textproduct: Portland

SYNOPSIS

Warmer than normal and dry conditions are expected to continue through the middle of next week. Confidence is increasing that hot temperatures peaking Monday and Tuesday will support Moderate to Major HeatRisk, however there remains uncertainty in the temperature forecast at this lead time.

DISCUSSION...Thursday morning through Wednesday

There has been very little change in the forecast since the last package. An upper- level ridge axis currently centered over the northeastern Pacific will shift eastward and inland through the end of the workweek, bringing warmer temperatures with a typical summertime northerly wind pattern. Temperatures will peak on Thursday at the coast and on Friday inland as troughing aloft supports a return to stronger onshore flow Friday into Saturday. Temperatures near 70 degrees on the coast will yield Minor HeatRisk on Thursday, while inland temperatures climb into the 80s to near 90 degrees both Thursday and Friday, yielding widespread Minor HeatRisk and locally Moderate HeatRisk from Salem north to Kelso/Longview and Portland east through the Columbia Gorge. The chances to exceed 90 degrees on Thursday are only around 20-35% from Hillsboro to northern Marion County and 5-15% elsewhere for the interior lowlands. These chances increase on Friday to 35-55% from Portland/Vancouver south to northern Marion County, 15-25% in the central Willamette Valley, and 5-15% elsewhere along the I-5 corridor. Aforementioned troughing and onshore flow will yield cooler temperatures near 60 degrees starting Friday on the coast, and upper 70s to low 80s within inland valleys on Saturday.

Ensemble guidance remains in good agreement that renewed ridging will develop from Sunday into early next week, raising the chances for another period of hot temperatures peaking Monday and Tuesday. Uncertainty in the position and amplitude of the ridge axis remain, leading to uncertainty in the temperature forecast, but given the model consensus, there are 70-95% chances for temperatures to exceed 90 degrees throughout inland valleys on Monday, and slightly lower chances, 65-85%, on Tuesday. The chances to exceed 95 degrees similarly peak at generally 30-80% each of Monday and Tuesday afternoon, while the chances to reach 100 degrees reach 15-35% only from Salem north to Vancouver. These daytime temperatures combined with overnight lows in the upper 50s to low 60s support widespread Moderate HeatRisk inland both Monday and Tuesday, with the coverage of Major HeatRisk largely dependent on the occurrence of overnight temperatures falling to lows only in the mid 60s. The chances of Major HeatRisk very nearly mirror those of nighttime lows of 65 degrees or warmer Monday night: 15-20% for the central Willamette Valley, increasing northward to 50% in the inner Portland/Vancouver metro, then decreasing to 20% near Kelso/Longview. Long-range guidance favors a cooling trend beginning Tuesday night and continuing into later next week, but there's still a 20-40% chance for temperatures above 90 degrees to persist into a third day on Wednesday. -36/03

AVIATION

VFR and dry over the next 24 hours with weak onshore flow. Overnight cooling with onshore flow will lead to marine stratus along the north OR and south WA coast. There's a 40-60% chance of MVFR ceilings continuing at any given time through at least 14z Thu, dissipating by 16z Thu. For coastal locations south of Clatsop county and Portland metro area terminals, chances of MVFR cigs are only around 20-30%. If any stratus forms, conditions will improve to VFR by 17z Thu. Light overnight winds will yield to another breezy day with northerly to northwesterly winds. Highest wind speeds will be along the central Oregon coast around KONP with gusts up to 20-25 kts after 17z Thu. Gusty conditions increase through the Willamette Valley between 20Z Thu and 02Z Fri, though confidence in the duration is a little less certain.

KPDX AND APPROACHES...VFR through the next 24 hrs with a 20-30% chance of brief MVFR stratus around sunrise Thu. Northwest winds increase after 20z Thu to 8-11 kt with gusts up to 18-20 kt, easing again by 03-06z Fri. -03

MARINE

High pressure offshore will maintain a summertime pattern through this week. Diurnally driven northerlies are expected to peak each afternoon and evening through at least Friday. Winds are expected to peak each afternoon and evening with gusts to 25-30 kts, decreasing a bit in the late overnight to morning hours. Winds will likely ease over the weekend as high pressure weakens and low pressure moves into northwest WA, turning winds more northwesterly on Saturday. Seas around 7 to 9 ft at 8-9 seconds are expected to build to 9 to 11 ft at 9-10 seconds later Thursday into early Saturday as a fresh northwesterly swell persists across the coastal waters. Seas are expected to subside later Saturday into Sunday. /DH/03

PQR WATCHES/WARNINGS/ADVISORIES

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

Small Craft Advisory until 5 AM PDT Friday for PZZ251>253.

Small Craft Advisory until 5 AM PDT Saturday for PZZ271>273.