Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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479 FXUS66 KOTX 242221 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 321 PM PDT Tue Sep 24 2024 .SYNOPSIS... A ridge of high pressure will deliver above normal temperatures through Wednesday. Strong winds accompany a cold front passage Wednesday afternoon and evening. Areas of blowing dust along with showers and thunderstorms will be possible with the frontal passage. Temperatures return to near normal by Thursday with another cold front passage Friday. Above average temperatures and dry early next week. && .DISCUSSION... ...ROBUST COLD FRONT TO BRING STRONG WINDS, BLOWING DUST, AND SHOWERS AND THUNDERSTORMS.... Tonight and Wednesday: As the trough continues to press into the Pacific Northwest, the ridge axis will shift east allowing for a cold front to begin to press into the region. Overnight lows will be unseasonably warm in the upper 50s and 60s. The start of Wednesday will be quiet. Ensembles continue to show a major pattern change during the day with a cold front passage starting late morning and lasting into the late evening. Wednesday will definitely be an interesting day. Ensembles continue to bring the cold front through the Inland Northwest 1PM-8PM. The main impacts with the cold front will be strong winds and isolated thunderstorms. With mostly clear skies before the front, daytime highs will be similar to Tuesday reaching into the 80s. The rain and thunderstorm will start late morning over the Cascades and spread East through the afternoon. Highest precip amounts will be in the higher terrain of the Cascades, the northern mountains, and Idaho Panhandle. These areas are seeing a spread of 0.1-0.2" for 25-75% probabilities. The thunderstorm threat is expected to be weak and isolated but has the potential to occur any location in the Inland Northwest. The thunderstorms could bring brief downpours and gusty outflows causing tree damage and isolated power outages. Winds will be main concern with frontal passage for the Basin and valley locations. The winds will start to ramp in the late morning, peak in the afternoon with passage, and dropping off overnight. Ensembles continue to show sustained speeds into the 20-30 range with gusts up to 50 MPH for the Basin. The northern valleys will see lighter speeds of 10-20 with gusts near 40 MPH. Potential impacts from the winds will be choppy lakes, blowing dusts, and fire concerns. For fire, the humidities will be on the high side of critical but with the dryness of the fuels across the Basin and winds, any new start has potential to spread rapidly. The blowing dust concerns will be mainly across the Basin along the I-90 and Hwy 2 corridors. But any location next to recently worked fields can expect reduced visibility from blowing dust. Thursday through Friday: A low pressure system will track across the Gulf of Alaska on Thursday and into western BC Thursday night. A fairly robust warm front with a P-wat plume of over an inch will push into southwestern BC and western WA by Thursday afternoon. The trailing cold front will occlude with the warm front and push east of the Cascades overnight Thursday into Friday morning. The parent low will track well to the north of the Inland Northwest resulting in a weakening frontal band. This will in turn result in decreasing potential for precipitation across the Inland Northwest compared to the west side of the state of Washington. There`s less than a 10% chance for precipitation away from the Cascades with only increasing cloud cover. Chances for precipitation increases to over 80% at the Cascade crest with up to around a quarter of an inch of rainfall expected. Very little cold air advection is expected with the passage of the frontal occlusion overnight Thursday. This will result in limited mixing and wind potential. Pre-frontal southerly winds sustained of 10-15 mph with gusts of 20-25 mph is expected around Grand Coulee, on the Waterville Plateau, and up the Okanogan Valley. Westerly post-frontal winds will occur on Friday with similar wind speeds across the exposed areas of the basin. This frontal passage will bring winds around 10-15 mph weaker than what is expected with the cold front passage tomorrow. Friday night through Tuesday: The far extended part of the forecast will remain active, but moisture may lacking as to produce appreciable precipitation across the region. The next shortwave disturbance to pass through will be on Sunday. This shortwave will have much less moisture associated with it and also limited on synoptic dynamics. It will bring passing high clouds but not much else. Winds will be out of the north with gusts of up to around 20 mph down the Okanogan Valley, Waterville Plateau and over the western basin. Shortwave ridging of high pressure moves in Monday into Tuesday with temperatures above normal and highs warming into the 70s. The next weather system to push through looks to be late Tuesday. Preliminary outlook has this frontal system also weakening as it traverses across the Inland Northwest with minimal to no impacts anticipated. /SVH && .AVIATION... 00Z TAFS: VFR conditions are expected through Wednesday morning. Cirrus clouds will slowly filter through the region with stable conditions over the region. A strong cold front will bring westerly winds and chance for thunderstorms Wednesday afternoon and early evening. Wind gusts in excess of 30 mph expected. Localized areas of blowing dust could impact visibility across the Basin impacting MWH-GEG-SFF-COE-PUW. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for VFR conditions at all TAF sites through tonight. Moderate confidence on VFR through the period. Blowing dust is expected to impact Basin sites during the afternoon and bring MVFR conditions. Low confidence on the potential IFR conditions due to dust and thunderstorms impacting TAF sites. /JDC && .PRELIMINARY POINT TEMPS/POPS... Spokane 60 85 46 70 50 73 / 0 20 40 0 10 0 Coeur d`Alene 58 84 48 69 49 72 / 0 10 60 0 10 0 Pullman 56 84 45 68 47 71 / 0 20 70 0 0 0 Lewiston 64 91 56 76 55 78 / 0 20 60 0 0 0 Colville 47 83 36 69 39 72 / 0 20 40 0 10 0 Sandpoint 53 80 45 65 45 69 / 0 20 70 10 10 10 Kellogg 62 82 50 66 51 68 / 0 10 80 10 10 10 Moses Lake 57 84 43 72 46 75 / 0 20 10 0 0 0 Wenatchee 62 80 48 71 54 72 / 0 40 10 0 20 0 Omak 58 84 43 71 48 74 / 0 30 10 0 20 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Wind Advisory from 11 AM to 11 PM PDT Wednesday for Central Panhandle Mountains-Coeur d`Alene Area-Idaho Palouse- Lewiston Area-Northern Panhandle. WA...Wind Advisory from 11 AM to 11 PM PDT Wednesday for Lower Garfield and Asotin Counties-Northeast Blue Mountains- Northeast Mountains-Okanogan Highlands-Okanogan Valley- Wenatchee Area. Blowing Dust Advisory from 11 AM to 11 PM PDT Wednesday for Moses Lake Area-Spokane Area-Upper Columbia Basin- Washington Palouse-Waterville Plateau. && $$