352
FXUS66 KMFR 021812
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1112 AM PDT Sun Jun 2 2024

...Updated AVIATION discussion...

.DISCUSSION...No changes are needed to the forecast this morning.
Cloud cover ahead of an approaching front will persist through the
day. Rainfall chances along the coast and over the Cascades will
increase through the day, with more widespread showers starting
this evening and into Monday morning.

Please see the previous discussion for more detail about the
short- and long-term forecasts. -TAD

&&

.AVIATION...02/18Z TAFs...MVFR and IFR levels are present along the
Oregon coast as a warm front approaches from the Pacific, with VFR
levels presently over inland areas. Radar is showing showers across
areas west of the Cascades, with rainfall frequently affecting
visibilities at North Bend. Very little activity is getting east of
the Cascades so far.

Showers will continue across areas west of the Cascades today.  A
cold front will arrive tonight and bring moderate to heavy rainfall
over the Oregon coast and the Cascades through early Monday morning.
Light rainfall is expected across all other areas. Heavy or steady
showers can locally lower ceilings and visibility as well as obscure
terrain, so extra caution is encouraged. Gusty winds and low level
wind shear will be possible over the Cascades and higher terrain to
the east, especially early Monday morning. Model guidance does not
show shear over any airports, but wide areas of shear from the
southwest and at speeds of up to 50 kts are present over Lake and
Klamath counties until 14Z. -TAD


&&

.MARINE...Updated 800 AM Sunday, June 1, 2024...A strong front
for this time of the year will move into the waters this morning
bringing increasing south winds with Small Craft Conditions likely
for most of the waters. The exception will be south of Brookings.
Also areas beyond 5 nm from shore west of Bandon, closer to shore
north of Lakeside, and out to 60 nm from shore west of Florence
could experience low end Hazardous Seas Warning conditions late
this morning into early this evening. Therefore a Hazardous Seas
Warning has been issued for the areas mentioned above. The front
will also bring a period of moderate to heavy rainfall this
afternoon into Monday morning.

The front will move inland late this afternoon and winds will
diminish briefly, but will increase again later this evening as
another front will approach the waters tonight bringing increasing
southwest winds. At the same time west swell will increase some and
the combination of both will keep the Small Craft conditions going
and will eventually impact all of the waters by early Monday
morning.

Another front will bring increasing south winds Tuesday, The general
consensus is winds are not expected to be as strong as with the
first two fronts. However, hazardous conditions are likely to
continue through the week, though due to varying weather patterns. A
heavier, longer period swell (9 to 12 ft at 12 to 14 seconds) will
move into the waters Tuesday night into Wednesday. Meanwhile, a
strong thermal trough will develop along the south Oregon coast,
bringing the return of strong north winds and steep to very steep
wind driven seas Wednesday and lasting through Friday afternoon.
-Petrucelli


&&

.PREV DISCUSSION... /Issued 608 AM PDT Sun Jun 2 2024/

SHORT TERM...A warm front is approaching the coast this morning.
This front will move inland during the day today, followed by a
strong and very, moist cold front tonight and Monday morning.
This frontal system is unusually moist for this time of year and
is associated with a strong plume of moisture (atmospheric river)
with precipitable water values of 1.5" or higher and moisture
transport values (IVT) of 600-1000 kg/ms.

As the warm front moves inland today, overrunning will produce
light precipitation along and west of the Cascades. The main belt
of moisture arrives tonight, ahead of the cold front which will
pass through the area early Monday. Snow levels will be high (7500
to 11000 feet) ahead of the front so expect rainfall even in the
higher mountains. Precipitation amounts will be unusually high
for early June, especially for coastal areas, across
northern/central Douglas County and into the southern Oregon
Cascades. Moderate to heavy rainfall (1 to 2.5 inches but locally
up to 3 inches in coastal mountains) is expected along the coast,
coast ranges, northern Douglas County and into the southern
Oregon Cascades (mainly north of Highway 140), with the rest of
the area seeing mostly light to moderate rain. However, its worth
noting that some locally heavier amounts up to an inch are
possible in southwest Josephine and far western Siskiyou counties.
Along the coast, where rainfall will be heavy at times, models
support 1 hr rainfall rates reaching 0.25 to 0.5 inches tonight.
Areas that see the heaviest rain, mainly along the coast, may
experience localized ponding of water on roadways, especially in
urban areas or areas of poor drainage.

Behind the front, there will be some lingering, light post-
frontal showers Monday afternoon across the area, with
precipitation tapering off by Monday evening.

Additionally, with this front, gusty west winds are expected
ahead of and with the frontal passage. The strongest winds are
expected along the immediate coast, over the ridgelines, and east
of the Cascades. Our typical windy valley locations (Shasta and
Rogue) will not be impacted as much due to the mostly westerly
flow, but east of the Cascades, 700mb winds of around 45-55 kt
and support wind advisory conditions (with guidance showing gusts
around 45 kt) along higher terrain and in the Summer Lake area.
These winds are expected to peak Sunday night through early Monday
afternoon.

A weaker front moving inland north of the area Monday night into
Tuesday morning, may bring some light rain to northern Coos and
portions of Douglas counties. Then, confidence is moderate to high
for a significant warm up late in the week as a high pressure
ridge builds into the area. A weak disturbance may move over the
ridge which combined with mid level moisture moving up from the
south- southwest, may bring a chance for thunderstorms, as early
as Thursday, to central and eastern portions of the area.
Confidence is low on the details of the thunderstorm forecast and
we will continue to monitor this portion of the forecast. For
additional details on the warm up and thunderstorm/shower chances,
please see the previous discussion below.

LONG TERM...Tuesday through Saturday night.

After the wet start to the work week, temperatures on Tuesday are
anticipated to trend 10 degrees warmer with highs slightly warmer
than normal for this time of year.

This trend of warming temperatures will continue into Wednesday as
high pressure begins to build over the four corners and some light
east to northeast flow develops over southern Oregon. Models suggest
a trough over the Pacific will be lingering and that could influence
our weather by Thursday.

The latest deterministic models hint at convection and thunderstorms
developing over southern Oregon and northern California as a weak
shortwave begins to ride over the ridge on Thursday. The GFS denotes
some modest instability around 1000J/kg of convective available
potential energy with some modest shear at 35 knots out of the
south. The ECMWF also initiates some convection over northern
California Thursday afternoon and evening. The NBM PoP forecast is
most confident is shower or storm active east of the Cascades,
although we can`t rule out storms west of the Cascades as well. In
any case, Thursday will be a day to watch with regards to
thunderstorms in future model runs.

The summer like temperatures continue towards the end of the week
with highs in the upper 90`s and some warmer lower temperatures as
well. The NWS heat risk algorithm is picking up on some elevated
heat risk due to warm daytime temperatures on Friday and Saturday,
although it appears the overnight lows cool off enough to dismiss
the need for any heat products at this time. Regarding the chance
for 100 degrees in a few of the valley locations, it appears the
chances have lowered a bit compared to a few days ago. The upper
level ridge doesn`t appear as built in and temperatures could trend
lower if the ridge ends up farther to the east. The inverse could
also happen as temperatures could move higher with a more westward
position. In any case, the chance of 100 degrees in Medford and
Montague is roughly 35% on Friday.

Overall, thunderstorms on Thursday and the moderate heat risk on
Friday into Saturday are the big weather features in the extended
forecast.  Weather risk to the population at large is low, although
heat will bring an increased threat to those that are sensitive to
heat in valleys west of the Cascades.

-Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 11 PM this evening to 5 PM PDT Monday for
     ORZ031.

CA...None.

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

     Hazardous Seas Warning until 8 PM PDT this evening for PZZ350-
     370.

&&

$$