Area Forecast Discussion
Issued by NWS Portland, OR
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Issued by NWS Portland, OR
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-- Discussion containing changed information from previous version are highlighted. --173 FXUS66 KPQR 221824 AAC AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 1124 AM PDT Wed May 22 2024 Updated aviation and short term discussions .SYNOPSIS...A weather system today will bring additional breezy winds, cooler temperatures, and scattered showers with less rain accumulation than yesterday. Brief period of dry and warmer temperatures Thursday before unsettled weather with scattered showers continues Friday into Saturday. Mostly dry with warming temperatures Sunday into early next week. && .SHORT TERM...-- Changed Discussion --Wednesday through Friday...The upper low continues to shift eastward with the low centered over southeast Washington but it will quickly transition over eastern Oregon by the afternoon. Radar continues to show shower conditions with some breezy westerly winds. While areas will continue to dry out through the afternoon, orographic lift will enhance showers over the Cascades causing them to persist a bit longer. Although the main cold core of the low is expected to miss our area to the north and east, latest hi-res models indicate enough cold air aloft will move over the area to produce around 100-250 J/kg of CAPE this morning and afternoon, mainly over the Cascades and lowlands north of Salem. This likely won`t be enough instability for thunderstorms except for potentially along the western slopes of the Cascades if orographic lift is enough to produce a lightning strike or two. However, expect periods of moderate to heavy rain in stronger showers as well as small hail. With the colder temperatures, snow levels are expected to lower enough 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 Columbia River Gorge. Shortwave ridging returns Thursday as the closed upper low moves east into the northern Rockies. This will bring dry weather, mostly sunny skies, and warmer temperatures. Temperatures are forecast to rise to the upper 60s in the interior lowlands with only a 10-25% probability of temperatures reaching 70 degrees. Ensemble guidance is in good agreement that an upper shortwave and surface front will move through the PacNW Friday, bringing additional scattered showers in the late morning through evening hours. These will be pretty weak and lacking much moisture and forcing, so once again, limited precipitation is expected in the lowlands with only about 0.1-0.25 inches of rain over the Cascades through Friday night. -Muessle/HEC .LONG TERM...Saturday through Tuesday...WPC 500 mb cluster analysis indicates another weak trough will move through the PacNW on Saturday, though the depth of the trough and therefore precipitation amounts are still uncertain. Overall, even on the higher end of ensemble guidance, precipitation amounts look pretty similar to Friday`s precipitation with limited amounts in the lowlands and slightly higher over the Cascades and Coast Range. On Sunday, the majority of 500 mb clusters indicate either zonal flow or slight ridging returning to the PacNW. This will bring dry weather except for the potential for some lingering showers over the northern counties of Oregon and SW Washington counties if more zonal flow continues. By Monday and Tuesday, clusters indicate ridging continues to build over the Western US, though exact amplitude and location of the ridge is still a little uncertain. This would still bring mostly dry and warmer conditions to NW Oregon and SW Washington, though just how warm is the question. The NBM spread for the 25th and 75th percentiles along the inland valleys is anywhere from upper 60s to low 80s. Latest NBM deterministic and median temperature forecasts puts temperatures in the low to mid 70s. -HEC-- End Changed Discussion --&& .AVIATION...-- Changed Discussion --Widespread VFR across the airspace. Given the post frontal environment, expect showers along with a 30% probability MVFR conditions. MVFR conditions will likely be associated with precipitation. Predominant CIGS will fluctuate between 3500-5500 ft. MVFR conditions likely to become the dominant flight category along the coast around 03Z Thursday. Northerly to westerly winds with gusts up to 25 kt possible at all terminals through around 00Z Thursday. PDX AND APPROACHES...Widespread VFR with postfrontal showers. CIGs expected to fluctuate between 3500-5000 ft with a 20%-40% probability for intermittent MVFR conditions that will likely be associated with passing showers. Westerly winds with gusts up to 20 kt through around 00Z Thursday. -42-- End Changed Discussion --&& .MARINE...-- Changed Discussion --Northwesterly flow in the post-frontal environment will continue to produce breezy winds today with gusts around 20-25 knots common place across the coastal waters. This morning a sharp rise in seas is also anticipated with the arrival of a fresh northwesterly swell peaking around 10-13ft at 9-10 seconds across waters mainly north of Cape Falcon. Fortunately, the southern waters shouldn`t see nearly as much of a rise but waves will still remain fairly steep. Thus the current Small Craft Advisory continues until this afternoon/evening as winds and seas stay elevated. The upper-level low responsible for the active conditions departs Wednesday night into Thursday accompanied by calmer winds/seas returning for a brief period of time. Yet another weather disturbance swings into the region from the NNW the second half of Friday through Saturday continuing the rather progressive and active weather pattern. Seas likely rise to 7-9 feet at 8-9 seconds on Saturday before decreasing to 4-5 feet at 9 seconds 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/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland