SPC AC 190550
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1250 AM CDT SAT JUN 19 2010
VALID 191200Z - 201200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTN AND EVEN ACROSS PARTS
OF THE UPPER OHIO VALLEY/LOWER GREAT LAKES REGION...
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND TONIGHT
ACROSS THE NORTH CENTRAL PLAINS...
...SYNOPSIS...
SUBTROPICAL RIDGING...CENTERED NEAR OR JUST INLAND OF THE
WESTERN/CENTRAL GULF COAST...APPEARS LIKELY TO REMAIN STRONG THROUGH
THIS FORECAST PERIOD...ENCOMPASSING MUCH OF THE CENTRAL AND SOUTHERN
TIER OF THE U.S. TO THE EAST OF THE ROCKIES. WITHIN THE PERSISTENT
LARGE-SCALE UPPER TROUGH OVER THE WEST...MODELS INDICATE THAT A
SIGNIFICANT CLOSED LOW WILL CONTINUE DIGGING INLAND ACROSS THE NORTH
CENTRAL PACIFIC COAST. MEANWHILE...A SERIES OF JET STREAKS
EMANATING FROM THE SUBTROPICAL PACIFIC IS PROGGED TO CONTINUE INLAND
THROUGH THE BASE OF THE TROUGH ACROSS SOUTHERN CALIFORNIA...BEFORE
NOSING AROUND THE WESTERN AND NORTHERN PERIPHERY OF THE UPPER RIDGE.
AS THIS OCCURS...REMNANT SHORT WAVE TROUGHING WITHIN THE SOUTHERN
BRANCH OF CONFLUENT BELTS OF WESTERLIES NEAR/NORTH OF THE
CANADIAN/U.S. BORDER IS EXPECTED MIGRATE EAST OF THE UPPER GREAT
LAKES. DOWNSTREAM OF BROADER SCALE RIDGING...THIS LATTER FEATURE
MAY SUBTLY DIG TOWARD THE NORTHEASTERN U.S. LATE THIS AFTERNOON AND
TONIGHT.
...LOWER OH/TN VALLEYS AND NRN GULF STATES INTO THE NORTHEAST...
A REMNANT OUTFLOW BOUNDARY ASSOCIATED WITH ONGOING CONVECTION IS
EXPECTED TO ADVANCE SOUTHEASTWARD THROUGH THE REMAINDER OF THE
NIGHT...A BIT MORE RAPIDLY INTO/THROUGH THE LOWER OHIO VALLEY THAN
THE LOWER MISSOURI/MID MISSISSIPPI VALLEY REGION. THIS WILL
PROBABLY SLOW...IF NOT CUT OFF...BETTER RETURN FLOW OF MOISTURE FROM
THE SOUTH CENTRAL STATES...BUT SUFFICIENT MOISTENING IS EXPECTED
AHEAD OF A COLD FRONT ADVANCING ACROSS SOUTHEASTERN CANADA AND THE
LOWER GREAT LAKES TO CONTRIBUTE TO WEAK TO MODERATE INSTABILITY BY
LATE AFTERNOON. DESTABILIZATION IN THE PRESENCE OF 30-40+ KT DEEP
LAYER SOUTHWESTERLY MEAN FLOW AHEAD OF THE APPROACHING UPPER TROUGH
PROBABLY WILL BE SUFFICIENT FOR SCATTERED VIGOROUS STORM
DEVELOPMENT. A FEW SEVERE STORMS ARE POSSIBLE... PARTICULARLY TO
THE LEE OF THE LOWER GREAT LAKES DURING THE LATE AFTERNOON AND
EVENING...BUT PERHAPS ALSO ACROSS THE INTERNATIONAL BORDER INTO
NORTHERN NEW ENGLAND DURING THE EVENING HOURS.
FARTHER WEST AND SOUTHWEST...FORCING FOR NEW CONVECTIVE DEVELOPMENT
ALONG THE STALLING/WEAKENING OUTFLOW BOUNDARY DURING THE DAY IS
UNCLEAR. IT MAY BE THAT REMNANT MESOSCALE CONVECTIVE VORTICES
CONTINUE SOUTHEASTWARD...AND CONTRIBUTE TO NEW CONVECTION IN WEAKLY
CAPPED MOIST/UNSTABLE AIR SOUTH OF THE OHIO RIVER INTO PARTS OF THE
NORTHERN GULF STATES AND OZARK PLATEAU. THOUGH WELL SOUTH OF THE
STRONGER WESTERLIES...THERMODYNAMIC PROFILES MAY BE CONDUCIVE TO
LOCALIZED DOWNBURSTS IN STRONGER STORMS.
...CENTRAL PLAINS...
GREATER SEVERE POTENTIAL TODAY SEEMS TO EXIST NEAR A STALLING...
EAST-WEST FRONTAL ZONE ACROSS THE CENTRAL PLAINS. VERY WARM
ELEVATED MIXED LAYER AIR WILL PROVIDE STRONG CAPPING...WHICH MAY
PRECLUDE CONVECTIVE ACTIVITY TO THE SOUTH OF THE FRONT. BUT
MOISTENING ON EASTERLY LOW-LEVEL FLOW ALONG AND NORTH OF THE SURFACE
FRONT INTO THE FRONT RANGE OF THE ROCKIES IS EXPECTED TO CONTRIBUTE
TO MODERATE TO STRONG DESTABILIZATION BY LATE AFTERNOON.
STEEP MID-LEVEL LAPSE RATES AND MIXED LAYER CAPE OF 2000-3000+ J/KG
WILL PROVIDE A FAVORABLE ENVIRONMENT FOR INTENSE STORMS...WHICH
SHOULD INITIATE OFF THE HIGHER TERRAIN BY PEAK AFTERNOON HEATING.
STORM INITIATION ALSO APPEARS PROBABLE PRIOR TO 20/00Z ON THE NOSE
OF A MODEST SOUTHERLY LOW-LEVEL JET ACROSS SOUTH CENTRAL NEBRASKA.
ALTHOUGH WESTERLY MID/UPPER FLOW NEAR THE FRONT MAY ALSO BE
RELATIVELY MODEST...PRONOUNCED VEERING WITH HEIGHT NORTH OF THE
FRONT WILL YIELD STRONG VERTICAL SHEAR. THE ENVIRONMENT IS EXPECTED
TO PROVE FAVORABLE FOR SUPERCELLS TRANSITIONING TO ONE OR MORE
ORGANIZED MESOSCALE CONVECTIVE SYSTEMS...CAPABLE OF GENERATING
ISOLATED VERY LARGE HAIL... EVENTUALLY AT LEAST LOCALIZED VERY
STRONG WIND GUSTS. STRONG WIND GUSTS AND HAIL MAY PERSIST WITH
CONVECTION THROUGH THE EVENING...AND INTO OVERNIGHT HOURS.
..KERR/HURLBUT.. 06/19/2010
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
|
