Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 250406
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
906 PM PDT FRI APR 24 2015

.UPDATE...
THE FORECAST HAS BEEN UPDATE TO FINE TUNE SHOWER LOCATION AND
COVERAGE FOR THIS EVENING, ADJUST SNOW LEVELS DOWNWARD FOR
SATURDAY MORNING, AND TO INCREASE WEST SIDE SHOWER CHANCES FOR
SATURDAY MORNING. BTL

&&

.DISCUSSION...
SHOWERS, BRIEFLY AND LOCALLY MODERATE TO HEAVY IN A FEW LOCATIONS
EARLIER, CONTINUE IN SOME AREAS THIS EVENING. RADAR AND SURFACE
OBSERVATIONS SHOW THESE CURRENTLY DIMINISHING IN BOTH COVERAGE AND
INTENSITY.

OVERNIGHT INTO EARLY SATURDAY, HOWEVER, UPPER LEVEL SUPPORT FOR
SHOWER ACTIVITY WILL INCREASE ACROSS THE AREA AS THE FRONT
LEFT PORTION OF A 130+ KNOT JET STREAM MAXIMUM MOVES INTO AND
ACROSS THE AREA. THIS WILL CAUSE 500MB TEMPERATURES OVER MEDFORD
OF AROUND -22C UNDER WEST-SOUTHWEST FLOW TO FALL TO AROUND -25C
UNDER WEST-NORTHWEST FLOW BY MORNING. THUS, WE EXPECT SHOWER
ACTIVITY TO PICK UP ACROSS THE AREA TONIGHT CONTINUING THROUGH
SATURDAY MORNING. UPPER LEVEL SUPPORT FOR SHOWERS WILL WANE MAINLY
INTO THE MOUNTAINS SATURDAY AFTERNOON AND EVENING AS THE BULK OF
THE FAVORABLE DYNAMICS MOVE MOSTLY SOUTH AND EAST OF THE FORECAST
AREA. A WELCOMED 0.10" TO 0.30" OF WATER IS EXPECTED TO FALL OVER
DROUGHT PARCHED MODOC AND SOUTHERN LAKE COUNTIES DURING THIS TIME
PERIOD WITH MOSTLY LESSER AMOUNTS ELSEWHERE. SNOW ACCUMULATION
LEVELS WILL BE MOSTLY 4500 FEET AND UP WITH LESS THAN 2 INCHES
EXPECTED AT MOST LOCATIONS. PRECIPITATION WILL LIKELY FALL AS
SNOW DOWN TO BETWEEN 3500 FEET TO 4000 FEET IN AND AROUND THE
CASCADES, TO INCLUDE THE KLAMATH FALLS AREA, SATURDAY MORNING. BTL

&&

.PREV DISCUSSION... /ISSUED 505 PM PDT FRI APR 24 2015/

SHORT TERM...24/12Z NAM/GFS IN.

MOSTLY CLOUDY SKIES PERSIST ACROSS THE MEDFORD CWA THIS AFTERNOON
WITH SOME LIGHT SHOWERS HERE AND THERE. MORE BREAKS IN THE CLOUD
COVER THOUGH. AMOUNTS OVER THE PAST SIX HOURS HAVE BEEN LESS THAN
0.05 INCHES...WHERE ANYTHING HAS BEEN RECORDED AT ALL. ALL STATIONS
REPORTING MEASURABLE PRECIPITATION HAVE BEEN FROM THE CASCADES
WEST.

A LONG WAVE TROUGH IS NOW ALONG THE PACIFIC NORTHWEST COAST WITH
MOST OF THE ASSOCIATED ENERGY DIRECTED INTO BRITISH COLUMBIA AND
WASHINGTON STATE. THE GENERALLY UNSETTLED SHOWERY CONDITIONS OVER
THE MEDFORD CWA IS DUE TO WEAK SHORT WAVES ROUNDING THE BOTTOM OF
THE TROUGH. THE NEXT SIGNIFICANT WAVE WILL MOVE ONSHORE THIS
EVENING OVER NORTHERN CALIFORNIA...WHICH IS WHERE MOST OF THE
SHOWER ACTIVITY WILL BE. ONE MORE WAVE WILL MOVE THROUGH
SATURDAY...AND THIS ONE WILL BE SPLIT WITH ONE LOCAL MAXIMA
GRAZING THE DOUGLAS/LANE COUNTY BOUNDARY AND THE OTHER OVER
CENTRAL TO NORTHERN CALIFORNIA. THE LAST OF THE SHOWERS WILL
DISSIPATE SATURDAY EVENING.

AFTER THAT A LONG WAVE RIDGE WILL BUILD INTO THE WEST COAST...
WHICH WILL BRING A FEW DAYS OF DRY AND WARMER WEATHER TO THE AREA.
MONDAY LOOKS DOWNRIGHT HOT WITH INLAND HIGH TEMPERATURES 15 TO 25
DEGREES ABOVE NORMAL.

THE RIDGE WILL BREAK TO THE EAST OF THE AREA MONDAY...BUT IT WILL
REMAIN STRONG OVER THE AREA WITH 500 MB HEIGHTS GENERALLY ABOVE
5760M.

LONG TERM...TUESDAY THROUGH FRIDAY NIGHT...CONFIDENCE DEGRADES
THROUGH MUCH OF THE LONG TERM, AS MODEL AND VARIOUS ENSEMBLES SHOW A
WIDENING ARRAY OF SOLUTIONS. THESE DIFFICULTIES APPEAR TO ARISE DUE
TO THE VARIOUS WAYS EACH MODELS IS ATTEMPTING TO HANDLE SEVERAL
UPPER LEVEL CLOSED LOWS IN THE NORTHERN HEMISPHERE, AND ALSO HOW AND
WHEN A BAND OF ZONAL FLOW ACROSS THE NORTHERN PACIFIC WILL
EVENTUALLY BEND AND DISTORT INTO DISCERNIBLE WAVES. THROUGH THE
NOISE, THERE IS A HINT OF AGREEMENT CONCERNING THE GENERAL PATTERN,
BUT THERE IS LITTLE ELSE TO PROVIDE ANY CERTAINTY, ESPECIALLY
REGARDING THE DETAILS OF TIME AND PLACEMENT. HAVE OPTED FOR A VERY
GENERALIZED FORECAST, AND WOULD NOT BE SURPRISED IF THERE ARE MANY
CHANGES OVER THE NEXT SEVERAL FORECAST CYCLES.

THE FIRST OF SEVERAL UPPER LEVEL TROUGHS IS EXPECTED TO MOVE INTO
THE REGION TUESDAY AFTERNOON AND EVENING, FOLLOWED BY SEVERAL OTHER
SHORTWAVES AND/OR TROUGHS THROUGHOUT THE WEEK. IN BETWEEN EACH WAVE,
THERE SHOULD BE SHORT PERIODS OF RIDGING AND POSSIBLY OFFSHORE FLOW.
HAVE THEREFORE KEPT SLIGHT TO CHANCE PRECIPITATION PROBABILITIES IN
PLACE FOR MUCH OF THE TERM, AND ALSO KEPT TEMPERATURES AT OR
SLIGHTLY ABOVE NORMAL, WITH DRY AND WARMER PERIODS INTERSPERSED
THROUGHOUT. EACH WAVE HAS THE POTENTIAL TO BRING THUNDERSTORMS TO
THE AREA, BUT MUCH DEPENDS ON FACTORS THAT ARE TOO UNCERTAIN AT THIS
TIME RANGE. ANY PRECIPITATION EVENTS THAT DO OCCUR ARE LIKELY TO BE
LACKING IN ANY SUBSTANTIAL MOISTURE. -BPN

&&

.AVIATION...FOR THE 25/00Z TAF CYCLE...SHOWERS WILL CONTINUE TO
SPREAD THROUGHOUT THE AREA THROUGH THE EVENING. A MIX OF VFR AND
MVFR CEILINGS WILL ACCOMPANY THESE SHOWERS...WITH MOUNTAIN
OBSCURATION OCCURRING THE FORECAST AREA DURING THE EVENING AND
OVERNIGHT. TONIGHT...A MIX OF MVFR AND IFR CONDITIONS WILL AFFECT
THE EAST SIDE AND NORTHERN CALIFORNIA WHERE MODERATE RAIN AND SNOW
SHOWERS ARE EXPECTED. CONDITIONS WILL GRADUALLY IMPROVE SATURDAY MORNING.
-SCHAAF/SPILDE

&&

.MARINE...UPDATED 220 PM PDT FRIDAY, APR 24, 2015...SHOWERS WILL
ACCOMPANY A FRONTAL SYSTEM MOVING THROUGH THE WATERS THIS EVENING.
WINDS WILL CONTINUE TO BE LIGHT TO MODERATE FROM THE SOUTH AND
SOUTHWEST, BUT NORTHWEST SWELL WILL CREATE SMALL CRAFT CONDITIONS
FOR SEAS. CONDITIONS WILL IMPROVE AS HIGH PRESSURE BUILDS IN
SATURDAY. A WEAK WARM FRONT IS EXPECTED TO MOVE NORTH OF THE AREA
SUNDAY BUT LIGHT TO MODERATE WINDS AND SEAS ARE EXPECTED THROUGH
TUESDAY.

CONFIDENCE IN THE EXTENDED PERIOD CONTINUES TO BE LOW AS THE MODELS
ARE STILL DISAGREEING REGARDING THE TIMING OF A TROUGH MOVING
THROUGH OUR WATERS TUESDAY NIGHT AND WEDNESDAY. THERE IS THE
POTENTIAL FOR SMALL CRAFT ADVISORY SEAS AGAIN. -SCHAAF/SPILDE

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...
- SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THIS
  EVENING FOR PZZ350-356-370-376.

$$

BTL/15/BPN/MAS/BMS


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