>Today’s SPC Day 1 Forecasts.

>


SPC AC 070559

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT FRI MAY 07 2010

VALID 071200Z – 081200Z

…THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF IND AND OH…

…THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM
THE OH VALLEY TO SERN TX…

…OH VALLEY/LOWER GREAT LAKES…

00Z NAM/GFS GUIDANCE IS IN REASONABLE AGREEMENT WITH SPEED/MOVEMENT
OF MID LEVEL TROUGH AND ASSOCIATED H5 SPEED MAX ACROSS THE MID MS
VALLEY INTO THE OH VALLEY DURING THE LATTER HALF OF THE PERIOD.
THIS FEATURE WILL FORCE CNTRL PLAINS SFC LOW TO A POSITION JUST
SOUTH OF CHI OVER ECNTRL IL AT 18Z…THEN DEEPENING IS EXPECTED AS
THE CYCLONE LIFTS NEWD INTO LOWER MI DURING THE EVENING HOURS.
ALTHOUGH BOUNDARY LAYER MOISTURE IS SOMEWHAT LIMITED ACROSS THE
CNTRL/SRN CONUS EARLY THIS MORNING…A MODIFIED MOIST PLUME HAS
RETURNED ACROSS THE SRN PLAINS/LOWER MS VALLEY AND THIS AIRMASS
SHOULD EASILY RETURN TO THE OH VALLEY DUE TO STRENGTHENING LOW
PRESSURE SYSTEM AND INCREASINGLY CONVERGENT FLOW REGIME. NAM…IN
PARTICULAR…SUGGESTS THE CYCLONE WILL DEEPEN SIGNIFICANTLY AS SPEED
MAX INCREASES TO AROUND 110KT BY THE END OF THE PERIOD OVER
OH…WITH INTENSE 12HR HEIGHT FALLS INCREASING TO 240-300M.
NEEDLESS TO SAY VERY STRONG FLOW AND SUBSTANTIAL VERTICAL SHEAR WILL
EXIST ACROSS THE OH VALLEY ALONG THE RETREATING WARM FRONT AND
ACROSS MUCH OF THE WARM SECTOR PRIOR TO SEVERE CONVECTIVE
DEVELOPMENT.

LATEST THINKING IS ONGOING ELONGATED SW-NE ORIENTED MCS WILL
SPREAD/DEVELOP AHEAD OF SFC LOW ACROSS NRN IL INTO LOWER MI EARLY IN
THE PERIOD. STRONG WARM ADVECTION SHOULD MAINTAIN DEEP CONVECTIVE
THREAT MUCH OF THE PERIOD NORTH OF THE RETREATING WARM FRONT. OF
PARTICULAR CONCERN IS NEAR AND JUST SOUTH OF THE WARM FRONT AHEAD OF
THE SFC LOW. STRONG SHEAR WILL CERTAINLY SUPPORT SUPERCELLS AND BOW
ECHO-TYPE STRUCTURES COULD ALSO EMERGE. IF STORM MODE TRENDS
TOWARDS BOW ECHOES THEN DAMAGING WINDS WILL BE THE PRIMARY SEVERE
THREAT. HOWEVER…THERE IS SOME REASON TO BELIEVE MORE DISCRETE
ACTIVITY COULD BE THE NORM ACROSS THE WARM SECTOR AS MODELS SUGGEST
VERY STEEP MID LEVEL LAPSE RATES WILL OVERSPREAD THE OH
VALLEY…CAPPING THE WARM SECTOR INTO THE MID AFTERNOON HOURS.
GIVEN THE STRONG DYNAMICS AND RECOVERING/MOISTENING AIRMASS FEEL A
MODERATE RISK FOR SEVERE THUNDERSTORMS IS CERTAINLY WARRANTED…EVEN
IF THE STORM MODE IS SOMEWHAT IN QUESTION. LARGE HAIL IS ALSO
LIKELY WITH ROTATING UPDRAFTS AS LAPSE RATES WILL BE STEEP AND
SUPPORTIVE OF HAIL PRODUCTION.

…TN VALLEY TO SERN TX…

STRONG HEATING WILL BE REQUIRED FOR CONVECTIVE DEVELOPMENT ALONG
TRAILING COLD FRONT INTO SERN TX AS LARGE SCALE ASCENT LIFTS WELL
NORTH OF THE REGION. MODEL FORECAST SOUNDINGS SUGGEST SFC PARCELS
WILL HIT CONVECTIVE TEMPERATURE IN THE LOWER 90S ACROSS TX WITH
MID-UPPER 80S LIKELY SUFFICIENT INTO THE WRN TN VALLEY. THIS
ACTIVITY SHOULD DEVELOP WITHIN A MODESTLY SHEARED ENVIRONMENT…BUT
NOT PARTICULARLY SUPPORTED IN THE LARGE SCALE…THOUGH THUNDERSTORMS
SHOULD LINGER WELL INTO THE OVERNIGHT HOURS DUE TO CONVERGENCE ALONG
COLD FRONT. LARGE HAIL AND DAMAGING WINDS ARE POSSIBLE.

…FL…

STRONG DIABATIC HEATING WILL ENHANCE THERMAL CIRCULATIONS ALONG SEA
BREEZES LATER TODAY ACROSS THE CNTRL/SRN PENINSULA. NWLY FLOW AT
MID LEVELS IS A EXPECTED TO BE A BIT STRONGER THAN THURSDAY…THUS
ACTIVITY MAY BE MORE ORGANIZED AND POSSIBLY REQUIRING AN UPGRADE TO
SLIGHT RISK AS THE EVENT UNFOLDS. LARGE HAIL AND DAMAGING
DOWNBURSTS ARE POSSIBLE WITH STRONG MULTI CELL…AND PERHAPS A FEW
SUPERCELL STRUCTURES.

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