Alturas, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

902
FXUS66 KMFR 221147
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
347 AM PST Sun Dec 22 2024

.DISCUSSION...Active weather will continue across SW Oregon and
northern California today and through much of the next week,
taking us through Christmas and toward the New Year. We are smack
dab in the middle of our climatologically wettest part of the
year, and much of this week will confirm that. Several windy, wet
frontal systems will roll through the area between now and next
weekend in a largely progressive weather pattern with an active
Pacific jet stream that will ensure the parade of storms into the
PacNW. Of course, the details matter, so we`ll attempt to hash
them out for you over the course of the week.

One thing that stands out is, for the most part, snow levels will
be high enough to keep the most impactful snowfall near and above
the higher major passes (Siskiyou Summit/Lake of the Woods)
through Christmas Day. That isn`t to say there won`t be any winter
impacts during the period, just that they will be relatively
minor compared to what could occur in a wet pattern like this. Two
fronts, one this afternoon into this evening and another stronger
one later Monday into Tuesday, will bring rain and breezy to
windy conditions followed by post-frontal showers. There should be
about a 6-12 hour break following each of these fronts through
Christmas Day. The first one today looks pretty typical. Expect
some rain to develop at the coast late this morning, then spread
inland across the area this afternoon, eventually to the east side
by late afternoon. Model pressure gradients peak in the -4 to -5
mb range OTH-ACV, so we expect some breezy winds along the coast,
but not enough for warnings. MFR-RDD gradient peaks around -6 mb
and this will result in gusty south winds in the Shasta Valley
and the southern end of the Rogue Valley prior to the onset of
precip. A Wind Advisory is in effect for those areas, where wind
gusts could reach 45 to 50 mph. We are expecting gusty south
winds over the east side too late this afternoon/evening, but
these probably remain just below advisory levels. Rain amounts of
0.10-0.30 of an inch seem like a good bet in most west side
valleys as well as over most of the east side, though less than
0.10 of an inch will occur in portions of Modoc County and the
deserts east of Winter Rim. The most precip will fall along the
coast, particularly in the coast ranges of Curry County and into
portions of western/southern Siskiyou County where amounts of
0.75-1.50 inches will be common. As mentioned before, snow levels
stay largely high enough to keep any snow confined to the highest
mountains above 5500 feet tonight.

The second front will take aim at the coast Monday night. This
front will be supported by a strong upper level disturbance that
will spawn a rapidly deepening surface low that will track
northward just outside of 130W. Pressure falls associated with
the low are significant with the low bombing out just west of
Vancouver Island late Monday night. Models are showing surface
pressures down below 970 mb with some of the strongest solutions
showing it reaching below 960 mb. This one should be windier than
its predecessor, as model wind fields do show a 55-65 kt mid-
level jet crossing the area late Monday afternoon/evening. We`ve
issued a High Wind Watch for the Shasta Valley and it should be
windy enough again for additional wind advisories in the Rogue
Valley and east side. It`s tricky along the coast, since the flow
backs to the south/southeast, which isn`t favorable for high winds
along the coast (and the gradient OTH-ACV is only -6 mb). We`ve
held off any headlines there despite the strength of the low well
offshore. Once again, another slug of high PWATs/IVT will move
inland with the front, so once the flow shifts to SSW, downslope
effects here in the valley should give way to rapidly increasing
rain chances Monday evening. Since this front is moving quickly,
the associated moderate AR should pass through in relatively short
order. The steadiest precip will push east of the Cascades
Tuesday morning and precip becomes more showery behind it. All in
all, rain amounts are more impressive with this one, especially
inland. Amounts are largely in the 0.50-2.00 inch range area wide,
but again, highest in Curry and western/southern Siskiyou
counties, where tallies could reach 3.00 inches in some areas.

Colder air will move in behind this system with snow levels
dropping to around the higher passes by Tuesday morning. As
mentioned, though, much of the precip will be ending by then, so
accumulations in the mountains should be relatively minor and in
the 2-6 inch range during Tuesday. Christmas Eve into Christmas
Day, weak short wave ridging should arrive resulting in a period
of drying, but this could also mean a red-nosed guided sleigh may
be necessary. The break will last most of Christmas Day for much
of the area, but the next moisture-laden front will push toward
the PacNW with precipitation breaking out along the coast by
afternoon, and spreading inland by evening. Wednesday night into
Thursday will be another wet one. This time, snow levels will be
low enough to support significant mountain snowfall with
preliminary amounts of 10-20 inches in the Cascades/Siskiyous and
Mt Shasta region. Most of the accumulation should be up above I-5
(above 4000 feet), but could briefly come down to pass level.

At least a few more wet fronts will come in late in the week and
into next weekend. As such, rivers, creeks and streams will be on
the rise. We`ll be monitoring this for flood potential as we head
toward the New Year. The good news is that extended guidance (Week
2 after Dec 30) is showing a trend toward drier conditions.
-Spilde


&&

.AVIATION...22/12Z TAFS...Mainly VFR conditions prevail this
morning, though there are some areas of low clouds resulting in LIFR
conditions in West Side Valleys. Another strong front will affect
the region today, bringing another round of widespread showers and
gusty southerly winds, including areas of low level wind shear near
the coast  and over the Umpqua Basin with south to southwest winds
of 40 to 50 kts at 2000 feet. This front will push inland late
morning and through the afternoon, bringing areas of MVFR and
widespread terrain obscurations. /BR-y

&&

.MARINE...Updated 200 AM PST Sunday December 22, 2024...Very high,
steep, and chaotic mixed seas will be a persistent feature in the
marine waters through much of the forecast period. Multiple strong
fronts will pass through the area today and through the holiday
week, bringing multiple rounds of gale force south winds, with storm
force gusts a possibility with each front.

The next front in the series arrives early this morning and south
winds increase rapidly to gales with occasional storm force gusts by
late morning and afternoon along with very high, steep, and chaotic
mixed seas. The pattern repeats again Sunday night and Monday as
winds ease while very high background west swell remains. This is
immediately followed by another strong front later Monday. As a
deepening low pressure moves along 130W Monday afternoon, pressure
gradients will be stronger with this front, and as a result winds
will be higher - gales at least and storm force winds are possible.
We`ve extended hazards out through late Monday night, which includes
a Hazardous Seas Warning for all areas from late tonight into Monday
afternoon and then a Gale Watch for all areas starting Monday
afternoon. Currently, seas of 15 to 24 feet are forecast today into
Tuesday.

Conditions briefly "improve" as seas lower below 15 feet late
Tuesday into early Wednesday (Christmas Day), but seas will remain
high and steep with conditions hazardous to small craft likely
during this time. Yet another deep low pressure system and strong
front is expected late Christmas day into Thursday. High end gales
look likely with this front, possibly even storm force. Guidance has
trended lower with the swell train behind the Christmas front, but
seas will continue to be very high, steep and chaotic into next
weekend. /BR-y/Wright

&&

.BEACH HAZARDS...Updated 200 AM PST Sunday, December 22, 2024...
Numerous fronts will bring periods of increasing swells and
dangerous surf conditions this weekend and through next week. A High
Surf Advisory remains in effect through this evening, with large
breaking waves of 21 to 26 feet expected. It will be followed
immediately by a High Surf Warning from late this evening through
Monday evening as the next, stronger front will bring dangerously
large breaking waves of 25 to 33 feet. Conditions are expected to
slowly improve on Tuesday, but another round of dangerous surf
conditions can be expected late Wednesday (Christmas Day) through
Thursday, if not longer.

Extremely large breaking waves will create very hazardous conditions
along beaches and area shorelines. Waves will inundate beaches and
surge into normally dry areas. Infrastructure damage and significant
beach erosion can be expected. Stay away from area beaches during
this period of active weather. /BR-y

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 10 AM this morning to 7 PM PST this evening
     for ORZ026.

     High Surf Advisory until 10 PM PST this evening for ORZ021-022.

     High Surf Warning from 10 PM this evening to 4 AM PST Tuesday
     for ORZ021-022.

CA...Wind Advisory from 10 AM this morning to 7 PM PST this evening
     for CAZ081.

     High Wind Watch from Monday afternoon through late Monday night
     for CAZ081.

PACIFIC COASTAL WATERS...Hazardous Seas Warning until 4 AM PST early
     this morning for PZZ350-356-370-376.

     Gale Warning until 7 PM PST this evening for PZZ350-356-370-376.

     Gale Watch from Monday afternoon through late Monday night for
     PZZ350-356-370-376.

&&

$$

MAS/MNF