Flash Flood Watch 1, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
800 PM PDT SAT SEP 20 2014

.DISCUSSION...21/00Z NAM IN.

LOTS OF LOW CLOUDS AND FOG ALONG THE COAST AND OVER THE COASTAL
WATERS THIS EVENING. SOME HIGH LEVEL CONVECTIVE DEBRIS HAS MOVED
INTO MODOC COUNTY...EASTERN SISKIYOU COUNTY...AND SOUTHERN LAKE
COUNTY.

A WEAK REX BLOCK ALONG THE WEST COAST IS NOW BREAKING DOWN AS THE
RIDGE MOVES EAST AND THE CUTOFF LOW BEGINS TO LIFT OUT DUE TO A
STRONG LONG WAVE TROUGH APPROACHING FROM THE WEST. FOG AND MARINE
STRATUS HAS RETURNED TO THE COAST FROM JUST NORTH OF NEWPORT SOUTH
INTO CENTRAL CALIFORNIA.

THE CUTOFF LOW WILL BE NEAR THE IDAHO/OREGON/NEVADA TRIPLE POINT
SUNDAY AFTERNOON AND A SHORT WAVE ROTATING AROUND IT WILL INDUCE
SOME INSTABILITY OVER THE EAST SIDE...SO A SLIGHT CHANCE OF
THUNDERSTORMS IS IN THE FORECAST FOR THAT AREA...WITH THE EXCEPTION
OF NORTHERN KLAMATH AND NORTHERN LAKE COUNTIES. THIS LINES UP WELL
WITH THE CURRENTLY FORECASTED LIFTED INDICES IN THE NAM/GFS MODELS.
SUNDAY WILL ALSO BE AROUND 5 DEGREES COOLER THAN SATURDAY OVER THE
INLAND AREAS...EXCEPT FOR THE UMPQUA BASIN WHICH WILL COOL OFF
AROUND 10 DEGREES.

THE LONG WAVE TROUGH WILL CONTINUE TO APPROACH THE COAST MONDAY
INTO TUESDAY. SEVERAL SHORT WAVES WILL RIDE IN ON SOUTHWEST FLOW
ALOFT. ONE OF THEM WILL INDUCE SOME INSTABILITY OVER THE CASCADES
AROUND CRATER LAKE MONDAY AFTERNOON AND EVENING...BUT ANY
THUNDERSTORMS WILL BE ISOLATED AND THE ASSOCIATED PRECIPITATION
WILL BE LIGHT. THERE WILL ALSO BE A CHANCE OF SOME LIGHT RAIN
ALONG THE COAST MONDAY NIGHT WHEN A WEAK FRONT MOVES ONSHORE.
TUESDAY WILL BE WINDY EAST OF THE CASCADES AS GRADIENTS TIGHTEN.

THE PATTERN CHANGE WILL BEGIN IN EARNEST TUESDAY NIGHT INTO
WEDNESDAY...WHEN A STRONG SHORT WAVE AHEAD OF THE LONG WAVE
TROUGH WILL PUSH A WET FRONT ONSHORE.

EXTENDED DISCUSSION FROM THE SATURDAY AFTERNOON AFD...TUESDAY
NIGHT THROUGH SATURDAY. THERE IS A SLIGHT TIMING DIFFERENCE
BETWEEN THE GFS AND EURO MODELS WITH THE ASSOCIATED COLD FRONT.
THE EURO BRINGS THE FRONT TO THE COAST AROUND MIDNIGHT TUESDAY
NIGHT WHILE THE GFS MAKES LANDFALL AT SUNRISE WEDNESDAY. CURRENT
FORECAST TIMING LEANS TO THE EURO SOLUTION. THE ENSEMBLE MEMBERS
FROM BOTH THE EURO AND GFS FOR WEDNESDAY HAVE A SMALL SPREAD WHICH
MEANS THAT BOTH ARE RATHER CONFIDENT IN THEIR SOLUTIONS...SO I
HAVE NO COMPELLING REASON MAKE A CHANGE AT THIS TIME.

AFTER THE FRONT PASSES OVER...A LARGE POOL OF COOL UNSTABLE AIR WILL
COVER THE AREA. HIGH TEMPERATURES WILL DROP FROM 15 DEGREES ABOVE
NORMAL TODAY TO 15 DEGREES BELOW NORMAL BY THURSDAY. WIDESPREAD
FROST/FREEZE CAN BE EXPECTED EAST OF THE CASCADES. JBL

&&

.AVIATION...BASED ON THE 21/00Z TAF CYCLE...A SOUTHERLY SURGE OF
IFR CIGS/VSBYS HAS MOVED UP THE COAST AS FAR NORTH AS NEWPORT.
THE LOW CONDITIONS WILL SPREAD INTO THE COASTAL VALLEYS INCLUDING
THE NORTHWEST PORTION OF THE UMPQUA VALLEY AND PERSIST INTO
SUNDAY MORNING. CONDITIONS WILL IMPROVE AFTER 16Z SUNDAY, HOWEVER,
IFR WILL PERSIST IN AREAS AT THE IMMEDIATE COAST INTO SUNDAY
AFTERNOON. INLAND...VFR CONDITIONS WILL PREVAIL THROUGH
SUNDAY...EXCEPT FOR LOCAL MVFR VSBYS IN SMOKE NEAR WILDFIRES IN
JOSEPHINE COUNTY AND THE WESTERN PORTION OF SISKIYOU COUNTY.
-BPN/SVEN

&&

.MARINE...UPDATED 300 PM PDT SAT 20 SEP 2014...NORTHERLY WINDS WILL
BECOME SOUTHERLY FROM SOUTH  TO NORTH THROUGH THIS EVENING, AS THE
THERMAL TROUGH WEAKENS AND HIGH PRESSURE BUILDS INTO THE AREA. WIND
WAVES HAVE DIMINISHED TODAY, BUT MODERATE NORTHWEST SWELL HAS KEPT
SEAS AT JUST BELOW 10 FEET. WINDS AND SEAS WILL DIMINISH TONIGHT
THROUGH MONDAY NIGHT, AND BEGINNING TUESDAY, A SERIES OF FRONTS WILL
BEGIN TO IMPACT THE AREA WITH INCREASED WINDS AND STEEP TO VERY
STEEP HEAVY SEAS TROUGH THE REST OF THE WEEK. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

15/15/15