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Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
783 FXUS66 KPQR 132232 AFDPQR Area Forecast Discussion National Weather Service Portland OR 332 PM PDT Thu Jun 13 2024 .SYNOPSIS...High pressure today will give way to a low pressure system this weekend. Friday will be the transition day with strengthening onshore flow and a slight chance (20%) of thunder along the north coast. This low pressure system will be the next weather maker bringing showers, and southwesterly flow. Cannot rule out another round of thunder north of Salem on Saturday into Sunday. Persistent showers through early next week. .SHORT TERM...Now through Friday Night...High pressure shifts inland tonight and low pressure system drops down from the northeast Pacific. The combination of these two features will increase onshore flow in the evening. The pressure gradient between Troutdale and the Dalles is around 5 mb which is indicative of strong westerly flow. Based on today`s wind speeds and how that pressure gradient compares to the forecast tomorrow, have increased wind speeds through the Columbia River Gorge around Cascade Locks and the Upper Hood River Valley. Ultimately, weather on Friday will be uneventful with near normal temperatures - though on the cooler side. Friday night the low will begin it`s advection inland which coincides with an upper level jet streak. The NBM is suggesting around a 20% chance of thunder over the north Oregon/south Washington coast and Coast Range in the afternoon. Very few models are showing a true sign of this with minimal CAPE and instability. However, the orographic lift with a slight southwesterly flow will enhance convective potential. Shower chances look to be generally confined to areas along and north of a Lincoln City- Portland-Mt St Helens line through Friday evening before more widespread shower activity spreads across the area Friday night. Model QPF remains on the light side Friday through Saturday morning. -Muessle .LONG TERM...Saturday through Wednesday...Minimal change in the long term forecast as models appear to be generally in consensus. On Saturday, the onshore flow intensifies from the southwest which may promote more convective potential. This time, the convection could be more widespread. The NBM brought in a 30-40% chance for thunderstorms in southwest Washington on Saturday. However, areas aside from the Cascades wills struggle to see enough "oomph". Decided to lower chances for thunderstorms. Even if they do occur, not looking at any major impacts. Ensembles show broad troughing from Sunday night through Tuesday. Cool temperatures and isolated scattered showers through mid-week. Once we make it through this troughing and showery weather, ridging is possible which will bring warmer and drier weather our way. -Muessle && .AVIATION...VFR conditions persist under mostly clear skies. North/northwesterly flow with winds generally below 10 kt for inland locations. Winds along the coast are slightly stronger with gusts through the evening up to to 20 kt through around 03Z Friday. A weak frontal passage around 10Z Friday will bring southerly winds to the coast along with a the 25%-35% probability for MVFR/IFR conditions to develop along the coast. Could also see some very light rain showers as well. Guidance is also suggesting that this weak front could push marine stratus around the Coast Range as well as down the Columbia River. If this happens could see some MVFR conditions (15-20% probability) stating around 12Z-15Z Friday for KPDX and KEUG. Will be leaving the MVFR conditions for inland locations out at this time as the probability is minimal. PDX AND APPROACHES...VFR under clear skies. Northwesterly winds up to 10 kts. Weak frontal passage around 12Z-14Z Friday will result in a 10-20% probability MVFR marine stratus, pushed along the Columbia River impacting areas on or near the terminal. However, will be leaving the MVFR conditions out of the current TAF package as the probability is minimal. -42 && .MARINE...Small Craft Advisory linger through this evening for zones PZZ252, PZZ253, PZZ272 and PZZ273 with northerly wind gusts up to 25 kt. Seas around 4 to 6 ft at 9 to 11 seconds through Saturday afternoon. A weak front, late tonight/early Friday will be the signal for an upcoming pattern change late Friday and into the weekend. Expect southerly winds tonight and into Friday morning, before the stronger front late Friday will bring a return to relatively stronger, westerly winds across all waters. Seas will slowly build through Saturday towards 5 to 7 ft on Sunday, before subsiding again towards 4 to 6 ft by the start of the upcoming week. -42 && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. 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