Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
963 FXUS66 KPQR 220424 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 924 PM PDT Sat Sep 21 2024 Aviation Discussion updated... .SYNOPSIS...A weak front will push across the region Sunday/early Monday, but little if any rain expected.High pressure rebuilds over inland Pac NW, bringing much warmer temperatures with weak offshore flow on Tuesday. Then, back to more typical late September temperatures for the middle through through latter part of next week as onshore flow returns with the potential for precipitation for the end of next week. && .DISCUSSION...Tonight through Saturday...Overall a warming and drying trend will continue through the weekend and into the middle of next week. A very weak frontal passage will scrape across the northern portions of our CWA Sunday/Monday morning, but little to no rain is expected with the frontal passage. After the front, high pressure will return as the dominant synoptic feature and will result in temperature peaking on Tuesday with daytime highs in the 70s along the coast, upper 80s to low 90s for inland locations and upper 70s to mid 80s for the Cascades. NBM probabilities are showing around a 15% probability for the Portland/Vancouver Metro area reaching 90 degrees F, but as you progress further south within the Willamette Valley that probability increase towards 40% for Eugene, OR. It should be noted that this warm up will be very short lived as Wednesday highs are expected to be in the 60s to 70s. What else that should be noted is that their is the potential (85%-95% probability) of weak offshore flow on Tuesday. It should be noted that the overall synoptic pattern is sub-optimal for a stronger wind event as guidance. The upper level ridge axis is expected to move quickly inland with a weak thermally induced surface trough briefly developing. As a result, forecast offshore pressure gradients remain rather weak around -1mb to -3mb from TTD-DLS and -3mb to -6mb from OTH-GEG. As such, ensemble members are mostly clustered around maximum wind gusts in the 20-25 mph range through the Gorge and over higher Cascade slopes, with the a few of the higher end members maxing out around 30-40 mph in those locations. There still is some variability within the models so, we will continue to monitor and adjust the forecast as needed. Also, the bulk of model guidance currently points to a lower end of the wind range as well as maintaining a short lived offshore flow event. Beyond Tuesday, GEFS,ENS and other ensembles to include the NBM, are showing a cooling trend returning. This will bring temperatures more inline with late September normals. As the end of next week approaches, models are also showing precipitation coming back into the forecast, with two slugs of moisture coming into the region Wednesday and Thursday. While these aren`t looking to be season enders, these systems could be the vanguard for the fall/autumn season. Only time will tell if this becomes true or not. /42 && .AVIATION...Weak northwesterly flow into Sunday as a weak front moves southeast towards the PNW. This front is expected to bring at least MVFR conditions along the coast by 12-14Z Sunday. Chances of stratus lowering to IFR range between 30-60%, highest at KONP. There are chances of LIFR CIGs along the coast as well, with chances between 20-30% at KONP, and 10-20% at KAST and KTMK. Conditions look to improve back to VFR by 16-19Z Sunday. Onshore winds will push stratus into the coastal valleys, but not far enough to move into the interior valley (chances of MVFR CIGs less than 15%). Expect VFR conditions inland through the TAF period. PDX APPROACHES...Prevailing VFR conditions with light northwesterly winds. Clear skies, then high clouds by 18Z Sunday. -Hall && .MARINE...High pressure across the NE Pacific with low pressure near the California coast will maintain north winds across the waters through Tuesday.The northerly surface pressure gradient will strengthen across the waters, mainly south of Cape Falcon this afternoon supporting a marginal small craft advisory. A fetch associated with a low in the west Pacific near 48N 170E will produce a building NW 7 to 9 ft swell across the waters Tuesday and Wednesday. A front associated with this low will move across the waters Wednesday and Thursday for a period of south to southwest winds. Another low currently developing near Japan will strengthen as it moves across the Pacific towards the Pacific NW through the week. Models are forecasting a larger NW swell with potentially 13 to 15 ft seas in the Oregon waters Friday. ~TJ && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 10 PM PDT this evening for PZZ272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland