FXUS66 KMFR 082306
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
306 PM PST TUE DEC 8 2009
.SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT...A WEAK SHORTWAVE IS
CURRENTLY ROTATING THROUGH OREGON AND THE COASTAL WATERS IN THE
DRY NORTHWESTERLY FLOW ALOFT. THIS SHORTWAVE WILL EXIT THE AREA
AND MOVE TOWARD THE ROCKIES TONIGHT....PRODUCING NOTHING MORE THAN
A FEW HIGH TO MID LEVEL CLOUDS OVER THE CWA. LOW TEMPERATURES
TONIGHT WILL AGAIN BE AS FRIGID AS LAST NIGHT WITH THE COLD AIR
MASS REMAINING IN PLACE...AND FROST IS EXPECTED TO FORM INSTEAD OF
FOG AS THE DRY AIR CONTINUES.
THE CWA WILL GENERALLY REMAIN UNDER A DRY SPLIT FLOW WEDNESDAY AND
THURSDAY WITH THE STRONG NORTHERN JET OFF TO OUR NORTHEAST AND THE
SOUTHERN JET SUPPRESSED WELL TO OUR SOUTH. THE RIDGE AXIS WILL BE
LOCATED JUST OFFSHORE WEDNESDAY BEFORE SHIFTING INLAND ON THURSDAY.
IT WILL BE ANOTHER COLD NIGHT WEDNESDAY NIGHT...ALTHOUGH LOW
TEMPERATURES WILL NOT BE QUITE SO COLD AND GENERALLY A FEW DEGREES
ABOVE TONIGHTS LOWS. HIGH TEMPERATURES ON THURSDAY WILL ALSO BE A
FEW DEGREES HIGHER THAN TOMORROW BUT STILL BELOW NORMAL FOR THIS
TIME OF YEAR.
BY FRIDAY...THE MODELS AGREE ON THE RIDGE AXIS CONTINUING TO MOVE
FARTHER INLAND TOWARD NEVADA AND UTAH WHILE A SHORTWAVE APPROACHES
FROM THE WEST BUT THAT IS GENERALLY WHERE THE AGREEMENTS END. THE
LATEST ECMWF WEAKENS THE SHORTWAVE CONSIDERABLY AND KEEPS IT
FARTHER SOUTH IN CALIFORNIA BY FRIDAY WHILE THE GFS SHOWS
PRECIPITATION BEGINNING TO OVERRUN CALIFORNIA INTO OREGON ON
FRIDAY. THE TREND OVER THE PAST FEW DAYS HAS BEEN TO SLOW DOWN THE
PRECIPITATION AND WEAKEN THE SHORTWAVE. WE SPLIT THE DIFFERENCE
AND REDUCED POPS ON FRIDAY WHILE TRENDING TEMPERATURES
COOLER...THINKING THAT ANY PRECIPITATION THAT DOES FALL INITIALLY
WILL NOT MAKE IT TO THE GROUND IN THE DRY AIR MASS. WE MAINTAINED
THE HIGHER POPS ON FRIDAY NIGHT WITH THE SHORTWAVE EXPECTED TO
MOVE CLOSER.
.LONG TERM...MODELS ARE STRUGGLING WITH SOLUTIONS FOR WHAT WILL TRANSPIRE
FROM SATURDAY ONWARD. THE GFS ENSEMBLE SPREAD GROWS DRAMATICALLY AFTER
FRIDAY...INDICATING UNPREDICTABILITY IN THE FUTURE OF THE LONG WAVE
RIDGE AMPLITUDE AND POSITION. ECMWF HAS TRENDED DRIER OVER SOUTHERN
OREGON WITH THE NEXT WEATHER SYSTEM ON SATURDAY...AS IT NOW SWINGS THE
LOW INTO CALIFORNIA. ON PREVIOUS DAYS...THE GFS HAS BEEN THE DRIER MODEL
AND MORE CORRECT THAN THE ECMWF AS IT HAS MAINTAINED THE CURRENT RIDGE
THE LONGEST WITH LOWS VEERING AWAY FROM THE OREGON COAST...SO IT PRESENTS
A CHALLENGE IN DECIDING WHICH MODEL TO RELY ON FOR SATURDAY. FORECAST
NOW HAS LIKELY POPS FOR SATURDAY BUT LEANS TOWARDS CLIMO FROM SUNDAY
ON...REFLECTING A BLEND BETWEEN THE GFS AND ECMWF. ANOTHER INTERESTING
FACET OF THE LONG RANGE FORECASTS INVOLVES SNOW LEVELS. GIVEN THE
PERSISTENT...VERY COLD AIRMASS IN PLACE...SNOW LEVELS WILL LIKELY BE
AT OR BELOW WHAT MODELS ARE PREDICTING FOR SATURDAY THROUGH SUNDAY.
SATURDAY AND SATURDAY NIGHT SOME SNOW WILL LIKELY AFFECT ELEVATIONS
3500 FEET AND ABOVE...INCLUDING SISKIYOU SUMMIT ALONG I-5. GIVEN VARIANCE
IN MODELS...SNOW AMOUNTS ARE DIFFICULT TO ESTIMATE AT THIS TIME AND
WILL NEED TO MONITOR TRENDS CLOSELY TO FINE-TUNE POPS AND QPF FOR THIS
TIMEFRAME. AFOREMENTIONED DATA SUGGESTS THAT NO MAJOR SNOWFALL WILL
OCCUR OVER THE WEEKEND FOR SOUTHERN OREGON AND EXTREME NORTHERN CALIFORNIA.
GENERAL RIDGING PATTERN RESUMES SUNDAY INTO MONDAY...WITH A LOW PRESSURE
SYSTEM NEARING THE COAST TUESDAY.
&&
.AVIATION...THE AIR MASS WILL REMAIN DRY ENOUGH NEAR THE SURFACE
AND ALOFT TO PREVENT FOG FROM DEVELOPING AT NIGHT. SKIES WILL
REMAIN MAINLY CLEAR WITH VFR CONDITIONS EXPECTED THROUGH WEDNESDAY.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FREEZE WATCH FROM THURSDAY EVENING THROUGH FRIDAY MORNING FOR
ORZ021-ORZ022.
FREEZE WARNING FROM 11 PM THIS EVENING TO 9 AM PST WEDNESDAY FOR
ORZ021-ORZ022.
FREEZE WARNING FROM 11 PM WEDNESDAY TO 9 AM PST THURSDAY FOR
ORZ021-ORZ022.
CA...NONE.
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS
UNTIL 4 PM PST THURSDAY FOR PZZ350-PZZ356-PZZ370-PZZ376.
$$
SHORT TERM: MW
LONG TERM: NSK
MARINE: KES
