FXUS66 KPQR 141058 AFDPQR Area Forecast Discussion National Weather Service Portland OR 357 AM PDT Sun Jul 14 2024 .SYNOPSIS...Above normal temperatures will persist for inland portions of SW Washington and NW Oregon through next weekend, though onshore flow should help to guard against more extreme temperatures. Flow aloft will turn more southerly Tuesday, potentially carrying moisture and instability northward from California. This will lead to about a 10-20% chance of thunderstorms Tuesday afternoon into Tuesday night, with the best chance being east of Interstate 5. && .SHORT TERM...Now through Tuesday...Little change is expected in the weather today versus Saturday as stable but warm west-southwesterly flow persists over the Pac NW. Strong upper level high pressure remains anchored over the Four Corners region, with a weak cutoff low festering off the coast of California. The air mass remains warmer than normal, even for mid-July, with 500 mb heights remaining in the mid to upper 580s dam and thus roughly 50-75 dam above normal. The subsidence associated with the high pressure aloft is compressing the marine layer, making it less effective at cooling the interior than it usually is despite persistent onshore flow. Weak shortwave energy dribbling through the Pac NW is deepening the marine layer a little, latest Astoria PSL Profiler data suggest the marine layer was about 1500 ft deep as of 2 AM (up from 700-1000 ft Sat afternoon), and this compares well with the satellite presentation of the marine layer along the west slopes of the Coast Range on GOES-West 10.3-3.9um fog product. As of 245 AM, stratus was knocking on the door of Kelso/Longview, and it may briefly make it into north/east portions of the PDX metro despite 06z HREF showing little to no chance of it doing so. Even if clouds do make it into portions of the PDX metro, it won't last long and will have almost no impact on temperatures later in the day. Latest 00z GFS/EC ensembles show good agreement on 850 mb temps cooling a little today, from around +20 deg C Sat afternoon to around +17 deg C this afternoon. This could provide a few degrees of cooling today, especially to areas Salem northward. "Cooling" is all relative though, as cooling a few degrees from Sat still means highs in the upper 80s to mid 90s for the inland valleys - which is still a good 10 degrees above mid-July climatological averages. Latest indications are that the marine layer will continue to deepen slightly through this evening, potentially allowing for a more intrusive push of stratus inland Monday morning. The 06z HREF does show it this time, with 30-40% chances of stratus for the Vancouver metro wrapping into the east side of Portland and southward to Aurora. This marine influence, combined with continued robust onshore flow, may be deep enough to have some impact on high inland, even giving Salem a 20-30% chance of staying below 90 degrees Monday afternoon. If so, it would be the first time Salem Airport remained below 90 degrees since July 3 - ending an 11-day streak (assuming today reaches 90 degrees, which is highly likely). The longest streak of 90+ degree highs on record for Salem was 13 days, ending on August 10, 2017. Records have been kept in Salem since 1892. If the marine influence fails to cool off Salem enough to keep them below 90 degrees Monday, NBM suggests the sky is the limit as for how long the streak may run, as each day has at least a 70% chance of reaching 90 deg F all the way through Saturday July 20. If that were to occur, the streak could go as long as 17 days or even longer. Thirteen days into the month, Salem is +9.6 deg F above normal, Portland is +8.2 deg F above normal, Eugene is +8.5 deg F above normal, and even Astoria is +5.8 deg F above normal. After the brief, relative "cooldown" today into Monday, the trend reverses sharply on Tuesday as the upper low off California dislodges and begins to lift northward. This will turn mid-level flow more southerly and potentially even southeasterly, advecting some of the hotter eastside air west of the Cascades. Unless debris from earlier convection to our south leads to significant cloud cover Tuesday afternoon, Tuesday has the potential to be the hottest day of the week as 850 mb temps rise to +23 or +24 deg C. With full sunshine and no marine influence, this could cause a few inland locations to flirt with 100 deg F Tuesday (NBM now shows a 15-30% chance of this for the Willamette Valley). If cloud cover is sufficient to hold down temps, Tuesday afternoon, it will probably come with more humidity - likely negating much benefit from the cooler temperatures. A lot will depend on the timing of the disturbance lifting northward from California - some of the more aggressive models suggest it may lift fast enough northward to allow a southwesterly marine push to cause temps to plateau in the lower 90s mid-Tuesday afternoon for Eugene and Corvallis. Other, slower models show no such relief until at least Wednesday. Another factor to consider will be convection Tuesday afternoon... guidance continues to get more aggressive in the potential for surface-based convection in the Cascades Tuesday afternoon, evolving to elevated convection over most of our interior Tuesday night. Again - timing is important here - and models notoriously struggle with the timing of cutoff lows. But the way the 00z suite of models are depicting the situation, there is some concern for the potential of numerous lightning strikes across especially eastern portions of our CWA Tuesday night - and these lightning strikes would be upon fuels that are much more prone to ignition than they were just a couple weeks ago. For now, we handled this with an area of slight chance of thunder developing over Lane County Tuesday afternoon, progressing northward as elevated convection and focusing mainly east of I-5 Tuesday night. This will obviously need to be monitored closely, as fire weather headlines may be necessary if guidance continues along this path. Weagle .LONG TERM...Tuesday night through Saturday...With plenty of cloud cover expected after a hot, somewhat humid day, Tuesday night will probably be unpleasantly warm north and east of Salem. Likely as a result, the greater Portland/Vancouver metro area, western/central Columbia Gorge, and Hood River Valley are all now showing Major HeatRisk on Tuesday into Tuesday evening. Currently our high temperatures are close to NBM guidance with highs Tuesday in the mid to upper 90s for most of these areas. If this continues, we may need to consider a Heat Advisory for these areas, but did not feel comfortable issuing that just yet given the concerns mentioned above regarding cloud cover. Areas south of Salem, as well as the coastal valleys, have a better chance of seeing substantial onshore flow Tuesday night into Wednesday as the upper disturbance will likely deepen the marine layer, potentially even pulling stratus inland behind it. If the upper disturbance indeed lifts through western Oregon Tuesday night, Wednesday, could be cooler than the lower 90s we are generally showing for the interior lowlands Wednesday afternoon. For those hoping for an end to the unusually warm weather this July, looking at the long term forecast may be a bit of a disappointment as GFS/EC ensembles show good agreement on 500 mb heights climbing back toward 590 dam Friday and Saturday. If this occurs, it would again compress the marine layer to the point where it can only effectively cool the coast and coast range, and low clouds would likely be limited to the coast. So, expect inland valleys to see highs remaining around 90 degrees on average through next weekend, likely with mild to warm nights in between. Weagle && .AVIATION...Surface high continues to impact the region, with marine stratus currently pressed along the coast. Inland terminals continue to remain VFR throughout the TAF period, with northwesterly sustained winds picking up to around 10 kt at most terminals beginning Sunday afternoon. Coastal terminals are expected to stay socked in with low stratus, lowering conditions to at least MVFR/IFR throughout the TAF period. There is about a 20-40% chance for conditions to lower to LIFR for coastal areas north of KTMK, and a 60-80% chance for KTMK and southward. Probabilities of LIFR conditions will lower to around 10-20% between 18Z Sunday to 00Z Monday. Otherwise, expect sustained winds around 10-15 kt with gusts up to 20-25 kt between 18Z Sunday to 06Z Monday. PDX AND APPROACHES...VFR conditions through the TAF period. Northwesterly sustained winds around 10 kt during the afternoon (between 00-06Z Monday), with gusts up to 20 kt. -JH && .MARINE...High pressure will maintain northerly winds across the waters for much of the next week. Winds will generally be strongest off the central coast of Oregon and lightest off the mouth of the Columbia River each day. Winds will typically peak each day in the late afternoon and evening hours, with gusts at times just barely meeting Small Craft Advisory criteria at 20-25 kt. Probabilities of 20 kt winds or greater do decrease substantially (to less than 20%) across the waters off even the central coast of Oregon towards next Tuesday and Wednesday. In the meantime, seas will primarily be a hybrid of fresh swell/wind-driven waves through the weekend. -JH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 5 AM PDT early this morning for PZZ271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland