SWODY1
SPC AC 171552
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1052 AM CDT SAT OCT 17 2009
VALID 171630Z - 181200Z
...NO SVR TSTM AREAS FORECAST...
...PACIFIC NW...
A VERY MOIST...WARM CONVEYER BELT AHEAD OF THE STRONG UPPER TROUGH
IS NOW SPREADING CONSIDERABLE PCPN ACROSS WRN WA/NWRN OR. BY MID
AFTERNOON ALL THE MODELS ARE IN BASIC AGREEMENT THAT A STRONG WIND
MAX AND MID LEVEL COLD ADVECTION WILL ACCOMPANY THE TROUGH
INLAND...CHANGING THE CHARACTER OF THE PCPN TO MORE CONVECTIVE IN
NATURE. THIS IS CONFIRMED BY THE OBSERVED LIGHTNING THIS MORNING
OFFSHORE AHEAD OF THE TROUGH AND SURFACE LOW.
THE ACCOMPANYING SURFACE LOW WILL BE MOVING NEWD ACROSS VANCOUVER
ISLAND BY THIS EVENING MAINTAINING A MOIST ONSHORE FLOW OVER WRN
WA/NWRN OR...WHICH COUPLED WITH THE STRONG MID LEVEL COOLING WILL
LEAD TO A MARGINALLY UNSTABLE AIR MASS WITH MLCAPES OF A FEW HUNDRED
J/KG DEVELOPING W OF CASCADES.
GIVEN THE STRONG DEEP LAYER CYCLONIC SHEAR OF 50-60KT...THERE IS THE
POTENTIAL FOR DEVELOPMENT OF LOW TOPPED ROTATING THUNDERSTORMS THIS
AFTERNOON. WITH REGARDS TO ANY TORNADO THREAT...WHILE THE SHEAR AND
POTENTIAL INSTABILITY WOULD SEEM TO BE SUFFICIENT...THE LACK OF
FAVORABLE BOUNDARY LAYER FLOW GIVEN THE SURFACE LOW OFFSHORE IS NOT
PARTICULARLY STRONG...WOULD LIMIT THE EFFECTS OF TERRAIN ENHANCEMENT
WHICH USUALLY PLAYS A ROLE IN THESE TYPE OF SITUATIONS W OF THE
CASCADES.
WILL CONTINUE WITH A LOW PROBABILITY OF ISOLATED TORNADOES...WITH
THE POSSIBILITY OF AN UPGRADE TO A SLIGHT IN THE 20Z OUTLOOK IF
BOUNDARY LAYER CONDITIONS SEEM MORE FAVORABLE THAN NOW EXPECTED.
..HALES/SMITH.. 10/17/2009
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