textproduct: Portland

SYNOPSIS

Light showers will continue to stream into the region from the south as an the upper level low shifts eastward. The best signal for the coolest and most unsettled stretch remains Tuesday into Wednesday as upper level low moves further inland. Beyond that, guidance supports a return of dry and warmer weather beginning Thursday and continuing into the weekend as high pressure rebuilds.

DISCUSSION...Now through Monday

High and mid level clouds along with light shower continue to stream into the region from the south as an upper level low pressure system continues to slowly moving east/southeast towards the OR/CA border. This low will be the dominant synoptic feature through at least the middle of the week. As this low continues to trek east/southeast, it will bring widespread cloud cover along with increasing PoPs, with low QPF values across the CWA through late Wednesday. As the latter part of the week approaches and the aforementioned low pushes further into the Great Basin, weak high pressure will build in behind the low and will bring about a warming and drying trend that will persist through the weekend and into the start of next week.

Tonight through Wednesday night, an upper level low will bring increasing cloud cover, generally cooler temperatures as well as as a moderate/high PoPs and a low QPF pattern. Broken cloud cover through this evening and tomorrow will result in a 10-20% chance for thunderstorms, with the highest probability for thunderstorms along the Cascades. Daytime highs on Tuesday and Wednesday will be in the mid 50s to mid 60s, with Wednesday shaping up to be the coolest day this week. Overnight lows during this time frame will also be in the low 40s to low 50s. Precipitation totals through tonight will range around 0.05-0.25 inches with the highest totals expected along the Coast Range. Tuesday and Wednesday, precipitation totals look to be fairly similar with 24 hour totals for most areas between 0.10-0.50 inches, with the highest accumulations expected within the Cascades. It should be noted that if a thunderstorm does develop, then total precipitation will likely be higher.

Thursday through Sunday, conditions trend drier and warmer as high pressure returns to the Pac NW. Daytime highs are expected to warm back into the 60s on Thursday and further warming into the upper 60s and mid 70s by Friday with those daytime highs persisting through the weekend and likely (60-80%) into the start of next week. Overnight lows in the during this time frame will be in the low 40s to low 50s. Looking towards the start of next week, a pattern change looks to occur as the ridge looks to break down. However, uncertainty is very high with the WPC 500 mb cluster multi-model ensemble keeping very weak and broad troughing over the western part of CONUS. This generally supports a slight cooling trend with a very low chance of light precipitation. /42

AVIATION

High clouds persist over the area this afternoon, maintaining VFR flight conditions aside from occasional IFR to MVFR cigs at KONP. A weak front associated with a low pressure system offshore is now lifting northward over northwest OR this afternoon, bringing scattered light rain showers and sprinkles with it. Southwest winds will increase to 5-15 kt this afternoon and early evening as this front moves through before winds weaken again after 03-06Z Tuesday. Aside from KONP, CIGs are very likely to remain VFR at all inland terminals through at least 00-06Z Tuesday. After 06Z Tuesday, chances for MVFR CIGs of 2-3 kft increase to 40-50% or higher at all terminals. Note an isolated thunderstorm or two is possible around 00Z Tuesday somewhere over the Cascades, foothills and/or Willamette Valley, however the probability for thunderstorms at any given TAF site is only 5-15%.

KPDX AND APPROACHES...Predominately VFR conditions continue today with CIGs between 10 kft. West-southwesterly winds have increased this afternoon as the next front moves in, but most likely remaining around 10 kt or less aside from infrequent gusts up to 15 kt. Also expecting some non-impactful sprinkles or light showers with this frontal passage this afternoon. CIGs will most likely lower to around 3000 ft or less by 08-09Z Tuesday as more persistent rain showers move in from the south. Note there is a 15% chance of thunderstorms at the KPDX terminal between 00-03Z Tuesday. Probabilities for thunderstorms are not high enough to warrant a PROB30 group. -23

MARINE

Benign conditions continue today into Tuesday. Buoy observations from Monday afternoon showed seas hovering around 6 to 7 ft with light southwest to west winds. Scattered light rain showers and sprinkles are also occurring over the coastal waters Monday afternoon with a weak frontal passage.

An upper level low off the coast will support additional showers Monday night through Tuesday night as the center of the low nears the coast, with seas likely staying under 8 ft and winds staying under 15 kt. By early Wednesday morning, a northwest swell will push seas up to 7 to 8 ft. Seas and winds both increase more considerably Wednesday afternoon and evening with another frontal passage. Expect seas to peak between 10 and 12 ft by Wednesday evening with west to west-northwest winds around 10 to 15 kt with gusts up to 20-25 kt Wednesday afternoon and evening. There is a 50-80% chance seas peak above 10 feet beyond 10 nm offshore and a 30-50% chance for seas above 12 feet over the northern outer waters beyond 30 nm offshore. Seas are expected to peak closer to 9-10 ft over the inner waters. Winds decrease Wednesday night behind the frontal passage, however seas will remain elevated until significant wave heights fall below 10 ft sometime Thursday afternoon or evening.

A very strong ebb current will occur during the Tuesday morning ebb cycle, pushing seas up to 6 ft with steep ebb chop. Have decided not to issue a Small Craft Advisory for this ebb cycle as this is slightly below criteria thresholds. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.