Mount Shasta, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

714
FXUS66 KMFR 150121
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
521 PM PST Thu Nov 14 2024

.Updated AVIATION Discussion...

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.AVIATION...15/00Z TAFS...Showers will continue through the evening
hours and into the overnight but gradually diminish after midnight.
Overall, expect a mix of VFR/MVFR ceilings/visibilities, lowest in
showers, but also areas of higher terrain obscured. Shower activity
won`t impact the terminals continuously, but mostly on and off
through about midnight. Though there should be a decrease in
coverage overnight into Friday morning as the trough moves inland,
some showers will continue focused near the Cascades, the Cascade
Foothills, the Siskiyous and over by the Warner Mtns.

If there`s enough breaks in the cloud cover later tonight, it could
result in IFR ceilings and visibilities for the interior westside
valleys late tonight into Friday morning. -Petrucelli/BR-y

&&

.PREV DISCUSSION... /Issued 233 PM PST Thu Nov 14 2024/

SHORT TERM...Thursday evening through Sunday morning...A lingering
upper trough will keep scattered showers in the forecast through
Friday evening across northern California and southern Oregon.
Southwest flow aloft will support shower chances west of and along
the Cascades today, while northerly flow on Friday could bring more
activity east of the Cascades. Slight chances for thunder (10-20%)
remain in the forecast for areas west of the Cascades through this
evening given upper level instability, but lightning flashes have
not been sensed so far today so thunderstorms seem unlikely. Snow
levels of are currently between 4000-5000 feet and will lower to
2500-3500 feet on Friday. Snow showers will be possible over the
Cascades, but with only 1 to 2 more inches expected in this area
through Friday afternoon. The upper flow on Friday could bring 2 to
6 inches of snow over the highest peaks in southern Lake County
while other areas will get an inch of snow or less. Overall, both
rain and snow showers look to be unimpactful through Friday night.

An upper ridge will start developing over the area early Saturday
morning, bringing a few dry hours on early Saturday morning. Later
in the morning to early Saturday afternoon, a warm front will bring
precipitation chances back to the area through early Sunday morning.
Warm air behind the front will lift snow levels to 6500 feet or
higher, so snowfall is not a concern for this part of the weekend.
Showers will start at the coast and move eastward through the day,
with the highest precipitation amounts over the Oregon coast and
eastern Douglas County up into the Cascades. These areas are
forecast to get between 0.75 and 1.0 inches of rain. The Umpqua and
Illinois valleys are expected to get about 0.4 to 0.5 inches, and
the Rogue Valley could get 0.2 inches or less. For areas east of the
Cascades, northern Klamath County could get between 0.25 and 0.33
inches, while other areas will get 0.1 inches or less.

This front will not be impactful as far as hazardous conditions.
Moderate to heavy showers will be possible, especially along the
coast and higher terrain. Strong winds and thunderstorms are not
expected. Taking a look at river forecasts shows a reasonable rise
given expected additional precipitation, but area rivers are not
near flood levels. A cold front follows the warm front on Sunday
afternoon, which will be discussed in the long-term forecast. -TAD

EXTENDED DISCUSSION...(Sunday through Thursday)...The cold front
will push into the area Sunday at which point we`ll have moderate to
occasional precipitation along and just ahead of the front, with
snow levels possibly lowering to the higher passes as colder air
aloft gets dragged down in areas of moderate to heavy precipitation.
The front will move from northwest to south late Sunday afternoon
and night, and we`ll see snow levels dropping down between 3000 and
3500 feet early Monday morning. However precipitation will become
more showery which should put a cap on the amount of snow for the
passes. Even so, snow covered roads for Diamond Lake, Lake of the
Woods, and Siskiyou Summit are likely.

Monday will be a transition day with the upper trough exiting out
with showers diminishing during the morning followed by increasing
dry time in the afternoon.

An upper ridge axis will build into the area Monday night and
continue into Tuesday. It will be dry, but with a subsidence
inversion, could lead to fog and low clouds for the interior
westside valleys.

There`s good agreement among the operational models and ensembles
the upper ridge axis will shift just east of the forecast area
Tuesday night as upper troughing over the eastern Pacific digs.
However the upper trough won`t make much progress east between
Tuesday night and Thursday. At the same time a front will slowly
nudge towards our forecast area during this time, but it will be
nearly parallel to the upper flow. Usually when this happens, front
will have a difficult time making much if any progress. looking f
further into the individual ensembles (ECMWF and GFS) and clusters
show the mean upper trough far enough offshore with a ridge presence
over our area. Given the above, the odds are in our favor of dry
conditions to continue during this time. -Petrucelli

MARINE...Updated 200 PM PST Thursday, November 14, 2024...

Showers and an isolated thunderstorm or two will continue through
tonight. Westerly winds this afternoon will continue to shift, and
will eventually be northerly tonight into Friday. Seas will remain
elevated and hazardous to small craft through tonight. Eventually,
seas lower below 10 feet by Saturday morning. That said, this
improvement will be short lived. Another front is expected late
Saturday through Sunday with gusty south winds and steep to very
steep seas. This will be followed by another large swell late Sunday
into Monday. Lastly, while uncertainty is high (standard deviations
are very high) at this time, it is noteworthy to mention the
potential for very strong wind speeds middle of next week (Tues-Wed
night). Deterministic models are showing sustained wind speeds of 40
knots which would put gusts upwards of 60 knots. Currently, we have
not gone this high in the official forecast given the spread in
outcomes, so we will continue to monitor this threat as a Storm
Warning could come to fruition.

-Guerrero

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 10 PM PST Friday
     for PZZ350-356-370-376.

&&

$$