Marine Weather and Tide Forecast for Carson, WA

SHORT TERM
Now through Wednesday night...This morning satellite and radar observations show moisture associated with our next potent weather disturbance streaming into far northern Washington and Vancouver Island, the first signs of a rather significant pattern change anticipated to occur later today into the middle of the week. the robust upper-level low helping to steer this frontal boundary is slated to continue its dive out of the Gulf of Alaska bringing a swath of widespread precipitation and eventually cooler conditions. QPF values have changed little with the latest forecast guidance amounts from today through Wednesday generally ranging from 0.75 to 1.25 inches across the Willamette Valley and Portland metro, 1.00 to 2.25 inches along the coast and Coast Range, and 1.10 to 2.30 inches across the Cascades. However, for the latter region, especially at pass level, the precipitation will likely be falling as snow for a good chunk of this event.

Speaking of snow the incoming system looks to bring roughly 10 to 22 inches of snowfall to the Cascades starting this afternoon through early Thursday morning mainly above 3500-4000 ft although, snow levels likely bottom out around 2000-3000ft on Wednesday just behind the front - higher elevation, more impacts. The latest NBM probabilities show a 60-90% probability of 12 inches or greater snowfall over a 48 hour period from today through Thursday afternoon at Santiam level and Willamette Pass, slightly lower (30-40%) at Government Camp. Overall the highest amounts likely fall in the high Cascades from Marion to Lane County. The period to watch as far the greatest travel impacts are will be from 4-10am on Wednesday when snowfall rates in the heavier precipitation bands right along the front may exceed 1-1.5 in/hr. So, if you are planning to travel over the Cascades passes, particularly Wednesday morning, please prepare for winter-like travel conditions.

One other interesting facet of the forecast we're watching is the potential for 1-3 hr period of dynamic cooling temporarily punching snow levels into the 500-1500ft range near sunrise Wednesday morning. This has been a feature hinted at by the last several runs of the higher resolution guidance like the HRRR and NAMNEST right on the back edge of the cold-frontal boundary where persistent heavier precipitation combined with cold air just above the surface (-5C at 850mb) could facilitate this process, assuming all the proper variables align. The areas of particular interest are southwest Washington into the Portland Metro and the higher coast range/Cascade valleys. If this were to occur elevations as low as 500ft could see a rain/snow mix or "chunky rain" for an hour or two with no impacts. The chances for a light slush-up in the grass gets higher once you reach 1500ft, particularly in the Cascade foothills/valleys, but due to the warm antecedent conditions most impacts remain 2000ft+.

Progressing through Wednesday a showery post frontal environment quickly overtakes the region coupled with increasing instability during the afternoon thanks to the core of the upper level low moving overhead. Most models show Convective Available Potential Energy (CAPE) values peaking around 200-500 j/kg, which is decent for our post-frontal environment weak thunderstorm set-ups. The main time period of focus is 11AM to 7PM on Wednesday when heating between shower bands may be maximized. Given this information, there is a 15-25% chance for thunderstorms across the majority of our CWA Any of these pop- up thunderstorms may produce moderate to heavy rain, infrequent lightning, small hail/graupel, gusty and erratic winds. So, when thunder roars, go indoors or when you see a flash (of lightning), dash inside. With the loss of daytime heating thunderstorm chances decrease Wednesday night although showers likely persist. -99/42

LONG TERM
Thursday through Monday...By Thursday, the upper level low and associated front have left the CWA, but will leave the region under cooler conditions with increasing clearing.
Thursday into Friday looks to have overnight lows below normal bottoming out in the mid 30s across the lowlands and spelling a potential for frost. Below freezing temperatures are even forecast for the higher coast range/Cascade valleys, including the Hood River Valley. Currently, the Portland/Vancouver Metro there is a 10-40% chance of overnight lows at or below 36 degrees F. From the Portland/Vancouver Metro areas southward towards Salem and Eugene, OR, expect a 45-85% chance of overnight lows at or below 36 degrees F. For locations north of Vancouver, expect a 50-75% chance of overnight lows at or below 36 degrees F. Additionally, there is a 80-95% chance of at least freezing temperatures in the Upper Hood River Valley for Wednesday night into Thursday morning. Similar conditions may develop again Thursday night into Friday morning, though with slightly lower probabilities (only 10-30% lower).

Looking towards the weekend, temperatures gradually warm, reducing these morning frost concerns. Ensembles show a shortwave ridge of high pressure moving quickly overhead on Saturday, but being quickly followed by another low pressure system on Sunday originating from the Gulf of Alaska. Now, beyond Sunday and into the start of next week, WPC Cluster Guidance is favoring this low holding just off the OR/WA coast or moving over the inland Pac NW, which means that cooler and moister conditions are favored for the start of next week. -99/42



AVIATION
Conditions are generally VFR across the region this morning with increasing southerly flow ahead of a quickly approaching cold-frontal system. Chances for MVFR CIGs along the coast quickly increase to 70-80% by 14-16z this morning as rain moves overhead with a 40-60% chance for IFR conditions during the afternoon and evening. Inland terminals will hold on to VFR conditions a bit longer with MVFR probabilities increasing after 18z to 40-60% as rain increases, but CIGs may fluctuate until the later afternoon and evening when more uniform cloud cover is expected to move in overhead and MVFR conditions likely settle in.
Along with rain, winds will increase also increase today with gusts along the coast reaching to 25-35 kt after 18z and 20-25 kt for inland locations.

KPDX AND APPROACHES...VFR conditions likely persist through the morning hours however stratiform rainfall increases midday into the mid afternoon. CIGs are expected to respond in-kind with chances for MVFR conditions rising after 16-18z - probabilities between 70-80% after 20z. Southerly winds also increase during the afternoon with gusts between 20-25 knots persisting through the evening. -99

MARINE
The focus today remains on the arrival of a robust cold-frontal boundary slowly spreading across the waters north to south. As a result expect southwest winds to increase with gusts up to 30 kt across all coastal waters. Winds are expected to be strongest this afternoon into early Tue evening. During this time, there will be around a 3-6 hour period when gusts could (30-50% chance) exceed 34 kt, producing marginal Gale Force wind gusts. A Small Craft Advisory is in effect across the inner and outer waters including the Columbia River Bar starting this morning. The increased wind waves are expected to build seas to around 7 to 10 ft with a period of around 8-10 seconds. Seas remain steep and choppy through Tue night as well.

Behind the frontal boundary Tuesday night winds abruptly shift northwest with gusts increasing back up to 20-25 kt as an area of low pressure drops along the Canadian coast toward the Puget Sound. This will also bring a 15-25% chance of thunderstorms over the waters through Wed evening. Seas are expected to persist at around around 8 to 10 ft on Wednesday, building slightly to around 9 to 11 ft Wed night as a northwest swell moves through the waters. Given these seas the Small Craft Advisory was extended out into Thursday morning. High pressure then builds over the waters later this week as northerly winds return and seas gradually subside to around 3 to 6 ft Friday into Saturday. There is potential for another weather system to impact the waters the second half of the weekend into early next week likely increasing winds and seas yet again. -99/DH

PQR WATCHES/WARNINGS/ADVISORIES
OR...Winter Storm Warning from 5 PM this afternoon to 5 AM PDT Thursday for ORZ126>128.
WA...Winter Storm Warning from 5 PM this afternoon to 5 AM PDT Thursday for WAZ211.
PZ...Small Craft Advisory from 8 AM this morning to 5 AM PDT Wednesday for PZZ210.
Small Craft Advisory from 5 AM early this morning to 5 AM PDT Thursday for PZZ251-271.
Small Craft Advisory from 8 AM this morning to 5 AM PDT Thursday for PZZ252-253-272-273.