textproduct: Portland

SYNOPSIS

The overall weather pattern remains fairly progressive heading into mid-September with temperatures gradually cooling into the weekend. Saturday through the first half of Sunday a low pressure system ushers in a period of widespread rain shower activity and unsettled conditions. However, we'll quickly transition back into a sharp warming and drying trend by the early to middle portion of next week.

LONG TERM...Monday through Wednesday

Headed into the middle of next week conditions trend noticeably warmer as ensemble models begin to converge regarding the upper-level pattern. The vast majority (>90%) of ensemble guidance depicts the upper level low overhead ejecting eastward into the the Rockies and Northern Plains by Monday. A weaker secondary upper-level trough on the backside of this low looks to remain over Oregon and Washington through at least Tuesday albeit degrading day to day while a ridge of high pressure attempts to amplify over the eastern Pacific. This will allow temperatures to rebound, likely rising up into the mid 70s to low 80s across the inland valleys by Tuesday afternoon. Come Wednesday the ensemble space is now favoring (70-75% chance) the ridge of high pressure over the eastern Pacific nudging closer towards the region pushing temperatures even higher into the mid 80s across the lowlands - only 25-30% of ensembles leave weak troughing overhead by this point (thus lower temperatures than forecast). Given the average placement of the ridge, offshore easterly flow is also appearing more likely in the midweek timeframe as well - something to watch. -99/03

AVIATION...Through 06z Saturday

Largely VFR flying conditions expected with increasing chances for MVFR cigs as low stratus develops overnight. Higher confidence in persistent 60-80% chances for MVFR cigs at coastal terminals after 08-10z Fri, while the likelihood of MVFR cigs at inland terminals is generally lower, 30-60%, highest along the Cascade foothills and at Portland-area terminals after 12-14z Fri, and lower elsewhere along the Willamette Valley. There are additionally 10-20% chances for restricted vis within fog/mist within sheltered valleys. Low clouds will tend to mix out by 16-18z Fri, yielding a return to widespread VFR conditions.

Light west to northwest winds will ease to 3 kt or less overnight, before building to 5-10 kt along the coast and to around 5 kt inland by midday Friday.

KPDX AND APPROACHES...VFR conditions favored through at least 12z Fri, before chances for MVFR cigs reach 50-60% in the hours around sunrise Friday morning. High confidence in further VFR conditions after low clouds mix out after 18-19z Fri. Northwest winds ease to 2-3 kt overnight, then build to around 5 kt by midday Friday. -36

MARINE

High pressure will maintain northerly winds across all waters through at least Friday. Breezy north winds with gusts reaching 20-25 kt will continue through this evening. Marginally steep seas of 6-8 ft at 9 seconds will also continue to pose a hazard to small craft beyond 10 NM through tonight before easing. Therefore, Small Craft Advisories remain in effect through 8 PM PDT this evening across the inner water (within 10 NM) and across the outer waters (beyond 10 NM) through 8 AM PDT Friday.

Another weaker system is expected to approach the coastal waters from the north late Friday into Saturday. This will result in a southerly wind shift along with seas subsiding towards 4 to 6 ft and gusts below 20 kts. A more active pattern is expected to return next Tuesday. This system looks to bring northerly winds back into the forecast with gusts approaching 20 kt. Seas are also expected to build towards 5 to 7 ft. -42/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory until 8 AM PDT Friday for PZZ271>273.