FXUS66 KMFR 160627
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
1027 PM PST TUE DEC 15 2009
.UPDATE...
JUST A QUICK UPDATE TO PASS ALONG THAT THE WIND ADVISORY IN THE
SHASTA VALLEY HAS BEEN EXTENDED THROUGH 4 AM PST AND THAT THE
WINTER WEATHER ADVISORY IN MODOC COUNTY HAS BEEN EXTENDED THROUGH
7AM PST.
CONTINUING SURGE OF PRECIPITATION AND ASSOCIATED DYNAMICS
HAS KEPT THE MEDFORD TO REDDING PRESSURE GRADIENT ABOVE 6
MILLIBARS AND ADVISORY LEVEL WINDS HAVE CONTINUED.
RADAR TRENDS INDICATE A PRECIPITATION SURGE ABOUT TO HIT THE SLOT
BETWEEN MOUNT SHASTA AND MOUNT LASSEN WHICH WILL SEND IT INTO
MODOC COUNTY. THIS AREA HAS SEEN LITTLE PRECIPITATION OVER THE
LAST 24 HOURS. WHILE MOST AREAS WILL LIKELY GET LESS THAN TWO
INCHES OF NEW SNOW...THE POTENTIAL EXIST FOR UP TO 4 ABOVE 5000
FEET...AND 4 OR MORE IN THE WARNER MOUNTAINS TONIGHT. LUTZ
&&
.PREV DISCUSSION... /ISSUED 927 PM PST TUE DEC 15 2009/
DISCUSSION...
A JET STREAM MAXIMUM AND A COUPLE OF ASSOCIATED VORTICITY MAXIMA
EVIDENT WEST OF THE COAST ON WATER VAPOR IMAGERY THIS EVENING LED
TO CLOUD TOP COOLING OVER THE FORECAST AREA THIS EVENING AS
EVIDENCED ON THE INFRARED SATELLITE IMAGERY. THIS...IN TURN...SENT
A SURGE OF PRECIPITATION NORTHWARD THROUGH MAINLY SISKIYOU COUNTY
THIS EVENING WITH PRECIPITATION RATES OF 0.10" TO 0.25" PER HOUR
FOR ABOUT 3 HOURS. THIS PUSHED INTO AND THEN TRICKLED OVER THE
SISKIYOUS INTO JACKSON COUNTY AND THE EAST SIDE. ALTHOUGH
INTENSITIES HAVE NOW WEAKENED TO ABOUT HALF...THIS PATTERN OF
PRECIPITATION CONTINUES AND AN ADDITIONAL SURGE HAS SHOWN UP WEST
OF INTERSTATE 5 IN OREGON.
A WINTER WEATHER ADVISORY WAS ISSUED FOR THE MOUNT SHASTA AREA
THIS EVENING FOR ELEVATIONS ABOVE 4000 FEET...VALID THROUGH 7AM
PST WEDNESDAY MORNING. PRECIPITATION RATES HAVE MET OR SLIGHTLY
EXCEEDED MODEL PROJECTIONS THERE SINCE LATE THIS AFTERNOON...WITH
SNOWFALL RATES LIKELY A HALF INCH TO ONE INCH AN HOUR. 5000 FOOT
MSL LOW LEVEL SOUTH FLOW HAS AIDED PRECIPITATION DESPITE A STEADY
SOUTHWEST 700MB FLOW. WHILE RADAR TRENDS DO SHOW SOME WEAKENING
OVER THE LAST COUPLE OF HOURS PRECIPITATION WILL CONTINUE THROUGH
THE MORNING. AMOUNTS LIKELY HAVE ALREADY REACHED THE 3 INCHES
REQUIRED TO VERIFY THE ADVISORY AND EXPECT 2-4 MORE OVERNIGHT.
CURRENT PLAN IS TO EXPIRE THE CURRENT PRODUCTS OUT AS THEY EXIST.
WHILE SNOW AND WIND WILL CONTINUE ACROSS THE WARNING AND ADVISORY
AREAS TONIGHT RATES WILL DIMINISH. IT SHOULD BE NOTED THAT SNOW
LEVELS WILL LIKELY NOSE DOWN CLOSE TO MOUNT SHASTA CITY...KLAMATH
FALLS...AND ALTURAS BUT ACCUMULATIONS WILL BE LIGHT...GENERALLY A
TRACE TO ABOUT AN INCH.
THE REST OF THE FORECAST REMAINS UNCHANGED AT THIS TIME. FAIRLY HIGH
SNOW LEVELS AND SOMEWHAT UNSETTLED CONDITIONS...THOUGH NOTHING AS
SIGNIFICANT AS THE CURRENT STORM SYSTEM...ARE EXPECTED THIS WEEK.
LUTZ
AVIATION...
MVFR TO VFR CONDITIONS DUE TO CEILINGS AND REDUCED VISIBILITIES
FROM PRECIPITATION AT LOWER ELEVATIONS WILL CONTINUE OR WORSEN A
CATEGORY OVERNIGHT THROUGH WEDNESDAY MORNING. SNOW LEVELS ARE
NEAR 5000 FEET ON THE WEST SIDE AND 4000 FEET ON THE EAST SIDE AND
WILL LOWER 500 TO 1000 FEET BY MORNING. WIDESPREAD MOUNTAIN
OBSCURATIONS EXIST AND WILL THROUGH WEDNESDAY. PRECIPITATION WILL
SLOWLY DIMINISH IN AREAL COVERAGE AND INTENSITY THROUGH WEDNESDAY
MORNING...AND THEN SEE AN UPSWING OVER NORTHWEST SECTIONS ALONG
THE COAST...IN THE COASTAL MOUNTAINS...AND UMPQUA BASIN WEDNESDAY
AFTERNOON AS ANOTHER FRONTAL WAVE PUSHES IN FROM THE WEST. EXPECT
MVFR TO VFR CONDITIONS IN THE VALLEYS WEDNESDAY AFTERNOON. LUTZ
PREV DISCUSSION... /ISSUED 205 PM PST TUE DEC 15 2009/
DISCUSSION...
A SLOW MOVING COLD FRONT HAS STARTED TO MOVE INLAND THIS AFTERNOON.
HIGH WINDS AT THE COAST WILL BEGIN TO DIMINISH AND TAPER OFF
THROUGH THE EVENING SO THE HIGH WIND WARNING AT THE COAST WILL BE
ALLOWED TO EXPIRE AT 300 PM THIS AFTERNOON.
MODERATE TO HEAVY SNOWS FALLING IN THE MT SHASTA AREA WILL DIMINISH
THIS AFTERNOON AS THE COLD FRONT MOVES INLAND RESULTING IN DECREASED
WINDS AND SNOW FALL RATES. SNOW LEVELS HAVE BEEN RISING AS WELL SO
THE WARNING WILL BE ALLOWED TO EXPIRE AT 300 PM AS WELL. THE SAME
REASONING APPLIES TO THE HIGHER PORTIONS OF THE SHASTA VALLEY AND
THE SISKIYOU AND SOUTHERN OREGON CASCADES. THE SNOW ADVISORIES FOR
THESE AREAS WILL EXPIRE AT 300 PM AS WELL.
SNOW ADVISORIES FOR PORTIONS OF KLAMATH LAKE AND MODOC COUNTIES WILL
REMAIN IN EFFECT SINCE THEY ARE LOCATED WELL TO THE EAST OF THE
COLD FRONT AT THIS TIME. SNOW FALL RATES WILL DECREASE THERE LATE
THIS EVENING AS THE COLD FRONT WEAKENS ONCE IT IS WELL INLAND. THE
SAME IS TRUE FOR THE WIND ADVISORY IN THE SHASTA VALLEY WHERE WINDS
WILL TAPER OFF LATER THIS EVENING AS THE FRONT WEAKENS.
LATE TONIGHT WINDS PRECIPITATION BECOME LIGHT AS THE COLD FRONT
BECOMES QUITE WEAK. WEAK MID LEVEL DISTURBANCES KEEPS LIGHT
PRECIPITATION GOING THROUGH WEDNESDAY.
THURSDAY A WARM FRONT BRINGS MORE LIGHT PRECIPITATION WITH SNOW
LEVELS AROUND 5000 FEET. THURSDAY NIGHT A WEAK COLD FRONT MOVES
THROUGH THE AREA. FRIDAY AND SATURDAY WEAK MID LEVEL DISTURBANCES
KEEP THE REGION CLOUDY AND THERE WILL BE LIGHT PRECIPITATION OFF
AND ON.
NEXT MONDAY AND TUESDAY A STRONGER LOW PRESSURE SYSTEM WILL LIKELY
AFFECT OUR AREA.
AVIATION...WITH A SLOW MOVING COLD FRONT ACROSS THE REGION
GENERALLY MVFR CIGS AND VSBY IN RAIN AND SNOW AREA WIDE THROUGH
THIS EVENING. IFR CIGS VSBY IN SNOW OVER THE HIGHER TERRAIN.
ALSO...LOCAL LOW LEVEL WIND SHEAR WILL AFFECT THE COAST AND INLAND
PROTECTED VALLEYS AS UPPER WINDS REMAIN STRONG THROUGH THIS EVENING.
CONDITIONS WILL IMPROVE WEDNESDAY. LATE TONIGHT THE COLD FRONT
WEAKENS AND PRECIPITATION DECREASES. ON WEDNESDAY MOST AREAS WILL
BE VFR WITH ISOLD OBSCUREMENT OF HIGHER RIDGES.
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
CA...WIND ADVISORY UNTIL 4 AM PST WEDNESDAY FOR CAZ081.
WINTER WEATHER ADVISORY UNTIL 7 AM PST WEDNESDAY FOR CAZ082-
CAZ083-CAZ085.
PACIFIC COASTAL WATERS...HAZARDOUS SEAS WARNING UNTIL 10 AM PST
THURSDAY FOR PZZ350-PZZ356-PZZ370-PZZ376.
$$
BTL/MTS/11
