Winter Storm in Oregon, February 13 to 15, 2024

Area Forecast Discussion
National Weather Service Medford OR
919 PM PST Tue Feb 13 2024

.DISCUSSION...Satellite imagery is showing some low stratus
starting to form across inland west side valleys as well as a
cirrus shield associated with our next system moving in from the
southwest. Overall, expect the dry weather to turn more active
tonight. For additional details on the forecast, please see the
previous discussion below. -Schaaf

&&

.MARINE...Updated 900 PM Tuesday February 12, 2024...High
pressure has settled into the area, and as a result, winds and seas
will remain relatively calm through tonight. The first in a series
of fronts arrives Wednesday, with increasing south winds and seas
becoming very steep. The occasional gale force gust is possible
Wednesday afternoon through Wednesday night as the front passes, but
widespread gales are not expected. With a surface low lingering
along the coast to our north, south winds and steep seas are
expected to continue, with the next front arriving Friday into
Saturday. We expect increasing south winds and building seas once
again, with gales and very steep seas possible, mainly across the
outer waters. Behind this front, A long period, west swell is
forecast build into the area on Saturday. This will continue the
high and steep seas into Sunday.
-CC

&&

.PREV DISCUSSION...Issued 414 PM Tuesday Feb 13, 2024...

SHORT TERM...

THERE ARE PLENTY OF FAIR WEATHER CUMULUS CLOUDS OUT THERE THIS
AFTERNOON AS THE BOUNDARY LAYER BEGINS TO DESTABILIZE. THE CHANCE
FOR SOME SHOWERS IS VERY LOW(~5%) THIS AFTERNOON AND EVENING,
GENERALLY IN NORTHERN CALIFORNIA AND THE SOUTHERN SECTIONS OF LAKE
AND KLAMATH COUNTIES. HIGH CLOUDS AHEAD OF THE WARM FRONT WILL
INCREASE LATER THIS EVENING INTO TONIGHT AHEAD OF THE NEXT WINTER
WEATHER EVENT.

THE WARM FRONT WILL BRING MOST OF THE PRECIPITATION TO WESTERN
SISKIYOU COUNTY FIRST OVERNIGHT BEFORE IT LIFTS FARTHER NORTH.
THESE LOCATIONS SHOULD SEE SNOW LEVELS IN NORTHERN CALIFORNIA AND
SECTIONS OF SOUTHERN OREGON PUSH TOWARDS 5500 FEET BEHIND THE WARM
FRONT. SNOW SHOULD START TO ACCUMULATE IN THE CASCADES IN THE
LATER MORNING HOURS. BY WEDNESDAY AFTERNOON AND EARLY EVENING, AN
OCCLUDED FRONT PUSHES THROUGH OUR FORECAST AREA WITH WIDESPREAD
PRECIPITATION AND SNOW ABOVE 4500 FEET. THESE SNOW LEVELS ARE
ANTICIPATED TO DROP A LITTLE FURTHER, PERHAPS EVEN TO 3500 FEET AS
THE NBM CAN BE A LITTLE TO HIGH ON THE SNOW LEVELS, ESPECIALLY IN
HIGHER PRECIPITATION RATES.

SNOW ACCUMULATION IS EXPECTED TO PERSIST INTO THURSDAY AS THE
DISTURBANCE BRINGING ALL THIS WEATHER ESSENTIALLY STALLS OUT A FEW
DOZEN MILES WEST OF PORTLAND. WE'LL REMAIN IN A RELATIVELY MOIST
WEST FLOW WITH AT LEAST SOME SYNOPTIC LIFT. THE END RESULT IS
PERSISTENT PRECIPITATION INTO THURSDAY WITH SNOW ABOVE ROUGHLY
5000 FEET.

OVERALL, IMPACTS FROM THIS EVENT APPEAR TO BE MODERATE AT BEST
ACCORDING TO THE WPC WINTER STORM SEVERITY INDEX(WSSI). TAKING A
MORE PROBABILISTIC LOOK AT THIS INDEX SUGGESTS THAT EVEN MODERATE
IMPACTS ARE NOT GUARANTEED AND THE BEST LOCATION FOR THOSE
IMPACTS ARE IN WESTERN SISKIYOU COUNTY, WHICH HAS MANY HIGH REMOTE
LOW IMPACT LOCATIONS.

FURTHERMORE, WE WOULD LIKE TO SEE SOME HIGHER IVT VALUES FOR A
MAJOR IMPACT WINTER STORM HERE IN SOUTHERN OREGON AND NORTHERN
CALIFORNIA. THERE IS NOTHING IN THE ENSEMBLES SUGGESTING IVTS WILL
BREACH 500, WHICH IS WHAT SOME WOULD CONSIDER A STRONG AR. THE
ENSEMBLES ALSO SHOW A PRETTY HIGH SPREAD BETWEEN THE 10TH AND 90TH
PERCENTILES IN SNOW ACCUMULATION OVER 48 HOURS ENDING 12Z FRIDAY.
THE 10TH PERCENTILE SHOWS ~8 INCHES OVER 48 HOURS WHEREAS THE
90TH SHOWS UP TO ~24 INCHES OVER 48 HOURS.

THEREFORE, WE DECIDED TO GO WITH A LONGER DURATION WINTER WEATHER
ADVISORY INSTEAD OF A WINTER STORM WARNING IN THIS CASE. THIS
EVENT IS NOT ALL THAT ABNORMAL COMPARED TO WHAT WE USUALLY SEE
THIS TIME OF YEAR AS WELL.

-SMITH

LONG TERM...FRIDAY INTO NEXT TUESDAY...

A FRONT WILL REACH THE COAST FRIDAY EVENING WITH RAIN LIKELY AT
THE COAST AND COASTAL COUNTIES. FRIDAY NIGHT, THE FRONT WILL MOVE
ONSHORE BRINGING MORE WIDESPREAD PRECIPITATION OVER THE FORECAST
AREA, ALTHOUGH THE COAST AND SISKIYOU COUNTY WILL BE THE AREAS
WITH THE MOST RAIN THROUGH THIS EVENT.

SATURDAY WILL BE COOL AND UNSETTLED WITH PRECIPITATION JUST ABOUT
EVERYWHERE AND THE SOUTHERLY FLOW WILL BRING MORE SNOW TO MOUNT
SHASTA. SNOW LEVELS SATURDAY ARE EXPECTED TO BE BETWEEN 5000 AND
5500 FEET, THEREFORE IMPACTS FROM THE SNOW WILL BE LIMITED TO
DIAMOND LAKE AND CRATER LAKE. EVEN THEN SNOWFALL AMOUNTS ARE NOT
EXPECTED TO BE ANYTHING SIGNIFICANT.

WE COULD CATCH A RELATIVE BREAK IN THE WEATHER SUNDAY AS SATURDAY'S
UPPER TROUGH DEPARTS WITH WEAK RIDGING AS ANOTHER UPPER MOVES
TOWARDS THE BAY AREA. IF THE UPPER LOW TRACKS FARTHER SOUTH, THEN WE
COULD END UP WITH LITTLE TO NO PRECIPITATION IN OREGON AND LIGHT
PRECIPITATION IN NORTHERN CALIFORNIA. THE ENSEMBLES SHOW VARYING
SOLUTIONS WITH THE GFS ENSEMBLE SHOWING THE UPPER FARTHER NORTH AND
THE ECMWF SLIGHTLY SOUTH. HOWEVER, THE CLUSTERS ARE IN PRETTY GOOD
AGREEMENT WITH THE POSITION OF THE UPPER TROUGH, ONE THAT WOULD PUT
US IN A SOUTHWEST FLOW ALOFT WITH ENERGY MOVING INTO THE AREA, THUS,
A CONTINUATION OF COOL AND WET WEATHER AS EARLY AS SUNDAY NIGHT INTO
WEDNESDAY. -HERMANSEN/PETRUCELLI

AVIATION...14/00Z TAFs... VFR conditions will persist through this
evening, except for local MVFR ceilings possible along the coast.
Then a front will spread precipitation into the area tonight into
Wednesday with widespread MVFR and areas of IFR and LIFR conditions
west of the Cascades and a mix of IFR and MVFR conditions from the
Cascades east. Wind shear will be a concern in the morning as this
front moves into the area, especially along the coast and for some
inland areas such as near Klamath Falls (KLMT). -CC

MARINE...UPDATED 200 PM TUESDAY FEBRUARY 12, 2024...HIGH
PRESSURE HAS SETTLED INTO THE AREA, AND AS A RESULT, WINDS AND SEAS
WILL DIMINISH TODAY AND REMAIN RELATIVELY CALM THROUGH TONIGHT. THE
FIRST IN A SERIES OF FRONTS ARRIVES WEDNESDAY, WITH INCREASING SOUTH
WINDS AND SEAS BECOMING VERY STEEP. THE OCCASIONAL GALE FORCE GUST
IS POSSIBLE WEDNESDAY AFTERNOON THROUGH WEDNESDAY NIGHT AS THE FRONT
PASSES, BUT WIDESPREAD GALES ARE NOT EXPECTED. WITH A SURFACE LOW
LINGERING ALONG THE COAST TO OUR NORTH, SOUTH WINDS AND STEEP SEAS
ARE EXPECTED TO CONTINUE UNTIL THE NEXT FRONT ARRIVES FRIDAY INTO
SATURDAY. EXPECT INCREASING SOUTH WINDS AND BUILDING SEAS ONCE
AGAIN, WITH GALES AND VERY STEEP SEAS POSSIBLE, MAINLY ACROSS THE
OUTER WATERS.  AS LONG PERIOD, WEST SWELL BUILDS INTO THE AREA ON
SATURDAY, EXPECT HIGH AND STEEP SEAS, CONTINUING INTO SUNDAY.
-CC

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 AM PST Friday for ORZ029>031.

     Winter Weather Advisory until 4 AM PST Friday above 5000 feet
     for ORZ027-028.

CA...Winter Weather Advisory until 4 PM PST Thursday above 4500 feet
     for CAZ080.

     Winter Weather Advisory until 4 PM PST Thursday above 4500 feet
     for CAZ082-083.

     Winter Weather Advisory until 4 AM PST Friday for CAZ085.

PACIFIC COASTAL WATERS...Small Craft Advisory from 1 AM to 7 AM PST
     Wednesday for PZZ350-356-370-376.

     Hazardous Seas Warning from 7 AM Wednesday to 10 AM PST Thursday
     for PZZ350-356-370-376.

&&