textproduct: Portland

SYNOPSIS

The region remains under the influence of a progressive onshore flow pattern with little to no notable weather impacts through the next week. A weak frontal passage this morning will usher in occasional light rain, mainly along the coast and in higher terrain. After a return to drier and warmer weather Sunday into Monday, the forecast trends towards more widespread rainfall chances by the middle of next week, with some uncertainty remaining in rainfall timing and amounts.

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 18z Sunday

Scattered rain showers continue to track eastward across the airspace as an upper-level low moves inland over Washington State late this morning. Light rain may briefly reach the ground at area terminals, but aviation impacts are unlikely. Otherwise, largely VFR conditions persist as skies trend clearer and showers end this afternoon as the low departs to the east. Additional marine stratus will yield sct- bkn skies after 06-12z Sun, with high chances for MVFR cigs at coastal terminals and modest chances, 30-60%, at inland sites. Light southwest winds this morning will build out of the northwest to north at 5-10 kt this afternoon, then ease below 3-5 kt again after 06z Sun.

KPDX AND APPROACHES...VFR conditions favored to persist throughout the period. Light rain showers are possible through 21-24z Sat, but any precipitation would be very light and terminal impacts are not anticipated. Skies trend clearer after 00z Sun, until marine stratus builds inland from the coast near 12z Sun yielding 60% chances of MVFR cigs late in the period. Winds will build out of the northwest to 5-10 kt this afternoon, then ease below 3-5 kt this evening. -36

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.