textproduct: Portland

SYNOPSIS

Going through the weekend into next week Western Oregon and Southwest Washington remain under the influence of a progressive westerly flow pattern with little to no notable weather impacts. Expect a weak frontal passage through this morning ushering in occasional light precipitation mainly along the coast and at higher terrain features. Then after a temporary return to drier/warmer weather Sunday into Monday, model guidance continues to trend towards more appreciable widespread rainfall around the middle of next week. However, beyond the broader favorable set-up for rainfall, details regarding the exact timing/amounts are uncertain.

LONG TERM...Tuesday Night through Friday

Looking into the middle of next week, ensemble guidance continues to heavily favor the development of an early fall-like, cooler and wetter weather pattern. While the general consensus of the ensembles are supportive of this pattern, the finer details such as: placement of the upper level low along with the amplitude of the upper level low is what is driving the overall uncertainty within the forecast as a whole. For example, some ensembles bring increasing rainfall as early as Tuesday morning (weaker trough feature), while others hold it off until later Tuesday and Wednesday (stronger trough). With that said, at this point almost all deterministic models and their respective ensembles show at least a wetting rain (0.25 inches or more in a 12 hour period) sometime in the late Tuesday through late Thursday night timeframe. Looking at the latest NBM probabilistic guidance, there is a 70-85% chance for greater than 0.5 inches of rainfall across the entire region, and even a 50-75% chance for greater than 1.0 inch of rainfall and a 25-50% chance for 1.25 inches over that same 48 hr timeframe.

Overall, while this mid-week system isn't shaping up to be a "fire season ender" (unless precipitation amounts trend much higher, the forecast rainfall will definitely work to heavily moderate fire weather related concerns for our side of the Cascades assuming the forecast remains on track as more high resolution models come online. /42-99

AVIATION...Through 12Z Sunday

West to northwesterly flow continues through the TAF period as the upper level trough passes overhead. North to northwest winds will increase in the afternoon to around 8-11 kt before easing around 03Z-05Z Sunday.

A weak front will move across the airspace through 18Z Saturday, bringing chances of light rain to most terminals north of KSLE between through 18Z Saturday. Expect a mixture of low-end VFR/high- end MVFR through 18Z Saturday across the airspace. Around 18Z-20Z Saturday, conditions are expected to improve towards VFR and are expected to remain there through the remainder of the TAF period.

KPDX AND APPROACHES...Generally VFR conditions expected through the TAF period. However, from 13Z-18Z Saturday expect mixture of low-end VFR/high-end MVFR along with some very light precipitation. /42

MARINE

A broad, upper level trough will continue to push eastward through today and maintain north/northwest winds across the coastal waters into early next week. A weak front pushes across the northern waters this morning with little to no impact expected. Winds are generally expected to remain around 15 kt or less, with predominately wind driven seas remain at around 3 to 5 ft.

The pattern looks to become more active by the middle of next week as a series of stronger frontal systems approach the region Tuesday into Wednesday, followed by low pressure moving southeast from the Gulf of Alaska. There is at least a 50% chance that this system brings low end gale force, southerly wind gusts in excess of 34 kt, as well as resulting in seas building towards 10-12 ft by the middle/latter part of next week. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.