SWODY2
SPC AC 251743
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1243 PM CDT THU JUN 25 2009
VALID 261200Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CENTRAL/NRN
PLAINS TO UPPER MS VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID ATLANTIC STATES TO
SRN NEW ENGLAND...
...SYNOPSIS...
NRN STREAM IS EXPECTED TO BECOME MORE AMPLIFIED DURING THE DAY 2
PERIOD AS A PAIR OF SHORT WAVE TROUGHS OVER HUDSON BAY/ONTARIO
CONSOLIDATE INTO A CLOSED LOW ACROSS THE NERN STATES ON FRIDAY.
MEANWHILE...AN UPSTREAM TROUGH...CURRENTLY LOCATED OVER WRN
CANADA/PACIFIC NW...ADVANCES EWD BREAKING DOWN THE NRN EXTENT OF THE
CENTRAL U.S. RIDGE ACROSS THE NRN PLAINS/CENTRAL CANADA. ANOTHER
SHORT WAVE TROUGH EMANATING FROM THE SWRN STATES IS FORECAST TO
PRECEDE THE WRN CANADA TROUGH AND AID IN INITIALLY LOWERING
HEIGHTS/WEAKENING THE CAP OVER THE NRN PLAINS FRIDAY AFTERNOON.
...NORTH CENTRAL STATES...
12Z NAM/GFS 00Z ECMWF ARE IN GENERAL AGREEMENT WITH THE SWRN STATES
SHORT WAVE TROUGH MOVING NEWD ACROSS THE NRN PLAINS FRIDAY AFTERNOON
AND REACHING MN BY 12Z SATURDAY. FORCING FOR ASCENT ATTENDANT TO
THIS LEAD IMPULSE/ADDITIONAL HEIGHT FALLS WITH WRN CANADA TROUGH
COMBINED WITH LOW LEVEL CONVERGENCE ALONG A COLD FRONT MOVING EWD
ACROSS THE DAKOTAS AND ALSO INTO SERN WY/NERN CO WILL SUPPORT TSTM
DEVELOPMENT FRIDAY AFTERNOON IN THE WAKE OF A MORNING ERN DAKOTAS
MCS. TSTM DEVELOPMENT SHOULD ALSO BE FOCUSED ALONG A PAIR OF WARM
FRONTS EXTENDING ESEWD FROM SRN ND INTO WRN MN AND FROM SRN SD TO
IA. MOIST WARM SECTOR IS EXPECTED TO BECOME MODERATELY UNSTABLE
BENEATH PLUME OF STEEP MID LEVEL LAPSE RATES. STRENGTHENING DEEP
LAYER SHEAR WILL SUPPORT SUPERCELLS PRODUCING HAIL/DAMAGING WINDS
ALONG THE COLD FRONT/WARM FRONTS. THE MOIST BOUNDARY LAYER AND 1 KM
SRH 100-200 M2/S2 WILL ALSO BE FAVORABLE FOR A TORNADO THREAT...
ESPECIALLY IN THE VICINITY OF THE PAIR OF TRIPLE POINTS AND ESEWD
ALONG THE ATTENDANT WARM FRONTS WHERE DIRECTIONAL SHEAR WILL BE
ENHANCED AS THE SWLY LLJ STRENGTHENS FRIDAY AFTERNOON/EVENING.
FURTHER STRENGTHENING OF THE LLJ SUGGESTS ONE OR TWO CONVECTIVE
CLUSTERS WILL EVOLVE FRIDAY NIGHT AND MOVE ACROSS THE ERN DAKOTAS/
NRN NEBRASKA INTO MN/NRN IA...WITH WIND DAMAGE BECOMING THE PRIMARY
THREAT. THIS OUTLOOK HAS INCREASED THE SEVERE PROBABILITIES ACROSS
ERN DAKOTAS INTO WRN MN/ NWRN IA WHERE STORMS WILL BE POSSIBLE FROM
THE AFTERNOON INTO THE OVERNIGHT PERIOD...ENHANCING THE OVERALL
SEVERE WEATHER THREAT.
...MID ATLANTIC STATES TO SRN NEW ENGLAND AND LOWER GREAT LAKES...
A LEAD SHORT WAVE TROUGH WILL MOVE ACROSS SRN NEW ENGLAND FRIDAY
MORNING/AFTERNOON...WHILE THE UPSTREAM HUDSON BAY TROUGH DEVELOPS
SEWD ACROSS THE LOWER GREAT LAKES TO NEW ENGLAND. TSTMS ARE
EXPECTED TO DEVELOP BY FRIDAY AFTERNOON WITHIN A MOIST/MODERATELY
UNSTABLE AIR MASS EXTENDING FROM THE MID ATLANTIC REGION TO SRN NEW
ENGLAND AS A SURFACE FRONT SPREADS ACROSS THIS REGION. DEEP WSWLY
WIND FIELDS AND EFFECTIVE BULK SHEAR AROUND 30 KT SUGGEST ORGANIZED
LINE SEGMENTS WILL BE POSSIBLE WITH DAMAGING WINDS BEING THE PRIMARY
THREAT. FARTHER WNW...COLD MID LEVEL TEMPERATURES SPREADING ACROSS
THE LOWER GREAT LAKES SUGGESTS TSTMS DEVELOPING WITHIN CYCLONIC
UPPER LEVEL FLOW REGIME AND ALONG A SECONDARY SURFACE TROUGH SHOULD
SUPPORT AN ISOLATED THREAT FOR STRONG TO SEVERE STORMS FRIDAY
AFTERNOON.
...OH VALLEY TO CAROLINAS...
THE WRN EXTENT OF THE COLD FRONT MOVING THROUGH NEW ENGLAND WILL
SHIFT SLOWLY SWD THROUGH THE OH VALLEY FRIDAY. TSTMS ARE EXPECTED
TO DEVELOP ALONG THIS BOUNDARY BY FRIDAY AFTERNOON AS THE AIR MASS
BECOMES MODERATELY UNSTABLE BENEATH WEAK UPPER FORCING. NWLY FLOW
ALOFT SHOULD SUPPORT EFFECTIVE BULK SHEAR AROUND 25 KT AND THE
POTENTIAL FOR A FEW STORMS TO PRODUCE STRONG/DAMAGING WINDS AND/OR
HAIL. A FEW STRONG TO SEVERE STORMS WILL ALSO BE POSSIBLE ALONG A
SEA BREEZE BOUNDARY MOVING INLAND ACROSS NERN GA/CAROLINAS.
HERE...TOO...MODERATE INSTABILITY AND MODEST DEEP LAYER SHEAR SHOULD
SUPPORT A FEW ORGANIZED STORMS WITH AN ISOLATED THREAT FOR MAINLY
STRONG WIND GUSTS.
..PETERS.. 06/25/2009
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