959
FXUS66 KMFR 031739
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1039 AM PDT Mon Jun 3 2024

.UPDATE...Updated aviation discussion for 18z TAFs.

&&

SHORT TERM...A very moist cold front associated with an
atmospheric river is moving inland across the area this morning.
This front is located just west of the Southern Oregon Cascades
and rain has spread inland across areas from the Cascades west
and is spreading into portions of the east side. 24 hour Rainfall
totals along the coast have been between 1 and 2 inches, with
heavier amounts of 2 to 4.5 inches in the coast ranges. Inland,
rainfall of 0.3 to 1 inches has been observed overnight in
northern Douglas County, the Southern Oregon Cascades and
southwest Josephine County with lighter rainfall observed
elsewhere. Slick roads from layers of water or from oils brought
to the surface are possible hazards and are worth being aware of.
Urban ponding is also a possibility, especially in areas with poor
drainage or accumulated debris. This front will shift eastward
early this afternoon, with rainfall tapering off over the area.

Gusty west to southwest winds are also occuring with this frontal
passage. Winds have increased across the mountains and higher
terrain (gusts 30 to 45 mph) with strongest winds from the
Cascades east. A Wind Advisory is in place for parts of Lake
County expected to see the strongest winds, including the Winter
Rim, Christmas Valley, and areas east of Adel. This Advisory is in
place through 5 PM this afternoon. Please see NPWMFR for more
details. Breezy to gusty winds will also develop across inland
valleys later this morning into this afternoon, especially for
valleys east of the Cascades.

A weaker front moves inland north of the area. This will bring a
chances (10-30%) for light rainfall along the coast (mainly from
Cape Blanco north), over far northern Douglas County and the
south-central Oregon Cascades. Elsewhere, expect dry weather on
Tuesday. Inland, temperatures will warm on Tuesday, with west
side valleys forecast to reach the upper 70s to mid 80s and areas
east of the Cascades will be in the mid to high 70s.

AVIATION...03/18Z TAFs...Along the coast and just offshore, MVFR
conditions are the predominate condition and this is expected to
persist through at least the 18z TAF cycle. Some improvement to
ceilings could be expected later in the afternoon, but passing
showers will still keep MVFR possible.

Inland west of the Cascades, VFR ceilings will prevail for the rest
of the day, although a stronger shower across Douglas county could
briefly bring MVFR back to the Roseburg terminal. Otherwise, we are
expecting gusty north-northwest winds to be present this afternoon
and continued obscured terrain.

East of the Cascades, MVFR ceilings are expected through the TAF
period, with the terrain partly obscured. Strong winds gusting above
20 kt are likely in the afternoon, especially over the higher
terrain. Peak wind gusts could push towards 30 kts at the Klamath
Falls terminal this afternoon and is most likely to occur around 19z
or 20z. Some clearing towards a mix of VFR/MVFR conditions are
expected in the afternoon.

-Miles

MARINE...Updated 845 AM Monday, June 2, 2024...Moderate west
southwest winds and west swell are expected today with conditions
hazardous to small craft. Seas will likely remain hazardous to small
craft through Tuesday as southerly winds briefly increase again
ahead of another, weaker, cold front. Another west swell around 10
to 12 ft at 14 to 15 seconds will build into the waters late Tuesday
into Wednesday and combine with some stronger northerly winds on
Wednesday and Thursday as weak thermal trough develops. Overall,
conditions hazardous to small craft will likely continue through the
week. -Petrucelli/Spilde

PREV DISCUSSION... /Issued 221 PM PDT Sun Jun 2 2024/

LONG TERM...Wednesday through Sunday...

BY Wednesday morning, upper level ridging will have built in over
the western half of the country, bringing an end to the slight chance
of showers over the northern portions of the area. By Wednesday
evening, however, the ridge will shift slightly to the east, with
the main ridge axis extending north along the Rocky Mountains from
Mexico. Meanwhile, a closed low is expected to develop just west of
Baja California, creating a conduit for warm, moist air to feed
north from the tropics and into portions of southern Oregon and far
northern California. This pattern is then forecast to remain
relatively similar through the rest of the week and into the week,
before breaking down under pressure form the next approaching trough
over the weekend.

All of this will result in a very warm forecast for the area, with
inland high temperatures of around 15 to 20 degrees above normal for
early June. Some of our warmer spots, such as the Rogue Valley and
the valleys of Siskiyou County, may even touch on the triple digits
Friday and/or Saturday. Most coastal areas will be warm as well,
although not quite as warm as the inland areas, with the exception
of a very warm Bookings, where a Chetco effect is expected to
develop along with the thermal trough, and high 80s or low 90s are
quite possible Wednesday and Thursday. One thing could significantly
limit how hot highs will be late in the week: clouds.

With the moist inflow form the south, we will also be concerned with
a daily threat of afternoon and evening thunderstorms, or even
overnight thunderstorms, as some models suggest and the pattern
would support. The main area of concern for convection will be
northern California and areas along and east of the Cascades, where
moisture will be most abundant and lifting mechanisms will be
strongest, but we can not rule out a stray storm or two making it
over to the West Side. Wherever the storms may be, clouds are likely
to spread over much of the area, and these will be the wild card in
terms of how high the highs get throughout the rest of the week.

Late this weekend or early next week, another trough approaches the
area from the west, putting pressure on the ridge and Baja low,
shifting them to the east. However, the exact nature of this trough
is very uncertain, with a wide range of possibilities across the
model suites. There does seem to be two major possibilities. The
first would be a trough that simply replaces the previous one off of
Baja, while the ridge remains in control overhead, and this would
result in continued warmth and keep us under threat of convection.
The other solution has the trough arriving later, but fulling
eroding the ridge, allowing for a brief cooling trend and reducing
the threat of convection, at least temporarily. Hopefully the model
suites can come to a better consensus on the forecast, but this may
take several cycles given the known difficulty models have with
closed low scenarios. -BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 5 PM PDT this afternoon for ORZ031.

CA...None.

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

&&

$$