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 06Z Wednesday

VFR conditions hang on for a bit longer for all terminals before chances for sub-VFR conditions increases tonight. Mid level clouds continue to increase over the area ahead of a shortwave trough that will skirt north of SW WA and NW OR late tonight into Tuesday. Probabilities for MVFR CIGs increase to greater than 80% along the coast between 07-11z and spread inland after 12-14z. Probabilities for inland terminals are highest around the Portland metro at 50-70% between 16-20z. Low clouds are likely more SCT to BKN throughout the Willamette Valley with MVFR chances at 20-40% any given hour between 14-20z. Generally light southerly winds will gradually increase to 5-10 kt as a cold front associated with the trough moves through the region. Higher speeds at KAST up to 15 kt with gusts up to 25 kt expected.

KPDX AND APPROACHES...VFR conditions prevail with mid level cloud cover increasing. Expect MVFR CIGs to enter the metro between 12-14z with the greatest probabilities after 14z. Winds light overnight, increasing to around 5 kt from the south after 18z. -19

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 until 5 PM PDT Tuesday for PZZ210-251-271. Small Craft Advisory from 5 AM to 5 PM PDT Tuesday for PZZ252- 272.