Area Forecast Discussion
Issued by NWS Portland, OR

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000 FXUS66 KPQR 141247 AFDPQR Area Forecast Discussion National Weather Service Portland OR 319 AM PST Wed Nov 14 2018 .SYNOPSIS...A couple weak fronts will bring a chance of light rain today and then again on Friday across southwest Washington and far northwest Oregon, but the weather will be predominantly cool and dry through early next week. && .SHORT TERM...Today through Saturday...Water vapor satellite imagery this morning depicts zonal flow spreading across the Pacific Northwest. This has led to plenty of clouds spreading across the region. A weak low to mid level front is dropping southeastward across our northwest zones this morning and resulting in a few light showers stretching from Clatsop to Skamania Counties. This feature will continue to slowly drop southeastward before stalling and weakening in place across northwest Oregon this afternoon and evening. This will continue to produce plenty of clouds today, but rain chances will drop dramatically as one heads south of a line extending between Tillamook and Portland. It should be noted that temperatures remain well below freezing around Hood River, Odell and Parkdale early this morning. While measurable precipitation appears unlikely east of the Cascades, any precipitation that falls below ~2000 feet appears increasingly likely to fall as freezing rain this morning. As a result, a quick glaze of freezing rain will be possible around Hood River, but will evaluate precipitation trends before issuing any products. Surface observations indicate the cross Cascade pressure gradient is continuing to drop and is now down to -2.9mb between KTTD-KDLS. This gradient is forecast to flip onshore and top out around 1mb this afternoon according to the NAM. Still not sure if it will turn enough onshore to result in westerly winds through the Columbia River Gorge given the cold air and stratus that remains entrenched in the Columbia Basin, but east winds near the mouth of the Columbia River Gorge will continue to trend downward and will become nearly nonexistent by later today. Models are in good agreement shortwave ridging will then build northward over the northeast Pacific Thursday and Friday. A shortwave trough dropping southward out of British Columbia could result in a few light showers across mainly southwest Washington on Friday, but this trajectory is not favorable for any significant precipitation. The bigger story with this storm system is that it will likely reinforce cold air east of the Cascades and help to turn pressure gradients offshore once again. This will result in east winds ramping upward Friday night and Saturday, particularly near the mouth of the Columbia River Gorge. Finally, a combination of local pollution and smoke from California wildfires has led to worsening air quality across northwest Oregon and southwest Washington over the past 24-72 hours. Surface high pressure will be squarely centered over the CWA today, which should result in very light surface winds across interior valleys. In addition, model soundings indicate very little mixing will occur today due to the cloudy conditions. As a result, stagnant air conditions will likely persist into Thursday morning. However, by Thursday afternoon, a combination of a bit more sunshine to aid in vertical mixing (approximately up to 1500 feet) and increasing northerly winds in the Willamette Valley, there should begin to be some relief from the stagnant air conditions plaguing the region currently. /Neuman. .LONG TERM...Saturday Night through Wednesday...Operational models remain in agreement shortwave ridging will more than likely bring dry conditions to the region Saturday night through Monday. Expect east winds to persist near the mouth of the Columbia River Gorge for much of the extended forecast period. However, winds away from the Gorge will likely be light and mixing will be limited so we may need Air Stagnation Advisories for the Sunday through Tuesday timeframe if current model depictions of the basic weather pattern hold. With that said, models do diverge on how the synoptic pattern will evolve beginning Monday night and Tuesday. The operational EC suggests a weakening front could bring rain as early as Monday night or Tuesday to the region while the GFS suggests rain could hold off until after Wednesday. However, most members of the GEFS suggest rain will likely arrive Tuesday or Wednesday. Given the somewhat splitty nature of the pattern depicted by the models, suspect precipitation will arrive on the later end of the spectrum, but for now trended PoPs towards a blend of the model solutions given the uncertainty. /Neuman && .AVIATION...Front remains offshore but rain ahead of the front is moving inland roughly along a Pacific City to Mt. Hood line as of 11Z. Cigs along the north coast in high end MVFR category should lower more with the front. Further to the south and east cigs will be slower to come down, as late as 18Z to 00Z in the south willamette Valley. The likelihood of cigs dropping into MVFR category also decreases to the south and east, although all locations in nw Oregon stand at least a chance of doing so. MVFR conditions may continue at the coast tonight, though it looks like developing offshore flow in the KONP area may bring VFR conditions. Inland areas a little more challenging since the remnants of the front may stall somewhere over the area bringing MVFR conds to some areas while VFR to others. PDX AND APPROACHES...VFR conds most likely to continue through 18Z-20Z Wed with MVFR cigs around 2500-3000 feet becoming more likely after that. There is a good chance for low end VFR to MVFR cigs to continue tonight. /mh && .MARINE...Weakening front slow to move eastward as it is far from its parent low near the Alaska panhandle. Hard to pick out the front on satellite or buoy obs, but looks like it is still west of buoy 46089, ~70NM off Astoria, OR. Hi-res models show a windshift moving into the waters near sunrise and then ashore by midday. Marginal SCA winds look good so will keep the advisory as is. Winds ease in the afternoon becoming light tonight as a ridge of high pres lay over the waters into Friday. Offshore flow is looking increasingly likely for the weekend for a return of moderate north-northeast winds. Seas will remain 5 ft then build into the 7 to 9 ft range tonight with the front. A trailing dynamic swell train will then briefly bring westerly seas near 10 ft Late wednesday night and early Thursday. Seas than drop to between 5 and 8 feet for several days thereafter. /mh /JBonk && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory for winds until 10 AM PST this morning for Waters from Cape Shoalwater WA to Cascade Head OR from 10 to 60 NM. Small Craft Advisory for hazardous seas from 7 AM to 8 PM PST Thursday for Coastal Waters from Cape Shoalwater WA to Florence OR out 60 NM. Small Craft Advisory for winds until noon PST today for Coastal waters from Cape Shoalwater WA to Cascade Head OR out 10 NM. && $$ 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. This area is commonly referred to as the forecast area.

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