445
FXUS66 KMFR 040405
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
905 PM PDT Mon Jun 3 2024

.DISCUSSION...Radar is showing a few showers moving across
portions of Coos and Douglas Counties this evening with widespread
clouds across much of the rest of southern Oregon and northern
California. This is all part of a second weak disturbance moving
across the area tonight. This front will be relatively short-
lived, but may produce some rainfall in areas previously thought
to remain dry. Have increased rain chances for the next few hours
for much of Douglas and Coos Counties.

Otherwise, for more details about the forecast, please read the
previous discussion below. -Schaaf

&&

.MARINE...Updated 830 PM Monday, June 3, 2024...Moderate south to
southwest winds and west swell are expected through tonight, with
conditions hazardous to small craft from the combination of swell
and wind wave. Another west swell around 10 to 12 ft at 14 to 15
seconds will build into the waters late Tuesday into Wednesday,
which will bring advisory level seas to all areas, as well as
uncommon surf heights for June of 16-19 feet.

Wednesday evening, a thermal trough will return along the coast.
Winds are forecast to gust up to 35 kt between Port Orford and
Brookings, which could lead to very steep and hazardous seas beyond
5 nm from shore. However, confidence is too low for a Hazardous Seas
Watch for Wednesday evening, but confidence is much higher for
Thursday. Thursday, very steep, hazardous seas are expected, with a
low chance for gales south of Brookings, too. By Thursday, the west
swell should diminish to around 6 ft, but when combined with the
wind wave, should be enough to maintain advisory seas north of Cape
Blanco also.

Calmer seas look to be possible Friday into Saturday. -Miles


&&

.PREV DISCUSSION... /Issued 439 PM PDT Mon Jun 3 2024/

UPDATE...Updated aviation discussion for 00z TAFs.

SHORT TERM...Tonight through Wednesday Night...A few light
showers continue on opposite sides of the forecast area: along
the Coos and Douglas county coasts, and over Modoc county. The
showers over Modoc County are the last lingering effects of the
departing front, and should diminish and end over the next several
hours, while the showers at the coast are a result of onshore
flow, and these could continue through tomorrow afternoon.

The onshore flow is resulting from the area lying between the
broad ridge to our south and a trough to the northwest, and the
resulting swift zonal flow that lies in between them. Although the
main belt of this flow lies to our north, the southern periphery
does and will continue to overlap into Coos and Douglas counties.
Not much will change in this regard over the next 24 hours or so,
when the ridge will build north, disrupting the flow, and coming
into complete control of the weather over our area.

The ridge will result in dry and very warm conditions for our
area, with inland highs on Wednesday jumping up to 10 to 15
degrees above normal for this time of year. Temperatures will be
warm at the coast as well, although not as drastic.

Meanwhile, well to our south, a closed low is forecast to take
position just to the west of Baja. Working with the ridge, this will
begin to push some moisture north through California and the Great
Basin, potentially reaching far southeastern Modoc County by
Wednesday afternoon and evening. As a result, an isolated
thunderstorm is possible, but the most likely result will be some
increased cloudiness through Wednesday night. -BPN

LONG TERM...Thursday through Monday, June 6-10, 2024...The
hottest weather of the season thus far is expected Thursday and
Friday across southwest Oregon and northern California as a strong
upper level ridge sets up over the Four Corners.

The axis of the upper ridge will extend far to the north all the way
into the PacNW and along the coast of British Columbia, Canada. Mid-
level temperatures will soar to around 20C Thursday afternoon, then
22-23C on Friday. This supports highs in the 90s for many west side
valleys, including Medford, with 80s/low 90s east of the Cascades.
While not a widespread record-breaking heat wave, a few records
across the area could be challenged. Mount Shasta City could reach
or exceed their records for both Thu/Fri (94F in 2013, 92F in 2015,
respectively). Klamath Falls is mostly likely to challenge their
record on Friday (91F in 1996) as is Alturas (93F in 1996). The peak
of the heat is on Friday with inland temperatures averaging 15-20F
above normal. Here in Medford, the official forecast is for 98F and
the record high is 101F set in 2015. We`ve seen probabilities of
>=100F drop a bit during the last few days and they now stand at
29%. Looking at NWS HeatRisk, this level of heat doesn`t really rise
to the point of issuing a heat advisory and falls squarely on the
orange moderate (2) scale for our west side valley locations. This
is likely due to some relief expected during the overnight hours.
Still, it will be hot, so folks sensitive to the heat should
consider all the potential heat-related impacts and try to stay cool
during the peak afternoon heating period (2-6 pm).

Although our forecast area will be primarily influenced by the upper
ridge supporting dry weather Thu/Fri, there is a weakness in the
upper ridge on its NW periphery. This could provide just enough
moisture, instability and trigger to initiate some convective
development in portions of NorCal and south-central Oregon both
Thu/Fri pm/eve. Flow aloft will be from the south to southwest, so
convective clouds likely initiate over higher terrain and there
is a slight chance (generally <25%) of thunderstorms. This chance
exists mostly from the Cascades/Siskiyou mountains south and east.
The rest of the area will remain dry.

This weekend, a weak upper trough will move across the area allowing
temperatures to trend slightly lower, but still remain well above
normal. With the upper trough moving through, a slight chance of
thunderstorms persists from the Cascades eastward in Oregon, with
the best chance on Sunday. It`s also not out of the question that
something pops up near the Trinity Alps during this time period, but
right now thunder probabilities are fairly low (<15%).

Model ensembles and clusters show a majority of members rebuilding
the ridge over the area on Monday of next week, potentially
persisting through mid next week. This would keep the PacNW in a
pattern of above normal warmth. -Spilde

AVIATION...04/00Z TAFs...Conditions have become VFR across the
region and are expected to remain that way through tonight. Some
terrain obscuration will remain across Douglas County and the
Cascades, as some rain showers will remain across the higher
terrain.

Another weak front will move through the area on Tuesday, bringing
low chances for rain showers and possibly MVFR ceilings to the
coast, but VFR should remain for all other places. Winds will be
gusty at ridge level and east of the Cascades, especially across
northern Lake County and at the coast.

-Miles


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Beach Hazards Statement from Tuesday evening through Wednesday
     evening for ORZ021-022.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 AM PDT Tuesday
     for PZZ350-356-370-376.

&&

$$