Saturday, September 7, 2013

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 071944
SWODY1
SPC AC 071941

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0241 PM CDT SAT SEP 07 2013

VALID 072000Z - 081200Z

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

...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF FAR ERN IA AND
NRN/CNTRL IL...

NO CHANGES HAVE BEEN MADE TO THE PREVIOUS D1 OUTLOOK.

..GARNER.. 09/07/2013

.PREV DISCUSSION... /ISSUED 1129 AM CDT SAT SEP 07 2013/

...SYNOPSIS...

AN UPPER HIGH WILL REMAIN ANCHORED OVER THE CNTRL PLAINS WITH AN
AMPLIFYING LONG-WAVE TROUGH OVER ERN CANADA INTO THE NERN U.S.
ELSEWHERE...AN UPPER LOW WILL REMAIN QUASI-STATIONARY OVER THE NRN
INTERMOUNTAIN REGION AND SRN CANADA ROCKIES. MORNING WATER VAPOR
IMAGERY AND UPPER-AIR ANALYSIS INDICATE A COUPLE LOW-AMPLITUDE
PERTURBATIONS WHICH MAY CONTRIBUTE TO STRONG TO SEVERE TSTM
DEVELOPMENT LATER TODAY. ONE OF WHICH WILL TRACK FROM NRN UT INTO
THE NRN HIGH PLAINS BY EVENING...WHILE ANOTHER PROGRESSES SEWD FROM
THE UPPER MIDWEST TOWARD THE MID MS VALLEY.

IN THE LOW LEVELS...MID-MORNING MESOANALYSIS SHOWED THE PRIMARY
SYNOPTIC COLD FRONT FROM THE WRN U.P. OF MI WSWWD THROUGH CNTRL
MN...NRN SD...INTO CNTRL MT. THE ERN PORTION OF THIS FRONT WILL
CONTINUE SWD THROUGH THE GREAT LAKES IN CONJUNCTION WITH THE
AMPLIFYING ERN CANADA/NERN U.S. TROUGH. MEANWHILE...THE WRN SEGMENT
OF THE FRONT WILL REMAIN QUASI-STATIONARY OVER THE NRN HIGH
PLAINS.

...NRN HIGH PLAINS THIS AFTERNOON INTO TONIGHT...

WIDELY SCATTERED ELEVATED TSTMS OVER PARTS OF CNTRL/ERN MT INTO THE
WRN DAKOTAS ARE LIKELY BEING FORCED BY LOW-LEVEL CONVERGENCE/UPLIFT
ALONG AND TO THE N OF THE SYNOPTIC BOUNDARY WHERE THE PRESENCE OF
STEEP MIDLEVEL LAPSE RATES AND A SEASONALLY MOIST ENVIRONMENT /I.E.
PW VALUES OF AROUND 1.50 INCHES/ ARE ALREADY CONTRIBUTING TO
MODERATE INSTABILITY FOR MOST-UNSTABLE-LIFTED PARCELS. INCREASED
FORCING FOR ASCENT/DCVA ASSOCIATED WITH THE DISTURBANCE MENTIONED IN
THE SYNOPSIS WILL LIKELY SUSTAIN A SUBSET OF ONGOING TSTMS INTO
AFTERNOON WITH ADDITIONAL STORM DEVELOPMENT LIKELY ALONG THE FRONT
AS WELL AS ALONG FAVORED TERRAIN.

THE COLOCATION OF A MOIST...MODERATELY UNSTABLE AIR MASS /I.E.
MLCAPE OF 1000-2000 J PER KG/ WITH A VERTICALLY VEERING WIND PROFILE
WITH 35-45 KT OF DEEP-LAYER SHEAR SUGGESTS THE POTENTIAL FOR
SUPERCELLS CAPABLE OF LARGE HAIL...DAMAGING WINDS...AND PERHAPS A
BRIEF TORNADO. COALESCING STORM-SCALE OUTFLOWS AND THE DEVELOPMENT
OF A NOCTURNAL LOW-LEVEL WIND MAXIMUM THIS EVENING MAY PROMOTE
UPSCALE GROWTH OF STORMS INTO ONE OR MORE TSTM COMPLEXES WITH THE
DAMAGING WIND AND HAIL THREAT PERSISTING THROUGH LATE EVENING OVER
THE WRN DAKOTAS.

...MIDWEST THIS AFTERNOON AND EVENING...

12Z UPPER-AIR ANALYSIS INDICATED THE PRESENCE OF A WARM EML /I.E.
STEEP MIDLEVEL LAPSE RATES AND A STRONG CAP TO SURFACE-BASED
PARCELS/ FROM THE CNTRL ROCKIES SOURCE REGION ENEWD THROUGH THE MID
MO VALLEY. THE MOST PROBABLE LOCATION FOR SURFACE-BASED AFTERNOON
STORM DEVELOPMENT WILL BE OVER ERN IA INTO NRN/CNTRL IL ALONG THE
ERN FRINGE OF THIS EML WHERE LOW-LEVEL UPLIFT ALONG THE COLD FRONT
AND DCVA ATTENDANT TO THE SEWD-MOVING PERTURBATION WILL BE
SUFFICIENT TO OVERCOME THE CAP.

WHILE VERTICAL SHEAR IS NOT EXPECTED TO BE PARTICULARLY STRONG
/30-35 KT/...THE PRESENCE OF THE STEEP LAPSE RATES AND MLCAPE OF
1500-2500+ J/KG WILL BE SUPPORTIVE OF ORGANIZED STORM MODES
INCLUDING THE POSSIBILITY OF A FORWARD-PROPAGATING MCS...AS
SUGGESTED BY RECENT CONVECTION-ALLOWING MODEL GUIDANCE. DAMAGING
WINDS AND HAIL WOULD BE THE PRIMARY SEVERE WEATHER HAZARDS WITH
THESE STORMS.

...LOWER MI THIS AFTERNOON...

MIDLEVEL HEIGHT FALLS/FORCING FOR ASCENT WILL INCREASE ACROSS THE
REGION IN CONJUNCTION WITH THE AMPLIFYING LARGE-SCALE TROUGH. THIS
COUPLED WITH THE INFLUX OF A WARM/MOIST LOW-LEVEL AIR MASS FROM THE
WEST SHOULD FOSTER AN INCREASE IN STORM COVERAGE ALONG THE FRONT
LATER TODAY. WHILE INSTABILITY WILL REMAIN SOMEWHAT
LIMITED...STRENGTHENING MID AND UPPER-LEVEL FLOW WILL OVERSPREAD THE
AREA...POTENTIALLY CONTRIBUTING TO SOME STORM ORGANIZATION WITH A
RISK FOR LOCALLY STRONG WIND GUSTS.

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