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000
FXUS66 KMFR 240948
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
248 AM PDT Wed Apr 24 2024

.DISCUSSION...There will be a shift in the warm and dry pattern
that we have been having. This shift back to cool, frequently
wet, more typically spring-like weather will be more readily
apparent beginning on Thursday. But, the cooling trend will begin
today, with highs around 5 to 10 degrees lower than today.

The most notable aspects of the short term are areas of coastal
low clouds, and a chance of afternoon and evening showers and
thunderstorms for northern California, northward into the
Siskiyou Mountains of far southern Jackson County, and
northeastward into south central Oregon..Klamath and Lake
counties. This includes Fort Jones, Yreka, Weed, Mt. Shasta,
Tennant, Lava Beds, Alturas, and Lakeview.

Our area of thunderstorm activity will shift very slightly
southeastward today with a late day slight chance to chance of
thunderstorms again for southern, central, and eastern Siskiyou
County eastward and northeastward across Modoc and southern
portions of Klamath and Lake counties. This includes Tennant,
Alturas, and Lakeview.

By the end of Wednesday night, a wet cold front is expected to be
just west of the coastal waters, with rain developing at the coast
Thursday morning.

PREVIOUS LONG TERM...Thursday morning through Tuesday night.

The warm and dry weather comes to an end on Thursday as the next
wave and frontal system hits the region. We`re expecting rain
along the coast and west of the Cascades. The NBM is predicting a
100% chance of precipitation late Thursday morning through late
Thursday evening with chances of precipitation lowering to around
60% east of the Cascades. Snow levels will be around 5000 to 7000
feet depending where one is located with the higher snow levels
east of the Cascades. Like always, snow over the higher Cascades
is expected and Crater Lake will see accumulating snow fall
Thursday into Friday morning.

The atmosphere shows some instability by later Friday, so
thunderstorms were inserted into the forecast around that time. The
probability of thunder is around 15% and covers large swaths of the
forecast area. Given that an upper level wave is starting to depart
the region, thunderstorms that do form will likely be weak and a few
cloud to ground flashes seems the most likely scenario.

Another shortwave and warm front will push into the forecast area
around Saturday.  The chance of precipitation is only about 50% west
of the Cascades as the ensembles might have some issues with timing
or perhaps moisture content. Those probabilities drop off in
northern California and east of the Cascades down to 20 percent. So
some of the forecast area as a modest chance of rain, other areas
will likely stay dry.

Finally, the ECMWF and GFS are both showing a stronger low in the
Gulf of the Alaska, although the ensemble anomalies are not as
excited about how unusual it is for this time of year.  In general,
it looks like zonal flow is setting up under a strong west to east
mid level jet,  which will likely keep Spring like temperatures in
check with a cooler moist flow for the weekend into next week. There
is a small set of ensemble members(15%), which show a stronger ridge
building in southern Oregon between Sunday evening and Monday
evening, which would lead to warmer temperatures and drier weather
than what is currently in the forecast.

-Smith

&&

.AVIATION...24/00Z TAFs...VFR ceilings and visibilities are most
likely across the forecast area outside of lower stratus (with MVFR
and IFR ceilings) along the coast from Cape Blanco northward. Areas
of MVFR/IFR may also develop late tonight and early Wednesday
morning in the southern Umpqua, south of Roseburg.  Elsewhere expect
mainly VFR. Wednesday afternoon and evening, isolated to scattered
showers and thunderstorms are expected again over southern/eastern
Siskiyou, Modoc, southeast Klamath and southern Lake counties. L
Gusty winds are possible near thunderstorms that develop Wednesday
afternoon and evening. -CC

&&

.MARINE...Updated 225 AM Wednesday, April 24, 2024...Seas will
remain low today and into Thursday morning, with light northerly
winds continuing in a period of calm weather.

A weak front will approach the area late Thursday morning, bringing
showers and southerly winds with gusts up to 30 kts over waters
north of Gold Beach. Wind-built steep seas are expected in these
waters, and a Small Craft Advisory will be in place on Thursday from
11 AM through 11 PM to highlight these conditions.

Winds will calm on Friday, but westerly swell behind Thursday`s
front could maintain steep seas. While there`s moderate confidence
in these general conditions, the timing and areas affected will
benefit from additional information. Current guidance still suggests
very low chances (10-20%) of seas exceeding 9 feet in this period,
so more hazardous conditions are not expected.

Active weather looks to continue through the weekend and into next
week, with a weak front approaching the Oregon coast on Saturday
afternoon and a low pressure system settling near the Canadian coast
late Monday bringing westerly winds and swell. Current outcomes
suggest the Saturday system will be unimpactful but more chaotic
conditions are possible on Monday evening. -TAD

&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory from 11 AM to 11 PM PDT
     Thursday for PZZ350-356-370-376.

&&

$$

SBN/SBN/SBN