Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 010534
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
910 PM PST SAT JAN 31 2015

.DISCUSSION...LATEST MODELS RUNS ARE IN LINE WITH SATELLITE IMAGES
SHOWING A SLIGHTLY FASTER TRACK OF THE SYSTEM APPROACHING THE COAST
THIS EVENING. HOWEVER...THERE IS A VERY DRY LAYER UP TO A LITTLE
ABOVE RIDGE LEVELS AND PRECIP WILL HAVE TO FILL IN THIS DEFICIT
BEFORE IT REACHES THE VALLEY FLOORS. HAVE ADJUSTED POPS TOMORROW
MORNING TO ACCOUNT FOR THIS.

.SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT. LOW CLOUDS CONTINUE
TO LINGER NEAR GRANTS PASS, BUT IT`S SLOWLY ERODING AND EXPECT IT
TO CLEAR OUT BY THIS EVENING. ELSEWHERE, SKIES ARE CLEAR WITH A
FEW SCATTERED HIGH CLOUDS MOVING THROUGH. DRY WEATHER CONTINUES
TONIGHT WITH LOW CLOUDS AND FOG DEVELOPING IN THE SAME LOCATIONS.
HOWEVER, MID LEVEL CLOUDS WILL INCREASE AHEAD OF A FRONTAL
BOUNDARY AND IT`S POSSIBLE THIS MAY BE ENOUGH TO DELAY THE ONSET
OF LOW CLOUD DEVELOPMENT TONIGHT OR AT LEAST THE DURATION WILL NOT
BE AS LONG.

OUR FIRST MEASURABLE PRECIPITATION IN QUITE SOME TIME IS EXPECTED
SUNDAY AS A WEAK FRONTAL BOUNDARY MOVES INTO THE AREA. MOST OF
THE PRECIPITATION WILL BE WEST OF THE CASCADES WITH THE HIGHEST
QPF AMOUNTS ALONG THE COAST RANGE AND CASCADES. SNOW LEVELS WILL
BE HIGH, SO PRECIPITATION WILL BE ALL RAIN.

THE MODELS SHOW WEAK RIDGING SUNDAY EVENING WHICH COULD RESULT IN
A TEMPORARY BREAK IN RAINFALL, THEN ANOTHER AND STRONGER FRONT
ARRIVES EARLY MONDAY MORNING. IT WILL BRING MORE RAINFALL TO MUCH
OF THE AREA. QPF AMOUNTS MONDAY ARE EXPECTED TO BE HIGHER AND MOST
WILL BE ALONG THE COASTAL MOUNTAINS AND CASCADES.

THE NAM AND GFS CONTINUE TO SHOW THE FRONT BECOMING NEARLY
STATIONARY MONDAY NIGHT THROUGH TUESDAY NEAR THE OREGON/CALIFORNIA
BORDER WITH A WAVE DEVELOPING ALONG IT TUESDAY AFTERNOON. THIS
WILL ENHANCE THE PRECIPITATION IN THAT AREA. THE EC HAS THE
FRONTAL BOUNDARY POSITIONED FURTHER NORTH WITH THE FOCUS OF
PRECIPITATION IN COOS...NORTHERN CURRY AND DOUGLAS COUNTY. FOR NOW
HAVE LEANED MORE TOWARDS THE NAM/GFS SOLUTION, BUT FUTURE SHIFTS
WILL HAVE TO EVALUATE AND ADJUST IF THE MODELS COME INTO BETTER
CONSENSUS.

THE EC AND GFS DIFFER WITH THE POSITION OF THE FRONTAL BOUNDARY
(GFS FURTHER SOUTH, EC NORTH) TUESDAY NIGHT. HOWEVER BOTH SHOW
RIDGING BUILDING INTO THE AREA WHICH LENDS ME TO BELIEVE THAT
WE`LL HAVE A BREAK IN THE WEATHER WITH LITTLE IF ANY PRECIPITATION.
-PETRUCELLI

.LONG TERM...WEDNESDAY THROUGH SATURDAY. A SIGNIFICANT AMOUNT OF
PRECIPITATION MAY OCCUR IN OUR AREA DURING THE LATTER PORTION OF
THE LONG TERM...ALTHOUGH MOSTLY IN THE FORM OF RAIN WITH SNOW
LEVELS MUCH ABOVE NORMAL.

THERE IS HIGH CONFIDENCE IN THE GENERAL CHARACTER OF THE LARGE SCALE
PATTERN ON WEDNESDAY AND ITS EVOLUTION INTO NEXT WEEKEND. THE MODEL
DIFFERENCES IN STRENGTH AND TIMING OF INDIVIDUAL FEATURES ARE
SIGNIFICANT THOUGH TYPICAL FOR DAYS 4 TO 7 IN AN ACTIVE WINTER
PATTERN. HIGH PRESSURE WILL BUILD OVER THE WEST COAST ON WEDNESDAY
THEN LIKELY SHIFT EAST OF OUR AREA. THIS MOVEMENT WILL OCCUR WITH
THE APPROACH OF A DEEP TROUGH. THE TROUGH AXIS WILL REMAIN FAR
OFFSHORE THROUGH THE WEEKEND AND LIKELY RESULT IN A VERY WET AND
WARM SOUTHWEST FLOW ALOFT.

ON WEDNESDAY A HIGH PRESSURE RIDGE WILL PROVIDE DRY WEATHER TO
SOUTHERN AND CENTRAL CALIFORNIA AND BUILD NORTHWARD WHILE THE
STATIONARY FRONT WILL STILL BE NEAR OR IN OUR AREA AND WEAKEN AS IT
MOVES NORTH. AS A RESULT, THE PROBABILITY OF PRECIPITATION HAS BEEN
LOWERED SOUTH OF A LINE FROM CAPE BLANCO ALONG THE UMPQUA DIVIDE TO
CHILOQUIN AND VALLEY FALLS...ESPECIALLY IN NORTHERN CALIFORNIA. IF
THE STATIONARY FRONT DOES REMAIN IN OUR AREA ON WEDNESDAY,
PRECIPITATION AMOUNTS WILL LIKELY BE LIGHT.

THERE IS GOOD AGREEMENT BETWEEN THE ECMWF AND GFS THAT THE RIDGE
AXIS WILL MOVE TO IDAHO WEDNESDAY NIGHT WITH A RELATIVELY WEAK COLD
FRONT REACHING THE COAST THURSDAY MORNING THEN WEAKENING OVER THE
WEST SIDE DURING THE DAY. THE SNOW LEVEL IS FORECAST TO BE AROUND
7500 FT MSL ON THURSDAY WITH WEST SIDE POPS IN THE CHANCE TO LIKELY
CATEGORY AND A SLIGHT CHANCE TO CHANCE ON THE EAST SIDE.

A SERIES OF STRONGER FRONTS ARE EXPECTED IN THE PERSISTENT SOUTHWEST
FLOW THURSDAY NIGHT THROUGH SUNDAY NIGHT WITH THE SNOW LEVEL
REMAINING ABOVE 7000 FT MSL. AT THIS TIME, FOUR DISTINCT FRONTS ARE
INDICATED. THESE SYSTEMS LOOK TO BE FAST MOVING BUT MAY PRODUCE
HEAVY RAIN AND STRONG, GUSTY SOUTHERLY WINDS. /DW

&&

.AVIATION...BASED ON THE 01/00Z TAF CYCLE... WARMER AFTERNOON
TEMPERATURES AND SOME LOWER DEWPOINTS VERSUS 24 HOURS AGO COUPLED
WITH INCREASING HIGH AND MID LEVEL CLOUDS MEAN THAT ONLY MVFR VIS
WITH LOCAL IFR CIG/VIS ARE EXPECTED IN THE WEST SIDE VALLEYS
OVERNIGHT, EXCEPT IN THE ILLINOIS VALLEY AND NEAR GRANTS PASS, WHERE
IFR AND LOCAL LIFR SHOULD BE EXPECTED. AN INCOMING WEAK FRONTAL
SYSTEM WILL BRING SHOWERS AND SOME WEST SIDE MVFR THROUGH THE DAY
SUNDAY, MAINLY COAST AND UMPQUA BASIN. OTHERWISE, EXPECT PARTIAL
TERRAIN OBSCURATIONS CASCADES WEST. BTL

&&

.MARINE...UPDATED 215 PM PST SATURDAY, JANUARY 31, 2015... LIGHT
NORTH WINDS WILL PREVAIL THIS AFTERNOON, EXCEPT ALONG AND NEAR THE
IMMEDIATE COAST WHERE THEY WILL BE MORE VARIABLE AND GENERALLY
ONSHORE. LIGHT WINDS WILL BECOME SOUTHERLY AROUND SUNRISE ON SUNDAY
AS A WEAK FRONTAL SYSTEM PUSHES IN FROM THE WEST WITH PERIODS OF
RAIN. SUNDAY NIGHT THROUGH MONDAY MODERATE WEST SWELL WILL BUILD AS
A SOMEWHAT STRONGER FRONTAL SYSTEM ARRIVES. UNSETTLED CONDITIONS MID-
WEEK WILL BUILD TO A STRONG STORM SYSTEM WITH GALES...AND EVEN STORM
FORCE WINDS POSSIBLE...ON OR ABOUT FRIDAY. BTL

&&

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 1 PM PST SUNDAY FOR
     ORZ023-024-026-616-620-622.
     AIR STAGNATION ADVISORY UNTIL 1 PM PST SUNDAY FOR
     ORZ029>031-623>625.

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

MAP/DW/BTL



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