textproduct: Portland

SYNOPSIS

Warm and dry conditions continue through the upcoming week as temperatures gradually moderate towards August normals. Renewed onshore flow will keep smoke east of the Cascades, while precipitation chances remain very low through at least the middle of next week. Temperatures may trend warmer later next week as a ridge of high pressure looks to develop.

DISCUSSION...Tonight through Saturday

Daytime highs this week are expected to be near normal for this time of year reaching into the lower to mid-80s for inland locations, upper 60s to mid 70s along the coast and in the Cascades. The cause of this is a shift in the upper level synoptic pattern has become more zonal and is expected to remain predominately zonal through at least the middle of the week. As a result, expect mostly sunny skies for inland locations with marine stratus developing along the coast before retreating by the late morning/early afternoon. This marine stratus will then return by the evening as this ebb and flow pattern looks to continue along the coast through at least Tuesday. This overall weather pattern generally remains in place through at least Tuesday.

By Wednesday, ensembles are showing a general trend toward upper level troughing dropping out of British Columbia, though chances for rain here remain very low (below 5%). This could bring in some cooler temperatures for the latter part of the week, as indicated by growing uncertainty in the daytime high temperature spread into late next week. For example, the spread between the 10th and 90th percentiles on Thursday at PDX range between 77 and 92 degrees F, with Friday ranging between 81 to 96 degrees F. The cause for the very high uncertainty is because ensembles are split between upper level ridging possibly developing offshore, while others show some sort of troughing persisting over the area. Looking at WPC 500mb clusters has an almost even spread between the 4 cluster options for Friday. Cluster 1, with 29% of the models show very broad ridging developing over western CONUS. Cluster 2, with 27% of the models shows very weak troughing over the Pac NW. Cluster 3, with 25% of the models has a more robust troughing pattern over the Pac NW and Cluster 4, with 19% of the models shows a closed low developing just off the coast of Central California. Overall, near normal daytime highs looks to be in the forecast through the upcoming week, with no signs of precipitation. /42-DH

AVIATION...Through 00Z Tue

Westerly flow aloft continues today with VFR conditions and mostly clear skies expected through the period for inland terminals. The only exception is between 11-18Z Mon for KPDX, KHIO, and KTTD, with guidance suggesting a 20-30% chance of marine stratus pushing up the Columbia River and bringing MVFR CIGs. All coastal terminals are now VFR, but some marine stratus lingers near KAST which may cause moments of MVFR CIGs (40-50% chance of MVFR). Chances for marine stratus redeveloping at the coast increase again by 03-06Z Mon, with chances around 70-90% for MVFR, 30-50% for IFR, and 10-15% for LIFR between 06-18Z Mon (highest chances at KAST). Otherwise, expect north to northwest winds with gusts up to 25 kt along the coast and up to 20 kt inland through this afternoon and evening, weakening overnight, then increasing again Mon afternoon.

KPDX AND APPROACHES...VFR through the TAF period with clear skies. There is a 20-30% chance for stratus to develop between 11-18Z Mon. Northwest winds around 10-12 kt with gusts up to 20 kt will weaken heading into the evening. ~12

MARINE

High pressure offshore will maintain northerly winds through much of next week. Tightened surface pressure gradients continue to bring high chances for wind gusts up to 25 kt south of Cape Foulweather today and into early next week. As a result, a Small Craft Advisory remains in effect for the inner and outer waters south of Cape Foulweather until 2 AM Monday. Additionally, a Small Craft Advisory for the inner waters south of Cape Foulweather has been issued from noon to 11 PM Monday. Similar small craft conditions may reoccur Tuesday however with much less confidence (30-40% chance of wind gusts up to 21 kt). Wind driven seas are expected to remain around 4 to 6 ft through most of next week. ~12/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 2 AM PDT Monday for PZZ253-273.

Small Craft Advisory from noon to 11 PM PDT Monday for PZZ253.