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Severe Weather Thread (April 26 - May 3)


David Reimer

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248

WWUS20 KWNS 290338

SEL1

SPC WW 290338

OKZ000-290700-

URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 201

NWS STORM PREDICTION CENTER NORMAN OK

1035 PM CDT SAT APR 28 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF

SOUTHWEST THROUGH CENTRAL OKLAHOMA

EFFECTIVE THIS SATURDAY NIGHT AND SUNDAY MORNING FROM 1035 PM

UNTIL 200 AM CDT.

TORNADOES...HAIL TO 3 INCHES IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 40 STATUTE

MILES EAST AND WEST OF A LINE FROM 25 MILES SOUTH SOUTHEAST OF

FORT SILL OKLAHOMA TO 35 MILES NORTHWEST OF CHANDLER OKLAHOMA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU1).

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 200...

DISCUSSION...SUPERCELLS THAT FORMED JUST W OF SW-NE FRONT THROUGH

SW/CNTRL OK EXPECTED TO CONTINUE MOVING ENE THROUGH EARLY SUN. AS

THE STORMS ENCOUNTER WARMER/MORE MOIST AIR E OF BOUNDARY...INCREASE

IN THETA-E MAY SUFFICIENTLY ENHANCE LOW LVL MESO STRENGTH TO POSE A

RISK FOR TORNADOES...IN ADDITION TO ON-GOING RISK FOR LARGE

HAIL/HIGH WIND.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL

SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE

WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO

500. MEAN STORM MOTION VECTOR 25025.

...CORFIDI

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MESOSCALE DISCUSSION 0617

NWS STORM PREDICTION CENTER NORMAN OK

1054 PM CDT SAT APR 28 2012

AREAS AFFECTED...CNTRL AND WRN OKS INTO NWRN TX

CONCERNING...SEVERE THUNDERSTORM WATCH 200...

VALID 290354Z - 290600Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 200

CONTINUES.

SCATTERED SUPERCELLS EXIST FROM NWRN TX INTO CNTRL OK. TWO CELLS

WERE N OF THE SURFACE BOUNDARY OVER CNTRL OK...BUT WERE MOVING

MOSTLY IN AN EWD DIRECTION. ALTHOUGH CELLS ARE FIGHTING SOME CAPPING

AND CIN...FAVORABLE WIND PROFILES ARE LIKELY TO KEEP THESE CELLS

GOING FOR A WHILE. AS THEY APPROACH THE SURFACE FRONT...THEY WILL

ENCOUNTER SLIGHTER WARMER AND MOISTER LOW LEVEL AIR MASS...WHICH

COULD HELP IN VERTICAL ACCELERATIONS DOWN LOW. THIS...ALONG WITH

MORE THAN ADEQUATE LOW LEVEL SHEAR...COULD RESULT IN A BRIEF

TORNADO.

TO THE S...LARGE HAIL WAS THE MAIN THREAT OVER NWRN TX WHERE LOW

LEVEL T/TD SPREADS WERE LARGER. SOME OF THESE CELLS WERE LEFT

MOVING...AND WILL EXIT THE WATCH INTO PORTIONS OF THE ERN TX

PANHANDLE...BUT AN ADDITIONAL WATCH IS NOT EXPECTED AT THIS TIME.

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Just observed a very large, ominous wall cloud ~3 S Yukon around 10:50pm. Agree that new activity popping up in this cell's inflow may disrupt it at least temporarily, though.

I also wonder if it might add locally to the vorticity being ingested into the storm or cause it to redevelop closer to the boundary. We'll see.

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New D3 has a slight risk for a sizable chunk of the Central/Northern Plains towards the Upper MS Valley, with an embedded 30%/sig-hatched area. Looking at the models, instability doesn't appear to be an issue much at all, so the main concern will likely revolve on where the juxtaposition of most favorable wind profiles and shear will be located.

2ro1bhc.jpg

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0236 AM CDT SUN APR 29 2012

VALID 011200Z - 021200Z

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

NRN PLAINS INTO THE UPPER MS VALLEY...

...SYNOPSIS...

SYNOPTIC PATTERN WILL REMAIN DOMINATED BY A BROAD LOW AMPLITUDE

CYCLONIC FLOW REGIME OVER MUCH OF THE COUNTRY TUESDAY. UPPER JET

STREAK AND ATTENDANT SHORTWAVE TROUGH LOCATED ABOUT 600 SM SOUTH OF

THE ALEUTIAN ISLANDS AS OF EARLY SUNDAY MORNING WILL REACH THE NRN

PLAINS TUESDAY. THIS FEATURE WILL BE ACCOMPANIED BY A COLD FRONT

THAT WILL MOVE SEWD THROUGH THE NRN/CNTRL PLAINS AND UPPER MS

VALLEY. A DRYLINE WILL STRETCH FROM THE SRN THROUGH THE CNTRL HIGH

PLAINS DURING THE DAY. FARTHER EAST A WARM FRONT WILL LIFT NWD

THROUGH THE UPPER MS AND OH VALLEYS.

...UPPER MS VALLEY THROUGH NRN AND CNTRL PLAINS REGIONS...

LEE TROUGHING WILL HAVE BECOME ESTABLISHED OVER THE HIGH PLAINS

WITHIN THE QUASI-ZONAL UPPER FLOW REGIME. AS THE WARM FRONT LIFTS

NWD A BROAD...MOIST WARM SECTOR WILL ADVECT THROUGH THE REMAINDER OF

THE PLAINS AND UPPER MS VALLEY WITH UPPER 50S DEWPOINTS AS FAR NORTH

AS THE ERN DAKOTAS INTO MN AND LOW 60S FARTHER SOUTH. ZONE OF

MODERATE INSTABILITY IS LIKELY OVER THIS REGION AS PLUME OF STEEP

MID LEVEL LAPSE RATES ADVECT EWD ABOVE RETURNING MOIST AXIS AND AS

THE BOUNDARY LAYER WARMS DURING THE AFTERNOON. STORMS MAY DEVELOP

WITHIN ZONE OF DEEPER FORCING ALONG THE SEWD ADVANCING COLD FRONT

ACROSS THE ERN DAKOTAS INTO NEB WITH MORE ISOLATED ACTIVITY POSSIBLE

FARTHER SOUTH ALONG THE DRYLINE ACROSS KS. VERTICAL SHEAR FROM 35-45

KT WILL SUPPORT ORGANIZED STORMS INCLUDING SUPERCELLS.

HOWEVER...SOME OF THE STORMS DEVELOPING ALONG THE FRONT FROM NEB

INTO THE DAKOTAS MAY EVENTUALLY EVOLVE INTO LINES AS THEY ADVANCE

TOWARD THE UPPER MS VALLEY...WHILE FARTHER SOUTH ACTIVITY WILL

LIKELY REMAIN DISCRETE. LARGE HAIL AND DAMAGING WIND SHOULD BE THE

MAIN THREATS...BUT ISOLATED TORNADOES WILL ALSO BE POSSIBLE.

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I know I'm late, but a word in on the Friday events. I think a lot of the highway patrol and police may have been extra ramped up as there were multiple accidents along Highway 18 between Ogden and Manhattan having to deal with those messes - just normal traffic but seriously stop and go as construction were sending heavy equip back and forth across the highway all afternoon long stop go, go faster, stop... slam into the person in front of you, or person behind you hits you. I think we counted two each way at least 3 cars involved in each... with HP and County Sheriff dealing with mess. chain reaction type stuff that had happened probably in the rain or the approaching storm. This would have been about the time as the Junction City storm was heading towards Manhattan, it became less than severe quickly...but left a lot of crushed cars in its wake.

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SPC must be going strongly NAM...both the ECMWF/GFS have a weaker wave/wind fields and a surface COL over the region of greatest instability. I guess I am not terribly excited yet about that potential event day 3.

I do think all three models have potential in the northern threat area (where the better upper/mid level flow overspreads the warm sector). The LLJ is weaker on the GFS/Euro, but still strong enough to create some nicely clockwise curved LL hodographs. The bigger question would probably be how far the quality deep layer moisture can make it prior to possible initiation.

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I do think all three models have potential in the northern threat area (where the better upper/mid level flow overspreads the warm sector). The LLJ is weaker on the GFS/Euro, but still strong enough to create some nicely clockwise curved LL hodographs. The bigger question would probably be how far the quality deep layer moisture can make it prior to possible initiation.

I actually disagree...I think the bigger question is the dryline placement, strength of convergence, and the mid level wind fields. The globals do not enthuse me. NAM backing off too.

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I am a bit surprised they decided to go with a 30% hatched area considering the obvious questions with the quality of the deep layer wind fields, particularly where the 30%/sig-hatched is placed, and as you mentioned the convergence along the boundary is not by any means a slam dunk either. From what I can tell, the models at the time of the D3's issuance also showed the same issue with the convergence.

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