066 FXUS66 KOTX 211206 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 406 AM PST Tue Feb 21 2017 .SYNOPSIS...The last in a series of wet weather systems will impact the Inland Northwest today leading to a mix of rain and snow. Cooler and showery weather is forecast for Wednesday and continuing for the rest of the work. Drier but cooler weather is forecast for the upcoming weekend. DISCUSSION... A dynamic and very moist system is approaching the Oregon coast early this morning. The associated warm front moving north out ahead of the system is leading to a broad area of overrunning moisture. As indicated in the evening update, radar returns are a bit quicker than models had predicted. Areas of dense fog have developed just ahead of the band of precipitation. This dense fog should be shortlived as precipitation should be beginning soon. The biggest challenge this morning is the precip type as the moisture arrives. Temperatures are near or just below freezing across the I-90 corridor. The temperature profile may support a period of freezing rain briefly early this morning in the upper Columbia Basin. Rain will be the main precip type south of I-90...but snow will mix in or be the predominant precip type I90 north. High res models vary on the precip type right along that I90 corridor. Thinking this morning that Spokane to Coeur d'Alene will see snow initially before transitioning over to rain later this morning. Models also continue to shift the axis of heavier precip south and east...so feeling better about leaving out any snow highlights. The exception that we'll be watching very closely this morning is the higher elevations of Kootenai and Shoshone counties...where brief periods of snow could overcome the warm pavement temperature and accumulate rapidly. At this time, we won't issue an advisory but plan to hit this area with social media and weather stories to address the potential hazard. As the shortwave moves across the region through the day and evening, winds will shift to the west and increase (similar to what happened Monday afternoon/evening). Freezing levels will drop again so lingering moisture will fall in the form of snow during the evening and overnight hours. This time has the best potential for accumulating snow in the Idaho panhandle. The impacts should be limited to just the highest mountain passes. Flood Watch Update: Models continue to trend wetter in the southern and eastern portion of the CWA and backing off on precip to the north and west. I'm reluctant to drop Grant, Pend Oreille, and Stevens counties from the flood watch at this time. Complicating matters is the relatively low snow levels in the Idaho panhandle through this last event. Given the very saturated ground and .5 to 1.00+ inch of potential rain in the valleys, will keep the watch as is for now and let the day shift call around and re-evaluate the situation. /AB Wednesday through Monday: The Inland NW transitions to a colder, showery pattern. A long-wave trough carves itself out over the western U.S. and the primary jet stream and storm track largely steers the more robust/wetter systems away from the region. This isn't to say the region will be precipitation-free. Smaller scale features and west-northwest flow will provide some risk for snow showers perhaps mixed with some rain through the end of the week, particularly near and immediately downstream of the mountains and over the eastern Columbia Basin. Precipitation looks more hit-and-miss, especially outside of the mountains, and amounts look light compared to more recent systems. Much of the area dries out going into Saturday night and Sunday. Sunday night into Monday the jet stream nudges back north and a slightly wetter system slides up from the south, renewing precipitation chances from the lower Columbia Basin to the central Panhandle. That is several days out so the details are apt to change, including the threat shifting north or south. Yet at this time if any area has a better chance of more moderate precipitation it could be toward the Palouse southward but the deeper moisture still remains south. Overall colder than normal temperatures and limited precipitation amounts should mean less snowmelt and/or rain-swollen waterways, so the risk for flooding should abate for most of this period. Confidence in precise temperature going into the latter periods degrades and model agreement is poor (with as much as 10 degrees difference in values), but colder than normal is projected. /J. Cote' AVIATION... 12Z TAFs: Moisture is filling in over the Columbia Basin as the last in a series of systems impacts the Inland Northwest. TAFs are quite challenging with multiple hazards expected over the next 24 hours and especially the first 12 hours or so. Areas of dense fog should be lifting soon as snow and rain begin to fall. Visibility will improve from LIFR to MVFR once precipitation begins. I held on to the potential for light freezing rain during the onset of the precipitation early this morning, otherwise all TAF locations will transition from -SNRA to -RA...before changing back to -SN this afternoon and evening. Outside of KLWS and KEAT, I'm reluctant to clear things out and go VFR through early Wednesday morning. That may come in the 18Z or 00Z TAF packages later today. && .PRELIMINARY POINT TEMPS/POPS... Spokane 38 25 36 21 35 19 / 90 70 30 10 10 10 Coeur d'Alene 39 27 36 19 35 18 / 90 90 40 20 20 10 Pullman 41 29 38 21 36 21 / 100 90 30 10 30 20 Lewiston 48 33 43 27 41 26 / 100 80 30 10 20 20 Colville 41 23 38 21 37 19 / 30 20 30 20 20 10 Sandpoint 39 28 36 21 35 18 / 60 60 40 20 20 20 Kellogg 38 27 36 22 34 20 / 100 100 70 30 40 20 Moses Lake 39 23 37 20 36 20 / 50 20 10 10 10 10 Wenatchee 38 25 37 21 34 20 / 30 10 20 10 10 10 Omak 38 22 36 20 34 19 / 20 10 20 10 10 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Flood Watch through Wednesday afternoon for Central Panhandle Mountains-Coeur d'Alene Area-Idaho Palouse-Northern Panhandle. WA...Flood Watch through Wednesday afternoon for Moses Lake Area- Northeast Mountains-Spokane Area-Upper Columbia Basin- Waterville Plateau. && $$