Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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859 FXUS66 KOTX 092239 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 239 PM PST Sat Nov 9 2024 .SYNOPSIS... A weak weather system arrives over the weekend bringing a chance of light rain and high mountain snow. Unsettled weather will continue through next week with periods of mountain snow and lowland rain. Snow over mountain passes may be moderate to heavy at times with winter travel possible. && .DISCUSSION... ...Light snow to impact Cascade Passes this week, starting Sunday at Washington Pass and Monday at Stevens Pass. Heavy mountain snow arrives Tuesday evening into Wednesday... Tonight through Monday night: There will be two storm systems coming through the region through Monday night. The first system will be weak and mainly rain for the lowlands and mountain passes. The second system will have a lot more structure and moisture with periods of moderate precipitation intensity. A wintry mix of snow and rain will be possible in the far northern valleys with the second system, otherwise this will once again rain to the lowlands and snow to the mountains. Those planning to travel across the mountain passes are urged to keep an eye on the forecast and be prepared for winter travel conditions. Storm system 1: Saturday evening through Sunday morning. This is largely a decaying frontal band limping through the region bringing light rain and mountain snow. QPF amounts will range from a few hundredths in the lee of the Cascades to around 0.15" in portions of North Idaho and Eastern WA. Snow levels will be around 5000-6000 feet with only light snow accumulations expected on the highest passes. Overall impacts will be low. Storm system 2: Sunday evening through Monday evening. This system will be more typical of our winter storm systems with a 6-8 hour period of warm sector precipitation for most areas outside far SE WA and the lower Idaho Panhandle under south/southeast flow. This will erase the Cascade rain shadow but bring some downsloping in the foothills of the Blue Mountains and Lewiston Area. That will change Monday morning as an occluded front presses inland and ushers a north to south band of precipitation through the region with drying in the lee of the Cascades and slowly progressing east through the afternoon. Precipitable waters are near 200% of normal with this system and given the stronger dynamics, QPF amounts will range from 0.25-0.75" with some of the northern mountains receiving over an inch. The aforementioned drier areas around Pomeroy, Lewiston, and Winchester only look to pickup around a tenth or less. As for precipitation type, the cloud shield arrives Sunday afternoon-evening trapping the warmest temperatures of the day. This does not bode well for lowland snow despite the classic cold air damming setup. This leads to moderate to high probabilities for rain vs snow in the lowlands. Precipitation intensity may drive wet snow as low as 3000 feet at times around Winthrop, Republic, and Colville with no accumulation. WA Pass has a 30% chance for a foot of snow from this event. Stevens Pass looks to start off as rain with a transition to snow Monday morning as the front passes through. Snow advisories have been issued for Washington Pass with a long duration period of light snow starting Sunday evening and continuing into Tuesday. We will be revisiting winter advisories for Stevens Pass for Monday evening into Tuesday. Winds will become breezy to gusty Monday afternoon shifting from the south to southwest with cold front passage. There is a 30-50% chance for gusts in excess of 30 mph across the open Columbia Basin with only a 5% chance for speeds to reach 40 mph. Temperatures Sunday will be seasonably cool with lows in the 30s and highs in the 40s. Monday will start off warmer with heavy cloud cover and precipitation falling then warm into the 40s and 50s in the afternoon with good mixing and end of the preciptiation by the afternoon. There is not high confidence for freezing temperatures but any breaks in the clouds at night could allow for radiational cooling and pockets of near freezing temperatures. Where this occurs, odds will be increased for areas of fog and potential for black ice. /sb Tuesday through Saturday: Our active pattern will continue for the mid-to-latter stages of the week as a series of weather systems impact the region. For Tuesday night into through Thursday, snow levels look to remain above 3500`, though they are likely to drop for Friday and Saturday. Expect valley rain and mountain snow with each system, with the mountains and mountain passes the main concern for accumulating snowfall. Widespread and largely beneficial rain will occur across the lower elevations. In addition to the precip, breezy southwesterly winds are likely each day from Tuesday through Thursday, especially across the Columbia Basin and Palouse. /KD && .AVIATION... 18Z TAFS: Areas of dense fog impacting the valleys of NE WA and North Idaho including COE, SFF, and GEG will begin to lift 18-20Z with potential for MVFR stratus through 22z. Otherwise, Midlevel clouds are moving in ahead of an approaching frontal band poised to bring light rain and MVFR or lower restrictions after 07z. This will be a top down lowering of cigs with -RA creating visibility 2-5SM. Following the rain, stratus is likely to remain across NE WA and N ID with periods of drizzle. Widespread mtn obscrns are expected. There are lower probabilities for restrictions in Central WA at EAT/MWH however, some radiation fog development cannot be ruled out 13-16z following light rain. This comes with low confidence. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate to high confidence for current dense fog to lift this morning with low to moderate confidence how quickly the stratus will break to return to VFR skies for NE WA and N ID. There is moderate confidence for low stratus to return with and following the rain Sunday morning. ----------------------- Confidence descriptors: Low - Less than a 30 percent chance Moderate - 30 to 70 percent chance High - Greater than a 70 percent chance For additional probabilistic information for NWS Spokane airports, please refer to the Aviation Dashboard on our webpage: https:/www.weather.gov/otx/avndashboard && .PRELIMINARY POINT TEMPS/POPS... Spokane 38 45 42 50 37 48 / 80 50 70 90 70 60 Coeur d`Alene 38 45 41 48 37 45 / 80 60 70 100 90 80 Pullman 39 47 42 50 37 46 / 80 60 50 100 90 70 Lewiston 42 53 44 56 41 53 / 60 50 30 90 80 60 Colville 36 47 40 47 36 45 / 80 40 90 100 80 60 Sandpoint 38 44 40 46 38 42 / 90 50 90 100 90 90 Kellogg 36 49 38 48 36 39 / 80 70 70 100 100 90 Moses Lake 36 50 44 54 40 53 / 60 10 80 80 20 20 Wenatchee 35 47 40 52 38 50 / 50 20 100 90 20 20 Omak 34 46 41 53 35 50 / 40 20 100 90 30 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...Winter Weather Advisory from 6 PM Sunday to 1 PM PST Tuesday for Western Okanogan County. && $$