Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 262206
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
306 PM PDT Sat May 26 2018

.SHORT TERM...Tonight through Tuesday night.
There is high confidence in the forecast of a drying and warming
trend into Tuesday as a ridge builds into the area. The pattern
will change on Tuesday. The GFS and ECMWF have trended a bit
deeper and wetter with a farther southerly track for an upper low
moving south-southeast along the Alaskan coast to near Vancouver
Island on Tuesday.

First, an upper low has tracked across Nevada today while high
pressure centered far offshore builds into our region. Early this
afternoon, the last few bands of light showers wrapping around the
back side of the low have been diminishing over Lake and Modoc
Counties. In the past 24 hours, amounts of a quarter of an inch to
an inch were common in Lake and Modoc Counties, including 2.08
inches measured at Browns Well in Lake County. Lighter amounts
were measured in Klamath and Siskiyou Counties.

With a building ridge aloft, the thermal trough will deepen along
the coast and the surface high offshore will strengthen. This will
produce a Chetco effect, thus the high temperature forecast for
Brookings on Sunday was nudged a few degrees higher...expected to
be in the mid 70s. Highs across the area will be noticeably warmer
than today, several degrees above normal...except normally cool at
the coast north of the Brookings area.

Late night/morning valley cloud cover will trend toward
lesser/shorter duration coverage during the next couple of
mornings with the highest probability of brief cloud coverage at
north facing slopes such as southern Douglas County and southern
Jackson County. Will maintain partly cloudy in those areas for
Monday morning, but, it is possible that all inland areas may stay
clear on Monday morning.

The strength, speed, and track of the upper low are in question.
This leads to uncertainty in the Tuesday forecast. Although the
models are generally trending stronger/wetter, this still looks to
be a weak disturbance with modest amounts of moisture available
aloft. There is a higher probability of virga than showers,
especially west of the Cascades. The probability of convective
showers and thunderstorms is low, a slight chance at best, but
worth mentioning for mainly the higher terrain from the Cascades
eastward late Tuesday into Tuesday evening. We will be watching
closely to see if the models continue to trend stronger.


.LONG TERM...Wednesday through Saturday.

Wednesday, the main long wave trough remains along the West Coast.
Isolated showers can be expected from the Cascades east with
thunderstorm potential mainly around the Warner Mountains, but a
more stable northerly flow will keep the west side dry. Both the GFS
and the ECMWF deepens the trough a bit on Thursday and expands areas
of instability back to SW Oregon. As a result parts of Jackson
County could see isolated to scattered showers with a chance of
thunderstorms from the Cascades east and part of the Marble
Mountains.

The trough is expected to finally lift out of the area Friday with
warming and drying expected into Saturday. However, there is a
potential for a marine push into Coos and Douglas County Saturday
as both the GFS and the ECMWF move a trough into the Pac NW
coast. While most of our forecast area will be dry, the coast and
Roseburg could see low clouds blanketing the valleys Friday night
into Saturday morning. -FB

&&

.AVIATION...26/18Z...VFR conditions are expected at all inland TAF
sites through the TAF period. Stratus/fog will form along the north
coast, including KOTH, tonight with conditions lowering to at best
IFR overnight and perhaps LIFR by morning. -Wright

&&

.MARINE...Updated 210 PM PDT Saturday 26 May 2018...After a very
brief period of sub-advisory conditions today, gusty north winds and
steep seas are expected to redevelop south of Cape Blanco this
evening as the thermal trough redevelops. As the thermal trough
strengthens along the coast and high pressure builds offshore on
Sunday, expect north winds and steep seas to gradually increase with
continuing small craft advisory level winds and seas south of Cape
Blanco.

By Monday, pressure gradients are expected to strengthen further,
spreading at least small craft advisory winds and seas to all areas.
There is still some model disagreement in when the gales start with
some models showing gales as early as Sunday evening and others
holding off until Tuesday. A gale watch remains in effect from
Monday through Wednesday. Conditions may not improve significantly
until late in the week into next weekend. -Wright

&&

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

CA...None.

Pacific Coastal Waters...Gale Watch from Monday morning
     through late Wednesday night for PZZ356-376.
     Small Craft Advisory until 5 AM PDT Thursday for
     PZZ350-356-370-376.

$$

DW/FJB/TRW



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