363
FXUS66 KMFR 221532
AFDMFR

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

.DISCUSSION...The forecast for northern California and southern
Oregon remains on track for the day. Some isolated showers remain
over Douglas County from an area of low pressure passing over
Washington, but that activity should clear out quickly this
morning. Cold air with this system will keep temperatures today
and tonight below seasonal levels, with chances for frost in the
Illinois, Applegate, and parts of the Rogue Valley tonight.
Temperatures will warm tomorrow under a weak upper ridge.

Please see the previous discussion for more details on the short-
and long-term forecasts. -TAD

&&

.AVIATION...22/12Z TAFs...A mixture of IFR and MVFR conditions are
expected through early parts of this TAF cycle. This will be
primarily due to low ceilings, but we are expecting some relief this
afternoon. In fact, inland TAF sites should see plenty of sunshine
(VFR) this afternoon as skies clear out. North Bend may hang on to
MVFR conditions through this evening before finally reaching VFR. It
will also be breezy this afternoon for inland TAF sites. Klamath
Falls will be under an Airport Weather Warning for gusts around 35
knots late this morning through late this afternoon.

-Guerrero

&&

.MARINE...Updated 830 AM Wednesday, May 22, 2024...Steep combined
seas will continue to build into this evening, and will result in
conditions hazardous to small craft for all of our waters.
Conditions improve Thursday into Friday. 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.

&&

PREV DISCUSSION... /Issued 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

&&

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

     Wind Advisory until 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.

&&

$$