-- Discussion containing changed information from previous version are highlighted. --
764
FXUS66 KMFR 212334
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
254 PM PDT Tue May 21 2024

.UPDATE...
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Updated aviation discussion for 00z TAFs.
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&&

.SHORT TERM...An upper low is seen in GOES-West satellite imagery
digging southward through British Columbia this afternoon. This
system is ushering a cold front into the PacNW this afternoon with
radar showing widespread rain occuring across Washington and
northwest through north-central Oregon.

Rain has progressed southward across western Oregon to a line
roughly from Florence to Eugene as of 245 pm. Throughout the
remainder of the afternoon and through tonight the center of the
upper low will advance into south-central Washington and then
into northeast Oregon by Wednesday afternoon. This transition will
allow areas of rain and cooler air to spread into southwest
Oregon but likely leaving most of the valleys south of the Umpqua
Divide dry. Snow levels will dip to between 5000-5500 feet by
about daybreak and by 10 am or so isolated areas from Crater Lake
through Willamette Pass may see a skiff to up to an inch of snow
on the gassy/wooded areas. Winter-related road impacts should be
slim to none.

High temperatures Wednesday will wind up 5-15 degrees cooler than
today`s, coolest across the Oregon Cascades and the east side.
While temperatures will be cooler, the gusty northwest winds will
be the main story that folks will likely talk about. Afternoon
breezes on the order of 15-20 mph should be common across exposed
areas of southwest Oregon and Western Siskiyou County. The
mountains and east side will experience afternoon winds increasing
to 20-30 mph with frequent higher gusts to 40 mph. Things quickly
settle down with fair and warmer weather on tap for Thursday.
Stavish

.LONG TERM...Friday through Monday, Memorial Day weekend. The main
weather feature will be upper low which will move down the British
Columbia coast on Friday. This low will drop into Washington Friday
night into Saturday. There are differences in the strength of this
low but timing is similar. This low will move away from the region
late Saturday.

Much of Friday will be dry with this approaching system along with
near normal temperatures. A cold front will pass through the region
Saturday morning with a chance of showers mainly north of the Umpqua
Divide. For those people traveling across the high passes, there
could be a mix of rain and snow or even snow showers Saturday
morning with snow levels falling to between 5500 and 5000 feet. No
appreciable accumulation is expected on the roads. Conditions dry
out Saturday afternoon as the upper low moves away from the area.
Saturday daytime temperatures will be cooler than normal with highs
in the 40s at Crater Lake, and 50s at Lake of the Woods and Howard
Prairie. Conditions on Saturday could be similar to tomorrow
(Wednesday) as the upper lows are of similar strength and their cold
fronts are forecast to move through in the morning.

Temperatures should rebound to near normal readings on Sunday with
weak high pressure possible. The models begin to differ more on
Monday. Just over half the models show stronger high pressure
nearby, a third of the models show high pressure farther east over
the Idaho/Montana border, and a small percentage of the models show
lower pressure which implies more clouds and cooler temperatures.
Right now, the warmer solutions are depicted in the forecast with
highs in the lower 80s in the western valleys but this could change
with updated forecasts.

To summarize: No heatwaves for the holiday weekend. Dry weather and
near normal temperatures are forecast Friday (morning and
afternoon), Sunday, and Monday. Saturday will likely see the most
inclement weather, especially for those in the mountains with cooler
temperatures and light rain or snow showers early in the day.
Sandler

&&

.AVIATION...
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22/00Z TAFs...Plenty of high clouds streaming into the
region ahead of a weak disturbance, with MVFR ceilings starting to
move into northwest Coos County. While this disturbance won`t bring
too much in the way of precipitation, it will strengthen the marine
push into inland areas, with IFR/LIFR conditions at North Bend and
MVFR ceilings moving into Roseburg this evening and possibly Medford
late tonight. Confidence is fairly high for deteriorating conditions
tonight as the disturbance comes into the region.

As the upper level disturbance moves southwards, 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. -CSP
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&&

.MARINE...Updated 200 PM Tuesday, May 21, 2024...Seas are
anticipated to stay fairly consistent with current conditions
through Wednesday with small fluctuations. Periods of small craft
advisory conditions are expected through Wednesday evening. However,
conditions will subside here and there before returning again. This
is due to a low pressure system moving southward across Oregon.

By Thursday, we are expecting to see a break in hazardous conditions
over the waters through the weekend. -Schaaf/Guerrero

&&

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

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

&&

$$

MTS/RES/BMS