textproduct: Portland

SYNOPSIS

Generally onshore flow with weak ridging at the mid levels. Will continue to see near to slightly above normal temperatures over the weekend, with the potential to warm further early next week. Overall, will see minimal change in the forecast from day to day though.

LONG TERM...Monday through Friday

High pressure at the surface really begins to take hold over the northeast Pacific on Monday which will trend conditions towards warmer and drier conditions. 850 mb temperatures continue to rise through at least Wednesday with the peak being Tuesday and Wednesday. around 15-17 deg C. There is an extensive ridge aloft building inland, with around half of the ensembles suggesting weak trough forming near the coast line. This pattern orientation will have a significant impact on just how hot conditions will be. The spread of possibilities is quite wide with around a 8-10 deg F spread between the 10th-90th percentile along the coast and around a 12 deg F spread in the interior valleys. Lets dive into a few of the locations for an example of the level of uncertainty we are dealing with. I will note that models have fluctuated quite a bit over the last 24-hours.

For Tuesday, Portland is showing a 10% chance of high temperatures of 85 deg F, and equal chances of them being 98 deg F. Elsewhere in the Willamette Valley shows similar ranges. The Upper Hood River Valley ranges from around 85-95 deg F, and Longview 82-95 deg F. Moving into Wednesday though the uncertainty grows significantly. In fact, the range from the coolest high temperature to the warmest (10th to 90th percentile) is around 20 deg for the Willamette Valley and 10 deg for the coast. In fact there is around a 10% chance of highs of 70-75 deg F for the coast, and 100-105 deg F for the inland valleys including some areas like Estacada and Stayton. With this being said though, there are equal chances of temperatures in the lower 80s. Therefore, not biting on any specific outcome in particular and have moreso stuck with the median within the forecast to account for some of the outliers. A similar trend occurs thus far on Thursday.

If these temperature forecasts remain, we are looking at the potential for Moderate HeatRisk with a 20% chance of Major HeatRisk for urban areas on Wednesday. -27

AVIATION

A weak upper level trough continues to move south towards airspace, turning the flow aloft more southwesterly. This trough will then shift northeastward around 00Z Sun, keeping precipitation out of the airspace. As of 06Z Sat, marine stratus remains pushed into the coast, maintaining a mix conditions from VFR to LIFR at coastal terminals. While guidance suggests that KAST will stay MVFR through the TAF period with only a 10-30% chance of IFR CIGs between 07-10Z Sat, KONP will likely stay under LIFR/IFR conditions through most of the TAF period. Probabilistic guidance suggests a 70-90% chance of LIFR conditions at KONP until 12Z Sat, then a 40-60% chance until 18Z Sun. Beyond 18Z Sat, KONP may stay IFR or improve to MVFR, with a 10-30% chance of LIFR. Disagreement between models leave much uncertainty beyond 18Z Sat for KONP.

As for inland terminals, expect VFR conditions to persist until 07-09Z Sat, possibly deteriorate to MVFR CIGs until 18-20Z Sat (50-70% chance), then return to VFR for the remaining of the TAF period. Back building off of the Cascades will be the main driver on whether we see the deep stratus develop inland.

Current west to northwesterly winds around 5-10 kt will gradually shift more west to southwesterly and become light towards 09Z Sat. Winds will then pick back up to 5-10 kt and gradually shift more westerly towards tomorrow afternoon.

KPDX AND APPROACHES...VFR conditions with a 50-70% chance of MVFR CIGs between 09-18Z Sat. Northwesterly winds around 5-10 kt will become light and variable by 12Z Sat, then increase back to 5-10 kt and shift southwesterly by 18Z Sat.~12

MARINE

High pressure rebuilds over the coastal waters through the weekend, returning northerly winds later Saturday and increasing pressure gradients on Sunday. Chances for gusts up to 25 kt return Sunday afternoon, mainly across the central and southern waters out to 30-40 NM. Seas are expected to remain around 4 to 6 ft as relatively benign conditions persist through the weekend and into the start of next week. -19/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.