textproduct: Portland

SYNOPSIS

High pressure is still in control this afternoon across northwest Oregon and southwest Washington, maintaining a warm and dry pattern. Farther west, a closed low over the Pacific continues to consolidate and will begin to influence the region on Monday with thickening cloud cover, followed by a more reliable increase in shower coverage late Monday into Tuesday. The best signal for the coolest and most unsettled stretch remains Tuesday into Wednesday as the system moves inland. Beyond that, guidance supports a return to drier weather and a warming trend beginning Thursday and continuing into the weekend as high pressure rebuilds.

DISCUSSION...Now through Saturday

For the remainder of today, expect the warm/dry theme to hold. High clouds will continue to stream overhead from time to time ahead of the offshore system. The low levels remain quite dry, so any light echoes on radar this afternoon would likely be virga (precipitation falling aloft but evaporating before reaching the ground). Temperatures are on track for inland highs in the low to mid 70s, with the coast generally topping out in the low to mid 60s.

Late-day temperatures in the Portland/Vancouver metro and the northern Willamette Valley will depend on how much the cloud deck thins during peak heating. Earlier cloud persistence has trimmed the odds of reaching 80, with probabilities now closer to 20-40% for Portland/Vancouver and nearby communities. Tonight will stay relatively mild for April with increasing mid/high clouds; lows mainly upper 40s to low 50s.

Monday marks the shift toward a more unsettled pattern as the offshore low drifts closer and begins to draw moisture inland. Expect a noticeably cloudier day, with shower chances developing first across the southern Willamette Valley late Monday morning into early afternoon, then spreading north into the central valley and toward the Portland/Vancouver metro by evening. There is a 10% chance of a stray thunderstorm or two Monday afternoon into the evening; however dry air in the mid-levels should limit development and keep storms isolated. Rainfall amounts through Monday night still appear light overall, but confidence is highest for measurable rain in the southern Willamette Valley and the higher terrain (around a 50-70% chance). Temperatures on Monday should remain mild inland, though a touch cooler near the coast and across the central/southern valley, generally upper 50s to low 60s for the coast and upper 60s to low 70s for much of the Willamette Valley. The metro area should still manage the mid 70s, but the chance of 80 has dropped further (roughly 15-25%) given the expected cloud timing.

By Monday evening and overnight, shower coverage should increase and press farther north as a steadier feed of moisture arrives. Ensembles are in fairly good agreement on the upper low making a more meaningful eastward move Monday night, supporting broader shower coverage into early Tuesday. Totals remain modest through early Tuesday morning, with the highest amounts favored along the coast and into the southern Willamette Valley (up to about 0.15 inch). Elsewhere, many locations should stay under 0.10 inch.

Tuesday looks to be the most likely day for widespread cool, showery weather as the low comes inland. Highs Tuesday and Wednesday are expected to run in the upper 50s to low 60s. Wednesday still has some uncertainty regarding where the steadiest showers set up, tied to how quickly the trough moves east and whether one or more smaller features rotate through and enhance rainfall. One scenario brings a secondary low near Vancouver Island southeastward, which would locally boost precipitation. While the exact distribution remains uncertain, current expectations support around 0.2 to 0.8 inches in the lowlands and about 1.0 to 1.8 inches in the Coast Range and Cascades from Tuesday morning through Wednesday evening.

Conditions improve later in the week as heights rise and shower coverage diminishes. Thursday into Friday trends drier and warmer, with showers most likely to linger the longest along the Cascades into Thursday night. Temperatures should rebound into the low to mid 60s Thursday, with potential for low 70s by Friday depending on how quickly clouds thin. Saturday looks very similar to Friday in terms of dry and warm weather conditions. Overall, confidence remains low heading into next weekend regarding the timing and strength of another weather system. ~12

AVIATION

High pressure will maintain widespread VFR conditions through at least 18Z Monday with high clouds in place. Cigs will generally remain above 10-15 kft. Winds will remain light and variable around 5 kt or less for most of the TAF period, except at KTTD where breezy easterly winds continue with wind gusts upwards of 20-25 kt and at the coast where breezy southwest winds will continue this afternoon. The pressure gradient over the Columbia River Gorge is expected to weaken around and after 00Z Monday, which will bring decreasing wind speeds to KTTD.

After 18-21Z Monday, a weak front will lift northward over the area, bringing increasing southwest to west winds, lowering cigs, and increasing chances for rain showers. However, cigs are very likely to remain VFR at all terminals through 00Z Monday, with potential exceptions at the coast. KONP has a 35-50% chance for cigs below 3000 ft between 18Z Monday and 00Z Tuesday, while KAST has a 20% chance by 00Z Tuesday. Note a stray thunderstorm or two is possible around 00Z Tuesday somewhere over the Cascades, foothills and/or Willamette Valley, however the probability for thunderstorms at any given TAF site is under 10%.

KPDX AND APPROACHES...VFR conditions will continue through 00Z Tuesday with cigs remaining above 10-15 kft. East-southeast to southeast winds have developed at the KPDX terminal, sustained around 7-10 kt with occasional gusts up to 15 kt. It appears winds will subside by 00-01Z Monday, however there is some uncertainty regarding the exact end time. -23

MARINE

Benign conditions continue through the weekend. Southerly to southwesterly winds between 5-15 kt continue today with seas under 5 ft. Winds will weaken and become east to southeast by Sunday evening. Winds then remain light through early next week with seas increasing by a few feet with the arrival of a northwesterly swell, however significant wave heights are expected to stay under 10 ft.

An area of low pressure sitting off the coast will move inland late Tuesday into Wednesday, bringing showers with increasing winds and seas. However, uncertainty remains regarding exact wind speeds and wave heights. The placement and strength of the low will determine what conditions materialize across the waters. The current forecast favors a period of increasing west to west-northwest winds late Tuesday into Wednesday with wind gusts reaching 20-25 kt or stronger by Wednesday afternoon. In fact, there is a 50-80% chance for max wind gusts over 25 kt. The highest probabilities are beyond 30 NM offshore. Seas are expected to reach at least 10-12 ft by late Wednesday, however there is a 25-45% chance seas will peak over 12 ft over the northern and central outer waters. There is a 1-5% chance seas will peak as high as 15 ft, which represents the worst case scenario.

Very strong ebb currents will continue across the Columbia River Bar each morning through Tuesday. With seas expected to build a few feet Monday morning during the time of a very strong ebb current, expect seas to peak near 9 ft with steep ebb chop. Therefore, a Small Craft Advisory has been issued for the Columbia River Bar from 5 AM - Noon PDT Monday. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 5 AM to noon PDT Monday for PZZ210.