739
FXUS66 KMFR 221004
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
304 AM PDT Wed May 22 2024

.DISCUSSION...A closed low will trek across Washington and through
NE Oregon today, then eventually into Idaho tonight. A cold front
associated with this low is moving through the area currently and
will push SE of the CWA by late morning. Radar is showing some
light showers associated with the front moving through at this
time, but amounts have been light. North Bend picked up 0.15" and
the big winner so far was Grandad RAWS in the northern Douglas
County foothills, with 0.22". Most other areas where it rained
picked up less than 0.10 of an inch. Showers around early today
will diminish as the air mass dries out behind the front. Strong
mid-level NW flow exists on the southwest periphery of the closed
low and this will result in breezy to windy conditions beginning
this morning, but especially this afternoon. Many areas will have
wind gusts of 25-35 mph this afternoon, but from the Cascades
eastward, a deeply mixed boundary layer in combo with the strong
winds aloft will result in wind gusts of 40-50 mph. We have
issued a wind advisory for ORZ031 (Lake County) from 8am-8pm PDT.
Overall, it will be cooler than yesterday with high temps in the
60s to near 70 over the west side valleys (except low to mid 70s
in the lower Klamath River Valley near Happy Camp) and in the 50s
to low 60s over the east side and in NE California.

NW flow aloft will persist tonight, but a dry air mass overhead
will lead to mainly clear skies and winds decoupling from the
boundary layer. As such, it will get quite cold east of the
Cascades and chilly over the west side. This could lead to frost
formation in some of the typically colder west side valley spots,
including the Illinois and Applegate valleys, as well as some
outlying areas in Jackson County. We have pushed out a frost
advisory, so if you have some sensitive vegetation, you may
consider protecting it from the cold tonight.

After a chilly start, short wave ridging will provide mainly dry,
sunny weather Thursday with a milder afternoon. A few high clouds
and fair weather cumulus may drift by from time to time, but
overall a nice day with highs in the 70s west side valleys and in
the 60s east of the Cascades.

Another upper trough will move southeastward into the PacNW on
Friday. This trough is a bit sharper than model depictions just 24
hours ago. So, in addition to increased shower chances (20-40%)
across areas north and west of the Rogue-Umpqua Divide Friday
pm/eve, there is also a slight chance of showers over portions of
Modoc and Lake counties during the late pm/eve. Weak instability
over there has increased the potential for thunder as well, but at
this time, thunder probs are <15%, so have left out of the
official forecast. Most areas though are dry much of the time with
high temperatures generally within a few degrees of where they end
up on Thursday.

Some models show the next closed low (Fri night into Saturday)
moving through the PacNW in a similar fashion to the one moving
through today (across WA/NE Oregon and into Idaho), while others
are farther north. This will keep PoPs highest (20-40%) north of
the Rogue-Umpqua Divide and in the Cascades north of Crater Lake.
Another breezy to windy day is expected Saturday with a slight
cool down, but it probably won`t be quite as windy as today.

It warms up for the remainder of the Memorial Day weekend with the
flow aloft becoming more zonal or even west-southwesterly. Other
than some low clouds along the coast, it should be mainly sunny
and dry. Models show heights and 850 temps increasing during this
time period with high temperatures in Medford near 80F on Sunday
and then in the low to mid 80s on Monday. The warmth could last
Tuesday and even beyond. Confidence, however, is on the low side.
While some ensemble guidance shows the upper ridge building mid-
late week (EC/Canadian), others (GEFS) show another Gulf of Alaska
trough pushing through PacNW to cool things off. The official
forecast out at that range shows some cooling into mid next week,
following the skillful NBM which gives a slight nod to the GEFS.

-Spilde


&&

.AVIATION...22/06Z TAFs...Increased cloudiness and light
precipitation in the northern parts of the region are a result of a
weak upper level disturbance. Conditions along most of the Oregon
coast, including at North Bend, are IFR to LIFR as the disturbance
has brought a stonger surge of marine moisture inland. Lowered
ceilings will spread inland tonight, with MVFR conditions expected
to move into the Umpqua Valley/Roseburg and possibly briefly into
the Medford area later tonight. Conditions should improve fairly
rapidly towards morning as the weak front moves out of the area and
skies start to clear, though some scattered to broken VFR ceilings
will likely stick around in Douglas and Coos counties, and cumulus
will develop over the higher terrain as the afternoon progresses.

As low pressure moves towards NE Oregon, northwesterly winds will
start to increase aloft early Wednesday morning, and gusty winds
will start to surface late Wednesday morning into the early
afternoon, continuing through the TAF period. At the surface, winds
will be strongest over ridges and east of the Cascades. In
particular, the Klamath Basin and most of Lake County could see
gusts to 30-35 kts. -CSP


&&

.MARINE...Updated 230 AM Wednesday, May 22, 2024...Steep combined
seas will continue to build through the overnight hours, and will
result in conditions hazardous to small craft through tomorrow for
all of our waters. Conditions improve Thursday into Friday, with at
least some break in hazardous conditions over this stretch. Another
low pressure system late Friday into Saturday will lead to periods
of light rain and a brief build in short period swell dominated
seas. Light seas are likely early next week.

-Guerrero


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Frost Advisory from 3 AM to 8 AM PDT Thursday for ORZ024-026.

     Wind Advisory from 8 AM this morning to 8 PM PDT this evening
     for ORZ031.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 PM PDT this
     afternoon for PZZ350-356-370-376.

&&

$$

MAS/JWG/CSP