Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 232146
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
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

&&

.AVIATION...For the 23/18Z 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.

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.

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

&&

.MARINE...Updated 200 PM PDT Thursday 23 May 2019...Offshore high
pressure and coastal thermal trough pattern will continue into
Friday  evening.  Strong north winds are expected through this
evening from Gold Beach south ,roughly 3 to 5 nm away from shore
today. Strongest winds are expected south of Brookings from 5 to 25
nm from shore this afternoon and evening with occasional gusts to 35
kt. Fresh swell and wind waves will combine to bring steep and
choppy hazardous seas across most the waters with very steep
hazardous seas for areas south of Brookings between 5 to 25 nm from
shore. North winds and seas will decrease slightly tonight but
expect continued small craft advisory level winds south of Gold
Beach through Friday evening and steep hazardous seas across most
all the waters.

A cold front will move into the waters Friday night into Saturday,
bringing a steep fresh swell into the area.  Wave heights will be
around 9 to 10 feet at 10 seconds when this front moves through.
Seas will gradually lower late Saturday. A period of increased north
winds and steep seas is possible on Sunday. Then as weak high
pressure builds into the region expect light seas to develop Monday.
-CC

&&

.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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