textproduct: Portland

SYNOPSIS

A cold front moving through the area will bring widespread rain early this afternoon. Rain transitions to showers late this afternoon/evening with a 10-20% chance for thunderstorms. Chances for showers and thunderstorms continue on Tuesday. Warmer and drier conditions return Wednesday to Thursday, but wrap-around moisture will return chances for showers across the Cascades on Thursday and Friday. Cooler temperatures return at the end of the week.

DISCUSSION...Today through Sunday

Radar, satellite, and surface observations as of early Monday afternoon depicts widespread rain along the coast and Coast Range as a cold front associated with an upper-level trough pushes through the area. Between now and 3 PM, this band of rain should spread into the I-5 corridor as the front pushes further inland. Rainfall amounts will be light and non-impactful, while southerly to southwesterly winds will be breezy as the front pushes through. Surface observations were showing wind gusts up to 30 mph along the coast. As this front moves inland, expect wind gusts to increase up to 20-25 mph along the I-5 corridor, and stronger gusts up to 30-40 mph through the central Columbia River Gorge, Upper Hood River Valley, and higher terrain across the Cascades.

After 2-4 PM today, rain transitions to post-frontal showers as the front exits eastward. Cooler air filtering in aloft with the incoming trough will lead to increased instability across the area. Based on REFS guidance and sounding profiles, CAPE appears limited (50-110 J/kg) this evening with the highest CAPE values along the coast. Therefore, there is a 10-20% chance for thunderstorms through this evening, with the highest chances along the north OR/south WA coast, inland southwest Washington, and the Portland/Vancouver Metro Area. Any passing thunderstorms may produce lightning, brief heavy downpours, erratic winds, and/or small hail.

Cool and showery conditions prevail on Tuesday as the upper- level trough turns into a closed low over Oregon and gradually shifts southward toward California/Nevada. Will see another 10-20% chance for thunderstorms on Tuesday, mainly between 11 AM-5 PM. Chances are better along the I-5 corridor for thunderstorms Tuesday afternoon compared to this afternoon as CAPE values are forecast higher around 100-200 J/kg.

Temperatures rebound Wednesday and Thursday as high pressure re- builds over the area and the aforementioned low drops down into the Great Basin. High temperatures are forecast near or slightly above normal along the I-5 corridor for this time of year, warmest from the Portland/Vancouver Metro northward. Chances for exceeding 80 degrees across the Portland/Vancouver Metro on Wednesday are around 15-25%, and 30-50% on Thursday. The rest of the interior valleys have a 20-30% chance for exceeding 80 degrees on Thursday. While Wednesday remains predominately dry and warm, will note that wrap-around moisture will result in a 30-50% chance for showers and a 10-20% chance for thunderstorms across the Cascades on Thursday. Areas west of the Cascades still trend dry on Thursday, but can't rule out a stray shower or two moving into the I-5 corridor. If shower or thunderstorm coverage is more widespread, cloud cover could result in slightly cooler temperatures (lower 70s as opposed to upper 70s and low 80s across interior valleys).

Friday into the weekend, temperatures cool down as ensemble guidance suggests another trough moving in from the northeast Pacific and lowering 500 mb heights. Chances for showers remain on Friday due to lingering wrap-around moisture from the Great Basin low, however, conditions dry out over the weekend due to limited moisture despite the troughing. -10

AVIATION

MVFR along the coast and VFR inland as a cold front continues to move inland. Light rain continues to move inland while transitioning to showers along the coast. Conditions should maintain low-end VFR for the most part, possible high- end MVFR in a heavier band of rain. Mix of south and southwesterly winds expected through the TAF period. Expect continued winds around 14-17 kt with gusts up to 20-25 kt at the coast until 03-06Z Tue, while inland will see winds increase to around 10-14 kt with gusts up to 20 kt through 03Z Tue. Additionally, there is a 15-30% chance of isolated thunderstorms through the evening, with most terminals at the low end of this probability range. Expect an isolated thunderstorm or two rather than widespread thunderstorms with this system.

KPDX AND APPROACHES...Expect VFR conditions through the TAF period with CIGs dropping closer to 5 kft this afternoon. Southerly winds will increase with gusts up to 20 kt through 03Z Tue. There is a 20-40% chance of MVFR CIGs with any passing shower today. Rain in the area with gusty winds may temporarily reduce VIS at times. 15-20% chance of isolated thunderstorms through the evening. -19

MARINE

A cold front continues to move east of the waters, leading to decreasing southerly winds through the day. Small Craft Advisories continue across all waters for steep and hazardous seas hazardous to small craft through 5 PM. A Westerly swell moves into the waters later this afternoon and evening, pushing seas in the mid teens around 14-16 seconds. Have upgraded the Hazardous Seas Watch to a Warning for all waters except the Columbia River Bar where conditions are more marginal. The Warning continues through 11 AM Tuesday and at the same time, the Small Craft Advisory for the Columbia River Bar has been extended for the same time frame. There is a 10-20% chance for thunderstorms across the waters this evening. Any passing thunderstorms may produce lightning, brief heavy downpours that reduce visibility, erratic winds, and/or small hail.Seas subside to 10-12 ft by Tuesday evening and gradually subside into Wednesday. -19

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory until 11 AM PDT Tuesday for PZZ210.

Small Craft Advisory until 5 PM PDT this afternoon for PZZ251>253-271>273.

Hazardous Seas Warning from 5 PM this afternoon to 11 AM PDT Tuesday for PZZ251>253-271>273.