textproduct: Portland

SYNOPSIS

Dry weather continues today with temperatures near seasonable norms. Then on Tuesday a weakening frontal boundary moving into the region from the northwest brings the next chance for rain through early Wednesday morning with the highest probabilities along the coast, Coast Range, and Washington/North Oregon Cascades. Dry weather is favored again by Wednesday afternoon through the latter half of the week into next weekend.

DISCUSSION...Now through Sunday

Expect a weak ridge of high pressure to remain overhead for one final day helping to facilitate dry conditions. Ample clearing headed into the sunrise hours this morning has allowed for patchy fog to form in some of the Coast Range Valleys and sheltered pockets of the Willamette Valley locally reducing visibility. As daytime heating gets underway, any patchy fog inland will quickly dissipate by the late morning hours followed by mostly clear skies with high clouds increasing later in the day. High temperatures will once again rise into the low 70s across the interior lowlands - close to average for late September. Enjoy days like these while they last, although it's likely we'll see the return of comparable conditions by the end of the week.

Our next noteworthy change to the weather pattern arrives on Tuesday as a upper-level trough and weakening frontal boundary move into the Pacific Northwest. Precipitation chances increase substantially along the north Oregon Coast and Coast Range into southwest Washington and the North Oregon Cascades with probabilities for rainfall around 60-90% Tuesday during the day before gradually decreasing Tuesday night into Wednesday morning. Farther inland, confidence in measurable rainfall remains much lower, with only around a 10-30% chance for measurable rain (>0.01) from the Portland metro through the Willamette Valley during this time period. However, just to the north, there is a 45-70% chance of at least measurable rainfall from Battle Ground to Longview. Most inland valley locations should therefore remain dry outside of a few trace amounts of rain here and there. You'll find the best chances for completely dry weather the further south you go (generally south of Salem).

Once the frontal system passes late Tuesday night dry conditions are expected to return as Wednesday morning progresses, with dry weather holding in place the remainder of the week into the weekend. Deterministic and ensemble modeling systems still show a bit of dissonance resolving the large scale pattern Thursday into Friday, mainly regarding a weak shortwave feature which has the potential to graze the region during this time period. That said, the vast majority (85%+) of the ensemble members now keep this shortwave far enough to our north to shunt any light rainfall out of our CWA. By next weekend, most models begin to hint at a more pronounced ridge of high pressure building overhead although there is still decent uncertainty in the exact amplitude and placement of this feature which will heavily impact just how warm temperatures may get. -99/12

AVIATION...Through 18Z Tuesday

Northwest flow aloft becomes westerly on Tuesday as high pressure gradually weakens over the area. Predominately VFR conditions expected today with increasing high level clouds. IFR stratus lingering at the coast expected to dissipate by 19-20z, but there is around a 20-30% chance that broken MVFR stratus persists. Stratus is likely to return to the coast by 00-03z Tuesday as a weak front begins pushing into southwest WA. Chances for light rain increase after 09-12z near KAST as conditions likely to deteriorate to lower MVFR along with a 40-50% chance of IFR conditions after 15z Tuesday. Chances for IFR near KONP also increase to around 40-50% by 10-12z Tue. CIGs are also expected to lower inland Tuesday morning, with around a 30-50% chance of MVFR after 16z Tue, mainly north of KSLE. Winds increase slightly along the coast to around 6-10 kt from the WNW, turning southerly by this evening and overnight.

KPDX AND APPROACHES...VFR conditions are expected through at least 15z Tuesday. Stratus likely increases Tue morning with CIGs lowering, with around a 30-50% chance of MVFR after 16z Tue. Light winds become southerly 4-6 kt Tue morning. /DH

MARINE

Expect fairly benign conditions through the daytime hours today as a frontal boundary begins to approach the coastal waters. Lingering northerly winds switch southwesterly and increase by the evening. This frontal feature finally moves through the waters the second half of Tuesday. There are high chances (70-90%) of wind gusts exceeding 21 kts (Small Craft Advisory criteria) Monday evening into Tuesday for the coastal waters north of Cape Foulweather, with gusts most likely peaking around 25-30 kts. Once the front passes, northerly winds return Tuesday night through the middle of the week. A longer period west to northwesterly swell of 5-8 ft at 12-16 seconds will also move into the coastal waters late Monday through Wednesday, resulting in a moderate sneaker wave threat and increasing significant wave heights into the 6-10 ft range. While seas gradually fall into the end of the week, models hint at the arrival of another WNW swell around Saturday. -99/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 11 PM this evening to 5 PM PDT Tuesday for PZZ210.

Small Craft Advisory from 8 PM this evening to 5 PM PDT Tuesday for PZZ251-271.

Small Craft Advisory from 5 AM to 5 PM PDT Tuesday for PZZ252- 272.