Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS66 KSEW 032325 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 325 PM PST Sun Mar 3 2024 .SYNOPSIS...
-- Changed Discussion --
An upper level and surface trough will continue to produce mixed precipitation through the remainder of Sunday and into Monday. Heavy snow is ongoing in the north Cascades, where a winter weather advisory has been issued for the eastern portions of Whatcom and Skagit counties through Monday afternoon for areas above 500 feet. While a weak ridge will move overhead midweek, a stationary front will keep a slight chance of precipitation in the forecast for the Cascades and Olympics. Precipitation is expected to return to finish the work week. Temperatures will remain below average through the end of the week.
-- End Changed Discussion --
&& .SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
-- Changed Discussion --
An upper level trough remains over southern B.C. Canada this afternoon, with ridging over Alaska and the northern Great Plains keeping the low virtually parked overhead throughout the weekend. The pattern finally begins to break to the east, allowing the upper-level low to begin to depart the region Monday afternoon. In the mid-levels, the low/trough essentially splits into two, with one feature remaining over in Canada, and a shortwave trough ejecting down into Washington/Oregon Monday afternoon that weakens/fills in as it moves onto shore. The surface trough will also break down as the shortwave moves onto shore (that has been a focus area for mixed precipitation this weekend). Temperatures aloft remain cool for this time of year, with 500 mb temps around -37 degrees celsius. 700 and 850 mb flow remains virtually onshore with moist air out ahead of the trough, and north flow beginning to wrap around the backside of the trough, bringing in cooler and drier air behind the system Sunday/Monday. For Sunday afternoon, continue to watch mix precipitation showers continue across mostly the coast and Olympic/Southwest Interior. A few show showers were seen across the Seattle metro this morning with activity that was able to track across more populated areas. For the remainder of this afternoon, precipitation is expected in a couple regions. The mixed precipitation showers will continue along the coast and interior region Sunday afternoon/evening, and track towards Puget Sound in the later part of the day. The lightest showers are expected to produce rain, but the heaviest showers will have mixed precipitation as the air cools via evaporation, allowing for snow and possibly graupel to mix down to the ground. There will be a break in activity early Monday morning before additional showers move in late morning/early afternoon. For the north Cascades, heavy snowfall rates of 1 to 2 inches per hour have been observed in around the Mt. Baker area. Ensemble guidance indicates most of the snow accumulations sticking at elevations greater than 500 feet (based on the snow levels). A winter weather advisory was issued from Sunday afternoon through Monday afternoon to cover the threat of heavy snow. Most likely accumulations will be anywhere from 3 inches in the lower areas/Valleys, to 11 inches in the mountains. Remaining Cascades passes will see a couple inches of snow, with higher amounts expected in the Glacier/Rainier peaks. Tuesday/Wednesday will dry out with the disturbance departing to the east, allowing for skies to clear out some Tuesday and a little on Wednesday. A stationary front will remain in the vicinity of the region however. This will keep a slight chance of precipitation in the Cascades/Olympics. Temperatures will also remain steady with highs in the 40s, and lows in the low 30s for the lowlands. Winds will become light and variable Tuesday into Wednesday. .LONG TERM /THURSDAY THROUGH SUNDAY/...Ensembles/deterministic models show the ridge departing to the east on Friday with a trough moving in from Alaska. This will return the chance of precipitation Friday into next weekend. An increase in temperatures to seasonal averages (highs in the 50s) will omit the threat for snow in the forecast for most areas (except the Cascades and Olympics). HPR
-- End Changed Discussion --
&& .AVIATION...
-- Changed Discussion --
A cool upper trough remains over the Pac NW tonight and Monday with additional showers expected. Ceilings are mainly in MVFR range with passing showers. There`s a slight chance of thunderstorms along the coast where instability is the greatest. Gusty south winds in the interior will ease between 06-12z. Snow levels will remain low overnight with rain/snow mix possible. Overall, a little less shower coverage Monday afternoon with the main focus over the coast and North Cascades. 33 KSEA...Showers in the vicinity tonight, at least through 09z. Gusty S winds also easing after 09z. MVFR conditions likely through Monday morning. 33
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Low pressure remains over western WA tonight. Gusty S winds in the interior waters will continue and a Small Craft Advisory remains in effect. On the backside of the low, over the outer Coastal Waters, NW flow will increase with Small Craft Advisory winds also expected. Winds will ease on Monday as the low weakens/fills over the region. The flow turns offshore Monday night and Tuesday. A weak frontal system arrives Wednesday night and Thursday, followed by a stronger system on Friday. 33
-- End Changed Discussion --
&& .HYDROLOGY...
-- Changed Discussion --
No river flooding is expected at this time for the next seven days.
-- End Changed Discussion --
&& .SEW WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
WA...Winter Weather Advisory until 4 PM PST Monday for West Slopes North Cascades and Passes. PZ...Small Craft Advisory until 10 PM PST this evening for Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 7 AM PST Monday for Puget Sound and Hood Canal. Small Craft Advisory until 2 AM PST Monday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm- Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.
-- End Changed Discussion --
&& $$

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