textproduct: Portland

SYNOPSIS

Light rain showers continue early Saturday morning, clearing by 9 AM. Dry weather and near normal high temperatures through Monday with morning low temperatures in the 30s, producing widespread frost Saturday and Sunday nights. A weather system brings widespread rain and breezy winds Tuesday into Wednesday along with light Cascades snow Tuesday night into Wednesday. No snow or flooding impacts expected. Dry weather returns Thursday into Friday.

LONG TERM...Tuesday through Saturday

A closed low pressure pressure will move into the northeast Pacific from the south Pacific on Tuesday ushering in warmer and moist air. Widespread rain and breezy winds are expected to return Tuesday into Wednesday. Latest guidance is hinting at the possibility of another, weaker surface low pressure system and associated upper level shortwave pushing another burst of rain into the region late Wednesday into Thursday morning though there is a lack of consistency between ensemble type. For example the GEPS is showing more members with precipitation, while the ECMWF stays nearly unchanged. It may be that these two incidences merge into one continuous pattern. Uncertainty still remains on exact precipitation amounts into Thursday, though high confidence remains in limited flooding impacts. Breezy winds are also expected with the frontal passage on Tuesday. Strongest winds will be along the coast and coast range where there is a 60-70% chance of maximum wind gusts exceeding 40 mph. Inland, it is less than a 20% chance. One area to watch will be the central Willamette Valley which tends to see higher winds with this northerly direction. The alignment of the pressure gradient is going to be a component to consider.

In terms of Cascade snow, the heaviest precipitation is expected to fall ahead of and along the cold front when snow levels are generally higher than pass level. Snow levels will fall quickly after the front passes late Tuesday into Wednesday to around 3500-4500 ft. However, the lowest snow levels will be in SW WA Cascades with snow levels rising moving south into the central OR Cascades. As showers will continue into Wednesday, there is the potential for some accumulating snow, though due to the current sun angle along with warmer road temperatures, it might be difficult for much accumulation in scattered showers. Snow levels will continue falling through Wednesday, especially Wednesday night, falling to around 2000-3000 ft by Thursday morning. The 10th percentile (only 10% chance of snow levels this low) does indicate snow levels could fall as low as 500-1500 ft by Thursday morning. However, if precipitation really is decreasing by this time, then there will be limited precipitation to even cause snow. Only a few ensemble members suggest any kind of accumulating snow in the interior lowlands like around Portland, and generally less than an inch. NBM probabilities for 6 inches of snow or more in a 48-hour period ending at 5am PDT Thursday continue to back this expectation up, as chances are only around 5% at Willamette and Santiam Passes, and 10% along highway 26 near Government Camp.

By Thursday afternoon into Friday, the weather system is expected to move out of the area with upper level flow becoming more zonal. Expecting dry conditions with clearing skies by midday Thursday, which could allow for temperatures to warm into the upper 50s on Thursday and right around 60 on Friday and into the mid 60s on Saturday for the interior lowlands. If you're someone who loves the warm weather, probabilities for maximum temperatures of 70 degrees have lingered in the 20-30% range for the Willamette Valley. Though, that is still quite far out to have any level of confidence. But, given the overall pattern, it's not out of the question. -27/03

AVIATION

As we enter into a zonal pattern for the entire TAF period, expect dry westerly flow aloft and VFR conds throughout the airspace. While VFR conds will persist through the TAF period throughout the airspace, a weak front will move through Washington around 12Z Sun, brushing southwest Washington and bringing low-end VFR CIGs with a 10-20% chance of MVFR CIGs at KAST between 12-18Z Sunday.

Clear skies tonight will support temperatures dropping towards the low to mid 30s, resulting in potential frost development over metal surfaces (generally around 9-16Z Sun). Winds remain northerly to northwesterly and under 10 kt through most of the TAF period. Winds will increase around 18-20Z Sun, resulting in northerly winds around 8-12 kt at interior terminals and 12 to 15 kt with gusts up to 21 kt at coastal terminals (highest chances of gusts at KONP).

KPDX AND APPROACHES...VFR conds with clear skies through the TAF period. Northwesterly winds under 8 kt until around 18Z Sun, then increasing to around 8-10 kt for the rest of the TAF period. Potential for widespread frost over metal surfaces between 9-16z Sun due to clear skies and calm winds. ~12

MARINE

High pressure over the waters will maintain northerly winds through Monday. The next very strong ebb will occur around 730 AM Sunday, so a Small Craft Advisory has been issued for the the Columbia River Bar between 5-10 AM Sunday as the ebb builds seas to around 8 ft along the Main Channel of the Bar.

A thermal trough develops along the southern Oregon coast Sunday afternoon through early Monday morning, tightening pressure gradients across the waters south of Cape Falcon. This will lead to breezier northerly winds with gusts up to 25 kt; therefore, a Small Craft Advisory has been issued for all waters south of Cape Falcon from 2 PM Sunday through at least 5 AM Monday. Northerly winds may last longer for the outer waters beyond 10 NM offshore, so the Small Craft Advisory for these zones will go through 8 AM Monday. Seas fall to 5-6 ft tonight, re-building to 8-9 ft at 11 sec as wind waves increase from the breezy northerly winds.

The next robust weather system returns Tuesday into Wednesday. This system will bring a return of breezy southerly winds across all waters. Current guidance suggests high confidence (90%+ chance) for widespread and frequent small craft wind gusts of 21 kt or greater, and a 35-55% chance for widespread and frequent Gale force wind gusts of 34 kt or greater on Tuesday. Chances for isolated Gale force wind gusts are around 75-90%, with the highest chances beyond 20 NM offshore. Latest guidance suggests the strongest winds occur between 8 AM to 5 PM Tuesday. Seas on Tuesday and Wednesday are also expected to build to around 13-16 ft in response to increasing wind waves along with an increasing westerly swell. There's a 30-60% chance seas could exceed 15 ft with a 5-15% chance for seas exceeding 20 ft. Chances increase from south to north, peaking across the waters north of Cape Falcon and mainly beyond 40 NM offshore. -10/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 5 AM to 10 AM PDT Sunday for PZZ210.

Small Craft Advisory from 2 PM Sunday to 5 AM PDT Monday for PZZ252-253.

Small Craft Advisory from 2 PM Sunday to 8 AM PDT Monday for PZZ272-273.