702
FXUS66 KMFR 201036
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
336 AM PDT Mon May 20 2024

.DISCUSSION...The weather pattern this week will be dominated by
progressive northwest flow aloft, which will keep the PacNW in a
regime of lower than normal heights and generally cooler than
normal temperatures. Embedded short wave disturbances could cause
showers from time to time, especially across the northern half of
the CWA, but there will also be long stretches of dry, pleasant
weather.

One upper trough is exiting to the east of the area today, moving
into Montana/Idaho from eastern Oregon. Satellite imagery is
showing patchy clouds lingering behind this trough over the
Cascade foothills, the Rogue-Umpqua Divide and near the Siskiyous.
These should dissipate by late morning yielding mostly sunny
skies and a nice afternoon, though NNW breezes will pick up again.
A few cumulus will develop near the Cascades and over the East
Side this afternoon. Hi-res CAMs are showing some echoes in their
composite reflectivity depictions near the Cascades, but the cloud
moist layer depth there is limited. So, while a brief sprinkle
cannot be ruled out, most areas will stay dry. Expect 3-6 degrees
of warming compared to yesterday for a large part of the area,
except for southern Lake, Modoc and southeastern Siskiyou
counties, where temperatures will likely be similar or down a
degree or two. Tonight, short wave upper ridging will provide dry
weather, but with some low clouds along the Coos coast and also
perhaps into portions of Douglas County.

The next upper trough originating in British Columbia will dive
SSE into the PacNW on Tuesday. Aside from the clouds at the Coos
coast and in the Umpqua, the day will start off sunny. Then, as
this system continues to move in, we expect increasing cloudiness
(especially of the high and mid level variety). Models are
keeping precipitation largely to the north, though shower PoPs do
increase to around 20-30% during the afternoon across northern
Douglas County (north of Roseburg). Expect most areas will see
another 4-8 degrees of warming compared to today (Monday).

This system will swing through the area Tuesday night into
Wednesday with the highest probability of showers (40-80%) from
the Coos coast across Douglas County to the Cascades. Rain amounts
in those areas will be mostly less than 0.10 of an inch, though
the foothills and Cascades north of Diamond Lake could get up to
0.25 of an inch. While showers are unlikely in
Medford/Ashland/Grants Pass, all have about a 20% chance. Areas
south of the OR/CA border largely remain dry, though an isolated
shower cannot be ruled out near the Warner Mountains. Gusty winds
will develop in many areas Wednesday afternoon, but especially
over the East Side, where mid-level flow peaks at 40-45 kt. A
well-mixed BL should lead to some gusts there near 40 mph at the
surface. Expect a reinforcing shot of cooler air on Wednesday with
temperatures down 5-10F compared to Tuesday.

The upper trough axis shifts to the east on Thursday with slight
warming expected to continue into Friday. We`ll do it all over
again Friday night into Saturday as the next upper trough pushes
through. This system looks slightly weaker and farther north than
the previous one, but could bring some showers across the north
along with breezy winds and a cooling trend area wide.

After that, it appears the flow becomes more zonal and this should
allow upper troughing to focus more in the Gulf of Alaska. This
would potentially force an upper ridge somewhere in the West by
early next week allowing things to warm up above normal. There are
still some uncertianties in position/strength of various features,
so confidence out at that range is still on the low side. -Spilde

&&

.AVIATION...20/06Z TAFs...VFR conditions will continue through the
TAF period, with gusty north to northwest breezes in the afternoon
and early evening hours, but guidance shows should not be as strong
as they were earlier this afternoon and early evening. -Petrucelli


&&

.MARINE...Updated 200 AM Monday, May 20, 2024...North gales and
very steep, wind-driven seas south of Cape Blanco will continue
through this evening. Model guidance continues to suggest periods of
off-and-on gales south of Cape Blanco, and a Gale Warning remains in
place for the areas where these gales are expected to surface.
Conditions will be relatively less severe north of Cape Blanco, but
still hazardous to small craft with breezy north winds and steep
seas.

Winds will briefly diminish at night, then increase again during
during the afternoon and evening hours today before winds ease
tonight.

Low pressure approaching from the north will disrupt the thermal
trough on Tuesday with winds diminishing. Moderate winds will likely
continue into Wednesday with northwest swell gradually increasing
Wednesday afternoon. -Petrucelli/CSP


&&

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

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT Tuesday
     for PZZ356-376.

Small Craft Advisory until 11 PM PDT this evening for PZZ350-
     370.

     Gale Warning until 11 PM PDT this evening for PZZ356-376.

&&

$$

MAS/CSP/MAP