Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
109 FXUS66 KPQR 120406 AAA AFDPQR Area Forecast Discussion UPDATED National Weather Service Portland OR 805 PM PST Mon Nov 11 2024 ...EVENING UPDATE, for aviation weather... .SYNOPSIS...Post frontal showers today ahead of a warm front that will move inland Tuesday night. Snow over the Cascades with periods of heavy rain for the next 24 hours. Heavy stratiform rain and strong winds Tuesday night into Wednesday. Gusts as high as 55+ mph possible along the coast. Tidal overflow concerns with high surf mid-week. Rain continues through the week. && .SHORT TERM...Now through Tuesday Night...Satellite and radar show post frontal showers trailing a cold front that moved through the area today. Onshore westerly flow is present with cold air aloft. Snow has been falling over the Cascades with snow levels above 5500 feet. The passes are clear at this time. There remains a 10-15% chance for thunderstorms today with a 20% chance along the coast. On Tuesday a closed low centered in the Gulf of Alaska will begin to shift southward. Within the flow around this low is a shortwave which is associated with a warm front that will make landfall on Tuesday. This warm front has ample support aloft as the jet streak will move nearly directly over the forecast area. This jet streak is coupled at both 250 mb, 500 mb, with a weak coastal jet at the surface. As the winds become more southerly Tuesday night, that coastal jet will compress against the coast. Wind gusts are expected to exceed 50 mph along the coast - especially the beaches and headlands. There is around a 50% chance for gusts to meet High Wind Warning criteria (58 mph gusts) along the beaches and headlands of the north Oregon and south Washington coasts until early Wednesday morning. Have issued a High Wind Watch at this time for those areas due to these probabilities and the pattern. Will note that the hi- resolution models seem to be running a bit high for the wind speeds with the 90th percentile gusts reaching nearly 70 mph. Again, this is the outlier in all of the ensembles both hi- resolution and the NBM. If winds shift more to the west or even southeast, winds will not be nearly as strong. It is still a good idea to anchor loose outdoor objects, outdoor decorations, and prepare for the case there are any power outages. Inland sites will be gusty from the south with gusts as high as 35 mph. Wind is just one of the components of the forecast for this system as rain too will be a feature to watch. Rainfall will start off stratiform with topographically driven amounts. The Coast Range and Cascades will see the highest precipitation totals. Let`s look at thee NBM 24 hour rainfall 25th-75th percentile rainfall totals for example. Around the Long Beach Peninsula, QPF ranges from 2.0-2.8 inches, and the central Oregon Coast Range ranges from 2.0-3.2 inches. Salem will see anywhere from 0.8-1.5 inches, and the south Washington Cascades will see precipitation amounts of liquid water around 2.5-3.7 inches. Snow levels will be 5000 ft during the period of the most rain. Thus, snow related hazards are not expected. As the days have progressed, river flooding concerns have subsided. For the flashiest rivers there is still elevated attention being paid in case rainfall amounts are higher than expected. There are concerns for tidal overflow and high surf conditions. For more details on these hazards, see the "Beach Hazards" section below.-Muessle .LONG TERM...Thursday through Monday...The long term forecast is highlighted by a cool and showery weather pattern typical of mid November. WPC`s cluster analysis for 500 mb heights and anomalies suggests excellent agreement between the GEFS/EPS/CMC, showing an upper level trough over the coastal waters late Thursday shifting inland over the western CONUS Friday. At 500 mb, there is a weak ridge attempting to build in but it is unsupported at the surface. Even with this being the case, northerly flow will dominate and cannot rule out clearing skies though which will support much cooler overnight lows. The probability for low temperatures near freezing overnight Friday into Saturday morning have increased since previous forecasts. For rural areas of the inland valleys and near Eugene, there is around a 30% chance of below freezing temperatures. Even higher probabilities (near 60%) for the valleys of the Cascade Foothills around Sweet Home, Creswell and Molalla. The greater Portland-Vancouver metro area will see less than a 5% chance of below freezing temperatures. This cooler and drier pattern will quickly come to an end as the flow becomes zonal on Sunday with increasing onshore flow. This onshore flow will send a Pacific frontal system inland bringing more significant rain amounts late in the weekend. That being said, expecting minimal impacts with this system as winds do not look significant and ensemble guidance for QPF suggest rain amounts will not be high enough for hydro concerns. Weak ridging attempts to build in once again early next week but will be difficult to overcome the pervasive troughing from this last week.-Muessle/TK && .AVIATION...Unstable air mass, with plenty of showers through tonight. Expect mix of lower VFR and occasional MVFR with passing showers. Does appear will have a period when showers decrease late tonight into tomorrow am, when will have more MVFR CIGS than VFR. Higher terrain frequently obscured in clouds. MVFR clouds will gradually break by midday Tue, with variable mid and high clouds remaining. This as next system approaches. Will see VFR through the afternoon into early evening, with rain spreading inland towards Tue evening. PDX APPROACHES...Mix of VFR and occasional MVFR with passing showers tonight into Tue am, though think will have more MVFR CIGS of 2500 to 3000 ft after 10Z until 18Z Tue. Then, VFR with variable mid/high clouds Tue afternoon. && .MARINE...An active and progressive weather pattern will continue to facilitate bouts of strong winds and fairly high seas over the next several days. Currently, an area of low pressure continues to move across the coastal waters to our north with wind gusts up around 25-30 knots persisting into the evening hours, gradually decreasing closer to 20 knots overnight. This same low pressure system has also facilitated isolated thunderstorms over the inner and outer waters today; a 20-30% chance of thunderstorms lasts until Tuesday morning any of which could produce erratic wind gusts and lightning. Seas have subsided to around 9 to 10 ft but a mid-period westerly swell begins to push into the waters as the evening progresses, building seas into the upper teens tonight through Tuesday. Expect significant wave heights to peak around 19 to 22 ft after midnight. Seas are very likely (greater than 90% chance) to remain near or above 15 ft through Tuesday, the current Hazardous Seas Warning will remain in place through Tuesday afternoon. Then, all eyes are on the next frontal system rapidly approach the coastal waters later Tuesday. Southerly winds associated with this strong disturbance are expected to peak Tuesday evening/night with the NBM and HREF still suggesting gusts likely exceed 48-50 knots (60-90% chance). Given the model consistency resolving the general magnitude and timing of these winds the Storm Force Watch has been upgraded to a Storm Force Warning between 4 PM Tuesday and 7 AM Wednesday for all coastal waters. The latest models continue to suggest the development of a coastal jet with this system around 500-1000ft off the surface. Should these winds get mixed to the surface as the front passes it`s within the realm of possibility(20-30%) for isolated gusts closer to 60 knots. Seas will likely remain elevated and chaotic, building back into the upper teens to lower 20s as a fresh southerly swell also develops. Winds will gradually ease behind the front Wednesday through Thursday, while seas likely remain in the mid to upper teens. -Schuldt/DH && .BEACH HAZARDS...It still appears a westerly swell leads to seas building to around 19-21 ft with a period of 15 seconds later tonight into Tuesday morning. This will produce large waves and hazardous surf conditions with breakers up to 22-25 ft. As a result a High Surf Advisory is still in effect for Tuesday. A high surf will affect beaches, producing rip currents, sneaker waves and beach erosion. Remain alert for exceptionally high waves and stay a safe distance from the water`s edge. While unrelated to the current series of weather disturbance, the perigean spring tides (sometime referred to as the king tides) will begin Friday November 15, increasing high tides along with a strong weather system on Wed into Wed night will bring possibility of tidal overflow and minor coastal flooding. -Schuldt/DH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...High Surf Advisory from midnight tonight to 4 PM PST Tuesday for ORZ101>103. High Wind Watch from Tuesday evening through late Tuesday night for ORZ101>103. Winter Weather Advisory until 10 AM PST Tuesday for ORZ126>128. WA...High Surf Advisory from midnight tonight to 4 PM PST Tuesday for WAZ201. High Wind Watch from Tuesday evening through late Tuesday night for WAZ201. PZ...Small Craft Advisory until 10 PM PST this evening for PZZ210. Hazardous Seas Warning until 4 PM PST Tuesday for PZZ210. Hazardous Seas Warning until 4 PM PST Tuesday for PZZ251>253- 271>273. Storm Warning from 4 PM Tuesday to 7 AM PST Wednesday for PZZ251>253-271>273. $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland