Molalla, OR 97038 Weather

Updated aviation discussion and PQR WATCHES/WARNINGS/ADVISORIES.

Synopsis

Seasonably cool and showery conditions continue through the workweek as repeated weather systems support persistent chances for rain. A drying trend beginning Friday may bring better trick-or-treating conditions by late Saturday. Could see benign conditions into early next week before the pattern becomes more unclear by the middle of next week.

Morning update

Winter Weather Advisories have been issued above 4500 feet for the north Oregon and south Washington Cascades through 11 PM this evening, and the Marion/Linn/Lane County Cascades through 5 PM. These locations above 4500 feet have been receiving accumulating snow the last couple days, and snow showers will continue throughout today. Given that some of our forest roads above the main passes are still open this early in the season and there may be some hikers or backpackers out, this is more an impact-based advisory issuance rather than for advisory-level snow amounts. Those traveling through the Cascades should take precaution. -10

Short term

Today through Friday Night: A wet and cool pattern is expected to continue through the work week as several weather systems impact the region. An upper level low over western Canada continues to drop south toward the PacNW, which will continue to send a series of embedded shortwaves into the region as the parent low slowly treks southward through the end of the workweek. This will keep the probability of precipitation elevated through the remainder of the work week with new rainfall totals from 5 AM Wednesday to 5 AM Thursday for the coast and coast range look to pick up around 0.15-0.35 inches, inland valleys around 0.05-0.20 inches and the Cascades picking up around 0.15-0.60 inches. Higher amounts are expected in the northern OR Coast Range, southern WA coast range with the highest accumulations expected in the northern OR Cascades and southern WA Cascades. There is a 15-35% chance that areas in the SW WA and N OR Cascades could receive and inch or more of rain during this time frame.

850 mb temperatures are expected to drop through Wednesday as the upper level low brings cooler air with it. This will drop snow levels towards 4000-4500 feet by this evening and towards 3000-4000 ft by Thursday morning. This could bring snow to some of the mountain passes which could create dangerous travel conditions through the Cascades. For travel around Mount Hood, including Government Camp, chances for 1 inch or more of snow from early today through Thursday morning are 35-45%. During the same period, chances are highest for Santiam Pass 75-85%. However, the bulk of the precipitation is not expected to coincide with the colder temperatures/lowest snow level.

Friday into Saturday is looking to be a transitional period as models have the aforementioned Canadian low being contested by a broad, upper level ridge developing over the Great Basin. Ensemble guidance is showing that the Great Basing ridge will keep the majority of the Canadian low just offshore. Thus bringing a bit of a reprieve to the precipitation for Friday. The NBM for example, is maintaining a high PoP, low QPF forecast which means we are likely to see rain but it will be light. However, there remains some uncertainty as to the exact placement of both the Canadian low and Great Basin high. For example if the Canadian low is able to push further inland, then precipitation will return to the forecast for the latter part of the week and likely continue into the weekend. On the other hand, if the Great Basin ridge is able to build, then a drier forecast would be expected. /42

Long term

Saturday through Tuesday: Ensembles and cluster analysis continue to point towards a drier pattern for the weekend, but models are suggesting that the aforementioned Canadian low, will come onshore Saturday afternoon. Again ensemble guidance is continuing to maintain a low/moderate PoP (10-25%) with little to no QPF as the low moves onshore. Looking beyond Saturday night and into early next week a shortwave ridge looks to develop late Sunday/early Monday, which will bring a return of relatively warmer daytime highs and dry conditions for the start of November. Exact timing and details of this progression still vary among the models. /42-19

Aviation

Through 18Z Thursday: At 1730Z Wednesday, a mix of VFR/MVFR ceilings were being observed across the area with scattered rain showers and breezy south to southwest winds. VFR ceilings are most predominant. Expect this trend to continue through this evening, albeit with showers decreasing in coverage after approximately 00Z Thursday.

Winds become relatively lighter tonight with cloud cover becoming scattered to broken. However, chances for rain showers after 10Z Thursday have increased, except from KSLE to KEUG. Probabilities for fog and surface visibilities below 1 SM are generally less than 10% through tonight and tomorrow morning, except 20-30% at KHIO and KEUG. Overall coverage of fog should be fairly patchy, forming in sheltered valleys where winds turn calm and cloud cover clears for a long enough duration of time. Confidence for at least a brief period of fog is highest at KEUG.

KPDX AND APPROACHES: Occasional rain showers will persist through 00-02Z Thursday, bringing a mix of VFR/MVFR flight conditions, albeit predominately VFR. Trending VFR most of tonight, before chances for showers increase again towards 10Z Thursday. Suspect a mix of VFR/MVFR ceilings will occur tomorrow morning, but predominately VFR as chances for ceilings below 3000 ft at any given tomorrow are only around 5-15% between 12-17Z Thursday and should be mainly tied to passing showers. -23

Marine

A low pressure system will keep conditions active across the waters through the middle of the week. This system is currently producing winds with gusts up to 25 kt and seas of 7-10 ft at 10-12 seconds. As a result, the current suite of Small Craft Advisories will be maintained through at least this morning. The aforementioned low will continue to move inland which will result in both winds and seas slowly subsiding through the morning and into the late afternoon. Therefore, the Small Craft Advisories are set to drop from south to north as the day progresses. Overall conditions will continue to subside Thursday into Friday with gusts below 15 kt and seas subsiding towards 4-6 ft at 10-12 seconds through the weekend. Looking towards the start of next week, another low pressure system from the Gulf of Alaska looks to bring building seas and winds back into the forecast, which could result in Small Craft conditions for the start of next week yet again. /42

Watches, warnings and advisories

OR: Winter Weather Advisory until 11 PM PDT this evening for ORZ126.

Winter Weather Advisory until 5 PM PDT this afternoon for ORZ127-128.

WA: Winter Weather Advisory until 11 PM PDT this evening for WAZ211.

PZ: Small Craft Advisory until 11 AM PDT this morning for PZZ210-251-252.

Small Craft Advisory until 5 PM PDT this afternoon for PZZ271- 272.