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Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
180 FXUS66 KPQR 151040 AFDPQR Area Forecast Discussion National Weather Service Portland OR 340 AM PDT Thu Aug 15 2024 .SYNOPSIS...Cool and cloudy across the area again today, with scattered showers and a slight chance of thunderstorms along the Cascades through early this evening. Widespread weeing rain appears likely across the area on Saturday as an unseasonably strong system impacts the area, with showers lingering into Sunday. Seasonably cool and cloudy weather then continues into the middle of next week. && .SHORT TERM...Now through Saturday Night...Regional radar as of early Thursday morning shows widespread showers across south- central Oregon, with some of this activity clipping parts of the Oregon Cascades as an upper level trough lifts northeastward accompanied by an influx of mid level moisture. This activity managed to produce a handful of lightning strikes along the crest in far eastern Lane County earlier in the night, but showers have mostly dissipated or remained just east of the area as they encounter a more stable, less favorable convective environment on the west side of the Cascades. Will continue to see some spotty shower activity spread north along the Cascades Crest today as the upper low continues to lift northeast across the state, with a 15-20 percent chance of thunderstorms hanging on along the Lane and Linn County Cascades through early this evening. Otherwise, locations west of the Cascades will see seasonably cool and cloudy conditions in onshore flow today. Partial clearing may allow for a few breaks of sunshine this afternoon in the Willamette Valley, but expect clouds to linger through much or all of the day in most locations, with highs generally in the mid to upper 70s. Expect little change for Friday as stable onshore flow maintains the status quo with another day of temperatures in 70s. A bigger change will arrive by Saturday as an unseasonably deep upper trough digs southward along the West Coast and brings wetter conditions across the area. Models depict a large closed low residing off the Oregon Coast by Saturday morning, with a piece of shortwave energy then swinging around the base of the trough and across western Oregon from the south during the day on Saturday. The combination of strong forcing and precipitable water values around 1.25 inches exceeding the 90th percentile of mid August climatology will produce widespread rain across the area from early Saturday morning continuing into Saturday night. Current probabilistic guidance gives most locations around a 50-60 chance to see a wetting rain of at least a quarter inch through Saturday evening, with the higher end solutions suggesting as much as 0.75-1.00" of rain in some locations by Saturday night. Most of the area will also see a 15-25 percent chance of thunderstorms during the day on Saturday, although these would obviously be expected to be accompanied by plenty of rain given the circumstances. /CB .LONG TERM...Sunday through Wednesday...Rain will be starting to taper off by Sunday morning as most of the energy associated with the upper trough shifts north of the region, but certainly could see a few showers linger into the day on Sunday and bring minimal additional rainfall amounts to the area. The Pacific Northwest will remain under the influence of broad upper level troughing centered offshore through the middle of next week, which is generally well agreed upon by ensemble guidance. As such, expect a continuation of seasonably cool and cloudy weather through the end of the period with daily highs remaining in the mid to upper 70s. The proximity to the upper level trough will yield continued chances for sporadic shower activity, but no significant rainfall or thunderstorm potential is signaled beyond Sunday morning. /CB && .AVIATION....AVIATION...An upper level trough continues to push through the region early this morning, maintaining onshore flow. Currently as of 10Z Thursday, VFR conditions inland and MVFR conditions along the coast. There is a 20-40% that CIGs along the coast will lower to IFR between 10-17Z Thursday. The one exception is KONP, with a 60-80% chance of IFR and 20-40% chance of LIFR between 10-16Z Thursday. Expect inland locations to remain VFR through the TAF period, with a 10-30% of MVFR CIGs between 12-18Z Thursday. Otherwise, expect southwesterly winds in the southern Willamette Valley, with wind direction shifting northwesterly as you move further north. PDX AND APPROACHES...Predominately VFR thresholds through the TAF period, with a 10-30% chance of MVFR cigs between 12-18Z Thursday. Northwest winds will remain well under 10 kt. /Sala && .MARINE...Expect benign conditions over the waters through early next week. Winds remain N/NW through Saturday before turning SW as surface low pressure develops. Winds are expected to remain at 10 kts or less with gusts up to 15 kts; wind-driven seas of 2 of 4 feet. -Batz && .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