Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/29/21

Area Forecast Discussion
National Weather Service Portland OR
244 PM PST Sun Nov 28 2021 .SYNOPSIS...Mild temperatures will continue tonight as a weakening atmospheric river slowly sags southward across southwest WA and northwest OR. Rain rates should peak early Monday morning before rain ends from north to south. Then, high pressure should bring mainly dry weather through Friday aside from occasional chances for light rain to the far north. && .SHORT TERM...Sunday evening through Wednesday...Southwesterly flow aloft continues to advect a warm and moist subtropical airmass into the region, resulting in temperatures that are well above normal for this time of year. Observed surface temperatures at 1 PM PST Sunday were already in the upper 50s to mid 60s, warmest over the central and northern Willamette Valley. Several unofficial record high temperatures have already been set for today, but will need to wait until midnight to obtain the final numbers. Similar to yesterday evening, temperatures should remain quite mild this evening as breezy south winds continue at the surface. That said, a steady rain is expected to develop over the area tonight into tomorrow as an atmospheric river that has been soaking southern B.C. and northwest WA slowly sags southward across southwest WA and northwest OR. The latest iterations of the HRRR/HiResW-ARW/HiResW-FV3/NAM Nest are all in good agreement when it comes to timing. Rain has already begun over the Willapa Hills, south WA coast, and far north OR coast, but these locations may see a brief break from the rain beginning around midnight before another round of rain moves in Monday morning. Rain should begin in the Portland/Vancouver metro area sometime between 6- 9 PM PST, before spreading southward through Salem and Corvallis early Monday morning. The Eugene area should also see rain begin Monday morning, but most likely closer to 11am-noon. While the atmospheric river will generally be weakening as it sags southward across the area, it appears rain rates will become enhanced for a ~4 to 6 hour period Monday morning (from a forcing perspective). The 12z GFS/EURO/NAM all show a shortwave trough and 500 mb vorticity maximum push eastward across the forecast area during the mid to late morning hours. Cyclonic vorticity advection ahead of the trough axis combined with weak warm air advection will favor synoptic scale forcing for ascent. Jet streak dynamics also appear to be favorable during that time, as northwest OR will be under the right entrance region of a 250 mb jet max. In addition, precipitable water values will be fairly high, most likely ranging somewhere between 1-1.25 inches based on models and their ensembles. All of these ingredients suggest rain could become heavy at times, and the UWWRF/HRRR are already depicting hourly rain rates peaking around 0.25-0.35 in/hr beginning early Monday morning. While rain rates this high are not enough to warrant much concern, it could be just enough to produce minor flooding in low-lying urban areas and locations with poor drainage. This is something to keep in mind if you will be commuting in the Portland/Vancouver metro area Monday morning, as some roads could have standing water on them. Rain should decrease in intensity and come to an end from north to south across the area late Monday morning through the mid afternoon hours, clearing the Eugene area last. Rainfall totals through Monday are still looking heaviest to the north of Salem, with amounts trailing off to the south. Our current forecast still has another 1.00 to 1.50 inches falling in the Willapa Hills, northern Oregon Coast Range, and the Cascades north of Mount Jefferson. There has been yet another uptick in QPF for the northern Willamette Valley and Clark County, where forecast rain amounts are now closer to 0.75-1.25 inches. This increase is due to what looks to be a 3-4 hour period of time before sunrise when the atmospheric river should briefly stall out over the northern valley. High pressure will build across the forecast area Monday night as the frontal zone dissipates somewhere between Salem and Roseburg. Given poor mixing and light winds, there will probably be areas of fog and low clouds Monday night into Tuesday. Onshore flow and another Pacific warm front will keep rain chances in the picture over western Washington Tuesday, with some models clipping areas north of Salem with a chance of rain. There will still be some subtropical influence to our air mass Tuesday, so expect temps to remain a few degrees above normal, especially above any valley inversions that may develop Monday night. It appears temperatures will warm yet again on Wednesday as a warm front lifts northward into southwest Washington. The NBM is already suggesting widespread high temperatures in the upper 50s to lower 60s for the lowlands. If the NBM 90th percentile forecast verifies on Wednesday, then expect highs in the mid 60s (which would be record breaking for some locations). -TK/Weagle && .LONG TERM...Wednesday night through Sunday...WPC`s cluster analysis for 500 mb heights depicts high confidence for westerly flow and above normal heights over the Pacific Northwest Wednesday through Friday with an upper level high centered over northern California. This setup will most likely result in a two day stretch of dry weather for northwest Oregon and southwest Washington on Thursday and Friday after a weak impulse brings chances for light rain to the north Wednesday night. The NBM suggests temperatures will be a bit cooler late in the week, but still slightly above normal. Models and their ensembles show a wide range of potential outcomes next weekend into early next week. While the deterministic EURO/GFS both show an upper trough bringing precipitation to the area for Saturday and Saturday night, this outcome appears to be an outlier solution compared to individual ensemble members from both models. The GEFS plumes for QPF displays this well as only 3 to 5 members are producing QPF during that time. There is also ensemble member packing around a dry solution with no rain at all this weekend. Uncertainty increase even more late Sunday into Monday when the deterministic GFS shows an impressive 972 mb low making landfall near Astoria on Monday. The EURO also shows this, except the low makes landfall much farther to the north in Vancouver Island. Similar to the potential system on Saturday, the chances of this system coming to fruition appear very low based on GFS/EURO ensemble guidance. In fact, the GEFS MSLP/member low locations only shows one member producing a surface low that comes close to the Oregon coast. Therefore, overall concerns are quite low at this time. The main takeaway message should be the potentially dry weather this weekend with near normal temperatures, while acknowledging the uncertainty that exists this far out in time. -TK && .AVIATION...00Z TAFs: Largely VFR across the forecast area as of 2130Z. The main exception to this was along the south Washington and north Oregon coast where IFR to low-end MVFR conditions were occurring. A nearly stationary frontal boundary over western Washington this morning is expected to slowly sag south through the evening and finally reach the south part of the area overnight. The south Washington and north Oregon coast should remain IFR to MVFR through about 15Z Mon, followed by improvement to VFR by late morning. Elsewhere, VFR to prevail into early evening then conditions lower to mainly MVFR from north to south after 03Z Mon. After 06Z Mon, widespread MVFR or lower conditions to prevail through 18Z Mon. The far southern part of the area, generally south of a KONP-KS12 line will likely see areas of LIFR overnight through Mon morning. For detailed regional Pac NW aviation weather information, go online to: KPDX AND APPROACHES...VFR at the terminal and vicinity at 22Z. There were areas of cigs 025-035, primarily over the Tualatin River Valley. VFR with cigs AOA 050 to prevail through early evening. Conditions lower into MVFR between 03Z and 06Z Mon, with about a 40-50 percent chance of IFR 10Z-18Z Mon. Conditions should improve to VFR Mon afternoon. Weishaar && .MARINE...At 2130Z a nearly stationary frontal boundary was situated over the Washington and far north Oregon waters. Wind gusts to 35 kt have been noted over the portions of PZZ250. The 19Z HRRR model provides a good representation of mid and late afternoon conditions. The 18Z NAMNest suggests a narrow band of 30-35 kt boundary layer wind speeds over PZZ250 through 00Z Mon. Do not expect these conditions to persist much beyond 00Z and they seem to be confined to a fairly small area per available observations. Thus, will continue with the current advisory and not bump up to a gale warning for PZZ250. Otherwise, wind speeds slowly decrease this evening and tonight. Current Small Craft Advisory timing (through 05Z Mon) over the north zones looks good. Wind speeds will be 15 kt or less Mon through late Mon night. Another warm front brushes the north zones late Mon night through Tue. Expect 25-30 kt wind gusts over the north zones with this system. Longer range models suggest a shift to a northerly wind pattern mid to late next week. Seas were running slightly higher than guidance early this afternoon. This was largely due to a higher fresh swell wind wave component, especially over the north zones. Wave heights ease to around 8 ft tonight and then hover around 6 ft Mon through Mon night and then build to 10 to 12 ft Tue. The GEFS Wave Probabilistic Guidance does not show seas above 15 ft through the next 7-10 days. Weishaar && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 9 PM PST this evening for coastal waters from Cape Shoalwater WA to Cascade Head OR out 60 nm. Small Craft Advisory until 3 PM PST this afternoon for coastal waters from Cascade Head OR to Florence OR out 60 nm. Small Craft Advisory until 2 PM PST this afternoon for Columbia River Bar. && $$ Interact with us via social media:
Area Forecast Discussion
National Weather Service Sacramento CA
221 PM PST Sun Nov 28 2021 .SYNOPSIS... Cool mornings with local fog in the Valley and mild afternoons expected over the next week. Dry weather continues. Locally breezy north to east winds Tuesday through early Wednesday. && .DISCUSSION... Skies are looking pretty clear on the visible satellite imagery this afternoon across interior Northern California. High pressure continues to build over California today, remaining over the area through the week. Fog development this morning was very localized and fairly shallow around and south of the Sacramento area. HREF and HRRR show better chances of fog and stratus development late tonight through tomorrow morning, though fog is still expected to be patchy to locally dense in nature through the Valley. Otherwise, dry weather continues this week with above normal temperatures. Valley and foothill temperatures will top out in the mid 60s to low 70s, warmest in the northern Sacramento Valley, with 50s to 60s in the mountains. The only slight change in the pattern is ensemble guidance shows upper level heights decreasing somewhat Monday night into Tuesday over California as a shortwave moves through the intermountain West. This would bring a tightening of the surface pressure gradients and shift in wind direction, causing locally breezy north to east winds Tuesday through Wednesday morning. -HEC && .EXTENDED DISCUSSION (Thursday THROUGH Sunday)... There is strong ensemble agreement in high pressure prevailing through the weekend over northern California. Dry conditions and above normal temperatures will continue. Late evening and early morning patchy Valley fog chances return late week under high pressure. -HEC && .AVIATION... General VFR conditions next 24 hours, except for areas of MVFR with local IFR/LIFR due to BR/FG in the Central Valley 09z-18Z. Surface wind gusts under 10 kts. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$