Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
604 FXUS66 KPQR 021025 AFDPQR Area Forecast Discussion National Weather Service Portland OR 325 AM PDT Tue Jul 2 2024 .SYNOPSIS...Warm and dry conditions persist through mid week before a drastic warmup starts late Thursday. the high pressure ridge intensifies through the week leading to potentially dangerously hot temperatures over the weekend. The ridge will shift eastward as a broad trough stemming from the Gulf of Alaska dips into the far northeastern Pacific. While not impactful to the area, could see a return of onshore flow. && .SHORT TERM...Now through Wednesday Night...Continued zonal onshore flow persists on Tuesday and Wednesday which will lead to warm, but not exceptionally warm conditions. The high pressure ridge is continuously building but will not reach it`s peak until later in the week. Looking at the mesoscale level, the pressure gradient between Troutdale and the Dalles is around 3-5 mb which is consistent with breezy westerly flow, especially through the Columbia River Gorge near Hood River, and the east- west aligned valleys in the Cascades. Along the coast and the Willamette Valley, a weak thermal trough will cause localized northerly winds to dominate. Overall, weather is not impactful. -Muessle .LONG TERM...Thursday through Monday...A much more active pattern in store towards the end of the week as high pressure intensifies over the entire West Coast. There is a digging broad scale trough over the Gulf of Alaska, which, when paired with a trough over the northern Plains, is creating an Omega Blocking pattern. These tend to be the most amplified of the ridging. This high pressure ridge will be coupled through all levels of the atmosphere which supports significant warming. For example around the Salem area, which is trending to wards being a hot spot, 850 mb (5000 ft) temperatures are around 25 deg C. This is matched at 500 mb (18,000 ft) where temperatures are around -4 deg F. The depth of this warm air will enhance the surface temperatures and provide little relief. While still different than the heatwave in 2021, this is not dissimilar in the overall structure. Let`s dive into the numbers. Based on the most recent model data (07Z NBM and 00Z Global Model suite), there has been little movement in the probabilities for the maximum temperatures on July 4-7th. However, between the ensembles, there is still a decent amount of disagreement. For example, in Salem, the global models are showing around a 35% chance of temperatures of 105 deg F or greater, and in Eugene around 17% on Saturday. In contrast, the NBM is closer to maximum temperatures of 105 deg F is around 75% in Salem, 65% in Eugene, and 50% in Hood River. The probability of temperatures greater than or equal to 110 deg F are around 20-40% with the highest probability along the I-5 corridor and near Hillsboro. There will be a slight east wind during this time which will help usher in warmer and drier air from east of the Cascades. While the wind may provide some relief in theory, a hot wind is not necessarily that helpful in the way of cooling. Of nearly as high of concern are the overnight temperatures as relief is truly needed in order to keep HeatRisk low. On Friday morning, there is around a 50% chance of temperatures dropping below 65 degrees in the urban areas between Aurora and Corvalis. Interestingly, some of the peaks of the Coast Range will remain warm - likely due to sitting in a warm pocket aloft which can be see in forecast soundings. On Saturday morning though, those probabilities plummet - even along the coast. Around Portland- Vancouver it is around 20-35% chance of temperatures below 65 deg F, 40% in Hood River, and in the 30-40% range from McMinnville southward. Ultimately, without the overnight relief, those without access to methods of cooling may experience impacts from the heat. Heat risk remains elevated with areas of Major heat risk popping up around the northern Willamette Valley and the valleys of the Cascades on both Friday and Saturday. A major HeatRisk means anyone without effective cooling and/or adequate hydration will be impacted, especially those who are particularly sensitive to heat. Be sure to do everything you can to stay cool during the upcoming heatwave, and don`t forget to check on your neighbors and loved ones from time to time. If you must work outdoors avoid doing so during the peak heating timeframe (12-5 PM). Lastly, never leave pets or people inside a hot car, and ensure your pets stay cool during this heatwave as well. Walking your dog in the afternoon will not be a good idea as their paws may easily burn. Sunday into Monday will bring a slight degrease in temperatures, but will still remain elevated in the 90s. One thing to note is the impact that marine stratus may have. It is common that marine stratus will move in with the onshore flow following a drastic warmup like this. The stratus will aid in keeping conditions cooler and more moist. -Muessle && .AVIATION...High pressure continues, with continued onshore flow. Coastal terminals continue to see mostly MVFR cigs through the night, with marine stratus. IFR looks increasingly unlikely, and cigs should just remain MVFR through the night. Inland terminals remain VFR through the period for most terminals. Exception will be KTTD and KPDX, which could see some MVFR cigs due to stratus clouds backbuilding off the Cascades between 12z-18z. Chances of MVFR cigs during this time will be around 50-70%. VFR conditions return by 18-20z for all terminals, and northwest winds will increase to 20-25 kts during daytime hours. PDX AND APPROACHES...A switchover to MVFR cigs is expected soon, with 50-70% chance of MVFR cigs between 12-18z Tue due to marine stratus clouds building off the Cascades. Afterwards, VFR conditions return with 90% confidence, with northwest winds between 10-15 kts possible during afternoon hours Tuesday. These ease going into Tuesday evening, back to 4-6 kt. -JLiu && .MARINE...Weak high pressure over the northeast Pacific with lower surface pressure over California and the Great Basin will persist through the week. NNW winds across all waters as high pressure strengthen. Winds will generally peak in the afternoon and evening hours each day with gusts up to 25 kt. Small Craft Advisory still on track, and likely to continue through much of the week. Because the thermal surface low will strengthen through the middle of the week, will likely see (75%-90% probability) northerly wind gusts up to 30 kt for zones PZZ272, 273, 252 and 253 by the middle of the week. Seas are becoming more wind driven and building towards 7 to 9 ft, remaining around that level through the week.-42 && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Watch from Thursday afternoon through Sunday evening for ORZ104>125. WA...Excessive Heat Watch from Thursday afternoon through Sunday evening for WAZ202>210. PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ251>253-271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland