textproduct: Portland

SYNOPSIS

Unseasonably warm and dry conditions continue through Thursday with areas of early morning valley fog and coastal fog. Weak onshore flow Monday and Tuesday transitions to weak offshore flow Wednesday and Thursday, bringing slightly warmer temperatures mid-week. A trough moving into the Pacific Northwest will bring cooler temperatures and chances for light rain Friday into next weekend.

LONG TERM...Thursday through Saturday night

Remaining warm and dry on Thursday with sunny skies and light offshore flow. Temperatures are expected to increase a few degrees compared to the middle of the week, with highs rising back into the low to mid 80s over inland valleys and around 70 degrees at the coast. This could very well be the last 80+ degree day of the year, as conditions will finally cool down close to seasonal normals Friday into next weekend. However, this is not a given based on climatological records. While we are already beyond the climatological average for the last 80+ degree day (which is September 28 for the Portland International Airport), the latest 80+ degree day ever recorded at Portland International Airport is October 21. This record was set back in 2003. Daily record highs for Thursday, Oct. 8, are generally in the 83-89 degree range for the Portland metro and Willamette Valley. The current forecast suggests most locations will not break daily record highs, but this cannot be completely ruled out for a site or two, especially Salem and Eugene where record highs are lowest (84 and 83 degrees, respectively).

As mentioned above, conditions trend cooler Friday into next weekend in response to an incoming upper level trough. Model ensemble guidance varies on the exact amplitude and timing of this trough and whether or not light rain will fall beginning sometime on Friday over southwest WA and northwest OR. Regardless of the exact evolution of this trough, confidence is high temperatures will become noticeably cooler by Friday with inland highs ranging somewhere between the mid 60s and mid 70s and somewhere in the 60s on Saturday. If rain does occur, confidence is high amounts would be light and non-impactful with total rain amounts under 0.25 inches (85-95% chance). Looking at the 12Z/Oct. 4 iteration of the ENS/GEFS/GEPS for 6-hr QPF, it is clear there are significant model ensemble differences. The ENS is confident at least some light rain will fall on Friday and/or Saturday as only 10% of the ensemble members are dry during that time. Meanwhile, nearly 75% of ensemble members from the GEFS are dry. Lastly, 30% of ensemble members from the GEPS are dry. As a result of these timing and amount differences, NBM 6-hr PoPs are fairly low and only peak between 10-30%. The highest PoPs are over the Cascades, south WA/north OR coast, and Willapa Hills.

Chances for morning frost increase next weekend over the Upper Hood River Valley and outlying rural areas within the Willamette Valley, especially the southern Willamette Valley. The NBM is showing a 5- 25% chance for morning lows below 37 degrees Saturday night/Sunday morning within these areas, except a 50-75% chance in the Upper Hood River Valley. Anyone growing outdoor vegetation that is susceptible to frost damage should monitor the forecast over the next several days. -23

AVIATION...Through 00Z Tuesday

Currently widespread VFR inland and almost widespread VFR along the coast as KTMK and KONP continues to clear out. Heading towards 03-06Z Mon, marine stratus will push back into the coast, bringing LIFR fog to the coastal terminals (25-50% chance of LIFR conditions). Additionally, chances for stratus in the southern Willamette Valley increase, with probabilistic guidance suggesting a 15-25% chance of LIFR conditions at KEUG between 09-17Z Mon. As for other inland terminals, a 10-15% chance of LIFR conditions between 12-17Z Mon.

North to northwest winds at around 5 to 7 kt this afternoon will ease around 03Z Mon. Winds of 8-12 kt with gusts up to 20 kt are possible this afternoon at KONP.

KPDX AND APPROACHES...VFR conditions throughout the period, with a 10-15% chance of IFR/LIFR conditions around 12-17Z Mon. Diurnal northwest winds around 5 to 7 kt this afternoon will ease by 03Z Mon. ~12

MARINE

High pressure offshore continues, maintaining northerly winds through the week. Chances for peak wind gusts of 20 to 25 kt increase Monday through Wednesday, generally during the afternoon and evening. Expect wind-driven seas around 4 to 6 ft through early this week, with a west to northwest swell at 8 to 9 seconds increasing to 10 to 12 seconds by Monday.

As a result of winds increasing and bringing gusts up to 25 kt on Monday, a Small Craft Advisory has been issued for the waters south of Cape Foulweather OR from 11 AM to 11 PM Monday.

High pressure aloft this weekend will also support areas of dense fog developing nightly as cloud bases are compressed down to the surface. We will continue to monitor conditions over the waters each night as fog may lower visibility to under 1 SM, resulting in difficult navigation.

More active marine conditions are likely in the latter half of the week as troughing over the Gulf of Alaska generates a building northwest swell and chances for rain return to the region Friday into next weekend. Seas will increase to around 7 to 9 ft Wednesday into Thursday, then decrease Friday. A longer period northwesterly swell may also bring a moderate sneaker wave threat Wednesday through Thursday. ~12/36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 11 AM to 11 PM PDT Monday for PZZ253- 273.