Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 270400
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
800 PM PST THU FEB 26 2015

.DISCUSSION...THE FIRST ROUND OF PRECIPITATION THAT MOVED THROUGH
THIS AFTERNOON AND EVENING IS DIMINISHING A BIT ON THE LATEST RADAR
IMAGERY, BUT THERE ARE STILL SOME SHOWERS OUT THERE. MOST AREAS
AROUND THE ROGUE VALLEY HAD FROM 0.10-0.20 OF AN INCH OF RAIN WHILE
AREAS ALONG THE COAST SAW THE MOST WITH 0.25-0.50 OF AN INCH. I WAS
HARD-PRESSED TO FIND MUCH MEASURABLE PRECIPITATION OVER THE EAST
SIDE. EVEN THOUGH WE`RE CURRENTLY SEEING A DOWNWARD TREND IN
PRECIPITATION, AN UPPER LEVEL TROUGH...LOCATED NEAR VANCOUVER
ISLAND...WILL MOVE SOUTHEASTWARD AND CLOSE OFF NEAR THE MOUTH OF THE
COLUMBIA RIVER FRIDAY MORNING. IT WILL GRADUALLY MOVE OVERHEAD
FRIDAY AFTERNOON AND NIGHT, THEN SHIFT SOUTHEAST OF THE AREA
SATURDAY. WITH COLDER AIR ARRIVING ALOFT, EXPECT SHOWERS TO PICK UP
AGAIN OVERNIGHT AND ESPECIALLY FRIDAY INTO FRIDAY EVENING. SNOW
LEVELS THIS EVENING ARE RUNNING AROUND 5000-5500 FT AND THESE WILL
LOWER DOWN TO AROUND 4000 FT BY FRIDAY MORNING. A WINTER WEATHER
ADVISORY IS OUT FOR THE CASCADES/SISKIYOUS AND CAN BE VIEWED AT
WSWMFR. THE AIR ALOFT IS COLD ENOUGH TO SUPPORT STEEP MID-LEVEL
LAPSE RATES, SO THERE IS SOME POTENTIAL FOR THUNDER JUST ABOUT
ANYWHERE FRIDAY. FRIDAY NIGHT INTO SATURDAY MORNING...THE 00Z NAM12
IS HINTING AT SOME PRECIPITATION WRAPPING BACK INTO EAST SIDE AREAS
AS COLDER AIR ARRIVES AND SNOW LEVELS DROP. WE`LL HAVE TO MONITOR
THIS FOR POTENTIAL WINTER WEATHER HEADLINES. SPILDE

&&

.AVIATION...FOR THE 27/00Z TAF CYCLE...ALONG THE COAST...MVFR CIGS
WITH AREAS OF IFR CIGS/VSBYS WILL PERSIST INTO FRIDAY MORNING...
SLIGHTLY IMPROVING IN THE AFTERNOON.  INLAND FROM THE CASCADES
WEST...AREAS OF MVFR CIGS/VSBYS AND LOCAL IFR CIGS/VSBYS WITH
HIGHER TERRAIN OBSCURED WILL PERSIST THROUGH FRIDAY
MORNING...IMPROVING SLIGHTLY IN THE AFTERNOON.  EAST OF THE
CASCADES...VFR CONDITIONS WITH LOCAL MVFR CIGS AND AREAS OF HIGHER
TERRAIN OBSCURED WILL PERSIST THROUGH FRIDAY. ISOLATED THUNDERSTORMS
ARE POSSIBLE FRIDAY AFTERNOON AND EVENING. SNOW LEVELS WILL LOWER TO
4000 TO 5000 FEET FRIDAY MORNING.

&&

.MARINE...UPDATED 4 PM PST THURSDAY 26 FEB 2015...WINDS WILL
CONTINUE TO TURN WESTERLY THIS EVENING AS A FRONTAL SYSTEM MOVES
ONSHORE TONIGHT INTO FRIDAY MORNING. SHOWERS ARE EXPECTED AHEAD
OF...ALONG...AND BEHIND THIS FRONT. THE RAIN WILL BE LOCALLY
MODERATE TO HEAVY AT TIMES AND THUNDERSTORMS ARE POSSIBLE ON
FRIDAY. STEEP SEAS WILL ALSO AFFECT THE WATERS ON FRIDAY BEHIND
THE FRONT. GUSTY NORTH WINDS WILL DEVELOP BEHIND THIS FRONT
SATURDAY AND SUNDAY AS THE ASSOCIATED LOW PRESSURE SYSTEM SHIFTS
SOUTHWARD.

&&

.PREV DISCUSSION... /ISSUED 402 PM PST THU FEB 26 2015/

DISCUSSION...
SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT...
EXTENSIVE CLOUD COVER AND SOME LIGHT PRECIPITATION HAVE POURED INTO
THE REGION EARLY THIS AFTERNOON AHEAD OF THE APPROACHING COLD LOW
PRESSURE SYSTEM. THIS LOW WILL SLIDE SOUTH ALONG THE PACIFIC COAST
TONIGHT AND TOMORROW, AND WILL LIKELY BRING MUCH NEEDED RAIN AND
HIGHER ELEVATION SNOW TO THE FORECAST AREA BEFORE IT PUSHES AWAY
SATURDAY AFTERNOON. MODELS ARE IN GOOD AGREEMENT THROUGHOUT THE
SHORT TERM, ALTHOUGH THERE STILL REMAINS A BIT OF UNCERTAINTY
REGARDING PRECIPITATION AMOUNTS, PARTICULARLY IN REGARDS TO SNOW.
THERE IS ALSO SOME QUESTION ABOUT SNOW LEVELS, WHICH MAY DROP A BIT
LOWER THAN EXPECTED GIVEN THE  DRY AIR THAT HAS BEEN IN THE AREA FOR
THE PAST WEEK OR SO. HAVE ERRED ON THE COLDER SIDE SLIGHTLY, BUT
GENERALLY DEPENDED ON A MIDDLE-OF-THE-ROAD SOLUTION.

SNOW LEVELS AS OF THIS WRITING ARE AT ABOUT 5000 TO 6000 FT, BUT BY
TOMORROW MORNING, THEY SHOULD DROP TO AROUND 4000 FT AND REMAIN
THERE FOR THE REMAINDER OF THE EVENT. THEREFORE, EXPECT SNOW TO
IMPACT NEARLY ALL CASCADE PASSES, AS WELL AS SISKIYOU SUMMIT
ALONG INTERSTATE 5. HOWEVER, WITH THE ORIENTATION OF THE SYSTEM,
THE CASCADES SHOULD RECEIVE THE BULK OF THE SNOWFALL, AROUND 5 TO
10 INCHES AT PASS LEVEL, WITH ONLY A FEW INCHES OF SNOW EXPECTED
AT SISKIYOU SUMMIT. ROAD TEMPERATURES THERE MAY ALSO IMPEDE ANY
SIGNIFICANT ACCUMULATIONS ALONG THE ROADWAY. GIVEN THE AMOUNT OF
SNOW EXPECTED NEAR THE DIAMOND LAKE INTERCHANGE, ALONG HIGHWAY
140, AND NEAR CRATER LAKE, HAVE OPTED TO ISSUE A WINTER WEATHER
ADVISORY AS TRAVEL IN THOSE AREAS COULD BECOME HAZARDOUS. LIQUID
PRECIPITATION AMOUNTS BELOW THE SNOW LEVELS WILL NOT BE OVERLY
SIGNIFICANT, WITH A QUARTER TO A HALF INCH EXPECTED WEST OF THE
CASCADES, AND A QUARTER INCH OR LESS TO THE EAST. HIGHER
ELEVATIONS OF THE EAST SIDE COULD PICK UP 3 TO 5 INCHES OF
SNOWFALL BY THE TIME THE SYSTEM DEPARTS.

ONCE THE TROUGH DEPARTS TO THE SOUTH SATURDAY, RIDGING WILL RETURN
TO THE AREA FOR SUNDAY. THIS WILL BE SHORT LIVED THOUGH, AS MODELS
ARE PRODUCING A REINFORCING SHORTWAVE WHICH WILL SLIDE SOUTH INTO
THE REGION SUNDAY NIGHT INTO MONDAY. MODELS HAVE PRODUCED WIDESPREAD
SOLUTIONS INVOLVING THIS SYSTEM, BUT HAVE COME INTO BETTER ALIGNMENT
IN THE LATEST RUNS. CURRENT THINKING IS THAT SOME LIGHT
PRECIPITATION COULD ENTER THE COAST NORTH OF CAPE BLANCO OVERNIGHT
SUNDAY, BUT THE BULK OF THE SYSTEM IS NOT EXPECTED UNTIL WE ENTER
THE LONG TERM. -BPN

LONG TERM...MONDAY, MARCH 2ND THROUGH THU NIGHT, MARCH 6TH... A
BREAK IN THE WEATHER ON SUNDAY IS LIKELY TO BE REPLACED BY ANOTHER
UPPER LEVEL SHORTWAVE TROUGH MOVING SOUTHWARD ON THE WESTERN EDGE OF
THE BROADER PARENT TROUGH ALONG THE WEST COAST MONDAY INTO TUESDAY.
MODEL GUIDANCE HAS HAD A DIFFICULT TIME WITH DETAILS RELATED TO THIS
SHORTWAVE TROUGH EARLY NEXT WEEK, PARTICULARLY WITH THE AMPLITUDE OF
IT. SPECIFICALLY, THERE ARE QUESTIONS ABOUT HOW MUCH OF A FRONTAL
SYSTEM DEVELOPS OFF OF THE PACIFIC NORTHWEST COAST, HOW MUCH
MOISTURE IT WILL PICK UP, AND HOW DEEP THE COLD POOL WILL BE WITH
THIS WEATHER SYSTEM. TODAY`S MODELS CONTINUE TO SHOW GOOD AGREEMENT
THAT THIS TROUGH WILL, INDEED, ARRIVE WITH ANOTHER ROUND OF COLD AIR
AND SHOWERS ACROSS THE AREA, BUT HAVE TRENDED EASTWARD AND SOMEWHAT
WEAKER WITH THE DEPTH AND WESTWARD EXTENT OF THE COLD AIR ALOFT,
ESPECIALLY AT 500MB. THE NET RESULT IS THAT THE PRECIPITATION
AMOUNTS AND DURATION WITH THIS WEATHER SYSTEM NOW APPEAR LESSER THAN
THEY DID 24 HOURS AGO WITH THE BEST CHANCE OF PRECIPITATION IN THE
SUNDAY NIGHT THROUGH MONDAY NIGHT TIME FRAME. AS WE OFTEN SEE WITH
WEATHER SYSTEMS OF THIS TYPE, PINNING DOWN SPECIFIC DETAILS OF
PRECIPITATION AMOUNTS WITH THIS SYSTEM IS LIKELY TO BE DIFFICULT
UNTIL ABOUT SATURDAY OR SUNDAY. WHAT IS CLEAR IS THAT THERE WILL BE
ANOTHER ROUND OF SHOWERS WITH SNOW LEVELS RELATIVELY LOW, SO THE
HIGHER MOUNTAIN PASSES SUCH AS WILLAMETTE, DIAMOND LAKE, AND
SISKIYOU SUMMIT COULD BE AFFECTED.

IN THE WAKE OF THIS SYSTEM, WEDNESDAY AND THURSDAY MORNINGS LOOK AS
IF THEY WILL BE CHILLY AGAIN, WITH LOWS IN THE 20S FOR PRIMARY STONE
FRUIT GROWING AREAS CURRENTLY SENSITIVE TO SUCH TEMPERATURES.
TEMPERATURES HAVE TRENDED A LITTLE WARMER WITH THIS SYSTEM AS
COMPARED TO 24 HOURS AGO. THURSDAY AND BEYOND THE TROUGH IS EXPECTED
TO SHIFT EASTWARD WITH TEMPERATURES AGAIN MODERATING TO SPRING-LIKE.
BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 10 PM PST FRIDAY FOR
        ORZ027-028-617-621-623.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS
        UNTIL 4 AM PST SATURDAY FOR PZZ350-356-370-376.

$$

18/18/18


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