textproduct: Portland

SYNOPSIS

Minimal change in the forecast as all features appear to be on track. High pressure continues to build through Tuesday with warming temperatures. Moderate HeatRisk is expected along the I-5 Corridor north of Salem, including the Portland/Vancouver Metro. Temperatures cool again to near seasonable averages by Wednesday as high pressure is replaced with more zonal flow aloft. Chances for precipitation continues to decrease with less than a 10% chance now through Thursday. Cooler conditions likely by next weekend as a low pressure system in the Gulf of Alaska brings increasing chances for rain later Friday into Saturday.

LONG TERM...Wednesday through Sunday

If you have been tracking the forecast over the last few days, you know that there is a low pressure system and negatively tilted trough positioned over the northeast Pacific off of the Alaska Panhandle. This low will advect cooler air over the region and enhance onshore flow. However, as has been the trend, each day this low continues to decay further with each model run. Therefore the impacts will be minimal in the way of potential precipitation, but we will see relief from warming temperatures with high temperatures dropping by around 15 deg F. An associated frontal band well ahead of the surface low will approach the coast, but guidance continues to trend down with minimal, if any, precipitation spreading inland. In fact, NBM guidance generally shows less than a 10% chance of accumulating rain through Thursday; except there is around a 20-30% showers in the Cascades Wednesday afternoon and evening as the afore- mentioned trough lifts across the region.

Uncertainty increases late in the week and into the weekend regarding the weakened low pressure system potentially dropping down from the Gulf of Alaska toward the Washington coast. In general, there are increasing chances for rain on Friday and Saturday, but very low chances for any impactful weather. Ensemble guidance suggests 24-hour rainfall accumulation could range anywhere from zero (10th and 25th percentiles) up to potentially exceeding 0.5 to 1.0 inch (closer to the 90th percentile). Despite the potential pattern discrepancies, onshore flow is likely which will usher in cooler marine air and thus lower temperatures. Showers linger through Sunday though will be light. -27/DH

AVIATION

Offshore high pressure will begin to move onshore through the period, supporting continued VFR flying conditions across the airspace. Largely clear skies aside from few-sct high cirrus at or above 25 kft will persist through tonight. Diurnal north to northwest winds will rise by 20-21z Mon to 8-12 kt inland. Along the coast, winds will reach 10-15 kt with the frequency of gusts as high as 20-25 kt increasing to the south. Winds ease below 5 kt out of the north to northeast tonight.

KPDX AND APPROACHES...VFR conditions expected throughout the period beneath largely clear skies aside from few-sct high cirrus at or above 25 kft. Diurnal north to northwest winds will rise to near 10 kt after 20-21z Mon, then ease below 5 kt by 03-06z Tue. -36

MARINE

High pressure offshore will continue to generate gusty north winds through much of Monday. The strongest winds with gusts up to 25 kt continue south of Cape Falcon, where Small Craft Advisories remain in effect through 11 PM PDT this evening. Seas continue at 4-8 ft at 9-10 seconds with a dominant WNW swell.

Low pressure shifts over the waters on Wednesday causing a southerly wind reversal on Wednesday. The frontal band along the leading edge moves over the waters through Wednesday and then winds shift to the northwest in the post frontal environment. Unsettled weather continues through the remainder of the week, with further rain possible next weekend as another front traverses the waters. A persistent westerly swell will support continued seas of 4-8 ft at 10-11 seconds. -27/36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ252- 253-272-273.