760 FXUS66 KPQR 040413 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 912 PM PDT Fri Jun 3 2022 Updated Short Term and Aviation Sections .SYNOPSIS...Broad low pressure over the northeast Pacific will funnel the upper jet stream and a few disturbances across the area through Monday. High pressure then builds and will start shunting following systems northward, but not completely away from the PacNW. Showers will transition to stratiform rain this evening as the first system moves across. Then expect moderate to heavy rain later Saturday and Saturday night across the region under second system and a weak to moderate atmospheric river. A round of thunderstorms follows Sunday with the potential to bring gusty winds. Showers taper off Monday with conditions to warm above normal and far more dry periods than not next week. && .SHORT TERM...Tonight through Sunday Night (EVENING UPDATE)...At 03Z GOES-17 water vapor revealed a 500 mb low pressure area parked over the eastern Pacific. A fairly strong 250 mb jet stream for this time of year (on the order of 110-120 kt) was feeding into this low pressure area. KRTX doppler radar indicated widespread 30-40 dbZ reflectivity values, indicative of light stratiform precipitation. Six hour rainfall amounts through 03Z have been generally one-tenth of an inch or less. The 00Z KSLE sounding showed a precipitable water content (PWAT) of 1.01 inches. This value is just above the 90th percentile climatological PWAT for the date. The 02Z Blended Total Precipitable Water satellite product showed a swath of 1.5 to 1.7 inch values along 30N extending from beyond 150W longitude to about 40N 130W. This moist plume eventually spreads to the Oregon coast Saturday. The GEFS ensemble mean Integrated Vapor Transport (IVT) model output yields 400-600 kg/m/s 00Z Sunday. This translates to a high-end weak or low-end moderate atmospheric river. All in all, minimal changes to the current forecast. Weishaar REMAINDER OF PREVIOUS SHORT TERM DISCUSSION: The large scale forecast pattern has remained somewhat consistent over the last few days. The broad upper low centered just off the coasts of B.C. and Alaska will generally remain stationary through Monday. This will keep the Pacific jet stream aimed over the PacNW. This acts as a conduit for multiple systems along the northern edge of a moist air mass to affect the region tonight through Monday. The first shortwave will arrive tonight and bring steady/stratiform rain across the area under PW values 0.75-1.00 inches. This will move past fairly quick and produce relatively minimal rain amounts for most areas. The shortwave will lift north of the region leaving a generally showery Saturday. Additionally, southerly winds will increase mainly over the waters and immediate beaches and headlands. Gusts 30-35 mph at brief times Saturday afternoon The second shortwave will follow later Saturday afternoon and bring periods of moderate to heavy rainfall, mainly Sunday evening closer to the coast range and I-5 Corridor and them mainly over the north Oregon/south Washington Cascades after midnight Saturday night. The main axis of the rain will fall along a line from roughly Newport to Mt. Adams. PW values increase to around 1.25 inches and expect to receive 1.50 to 2.00 inches over the 12 hour period. This should be enough to produce a quick rise on area rivers. Don't expect any mainstem river flooding, but a doubling of flow rates on Sunday is fairly plausible. Behind that shortwave, the air mass cools aloft as another shortwave begins crossing the region Sunday late morning. With these added dynamics, a very favorable combination of slight surface warming paired with the cooling aloft, and mid-level winds 40-50 kts, am keeping the 25-35% chance of thunderstorms across most of the area beginning early Sunday afternoon. Somewhat drier air arrives with this latest wave, however, PW values will be steadily falling through the day eventually to 0.60-0.80" by Sunday evening. Initial storms Sunday afternoon will have a mainly vertical speed shear profile bringing potential of brief heavy rains with around 0.25- 0.35" possible in an hour along with possible outflow gusts 35-40 mph at the high end. Then the heavy rain threat diminishes by late afternoon with the wind threat carrying through the early evening. Storms will generally weaken by midnight, but showers continue. /JBonk .LONG TERM...Monday through Friday: No notable evolution in the forecast from yesterday's model solutions. Medium range models come back in general agreement for the long term forecast although details still in question as expected. Shortwave high pressure builds northward as the upper low retreats northwest. Will see some lingering showers Monday, but Tuesday looks like it will be dry through sunset. A weak shortwave clips the area for some light rain Tuesday night. Wednesday, another lobe of the previous upper low's shortwave will swing toward the coast but models generally weaken the associated front. Still may see some light showers across the region and the trend has been to lessen the QPF amounts. Thursday has another shortwave ridge building across the area for dry weather. This then transitions to longwave ridging pushing north again Thursday night and into Friday. However, the upper ridge has most model solutions placing the axis over the northern Rockies which keeps the PacNW along the western edge of the ridge and close enough for many solutions to bring light QPF Thursday and Friday. Our area will be staying on the warm side of the jet and easily keep temperatures above normal. /JBonk && .AVIATION...For the 06z TAFs: The initial swath of rain has pushed northeast with more of a showery pattern emerging from the south. VFR continues to be the predominant category across the area, though periodic MVFR conditions will become predominant along the coast with occasional IFR possible by 06Z. Light rain will continue across there area through the night and into Saturday. A warm front will then push in late Saturday afternoon to bring lowering ceilings and visibility in heavier rain. Look for widespread MVFR conditions with periods of IFR along the coast. Winds will mainly be out of the south to southeast as the warm front is approaching, with the central coastal areas seeing winds gusting in the 25 to 30 kt range after 18z. For detailed regional Pac NW aviation weather information, go online to: https://weather.gov/zse KPDX AND APPROACHES...VFR conditions with intermittent light rain is expected to continue through early Saturday afternoon. MVFR ceilings will spread in late Saturday afternoon as a frontal system brings in heavier rain. Winds generally out of the southeast through the period. /Kriederman && .MARINE...A low approaching the area from the southwest is resulting in a strengthening pressure gradient across the waters. As a result, southerly winds are increasing from south to north across the waters. Small Craft winds are expected to continue into Saturday morning, but then winds increase further during the late morning time period as the low passes immediately to our west. Gale Force wind gusts are expected from mid morning through late evening, especially across the outer waters. The inner waters, especially the central coastal waters, will have a chance of experiencing Gale Force southerlies, though most guidance is pointing at less than Gales. Therefore, at this time, they will continue to have a Small Craft Advisory due to high uncertainty surrounding whether a coastal jet can develop and result in an extended period of wind gusts greater than 33 kts. Model trends will continue to be monitored to determine whether an upgrade is necessary. Winds turn west-southwesterly and decrease fairly abruptly behind the cold front Saturday night into Sunday, though seas will likely remain steep and choppy for several hours after the strongest winds drop off at any given point within our waters. High pressure builds in Sunday to bring a return to relatively benign conditions through the early part of the upcoming work week. -Bumgardner/Kriederman && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 5 AM PDT Sunday for coastal waters from Cape Shoalwater WA to Florence OR out 10 nm. Small Craft Advisory until 11 AM PDT Saturday for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 nm. Gale Warning from 11 AM to 11 PM PDT Saturday for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 nm. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland