National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, OR

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-- Discussion containing changed information from previous version are highlighted. --173FXUS66 KPQR 221824 AACAFDPQRArea Forecast Discussion...UPDATEDNational Weather Service Portland OR1124 AM PDT Wed May 22 2024Updated aviation and short term discussions.SYNOPSIS...A weather system today will bring additional breezywinds, cooler temperatures, and scattered showers with lessrain accumulation than yesterday. Brief period of dry and warmertemperatures Thursday before unsettled weather with scatteredshowers continues Friday into Saturday. Mostly dry with warmingtemperatures Sunday into early next week.&&.SHORT TERM...
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Wednesday through Friday...The upper low continues toshift eastward with the low centered over southeast Washington butit will quickly transition over eastern Oregon by the afternoon.Radar continues to show shower conditions with some breezy westerlywinds. While areas will continue to dry out through the afternoon,orographic lift will enhance showers over the Cascades causing themto persist a bit longer. Although the main cold core of the low isexpected to miss our area to the north and east, latest hi-resmodels indicate enough cold air aloft will move over the area toproduce around 100-250 J/kg of CAPE this morning and afternoon,mainly over the Cascades and lowlands north of Salem. This likelywon`t be enough instability for thunderstorms except for potentiallyalong the western slopes of the Cascades if orographic lift isenough to produce a lightning strike or two. However, expect periodsof moderate to heavy rain in stronger showers as well as small hail.With the colder temperatures, snow levels are expected to lowerenough for snow to fall above pass level in the Cascades. Also,expect breezy westerly winds as the low passes with gusts up to 20-25 mph, except up to 35-40 mph over the high Cascades and ColumbiaRiver Gorge.Shortwave ridging returns Thursday as the closed upper low moveseast into the northern Rockies. This will bring dry weather,mostly sunny skies, and warmer temperatures. Temperatures areforecast to rise to the upper 60s in the interior lowlands withonly a 10-25% probability of temperatures reaching 70 degrees.Ensemble guidance is in good agreement that an upper shortwaveand surface front will move through the PacNW Friday, bringingadditional scattered showers in the late morning through eveninghours. These will be pretty weak and lacking much moisture andforcing, so once again, limited precipitation is expected inthe lowlands with only about 0.1-0.25 inches of rain over theCascades through Friday night. -Muessle/HEC.LONG TERM...Saturday through Tuesday...WPC 500 mb clusteranalysis indicates another weak trough will move through thePacNW on Saturday, though the depth of the trough and thereforeprecipitation amounts are still uncertain. Overall, even on thehigher end of ensemble guidance, precipitation amounts lookpretty similar to Friday`s precipitation with limited amounts inthe lowlands and slightly higher over the Cascades and CoastRange.On Sunday, the majority of 500 mb clusters indicate eitherzonal flow or slight ridging returning to the PacNW. This willbring dry weather except for the potential for some lingeringshowers over the northern counties of Oregon and SW Washingtoncounties if more zonal flow continues.By Monday and Tuesday, clusters indicate ridging continues tobuild over the Western US, though exact amplitude and locationof the ridge is still a little uncertain. This would still bringmostly dry and warmer conditions to NW Oregon and SWWashington, though just how warm is the question. The NBM spreadfor the 25th and 75th percentiles along the inland valleys isanywhere from upper 60s to low 80s. Latest NBM deterministic andmedian temperature forecasts puts temperatures in the low to mid70s. -HEC
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Widespread VFR across the airspace. Given the postfrontal environment, expect showers along with a 30% probabilityMVFR conditions. MVFR conditions will likely be associated withprecipitation. Predominant CIGS will fluctuate between 3500-5500 ft.MVFR conditions likely to become the dominant flight category alongthe coast around 03Z Thursday.Northerly to westerly winds with gusts up to 25 kt possible at allterminals through around 00Z Thursday.PDX AND APPROACHES...Widespread VFR with postfrontal showers. CIGsexpected to fluctuate between 3500-5000 ft with a 20%-40%probability for intermittent MVFR conditions that will likely beassociated with passing showers. Westerly winds with gusts up to 20kt through around 00Z Thursday. -42
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Northwesterly flow in the post-frontal environment willcontinue to produce breezy winds today with gusts around 20-25knots common place across the coastal waters. This morning a sharprise in seas is also anticipated with the arrival of a freshnorthwesterly swell peaking around 10-13ft at 9-10 seconds acrosswaters mainly north of Cape Falcon. Fortunately, the southernwaters shouldn`t see nearly as much of a rise but waves will stillremain fairly steep. Thus the current Small Craft Advisorycontinues until this afternoon/evening as winds and seas stayelevated. The upper-level low responsible for the activeconditions departs Wednesday night into Thursday accompanied bycalmer winds/seas returning for a brief period of time. Yetanother weather disturbance swings into the region from the NNWthe second half of Friday through Saturday continuing the ratherprogressive and active weather pattern. Seas likely rise to 7-9feet at 8-9 seconds on Saturday before decreasing to 4-5 feet at 9seconds Sunday into early next week. -Schuldt
-- End Changed Discussion --&&.PQR WATCHES/WARNINGS/ADVISORIES...OR...None.WA...None.PZ...Small Craft Advisory until 5 PM PDT this afternoon for PZZ210- 251-252-273. Small Craft Advisory until 8 PM PDT this evening for PZZ271-272.&&$$www.weather.gov/portlandInteract with us via social media:www.facebook.com/NWSPortlandwww.twitter.com/NWSPortland