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...Now through Tuesday Night

An upper-level ridge axis currently centered over the northeastern Pacific will shift eastward and inland through the end of the workweek, bringing a warming trend 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 Friday 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 generates attendant uncertainty in the temperature forecast, but given the model consensus, there are 65-95% chances for temperatures to exceed 90 degrees throughout inland valleys on Monday, and slightly lower chances, 55-85%, on Tuesday. The chances to exceed 95 degrees similarly peak at generally 30-60% each of Monday and Tuesday afternoon, while the chances to reach 100 degrees reach 5-15% 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: 20% near Albany/Corvallis, increasing northward to 50% in the inner Portland/Vancouver metro, then decreasing to 20% near Kelso/Longview. Long-range guidance favors a cooling trend later next week, but there are still low chances, 10-20%, for the heat to persist into a third day next Wednesday. -36

AVIATION

High pressure over the region will lead to persistent northwesterly flow aloft through the period. Marine stratus has dissipated off the north OR and south WA coast while inland skies have mostly cleared. Expect predominately VFR conditions to persist across most terminals through the TAF period. High pressure strengthens later tonight into Thu which will lead to drier conditions, thus cloud cover will be more challenging to observe outside of the coastal locations. There is around a 40-60% chance for MVFR stratus to return to the coast after 09-12z Thu, with around a 20-30% chance of IFR CIGs occurring with the stratus along the coast (highest chances near KONP).

Winds along the coast are expected at around 12-18 kts with gusts to around 25 kts this afternoon. Inland, winds increase after 20z to 8-12 kts with gusts up to 20 kts. Winds are expected to decrease after 06-08z Thu.

KPDX AND APPROACHES...Expect VFR to continue through the TAF period under mostly clear skies. Lower chances (less than 20%) for brief MVFR stratus to develop between 12-18z Thu. Northwest winds increase this afternoon to 8-11 kt with gusts up to 18-20 kt, easing again by 07z Thu. /DH

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 Friday as a fresh northwesterly swell persists across the coastal waters. Seas are expected to subside over the weekend. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory from 5 AM to 10 AM PDT Thursday for PZZ210.

Small Craft Advisory until 5 AM PDT Friday for PZZ251>253- 271>273.