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Thread: Weather Service Forecasts "High-End Severe Potential" in Midwest Saturday

  1. #1
    Administrator GothamSpotter's Avatar
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    Weather Service Forecasts "High-End Severe Potential" in Midwest Saturday

    The National Weather Service is forecasting a significant tornado, hail and severe storm outbreak stretching from Oklahoma through Kansas, Nebraska and Iowa, more than 24 hours ahead of time. NWS has only issued such a dire prediction this far ahead of time once before, in April 2006. That time they were right: The next day, over 100 tornadoes killed a dozen people and damaged over 1,000 homes in the southeast.

    The map below indicates the likelihood of severe weather impacting within 25 miles of any point within a shaded area.



    DAY 2 CONVECTIVE OUTLOOK
    NWS STORM PREDICTION CENTER NORMAN OK
    1231 PM CDT FRI APR 13 2012

    VALID 141200Z - 151200Z

    ...THERE IS A HIGH RISK OF SVR TSTMS OVER ERN NEB AND FAR WRN IA...

    ...THERE IS A HIGH RISK OF SVR TSTMS FROM S CNTRL KS INTO W CNTRL
    OK...

    ...THERE IS A MDT RISK OF SVR TSTMS FROM WRN OK INTO NEB AND IA...

    ...THERE IS A SLGT RISK OF SVR TSTMS FROM NW TX NWD INTO SRN MN AND
    WRN IL...

    ...SYNOPSIS...
    A LARGE UPPER TROUGH WILL EXIST OVER THE WRN U.S. WITH UPPER LOW
    CENTER NEAR THE FOUR CORNERS AREA AT 00Z...THEN CONTINUING INTO THE
    CNTRL PLAINS BY SUN MORNING. AROUND THE BASE OF THIS TROUGH...A
    MIDLEVEL JET CORE IN EXCESS OF 100 KT WILL BE NOSING INTO THE OK/TX
    PANHANDLE BY 00Z...TIGHTENING FURTHER AS THE UPPER LOW ROTATES NEWD
    ACROSS KS AND NEB. THIS BROAD BELT OF SWLY FLOW ALOFT WILL CREATE
    FAVORABLE SHEAR FOR SEVERE WEATHER OVER A LARGE PART OF THE PLAINS.

    AT THE SURFACE...A LOW WILL DEEPEN DURING THE DAY OVER ERN CO INTO
    SWRN NEB...WITH THE 00Z DRYLINE POSITION ROUGHLY FROM CNTRL NEB NEAR
    THE LOW SWD ACROSS KS AND INTO WRN OK AND NW TX. DURING THE
    AFTERNOON AND EVENING...A WARM FRONT WILL EXTEND FROM THE LOW NEWD
    ACROSS SERN SD INTO SRN MN.

    SLY LOW LEVEL FLOW IN ANTICIPATION OF THE UPPER TROUGH WILL MAINTAIN
    FAVORABLE MOISTURE TRAJECTORIES...WITH A NARROW AXIS OF MID 60S F
    BOUNDARY LAYER DEWPOINTS EXTENDING FROM CNTRL TX ACROSS OK AND INTO
    SRN KS AT 00Z. DEWPOINTS NEAR 60 F WILL BE POSSIBLE AS FAR N AS THE
    WARM FRONT. COMBINED WITH COOL TEMPERATURES ALOFT...AMPLE
    INSTABILITY WILL BE PRESENT FOR SEVERE STORMS FROM TX TO NEB.

    ...CNTRL NEB INTO WRN IA...
    A STRONG SLY LOW LEVEL JET WILL HELP FORCE MORNING RAIN AND STORMS
    OVER MUCH OF THE AREA...AND WILL ALSO ALLOW FOR DESTABILIZATION
    DURING THE DAY BEHIND THIS INITIAL ACTIVITY. WITH THE SURFACE LOW
    DEEPENING JUST TO THE W...AND A BROAD WARM FRONT AND/OR OUTFLOWS IN
    PLACE...LOW LEVEL WINDS WILL REMAIN BACKED AND RH LEVELS SHOULD
    REMAIN RELATIVELY SHELTERED AS WELL...PROVIDING A FAVORABLE AREA FOR
    STRONG TORNADOES. CELLS WOULD LIKELY FORM OVER WRN SECTIONS OF THE
    HIGH RISK AREA WHERE HEATING WILL STEEPEN LOW LEVEL LAPSE
    RATES...THEN WOULD PROCEED RAPIDLY NEWD WITH AN INCREASING TORNADO
    THREAT. VERY LARGE HAIL WILL ALSO BE LIKELY. THE NRN EXTENT OF THE
    TORNADO THREAT WILL DEPEND ON THE ACTUAL LOCATION OF THE PRIMARY
    BOUNDARIES.

    ...CNTRL KS...WRN AND CNTRL OK...NWRN TX...
    SUBSTANTIAL UNCERTAINLY EXISTS IN REGARD TO STORM COVERAGE ALONG THE
    DRYLINE DURING THE DAY FROM KS INTO OK AND NW TX. HOWEVER...HIGH END
    SEVERE POTENTIAL EXISTS AND WILL MAINTAIN CATEGORICAL HIGH.

    LOW CLOUDS AND SCATTERED SHOWERS ARE EXPECTED EARLY ON SAT...WITH
    ONLY SLIGHT CAPPING IN PLACE EARLY. BREAKS IN THE CLOUDS AND HEATING
    SHOULD QUICKLY ERODE MOST INHIBITION BY AFTERNOON...WHEN WITH
    MODERATE INSTABILITY DEVELOPING WITH MUCAPE GENERALLY 2000-2500
    J/KG.

    STRONG HEATING AND STEEPENING OF LOW LEVEL LAPSE RATES WILL OCCUR
    ALONG AND W OF THE DRYLINE. HOWEVER...CONVERGENCE WILL BE RELATIVELY
    WEAK...WHICH MAY ACTUALLY HELP KEEP STORMS DISCRETE. FAVORABLY
    ORIENTED DEEP LAYER SHEAR ALONG THE DRYLINE...AS WELL AS VEERING AND
    INCREASING WINDS WITH HEIGHT WILL STRONGLY FAVOR SUPERCELLS.

    THERMODYNAMIC PROFILES SHOULD BE SUFFICIENT FOR VERY LARGE
    HAIL...AND LOW LEVEL SHEAR WILL FAVOR TORNADOES AS WELL. LAPSE RATES
    ALOFT ARE MARGINAL FOR TYPICAL PLAINS VIOLENT TORNADO DAYS...BUT
    SHEAR PROFILES WOULD CERTAINLY FAVOR A FEW STRONG TORNADOES.

    CURRENT THINKING IS FOR ISOLATED TORNADIC SUPERCELLS WITH VERY LARGE
    HAIL TO FORM ALONG THE DRYLINE...AND TO PROCEED NEWD ACROSS THE HIGH
    RISK AREA LATE AFTERNOON INTO THE EVENING. THEN...THE PACIFIC FRONT
    WILL MOVE IN FROM THE W...LIKELY RESULTING IN A SQUALL LINE CAPABLE
    OF DAMAGING WINDS WITH EMBEDDED AREAS OF ROTATION CAPABLE OF DAMAGE.


    FARTHER S INTO TX...DAYTIME DRYLINE ACTIVITY IS LESS LIKELY...WITH
    THE MAIN SEVERE THREAT COMING FROM THE OVERNIGHT SQUALL LINE WITH
    DAMAGING WINDS AND PERHAPS TORNADOES WITH SUPERCELLS EMBEDDED WITHIN
    THE LINE.

    ..JEWELL.. 04/13/2012
    Last edited by GothamSpotter; 04-13-2012 at 08:12 PM.
    Ladies and gentlemen, this is your captain speaking. We have a small problem.
    All four engines have stopped. We are doing our damnedest to get them under control.
    I trust you are not in too much distress. —Captain Eric Moody, British Airways Flight 9

  2. #2
    Senior Member
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    Guess I better keep my ears tuned to the radio,and tv,and eyes towards the sky.

    Doug

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