692 FXUS66 KPQR 172312 AFDPQR Area Forecast Discussion National Weather Service Portland OR 412 PM PDT Fri Mar 17 2017 .SYNOPSIS...A warm front continues to push slowly northward across NW Oregon this afternoon. Steady rain to the north of the front will taper to showers with gusty south winds this evening. Low pressure well off the Oregon and northern California coast will move northeast and make landfall on the Olympic Peninsula later tonight or early Sat morning. The associated cold front will reach the coast around the same time, then push inland Saturday. Snow levels will be well above the Cascade passes tonight, but fall below pass level by Saturday afternoon. High pressure returns Saturday night and Sunday for a brief drying trend. A more moist south flow aloft develops Monday and continues through at least Tuesday night for an increasing threat of precipitation. An unsettled pattern persists during the latter half of next week. && .SHORT TERM...Tonight through Monday...Diffuse low pressure off the Oregon and northern California coast will continue northeast, making landfall on the Olympic Peninsula later tonight or early Saturday morning. This system continues to push a warm front slowly northward across NW Oregon, which is expected to cross the Columbia into Washington this evening. To the north of the warm front, plenty of isentropic lift has resulted in several hours of steady light to moderate rain; the back edge of which is near Salem as of 345 pm this afternoon. In the warm sector south of the front, precipitation is more showery in nature...with temps generally in the 50s. Tonight should be a mild night for much of the district, with increasing south winds as the associated cold front approaches the coast. 18z NAM/GFS did not change much from previous runs...with 850 mb winds S-SW on the order of 55-65 kt ahead of the cold front. While it is possible a couple of our windier coastal sites could briefly touch 55-60 mph gusts, winds are generally expected to remain below warning criteria. Models appear a little overdone with the wind profile given the modest pressure gradients. The secondary low/trough within the southern part of our complex low (presently near 38N/135W) may also rob some of the S-N gradient as the cold front pushes onshore and across our forecast area later tonight and Sat morning. The secondary wave of low pressure also slows down the progress of the cold front a bit...which will probably boost rainfall totals across the CWA as light to moderate stratiform rain continues near the front well into Sat. Overall, expect about 0.50 inch for the inland valleys with 1-2 inches along the coast and in the higher terrain. A couple of the wetter spots in the Coast Range and S WA Cascades may approach 3 inches of rain from this system. While not likely enough to create hydrologic issues by itself, the mild rain ahead of the cold front will likely add to snowmelt and keep rivers fairly high for the next few days. Mild air advecting in with the warm front will generally keep snow levels above the Cascade Passes for much of this event, though snow levels will drop back to pass level or lower Saturday as the cold front moves through. While some of the higher ski resort elevations may eek out 6 inches of snow out of this system Saturday, these accumulations do not appear to be widespread enough to warrant an advisory. Post-frontal showers will linger into Sat night, ending by Sunday as cool high pressure builds into the Pac NW. After a wet Saturday, Sunday may be a decent fair weather day...with at least some sunshine. Temps will probably start off fairly chilly Sun morning... likely close to freezing for the valleys. However with ample sunshine, temps should climb well into the 50s for the lowlands despite 850 mb temps starting off in the -2 to -4 deg C range Sun morning. Weak low pressure at the tail end of our current cold front is expected to linger off the California coast through the weekend. Most models energize this system a little as the Pacific jet noses toward California Sun night/Mon. An incoming upper trough is expected to pick up this system and lift it northward, potentially spreading rain northward into Oregon. Pressure gradients will be easterly through the Columbia Gorge at that time, and the 12z ECMWF/18z GFS continue to hint that some low-level cold air may remain dammed up along the east slopes of the Cascades Mon morning. Luckily current guidance holds off precipitation in the Columbia Gorge until Mon afternoon, which would likely see temps well above freezing by the time precip reaches the ground. Otherwise, expect Monday to bring an increasing chance for rain from south to north, with snow levels somewhere near the Cascade passes. Weagle .LONG TERM...Monday night through Saturday...Longer range guidance shows decent agreement in having deep, persistent upper troughing off the U.S. West Coast, while upper ridging generally dominates the Rockies. The S-SW flow aloft in between these two features will likely guide a series of disturbances northward into our region from the California waters. This will keep our weather unsettled with showers or periods of rain and snow levels near the Cascade passes for much of next week. None of these systems are expected to be particularly strong at this point; but given the current guidance next week looks fairly damp with near to slightly below normal temperatures. Weagle && .AVIATION...A cornucopia of conditions this afternoon with rain ahead of a warm front. Most inland sites seeing VFR CIG with rain but it appears offshore flow near the mouth of the Columbia River Gorge is keeping that area's terminals VFR. Persistence appears to be the most likely forecast, at least until the warm front comes through this evening. Then may see a break in rain and improvement to MVFR or even VFR for a few hours before MVFR or IFR conditions develop with moderate rain along the cold front later tonight and Saturday morning. Look for strong winds out of the south along the coast this evening with gusts as high as 40 kt, and breezy conditions out of the south inland tonight with gusts as high as about 30 kt. KPDX AND APPROACHES...Offshore flow appears to be keeping conditions VFR with light rain. May still see MVFR conditions develop with more moderate rain starting after 12Z Saturday. Winds will become gusty out of the south this evening for a few hours and could see gusts as high as 30 kt in the area. Bowen && .MARINE...Not much change to the forecast this afternoon as the general trends remain on track. The only real difference is a shift of peak winds to a little bit later based on current observations and a timely ASCAT pass around 12:30 pm which showed the surface low quite well. The main story is a deepening strong low will approach the waters from the SW this evening, with a warm front moving N across our coastal waters. The low will deepen to around 1000 mb and make landfall along the northern Washington coast around midnight tonight. The associated cold front will move through the waters tonight and onshore from N to S from around midnight to 4 or 5 am early Saturday. Look for brisk E to SE winds to become strong southerly gales as the warm front moves N through the waters, then continue until the cold front moves onshore later tonight. Will maintain the current Gale Warnings. Behind the front will be a period of NW winds with gusts up to about 25 kt, but easing up by Saturday afternoon. As high pressure builds in on Saturday and northward on Sunday, we will see a bit of N to NE flow on Sunday with a weak thermal trough developing along the S Oregon coast. Seas still running 6 to 7 ft this afternoon, but will build above 10 ft this evening as winds pick up, and peak at 15 to 18 ft tonight. Seas should drop below 10 ft later Saturday and continue below 10 ft into early next week. Bowen && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Gale Warning until 2 AM PDT Saturday for Coastal Waters from Cape Shoalwater WA to Cascade Head OR out 60 nm. Gale Warning until 5 AM PDT Saturday for Coastal Waters from Cascade Head OR to Florence OR out 60 nm. Small Craft Advisory for Rough Columbia River Bar from 7 PM this evening to 7 AM PDT Saturday. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland This discussion is for Northwest Oregon and Southwest Washington from the Cascade crest to 60 nautical miles offshore. The area is commonly referred to as the forecast area.