SWODY3
SPC AC 160731
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0231 AM CDT SUN OCT 16 2011
VALID 181200Z - 191200Z
...SYNOPSIS...
MODELS DIFFER WITH RESPECT TO THE DETAILS OF THE EVOLUTION OF A
LARGE-SCALE TROUGH EXPANDING ACROSS THE ERN U.S. THIS PERIOD.
HOWEVER...GENERAL AGREEMENT EXISTS THAT HIGHLY AMPLIFIED FLOW ALOFT
WILL PREVAIL...WITH A TROUGH MOVING ONSHORE IN THE WEST...A SHARP
RIDGE OVER THE ROCKIES...AND THEN THE EXPANSIVE/EVOLVING TROUGH OVER
THE EAST.
AT THE SURFACE...DIFFERENCES AMONG THE MODELS ARE EVEN MORE
PRONOUNCED...WITH THE NAM...GFS...AND ECMWF EACH SHOWING VARIANCES
IN TIMING AND LOCATION OF THE LOW CENTER/CENTERS AND ASSOCIATED
SURFACE FRONTS. EACH MODEL HINTS AT A MORE NRN LOW MOVING INTO THE
MID-ATLANTIC REGION AND A MORE SRN LOW SHIFTING NEWD OUT OF THE ERN
GULF OF MEXICO INTO THE SOUTHEAST...BUT EXACT EVOLUTION REMAINS
QUITE UNCERTAIN ATTM.
...THE SOUTHEAST U.S. AND ATLANTIC COAST...
THE DIFFERENCES IN SURFACE PATTERN EVOLUTION OVER THE ERN THIRD OF
THE U.S. THIS PERIOD CAST SUBSTANTIAL UNCERTAINTY INTO THE FORECAST
WITH RESPECT TO SEVERE POTENTIAL. IN THIS SITUATION...DEGREE AND
LOCATION OF ANY SEVERE THREAT WILL LIKELY BE STRONGLY ASSOCIATED
WITH AREAS OF ENHANCED LOW-LEVEL SHEAR INVOF ANY SURFACE LOWS...AND
BY FRONTAL LOCATION AS IT RELATES TO AREAS OF FAVORED STORM
DEVELOPMENT.
IN GENERAL...WITH MODEST DESTABILIZATION AND INCREASING MID-LEVEL
FLOW AHEAD OF THE EVOLVING UPPER TROUGH...AT LEAST LOW-END SEVERE
POTENTIAL APPEARS TO EXIST ACROSS A RELATIVELY LARGE AREA -- WITHIN
A BROAD ZONE FROM THE CENTRAL GULF COAST REGION EWD ACROSS FL...AND
NEWD INTO THE MID-ATLANTIC AREA. THEREFORE...A LOW-PROBABILITY
SEVERE THREAT AREA WILL BE INTRODUCED THIS FORECAST CORRESPONDING TO
THIS REGION.
SMALLER AREAS OF ENHANCED/HIGHER-PROBABILITY SEVERE -- AND POSSIBLY
TORNADO -- THREAT WILL LIKELY EVOLVE...MOST LIKELY WITHIN THE
PORTIONS OF THE ZONE EXTENDING FROM FL NWD...PERHAPS AS FAR N AS THE
MID-ATLANTIC REGION. HOWEVER...GIVEN THE CLOSE ASSOCIATION OF
SURFACE FEATURE LOCATION TO ANY POCKETS OF ENHANCED SEVERE POTENTIAL
THAT IS EXPECTED TO EXIST...CORRIDORS OF HIGHER THREAT REMAIN HIGHLY
UNCERTAIN ATTM. THEREFORE...WILL REFRAIN FROM INTRODUCING ANY
SLIGHT RISK AREAS UNTIL LATER FORECASTS WHEN PLACEMENT OF SUCH AREAS
CAN BE DONE WITH MORE CERTAINTY.
..GOSS.. 10/16/2011
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