textproduct: Portland

SYNOPSIS

High pressure aloft will keep the pattern rather benign and mostly dry over the weekend and into the middle of next week. Night and morning marine clouds will continue to be the main temperature wildcard, especially where clouds linger into midday. We may see another warming trend towards the beginning of next week.

DISCUSSION...Now through Thursday Night

Today and through the weekend, the most reliable part of the forecast is the overall dry pattern, with the less reliable part being exact high temperatures. Marine stratus will continue to re-form and surge inland each night and will potentially push all the way to the Cascades, then gradually retreat back toward the coast as the day progresses. Guidance suggests earlier clearing of the marine stratus through the weekend for many inland locations as the upper level ridge axis moves overhead. Overall, expect coastal and higher terrain daytime highs in the upper 50s to upper 60s, with inland valleys generally low 70s to low 80s. As for Mother's Day (Sunday), while afternoon temperatures will be slightly cooler due to a shortwave trough sliding into the region, weather will continue to look favorable for outdoor plans with inland highs in the 70s and upper 50s to mid 60s elsewhere under a mix of sun and passing clouds.

As the start of next week approaches, upper level ridging looks to return to the Pac NW. This will bring about another round of warm, daytime highs. Temperatures early next week will depend on the exact placement and strength of the upper level ridge axis. If the axis remains farther west, that will generally favors warmer daytime highs, while a more inland ridge axis placement would keep temperatures a touch cooler. Currently, model and ensemble guidance are leaning towards a warmer solution. Tuesday, remains the primary day to watch as ensemble guidance continues to show substantial spread in potential temperatures and synoptic pattern. The GFS and its ensembles are pointing towards a more stagnant pattern, which has an Alaskan low remaining well west of the region and said low looks to remain in the central eastern Pacific through the majority of the week. This set up for keep up very warm and dry with 850 mb temperatures in the 14-16 degree range. On the other hand, the ECMWF and its ensembles are generally pointing towards a more progressive pattern. Again, an Alaskan low looks to develop, but will take a more drastic route in comparison to the GFS. The track of this low looks to take a more direct line from the northeastern Pacific towards the OR/CA border. This solution would still keep the region warm, but slightly cooler (relatively speaking) when compared to the GFS as 850 mb temperatures range from 13-15 degrees C. Overall, current guidance suggests highs could range anywhere from the lower 70s into the lower 90s Tuesday, with similar broad spread lingering into Wednesday. Looking at the ECMWF Extreme Forecast Index does suggest that daytime high temperatures could exceed the model's climatological extremes for early/mid May, for the start of the upcoming week. However, confidence in any specific outcome remains low at this time. /42

AVIATION

Broken mid/high-level clouds will continue to stream into the airspace as a weak frontal system moving through the eastern Pacific pushes high pressure east of the Cascades. This will maintain southerly onshore flow and support re-development of marine stratus along the coast with 60-80% chance for MVFR CIGs or lower along the coast at any given hour from 06Z-18Z Friday. After 18Z Friday, expect stratus along the coast to improve to VFR. Marine stratus may also filter into the southern Willamette Valley, resulting in a 30-50% chance for MVFR CIGs developing at KEUG from 09Z-12Z Friday, increasing to 40-60% chance between 12Z-17Z Friday. Conditions inland to improve to VFR around 18Z Friday. South/southwest winds through 08Z Friday before northerly winds return through at least the remainder of the TAF period.

Weak high pressure builds over the coast starting around 00Z Saturday and this will limit the return of marine stratus to the coast, but a return of MVFR to LIFR conditions could return for locations south of KSLE starting around 12Z Saturday.

KPDX AND APPROACHES...VFR conditions with high clouds through the TAF period. Southerly winds through around 04Z Friday before northerly winds return and persist through the end of the TAF period. /42

MARINE

Northerly winds turn southerly through the early morning hours as a weakening front moves across the waters. High pressure returns towards the end of the weekend and into the start of next week. This will bring a return northerly winds across all waters, along with a chance for widespread gusts up to 25 kt towards the end of Monday and through the middle of next week, with the breeziest conditions expected south of Cape Falcon. There remains some uncertainty within the models as to the exact path of the system. However, there is a 50-75% chance for at least isolated small craft wind gusts Monday and Tuesday for areas south of Cape Falcon, OR. Seas remain around 4-6 ft through the weekend, with seas slowly building towards 5-8 ft as the aforementioned system moves across the waters towards the start of the upcoming week. /42

PQR WATCHES/WARNINGS/ADVISORIES

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