textproduct: Portland

SYNOPSIS

A transient ridge today will keep conditions seasonable and generally dry. A deeper trough and associated low pressure system shifts southward into the region Friday to Saturday increasing onshore flow and returning more widespread chances for precipitation. Slight chances for thunderstorms Friday and Saturday afternoon. Drier weather returns Sunday before another trough returns chances for precipitation early next week.

LONG TERM...Sunday through Wednesday

For those with Sunday plans, there will be a brief drier period as a shortwave ridge passes over the Pacific Northwest. 500 mb ensembles are falling into better agreement with another longwave trough moving over the area. Uncertainty remains in the exact track as it's quite messy with deterministic surface plots showing a number of small mesoscale lows embedded within the trough. However, this system will encourage overall more moist and cool air to move into the area. Therefore will maintain a trend of below normal high temperatures. When observing the 24-hr precipitation differences between the ensembles, around half of the solutions are trending drier than the composite ensemble and the other half wetter. This only emphasizes the level of uncertainty. Ultimately it will once again come down to the track of the system. When looking at individual ensemble members, there is consensus though that rain will start at some point on Monday but how much rain is undetermined.

Tuesday into Wednesday is a bit of a blur as the two days run seamlessly into one another. Post frontal rain showers expected with breezy westerly winds once again possible. One thing to consider is that some of the models are suggesting that the low will move almost directly over the forecast area. If this occurs, the jet stream will dip just to the south and we will be in a very dynamic pattern. In fact, there are a few of the model runs that suggest that we could see greater than 1 inch of rain on Tuesday into Wednesday. Again though, uncertainty is incredibly high and the larger trend is towards non-impactful accumulations. -27

AVIATION

Onshore flow continues to support low stratus along much of the coast and over the Cascades and Cascade Foothills. Sub-VFR conditions along the coast with VFR conditions across the interior lowlands continue. Chances for IFR to MVFR ceilings increase tonight into early tomorrow morning both inland and at the coast. By 12Z Thursday, chances for ceilings below 3000 ft increase to 25-50% for inland TAF sites, except 60-75% at KSLE and KEUG. Chances for ceilings below 3000 ft range between 75-95% at KAST and KONP through 12Z Thursday. Conditions expected to improve back to VFR for all terminals after 18-20z Thursday. Winds become light and variable after 08-10z then increase to 5-10 kt from the west after 20-22z Thursday.

KPDX AND APPROACHES...VFR conditions continue. There is a 30-40% chance for ceilings below 3000 ft between 08-17Z Thursday as lower clouds forming along the Cascade foothills attempt backbuilding westward towards the KPDX terminal. West winds 5 kt or less through the period. -19/23

MARINE

Looking at fairly benign conditions over the next several days despite a series of frontal systems moving through. Generally westerly flow over through Saturday. Seas are expected to remain around 5 to 6 ft as a westerly swell persists. Seas then build to 6-8 ft at 11 to 12 seconds late tonight night into Friday morning as a weak frontal boundary approaches the water. This front will also bring increasing westerly winds with gusts up to 20 kt. There is less than a 5% chance of wind gusts of 25 kt or greater.

A secondary front arrives on Saturday, bringing a shift to northwest winds. However, wind speeds are not expected to increase much with this frontal passage. There is less than a 15% chance of Small Craft Advisory winds. The time period with highest wind speeds will likely occur on Monday as stronger system moves over the waters, bringing south winds up to 20-25 kt and seas approaching 9-10 ft. -27/23

PQR WATCHES/WARNINGS/ADVISORIES

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