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  Forecast Discussion for Southern Oregon and Northern California  

Forecast: Forecast Discussion | 7 Day Forecast

Forecast Discussion for MFR NWS Office

000
FXUS66 KMFR 300406
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
906 PM PDT Sat Apr 29 2017

.DISCUSSION...The forecast was updated to issue a small craft
advisory south of Port Orford for Sunday afternoon and evening.
The 00Z GFS data has begun to arrive. It is consistent with its
depiction of a weak front weakening over the area during Sunday
morning. The probability of rain will be highest for Coos and
Douglas Counties northward late tonight into mid-morning. There is
a slight chance to chance of light showers for the remainder of
southwest Oregon, western and central Siskiyou County, and
northern portions of Klamath and Lake Counties. Cloud cover is
expected to diminish on Sunday afternoon while a ridge builds into
the area from offshore of California.

The ridge will linger into Monday then a similarly weak system
will move over the top of the ridge late Monday through Monday
night. The new GFS has trended weaker with what already was
expected to be a very weak disturbance. A warm front is expected
to lift northeast from offshore into northwest Oregon on Tuesday
followed by stronger ridging with temperatures far above normal
Wednesday into Thursday. This heat wave will most likely get
close but not quite to records, and may end with an episode of
scattered thunderstorms Thursday afternoon and evening. The
probability will be highest for the Siskiyous and Cascades.

&&

.AVIATION...30/00Z TAF CYCLE...VFR will prevail through this evening
with mid and high clouds increasing ahead of a weak cold front. The
front will bring MVFR ceilings to the coastal waters, the immediate
coast and into portions of the Umpqua Basin tonight into Sunday
morning along with a period of light rain. Conditions will improve
during Sunday afternoon. /FB

&&

.MARINE...Updated 800 PM PDT Saturday, 29 April 2017...A weak
cold front will slip through tonight into early Sunday morning.
The main effect with this front will be stronger veering winds to
the north, but wind speeds will stay below advisory level. Another
thermal trough will set up later on Sunday and this will produce
advisory strength northerly winds south of Port Orford with the
strongest winds south of Gold Beach from around 5 to 30 NM from
shore during the early evening. A weak system may disrupt the
thermal trough Monday and Monday night, but it should redevelop
Tuesday into Wednesday. A cold front will move through the coastal
waters on Thursday. Models continue to show the thermal trough
potentially becoming quite strong toward the end of next week. /FB

&&

.PREV DISCUSSION... /Issued 130 PM PDT Sat Apr 29 2017/

DISCUSSION...29/12Z NAM/GFS/EC in.

A relatively quiet afternoon weatherwise over the Medford CWA.
Skies are mostly clear except for a few patches of clouds here and
there. The morning low clouds and fog have cleared out.

A long wave ridge will persist offshore through Tuesday. Flow
aloft will be northwesterly most of the time until then...which is
usually a dry pattern for this area.

The one break in this pattern will occur tonight into Sunday...when
a short wave riding over the ridge will cause it to flatten and
flow aloft will become westerly. The short wave will support a
weak front which will move onshore Saturday night. The bulk of the
associated precipitation will fall along the coast...in the Coast
Range...the Umpqua Basin...and the Cascades.

As far as temperatures go...inland highs will warm to around 5
degrees above normal today over the west side and around normal
east of the Cascades. It will be cooler Sunday over the areas
affected by the front...around 5 degrees below normal in the
Umpqua Basin and around normal over the rest of the Oregon zones.
Northern California will remain up to around 5 degrees above
normal.

Post-frontal showers will end by Sunday night and the low level
flow will turn easterly. Low level flow will turn back onshore
Monday. Another weak short wave moving over the ridge will push
another front onshore Monday. At this time it looks like this
system will be similar to the Saturday night into Sunday system in
terms of precipitation coverage and amounts. This will keep the
north coast and Umpqua Basin high temperatures below normal
Monday...but the south coast and the remainder of the area will
warm to around 5 degrees above normal.

Dry and warmer weather will return as the offshore ridge rebuilds
Monday night into Tuesday. On Tuesday the coast and Umpqua Basin
will warm to around 5 degrees above normal while the rest of the
west side will be around 10 degrees above normal. The east side
will remain around 5 degrees above normal.

The long wave ridge will move onshore Tuesday night. That will
force the thermal trough to swing inland Wednesday...and that day
will be the warmest of the week over the inland west side valleys.

EXTENDED DISCUSSION...Wednesday through Saturday...Dry and very
warm weather continues Wednesday. The thermal trough will shift
inland over the west side valleys Wednesday afternoon. This will
allow temperatures to heat up and could get close to 90 degrees in
Medford. Meanwhile temperatures east of the Cascades will be cooler
with readings in the mid to upper 70s. Also offshore flow should be
sufficient enough for the Chetco Effect meaning Brookings will start
out mild in the morning and could end up close to 80 degrees in the
afternoon. Wednesday will be the warmest day of the forecast period
for many locations, then it will cool down.

The models are coming into better agreement with the evolution of
the upper trough and overall pattern for the rest of the forecast
period. The upper trough will approach the forecast area Thursday
and the models are in pretty good agreement convective precipitation
will break out Thursday afternoon into Thursday night. At this time,
thunderstorms should initiate along the Cascades and Siskiyous, then
migrate northeast later in the afternoon and early evening Thursday
with the 700mb flow from the southwest. Keep in mind it`s still a
ways out, so the details on the exact location could change.
Therefore watch for updates. For now kept in a slight chance mention
and if confidence increases, then they could be upgraded to chance.

An upper trough will replace the ridge Friday through Saturday with
cooler temperatures, lower snow levels and a chance of showers. The
models suggest the upper trough will split with a cutoff low
developing in southern California which could bring dry conditions a
week from Sunday. Stay tuned. -Petrucelli

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory from 5 PM Sunday to 2 AM
     PDT Monday for PZZ356-376.
     Small Craft Advisory for hazardous seas from 2 PM Sunday to 2 AM
     PDT Monday for PZZ356-376.

$$

DW/JRS/FJB

NWS MFR Office Area Forecast Discussion