Area Forecast Discussion
Issued by NWS Portland, OR

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000 FXUS66 KPQR 032236 AFDPQR Area Forecast Discussion National Weather Service Portland OR 235 PM PST Wed Mar 3 2021 .SYNOPSIS...Mild dry Spring-like weather will continue through early Thursday. A series of storm systems will bring valley rain and mountain snow starting Thursday afternoon and continue moving through the area into early next week. && .SHORT TERM...Tonight through Saturday...Water vapor satellite imagery continues to show a shortwave ridge over the region. At the same time water vapor imagery shows a trough diving southeast into the eastern Pacific, which will move east towards the region Thursday into Friday. As this trough moves east, an atmospheric river looks to impact the Oregon coast at the same time. Looking at GEFS and EPS data, Integrated Vapor Transport (IVT) values for this atmospheric river are around 500-600 kg/(ms), which places it into the moderate category for atmospheric rivers. The same guidance is showing that the strongest part of this AR will be focused towards the central Oregon coast, given that the AR has a south to north orientation the IVT values farther north will be less than 500 kg/(ms), which lowers the AR category to low. The exact start time for the precipitation is still variable but, the high resolution models using the SPC HREF Ensemble Viewer has the precipitation starting along the coast sometime between late Thursday morning and Thursday afternoon. Given that the overall flow of this AR will be south to north the potential for hydrological concerns continue to be limited. QPF totals for this event from Thursday afternoon through Friday night look to be around 1.5 to 2 inches along the coast and 0.75 to 0.25 inches along the eastern flank of the Coast range across to the Cascades. While overall hydrologic concerns are currently minimal, the Grays River continues to be the river of highest concern followed by the the Nehalem River. As the entire system moves farther south through Friday and into Saturday, the upper level trough will gradually weaken and drop snow levels to around 2500 to 3000 feet as 850 mb temperatures fall to around -3 C to -5 C. However, the majority of precipitation will be over by then so new snow accumulations are expected to be low at this time. Shortwave ridging looks to develop Saturday bringing a brief period of drier weather across the CWA with a some showers lingering into Saturday night. /42 .LONG TERM...Saturday night through Wednesday...Models remain in agreement that shortwave ridging will continue to migrate across the CWA which will result in the few light showers that are lingering to gradually come to an end. Models and their ensembles then generally agree the next shortwave trough will dive into the eastern Pacific from the Gulf of Alaska and push a weakening front into the region Sunday. Models suggest that the upper level trough will dig southward and broaden before swinging eastward into California Monday. Light precipitation will likely persist through Monday along with cooler temperatures. Embedded shortwave troughs within the broader trough will likely keep precipitation chances elevated through Wednesday. Given that the overall flow pattern and timing of these shortwaves is highly variable, have not deviated much from the NBM for PoPs and temperatures at this time. /42 && .AVIATION...Dry aloft, with variable flow. But, will see increasing southwest flow aloft later tonight and especially Thu. Will remain VFR across the region, with increasing high clouds later tonight into Thu. The exception will be for areas of MVFR stratus along the coast, which will become more solidified overnight, and persist into Thu. Farther inland, mostly clear skies. But, will see repeat of last night again tonight, with areas of fog and low stratus after midnight. This will likely persist into Thu am. For detailed regional Pac NW aviation weather information, go online to: KPDX AND APPROACHES...VFR, with mostly clear skies through this evening. But, will have repeat of patchy fog late tonight into early Thu am, though may not persist as long Thu am as will have a light east wind by that time. /Rockey && MARINE...Rather benign conditions at the moment, with northerly winds 10 to 15 kt at most. Seas generally 7 to 9 ft. That will change later tonight into Thu, as next front approaches. Winds will turn more southeast overnight, and then southerly and increase Thu am into Thu afternoon. Still look on track for strong southerly gales on the outer waters Thu am, spreading closer to shore in the afternoon. Current Gale Warnings cover this well for Thu. Still some question for potential storm force gusts to 50 kt on the outer waters west of Newport and Florence for time Thu afternoon into early evening. But, for now, will maintain strong gales. Seas will be on the increase, but likely to see more increase in choppy chaotic wind waves during the day. Likely to see 12 to 16 ft seas by Thu mid- afternoon. Larger fetch of swell will arrive Thu evening, with seas pushing 18 to 22 ft, with 20 to 25 ft on the outer waters Thu. Unsettled weather continues through the weekend with possible gale force winds at times for Fri and Fri night, and again Sat night./Rockehiga && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory from 10 PM this evening to 7 AM PST Thursday for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 NM. Gale Warning from 7 AM Thursday to 6 AM PST Friday for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 NM. Small Craft Advisory from 11 PM this evening to noon PST Thursday for coastal waters from Cape Shoalwater WA to Florence OR out 10 NM. Gale Warning from noon Thursday to midnight PST Thursday night for coastal waters from Cape Shoalwater WA to Florence OR out 10 NM. Small Craft Advisory from 6 PM to 10 PM PST this evening for Columbia River Bar. Small Craft Advisory from 4 AM to 10 PM PST Thursday for Columbia River Bar. && $$ Interact with us via social media: is the U.S. government's official web portal to all federal, state and local government web resources and services.