Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
211 FXUS66 KPQR 212147 AFDPQR Area Forecast Discussion National Weather Service Portland OR 247 PM PDT Tue May 21 2024 .SYNOPSIS...Slow moving front continues to move southeast, gradually blanketing the region with widespread rain. Rain will become scattered showers tonight into Wednesday. Dry and warmer Thursday before becoming unsettled for Friday into the weekend. && .SHORT TERM...Tuesday afternoon through Thursday...Satellite imagery around 2 PM Tuesday, front slowly moves southeast bringing widespread rain through most of the region (North of Eugene and Newport). With this front bringing northwesterly winds at the surface, lowlands and south areas of the region are expected to receive less rain due to the rain shadow effect. Rain will turn showery this evening, then isolated overnight for areas west of the Cascades. Behind this front, a closed low moving south southeast through western British Columbia will reach western Washington around 5 AM Wednesday. This low will then drift southeast into northeast Oregon through the rest of Wednesday. The core of this low will just miss our region, resulting in showers, similar to today. With northwesterly winds and the closed low coming from the north, precipitation along the Coast Range will be limited, with majority of the precipitation along the Cascades. Through Wednesday evening, chances to exceed 0.5 in of precipitation over 24 hours is 10-30% chance for the valley lowlands and 50-70% for coastal areas north of Tillamook. With the aforementioned low just missing our region, instability will be rather limited, therefore thunderstorm chances will be low across the Cascade foothills. The high Cascades will receive snow but snow levels will remain well above mountain passes. Thursday, a weak shortwave ridge builds over the region as the closed low moves east over the northern Rockies. This will bring sunny skies and warm temperatures up into the upper 60s (20-30% to exceed 70) for the interior lowlands and mid 50s/upper 50s along the coast. -JH .LONG TERM...Friday through Monday...An unsettled weather pattern is expected to continue through at least Saturday. WPC`s 500 mb cluster analysis indicates a week shortwave could bring light showers Friday followed by an upper level low bringing slightly more showers to the region Saturday. Timing and amount of precipitation continues to remain uncertain, though temperatures are expected to be near seasonal normals. The pattern becomes a bit more uncertain Sunday on whether troughing will still be present to continue showers. By Monday, dry conditions are expected, with 20% of clusters suggesting a weak trough approaching and 80% of clusters suggesting a ridge overhead or nearby (location and timing still uncertain). This brings significant uncertainty in temperatures with NBM 25th to 75th percentiles for inland valleys ranging anywhere from upper 60s to low 80s. -JH && .AVIATION...The front is in the process of moving ashore, and rain has begun at almost all areas. Cigs at the northern/central coast (KAST) are bouncing between IFR and MVFR, while inland cigs are high end MVFR/low end VFR. By 00z Wed, the coast sees 90%+ of firmly IFR cigs. Southern terminals (KONP/KEUG) remain VFR as precipitation is heavier up north, but will begin to lower within the next few hours, by 00z Wed. Between 06-10z Wed, conditions transition to post-frontal, and most terminals will trend back to VFR, with the valley transitioning faster. By 09z Wed, even the coast only sees 30-40% chance of MVFR or lower ceilings. West/southwesterly winds will also begin to pick up around that time, with gusts for most areas up to 20 kts (25-30 kt at KAST). PDX AND APPROACHES...VFR conditions are currently in place, but all surrounding terminals have already dropped to high end MVFR; expecting a drop in cigs down to MVFR within an hour or two, by 00z Wed. Conditions trend back to VFR around 08z, with less than 10% chance of MVFR conditions continuing past that time. Winds will pick up slightly, with top gusts up to closer to 15-16 kt from the west at that time. /JLiu && .MARINE...The front is passing through, bringing higher seas and gustier winds in the north and central waters. Winds are gusting to 25 kt or so north of Cape Foulweather, spreading southward to PZZ273 by 03Z, persisting at times through Tuesday night and Wednesday. With the persistent northwest fetch in the post- frontal environment, also expecting seas to become fairly steep Tuesday night into Wednesday with greatest impacts to PZZ251 as seas rise to 10 to 13 ft with a period 9 to 10 seconds. As we move into Thursday, calmer winds/seas return for a day followed by yet another weather disturbance moving into the region from the NNW late Friday/Saturday continuing the rather progressive and active weather pattern. Seas likely rise to 7-10 feet at 8-9 seconds on Saturday before decreasing Sunday into early next week - wave steepness may again be a concern Saturday. -mh/JLiu && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 5 PM PDT Wednesday for PZZ210. Small Craft Advisory until 5 PM PDT Wednesday for PZZ251-252-271- 272. Small Craft Advisory from 8 PM this evening to 5 PM PDT Wednesday for PZZ273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland