textproduct: Portland

SYNOPSIS

Temperatures warm up several degrees this weekend as an upper level shortwave ridge moves over the area. Temperatures gradually cool each day next week as an upper level trough slowly drops southward from the Gulf of Alaska. Dry conditions are heavily favored through Thursday afternoon with chances for rain increasing slightly to 10-25% Thursday night into Friday.

DISCUSSION..Now through next Saturday

Satellite, surface weather, and webcam observations from early Saturday morning depicted areas of fog and low clouds beginning to develop over the Willamette Valley and greater Portland/Vancouver metro. Meanwhile, the coast and Coast Range remained overcast. High pressure has strengthened aloft this morning compared to yesterday morning, which has allowed for a relatively shallower marine layer compared to yesterday. As such, fog and low clouds should scatter out and give way to sunshine earlier in the day compared to what was observed yesterday. Locations that observe low clouds around sunrise this morning should expect skies to clear out sometime between 10 AM and 2 PM. If cloud cover lifts by the early afternoon, temperatures will rebound nicely to around 75-80 degrees over inland valleys. Breaks of sun are expected at the coast as well this afternoon, with highs around ten degrees cooler than inland areas. Given minimal change in the overall pattern, expect similar conditions on Sunday aside from temperatures trending a few degrees warmer.

Model ensemble guidance is in good agreement on the synoptic scale pattern Monday through Thursday, with all clusters depicting dry southwest flow aloft ahead of broad troughing in the Gulf of Alaska. With this pattern in place, confidence is high dry weather will continue with high temperatures mainly in the low to mid 70s each day for inland valleys and 60s at the coast. Guidance favors the warmest temperatures early in the week with conditions becoming slightly cooler later in the week.

Beginning Thursday night into Friday, chances for rain begin to increase, albeit not by much. NBM 24-hr PoPs only peak between 10-25%, highest over southwest WA and near the coast. This seems reasonable based on the latest QPF guidance from the LREF, which shows close to 70% of ensemble guidance remaining dry while the remaining 30% produce light rain amounts. The outcome will be dependent on the location and amplitude of an upper level trough that will be somewhere over the northeast Pacific late in the week. If this trough is able to push inland, at least some rain would likely return to the area. If this trough hangs offshore of deamplifies as it moves towards the coast, conditions will likely remain dry. The latter solution is currently the most likely outcome at this time. Regardless of the outcome, there are no signs of any high impact weather on the horizon. -23

AVIATION...Through 12Z Sunday

At 1130Z Saturday, marine stratus remained locked in place along the coast with high-end IFR to low-end MVFR conditions being reported at KAST and KONP.

Meanwhile, areas of fog and low clouds continue to expand across the Willamette Valley and Portland metro. This has resulted in a mix of flight categories inland, with surface visibilities fluctuating between 1/2 SM and 3 SM at KHIO, KUAO, and KSLE. Dense fog is being observed at KEUG with visibilities of 1/4 SM or lower. Low stratus with ceilings ranging between 900-1200 feet has developed from KTTD to KPDX. TAF sites observing fog this morning should generally see fog lift into a low stratus deck with LIFR to IFR ceilings later this morning, while KTTD and KPDX remain socked in with high-end IFR to low-end MVFR ceilings.

Given how shallow the developing stratus deck is, expect skies to clear out a bit faster today when compared to yesterday with skies becoming mostly sunny sometime between 18-21Z Saturday. The exact timing skies will clear out remains uncertain, hence the range provided. That said, expect skies will clear out closer to 20-21Z rather than 18-19Z at most TAF sites.

KPDX AND APPROACHES...A stratus deck with ceilings around 1200 ft has developed at the KPDX terminal this morning, and is expected to linger through 19-20Z Saturday before skies clear out thereafter and bring a return to VFR conditions. There is a 60-65% chance ceilings will fall slightly below 1000 ft by sunrise. -23

MARINE

High pressure remains over the waters through the weekend. Light winds will strengthen out of the north Saturday afternoon and evening with gusts up to 15-20 kt, strongest over the central and southern waters. Northerly winds peak in strength Sunday afternoon and evening when there is a 50-90% chance for maximum wind gusts of 21 kt or slightly stronger across the waters, with the highest chances across the inner waters out to 10 NM offshore. Given wind gusts of this magnitude are not expected to be frequent or widespread, Small Craft Advisories are not anticipated at this time. Significant wave heights will remain around 3 to 5 ft through the weekend, mainly driven by a persistent northwesterly swell with a dominant wave period ranging between 7 and 9 seconds.

Northerly winds are expected to linger Monday through Wednesday, with wind gusts generally staying under 20 kt. A long period west-northwesterly swell is set to arrive either Monday afternoon or evening, pushing seas up by one or two feet. However, seas will not be particularly steep as the dominant wave period with this swell will be around 11-13 seconds. -23/03

PQR WATCHES/WARNINGS/ADVISORIES

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