446 FXUS66 KOTX 060503 AFDOTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SPOKANE WA 900 PM PST Sat Jan 5 2013 .SYNOPSIS... The weather pattern will begin to change this weekend. Light snow will fall for most areas tonight into Sunday morning. Snow levels will increase through early next week with valleys transitioning from snow over to rain or a wintry mix. The milder temperatures will last into mid week before a strong cold front drops temperatures back down below seasonal normals for Thursday through next weekend. && .DISCUSSION... Evening Update: Weakening...splitting trof is just reaching the WA Coast as of 8PM with very little surprise from earlier thoughts. The bulk of the dynamics are splitting north and south of the area with the southern branch taking aim on California and northern, southern BC. We have gone ahead and decreased snow amounts and PoPs slightly over the western zones with locations like Wenatchee and Omak where snow has ended for the time being. QPF amounts were generally spot on near Omak...roughly 0.05" while underachieved for Wenatchee which came in with 0.02" and snow amounts were shaved off slightly. Over the next hour, light snow will continue to fill across the Ern third of WA and into Nrn ID. 00Z KOTX sounding already shows the shallow but very dry layer near 700mb observed on the 12z sounding close to saturation which should allow snow to reach the ground between 8-9PM. Given the weakening nature of the system, we continued to favor the the drier SREF/EC/GFS slns but with a nod to the NAM which has initialized the onset of snow and lack of dryness on the 00z sounding. This continues to place the best chance for an inch or higher of valley snow in the valleys of Nrn WA and northern sections of the ID Panhandle. Snow will be light through much of the night then a heavier burst will be possible as the trof axis and weak dynamics trailing from the northern BC branch brushes the northern zones. Models show the best omega within the dendritic zone co-located with this feature which crosses the Cascades near 09z and toward the ID/WA border 12z. Because of this feature, we are hesitant to remove the chance for snow across the western zones where snow has tapered off currently. Any additional amounts will be light and westerly flow behind this feature should end the pcpn threat rather quickly. On the contrary, light snow will linger well into Sunday morning into the Idaho Panhandle and portions of far eastern WA. Areas of fog will be possible through the night for most locations. Currently, the dense fog near Ritzville looks to have drifted northward into Davenport or along the Highway 2 corridor between Airway Heights and Wilbur. As the snow ends for additional locations tonight, the threat for additional fog formation will increase for most lowlands between the Cascades and ID/WA border. Black ice will also be a concern. Several locations experienced some sun and/or temperatures near freezing today. This allowed roads to remain wet through the light snow this evening via cams and now temperatures are once again cooling into the 20's suggested the potential for re-freezing. /sb && .AVIATION... 00Z TAFs: Fog has developed across the Palouse and upper basin and may get into KGEG around 01-02z this would result in lowering cigs/vsby. Otherwise a frontal band will move across the forecast area this evening with snow beginning at KMWH around 00z continuing to push east across the forecast area this evening. Light snow is expected to last through at least mid-day Sunday. As such expect cigs and vsby to begin deteriotating as snow moves into an area. Expect conditions to drop to MVFR/IFR cigs/vsby through the night. Some improvement is possible after 20-22z Sunday afternoon as snow begins to dissipate. /Tobin && .PRELIMINARY POINT TEMPS/POPS... Spokane 24 29 27 34 31 38 / 90 50 50 70 60 50 Coeur d'Alene 25 30 28 34 31 37 / 90 90 50 80 60 60 Pullman 22 33 29 37 33 41 / 50 60 50 80 70 60 Lewiston 28 39 32 42 38 46 / 20 30 20 50 50 50 Colville 25 30 28 33 30 39 / 90 50 40 70 60 50 Sandpoint 26 30 28 32 31 38 / 90 90 50 80 80 80 Kellogg 24 31 27 32 29 37 / 80 90 50 80 80 90 Moses Lake 23 31 28 36 31 39 / 90 10 30 40 20 10 Wenatchee 23 31 27 33 29 37 / 40 10 30 40 30 20 Omak 22 27 26 32 28 36 / 70 10 20 40 40 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$