DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0356 AM CDT SUN JUL 14 2013

VALID 171200Z - 221200Z

...DISCUSSION...
MULTI-DAY SEVERE EVENT POSSIBLE D5 /THU JUL 18/ THROUGH D7 /SUN JUL
20/

MEDIUM RANGE GUIDANCE FROM THE GFS...ECMWF AND CMC GLOBAL MODELING
SYSTEMS HAS BEEN CONSISTENT WITH THE LARGE SCALE PATTERN EVOLUTION
DURING THE D4-8 PERIOD SHOWING DEVELOPMENT OF BROAD LONG WAVE TROUGH
MOVING ACROSS SERN CANADA...THE GREAT LAKES AND NERN STATES. AS
THIS OCCURS A SURFACE LOW...INITIALLY OVER THE NRN PLAINS...WILL
MOVE ENEWD ACROSS THE NRN GREAT LAKES AND SERN CANADA WHILE A
TRAILING COLD FRONT EXTENDING SWWD FROM THE LOW ADVANCES SEWD ACROSS
GREAT LAKES AND NERN STATES. ALTHOUGH THE ECMWF DETERMINISTIC RUNS
AND ENSEMBLE SYSTEMS HAVE EXHIBITED MORE RUN-TO-RUN CONTINUITY THAN
THE GFS IN THE HANDLING OF THE SHORT WAVE FEATURES AND ASSOCIATED
WIND FIELDS ASSOCIATED WITH THE LONG WAVE TROUGH...A SIMILAR LARGE
SCALE SIGNAL FROM MULTIPLE MODELING SYSTEMS SUGGESTS PATTERN
PREDICTABILITY IS RELATIVELY HIGH DURING THIS PERIOD IN THE REGION
OF INTEREST.

A VERY MOIST AND UNSTABLE AIR MASS IS LIKELY TO BE PRESENT OVER THE
NRN PLAINS/UPPER MS VALLEY AND INTO THE NERN STATES ON D4-5 IN
ADVANCE OF THE SURFACE LOW AND COLD FRONT. THIS WILL INCREASE THE
POTENTIAL FOR WIDESPREAD DAMAGING WIND GUSTS AND OCCASIONAL HAIL TO
OCCUR WITH SEVERE STORMS ALONG AND AHEAD OF THE COLD FRONT.
ALTHOUGH PRIMARY THREAT AREAS MAY BE MODULATED BY EFFECTS OF PRIOR
CONVECTION/OUTFLOW BOUNDARIES...OVERALL SYNOPTIC SCALE FORCING
APPEARS SUFFICIENT TO DELINEATE REGIONS OF ENHANCED SEVERE POTENTIAL
DURING THIS PERIOD.

D5 /THU JUL 18/...SEVERE STORM POTENTIAL IS EXPECTED TO INCREASE BY
LATE AFTERNOON/EVENING OVER THE UPPER MS VALLEY ALONG/NORTH OF A
WARM FRONT...WITH SEVERE STORMS POSSIBLY SPREADING EWD DURING THE
OVERNIGHT HOURS TOWARD THE GREAT LAKES. THIS WILL OCCUR AS THE
SURFACE LOW MOVES EWD AND THE LOW LEVEL JET VEERS...STRENGTHENS AND
BECOMES COUPLED WITH A STRONG WNWLY MID/UPPER LEVEL JET POSITIONED
IMMEDIATELY TO ITS NORTH.

D6 /FRI JUL 19/...THE ELONGATED COUPLED LOW/MID LEVEL JET STRUCTURE
IS EXPECTED TO PROGRESS EWD ACROSS THE GREAT LAKES AND INTO THE NERN
STATES AS THE SURFACE LOW MOVES ACROSS SRN CANADA...AND THE COLD
FRONT MOVES SEWD ACROSS THE GREAT LAKES. SEVERE STORM POTENTIAL IS
EXPECTED TO CONTINUE EWD/ESEWD ALONG AND AHEAD OF THE COLD FRONT
FROM THE GREAT LAKES INTO NRN PARTS OF THE NERN STATES.

...SYNOPSIS...
TROUGHING WILL PREVAIL OVER THE WRN AND ERN PORTIONS OF THE U.S.
THIS PERIOD...WITH LARGE-SCALE RIDGING IN BETWEEN. WITHIN THE RIDGE
HOWEVER...AN UPPER FEATURE IS FORECAST TO MOVE ACROSS THE NRN PLAINS
VICINITY -- WHICH WILL BE A PRIMARY CONTRIBUTOR TO SEVERE POTENTIAL
THIS PERIOD.

AT THE SURFACE...A LOW WILL ACCOMPANY THIS CENTRAL U.S.
IMPULSE...PROVIDING AMPLE ASCENT FOR CONVECTIVE DEVELOPMENT DURING
THE AFTERNOON AND EVENING HOURS.

...SD EWD ACROSS THE SRN MN/IA VICINITY...
AS THE UPPER VORT MAX CROSSES THE NRN PLAINS VICINITY...AIRMASS
DESTABILIZATION IS FORECAST ACROSS AREAS N AND E OF THE ACCOMPANYING
SURFACE LOW -- PROGGED TO TRACK ACROSS THE NEB VICINITY THROUGH THE
DAY. CAPPING IS FORECAST TO BE A CONCERN ACROSS MUCH OF THE PLAINS
/GIVEN BACKGROUND LARGE-SCALE RIDGING/...BUT MAXIMIZED ASCENT JUST
N/E OF THE LOW AND IN ADVANCE OF THE UPPER FEATURE SHOULD RESULT IN
STORM DEVELOPMENT AS THE AIRMASS DESTABILIZES DURING THE AFTERNOON.
WITH STRONGLY VEERING WIND PROFILES...SHEAR WILL SUPPORT
SUPERCELLS...BUT GIVEN CAPPING ISSUES AND THUS CONCERNS ABOUT STORM
COVERAGE...WILL INITIATE ONLY 15%/SLIGHT RISK ATTM. STORMS MAY
INCREASE IN COVERAGE DURING THE EVENING AS A LOW-LEVEL JET DEVELOPS
-- WITH AN MCS POSSIBLY EVOLVING AND MOVING ACROSS ERN SD/SRN MN/NRN
IA. IF THIS OCCURS...THREAT FOR DAMAGING WINDS AS WELL AS HAIL WILL
LIKELY CONTINUE THROUGH THE EVENING.

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0349 AM CDT SUN JUN 09 2013

VALID 121200Z - 171200Z

...DISCUSSION...
MEDIUM-RANGE MODELS ARE IN BROAD/GENERAL AGREEMENT THAT THE UPPER
PATTERN WILL REMAIN CHARACTERIZED BY A LARGE CENTRAL U.S. LONG-WAVE
RIDGE SANDWICHED BETWEEN WRN CONUS AND ERN CONUS TROUGHING THROUGH
THE LATTER STAGES OF THE PERIOD.

DESPITE THE BROAD AGREEMENT HOWEVER...THE MODELS DIFFER WITH RESPECT
TO INDIVIDUAL/SMALL-SCALE FEATURES PROGGED TO EJECT FROM THE WRN
U.S. TROUGH AND PROGRESS ANTICYCLONICALLY EWD ACROSS THE CENTRAL
U.S. AROUND THE NRN FRINGE OF THE LONG-WAVE RIDGE.

THE FIRST OF A SERIES OF SUCH SMALL-SCALE FEATURES IS FORECAST TO BE
CROSSING THE UPPER MIDWEST DAY 4 /WED. 6-12/...WITH SOME SEVERE
POTENTIAL EVIDENT ACROSS PARTS OF THE OH VALLEY REGION. ATTM
HOWEVER...POTENTIAL DOES NOT APPEAR TO WARRANT INTRODUCTION OF A 30%
EQUIVALENT THREAT AREA.