Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
340 FXUS66 KPQR 010507 AAB AFDPQR Area Forecast Discussion...Update National Weather Service Portland OR 1007 PM PDT Sun Jun 30 2024 .UPDATE...Made some quick updates to the forecast this evening to accommodate some dense fog that has developed along Oregon`s Central Coast and the adjacent waters. The fog is likely so dense due to relatively high-dewpoint air moving over the cooler waters, with the fog being pushed onto the coast by light onshore flow. The fog will probably be slow to lift Monday morning, but 00z HREF shows gradually decreasing probs of dense fog after sunrise. Aviation section was recently updated below as well. Weagle && .SYNOPSIS...Onshore flow will maintain near to slightly above average temperatures through midweek. Building high pressure over the eastern Pacific and Pacific Northwest will bring a 60-70% chance for the hottest temperatures of the Summer so far by the end of the work week. && .SHORT TERM...Tonight through Wednesday...In the short term, visible satellite imagery and radar reveal a few very light showers over mainly the north Oregon Coast Range and Willapa Hills. The convection appears to be capped well below 700mb, which is limiting rainfall generation and resulting in mostly shallow cumulus clouds forming over the region. Meanwhile, visible satellite imagery reveals a weak surface trough off the Oregon coast that models agree will shift towards the coast overnight. Some HREF members and global ensemble members suggest light showers will return the coast late tonight into Monday morning. Any rainfall amounts appear most likely to be a couple hundredths of an inch or less. Another round of areas of fog will once again develop over the waters and along portions of the coast. Otherwise, an upper level shortwave trough will slowly shift eastward away from the Pacific Northwest early this week. This process will result in only a very gradual warming trend through midweek with temperatures remaining near to slightly above average during this period. /Neuman .LONG TERM...Thursday through Sunday...The global ensembles appear to be converging on a solution that results in high pressure shifting over the Pacific Northwest late in the work week into next weekend. However, there are still some differences in the magnitude of the ridge and the timing of the ridge. The net result is that there still remains a fairly wide range of possibilities for temperatures, particularly on any given day with the main uncertainty revolving around which day will be the hottest, and perhaps more importantly, the duration of the heat. The most likely scenario (generally a 60-70% probability) is that we heat up enough to experience our hottest temperatures (at least the low to mid 90s) of the Summer so far by Friday or Saturday. However, the probabilities for 100F temperatures are not insignificant and currently lie around the 40-50% range per the NBM for Friday and Saturday in the Willamette Valley. Note there is a small subset of the global ensembles that produce 100s on Friday and Saturday that keep us locked in a pattern that keeps 100s around well into the following week for a long duration heatwave. At this point, this scenario appears to have a low probability (~10-20%) of coming to fruition, but it`s not certainly not a zero percent chance of happening either. On the opposite side of the spectrum, there is a small subset of the ensemble guidance (~10-20%) that suggests ridging will be short lived and/or low amplitude enough to make 90F difficult to achieve on any given day between Thursday and Saturday. Overall, NBM temperature and RH values appear completely reasonable given the uncertainty in exactly how hot the area will get and the magnitude of the ridge (and height of the resulting subsidence inversion) so stuck with the deterministic NBM throughout the extended. /Neuman && .AVIATION...Increasing northwest flow aloft while marine stratus developing along the coast this evening expected to fill in overnight with IFR to LIFR cigs persisting through Monday morning. Chances for VFR increase to around 70-80% after 20Z Monday for coastal terminals. Expect low VFR to MVFR cigs to form inland overnight with a 30-50% chance of MVFR between 12-18Z Monday. Onshore flow increases again by Monday afternoon with breezy northwest winds expected. PDX AND APPROACHES...Predominately VFR expected through the period. Guidance suggests there is a 40-50% chance for MVFR cigs 2000-3000 ft between 12-18Z Monday morning at PDX, higher chances (60-70%) at KTTD. Northwest winds around 5-7 kt becoming light overnight, then increasing again Monday afternoon. /DH && .MARINE...Weak high pressure over the northeast Pacific with lower surface pressure over California and the Great Basin will more or less continue through the week. A weak area of surface low pressure will pass over the area through tonight, supporting initially southwest winds before turning to the west in its wake. Otherwise, expect north to northwest winds across the waters as high pressure strengthens toward the middle of next week, with the strongest winds generally off the central coast of Oregon and lighter winds farther north. Winds will generally peak in the afternoon and evening hours each day. For now have issued a Small Craft Advisory for the central zones, but may need to expand further north. Because as a thermal low develops along the northern California/southwest Oregon coast on Tuesday and strengthening/spreading north into Wednesday and thereafter. As a result will see an increase the pressure gradient along the coast and over the waters with a >90% chance that northerly wind gusts of 20-30 kt spread northward across the waters by mid week. This will in return develop steep wind driven seas of 5-8 ft with a dominant period of 7-8 seconds by late Tuesday or Wednesday. /mh -Batz && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Dense Fog Advisory until 9 AM PDT Monday for ORZ103. WA...None. PZ...Dense Fog Advisory until 9 AM PDT Monday for PZZ253-273. Small Craft Advisory from 5 PM Monday to 5 AM PDT Wednesday for PZZ253-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland