VALID 042000Z – 051200Z

…NO SVR TSTM AREAS FORECAST…

NO CHANGES WERE REQUIRED TO THE PREVIOUS OUTLOOK FOR THE MAJORITY OF
THE CONUS…THE EXCEPTION BEING NV.

…SIERRA INTO NWRN NV…
A WEAK SHORTWAVE TROUGH IS NOW MOVING ACROSS NRN CA AND INTO NW NV
WHICH IS PROVIDING COOLING ALOFT AS WELL AS ENHANCING SHEAR PROFILES
LOCALLY. STORMS WERE BEGINNING TO FORM OVER THE SIERRA AS WELL AS
OVER NRN CA INTO NWRN NV WITH PWAT AROUND 1.00 INCH. WITH CONTINUED
HEATING…STORMS WILL INCREASE IN COVERAGE…AND SHOULD PROPAGATE
GENERALLY IN AN EWD DIRECTION. DOWNDRAFTS WILL LIKELY BE COLD WITH
SOME HAIL POSSIBLE…WHICH WILL FURTHER HELP TO PRODUCE STRONG
OUTFLOW AND PERHAPS AN ISOLATED SEVERE GUST.

..JEWELL.. 07/04/2013

.PREV DISCUSSION… /ISSUED 1126 AM CDT THU JUL 04 2013/

…SYNOPSIS…

LITTLE CHANGE TO THE LARGE-SCALE PATTERN IS FORECAST THROUGH THE D1
PERIOD WITH A RIDGE-TROUGH-RIDGE CONFIGURATION EXTENDING FROM THE
SWRN DESERTS TO WRN ATLANTIC. SOME LOWERING OF MIDLEVEL HEIGHTS
WILL OCCUR OVER THE PACIFIC NW INTO NRN INTERMOUNTAIN REGION IN
CONJUNCTION WITH A POLAR-BRANCH SHORT-WAVE TROUGH MOVING ONSHORE.
IN THE LOW LEVELS…A BAROCLINIC ZONE /REINFORCED BY CLOUDS AND
PRECIPITATION/ WILL REMAIN QUASI STATIONARY FROM THE CNTRL GULF
COAST TO LOWER GREAT LAKES WHILE FARTHER TO THE W…A WEAK COLD
FRONT EDGES EWD TOWARD THE UPPER MS VALLEY.

…CNTRL/ERN GULF COAST STATES INTO TN VALLEY TODAY/TONIGHT…

A VORTICITY MAXIMUM OVER THE LOWER MS VALLEY WILL PROGRESS NNEWD
TODAY INDUCING A WEAK FRONTAL WAVE AND ENHANCING DEEP-LAYER ASCENT
ACROSS A VERY MOIST BUT ONLY WEAKLY UNSTABLE WARM SECTOR. THE NET
RESULT WILL BE A GRADUAL INCREASE IN TSTMS WITHIN THE WARM CONVEYOR
AIR STREAM ASSOCIATED WITH THE LARGE-SCALE TROUGH. LOW-LEVEL SHEAR
SHOULD CONTINUE TO STRENGTHEN WITH THE DEVELOPMENT OF A 35-45 KT LLJ
FROM ERN AL/WRN GA INTO MIDDLE/ERN TN. GIVEN THE VERY MOIST/LOW LCL
PBL…THE POTENTIAL WILL EXIST FOR EMBEDDED SUPERCELL STRUCTURES
WITH A RISK FOR A BRIEF TORNADO OR TWO IN ADDITION TO LOCALLY
DAMAGING WIND GUSTS. THE MARGINAL INSTABILITY IS EXPECTED TO
PRECLUDE A MORE ROBUST SEVERE WEATHER THREAT.

…UPPER OH VALLEY INTO NEW ENGLAND THIS AFTERNOON/EVENING…

BREAKS IN THE CLOUDS MAY ALLOW FOR STRONGER DAYTIME HEATING THAN
POINTS TO THE SOUTH WHICH WHEN COUPLED WITH BOUNDARY LAYER DEWPOINTS
IN THE UPPER 60S TO LOWER 70S WILL CONTRIBUTE TO AFTERNOON MLCAPE
VALUES OF 1000-2000 J/KG. THE WRN/NRN BOUNDS OF THIS INSTABILITY
AXIS WILL COINCIDE WITH A RIBBON OF ENHANCED MIDLEVEL FLOW /I.E.
40-45 KT AT 500 MB/…RESULTING IN A POTENTIAL CORRIDOR FOR
ORGANIZED STORM DEVELOPMENT WITH A RISK FOR ISOLATED DAMAGING
WINDS…HAIL…AND PERHAPS A TORNADO. THE PRIMARY UNCERTAINTY IS
THE COVERAGE/LONGEVITY OF ANY TSTM ACTIVITY OWING TO THE TENDENCY
FOR MIDLEVEL DRYING/SUBSIDENCE PER MORNING WATER VAPOR IMAGERY.

…NRN HIGH PLAINS THIS AFTERNOON/EVENING…

THE EWD PROGRESSION OF THE ABOVE-MENTIONED POLAR-BRANCH SHORT-WAVE
TROUGH INTO THE PACIFIC NW AND BRITISH COLUMBIA WILL INDUCE A LEE
CYCLONE/TROUGH OVER WRN/CNTRL MT LATER TODAY. THE 12Z GREAT FALLS
SOUNDING SHOWED THE PRESENCE OF A MOIST LOW-LEVEL AIR MASS WHICH
WILL COMPENSATE FOR MIDLEVEL LAPSE RATES OF GENERALLY LESS THAN 7
C/KM TO YIELD A MODERATELY UNSTABLE ENVIRONMENT BY AFTERNOON. WHILE
STRONGER FORCING FOR ASCENT ASSOCIATED WITH THE SHORT-WAVE TROUGH
WILL REMAIN TO THE WEST OF THE REGION THROUGH THE PEAK OF THE
DIURNAL HEATING CYCLE…LOW-LEVEL CONVERGENCE INVOF THE LEE
CYCLONE/TROUGH WILL FOSTER ISOLATED STORM DEVELOPMENT BY MID TO LATE
AFTERNOON WITH A RISK FOR LOCALLY DAMAGING WINDS AND/OR LARGE HAIL.

…SERN AZ INTO SRN ROCKIES AND SRN HIGH PLAINS…

HEATING ALONG THE HIGH TERRAIN WILL FOSTER SCATTERED STORM
DEVELOPMENT THIS AFTERNOON WITHIN A SIMILAR ENVIRONMENT TO PAST
DAYS. THE STRONGEST STORMS WILL BE CAPABLE OF ISOLATED OCCURRENCES
OF LARGE HAIL AND DAMAGING WINDS THROUGH THIS EVENING.