Air Resources Laboratory banner image
Air Resources Laboratory web site National Oceanic and Atmospheric Administration (NOAA)

or discuss

Office: MFR

FXUS66 KMFR 250642

Area Forecast Discussion
National Weather Service Medford OR
1042 PM PST Sat Feb 24 2018

.UPDATE...We are in the process of making some updates this
evening. First, pops will be lowered and dependent grids will be
adjusted. Things have calmed down over southern Oregon and NorCal
this evening. Radar is devoid of meaningful echoes, and other than
the isolated shower along the coast and patchy light snow in the
Douglas Cascades, there hasn't been any precipitation at any of
the obs sites for several hours. Based satellite and high
resolution model guidance, this will continue to be the case
through at least dawn tomorrow.

The other change will be to the timing of the winter storm
headlines. Latest guidance shows snow developing later than
previously thought in the Cascades from Highway 140 south and the
Siskiyous. Snow will also be delayed across the mountains of the
east side. As a result, the start of the winter storm warnings in
these areas will be pushed back until 00Z Monday (4 PM LST
tomorrow). Expect these updates to be sent by 10 PM. -Wright

PREV DISCUSSION... /Issued 425 PM PST Sat Feb 24 2018/

SHORT TERM...Through Tuesday...
Winter weather and wind headlines for this afternoon and evening
have been expired since the current weather system and resultant
impacts have ended. Snow levels rose to between 2500 and 3500 feet
this afternoon and, with the higher sun angle warming the surface,
roads across most areas have become mostly wet. Those in
mountains and the east side that are still snow covered have seen
lesser accumulations and main thoroughfares have been treated by
road crews, so impacts should be minimal. Altogether, while we
did see the Oregon Cascades get some strong accumulations today,
the storm system appears to have pushed a bit stronger to the
south and east, into the Siskiyous, than model guidance had
previously indicated.

For Sunday through Monday we've issued the next round of headlines
as well as a weather story graphic with expected snow
accumulations. Model guidance has increased precipitation amounts
with this weather system, especially along and near the coast,
coastal mountains, into the Siskiyous, and across northern
California and the east side.

Precipitation will push into the area Sunday morning across Coos
and Douglas counties. Models have slowed the southeastward
progression of the frontal system on Sunday, with the bulk of the
snow impacts reaching areas south of the Umpqua Divide and Lake of
the Woods now expected to arrive Sunday evening and night. We'll
need to continue to keep an eye out for how fast snow levels fall
and how much resultant snow accumulates in the Sexton and Canyon
Mountain Pass areas as well as in the West Side valleys Sunday
night into Monday morning. For now, we've issued advisories for
areas above 2kft.

The weather will settle down briefly for Monday afternoon into
Tuesday before becoming active again. BTL

LONG TERM...Wednesday through Saturday...
Models continue to show good agreement with active pattern over
the Pacific Northwest. An upper trough and low pressure system is
forecast to shift down the Pacific Northwest coast Wednesday and
Wednesday night. With the low moving into the Pacific Northwest,
there is the potential for a strong cold front to move inland and
impact the area late Wednesday into Wednesday night. This front
shifts east of the area on Thursday with an upper trough moving
over the area and bringing a showery pattern. Then a cold and
showery pattern continues Friday into Saturday.

On Wednesday, there is general agreement that a relatively strong
and moist frontal system will approach the Pacific Northwest coast
then move inland Wednesday night into Thursday morning. Models
indicate that this front may bring abundant moisture into the area
late Wednesday through early Thursday. Areas of moderate to heavy
rain and snow are possible, especially from the Cascades west. Snow
levels are expected around 3000 to 4000 feet with this system. So,
impacts from accumulating snow are possible on higher mountain
passes and as well as for the Mount Shasta area. East of the
Cascades, expect light to moderate precipitation, mostly falling as
snow. Also models indicate that a strong mid level 700 mb jet of
around 45 to 55 kt may move into the area ahead of the front. This
jet aloft combined with an increasing surface pressure gradient will
bring the potential for areas of strong gusty to develop, mainly in
the Shasta Valley and from the Cascades east.  However, due to
variability in the details on the strength and track of this low
pressure system, there is lower confidence on the exact details and
impacts with this storm. Will need to monitor this system
with future model runs.

Thursday into Friday, an upper trough is forecast to gradually move
inland over the region and bring widespread showers. Additional
disturbances moving around the trough and inland may bring enhanced
showers during this period. Snow levels will lower late Thursday
into Friday and are expected to lower from 2500 to 3500 feet down to
1000 to 2000 feet on Friday.

Friday night into Saturday, the trough will gradually shift eastward
and a shortwave ridge will build into the area resulting in
decreasing showers. There is significant variability on the  timing
of this ridge building into the area and decreasing shower activity.
May continue to see showers across the area on Saturday with
diminishing activity Saturday evening/night. However, given the
upper ridge is weak and models show another low pressure system
developing off the coast, expect only a brief break in the active
pattern next weekend. -CC


.AVIATION...25/06Z TAF CYCLE...A front will approach the area then
shift inland Sunday. As precipitation spreads into the coast late
tonight, expect MVFR cigs/vis to develop along coastal areas between
07-10z. Rain and snow will spread inland with MVFR cigs/vis and
mountain obscuration becoming widespread from the coast into the
Umpqua Valley. Expect gusty south to southwest winds starting late
tonight... and increasing Sunday afternoon with a stronger west
component as the cold front shifts inland. Precipitation rates will
increase and snow levels will drop substantially along and behind
the front...expect snow and rapidly changing conditions east of the
Cascades late Sunday afternoon or early evening. -CC/MSC


.MARINE...Updated 1036 PM PST Saturday 24 Feb 2018...A cold front
will drop from the north tonight, bringing stronger west winds and
wind waves of 6 to 8 feet. In addition, heavy northwest swell will
continue through Sunday...thus expect steep seas to continue.
Winds shift to northerly behind the front Sunday night into Monday
and wind waves diminish... however an even steeper northwest swell
will approach, causing very steep combined seas beginning late
Sunday night. Seas will gradually subside Tuesday into Wednesday.
Then, another round of steep heavy swell will come in late Wednesday
into Thursday, with possible gales as well. -MSC


OR...Winter Weather Advisory from 4 PM Sunday to 4 AM PST Monday for
     Winter Storm Warning from 4 PM Sunday to 4 AM PST Monday for
     Winter Weather Advisory from 4 PM Sunday to 4 AM PST Monday
     above 2000 feet in the for ORZ023-024-026.
     Winter Storm Warning from 4 AM Sunday to 4 AM PST Monday above
     2500 feet in the for ORZ025.
     Winter Storm Warning from 4 PM Sunday to 4 AM PST Monday for
     Winter Weather Advisory from 4 AM Sunday to 4 AM PST Monday
     below 2500 feet in the for ORZ025.
     Winter Storm Warning from 10 AM Sunday to 4 AM PST Monday for
     Winter Storm Warning from 4 PM Sunday to 4 AM PST Monday for

CA...Winter Weather Advisory from 4 PM Sunday to 4 AM PST Monday for
     Winter Storm Warning from 4 PM Sunday to 4 AM PST Monday above
     2000 feet in the for CAZ080.

Pacific Coastal Waters...Small Craft Advisory until 4 AM PST Tuesday for



Office: PQR FXUS66 KPQR 250539 AFDPQR Area Forecast Discussion National Weather Service 939 PM PST Sat Feb 24 2018 Updated Aviation section. .SYNOPSIS...Showers decreasing this evening. A cold front will produce rain and higher elevation snow late tonight through Sunday evening. The Cascades can expect a lot of snow during this period and expect winter traveling conditions if planning on travelling over the Cascade passes. Snow levels lower to near the valley floor Sunday night and Monday, as showers decrease. Dry weather is expected Monday night with additional rain and low elevation snow possible Tuesday. An active weather pattern continues through next weekend. && .SHORT TERM...Tonight through Tuesday. Showers will decrease this evening, before a precipitation ahead of an approaching cold front produces rain and higher elevation snow across SW Washington and NW Oregon late tonight through Sunday night. Snow levels are expected to be around 1500 feet this evening then rising to 2000-2500 feet for the coastal mountains tonight, and for the Oregon Cascade Foothills Sunday morning. The parent surface low associated with the front is currently over the Gulf of Alaska. The models are fairly consistent on the strength and position of this low and are initializing well with satellite imagery. This allows for good forecast confidence on the timing and probability of the precipitation. Snow levels are expected to remain around 1500 feet for the SW Washington Cascades as the precipitation arrives late tonight (around midnight), and will likely remain around 1500 feet through Sunday. Have therefore issued an elevation based (above 1500 feet) Winter Weather Advisory for the South Washington Cascades early Sunday morning through Sunday afternoon. Have otherwise made no changes to the Winter Weather Warnings for the Washington and Oregon Cascades as 1 to 2 feet of snow is still expected. Onshore winds will favor higher precipitation totals for the higher elevations, and expect around 0.5 inch of rain for the Willamette Valley and interior low lands rainshadowed by the coast range from late tonight through Sunday afternoon. Colder air moves in behind the cold front Sunday night, and snow levels will lower to near the valley floor Sunday night and remain low through Monday morning. The showers will dramatically decrease as the colder air moves in, and although snow showers are likely down to the valley floor, do not expect snow accumulations below 500 feet. Less than an inch of snow is expected between 500 and 1000 feet with an exception for the Coastal Mountains and Cascade Foothills where orographic lift will result in slightly higher accumulations (up to 2 inches). Dry weather is expected Monday evening with clearing skies. THis will favor radiation cooling and maintain temperatures near or below freezing Monday night. A weaker cold front is expected on Tuesday. The snow levels will start out low (500-1000 feet) Tuesday morning, but south winds should rise them up to around 1500 feet in the afternoon. QPF is fairly light with this front, and do not expect much if any accumulations at the valley floor. Up to 2 inches of snow is possible for the coast range and the Cascade foothills ,with slightly higher amounts possible for the Cascades Tuesday morning through Tuesday evening. ~TJ .LONG TERM...Tuesday night through Saturday. A rather active weather pattern looks to continue through the long term forecast period with a longwave trough remaining across the western portion of the U.S. through the period. Outside of the broad pattern, however, specific details remain uncertain given large spread in the model guidance. While the 12z GFS depicts a rather deep low pressure system just off the Oregon/Washington coasts by Wednesday evening, there is considerable spread in NAEFS members. It should be noted that the ECMWF does show a somewhat similar low developing but with much less impressive structure. Therefore, will maintain the forecast along a compromise solution. Eventually, the large upper level trough becomes more solidly centered over the far NE Pacific by late Thursday. This would maintain an unseasonably cool air mass over the region with snow levels again lowering to around 1000 feet. Will need to continue to monitor the potential for some snow at least mixing in below 1000 feet early next weekend as the cold air mass looks to remain in place with at least enough moisture to support showers. At this point, however, expect that the extended period will feature continued enhancement of the Cascade snowpack but not any additional low elevation snowfall. Cullen && .AVIATION...Showers decreasing this evening with generally VFR conditions. Next warm front reaches the area after 09Z Sun. Expect increasing MVFR at that point, especially for the coastal areas and SW Washington interior. Widespread MVFR or worse through Sun morning, followed by increasing VFR for the interior valleys late Sun afternoon. Gusty southwest winds developing ahead of the front and lasting through the day Sunday. PDX AND APPROACHES...VFR into the overnight. Precipitation returns by 12Z Sun, with MVFR conditions likely. May see a period of IFR vis with heavier rain during the morning. Gusty southwest winds develop overnight. && .MARINE...Solid small craft advisory wind continues over the waters this afternoon. Latest model guidance shows boundary layer wind speeds peaking at 30-35 kt across PZZ270 shortly after midnight. Have opted to upgrade the gale watch to a warning valid through 18Z Sun, although it will be a marginal event. Extended the existing small craft wind advisories for PZZ255 and PZZ275 through 06Z Mon. Wind speeds start to diminish Mon morning and are expected to fall below small craft advisory criteria by Mon afternoon. Another frontal system Mon night and Tue will likely produce small craft advisory wind. Forecast confidence suffers a large drop Wed night through the end of the week as models show a large variance regarding a developing low pressure. For example, the ECMWF valid 06Z Thu shows a 984 mb surface low at the north end of Vancouver Island with a trailing frontal system over the waters. This would result in possible low-end gale force wind. The GFS, on the other hand, has a sub-980 mb low near 45N 127W, then deepens it to around 975 mb near Cape Disappointment 12Z Thu. This would bring the potential for storm force wind. Have trended the forecast more toward the ECMWF for this time frame. Seas have peaked in the mid teens and will slowly subside a little this evening and tonight. Seas increase into the mid and upper teens late Sun into Mon as the fetch remains directed at WA & OR. Latest ENP guidance shows seas falling just under 10 ft Tue morning. The latest ENP model develops a core of 30 ft seas off the South Oregon coast 12Z Thu, in response to the deep low pressure as seen in the GFS. The ECMWF model has 12 to 15 ft seas over the waters 12Z Thu and is the favored solution. Weishaar && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Winter Storm Warning from 4 AM to 10 PM PST Sunday for Cascades in Lane County-Northern Oregon Cascades. WA...Winter Weather Advisory from 4 AM to 4 PM PST Sunday for South Washington Cascade Foothills for elevations less than 1500 feet. Winter Storm Warning from 1 AM to 7 PM PST Sunday for South Washington Cascades. PZ...Small Craft Advisory for winds until 10 PM PST Sunday for Coastal waters from Cape Shoalwater WA to Cascade Head OR out 10 NM-Coastal Waters from Cascade Head OR to Florence OR out 60 NM. Small Craft Advisory for hazardous seas until 6 AM PST Monday for Coastal waters from Cape Shoalwater WA to Cascade Head OR out 10 NM-Coastal Waters from Cascade Head OR to Florence OR out 60 NM. Small Craft Advisory for winds until 1 AM PST Sunday for Waters from Cape Shoalwater WA to Cascade Head OR from 10 to 60 NM. Gale Warning from 1 AM to 10 AM PST Sunday for Waters from Cape Shoalwater WA to Cascade Head OR from 10 to 60 NM. Small Craft Advisory for hazardous seas until 1 AM PST Sunday for Waters from Cape Shoalwater WA to Cascade Head OR from 10 to 60 NM. Small Craft Advisory for Rough Columbia River Bar until 4 PM PST Sunday. && $$ Interact with us via social media: This discussion is for Northwest Oregon and Southwest Washington from the Cascade crest to 60 nautical miles offshore. This area is commonly referred to as the CWA or forecast area.
Office: PDT FXUS66 KPDT 250632 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1032 PM PST Sat Feb 24 2018 updated the aviation discussion UPDATE...The latest ir satl was showing some mid and high level clouds and occasional breezy west winds were occurring. Overnight low temps will remain in the 30s mainly over the basin with 20s elsewhere. The next winter storm will approach the region tomorrow. Light snow will develop along the east slopes of the wa cascades tonight and move further inland tomorrow. A challenge will be with snow amounts that could approach advisory criteria along the oregon cascades and further east into the john day highlands and blue/wallowa areas. Snow levels may be higher than yday but should lower by afternoon and evening. A winter weather advisory remains in effect along the wa east slopes and additional advisories were issued as well for portions of the region that includes the or cascades and locations in and near the blue/wallowas. .AVIATION...vfr conditions will give way areas of mvfr ceilings and vsby with the next incoming storm system. Taf sites kdls and kykm will be effected after 08z and the remaining taf sites will be effected after 12z. Light snow mixing with rain at times will effect all taf sites Sunday along with occasional breezy winds gusting to 25 kts at times. In addition lcl ifr conditions are possible at all taf sites except for kykm and kpsc. PREV DISCUSSION... /issued 345 PM PST Sat Feb 24 2018/ SHORT TERM...Tonight through Sunday night...The latest system continues to move southeast away from the Pacific Northwest. Showers continue to affect the area, especially over the Blue mountains and along the Oregon Cascade east slopes. Will see showers decrease this evening, but should see isolated to scattered snow showers linger at times over the higher terrain through the night. With snow showers decreasing will allow the remaining advisories for today to expire as further accumulations will be light and spotty. The next system will begin to approach the region late tonight. This system will move through the region Sunday and Sunday evening. Expect to see snow begin late tonight along the Washington Cascade east slopes. This snow will increase and become moderate at times Sunday morning. As such will issue a winter weather advisory for the Washington Cascade east slopes for late tonight into Sunday evening. Elsewhere Sunday will see snow increase Sunday morning over the Blue mountains, then increase over other areas Sunday afternoon and/or Sunday evening. Snow levels will rise Sunday morning across the area with levels rising to 1800 feet over Kittitas county, to around 3400 feet in central Oregon and around 2500 feet in northeast Oregon. Will hold off on issuing other winter weather advisories due to a slower precip arrival and some uncertainty with snow levels. Winds will again increase late tonight into Sunday with this next system with many locations seeing breezy to windy conditions. Temps will remain below seasonal, but will be milder than in recent days. 90 LONG TERM...Monday through Saturday...Showers will taper off on Monday when an upper level trough traverses into Idaho followed by a weak transitory ridge. A mostly dry but continued cold forecast is in store Monday night. The ridge will flatten and give way to a shortwave trough moving southeast across Washington on Tuesday. The strong northwest flow aloft will return, therefore precipitation will be mainly be confined to the Cascades, the Blue Mountains and the Wallowas Tuesday and Tuesday night. Snow levels may only rise to around 1500-2500 feet, but PoPs will only be 10-30% for most of the Columbia Basin and surrounding valleys down to the Columbia Deschutes Plateau. A more organized system is progged to bring rain, snow and gusty winds to the region Wednesday through Thursday. A warm front will force snow levels to rise to around 2000-3000 feet Wednesday night and Thursday. Breezy to windy conditions can also be expected during this time, and the Grande Ronde Valley, Joseph area, Long Creek area, and the base of the Blue Mountain Foothills could get very windy. Precipitation is likely in all areas Wednesday night through Thursday. A cold front will follow Thursday night and Friday, and snow levels will once again fall to near the Basin floor. The air mass will be moist and unstable Friday through Saturday as the Pacific NW remains under a deep upper level trough. This will result in scattered snow showers (snow/rain mix at the lowest elevations) across the region. Wister && .PRELIMINARY POINT TEMPS/POPS... PDT 32 45 27 38 / 10 60 40 10 ALW 35 48 30 42 / 20 60 40 10 PSC 35 49 29 45 / 10 20 20 10 YKM 27 48 22 44 / 10 40 20 10 HRI 34 48 27 43 / 10 40 20 10 ELN 27 43 22 41 / 20 50 20 10 RDM 26 44 18 35 / 10 80 80 20 LGD 27 38 23 33 / 30 90 70 20 GCD 26 40 24 31 / 30 70 80 20 DLS 34 46 29 45 / 20 80 60 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory from 7 AM Sunday to 1 AM PST Monday for ORZ506. Winter Weather Advisory from 4 AM Sunday to 1 AM PST Monday for ORZ049-050-502-503-509. WA...Winter Weather Advisory from 4 AM Sunday to 1 AM PST Monday for WAZ030. Winter Weather Advisory until 10 PM PST Sunday for WAZ520. && $$ 97/97