Marine Weather and Tide Forecast for Seaside, OR

SHORT TERM
Now through Tuesday...This afternoon, a broad upper-level low that supported recent convective activity is shifting inland across the northern California, near the OR/CA border. In its wake, flow aloft will gradually shift to onshore west-northwesterly flow overnight, resulting in cooler temperatures and a transition away from thunderstorms. Current observations show scattered showers lingering over parts of southwest Washington and northwest Oregon, with additional bands expected through the remainder of today as wrap-around moisture persists.

Temperatures today have cooled compared to recent days, with inland highs generally in the 50s to low 60s. Shower probabilities remain elevated, ranging from 60-95% across most of northwest Oregon and elevated terrain in southwest Washington. Lower probabilities, around 20-40%, are expected along the north Oregon and south Washington coast due to the upper-level low continuing to distance itself as it moves southeastward.

On Monday, a weak shortwave is expected to move into the region from the northwest, maintaining widespread shower activity.
Precipitation probabilities remain in the 60-90% range, highest across the Cascades, Coast Range, and foothills where orographic lift will enhance precipitation. By late Monday into Tuesday morning, a transient ridge begins to build overhead.
While this may not fully eliminate shower chances, it should lead to decreased coverage across the interior lowlands, with activity becoming more confined to elevated terrain such as the Coast Range, Cascades, and adjacent foothills.

Attention then turns to an approaching Pacific frontal system.
By Tuesday afternoon, increasing southerly flow ahead of the front will bring locally breezy conditions, with gusts generally in the 20-35 mph range, strongest along the coast. The bulk of precipitation and impacts associated with this system are expected to hold off until Tuesday night into Wednesday.

LONG TERM
Tuesday night through Saturday...Ensemble and deterministic guidance remain in strong agreement that a cold front will sweep through the region Tuesday night into Wednesday morning (arriving any time between 11 PM Tue and 11 AM Wed), bringing widespread precipitation. Confidence has increased in moderate rainfall amounts, with 24-hour totals generally ranging from 0.7 to 1.2 inches across the Willamette Valley and Portland metro (10-30% chance to exceed 1.2 inches), 0.9 to 1.7 inches along the coast and Coast Range (5-15% chance to exceed 1.7 inches), and 0.9 to 2.0 inches across the Cascades (10-20% chance to exceed 2.0 inches).

Cooling temperatures along and behind the front will lower snow levels to near or below Cascade pass elevations, increasing the likelihood of winter travel impacts. Current probabilistic guidance indicates a 60-90% chance of 12+ inches of snowfall at the Cascade passes between Tuesday afternoon and Thursday afternoon (48 hours). As a result, a Winter Storm Watch has been issued for heavy snow possible above 3500 ft in the South Washington Cascades, North Oregon Cascades, Cascades of Marion and Linn Counties, and Cascades of Lane County from 5 PM Tuesday through 5 AM Thursday. Total snow accumulations between 9 to 18 inches possible, with the highest amounts in the high Cascades from Marion to Lane County. Roads, and especially bridges and overpasses, will likely become slick and hazardous, and winds may gust as high as 45 mph.

In addition to Cascade snowfall, cooler and potentially clearer conditions behind the system will bring renewed frost concerns to the interior valleys. The first opportunity appears Wednesday night into Thursday morning, with a 60-80% chance of frost across much of the interior lowlands, except for a 25-45% in the metro and at the coast. Additionally, there is a 60-90% chance of freezing temperatures in the Upper Hood River Valley. Similar conditions may develop again Thursday night into Friday morning, though with slightly lower probabilities (10-20% lower). While frost potential starts for most areas Thursday morning, the Upper Hood River Valley will have frost potential sooner and longer, with a 25-65% chance of frost Wednesday morning, 85-95% Thursday and Friday morning, and 60-80% Saturday morning. Chances of frost lower to 10-20% by Sunday morning for the Upper Hood River Valley. Temperatures gradually warm into the weekend, reducing frost concerns. ~12

AVIATION
Light scattered showers continue across NW OR and SW WA into Sunday evening, slowly dissipating from the interior lowlands between 04-10z Mon. Showers continue beyond this over the Cascades and Coast Range. Along the coast, expect mainly MVFR conditions, falling to IFR/LIFR at times in showers. Predominately MVFR conditions at valley terminals are likely to transition to mainly VFR after 21-22z Sun, though expect fluctuations between VFR and MVFR in showers. Guidance indicates widespread MVFR cigs return to valley terminals after 04-08z Mon. Conditions inland should improve to VFR by 18-21z Mon. Winds remain relatively light less than 10 kts, mainly westerly along the coast and southerly inland, shifting westerly after 21z Sun - 03z Mon.

KPDX AND APPROACHES.. MVFR conditions persist, should become VFR by 22-23z Sun. However, scattered showers through the evening could produce brief periods of MVFR/IFR cigs or vis. Showers dissipate by 04-06z Mon, then widespread MVFR cigs return.
Conditions should improve to VFR by 18-20z Mon. Southerly winds around 8-10 kts, becoming westerly after 03z Mon. -03

MARINE
North to northwesterly winds are expected to continue into Monday, albeit not particularly strong with gusts staying below 20 knots. Significant wave heights hold in the in the 4 to 7 foot range through this time period as well. Focus then turns to the next weather system that will caused increased winds and seas Tuesday and Wednesday. There is high probability (85-95% chance)
in Small Craft Advisory wind gusts greater than 21 kts with a 10-25% chance of a brief period of Gale Force gusts over 34 kts as a robust cold front passes through the waters Tuesday afternoon and evening. An increasing westerly swell along with the winds will cause seas to build to around 8-11 feet at 9-10 seconds.
Winds begin decreasing Wednesday while the seas remain elevated, decreasing on Thursday. -03

PQR WATCHES/WARNINGS/ADVISORIES

OR...Winter Storm Watch from Tuesday afternoon through late Wednesday night for ORZ126>128.

WA...Winter Storm Watch from Tuesday afternoon through late Wednesday night for WAZ211.

PZ...None.