Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
830 FXUS66 KPQR 042121 AFDPQR Area Forecast Discussion National Weather Service Portland OR 221 PM PDT Fri Jul 4 2025 .SYNOPSIS...Onshore flow continues as a series of short wave, upper level troughs move over the area tonight. This will increase mixing and bring some moist air into the region. As a result of this pattern there is a slight chance (15-20%) of rain showers through this evening along the Cascades. Could see isolated thunderstorms over the ridges through the same time period. Warming and drying trends returns by the weekend and is expected to persist through at least the middle of the upcoming week. && .SHORT TERM...Tonight through Monday Night...What remains of a broad shortwave that resulted in a very active period east of the Cascades, will have the potential to bring some very light showers and maybe some thunderstorms along the Cascades through this evening. CAMs via simulated reflectivity are putting around a 15-20% probability of showers and thunderstorms through this evening. Any thunder storms would be far and few between. As Saturday and Sunday approach, expect a gradual warm up as very broad high pressure builds over the Pacific NW. At the same time, models show an upper level low developing over northern California. Over the past 24 hours, the trajectory of this low have changed significantly. Previous model runs had this low further north as well as starting to make a more north/northeasterly track. This drastic change in the models is resulting in a fair amount of uncertainty in the forecast for the middle and latter parts of the upcoming week. Which will be given more detail in the Long Term Discussion below. Overall, expect a gradual warmup through the weekend and into the start of the week. Skies will continue to clear for inland locations, but consistent onshore flow will help the coast to stay cloudy and cooler until Tuesday. /42 .LONG TERM...Tuesday through Thursday...Given that deterministic models have changed significantly over the past 24 hours, there remains a lot of uncertainty in the forecast for the majority of next week. However, if the current forecast holds, the upper level low mentioned above is expected to move inland near the OR/CA border. If this happens, the warmest day of next week looks to be on Tuesday. The cause of these slightly cooler temperatures is the fact that the California low will help to tamp down some of the hotter 850 mb temperatures originating in the Great Basin. Models are showing 850 mb temperatures in the 13-15 C range which is about 5 degrees C cooler than yesterday. So, with that in mind, let`s take a look at the possible daytime high spreads across our CWA on Tuesday. Will look at the most likely 25th-75th percentile. Note: Temperatures in Degrees Fahrenheit Portland/Vancouver: 89-95 Salem: 94-98 Eugene: 91-97 Hood River: 89-96 Astoria: 68-70 Battle Ground: 86-92 Raymond: 71-78 Kelso/Longview: 85-93 Newport: 68-70 Transitioning into Wednesday, the low will continue to trek eastward into Idaho. This will result in increasing northwesterly flow and bringing in cooler, moister air. Given the significant change in the models over the past 24 hours, have chosen to hold with the NBM. The NBM has leaned into a slight cooler solution into the latter part of the week. Will continue to monitor and update as needed. /42 && .AVIATION...An area of low pressure aloft moves over NW Oregon through this evening before shifting east of the Cascades by Saturday morning. Southeasterly flow aloft will maintain high cirrus through this afternoon from convection east of the Cascades today. Predominately VFR conditions expected inland through at least 12z Sat. Marine stratus along the northern coast this morning will likely (60% chance) persist through much of today, with potential breaks in the clouds and possible (40% chance) improvement to VFR between 20-02z. Then, marine stratus expected to surge back onshore tonight with MVFR cigs after 02z Sat. PDX AND APPROACHES...VFR with broken high clouds expected through much of tonight. There is a 20-30% chance of MVFR stratus pushing up the Columbia River after 12z Saturday morning. Northwest winds expected to increase this afternoon to around 10 kt. /DH && .MARINE...Surface high pressure offshore will maintain north to northwest winds across the coastal waters through the weekend, and continuing into early next week. Pressure gradients over the waters increase Saturday and Sunday as the thermal trough strengthens over the south Oregon coast. This will bring stronger northerly winds with diurnally driven gusts up to 20-25 kt each afternoon and evening. A similar pattern is likely on Monday as well. Seas are also expected to remain fairly consistent at around 3 to 6 ft through early next week. /DH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland