textproduct: Portland

SYNOPSIS

Drier and warmer conditions persist through Thursday with temperatures gradually warming and peaking on Wednesday with the development of low-level offshore flow. The forecast becomes more uncertain Friday into Sunday, with the potential for weather conditions to range anywhere from cool and showery to warm and dry depending on the evolution of the large scale weather pattern.

DISCUSSION...Tonight through Sunday

Confidence remains high that dry and warm weather returns to the region through at least the middle of this week. Model ensembles are in good agreement that the upper level synoptic pattern will develop into a col over the western portion of CONUS. A col also referred to as a "saddle point", is formed when there is a set of lows and a set of highs, that are in opposition to each other and results in rather benign weather for locations near the center or peak of the col. For our region, models have us on the eastern portion, which will enable the upper level high over the Great Basin to exert a little more influence in comparison to the other synoptic features. As the Great Basin high develops it will induce a weak, surface thermal trough that will build from northern California into western Oregon, which will result in weak offshore flow. Also, this will result in daytime highs warming in the upper 70s to mid 80s for inland valleys, upper 60s to upper 70s for the coast and lows 70s to low 80s for the Cascades, with the warmest temperatures expected on Wednesday. Thursday as well looks to remain warm and dry, but daytime highs are expected to be around 5-10 degrees cooler than Wednesday.

Looking towards Friday and into the weekend, confidence in a cooler pattern developing has increased. WPC 500 mb clusters show around a 70% probability of a Canadian low dropping into the Pac NW, while the other 30% cut off the Canadian low and hold it in the northeast Pacific. Either solution will bring cooler temperatures to the are, with the more favored solutions bringing rain back into the forecast. Sill, even when looking at the favored solutions, uncertainty remains as to the strength, timing and location of the low. As such, ensembles are bringing cooler conditions back to the Pac NW for the latter part of the week and into the weekend. Deterministic, daytime highs for Friday through Sunday are in the mid 60s to mid 70s for inland valleys, upper 50s to upper 60s for the coast and upper 50s to upper 60s for the Cascades. However, it should be noted that daytime high temperature spreads from the 25th to the 75th percentile are around 5-10 degrees with the 10th to 90th spread around 8-15 degrees. So, there remains a lot of uncertainty with the forecast. The outcome will be highly dependent on how deep the trough becomes and if it tracks into Washington and Oregon or further to the east towards the Northern Plains, which will also determine whether or not rain will return to the area. As for rain, ensembles are pointing towards a more wetter solution, but precipitation totals are not expected to resemble what was observed last week. Current 48 hours totals ending 5 AM Monday is around 0.15-0.5 inches across most of the CWA, with the higher values over the Cascades. Overall, conditions through the middle of this week look to remain warm and dry. Cooler and wetter conditions are favored to return for the latter part of this week and into the weekend, but that doesn't mean that those conditions are guaranteed. /42-03

AVIATION...Through 18Z Tuesday

Upper level troughing remains over the region today with northwest flow aloft. Mostly dry conditions expected as morning stratus is expected to become more scattered by 19-20z this afternoon. As of 17z, a few terminals are still reporting MVFR to IFR CIGs, including KUAO and KEUG. Expect predominately VFR conditions returning after 20z and continuing into the evening hours. Higher pressure begins to build across the area tonight into Tuesday morning. Guidance suggests there is around a 40-50% chance for stratus or fog to deteriorate conditions at the coast after 11-12z Tuesday. Expect generally light and variable winds at most terminals through the TAF period, with the exception of northwest winds around 8 kt at coastal terminals during the afternoon.

KPDX AND APPROACHES...Expect VFR conditions to persist as skies gradually clear this afternoon. Light and variable winds becoming northwest around 4-6 kt this afternoon. /DH

MARINE

High pressure offshore will maintain predominately northerly winds across the coastal waters through the week. A strengthening pressure gradient on Tuesday will bring stronger northerlies with gusts up to 25 kt as there is an 80% chance of wind gusts exceeding 21 kt by Tuesday evening. As a result, Small Craft Advisories have been issued from 11 AM Tuesday to 6 AM Wednesday for the outer coastal waters south of Cape Falcon, and from 2 PM to 12 PM Tuesday for all other coastal waters. Breezy winds continue through Thursday, but should remain 20 kt or less. Seas of around 4 ft with a dominant northwest swell at 10-12 seconds will gradually build to around 6 ft late Tuesday as wind chop increases with the northerly winds. A weak low pressure system is expected to approach the coastal waters late Friday into Saturday. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 2 PM Tuesday to midnight PDT Tuesday night for PZZ210-251>253-271.

Small Craft Advisory from 11 AM Tuesday to 6 AM PDT Wednesday for PZZ272-273.