Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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639 FXUS66 KOTX 220932 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 232 AM PDT Sun Sep 22 2024 .SYNOPSIS... Temperatures will be chilly Sunday morning, promoting frost for many areas and freezing temperatures in the mountain valleys of northeast Washington. Yet afternoon will be mild. There is a small chance of light mountain showers in the north this afternoon and tonight. A ridge of high pressure will deliver above normal temperatures early in the week. A more active pattern is expected toward midweek and beyond, with the potential for breezy conditions and showers. Temperatures return to near normal by Thursday. && .DISCUSSION... ...Warm early this week then midweek pattern change... Today through Monday night: This morning will start off cool to cold over portions of northeast WA and the ID Panhandle an even some the Palouse. As of 2AM there were several areas reporting lower to mid 30s in these areas, while relatively warmer readings of 40s and 50s were found elsewhere to the west and south . Frost and freeze warnings remain in place in the those colder regions through 8 AM this morning. Clouds are starting to increase over the Cascades now and will continue to increase over the rest of the area through the day. This week starts somewhat seasonal with very limited precipitation chances. We start today off with a zonal flow, with a disturbance (now pushing onto West Coast) moving by. The jet stream stays north of the Canadian border and thus so does the brunt of the lift and moisture. Then tonight into Monday a low pressure trough starts deepening into the Gulf of AK and as a result a ridge begins to amplify over the eastern Pacific and a warm front lifts into the Pacific Northwest before that ridge builds over us. Rain chances come to the Cascade crest this afternoon and expand to the immediate Canadian border late this afternoon into tonight and linger there into Monday. The remainder of the CWA is generally expected to stay dry. Skies will become partly to mostly cloudy for today into Monday morning, before clouds erode into Monday afternoon the ridge of high pressure starts to come in. I cannot entirely rule out some passing sprinkles tonight into early Monday outside of the mountains, but the risk is very low. Winds will increase a bit this afternoon and evening near the Cascades into the Columbia Basin. On average with winds near 5-10 mph with gusts to 15 mph will be possible, except near the Cascade gaps where they will be locally higher this evening with gusts near 20-25 mph possible. Highs will be in the 70s to low 80s through Monday, with the more in the way of those 80s near the lee of the Cascade and deeper basin Monday. Lows tonight will be a milder than the past two nights, with mostly 40s to mid-50s. There will still be some 30s over the sheltered valleys of NE WA and ID. /Solveig Tuesday and Wednesday: We start with warm temperatures and relatively quiet weather, then return to broader precipitation chances, maybe some thunderstorms, and breezy/gusty winds. Tuesday a trough will still be deepening into the eastern Pacific and pushing toward the West Coast, with the ridge over the Pacific Northwest continuing to amplify and shift toward the Continental Divide. Clouds will be limited Tuesday save for some passing higher clouds. Tuesday night into Wednesday morning moisture starts to feed in ahead of the approaching low pressure system, leading to increasing clouds. By early Wednesday the threat of precipitation returns to the Cascades. Then Wednesday afternoon and especially Wednesday night the chances expand east as the cold front and supporting upper trough move in. I did increase PoPs a bit above the NBM over the east third of WA/north ID in that 18-00Z time frame Wednesday. Instability along ahead of the front will bring the chance of embedded thunderstorms, with the best chances Wednesday afternoon and evening near the mountains. I cannot entirely rule out some coming up through the eastern third of WA and lower ID too, but confidence is lower with models currently depicting chances less than 10 percent there. The overall best chances of wetting rains (>=0.10 inches) will remain near the Cascade crest and along the immediate Canadian border. Winds will be the other notable feature of this system. Tuesday they start off relatively light, but will be easterly ahead of the approaching system. Then heading through Wednesday winds turn southwesterly again and increase for afternoon and evening. By then speeds of 10-20 mph will be possible, with gusts of 20-30 mph. The higher of that range is expected over the Upper Columbia Basin to the Waterville Plateau. Strictly speaking afternoon RH values are not expected be at critical values, yet indices indicate a hot, dry and windy potential. So this will be something for the fire weather community and other with concerns to monitor, with the increased potential for spread with any fire starts, regardless of precise RH numbers. The southerly flow into our region and the ridge itself will promote warm temperatures, with highs in the 80s to low 90s. This will be some 10-15 degrees above normal. Tuesday night lows will be in the 50s to near 60s, with some localized 40s in the northeast valleys. At this point most locations Tuesday and Wednesday will be similarly warm. However the increased onshore flow will bring a relative cool down near the Cascades by Wednesday. If the system timing changes or cloud cover changes those highs temperatures may need to be adjusted up or down. /Solveig Thursday to Saturday: The region remains in a progressive pattern. The midweek trough shifts east Thursday. The westerly flow and minor impulses will keep some shower chances alive around the mountains, but amounts look light if anything. The rest of the area will be dry. Then the next frontal wave moves into the region between Thursday night and Friday, expanding precipitation chances again. Models do diverge over how much precipitation may come with this system. The higher probabilities remain around the Cascades and northern mountains. Yet elsewhere models show probabilities for measurable precipitation as low at 10 percent of as high as 50 percent. Roughly 65% of the ensembles lean toward the drier solution outside the mountains, with the other 35% wetter. Either way, the best chance of wetting rains remains around the Cascades and precipitation amounts elsewhere are not expected to be that much, if anything falls. By Saturday model diverge some but still generally show a more zonal flow again, with the higher precipitation risk retreating to the mountains. Precipitation will largely fall as rain, but some high mountain snow is expected in the Cascades and maybe some the higher mountains near the Canadian border. Ensembles show about 10-30% chance of >=1 inch of snow with the Friday system near the Cascade crest. For most that may not be impactful but if anyone is in the high mountains that is something to be monitoring. Also look for breezy conditions in the afternoon through this period, but especially Thursday. Winds are not expected to be as strong as Wednesday, but there could be still some gusts near 15-20 mph, with the higher range near the Waterville Plateau. Temperatures will also be notably, compared to temperatures found on Tuesday and Wednesday. Highs will be some 10 degrees cooler on Thursday than Wednesday, with many area seeing 70s. Overnight lows will be in the 40s and low 50s through Friday morning, then 30s and 40s toward next Saturday including the potential for more freezing temperatures in sheltered valleys. /Solveig && .AVIATION... 12Z TAFS: VFR conditions. Bands of mid and high clouds will move over the region, thickening this afternoon into tonight. Some showers possible in the Cascades late this afternoon into tonight. Gusty winds to 15kts or so near Cascade gaps into the Columbia Basin by late afternoon to early evening, including in vcnty of EAT, MWH and GEG. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for VFR conditions at all TAF sites. Low confidence sprinkles at TAF sites overnight. && .PRELIMINARY POINT TEMPS/POPS... Spokane 75 50 78 51 85 57 / 0 10 0 0 0 0 Coeur d`Alene 73 49 75 51 82 56 / 0 10 0 0 0 0 Pullman 71 47 73 49 82 55 / 0 0 0 0 0 0 Lewiston 78 56 80 56 87 62 / 0 0 0 0 0 0 Colville 73 39 78 42 83 45 / 10 10 0 0 0 0 Sandpoint 68 45 73 47 79 52 / 10 10 0 0 0 0 Kellogg 69 49 71 53 81 60 / 0 10 0 0 0 0 Moses Lake 79 52 81 52 86 55 / 10 10 0 0 0 0 Wenatchee 79 60 83 59 85 62 / 10 10 0 0 0 0 Omak 78 54 84 56 86 59 / 10 10 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Frost Advisory until 8 AM PDT this morning for Central Panhandle Mountains-Idaho Palouse-Northern Panhandle. WA...Frost Advisory until 8 AM PDT this morning for Washington Palouse. Freeze Warning until 8 AM PDT this morning for Northeast Mountains. && $$