HAMweather.com Area Forecast Discussion for County Warning Area MFR

Thu, 16 Feb 2012 07:43:57 GMT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
856 PM PST WED FEB 15 2012

.DISCUSSION...NO NEED TO UPDATE THE FORECAST THIS EVENING.
THINGS LOOK ON TRACK. STAVISH

.AVIATION...A DRIER AIR MASS HAS BROUGHT VFR CONDITIONS TO ALL 
TERMINALS THIS EVENING BUT ROSEBURG SHOULD FILL IN AND LOWER TO
IFR TONIGHT. SCATTERED STRATOCUMULUS IS SEEN IN SATELLITE IMAGERY
THERE THIS EVENING. THE COAST AND EAST SIDE SHOULD REMAIN MAINLY
VFR OVERNIGHT...WHILE SOME UNCERTAINTY EXISTS REGARDING THE ROGUE
VALLEY. SLIGHTLY LIMITED OVERNIGHT RADIATIONAL COOLING DUE TO
HIGH CLOUDS. AT PRESENT...MVFR VIS LOOKS LIKE THE BEST SOURCE FOR
MVFR CONDITIONS...AND NOT UNTIL 4 AM OR SO AND THROUGH AROUND 9
AM.

.MARINE...A WEAKENING SWELL WILL CONTINUE TO KEEP SEAS AT SMALL
CRAFT LEVEL THROUGH THIS EVENING BEFORE THEY COME DOWN BELOW 10
FEET AFTER MIDNIGHT. OUR ATTENTION THEN TURNS TO A VERY STRONG
STORM SYSTEM ENTERING THE WATERS OFF THE COAST OF BRITISH COLUMBIA
STARTING FRIDAY AND EVENTUALLY MOVING INLAND INTO THE PACIFIC
NORTHWEST LATE SATURDAY INTO SUNDAY. WINDS ARE EXPECTED TO RISE
ABOVE SMALL CRAFT FRIDAY NIGHT AND LAST INTO THE WEEKEND WITH
GALES REMAINING NORTH OF OUR COASTAL WATERS BUT THIS WILL BE
DEPENDENT ON THE EVENTUAL TRACK OF THE AREA OF LOW PRESSURE. THERE
REMAINS DISAGREEMENT IN THE GUIDANCE AS TO HOW FAR SOUTH THIS
LOW TRACKS AND HAVE LEANED TOWARD A MORE NORTHERLY TRACK AT THIS
TIME. THIS STORM SYSTEM ALSO SENDS A SIGNIFICANT WEST TO NORTHWEST
SWELL INTO THE COASTAL WATERS FRIDAY NIGHT THROUGH SATURDAY NIGHT
BEFORE EASING SUNDAY...WHICH WOULD ALSO PRODUCE HIGH SURF ALONG
THE COAST. THE GUIDANCE HAS CONSIDERABLY RAMPED UP FORECAST WAVE
HEIGHTS WITH THIS SWELL COMPARED TO THE MODEL RUNS AT THIS TIME
YESTERDAY BY AS MUCH AS 10'. WE HAVE INCREASED OUR WAVE HEIGHTS IN
COORDINATION WITH NEIGHBORING OFFICES TO 20-21' AS CONFIDENCE
REMAINS LOW ON THE MODELS' ABILITY TO ANALYZE AND PREDICT THIS
EVENT. WE WILL CONTINUE TO MONITOR UPCOMING MODEL RUNS TO
DETERMINE IF WAVE HEIGHTS MUST BE INCREASED FURTHER BUT THIS
CERTAINLY REMAINS A MARINE EVENT THAT BEARS WATCHING. /MAW

.PREV DISCUSSION... /ISSUED 418 PM PST WED FEB 15 2012/ 

SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT...THE GFS AND ECMWF
MODELS ARE IN GOOD AGREEMENT INTO FRIDAY MORNING. THE NAM ALSO HAS
A SIMILAR EVOLUTION BUT IS A BIT STRONGER/WETTER WITH A
DISSIPATING OCCLUDED FRONT THAT WILL REACH OREGON ON THURSDAY. THE
FOCUS OF THE SEVEN-DAY FORECAST IS ON A COLD FRONT AND TRAILING COLD
UPPER LEVEL LOW. THE FRONT IS EXPECTED TO IMPACT OUR AREA FRIDAY
AFTERNOON AND NIGHT THEN THE TROUGH SATURDAY INTO EARLY SUNDAY MORNING.

HIGH PRESSURE WILL PERSIST OVER OUR AREA TONIGHT. BUT...HIGH
CLOUDS AND VALLEY LOW CLOUDS WILL INCREASE. THE DISSIPATING FRONT
WILL LIKELY BRING LIGHT RAIN TO THE COAST...MAINLY NORTH OF CAPE
BLANCO BY THURSDAY AFTERNOON. FOR OTHER AREAS...SIMPLY A MOSTLY
CLOUDY DAY IS EXPECTED. THE REMNANTS OF THE FRONT WILL SLOWLY MOVE
EAST THURSDAY NIGHT WITH A CHANCE OF LIGHT SHOWERS OR SNOW
FLURRIES IN THE SOUTHERN OREGON CASCADES AND A SLIGHT CHANCE AT
MOST ELSEWHERE. THE SNOW LEVEL LOOKS TO RISE TO AROUND 6000 FEET.

SHORTWAVE RIDGING IS FORECAST FOR LATE THURSDAY NIGHT INTO FRIDAY
MORNING. THE NAM IS THE FASTEST AND WETTEST WITH THE COLD FRONT ON
FRIDAY WHILE THE GFS IS THE DEEPEST WITH THE UPPER LOW. I HAVE
LEANED TOWARD A COMPROMISE OF THE GFS AND ECMWF AS THEY HAD A
BETTER HANDLE ON OUR LAST COUPLE OF FRONTAL SYSTEMS. SNOW LEVELS
ON FRIDAY WILL BEGIN AROUND 6000 FEET AND ARE FORECAST TO FALL TO
2500 TO 3500 FEET FRIDAY NIGHT THEN PERSIST AT AROUND 2500 FEET AS
THE UPPER TROUGH MOVES INTO THE PACIFIC NORTHWEST ON SATURDAY. THE
TRACK OF THE UPPER LOW IS IN QUESTION AND WILL BE AN IMPORTANT
FACTOR IN TIMING AND AMOUNTS OF PRECIPITATION. SNOWFALL LOOKS TO
BE MORE SIGNIFICANT WITH THE PASSAGE OF THE UPPER TROUGH ON THE WEEKEND
THAN WITH THE FRIDAY FRONT...BUT AS DETAILS BECOME CLEARER...BOTH
EVENTS MAY LEAD TO THE ISSUANCE OF WINTER WEATHER ADVISORIES IN
OUR AREA.

AVIATION...A DRIER AIR MASS HAS BROUGHT VFR CONDITIONS TO ALL 
TERMINALS EXCEPT FOR THE UMPQUA BASIN...INCLUDING ROSEBURG. MVFR 
CEILINGS THERE SHOULD SCATTER OUT LATER THIS AFTERNOON BEFORE 
FILLING IN AND LOWERING TO IFR TONIGHT. THE COAST AND EAST SIDE 
SHOULD REMAIN MAINLY VFR OVERNIGHT...WHILE SOME UNCERTAINTY EXISTS 
REGARDING THE ROGUE VALLEY. DEW POINT TEMPERATURES HAVE DROPPED INTO 
THE 20S THIS AFTERNOON. THIS...AND THE FACT THAT MODELS ARE NOT 
SUGGESTING FOG TONIGHT...ARE REASONS TO KEEP MEDFORD MVFR OR 
GREATER. 

LONG TERM...SUNDAY THROUGH WEDNESDAY...ENSEMBLES SHOW LITTLE 
VARIANCE IN THE LARGE SCALE SOLUTION THAT A TRANSITION FROM TROUGHING
TO RIDGING WILL OCCUR DURING THIS PERIOD. THE SPECIFIC DETAILS OF
THE FORECAST...HOWEVER...ARE NOT CERTAIN GIVEN INDIVIDUAL MODEL
DIFFERENCES IN TIMING AND INTENSITY.

ON SUNDAY THE ECMWF IS FAVORED IN SHOWING A SHORTWAVE TROUGH 
IN A COLD NORTHERLY FLOW ALOFT BRINGING PRECIPITATION TO THE
REGION...WITH SNOW LEVELS ABOUT 3000 FEET. MONDAY REPRESENTS A
BREAK IN PRECIPITATION AS AN UPPER LEVEL RIDGE BUILDS IN FROM THE
WEST. ON TUESDAY A TROUGH RIDES OVER THE RIDGE AND INTO THE
FORECAST AREA...BRINGING INCREASED CHANCES OF PRECIPITATION AND A
CONTINUED RELATIVELY WARM AIR MASS. BY THIS TIME...WARM AIR ALOFT
WILL PUSH SNOW LEVELS TO AT LEAST 6000 FEET. 500MB HEIGHTS THAT
ARE 1.5 STANDARD DEVIATIONS ABOVE NORMAL WILL AFFECT THE REGION BY
WEDNESDAY...SIGNIFICANTLY DIMINISHING RAIN CHANCES AND BEGINNING
WHAT COULD BE A DRY END TO NEXT WEEK. /NSK

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

CA...NONE.
PZ...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 10 PM PST THIS 
     EVENING FOR PZZ350-356-370-376.