751
FXUS66 KMFR 070530
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1030 PM PDT Thu Jun 6 2024

.UPDATE...Updated aviation section for 06z TAFs.

&&

SHORT TERM...An upper level ridge is in place and hot
temperatures were observed across inland areas today with highs in
the upper 80s to upper 90s. A record high temperature of 95 was
set for Mount Shasta City. Along the coast, temperatures were
generally mild (except for locally warmer conditions across
southern coastal Curry County) with some breezy/gusty afternoon
winds. Meanwhile, mid level moisture and instability associated
with a weak upper level disturbance brought some isolated
thunderstorms to northern California and portions of Lake County.
Two strong thunderstorms were observed earlier this evening in
south- central and southeast Siskiyou County, where radar
indicated a potential for severe hail. Moderate CAPE, instability
and an upper level jet aloft provided extra instability and lift
for these storms. With the onset of sunset, storms have weakened
but isolated thunderstorms persist across central/eastern Modoc
and southern/eastern Lake counties. Models continue to support
these storms diminishing late this evening.

This pattern will remain in place on Friday, with hot temperatures
impacting all inland areas and isolated thunderstorms expected
again across portions of northern California and from the Southern
Oregon Cascades east as a weak shortwaves moves across the area.
High temperatures across inland valleys on Friday are expected to
be 2 to 6 degrees hotter than today and record to near-record
highs are possible for Klamath Falls, Alturas and Mount Shasta
City. Chances for thunderstorms (15-20%) will be highest from the
Cascades east and into western Siskiyou Counties on Friday. Storm
activity is expected to be isolated Friday afternoon and evening.
Also, models are showing lesser chances for severe thunderstorms
compared to today and no severe activity is expected on Friday.
Moderate CAPE and instability may be present across portion of the
east side, especially in Lake county, which may allow for a few
locally stronger storms.

On Saturday, the upper level ridge will shift east slightly as an
upper trough approaches from the west. This will result in daytime
temperatures trending slightly less hot. There will be continued
slight chances for thunderstorms (across northern California and
form the Cascades east) as moisture moves into the area from the
southwest and combines with daytime instability.

LONG TERM...Sunday morning through Friday.

We`ll start off the extended forecast with an upper level wave
pushing into the forecast area Sunday morning. Models are
anticipating plenty of cloud cover in the morning with modest upper
level divergence ahead of the wave. With modest synoptic lift,
thunderstorms still remain in the forecast on Sunday east of the
Cascades. The NBM probability of thunder is showing values around 30
to 35 percent within any point east of the Cascades and in Modoc
County for Sunday afternoon and evening. Deterministic models show
about 1000 j/kg of convective available potential energy with 20 to
30 knots of shear out of the south. These values are pretty good for
generic thunderstorms, although the widespread aforementioned cloud
cover could seriously impact available potential energy for any
storms. In any case, some thunderstorm activity seems likely
around our CWA on Sunday.

The trough axis eventually swings by with deeper moist west flow
pushing into the forecast area. This will result in temperatures
trending lower, although still above the seasonal normals(1991-2020)
for this time of year. This warmer than normal trend can be seen in
the ensemble forecasts, and we have pretty high confidence in warmer
than normal for much of next week. The 700 mb temperature around
9000 feet is in the 90th to 97.5th percentile for much of next week
according to the GEFS.

Other than that, nothing stands out in the extended forecast for
much of next week as the PoP forecast is between 0 and 5%. The
exception is around Day 7 as half of the ensemble members anticipate
the next trough to hit the Pacific Northwest. However, the other
half are expecting a ridge to still stay in control. One can note
that the PoP forecast does increase slightly Thursday night into
Friday with the more significant increase north of Douglas County.

-Smith

AVIATION...07/06Z TAFs...VFR conditions will prevail across
northern California and southern Oregon tonight. The exception is at
North Bend and elsewhere along the coast, where stratus caused
IFR/LIFR ceilings and vis last night, and is expected to do the same
again tonight based on a persistence forecast. This runs against
some model output and is causing a low confidence forecast for the
lower conditions along the coast.

Gusty north winds expected along the Oregon coast and over Roseburg
Friday afternoon. Thunderstorms are also expected again on Friday,
in much the same areas of south and Southeast Siskiyou County, and
east across Modoc and Lake Counties. Northeastern Klamath County may
also observe an isolated thunderstorm tomorrow.
-Miles

MARINE...Updated 830 PM Thursday, June 6, 2024...A thermal trough
will continue to produce gusty north winds and steep wind-driven
seas across the area coastal waters, with very steep and hazardous
seas south of Cape Blanco. Winds will decrease overnight and into
Friday morning. Even as winds decrease, very steep seas will
continue south of Cape Blanco into late Friday morning. Steep seas
will remain in all waters into late Friday night.

Please see MWWMFR to see more detailed areas of expected hazards as
well as timing for current Small Craft Advisories and Hazardous Seas
Warnings.

Seas will be calm through Saturday, although westerly swell will
start to increase during the day and a thermal trough will return
late Saturday night. Steep seas are expected to return to all waters
Sunday and continue into early next week as the thermal trough
strengthens. -BPN/Miles

PREV DISCUSSION... /Issued 300 PM PDT Thu Jun 6 2024/

DISCUSSION...A weak upper trough is moving slowly into SW
Oregon which is the triggering mechanism for mainly slight
(10-20%) chances over the east side this afternoon and tonight.
The exception is along the Warners and in far southeast Lake
county where there is a narrow region of 30-50% chances aligned
closest to the area of convection currently ongoing and developing
from parts of Washoe and Harney Counties. Storms are not expected
to be of great impact.

After tonight we move into Friday with concerns of very warm high
temperatures and another round of slight chance (15-20%)
thunderstorms over the east. The NBM has been fairly consistent
with advertising temperatures 3 to 7 degrees warmer than today
west of the Cascades, well into the 90s for the western valleys
and near 90 over the east. These are departing from normals by +15
to +20 degrees, so a fairly unusual warm spring day. Near-record
or record highs will be monitored at Klamath Falls (91/1996),
Alturas (93/1996) and Mount Shasta City (92/2015). Current records
are shown. The heat risk with this period only reaches 2 in the
warmest locales as overnight low temperatures will be fairly cool
and relieving generally in the 50s. Friday`s storms should be
slightly more numerous and extending further west into the
Cascades versus today with a more significant trough approaching.

The deep upper low digs into the PacNW by Saturday cooling
temperatures by 3-8 degrees. Stavish

&&

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

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

Hazardous Seas Warning until 11 AM PDT Friday for PZZ356-376.

&&

$$