LOW-LEVEL SHEAR DURING

THE EVENING SHOULD ALSO RESULT IN A TORNADO THREAT AS WELL.

..BROYLES.. 04/13/2012

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And here's why it's there...

NAM_221_2012041300_F48_VVELD_700_MB.png

GFS_3_2012041300_F48_VVELD_700_MB.png

Those are some pretty decent vertical velocities being spit out by both the GFS and NAM by 00z. And they only get stronger after dark, without the boundary layer being decoupled. Unfortunately, the worst of this will probably be quite bad and be at night. Throw the book out the window in term of your diurnal plains tornado climatology on this one, folks. With 65+ dews and a 60kt LLJ, your SB instability is going nowhere after dark.

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Broyles strikes again! I agree w/him regarding the issue of lack of model precip breaking out...it only suggests to me that the coverage will be scattered and discrete, but that might not necessarily be a negative in terms of how severe the tornado outbreak ends up being. The timing of the trough ejection is still and always has been the biggest question mark, but it would take a substantial slow down from here on out to prevent a major tornado outbreak from occurring, and frankly we're running out of time for that.

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And to think, models aren't even in agreement with Saturday initiation...0z NAM hints at small spatial coverage with a cell or two in Red River Valley and near the triple point with nothing in KS at all. GFS has entire dryline exploding by 0z Sunday.

Chip

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And to think, models aren't even in agreement with Saturday initiation...0z NAM hints at small spatial coverage with a cell or two in Red River Valley and near the triple point with nothing in KS at all. GFS has entire dryline exploding by 0z Sunday.

Chip

Hi-res NAM has a bunch of strong VV signatures going up along/ahead of the dryline by 00z Saturday evening...

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And to think, models aren't even in agreement with Saturday initiation...0z NAM hints at small spatial coverage with a cell or two in Red River Valley and near the triple point with nothing in KS at all. GFS has entire dryline exploding by 0z Sunday.

Chip

Just my personal opinion but this has a bust potential written on it. Just doesn't give me much confidence that the 12z and 0z nam and gfs haven't come into better agreement over time. But since I said this I jinxed myself so plan on another epic outbreak

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Good point. However, GFS has weaker vv's and still breaks the "cap" while the NAM doesn't. It could have something to do with grid spacing and thresholds, but still, something to watch. My only issue with vv's is that they look at a single layer without reference to the entire column.

Chip

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