Weather Service Report


517 
FXUS66 KMFR 270559
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1100 PM PDT Wed Apr 26 2017

Updated Aviation section...

.UPDATE...
Updates this evening were to increase precipitation probabilities
for this evening and overnight in northwest flow upslope areas 
northwest of and onto the Cascade and Siskiyou crest, as well as 
across portions of Coos and Douglas Counties. I also adjusted 
shower wording to coverage from probability. BTL

&&

.DISCUSSION...
After a wet day, by late April standards, across most of the 
area, we're left with mainly light showers under northwest flow 
along and northwest of the Cascade crest and, likely along and 
northwest of the crest of the Warner Mountains. 

The steady stream of moisture that has been feeding into the 
Pacific Northwest that extends westward to western Pacific 
Tropical Storm Muifa has become less concentrated over us this 
evening in wake of the front that moved through earlier today. A 
high pressure ridge north of Hawaii is building and, consequently,
spreading the subtropical moisture plume from the western Pacific
out more and pushing it more northward with time. 

Orographic showers will continue along and near the Cascades 
tonight into Thursday morning. High pressure will then build over 
the area, allowing high temperatures to climb higher over the 
region over the next week. We will also have larger diurnal 
temperature ranges Friday and Saturday morning which means that 
the mornings will start off cool despite mild afternoon highs. 

The medium range forecast guidance is still showing that Medford 
is likely to reach or exceed 80 degrees on or about Wednesday of 
next week for the first time this season. BTL 

&&

.AVIATION...27/06Z TAF CYCLE...Showers will gradually taper off as 
the evening progresses for most of the area. The exception will 
likely be north of the Umpqua Divide and along the northwest facing 
slopes where upslope flow will continue to wring out showers. 
Lingering low level moisture will likely result in the redevelopment 
of MVFR to lower LIFR CIGS this evening into Thursday morning, 
especially north of the Umpqua Divide and along the coast. Expect 
partial terrain obscurations through the night into Thursday. BTL

&&

.MARINE....Updated 815 PM PDT Wednesday, 26 April 2017...
High pressure will build in from the southwest on Thursday, 
persisting through the weekend. A thermal trough pattern sets up on 
Friday resulting in gusty northerly winds also persisting through 
the weekend. Swell dominated seas will become wind wave dominated 
over the weekend. Small craft conditions could return to the waters 
by Friday afternoon, with the strongest winds and steepest seas 
expected south of Cape Blanco. BTL/BR-y

&&

.PREV DISCUSSION... /Issued 502 PM PDT Wed Apr 26 2017/ 

DISCUSSION...

Short Term...Tonight through Saturday Night...Showers continue
to stream across the area this afternoon, but will gradually begin
to confine themselves to the western slopes of the Cascades and 
other north to south mountain ranges through this evening and 
tonight. Meanwhile, strong west flow in the mid levels is expected
to transfer to the surface across the East Side, producing gusty 
winds there. The latest model solutions are depicting weaker winds
than previous shifts, but already observations form the usual
trouble spots have increased to near advisory levels, and will
probably strengthen a bit more before the end of the day. Have
decided to let the wind advisory remain in place, but an early
cancellation is not out of the question a bit later this
afternoon. 

The upper level trough and associated surface system responsible 
for today's showers has shifted to the east, and as they lose 
influence over us, a broad, high-amplitude ridge will build in 
over the Eastern Pacific. This ridge, while not directly overhead,
will dominate our weather for the next several days. With the 
ridge placed to our west, and a general trough over the central 
United States, we will reside under swift northwest flow aloft. 
The ridge will also deflect most energy and precipitation 
producing systems to our north, leaving most of the area dry and 
warmer. However, the trailing edge of a few fronts passing to our 
north may skirt the northern half of the forecast area, producing 
showers and slightly cooler temperatures at times. The first of 
these will slide by on Thursday afternoon, then another on 
Saturday night. The models have not been consistent on the 
strength of the fronts as they pass to our north, nor have they 
agreed on where the best chances for showers will be. So, have 
kept a slight chance to a chance of showers in some areas and 
expanded coverage to others in an effort to more closely align 
with the latest guidance, but suspect this may change in later 
forecast cycles. 

LONG TERM...Sunday through Wednesday...The area will be under the 
influence of an upper ridge which is expected to be centered just to 
the west Sunday through Tuesday. However, a couple weak disturbances 
are expected to move over the ridge and into the area, bringing a 
chance for light precipitation. The first of these, a weak cold 
front, is expected to move inland on Sunday. Models indicate that 
this front will bring a chance for showers from the Southern Oregon 
Cascades west and into northern Klamath and Lake counties. The best 
chance for light precipitation is expected to be over the Cascades, 
in Douglas County and along the Southern Oregon coast. A period of 
dry weather is then likely Sunday night in to Monday as this front 
shifts east and out of the area. However, models show a shortwave 
trough moving over the ridge and into southern Oregon on Tuesday. 
This will allow another chance for light precipitation and cloudy 
conditions. The chance for precipitation is expected mainly from the 
Southern Oregon Cascades west on Tuesday. 

By Wednesday, models and ensembles indicate the upper ridge will 
build inland over the area and expect dry and warm conditions to 
develop. -CC

&&

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

CA...None.

Pacific Coastal Waters...None.

$$

BTL/BPN/CC

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Western Regional Climate Center, wrcc@dri.edu