textproduct: Portland

SYNOPSIS

Low pressure moves along the West Coast bringing periods of rain over the next several days. Will see periods of breaks, but will be short lived as short wave after short wave passes over. The big weather shift will be early next week as a long wave pushes eastward over the coast. Cold air wraps around the trough and will cause temperatures to drop. Increased probability for lowering snow levels and Cascade Pass snow.

For those who may have noticed, the NEXRAD Radar at KRTX is down for a mechanical issue. The time of restoration is unknown at this time. We apologize for the inconvenience.

LONG TERM...Sunday through Thursday

A slightly more complex scenario for early next week that is being driven by a broad low pressure system sitting over British Columbia. This low will push a robust long wave trough southward along the coast. This trough will usher in slightly colder air starting on Sunday with overnight temperatures dropping through mid-week. As the temperatures lower, will see snow levels fall suit. In the current forecast, snow levels will reach pass level late Sunday night or early Monday morning. However, if one were to look at the ensemble long range models there is much more uncertainty. This is due to a) the depth of the trough, and b) whether a closed low forms at the base. If the low does in fact form, the lift will be amplified with more impacts. Wrap around cold air will be more robust as will sinking air. In contrast though, if the low does form but further north then there will be active weather but less cold air intrusion. The second option is the low not manifesting. If this is the case, the cold air plunge will be less than if it were to. The same trend of a north or south track rings true in this case too.

With all that said, the timing of the cold air is going to have a major impact on if/when we get snow in the Cascades which could lower to pass level. The deterministic GFS has snow levels reaching pass level nearly 24-hrs later than the ECMWF at this point. Let's dive into the snow potential for advisory level snow on Monday into Tuesday. If we look at the probability of 6" or greater snow at the Cascade passes in the 48-hrs ending Tuesday afternoon, the probability has decreased significantly. At this point there is around a 35% chance of >6" of snow at Santiam and Willamette Passes. There is less than a 5% chance at Government Camp and even lower probability to the north. In fact, the highest probability that exceeds 50% is only along the volcanoes of the central Oregon Cascades.

There continues to be significant disagreement towards mid- week. -27

AVIATION

Light showers continue to dissipate over the next few hours, this will result in lingering mid/high level clouds. This will result in generally VFR conditions, but could see intermittent MVFR/IFR (15-25% probability) conditions through 15Z Friday. Higher probs of IFR along the coast. Light rain/aggressive drizzle could also persist through the TAF period, but better chances for rain don't return until 08Z-10Z Friday for the coast and 10Z-12Z Friday for inland locations. VFR conditions are expected to persist as the rain returns for the remainder of the TAF period. Winds generally out of the south less than 10 kt.

KPDX AND APPROACHES...VFR with lingering mid/high level clouds, along with intermittent MVFR/IFR (15-25% probability) conditions through 15Z Friday. Light rain/aggressive drizzle could also persist through the TAF period, but better chances for rain return around 10Z Friday. Winds generally out of the south less than 10 kt. /42

MARINE

Winds are beginning to ease behind a frontal system that moved through the central Oregon waters this afternoon. Winds remain from the south, mainly less than 10-15 kts, though zone Pzz273 will see gusts up to 20-25 kts through around 5 PM PST tonight. Seas are building towards 10-12 feet at 12-15 seconds for all waters due to an increasing westerly swell. The area south of Cape Falcon and beyond 20 NM off the coast will also have a 50-70% chance for seas building towards 13-15 ft tonight. Therefore, the current Small Craft Advisory for all marine zones remain in effect through at least 7 AM Friday, mainly due to seas. Seas gradually subside to 8-9 ft at 13 seconds Friday morning.

Another frontal system will swing through British Columbia and far northwest Washington Friday afternoon, maintaining relative breezy southwesterly winds over our coastal waters. There is a 30-50% chance for southwesterly winds with frequent gusts of 21 kt or stronger across the waters north of Cape Falcon including the Columbia River Bar by late Friday afternoon and evening. South of Cape Falcon, these chances drop to 15-30%. Winds ease on Saturday before another frontal system may bring another round of increased winds on Sunday. Seas continue falling Friday afternoon to 7-9 feet at 11-12 seconds, remaining here through Saturday before increasing to 9-11 feet at 12-14 seconds on Sunday. -10/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 7 AM PST Friday for PZZ210-251>253.

Small Craft Advisory until 1 PM PST Friday for PZZ271>273.