Area Forecast Discussion
Issued by NWS Medford, OR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
000
FXUS66 KMFR 191628
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
928 AM PDT Tue Sep 19 2017

.DISCUSSION...Cool moist northwest flow will remain over the area
today. The higher elevations like Mount Ashland Ski area, Crater
Lake Rim picked up slushy accumulation mostly on the ground,
except for some road slush around Crater Lake Rim and visitor
center. This will melt off in the next hour or two. We`ll have a
relative break in the action today. Showers will still continue,
but most will be light to occasionally moderate and snow levels
will come up, therefore were not expecting snow to stick to the
roads or ground near and at Crater Lake and Mount Ashland Ski
area.

Precipitation will increase in southwest Oregon and northwest
California this evening as a disturbance arrives from the west.
Showers are expected to be more active later tonight through Wednesday
as the upper trough axis shifts south with a continued moist west
to northwest flow and shortwaves moving through. -Petrucelli


&&

.AVIATION...19/12Z TAF CYCLE...
A mix of VFR, MVFR, and local IFR exist this morning in showers, and
much of the higher terrain is obscured from the Cascades westward.
Vertical mixing this morning will cause ceilings to lower to MVFR at
some locations after sunrise, lifting some this afternoon/evening. A
warm front will push in from the west this evening through tonight.
This is likely to cause ceilings and visibilities to lower to a mix
off MVFR and IFR from the Cascades westward. Low level wind shear
will be possible along portions of the coast this evening. BTL


&&

.MARINE...Updated 645 AM PDT Tuesday, 19 September 2017...
West swell has surged to 10 to 16 feet at the near shore buoys this
morning. Expect swell will peak late this morning through a little
after noon from north to south today. Otherwise, low pressure will
continue to spin and pivot southeastward into the area from the Gulf
of Alaska this week resulting in unsettled conditions through at
least Thursday. A few lightning strikes are possible north of Cape
Blanco this morning as a cold air mass moves overhead. Seas will
then remain steep through Thursday. The strongest winds are likely
to occur this evening through Wednesday morning as low presure
deepens as it moves northeastward across the waters north of Cape
Blanco. South winds are likely to rise quickly and then peak this
evening with a brief 3-6 hour period during which a coastal jet
could form, centered around mid-evening. Winds are expected to
increase to just below gale force, but the combination of short
period wind waves and longer period swell will make for hazardous
conditions for small craft. BTL


&&

.PREV DISCUSSION... /Issued 700 AM PDT Tue Sep 19 2017/

SHORT TERM...A deep and cold trough is over the region and is
bringing moist onshore flow. This pattern will result in rain
showers along the coast and in valleys with a mix of rain and
snow showers over the mountains through Wednesday. Today and
Wednesday, showers will be most numerous from the Cascades
westward. Showers are likely to decrease briefly during the day
today. Then as a couple disturbances rotate around the trough and
into the area, expect showers to increase by this evening and
continue through Wednesday with periods of moderate to locally
heavy precipitation expected over western areas. This rain will
be heaviest in the coastal mountains and over the Southern Oregon
Cascades and will bring a risk for flash flooding and landslides
on some area burn scars, including over the Chetco burn scar and
over portions of the North Umpqua Complex burn scar near Highway
138. Very cold air aloft will move into northern portions of the
CWA on Wednesday and expect convective showers along with
isolated thunderstorms to develop along the coast and inland over
northern portions of the area. On Thursday, expect lingering
showers over the area as the upper trough deepens to the south and
then gradually move inland. As the upper trough pushes to the
east Thursday night into Friday morning, expect showers to taper
off over the area.

An upper level disturbance combined with moist west flow and
cold air aloft will bring numerous light to moderate showers from
the Southern Oregon Cascades west and the Marble Mountains west
this morning with isolated to scattered showers east of these
mountain ranges. Showers are expected to decrease in intensity and
coverage late this morning and early this afternoon. However
another upper disturbance will move into the area from the west
this evening followed by a second stronger disturbance moving
into the area from the northwest tonight and Wednesday. These
disturbances will bring increased showers late this afternoon into
this evening and continuing through Wednesday. Very cold air
aloft associated with the second disturbance will also bring the
potential for thunderstorms on Wednesday.

Overnight shower activity has resulted in a few inches of
accumulating snow, mainly above 6000 feet elevation with a
rain/snow mix down to around 5000 feet elevation. Snow levels will
gradually rise this afternoon to around 6500 feet elevation then
to 7000 to 8000 feet tonight. So expect mainly light snow
accumulations in the Southern Oregon Cascades and Siskiyous this
morning with little or no accumulations later in the day into
tonight. Associated with the next disturbance expect a front into
the region from the northwest. This will bring  another surge of
cool and moist air with snow levels lowering to 5000 feet
elevation late Wednesday morning through Wednesday evening. Around
1 to 5 inches of snow is expected in the higher mountains in the
Southern Oregon Cascades and Siskiyous on Wednesday. Also the cold
air aloft will bring instability across northern portions of the
area and will result in a slight chance for thunderstorms
along the coast and inland over Douglas, northern Klamath and
northern Lake counties on Wednesday.

Periods of moderate to occasionally heavy rain will be a
significant concern for area burn scars, especially over the
Chetco burn scar in Curry and western  Josephine counties and
over the North Umpqua Complex burn scar where it borders highway
138 in eastern Douglas county. Flash Flood watches are out for
these areas late this afternoon through Wednesday afternoon.
Please see the FFAMFR for details.

In addition to precipitation, breezy to gusty winds will impact
the higher terrain through Wednesday. Winds are expected to
increase out of the west and northwest tonight into Wednesday over
the higher terrain. Gusts of around 35 to 50 mph are possible in
the mountains late tonight and Wednesday, especially in the
Southern Oregon Cascades and over the higher mountains east of the
Cascades.

Wednesday night into Thursday, expect showers to decrease in
coverage and intensity. However, the upper trough will deepen to
the south on Thursday and gradually shift to the east. As this
occurs expect a chance for lingering light showers over the area
with shower activity tapering off on Friday.

LONG TERM...Saturday through Tuesday...Models are showing good
agreement that an upper level ridge will build into place this
weekend then strengthen over the area early next week. This will
bring a return to warm and dry conditions across the area. A
couple weak disturbances are expected to move north of the area
late Sunday and Monday but models support dry weather over
Southwest Oregon and Northern California. North winds are likely
to become breezy to gusty along the coast and in the coastal
mountains due to a surface thermal trough strengthening along the
coast.

&&

FIRE WEATHER...Updated 655 PA PDT Tuesday, 19 Sept 2017...
A strong early season trough of low pressure powered by northwest
jet stream winds of 150 mph will continue to bring abnormally cold
daytime high temperatures and bouts of precipitation through at
least Thursday. 24 hour amounts in portions of eastern Douglas
County in Umpqua National Forest have already been over an inch, and
accumulating snow has been observed for locations near and above
6,000 foot elevations. High temperatures today through Thursday will
be around 20 degrees below daily normals. Snow levels around 6,000
feet are expected to briefly rise to near 8,000 feet tonight before
ending around 5,500 feet Wednesday night. It will be breezy to windy
on the upper slopes and ridges today through Wednesday, peaking
Wednesday morning. Precipitation amounts will be significant and
wetting from the Oregon Cascades and Marble Mountains westward, with
the greatest amounts of the week for Curry and western Siskiyou
County from this evening through Wednesday.

Warming and drying is expected beginning Friday. We are expecting
broad northeast to east flow over the weekend, and afternoon
humidity will likely lower into the 20s and 30s across the forecast
area. BTL/NSK

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Flash Flood Watch from 5 PM PDT this afternoon through Wednesday
     afternoon for ORZ022-024.
     Flash Flood Watch from this evening through Wednesday afternoon
     for ORZ025.

CA...None.

Pacific Coastal Waters...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT
     Thursday for PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 5 PM PDT this
     afternoon for PZZ350-356-370-376.

$$



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.