Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 052236
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
236 PM PST THU MAR 5 2015

.SHORT TERM...THIS AFTERNOON THROUGH MONDAY NIGHT...
SURFACE HIGH PRESSURE CENTERED NEAR THE MOUTH OF COLUMBIA RIVER
THIS AFTERNOON WILL STRENGTHEN AS IT RE-CENTERS INTO THE NORTHERN
ROCKIES TONIGHT THROUGH FRIDAY. THIS WILL RESULT IN LOW LEVEL
SOUTH FLOW OVER THE COASTAL WATERS, GIVING RISE TO INCREASING LOW
CLOUDS AND FOG IN THE COASTAL WATERS.

THUS FAR TODAY, SURFACE LOW PRESSURE ABOUT 70 NAUTICAL MILES WEST
OF BROOKINGS HAS NOT DEVELOPED MUCH IN THE WAY OF CLOUDS AROUND
AND NEAR IT, BUT EXPECT THAT IT WILL OVERNIGHT THROUGH FRIDAY
MORNING. HOWEVER, VERTICAL PROFILE FORECASTS FOR BROOKINGS AND
NORTH BEND INDICATE THAT LOW LEVEL OFFSHORE FLOW, ALBEIT LIGHT,
WILL PREVENT FOG FORMATION INLAND FROM THE BEACHES AND COASTAL
WATERS TONIGHT THROUGH FRIDAY MORNING. EVEN FRIDAY EVENING THROUGH
SATURDAY OFFSHORE FLOW ABOVE THE BOUNDARY LAYER, DUE TO THE
INFLUENCE OF A NEW SURFACE HIGH OVER THE PACIFIC, WILL RESULT IN
EAST WINDS AT THE 925MB AND 850MB LEVELS, LIKELY KEEPING INLAND
INTRUSION OF THE MARINE LAYER CONFINED TO ELEVATIONS BELOW 500
FEET AND, LIKELY IN THE FORM OF FOG. THUS, HAVE ADJUSTED THE
FORECAST ACCORDINGLY. IN SHORT, THIS SHOULD MEAN MORE SUN AT THE
COAST FRIDAY AND SATURDAY.

OTHERWISE, FOR THE REST OF THE FORECAST AREA, CHILLY MORNINGS AND
WARM AFTERNOONS WILL TREND A BIT WARMER THROUGH THE WEEKEND AND
THEN SHOULD MODERATE SOME EARLY NEXT WEEK. DIURNAL TEMPERATURE
RANGES WILL BE SIGNIFICANT DUE TO THE DRY AIR MASS IN PLACE.
EXPECT DIFFERENCES BETWEEN HIGHS AND LOWS IN THE FOG FREE WEST
SIDE VALLEYS TO BE 30 TO 40 DEGREES FAHRENHEIT THIS WEEKEND, AND
AS MUCH AS 40 TO 50 DEGREES FAHRENHEIT ACROSS MUCH OF THE EAST
SIDE. MORE TEMPERATE AREAS SUCH AS THE COAST AND UMPQUA BASIN WILL
SEE 15 TO 25F TEMPERATURES SWINGS. FOG WILL BE CONFINED TO THE
UMPQUA BASIN, LOWER KLAMATH RIVER VALLEY, AND ILLINOIS VALLEY TO
GRANTS PASS THROUGH FRIDAY AND WILL MOSTLY EXIST FROM JUST BEFORE
SUNRISE THROUGH MID-MORNING. THEREAFTER, BEGINNING LATE FRIDAY
NIGHT INTO SATURDAY MORNING, COASTAL AND NEAR COASTAL AREAS WILL
GET INTO THE FOG AND LOW CLOUDS, AT TIMES. BTL

.LONG TERM...TUESDAY THROUGH FRIDAY...THERE IS ENOUGH AGREEMENT IN
THE LONG RANGE GUIDANCE, INCLUDING THE DETERMINISTIC MODELS AND
THEIR RESPECTIVE ENSEMBLE MEANS TO SAY THAT WE CAN EXPECT A CHANGE
IN THE WEATHER PATTERN NEXT WEEK. THIS IS TO SAY THAT THE RIDGE
PROVIDING THE DRY, UNUSUALLY WARM WEATHER THROUGH MONDAY WILL
FINALLY BREAK DOWN ALLOWING A LARGE UPPER LOW OFFSHORE (OUT NEAR
150W) TO GRADUALLY EDGE EAST TOWARD THE WEST COAST. BROAD
SOUTHWESTERLY FLOW WILL DEVELOP AHEAD OF THIS SYSTEM TUESDAY AS THE
RIDGE AXIS SHIFTS TO SOUTHERN CALIFORNIA AND THE GREAT BASIN. WE
SHOULD BE ABLE TO SQUEEZE OUT ANOTHER DRY DAY, BUT HAVE INDICATED A
SLIGHT CHANCE OF RAIN ALONG THE COAST.

PRECIPITATION CHANCES INCREASE ACROSS THE AREA TUESDAY NIGHT THROUGH
WEDNESDAY NIGHT AS THE UPPER LOW MOVES EAST OF 140W ALLOWING SHORT
WAVES ROTATING AROUND IT TO MOVE ONSHORE. SNOW LEVELS LOOK PRETTY
HIGH ONCE AGAIN...AVERAGING BETWEEN 6000 AND 7000 FEET. BY
THURSDAY, MODELS DIVERGE IN HOW THEY BRING THIS SYSTEM ONSHORE INTO
THE WEST COAST. SOME SOLUTIONS OPEN UP THE SYSTEM INTO A TROUGH AND
MOVE IT INTO WASHINGTON AND OREGON, WHILE OTHERS MAINTAIN THE UPPER
LOW AND BRING IT INTO CALIFORNIA. EITHER WAY, EXPECT POPS NEAR OR
ABOVE CLIMATOLOGY FOR MOST OF THE AREA THROUGH THURSDAY WITH
DIMINISHING CHANCES BY FRIDAY AS THE SYSTEM MOVES INLAND. WE`LL SEE
A DOWNWARD TREND IN HIGH TEMPERATURES DURING THE PERIOD DUE TO THE
INCREASED CLOUD COVER AND PRECIPITATION POTENTIAL. LOW TEMPERATURES,
HOWEVER, WILL LIKELY EDGE HIGHER FOR THE SAME REASONS. OVERALL
THOUGH, TEMPERATURES PROBABLY STAY ABOVE NORMAL. SPILDE

&&

.AVIATION...FOR THE 05/18Z TAF CYCLE...VFR AREA WIDE FOR THE NEXT 24
HOURS EXCEPT FOR AREAS OF IFR LOW CLOUDS AND FOG IN THE COQUILLE
VALLEY AND THE UMPQUA BASIN INCLUDING KRBG TOWARD SUNRISE FRIDAY.
THIS SHOULD BURN OFF BY LATE MORNING. SPILDE

&&

.MARINE...UPDATED 230 PM PST, THURSDAY, 5 MAR, 2015...WINDS WILL
REMAIN RELATIVELY LIGHT WITH LOW SEAS LOW THROUGH FRIDAY NIGHT. A
THERMAL TROUGH WILL REDEVELOP SATURDAY WITH NORTH WINDS INCREASING.
IT`S POSSIBLE THEY COULD REACH SMALL CRAFT OVER THE SOUTHERN WATERS
LATE SATURDAY AFTERNOON AND EVENING. THE THERMAL TROUGH WILL WEAKEN
SATURDAY NIGHT INTO SUNDAY WHILE HIGH PRESSURE REMAINS NORTHWEST OF
THE WATERS. LIGHT WINDS AND LOW SEAS WILL CONTINUE INTO EARLY NEXT
WEEK. THE WAVE WATCH BULLETIN AND ENP WAVE MODELS SHOW AN INCREASING
SOUTHWEST SWELL STARTING NEXT WEDNESDAY AFTERNOON AND LASTING INTO
NEXT THURSDAY. THE WAVE WATCH BULLETIN SHOWS SOUTHWEST SWELLS
HEIGHTS REACHING 14 FEET BY WEDNESDAY EVENING. HOWEVER SUSPECT THE
WAVE HEIGHT IS OVERDONE FOR THE FOLLOWING REASONS. FIRST, THE LOW
PRESSURE THAT WOULD BE GENERATING THE FRESH SWELL IS NOT PROJECTED
BY THE EC OR THE GFS TO BE THAT STRONG AND SECOND IT`S THE FIRST
TIME THE WAVE WATCH AND ENP WAVE MODEL ARE SHOWING THIS. FUTURE
SHIFTS WILL NEED TO MONITOR THIS TREND. -PETRUCELLI

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

BTL/MAS/MAP


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