textproduct: Portland

SYNOPSIS

Cool and wet to hot and dry. This is a simple, concise and accurate summation of the weather conditions as we progresses through the next 7-9 days. Tonight will remain rather soggy and cool, with a very slow warming and drying trend expected through the remainder of the week. Confidence continues to increase for a multi-day heat event in the June 12th through June 16th timeframe. Don't get caught off guard and start preparing for heat related impacts, you'll thank yourself later.

SHORT TERM...Tonight through Wednesday

Cool, wet, and showery conditions will continue through the overnight hours as a upper level low moves northerly over the region. As the low moves over the region, southerly winds looks to increase which could bring isolated gusts up to 35-40 mph for inland locations from around 4PM through 10PM. Deterministic models and their ensembles remain in good agreement for broad upper level troughing to hold over the region Tuesday helping to maintain a cool and showery weather pattern. Given that more cloud breaks and slightly warmer daytime (think low to mid 60s for inland locations) highs are expected on Tuesday, general instability will also increase. Thus there is a 10-20% chance for thunderstorms across the CWA starting in the late morning through the late evening. Wednesday, is the start of the next major pattern change. The low which has been the dominant synoptic feature for the start of the week, will get slowly pushed eastward by an upper level ridge moving in from the eastern Pacific. As high pressure develops, daytime highs are expected to warm into the mid 50s to mid 60s along the coast and in the Cascades, with inland daytime highs reaching into the mid 60s to low 70s.

As far as precipitation totals concerned, the bulk of the precipitation is set to end around 5 AM PDT Wednesday. QPF amounts from the deterministic NBM during this 48-hour period range generally between 0.5-1.0" over inland valleys, around 1" at the coast, and 1-2" in the Coast Range, Willapa Hills, and Cascades. Probabilities for over 0.5" of rain have settled around 85-95%, and probabilities for 1" of rain or more are 25-50% over the Central Willamette Valley into Portland metro (only 10% near Eugene), and 80-95% along the coast, Coast Range, Willapa Hills, and Cascades. /42-99

LONG TERM...Thursday through Monday

Now that the cooler part of the week has been discussed, lets look at the warm and dry conditions of the long term forecast. As mentioned above, and upper level ridge looks to slowly build over the region for the latter part of the week and remain over the Pac NW through the weekend and into the start of next week. This synoptic pattern is resulting in moderate to high confidence in a prolonged multi-day heat wave beginning on Saturday.

However, before the heat kicks in, expect rather pleasant weather on Thursday with mostly sunny skies and high temperatures in the mid to upper 70s for inland locations and , upper 60s to mid 70s for the coast and Cascades. Friday through early next week, models and their ensembles show an upper level ridge amplifying over the far northeastern Pacific, with some lingering uncertainty regarding exactly how far east the ridge axis will move. Despite the uncertainty with the location of the ridge axis, confidence is high temperatures will be heating up significantly June 13-16. For Saturday, June 13th, the NBM probabilities for daytime highs above 90 degrees F is 45-75% for the Willamette Valley. NBM probabilities for daytime highs at or above 100 degrees F on June 14th are 30-60% and 20-70% on June 15th, with the highest probabilities each day towards the northern portions (Portland/Vancouver Metro) of the Willamette Valley. Also, there is a 10-20% chance for daytime highs on the 14th and 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.

Given the likely record breaking daytime highs, probabilities for a Moderate HeatRisk or higher on June 13th is 70-85%, on June 14th and 15th is 85-99%. For Major HeatRisk or higher, there is a 40-75% probability on June 14th and 25-70% on June 15th. The probability for Extreme HeatRisk across the CWA is 10% or less through June 13th through June 15th. Anyone who is sensitive to heat or those who have outdoor plans should pay attention to the forecast over the coming days and be prepared for potential extreme heat. Those planning on swimming in rivers or lakes to cool off should be mindful of cold water temperatures and swift currents, which can become life threatening.

Typically with this upper level pattern, a thermally induced surface trough also looks to establish itself somewhere west of the Cascade Crest, which could result in gusty winds within the Cascades and Willamette Valley. 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. /42

AVIATION

Radar imagery and terminal observations as of late Monday evening depict decreasing rain across northwest Oregon as today's frontal system exits the region. Post-frontal showers will linger through at least Tue morning, but conditions should gradually dry out by Tuesday afternoon. Visibility should improve to VFR for most terminals, but can't rule out brief reductions to IFR/MVFR during heavier showers. There is high confidence that LIFR/IFR CIGs linger along the coast tonight through 17-19z Tue. Afterwards, there is a 20-40% chance for MVFR CIGs or lower at any given hour along the coast through the remainder of the TAF period. For inland locations, high confidence that CIGs trend mostly high-end MVFR/low- end VFR through Tue morning. The northern Oregon coast and northern Willamette Valley has a 10-15% chance of thunderstorms between 12- 21z Tue. After 18-21z Tue, drier conditions with predominately VFR CIGs return across all inland terminals.

Winds remain southerly/southwesterly with gusts up to 30 kt along the coast and 20 kt inland. Will maintain this trend heading into Tuesday, but winds will gradually turn more westerly in the afternoon behind the system.

KPDX AND APPROACHES...Trending high-end MVFR/low-end VFR through 18- 19z Tue, then predominately VFR after 19-20z Tue. Showers continue overnight, then conditions dry out in the afternoon. South-southwesterly winds with gusts up to 20 kt turning more westerly Tue afternoon. -10

MARINE

A robust frontal system continues to traverse the coastal waters this afternoon, bringing a period of gale-force gusts reaching 30-40 kt south of Cape Falcon through 7 PM this evening. Otherwise, relatively steep seas of 7-10 ft at 8-9 seconds with a dominant westerly swell are expected, while southerly wind gusts of 20-30 kt turn out of the west behind the front this evening. Conditions across the waters and including the Columbia River Bar will therefore remain hazardous to small craft through much of Tuesday.

As high pressure builds offshore through the remainder of the week, west winds of 5-10 kt on Wednesday will steadily shift out of the north. Typical summertime northerlies will reach diurnal peaks of 15-25 kt each afternoon and evening from Thursday through the weekend, which may necessitate daily Small Craft Advisories, especially beyond 10 NM south of Cape Falcon. Seas will persist at 4-7 ft at 9-11 seconds with a continued westerly swell. -36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 11 PM PDT Tuesday for PZZ210-251>253- 271>273.