textproduct: Portland

SYNOPSIS

Cool and dry becomes hot and dry for the region as an upper level high slowly builds into the region over the next 24-48 hours. This will result in a multi- day heat event focused over the weekend and into early next week (June 13-16th). This time period will present some of the hottest temperatures we've seen so far this year. There is at least growing confidence in a return of cooler, closer to normal temperatures (70s/80s) by Wednesday of next week.

LONG TERM...Friday through Tuesday

Hot and dry conditions will be well entrenched across the Pac NW. Expect daytime highs to be the hottest of the year so far. These conditions are the main driver of our weather impacts through the remainder of the week, over the weekend and into the start of next week. Friday through early next week, models and their respective ensembles are in very good agreement that an upper level ridge will continue to strengthen over the far northeastern Pacific before shifting eastward. This will result in daytime highs about 5-10 degrees warmer than normal (normal this time of year is in the 60s along the coast and Cascades and in the 70s for inland valleys). By Saturday, June 13th, the NBM probabilities for daytime highs above 90 degrees F are 20-50% for the Willamette Valley. NBM probabilities for daytime highs at or above 100 degrees F on Sunday June 14th are 15-40% and 20-70% on Monday June 15th, with the highest probabilities each day towards the northern portions (Portland/Vancouver Metro) of the Willamette Valley. Also, there is a 5-15% chance for daytime highs on June 14th and June 15th of 105 degrees F or higher for locations between Salem, OR and Kalama, WA.

For reference, HeatRisk levels are as follows: Little to None, Minor, Moderate, High and Extreme.

Probabilities for a Moderate HeatRisk or higher on Saturday June 13th are 85-95%, then on Sunday/Monday (June 14th and 15th) 90-99% across almost the entire region. For Major HeatRisk, there is a 55-80% probability on Sunday June 14th and 25-80% probability on June 15th (highest Portland Metro, lowest near Eugene and along the coast). At least through this period the probability for Extreme HeatRisk across the CWA is 5-15% or less. Anyone who is sensitive to heat or those who have outdoor plans should prepare for and takes steps to mitigate potential heat impacts. For those planning to seek relief by swimming in local area rivers and/or lakes to cool off, be mindful of cold water temperatures and swift currents which can become life threatening if precautions like wearing a life preserver is not taken.

It's worth noting with this upper level pattern, a thermally induced surface trough also will establish itself somewhere west of the Cascade Crest-line which could result in locally breezy winds within the Cascades and/or Willamette Valley depending on its orientation. As daytime highs increase, relative humidities will also decrease. Therefore, with conditions drying out AND the potential for gusty winds, there are increasing fire weather concerns for the latter part of this week through the start of next week. So, be aware of potential ignition sources such as chains dragging on the pavement, hot vehicle components, as well as cigarette butts as these could easily result in the ignition of dry, fine fuels. Larger fuels may not have the time to dry out, but this is a variable that is being closely monitored by State and Federal Fire Partners.

By June 16/17th (Tuesday and Wednesday of next week), ensemble modeling systems do hint at the ridge finally breaking down and shifting eastward, bringing a return of relatively cooler, westerly flow. However, there's a large degree of uncertainty as to whether this transition takes place on Tuesday or Wednesday, but at least the majority of models do push temperatures downward back into the 70s and 80s by the middle of next week as in general the 25th-75th percentiles fall in-between these two values. The latest NBM only gives the inland valleys a 10-15% chance for highs to exceed 90 degrees F on Wednesday. So, confidence is moderate to high in a return closer to normal daytime highs by the middle of next week. /42-99

AVIATION

Largely VFR conditions continue across the airspace with widely scattered but increasing rain shower coverage to the north. North OR/south WA coast terminals (KAST) have the highest chances of MVFR vis/cigs, 40-70%. Elsewhere along the coast and inland, VFR conditions are favored (60-80% chance). Despite persistent showers, background conditions are expected to continue to improve as cigs lift and skies trend clearer after 18z Wed. West-southwest winds continue at 8-12 kt with gusts of 15-20 kt into this evening, but will ease to 5 kt or less by 09-12z Wed. Diurnal winds will rise out of the west to northwest at 5-10 kt from 15-18z Wed.

KPDX AND APPROACHES...VFR flying conditions expected through the period. Isolated light showers will persist through 09z Wed, but terminal impacts are unlikely. Cigs otherwise trend upward above 5 kft through the period. West winds of 10-12 kt gusting near 20 kt will ease below 5 kt tonight, then rise out of the west to northwest near 5 kt Wednesday afternoon. -36

MARINE

Lingering Small Craft conditions through the late evening across all waters as winds and seas gradually subside. Seas around 8-10ft at 9-10 seconds will slowly subside toward 5-7 feet by Wednesday morning and remain there through the weekend. Westerly winds with gusts up to 25 kt will also decrease through tonight and fall below 15 kt gusts by the middle of the week. From here our focus shifts to high pressure building offshore through the remainder of the week. West winds of 10-15 kt on Wednesday evening/Thursday will become more northerly. Typical summertime northerlies lock in place from this point forward, with gusts up to 25 kt each afternoon and evening from Thursday through the weekend. This may necessitate daily Small Craft Advisories. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...Extreme Heat Watch from Sunday morning through Monday evening for ORZ109-111-112-120.

WA...Extreme Heat Watch from Sunday morning through Monday evening for WAZ206-207-209.

PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ210- 251>253-271>273.