Severe Thunderstorm Warning 14, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
227 PM PDT THU AUG 8 2013

.DISCUSSION...THE UPPER LOW CONTINUES TO SPIN OFFSHORE AND BRINGING
IN MULTIPLE SHORTWAVES OVER THE FORECAST AREA. OF PARTICULAR CONCERN
IS ONE THAT IS CENTERED NEAR 40N/123W AND IS BEING PICKED UP WELL IN
THE WATER VAPOR IMAGE. THE VISIBLE IMAGE SHOWS MID AND HIGH CLOUDS
WITH THIS FEATURE WITH CUMULUS DEVELOPMENT ALREADY OCCURRING IN
WESTERN SISKIYOU COUNTY...SISKIYOUS AND CASCADES. WE DID A SPECIAL
18Z BALLOON LAUNCH AND IT SHOWS SLIGHT COOLING AT THE MID LEVELS AND
ERODING CAP. THE ABOVE MENTIONED SHORTWAVE WILL MOVE NORTH AND THIS
WILL BE ENOUGH TO BREAK THE CAP ALLOWING THINGS TO BLOW UP IN THESE
AREAS. COULD NOT RULE OUT IN ADDITION GUSTY AND ERRATIC WINDS IN THE
VICINITY OF THUNDERSTORMS WHICH WILL HAVE AN SIGNIFICANT IMPACT ON
FIRES. ALSO OF NOTE ARE THE UPPER WINDS. THE SOUNDING INDICATED THEY
WERE BETWEEN 7-9 KTS AROUND 700MB AND THIS SHOULD TRANSLATE TO
STORMS NOT MOVING VERY FAST WHEN THEY DEVELOP. THEREFORE AREAS THAT
GET CAUGHT UNDER THUNDERSTORMS COULD GET MODERATE RAINFALL TOTALS IN
A SHORT PERIOD OF TIME. SMALL HAIL IS ALSO POSSIBLE LATE THIS
AFTERNOON THROUGH THIS EVENING.

THE UPPER LOW WILL MOVE LITTLE TONIGHT THROUGH FRIDAY AND
REMAINS AT OR JUST OFF THE OREGON COAST AND WILL SEND PLENTY OF
SHORTWAVES THROUGH THE AREA. SO WE'LL MOST LIKELY SEE SIMILAR
CONDITIONS AS THURSDAY. FOR NOW LEFT THUNDERSTORMS IN FOR
TONIGHT...BUT IT'S POSSIBLE WE'LL HAVE CONVECTIVE SHOWERS WITH
ISOLATED THUNDER AS INSTABILITY DECREASES SOME.

ANOTHER ACTIVE DAY IS ON TAP FRIDAY WITH THE SAME AREAS LIKELY TO BE
AFFECTED BY STORMS. THE SHREF GUIDANCE PAINTS HIGHER PROBABILITY OF
STORMS OVER MICH OF THE AREA WHICH IS MORE COMPARED TO THIS
AFTERNOON.

THE UPPER LOW IS EXPECTED TO SLOWLY MOVE NORTH OVER SOUTHWEST OREGON
FRIDAY NIGHT. PLENTY OF MID LEVEL MOISTURE WILL BE PRESENT AND
MULTIPLE SHORTWAVES WILL MOVE THROUGH. WHILE ALL AREAS HAVE A THREAT
OF THUNDERSTORMS...MOST OF THE ACTION MAY END UP BE CONFINED TO THE
NORTHERN CASCADES AND NORTHERN LAKE AND KLAMATH COUNTIES. THE SHREF
SHOWS POPS AROUND 20 PERCENT DECREASING TO 10 PERCENT OVERNIGHT
FRIDAY. HOWEVER UNTIL THE UPPER LOW MOVES NORTH AND WE GET INTO A
MORE SOUTH TO SOUTHWEST FLOW...MOST OF NOT ALL AREAS WILL BE FAIR
GAME FOR THUNDERSTORMS.

THE UPPER LOW WILL SLOWLY MOVE NORTH SATURDAY. THE MODELS ARE IN
SIMILAR AGREEMENT THAT THUNDERSTORMS ARE POSSIBLE FOR MOST OF THE
FORECAST AREA.

THE UPPER LOW FINALLY MOVES NORTH OF THE AREA SUNDAY AND WE'LL GET
INTO A SOUTHWEST FLOW ALOFT. THEREFORE WE EXPECT MOST OF THE
THUNDERSTORMS TO BE ALONG AND EAST OF THE CASCADES...BUT IT SHOULD
NOT BE AS ACTIVE AS TODAY AND FRIDAY. -PETRUCELLI

&&

.AVIATION...MAINLY VFR CONDITIONS...EXCEPT FOR AREAS
OF  MVFR VSBYS AND LOCAL IFR VSBYS IN SMOKE...MOSTLY IN THE
SOUTHERN UMPQUA...ILLINOIS...AND ROGUE BASINS AS WELL AS SISKIYOU
COUNTY IN NORTHERN CALIFORNIA. SCATTERED THUNDERSTORMS
WILL DEVELOP OVER NORTHERN CALIFORNIA AND FROM THE CASCADES EAST
BY EARLY AFTERNOON...SPREADING WEST OF THE CASCADES IN OREGON IN
THE LATE AFTERNOON. STORMS MAY BRING VERY GUSTY AND ERRATIC
WINDS...BUT CONDITIONS WILL LIKELY REMAIN VFR. AT THE COAST...
NORTH OF CAPE BLANCO...VFR CONDITIONS WILL CONTINUE THIS EVENING
...THEN MVFR WITH LOCAL IFR CONDITIONS DEVELOP TONIGHT WHILE MVFR
WITH LOCAL IFR CONDITIONS PERSIST SOUTH.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...RED FLAG WARNING UNTIL 11 PM PDT FRIDAY FOR ORZ021>031.

CA...RED FLAG WARNING UNTIL 11 PM PDT FRIDAY FOR CAZ080>085.

PACIFIC COASTAL WATERS...NONE.