textproduct: Portland

SYNOPSIS

Dry weather continues through this evening, but expect sunny skies to give way to increasing clouds as a frontal system approaches from the north. On Tuesday, this decaying frontal system drops south across northern portions of the area bringing chances for rain through late Tue night, with the highest probabilities along the Washington and north Oregon coast and Coast Range. Dry weather is favored again by Wednesday with temperatures trending warmer this weekend.

DISCUSSION...Now through Monday

Satellite imagery shows mostly clear skies over the forecast area early this afternoon. But, mid to high level clouds are expected to increase through tonight as a weather system to the north gradually shifts southward. The weak ridge of high pressure over the area will be replaced by zonal flow over the region. With increasing cloud cover, do not expect overnight temperatures to cool as much as this morning's lows.

A decent plume of moisture associated with the frontal system is currently impacting Vancouver Island, but is expected to weaken as it drops south into western Washington as upper level support quickly moves eastward across Canada. But, there appears to be enough lingering moisture to bring some rain to the north Oregon coast and possibly into the Portland Metro area and locations northward. Latest guidance suggests there is around a 40-60% chance for 0.25 inch of rainfall from Tillamook northward, with about a 50% chance for a half inch of rain in the Willapa Hills. Rain will likely be more spotty with light amounts expected across portions of southwest WA and the Portland metro, generally less than 25% chance for exceeding 0.10 inch, while conditions Salem southward remaining dry.

Widespread dry conditions return by Wednesday morning, and likely continuing through the remainder of the week into the weekend. The one caveat includes a weak weather system potentially clipping northern portions of our forecast area again Thursday into Friday. But, most ensemble members are pushing the system farther north, with only 10% or less showing rain. Temperatures remain fairly seasonable through the end of September.

By the weekend, models and their ensembles are in fairly good agreement of a more pronounced ridge of high pressure building over the region. This would maintain dry weather and potentially trend afternoon temperatures around 5-10 degrees above normal for early October. Clusters hint at more uncertainty though heading into early next week. /DH

AVIATION...Through 18Z Tuesday

Northwest flow aloft becomes westerly on Tuesday as high pressure gradually weakens over the area. Predominately VFR conditions expected today with increasing high level clouds. Stratus is likely to return to the coast by 00-03z Tuesday as a weak front begins pushing into southwest WA. Chances for light rain increase after 09-12z near KAST as conditions likely to deteriorate to lower MVFR along with a 40-50% chance of IFR conditions after 15z Tuesday. Chances for IFR near KONP also increase to around 40-50% by 10-12z Tue. CIGs are also expected to lower inland Tuesday morning, with around a 30-50% chance of MVFR after 16z Tue, mainly north of KSLE. Winds increase slightly along the coast to around 6-10 kt from the west, turning southerly by this evening and overnight.

KPDX AND APPROACHES...VFR conditions are expected through at least 15z Tuesday. Stratus likely increases Tue morning with lowering CIGs, and around a 30-50% chance of MVFR after 16z Tue. Light winds become southerly 4-6 kt Tue morning. /DH

MARINE

High pressure will continue to weaken as a frontal boundary approaches the coastal waters tonight. Southerly winds are expected to increase overnight into Tuesday morning with gusts most likely peaking around 25-30 kt, strongest across the inner waters north of Cape Falcon. A Small Craft Advisory is in effect for coastal waters north of Cape Foulweather, including the Columbia River Bar where a strong ebb current is expected this evening. Winds are expected to abruptly shift to the northwest behind the cold front as is moves across the waters later Tue afternoon and evening. Once the front passes, northerly winds return Tuesday night through the middle of the week. Another weak system may approach the northern waters from the west on Thursday, but likely remains north as it moves toward the Washington coast.

A mid-period west-northwesterly swell of 6 to 8 ft at 13-15 seconds will move through the coastal waters today through Tue night, increasing significant wave heights into the 8 to 10 ft range. Seas then gradually subside to around 4 to 6 ft later in the week. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 5 PM PDT Tuesday for PZZ210.

Small Craft Advisory from 8 PM this evening to 5 PM PDT Tuesday for PZZ251-271.

Small Craft Advisory from 5 AM to 5 PM PDT Tuesday for PZZ252- 272.