Area Forecast Discussion

SYNOPSIS

High pressure overhead is keeping northwest Oregon and southwest Washington warm and dry today. Out over the Pacific, a storm system is organizing and is expected to become a slow-moving closed low. This system is expected to bring more cloud cover on Monday, then a better chance for cooler, wetter weather by the middle of the week. Confidence is increasing that showers become more likely late Monday into Tuesday as the system begins to spread moisture inland. Wednesday still looks like the coolest and most showery day overall.

SHORT TERM...Now through Monday

Another day of warm and dry conditions expected as upper level ridging remains in control over the region. A cut-off low will be positioned well off the coast, supporting areas of surface low pressure and associated fronts offshore. However, this low will support upper level cloud cover through the day. Temperatures are expected to reach around 10 degrees above average inland with highs topping out in the low to mid 70s. Along the coast, expect temperatures 5 degrees above average topping out in the low to mid 60s. cloud cover may thin out enough over the northern Willamette Valley, mainly the Portland/Vancouver metro, for some locations to hit 80 degrees. Probabilities remain around 30-60% for Portland/Vancouver and the surrounding communities. Overnight lows will again be on the mild side with upper 40s to low 50s expected.

Monday will see a shift during the latter half of the day as the upper level low begins to slowly shift eastward toward the coast. This will bring increasing cloud cover and the increasing PoPs from south to north through the day. Temperatures will be similar to Sunday, just a tad cooler along the coast and in the central and southern Willamette Valley. Temperatures top out in the upper 50s to low 60s along the coast and upper 60s to low 70s in the Willamette Valley. Temperatures around the Portland/Vancouver metro and in the western Columbia River Gorge will likely see the mid 70s with a 20-40% chance for isolated areas reaching 80 degrees. Chances for light rain creep northward through the day, entering the southern portion of the forecast area late Monday morning and reaching the metro during the evening. -19

LONG TERM...Monday Night through Saturday

Ensembles show good agreement in the upper low making a larger move eastward Monday night, bringing a better surge of moisture into the region. Precipitation remains light with the highest totals through early Tuesday morning expected along the coast and southern Willamette Valley where up to 0.15 inches could fall. Elsewhere, totals less than 0.10 inches and likely some places remaining dry.

Confidence is higher Tuesday and Tuesday night as the upper level low moves inland and begins to transition into an open wave trough. Shower activity is expected to continue more persistently over the area. There is some uncertainty heading into Wednesday with the model ensembles differing on how quickly the trough moves eastward along with some smaller scale features that could enhance precipitation over the area. Some models show an area of low pressure over vancouver Island dropping southeast over the area on Wednesday which could help enhance precipitation totals. While rain amounts remain uncertain, expect around 0.25 to 0.75 inches in the lowlands and around 1 to 1.75 inches in the Coast Range and Cascades from Tuesday morning through Wednesday evening. Temperatures both Tuesday and Wednesday top out in the upper 50s to low 60s.

Conditions Thursday and Friday tend drier and warmer with temperatures moderating back into the low to mid 60s on Thursday and possibly low 70s on Friday. Shower activity tapers off through Thursday, possibly lingering over the Cascades through Thursday night. Uncertainty increases again heading into next weekend. -19

AVIATION

High pressure will maintain widespread VFR conditions through the TAF period with scattered to broken high clouds around 20-25 kft. Winds will remain light and variable less than 5 kt, except for easterly winds 10-15 kt with gust 20-25 kt at KTTD as the pressure gradient increases between KTTD-KDLS. Light northerly winds inland around 5 kt could be variable at times with light southwesterly winds less than 10 kt along the coast.

KPDX AND APPROACHES...VFR conditions with CIGs above 20-25 kft through the TAF period. Variable winds around 5 kt through early Sunday morning, turning more easterly after 15z Sun and remaining light. -19/10

MARINE

Benign conditions persist into early next week. Winds turn more southeasterly today but remain around 10 kt or less. Wind direction fluctuates tonight into Monday becoming more northwesterly, then southerly Monday night and then westerly on Tuesday. Winds remain light at less than 10 kt through this period.

An area of low pressure sitting off the coast is expected to move eastward during the middle of the week, bringing increasing onshore flow, seas, and showers. There is a 25-50% chance for wind gusts reaching 20-25 kt on Wednesday, mainly during the morning and afternoon for waters beyond 30 nm. Probabilities for the waters within 30 nm are generally 10-25%. Seas will also increase increase late Wednesday into the overnight hours as a northwesterly swell moves into the waters. There is a 40-60% chance for seas to reach 10 feet or greater. Given the uncertainty and the long lead time, will hold off on any headlines but marginal conditions hazardous to Small Craft are possible.

Very strong ebb currents will continue across the Columbia River Bar each morning through Tuesday. With seas expected to build slightly by early next week, a steep ebb chop may necessitate Small Craft Advisories in the hours around peak flow each day. -19/23

PQR WATCHES / WARNINGS / ADVISORIES

OR...None.

WA...None.

PZ...None.