textproduct: Portland

SYNOPSIS

Warm and mostly dry weather is expected through the upcoming weekend as high pressure builds over the region. An upper level low near California will bring wrap around moisture into Oregon, increasing the chances for showers and thunderstorms across the Cascades. Sunday is expected to be the warmest day, with highs warming into the 80s, and potentially 90 degrees in the Portland/Vancouver Metro. Those seeking relief from heat in rivers and lakes should make sure to practice water safety and wear a personal flotation device. Dry and seasonably warm weather continues through the middle of next week.

DISCUSSION...Tonight through Thursday

A weak upper level ridge of high pressure will maintain dry conditions across the area today while a few high clouds drift eastward. Afternoon temperatures are expected to warm into the mid to upper 70s, while the Portland metro maintains the highest chances (80-90%) to reach 80 degrees. Light offshore winds turn back onshore on Friday as the upper ridge shifts east and an upper level trough approaches the Pacific NW. Expect this will moderate temperatures slightly, though afternoon highs remain seasonably warmer than average, in the lower to mid-70s. As the trough approaches, increasing moisture and south-southwesterly flow aloft will allow for increasing chances for showers, mainly over the Cascades and foothills, as well as a 10-20% chance for thunderstorms later Friday afternoon and evening. Showers, and potentially (10% chance) elevated thunder, may drift northward into the Willamette Valley Friday night.

The upper trough is then expected to develop into a cutoff low offshore by Saturday as it drifts south toward the central California coast through the weekend. The flow aloft turns more southeasterly on Saturday as the upper low moves over the waters off the northern CA coast. Embedded shortwave vorticity will likely kick off a few showers and potentially (15-25% chance) a thunderstorm. Expect afternoon heating to warm temperatures back into the 70s, and again near 80 degrees in the Portland metro area. There remains significant spread in potential high temperatures depending on cloud coverage. Areas that see more sun during the day will be closer to 80 degrees, and are more likely to see increased instability as surface based CAPE could increase in excess of 1000 J/kg along the Oregon Cascades.

By Sunday, ensemble guidance depicts the upper closed low located off the coast of central California, while upper level ridging rebuilds into the Pacific NW, setting up a rex block pattern. Ensemble guidance also suggests 850 mb temperatures rise to around 15-17 degrees C. There is high confidence that Sunday will be the warmest day of the week and year, so far. In fact, there is around a 70-90% chance that temperatures exceed 90 degrees across parts of the Portland/Vancouver metro. If PDX reaches 90 degrees on Sunday (May 3rd), it would be the second earliest 90 degree temp of the season at the airport (the earliest recorded 90F at KPDX was April 30, 1998). There is more uncertainty in the forecast across southern parts of the forecast area, in part due to the positioning of the upper low and how far north the wrap around moisture surges. Showers are likely for the Lane County Cascades, along with a 20% chance for thunderstorms, while easterly flow aloft spreads lower chances of showers (10-20%) and thunderstorms (10-15%) across the southern Willamette Valley, including Eugene. Temperatures are likely to be a few degrees cooler there if clouds and/or showers do manifest.

During this late-week warmth, those seeking relief from heat in rivers and lakes may be exposed to water hazards such as swift currents and/or cold water, both of which can be life- threatening. Make sure to practice water safety and wear a personal flotation device. Moderate Heat Risk on Sunday may also affect those who are sensitive to heat.

Ensembles and the clusters continue to show some form of the rex block persisting into early next week with full-scale ridging returning by mid-week as the low over California shifts eastward. Conditions likely remain dry for most areas, while temperatures remain seasonably warm, though are most likely to cool back somewhere into the low to mid 70s. There remains around a 50- 80% chance of temps exceeding 80 degrees on Monday from Salem northward into southwest Washington. A southerly wind reversal may push marine stratus back up the coast and potentially inland by Monday morning. /DH

AVIATION

Marine stratus along the central Oregon coast south of KTMK continues to linger into the afternoon hours with MVFR/IFR conditions. A few hours of VFR conditions are possible after 20z Thu, though a 20-30% chance of IFR ceilings continues through the afternoon and evening. Marine stratus will return this evening between 03-07z Fri at KONP and slowly spreading north along the coast to KAST by 08-12z Fri. Expect mainly IFR conditions at KONP and a mix of MVFR/IFR at KAST. Inland terminals remain VFR with SCT/BKN high clouds. Latest guidance also suggests a strong enough marine push for a 20-30% chance of MVFR marine stratus pushing into KEUG between 12-15z Fri. This would improve to VFR by 18-20z Fri. Winds generally northwesterly along the coast with occasional gusts up to 20 kt through 03z Fri when pressure gradients are tightest. For inland locations, winds generally north to northeasterly and under 10 kt.

KPDX AND APPROACHES...VFR conditions with SCT/BKN high clouds through the TAF period. North to northeasterly winds around 7-9 kt become northerly and decrease to around or below 5 kts after 02-04z Fri. -03

MARINE

High pressure offshore will continue to support northerly winds across the waters through the weekend. Winds will strengthen each afternoon and evening as pressure gradients tighten over the coastal waters. Today through Friday, there is high confidence (70-90% chance) for at least occasional Small Craft wind gusts up to 20-25 kt. While the strongest gusts will mainly be south of Cape Falcon through Friday, Small Craft winds and seas may spread north of Cape Falcon this afternoon through at least early Friday. Small Craft Advisories remain in effect for the inner waters south of Cape Falcon (0-10 NM offshore) and the waters north of Cape Falcon from this afternoon to early Friday morning, while the Small Craft Advisories for the outer waters south of Cape Falcon (beyond 10 NM offshore) remain in effect through early Saturday morning. In addition, a Small Craft Advisory is in effect for the Columbia River Bar for 3-8 AM Friday due to strong ebb currents.

Seas of 6 to 8 ft are expected to persist through the week with a northwesterly swell. Mid-period swells of 12-15 seconds will result in a moderate sneaker wave threat at beaches through at least Friday. Swell periods increase to 15-19 sec over the weekend, continuing the moderate sneaker wave threat. Those participating in razor clam digs and beach recreational activities should take extra precaution.

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 3 AM to 8 AM PDT Friday for PZZ210.

Small Craft Advisory until 5 AM PDT Friday for PZZ251>253-271.

Small Craft Advisory until 5 AM PDT Saturday for PZZ272-273.