Area Forecast Discussion

SYNOPSIS

An upper level ridge gradually builds over the far northeast Pacific then western WA/OR over the next several days ushering in a prolonged stretch of dry and warm/hot conditions. An Extreme Heat Watch is in effect Sunday afternoon through Tuesday evening for the greater Portland/Vancouver Metro, western Columbia Gorge, central Willamette Valley, and portions of the lower Columbia for daytime highs of 95-100 degrees and overnight lows in the mid 60s or warmer, resulting in Major HeatRisk. Heat related impacts are anticipated for much of the region. Temperatures will trend cooler for Wednesday onward with the return of onshore flow.

SHORT TERM...Now through Saturday Night

Seasonable conditions through Saturday as high pressure gradually builds over the Northeast Pacific. 500 mb height ensembles are in excellent agreement in regards to this ridging pattern which leads to a high confidence in warming and drying each day. Friday will be essentially a rinse and repeat of today with highs in the upper 70s and overnight lows in the mid 50s. On Saturday we will see a spike in temperatures where the median high temperature in the northern Willamette Valley will be in the lower 90s, southern Willamette Valley in the upper 80s, and along the coast in the 70s. Overall, Saturday sits under a Moderate HeatRisk. There are some areas of Major HeatRisk within the greater Portland-Vancouver Metro, but interestingly, there is a around a 30-40% chance within the Lane County Coast Range. Likely this is due to increased easterly winds and dry air aloft.

Now, with this pattern developing, there will be a trend towards easterly offshore winds. Conditions will begin to get breezy on Saturday within the Columbia River Gorge, and the southern and central Willamette Valley (where winds will be northerly). These speeds are not unusual though and nothing to write home about. -27

.LONG TERM...Sunday through Thursday...Heat remains the main headline for the start of next week as temperatures ramp up considerably on Sunday and Monday. The high pressure ridge will amplify on Sunday and shift slightly eastward aligning over the Coast Range. This alignment will coincide with a thermal through (low pressure caused by high temperatures) which will be a contributing factor to breezy winds in the afternoon. But first, let's look at those temperatures on Sunday and Monday.

Models have been fairly consistent with Sunday and Monday being the hottest of the next week, and Monday being the peak heating day. High temperatures will vary based on location but overall, there are increasing chances for records to be broken or tied. These records are listed below in a designated "climate" section. As it stands, reaching 100 deg on Monday with around a 25% chance in the Greater-Portland Metro. The coast could be impacted as highs are forecast to reach near 80 degrees. In areas like Tillamook, a high temperature of 85 degrees F is not out of the question. Downsloping east winds will amplify temperature rises along the coast and Willamette Valley on both Sunday and Monday. There is a mixed bag of Moderate and Major HeatRisk, but in the industrial areas of Portland there is also a 10% chance of Extreme HeatRisk. The Extreme Heat Watch remains in effect for Sunday through Tuesday and will continue to be evaluated. The consideration being taken at this point are the locations that may be impacted and our confidence level for the temperatures.

A factor to take into account in this forecast are also the overnight low temperatures. In general, we are seeing overnight lows in the mid-60s and even near 70 degrees on Monday into Tuesday night. These temperatures will leave little to no relief overnight. HeatRisk takes this into account in the calculation but in this case, those temperatures are sitting right on a threshold. Therefore, there remains a level of uncertainty in whether the overall risk will be there.

In addition to the heat, there will also be increasing fire weather concerns in areas with cured grasses and finer fuels. A thermally induced surface trough will establish itself somewhere west of the Cascade crest starting on Saturday helping to strengthening offshore flow for Sunday and Monday as well. This will bring breezy conditions within the western Columbia River Gorge/Cascades gaps and the Willamette Valley. As daytime highs increase, relative humidities will also decrease. Given the hot, dry, breezy conditions expected, there are increasing fire weather concerns over the weekend through the start of next week, especially Sunday afternoon through Monday afternoon. Based on feedback from area partners, fuels are not quite cured yet, but we are unsure how the days of drying and warm conditions will impact them. 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 cured grasses and dry, fine fuels. Live vegetation and larger fuels may not have enough time to dry out prior to the dry and breezy conditions, but this is a variable that is being closely monitored by our State and Federal Fire Partners.

Starting Tuesday, temperatures will start to decrease. This is due to a trend towards a troughing pattern from the northeast Pacific. While about half of the ensemble clusters suggest a trough, the other half maintain the ridging pattern. Therefore, confidence is quite low in regards to just how much cooler we will be on Tuesday. It is also not uncommon for models to degrade highly amplified ridges like this too early. Because there is not a robust system moving in, seeing a degradation of the ridge is going to be less drastic. On Tuesday, the most likely range (25th-75th percentile) ranges from 85-90 deg F within the Willamette Valley and 60-65 deg F along the Coast. The 90th percentile though, which would be the situation where the ridge maintains its position, would see highs around 92-94 deg F in the interior lowlands.

For those of you who are not heat fans, as we move into Wednesday, onshore zonal flow returns along with seasonable temperatures through Thursday. -27

AVIATION

VFR flying conditions beneath largely clear skies expected for most terminals throughout the period. Building high pressure offshore will see diurnal north to northwest winds of 5-10 kt in the afternoon ease to 3 kt or less overnight inland. At the coast, slightly stronger winds of 10-15 kt this afternoon and evening with gusts near 20 kt along the central OR coast will also ease to 5 kt or less tonight. Chances for MVFR cigs beneath low marine clouds increase along the coast and lower Columbia River after 09-12z, with chances over 50% only at KAST.

KPDX AND APPROACHES...VFR conditions beneath largely clear skies throughout the period. Diurnal northwest winds of 6-8 kt this afternoon will ease to 3 kt or less tonight. Low coverage of low clouds at 2-3 kft is possible early Friday morning, with very low chances of MVFR cigs. -36

MARINE

Expect a typical summertime pattern persist into next week as high pressure builds offshore. Diurnal northerly winds will strengthen, peaking each afternoon and evening starting today, but becoming more noticeable from Friday through at least early next week. Winds of 15-20 kt with gusts near 25 kt south of Cape Foulweather will trend weaker to the north. Due to these conditions, Small Craft Advisories have been issued for the waters south of Cape Falcon through Friday night. These Advisories will likely need to be extended as gusty conditions persist over the next handful of days. Seas continue to hold around 4-7 ft at 9-11 seconds with a persistent westerly swell. Long-range guidance brings a return of more active weather and a higher chance of elevated seas by the end of next week, but confidence in this pattern change is low. -36/99

CLIMATE

Record highs for Sunday, June 14

Portland Int'l 89F (1988) Vancouver, WA 93F (1986) Hillsboro 96F (1961) McMinnville 93F (1986) Salem 92F (1961) Eugene 92F (1914) Astoria 86F (1914)

Record highs for Monday, June 15

Portland Int'l 95F (1966) Vancouver, WA 95F (1930, 1966) Hillsboro 99F (1961) McMinnville 96F (1961) Salem100F (1966) Eugene 96F (1966) Astoria 91F (1966)

PQR WATCHES / WARNINGS / ADVISORIES

OR...Extreme Heat Watch from Sunday morning through Tuesday evening for ORZ108>115-120. WA...Extreme Heat Watch from Sunday morning through Tuesday evening for WAZ206-207-209. PZ...Small Craft Advisory from 2 PM Friday to 5 AM PDT Saturday for PZZ252-272. Small Craft Advisory until 5 AM PDT Saturday for PZZ253-273.