textproduct: Portland

SYNOPSIS

High pressure continues well offshore with general westerly flow over the region. Showers from the Thursday system will continue to dissipate through the morning with any lingering rain isolated to the Cascades. Marine stratus expected today. High pressure intensifies through Tuesday leading to increasing confidence in near record high temperatures on Monday and Tuesday. Pattern shift expected on Wednesday.

LONG TERM...Monday through Thursday

Monday starts the first of two days of drastically increasing temperatures. 500 mb heights are in good agreement of the ridge of high pressure intensifying, and the ridge axis shifting closer to the shore. In fact, the differences between clusters is minimal. This ridging is combined with widespread east flow aloft of significantly warmer temperatures in the midlevels. 850 mb temperatures will rise to around 12-13 deg C. This pattern will cause temperatures to spike once again by about 10 deg F with highs forecast to be in the mid to upper 80s inland, in the upper 60s to low 70s along the coast, and the Cascades in the 60s. There is currently around a 30-40% chance of the greater Portland-Vancouver Metro area seeing highs of 90 deg F or more on Monday, with the central Willamette Valley sitting closer to 20%. Elsewhere, chances are less than 5%. The big component to consider on Monday is the urban heat island effect and thus why Portland will be warmer. Overnight temperatures will still cool, but are not expected to be as cool as previous nights. This is due to the easterly flow aloft causing a weak downslope feature. This will cause warming from compression within the lower elevations.

Tuesday is marked to be the hottest day of the week with near record breaking temperatures forecast. There is high confidence (greater than 75%) that the Portland-Vancouver area will see highs of 90 deg F or more, around 50% in Salem, 45% in Longview, and 25% in Eugene. If we were to bump up that temperature to 95 deg F or greater, the Portland area remains the highest around 31% while other urban areas and along the I-5 corridor has less than a 10% chance. Overnight temperatures will provide little relief in major urban areas but elsewhere, lows of 50-55 deg F are expected. There is currently widespread Moderate HeatRisk, and around a 10% chance of Major HeatRisk in the greater Portland-Vancouver Metro. This means that those without cooling and hydration, as well as those exposed may be affected. Therefore, take precautions on Tuesday if participating in outdoor activities - especially in the afternoons during peak heating.

Luckily this heat will be short lived as the high pressure moves inland and a low pressure system begins to drop down from the Gulf of Alaska. 500 mb height cluster analysis has a moderate level of consensus in this low with around 32% of the members showing higher heights, and around 10% showing significantly lower heights. With that being said, the flow should become more zonal ushering in much needed relief from the Pacific. NBM temperatures show a steady temperature decline through the remainder of the week. In addition to the zonal flow, a frontal system will move over the area with around three quarters of the clusters showing precipitation of some kind over the region. At this time, confidence is low in the exact accumulations. One caveat to this is the fact that we will have had a few days of very dry air in place which may cause this front to weaken as it nears. Therefore, there remains around a 10% chance of highs in the upper 80s on Wednesday.

Some models are suggesting a transient ridge forming on Thursday which would cause conditions to dry once again. However, confidence is quite low as it will greatly depend on how the frontal system on Wednesday shakes out. -27

AVIATION

Satellite imagery shows marine stratus moving in creating widespread MVFR conditions. While high end MVFR, the marine stratus will linger well into the morning throughout the area until winds start to increase and high pressure begins to shift eastward. There is anywhere from a 10-50% chance of showers today though they will be light and lightning is not expected. Cannot rule out a stray outflow wind gust though with any passing showers. Will see a gradual lift to VFR today and winds increasing after 22Z Fri from the north. High resolution models are attempting to keep the coast from filling back in overnight but if the flow becomes more westerly, it will be difficult to keep the clouds at bay. Elsewhere, cloudy but VFR conditions expected.

KPDX AND APPROACHES...MVFR through at least 16Z Fri but may last as late as 20Z Fri if winds remain lighter. Gusty conditions expected after 22Z Fri with gusts as high as 20 kt. There is around a 20% chance of gusts exceeding 25 kt this evening. -27

MARINE

High pressure remains over the area with a persistent northwesterly swell. A low pressure system inland is encouraging a slightly elevated northwesterly wind wave which, when combined with the northwesterly swell, is maintaining elevated Small Craft Advisory seas. Seas have been a bit more dynamic as they are fluctuating greatly between 8-10 ft at 15 seconds overnight. Because we are expecting these conditions to continue, have extended the advisory through the early afternoon as a sign of caution. Some models are suggesting a 10% chance that seas greater than 10 ft could last well into tonight though based on the overall pattern that looks less likely. Will note that seas will ease from south to north with the waters of PZZ252/253, and PZZ272/273 easing below 10 ft by as early as 1100.

Winds are beginning to ramp up as a weak disturbance passes over the waters. Through the week, we will maintain the northwesterly primary swell with a steady decline below 8 ft at 10 seconds. On Sunday, an increasing pressure gradient due to the placement of a high pressure system will cause winds to increase in a typical summer like pattern. Cannot rule out gusts as high as 30 kt in the southern outer waters on Sunday afternoon.

A series of strong ebbs will take place through the Columbia River Bar in the evening through at least Sunday. -27

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 2 PM PDT this afternoon for PZZ210- 251>253-271>273. Small Craft Advisory from 1 AM to 7 AM PDT Saturday for PZZ210.