Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 240413
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
913 PM PDT Thu May 23 2019

.UPDATE...RADAR imagery this eveing shows a clump of showers
moving south along the western edge of the Cascades towards
Green Springs and Ashland. Clusters of showers also continue to
track south over Modoc County and far southeast Lake County. Have
adjusted the current forecats to account for these showers, which
should dissipate slowly through the evening.

Also, have significantly increased preciptiation chances for much
of the area on Saturday afternoon and evening, mainly due to
increased confidence provided by the newest model runs. The vast
majority of model suites show a significant area of showers moving
north to south across the area Saturday afternoon, and although
the timing is slightly different across each solution, there is
more than enough reason to say that it will rain nearly everywhere
on Saturday, which may pose an issue for several Memorial Day
Weekend festivities and events. In other wors, be prepared for
rain this weekend if you have any events scheudled outdoors.

For more information on the rest of the forecast, please see the
previous discussion below. -BPN


&&

.AVIATION...For the 24/00Z TAFS...Along the coast and over the
coastal waters...Widespread IFR cigs will persist through tonight
with patchy drizzle and fog, except south of Cape Blanco and 5-10
miles offshore where VFR conditions will prevail. Coastal terrain
will become obscured overnight as clouds move further inland.
Showers will develop Saturday morning with increasing coverage of
IFR into Friday evening.

Inland areas west of the Cascades...VFR conditions will prevail
through this evening, except for areas of late night into Friday
morning IFR/MVFR cigs, mostly over the Umpqua Basin. Mountain
obscuration is also expected tonight, especially over northwest-
facing terrain. Showers with increasing coverage of IFR is likely
north of the Umpqua Divide late Friday morning into Friday evening.

From the Cascades east...Mostly VFR conditions are expected through
Friday morning, but there will be isolated to scattered showers
Friday afternoon, mainly over Lake and Modoc counties. Keene/DW

&&

.MARINE...Updated 830 PM PDT Thursday 23 May 2019...The main update
this evening was to extend the small craft advisory by 3 hours into
Saturday afternoon. There will be 2 periods of peak seas. First,
this evening with very steep seas beyond 5 nm from shore south of
Gold Beach and steep seas elsewhere. Seas will diminish very
slightly early Friday morning, but then build to a higher peak of 8
to 11 feet on Saturday morning.  With persistent high pressure
offshore and low pressure inland, the steep to very steep seas will
be mainly due to the combination of north wind waves and fresh north
to northwest swell.

Seas will  diminish as a stronger low and it`s associated cold front
move south along the coast late Saturday into Sunday then pushes
inland on Monday. Through the long weekend, the strongest winds and
highest seas will occur south of Gold Beach beyond 5 nm from shore,
especially between 5 nm and 30 nm from shore.

Seas are likely to be at a minimum on Tuesday morning then high
pressure offshore and a thermal low along the coast are likely to
strengthen again. DW

&&

.PREV DISCUSSION... /Issued 246 PM PDT Thu May 23 2019/

DISCUSSION...We know there are lots of folks planning outdoor
activities this holiday weekend, so we spent a good bit of effort
coordinating our forecast ideas today for the Friday through
Monday time period.

The rest of today will be relatively quiet with a few showers moving
through Lake and Modoc Counties under the continued influence from
the upper low over the Great Basin. In the Umpqua Basin and towards
the coast, light rain is possible again due to some weak energy
aloft and continued deep marine layer. That rain chance continues
overnight.

Weather will be mostly dry Friday with afternoon temperatures
similar to Thursday. Low pressure will be moving south towards the
area from Washington, but it will be too distant to cause
significant weather impacts to our forecast area with the exception
of the Umpqua Basin and coast where rain chances will continue. On
Saturday conditions will begin to change. The low to the north will
be closer, and the air mass will cool significantly. Temperatures
Saturday will be about 10 degrees cooler than Friday. Clouds will
increase as the low approaches and rain will move into the area from
north to south. After a mostly dry first part of the day for the
Roseburg and the Coos County coast, rain should reach there in the
early afternoon. Latest data suggests rain affects the rest of the
forecast area between 5pm and 10pm and then continues overnight.
Snow levels late Saturday into Sunday morning will dip into the
Crater Lake level (between 6000 and 7000 feet), so those traveling
to the high mountains this weekend should be prepared for some cold
if not wintry conditions.

On Sunday the low will be over Central or Northern California (model
guidance has some spread), and there will be favorable dynamics and
moisture to support more rain over at least the southeastern half of
the forecast area. This would include areas from Medford south and
east towards Lake and Modoc Counties. GFS20 forecast Lifted Index
values of near zero along and east of the Cascades support a slight
chance of thunderstorms there Sunday afternoon. If the low hangs a
little farther north, like the EC operational model shows, then the
thunderstorm chances could extend westward to valleys west of the
Cascades. Keene

Monday through Thursday...Memorial Day could start out dry for
most locations west of the Cascades in the morning. It could
actually be perceived as a nice day in the morning hours. However
from late morning through the afternoon, we`ll see building clouds
with a chance for afternoon showers and a slight chance for
thunderstorms. Not everyone will get showers, but if you have any
outdoor plans, be prepared for changing weather conditions.

East of the Cascades, clouds cover could be more extensive and there
is a better chance for showers. This is because the upper low is
expected to set up southeast of our area and there is concern we
could be caught up in some wraparound moisture. it this turns out to
be the case, then we`ll have a higher chance for showers pretty much
all day with the highest chance for showers in the afternoon and
evening.

The upper should finally move far enough away where we could end up
with drier and milder conditions next Tuesday, but weak troughing
will remain over the area, so could not rule out isolated showers
mainly east of the cascades Tuesday afternoon.

Wednesday and Thursday should be mostly dry and milder. Any isolated
showers should be confined to northern California Wednesday
afternoon and east of the Cascades Thursday afternoon.
-Petrucelli


&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Saturday for
     PZZ350-356-370-376.
     Hazardous Seas Warning until 11 PM PDT this evening for
     PZZ356-376.

$$



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