Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
270 FXUS66 KPQR 201702 AFDPQR Area Forecast Discussion...Updated Aviation National Weather Service Portland OR 1002 AM PDT Sat Jul 20 2024 .SYNOPSIS...Hot inland today, with bit cooler weather along the coast where morning clouds will give way to sunshine. Upper disturbance offshore will lift north across the region Sat night and Sun, with some light showers and a few thunderstorms at that time. Bit cooler with mix of sunshine and clouds, and maybe a few showers on Sunday. Afterwards, increased onshore flow will maintain more comfortable temperatures for Monday and next week. && .SHORT TERM...(Saturday through Monday)... Key Messages: 1) Hot inland today, with highs in the 90s. 2) Scattered showers, and a chance of thunderstorms Saturday night into Sunday morning, first in Lane county, with that potential spreading northward. 3) Cooler air spreads inland Sunday night, with temperatures near what is expected for late July (lower 80s inland with 60s on the coast) for Monday. Typical mid-summer pattern over the region, with strong high pressure over the Great Basin states. This is maintaining warm air mass across the western USA. Overall, have seen slow warming of the 850 mb to 700 mb temperatures over past few days, with models showing 850 mb peaking today at 22 to 25 deg C. As such, with modeled soundings, seems reasonable to expect afternoon highs across the interior lowlands to reach the middle 90s. Cooler along the coast, where morning clouds and fog will break up and give way to sunshine. But, afternoon temperatures on the coast only rising to the upper 60s to lower 70s. Current forecast look on track, so no changes for temperatures, and will maintain current Head Advisory. Skies will gradually become more hazy as the day progresses, especially to south and east of Salem. This due to all the smoke that will be caught in the southerly flow aloft. Areas to east and southeast of Albany may have areas of smoke as well, as light winds will allow for smoke from the Ore Fire (near Blue River, Oregon) to drift westward, with somewhat limited dispersion. Now, bit of excitement returns Saturday night, as upper trough offshore will send a bit of energy towards the region. As it approaches, it will coincide with a plume of monsoonal moisture over the Sierras. Moisture pool is not all that deep, but think will be similar scenario that saw earlier in the week, with isolated to scattered showers developing over southern Oregon later Sat afternoon into the evening. With the south to southeast flow, will see the convective debris clouds (whats left of weakening showers over time) drifting north to northwest overnight. Models have been bit weak on depicting the thunderstorm potential. But, based on mid-level lapse rates for Sat night into Sun, seems will have a two areas of concern for higher potential of thunderstorms. First, with the convection drifting to the northwest out of south central Oregon into the Lane County Cascades, and then drifting westward over the west slopes of the Cascades and lower foothills. This activity will spread north and westward Sat night, likely reaching the Columbia River by daybreak Sunday. Again, moisture will be limited, so looks like another round of low-rainfall production from these storms. Then, as the main upper disturbance offshore nears closer to the region, will have another area of showers and few thunderstorms form over the west-central Oregon Coast Range and offshore Sat night into Sun am. So, bottom line: isolated to scattered light rain showers expected Sat evening over Lane County, with that spreading to the north and west through Sun am. Add to that, a chance of thunderstorms, though best chance will be over the Cascades and along the coast/over the Pacific waters. On Sunday, will see the showers/thunderstorms potential lift farther northward, mainly to north of a Tillamook to Salem line for Sunday am, then that shifting to the Cascades by mid-afternoon. So, mix of sunshine and clouds with lingering haze expected. But, with the clouds and bit more onshore flow, will see inland temperatures down a bit, with highs in the 80s. Onshore flow will gradually strengthen later in the day, as the upper system passes on the north and east of the region. So, will see chance of showers/thunderstorms end from west to east in the afternoon. The haze will gradually thin as well, as the south winds aloft turn more west to southwesterly and the haze is pushed towards the east-northeast. .LONG TERM...Monday through Thursday...Temperatures return to that more expected for mid to late July for next week. Upper level troughing nudges into the Pacific NW on Monday with strong onshore flow. Marine stratus more likely to push inland Monday morning, with inland highs in the upper 70s to near 80s. WPC cluster analysis remains in good agreement with model ensembles showing upper level low centered near Haida Gwaii on Tuesday, slowly shifting east into British Columbia by mid-week. NBM guidance suggests temps will likely trend closer to the mid-80s as near seasonal normals and dry weather persists next week. && .FIRE WEATHER...Only minor changes in forecasts, but overall pattern remains on track. An upper level disturbance offshore will lift across the region late tonight and Sunday. As such, will see isolated to scattered showers, with a chance of thunderstorms. Generally, looks like a 15-30% of thunderstorms over the region, with highest chance being over the Cascades/foothills, and along the coast. Now, given the forest fuels that are more conducive to ignition and carrying a fire, will maintain the current Fire Weather Watch. Even though there is a chance of similar conditions and a lightning ignition here and there across the north Oregon Coast Range and Willapa Hills, the forest fuels in those areas are not dry enough for significant fire spread. That is why those areas are not in the Fire Weather Watch. && .AVIATION...Marine stratus this morning continues to affect coastal terminals, with IFR conditions persisting at the moment. Northern coast likely clears to VFR within an hour or two (by 20z Sat), with 60-80% chance of IFR ceilings returning around 06z Sun. Southern coast sees 50-60% chance of remaining IFR throughout Saturday as stratus never fully clears. NNW winds at the coast will continue picking up going into the afternoon, with gusts up to 25 kt possible at times during Saturday afternoon and evening. Small chance of thunderstorms at times after 06-09z Sun beginning at the coast. The Willamette Valley will see chances beginning around 18z Sunday, with even lower chance than the coast. Should generally expect VFR conditions inland, though a high overcast deck is possible. PDX AND APPROACHES...VFR conditions expected through the forecast period. NW gusts to 20 kt possible Saturday evening, between 00-06z Sun. Very low chance of a stray thunderstorm at the end of the TAF period, around 18z Sunday. /JLiu && .MARINE...High pressure offshore will gradually strengthen today and with thermal low pressure on south Oregon coast, will see return of northerly winds. As pressure gradients tighten today, expect gusts up to 25 kt into Sunday. Seas 3 to 5 ft range, with a mix of variable period swell, but with gusty winds, will have choppy, steep seas. Cold water and shallow marine stratus will result in patchy, dense fog for near shore waters (visibility 1 NM or less) through mid morning. /mh && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Heat Advisory until 11 PM PDT this evening for ORZ111-112-115- 117-118-120>122. WA...Heat Advisory until 11 PM PDT this evening for WAZ205>207-209- 210. PZ...Dense Fog Advisory until 11 AM PDT this morning for PZZ210- 251>253. Small Craft Advisory until midnight PDT tonight for PZZ251>253. Small Craft Advisory until midnight PDT Sunday night for PZZ271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland