textproduct: Portland

SYNOPSIS

Warmer than normal and dry conditions 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 time.

DISCUSSION...Tonight 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 Saturday bringing warmer temperatures with a typical summertime northerly wind pattern. Temperatures peak on Friday for inland locations as troughing aloft supports a return to stronger onshore flow Friday into Saturday. As daytime highs reach to near 70 degrees on the coast and 80s to near 90 degrees on Friday, this will result in Minor HeatRisk for most areas within our CWA and locally Moderate HeatRisk from Salem, OR northward towards Kelso/Longview, WA and across the greater Portland/Vancouver Metro area. Aforementioned troughing and onshore flow will yield cooler temperatures near 60 degrees for Friday along the coast, with persistent onshore flow will help to cool inland locations down, which will bring daytime highs into the upper 70s to low 80s 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 for the start of next week with the warmest days looking to be 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 is 85-95% probability for daytime highs to exceed 90 degrees F throughout inland valleys Monday and Tuesday. The chances to exceed 95 degrees similarly peak at generally around 40-85% chance Monday and Tuesday, while the chances to reach 100 degrees reach 25-40% only from Salem, OR north to Vancouver, WA on Monday and 20-40% from Corvallis, OR north to Kelso/Longview, WA.

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 low temperatures falling into the mid 60s. Looking beyond, towards the middle of next week. Long-range guidance is favoring a cooling trend beginning Tuesday night and continuing into later next week, but there's still a 30-50% chance for temperatures above 90 degrees to persist on Wednesday. It should also be noted that there are no strong signals for any precipitation through the entire forecast. -42/03

AVIATION

Dry with widespread VFR conditions over the next 24 hours. Northerly winds transition to the west-northwest after 10Z Fri. Clouds will be minimal inland, but along the coast, the addition of westerly flow will cause CIGs to drop to MVFR levels. There is a 40% chance of IFR conditions along the coast from KTMK southward, and some hints of lower clouds are already starting to develop around KONP though have been bouncing between BKN and SCT.

KPDX AND APPROACHES...VFR with northerly winds. Periods of gusty winds up to 20 kt until 04Z Fri then will become light overnight. -27

MARINE

High pressure offshore will maintain a summertime pattern through the remainder of the week. Diurnally driven northerlies are expected to peak each afternoon and evening through at least Friday but there will be a slightly more westerly wind pattern in the inner waters. 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 9 to 11 ft at 9-10 seconds persists into early Saturday as a fresh northwesterly swell persists across the coastal waters. For those traveling across the Columbia River Bar, strong ebbs are expected around sunrise Friday morning. Seas are expected to subside later Saturday into Sunday. -27/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 5 AM to 10 AM PDT Friday for PZZ210. Small Craft Advisory until 5 AM PDT Friday for PZZ251>253. Small Craft Advisory until 5 AM PDT Saturday for PZZ271>273.