May 15, 2015

Post date: May 15, 2015 1:30:31 PM

Friday, May 15, 2015 @ 0825 CDT: Here's today's outlook.

*crosses fingers for a beautiful photogenic tornado out in the middle of nowhere*

SPC AC 151247

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0747 AM CDT FRI MAY 15 2015

VALID 151300Z - 161200Z

...THERE IS AN ENH RISK OF SVR TSTMS OVER SWRN/S CENTRAL SD AND

WRN/CENTRAL NEB...

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

INTO THE SRN HIGH PLAINS...

...THERE IS A SLGT RISK OF SVR TSTMS OVER SRN TX...

...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLIGHT RISK

OVER SRN TX...

...THERE IS A MRGL RISK OF SVR TSTMS FROM THE LOWER MO VALLEY TO THE

LOWER GREAT LAKES...

...SUMMARY...

SEVERE THUNDERSTORMS ARE EXPECTED ACROSS PARTS OF FAR NORTHEAST

COLORADO...SOUTHEAST WYOMING...NEBRASKA AND SOUTHERN SOUTH DAKOTA

THIS AFTERNOON AND EVENING. MORE ISOLATED STRONG/SEVERE STORM

DEVELOPMENT IS POSSIBLE SOUTHWARD INTO THE SOUTHERN HIGH PLAINS BY

THIS EVENING...WITH SOME INCREASE IN THREAT FROM WESTERN KANSAS INTO

WEST TEXAS LATER TONIGHT. A FEW SEVERE STORMS WILL BE POSSIBLE INTO

EARLY AFTERNOON OVER SOUTH TEXAS. A FEW STRONG TO ISOLATED SEVERE

STORMS ARE ALSO POSSIBLE THIS AFTERNOON AND EVENING FROM PARTS OF

THE MIDDLE MISSISSIPPI VALLEY EASTWARD ACROSS THE MIDWEST REGION TO

THE LOWER GREAT LAKES.

...SYNOPSIS...

AN EXPANSIVE UPPER LOW OVER THE PACIFIC COASTAL STATES IS FORECAST

TO CONTINUE EWD REACHING THE ROCKIES BY THE END OF THE PERIOD AS A

SERIES OF VORTICITY MAXIMA/SHORT WAVE TROUGHS ROTATE THROUGH THE SRN

AND ERN PERIPHERY OF THE LARGE-SCALE CIRCULATION. AT THE

SURFACE...A BROAD REGION OF LOW PRESSURE CURRENTLY OVER MUCH OF THE

WRN STATES WILL GRADUALLY CONSOLIDATE WITH THE PRIMARY LOW

DEVELOPING OVER THE CENTRAL HIGH PLAINS BY THIS EVENING...THEN MOVE

NWD INTO THE NRN HIGH PLAINS BY 12Z/16. A NORTH-SOUTH DRY LINE IS

FORECAST TO BECOME ESTABLISHED FROM THE HIGH PLAINS LOW SWD INTO

SWRN TX BEFORE IT IS OVERTAKEN BY A PACIFIC COLD FRONT LATER

TONIGHT. A WARM FRONT DEVELOPING ACROSS SRN NEB IS EXPECTED TO LIFT

NWD ACROSS PARTS OF SD TONIGHT.

...NRN/CENTRAL HIGH PLAINS REGION...

ELEVATED STORMS ARE OCCURRING IN A BAND FROM SWRN SD ACROSS CENTRAL

NEB AND NORTH CENTRAL KS WITHIN A ZONE OF FOCUSED WARM ADVECTION.

THIS ACTIVITY IS EXPECTED TO SPREAD NWD AND SLOWLY WEAKEN AS THE

SOUTHERLY LOW-LEVEL JET AND ASSOCIATED THERMAL ADVECTION DIMINISHES

LATER THIS MORNING. IN THE WAKE OF THESE STORMS...MOISTURE WILL

SPREAD NWD AS PRESSURE FALLS INCREASE OVER WRN PARTS OF NEB AND

SD...WITH SURFACE DEW POINTS IN THE 50S TO LOW 60S EXPECTED

ALONG/SOUTH OF THE WARM FRONT. STEEPER MID-LEVEL LAPSE RATES /7-8

DEG PER KM/ OVER THE HIGH PLAINS COUPLED WITH MODERATE DIABATIC

HEATING IN THE LOW LEVELS WILL RESULT IN AIR MASS DESTABILIZATION

WITH SBCAPE REACHING 1000-2000 J/KG THIS AFTERNOON.

FOCUSED LOW-LEVEL CONVERGENCE IS EXPECTED TO INCREASE THIS AFTERNOON

NEAR THE SURFACE LOW AND ADJACENT WARM FRONT. THIS WILL COMBINE

WITH UPSLOPE FLOW TO THE NORTH OF THE LOW AND DIVERGENCE ALOFT IN

LEFT EXIT REGION OF THE UPPER-LEVEL JET AS IT ADVANCES NWD ACROSS

THE SRN/CENTRAL ROCKIES TO ENHANCE UPWARD MOTION OVER THE AREA.

CONSENSUS OF MESOSCALE AND CONVECTION-ALLOWING MODELS INDICATE

STORMS WILL DEVELOP BY EARLY/MID AFTERNOON ACROSS SERN WY/NERN

CO/NEB PANHANDLE/SWRN SD REGION WITH ACTIVITY SPREADING NEWD THROUGH

THE EVENING HOURS. VEERING WIND PROFILES WITH HEIGHT...PARTICULARLY

ALONG AND NORTH OF THE WARM FRONT... WILL RESULT IN SUFFICIENT

DEEP-LAYER SHEAR /35-45 KT IN LOWEST 6 KM AGL/ FOR ORGANIZED STORMS

TO DEVELOP INCLUDING A FEW SUPERCELLS. STRONG CELLS WILL BE CAPABLE

OF PRODUCING LARGE HAIL...DAMAGING WIND GUSTS...AND A FEW TORNADOES

THROUGH THE EVENING HOURS. ACTIVITY MAY DEVELOP INTO ONE OR MORE

NEWD MOVING LINE SEGMENTS BY THIS EVENING WITH THE SEVERE THREAT

POSSIBLY TRANSITIONING TO MAINLY DAMAGING WIND GUSTS BEFORE STORMS

WEAKEN AFTER 03-06Z.

...WRN KS INTO WRN TX...

ALTHOUGH THE DRY LINE IS EXPECTED TO MIX EWD DURING THE

DAY...LIMITED FORCING FOR LARGE-SCALE ASCENT AND WEAK LOW-LEVEL

CONVERGENCE SUGGEST STORM DEVELOPMENT WILL REMAIN ISOLATED DURING

THE AFTERNOON AND EARLY EVENING. FAVORABLE INSTABILITY/STEEP

LOW-MID LEVEL LAPSE RATES AND 30-40 KT VERTICAL SHEAR WILL BE

SUPPORTIVE OF HAIL AND STRONG WIND GUSTS WITH ANY SUSTAINED CELL

THAT FORMS. THE DRY LINE IS FORECAST TO RETREAT WWD DURING THE

EVENING...AND AS THE COLD FRONT MOVES EWD AND OVERTAKES THE DRY LINE

FROM NORTH TO SOUTH DURING THE NIGHT...MORE STORMS ARE EXPECTED TO

INITIATE IN A BAND FROM EXTREME ERN CO/WRN KS SWD INTO PARTS OF WEST

TX. VERTICAL SHEAR WILL INCREASE AS THE MID/UPPER LEVEL JET SHIFTS

EWD/NEWD INTO THE SRN/CENTRAL HIGH PLAINS AND OVERSPREADS THE WRN

EDGE OF THE WARM SECTOR. THE PRIMARY THREAT FROM STRONGER STORMS

WILL BE DAMAGING WIND GUSTS AND LARGE HAIL INTO THE OVERNIGHT HOURS.

...SOUTH TX...

A SMALL LINEAR CLUSTER OF ORGANIZED STRONG TO SEVERE STORMS HAS

PERSISTED OVERNIGHT AND IS MOVING EWD INTO PARTS OF ERN LA SALLE AND

NRN WEBB COUNTIES. NEW DEVELOPMENT HAS TAKEN PLACE ON THE SRN FLANK

OF THE STORMS WHERE MOIST INFLOW IS PROMOTING NEW UPDRAFT FORMATION.

THE STORMS ARE LOCATED DOWNSTREAM FROM A WELL-DEFINED FEATURE IN

WATER VAPOR IMAGERY THAT IS PROGRESSING EWD ACROSS SWRN TX AND NRN

MEXICO. THIS SUGGESTS THE ACTIVITY MAY PERSIST THROUGH THE MORNING

AS IT SPREADS EWD/SEWD WITHIN AN ENVIRONMENT CHARACTERIZED BY 30-40

KT DEEP-LAYER SHEAR AND CAPE OF 1500-2500 J/KG. THIS WILL SUPPORT A

THREAT FOR LARGE HAIL...DAMAGING WINDS...AND POSSIBLY A BRIEF

TORNADO OR TWO GIVEN THE FAVORABLE LOW-LEVEL HODOGRAPH STRUCTURE

EXHIBITED BY CRP VAD WINDS.

...LOWER MO VALLEY INTO THE LOWER GREAT LAKES...

A RATHER BROAD ZONE OF CONVECTION IS FORECAST TO EVOLVE WITHIN A

BACKGROUND LOW-LEVEL WARM ADVECTION REGIME...AS GRADUAL MOISTENING

OF THE LOW-LEVEL AIR MASS COMBINES WITH SOME AFTERNOON HEATING TO

RESULT IN AN AMPLY UNSTABLE ENVIRONMENT. STRONGEST FLOW ALOFT

ACROSS THE REGION WILL LIKELY REMAIN CONFINED TO THE LOWER GREAT

LAKES REGION -- WHERE WEAKEST INSTABILITY IS EXPECTED. FARTHER

W...GREATER MOISTURE/INSTABILITY BUT WEAKER FLOW ALOFT SHOULD -- IN

AN OVERALL SENSE -- GREATLY LIMIT ORGANIZATION POTENTIAL/SEVERE

WEATHER RISK. STILL...WITH A STRONGER WIND GUST OR MARGINALLY

SEVERE HAILSTONE NOT OUT OF THE QUESTION...WILL MAINTAIN AN AREA OF

LOW /5%/ HAIL AND WIND SEVERE WEATHER RISK ACROSS THIS REGION.

..WEISS/LEITMAN.. 05/15/2015

Friday, May 15, 2015 @ 1055 CDT: Leaving Colby, KS now... headed north and west, into Nebraska...

Friday, May 15, 2015 @ 1145 CDT: Here's the updated tornado outlook from the SPC. We've got farther to go to get into position for today's chase...