125 FXUS66 KOTX 151148 AFDOTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SPOKANE WA 348 AM PST Tue Jan 15 2013 .SYNOPSIS... strong high pressure will build over the Inland Northwest today. Cold and stable conditions are expected through the weekend. Areas of low clouds and fog are expected to plague the Columbia Basin and West Plains. Air stagnation will become a concern for much of eastern Washington from Tuesday through at least Friday. && .DISCUSSION... Today and Tonight: Our biggest challenge has been deciding on the areal coverage of fog and/or stratus, and if there will be any light pcpn generated from these low clouds. We kept the valley fog in the fcst for Nrn Wa and most of N Id through at least the next 24 hours. As is fairly typical with this pattern, we expect that a dry surge of S/SE winds will come off the Palouse later today and into the evening hours, effectively limiting stratus-generated light pcpn. However, this will not be the case tonight as the upper ridge strengthens, with subsequent airmass drying and warming above a strong inversion of 3 to 5c capping the near-sfc fog and/or stratus below. Based on the soundings from a number of models, the moist sfc layer should be deep enough to produce at least pockets of very light pcpn...especially in locations where the low clouds are subjected to upslope flow. Independent of what model guidance we use, most fcst soundings show a favorable temp profile for either light snow flurries (snow grains), or a mix of flurries and pockets of freezing drizzle. Though confidence is not good that we'll be able to nail down the locations of these two pcpn types (or mixed types) exactly, the evidence suggests that the highest threat should be across the Nrn half of Wa and the N Id Panhandle. So...be prepared for low clouds and very low visibilities at times, and pockets of either light snow flurries or freezing drizzle. We'll have to monitor trends and update/modify the fcst to adjust for these low vsbys, flurries, or freezing drizzle. NOWCASTS will be a tool we'll use to refine the threat area...or areas of frequently changing pcpn type and vsby changes. Also, we may have to issue advsys for either dense fog or freezing drizzle, or both. bz Wednesday through Tuesday: A persistent and strong area of high pressure will be parked over the eastern Pacific and into the Pacific Northwest. With the storm track well to the north and east of the region, the main weather concern for the Inland Northwest will be low clouds and fog. With surface high pressure anchored over the region, low level inversions will be strengthening and trapping boundary layer moisture. Based on the light low level wind flow, it appears the best chance for low clouds and fog will span from the northern valleys, across the Spokane/Coeur d'Alene area to the Columbia Basin below 4k ft. Light easterly low level flow should help keep stratus from developing across much of the Palouse, LC valley and Camas Prairie. Light westerly flow will keep skies free from low clouds across the Cascade lee side valleys at least through the week. But as this flow weakens and becomes more easterly, expect the chance of low clouds and fog pushing into these valleys as well. Within the stratus deck there is the potential for light flurries or drizzle especially as the mid to upper level dry out and low level lift is enhanced. Yet chances of precipitation are slim and will stay that way through the weekend into early next week. Temperatures will again be tricky due to the cloud cover, but the models do indicate a slight warming through the period especially in the mountains and areas free from the low overcast. Low levels will be stuck in the stratus will continue to see cool conditions through mid January. The current highlight or air stagnation due to light winds and strong low level inversions will continue through the work week. /rfox. && .AVIATION... 12Z TAFS: High pressure aloft and deep low level moisture will be conducive for widespread fog and/or stratus most of today, and for reforming low clouds and fog Wednesday morning. A threat of snow flurries and pockets of brief freezing drizzle will remain possible once again, but should be limited to the Spokane area TAFs and possibly Moses Lake. Clearing skies and VFR weather at Pullman and Lewiston may be brief today before returning late evening and overnight. For the above-mentioned areas of dense fog, snow flurries and freezing drizzle, LIFR/IFR conditions will be a near certainty. && .PRELIMINARY POINT TEMPS/POPS... Spokane 25 16 25 17 26 19 / 10 10 10 10 10 10 Coeur d'Alene 26 17 29 18 30 20 / 0 10 10 10 10 10 Pullman 30 15 34 19 34 23 / 10 0 0 0 0 0 Lewiston 34 23 34 23 36 25 / 0 0 0 0 0 0 Colville 29 19 30 18 31 19 / 0 0 10 10 10 10 Sandpoint 28 15 28 19 29 19 / 10 10 10 10 10 10 Kellogg 28 17 27 21 30 20 / 20 10 0 0 0 0 Moses Lake 27 14 28 15 29 20 / 0 0 10 10 10 10 Wenatchee 26 17 25 17 26 22 / 0 0 0 10 10 0 Omak 22 9 22 13 25 17 / 10 0 10 10 10 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...Air Stagnation Advisory until 2 PM PST Friday for East Slopes Northern Cascades-Moses Lake Area-Northeast Mountains- Okanogan Highlands-Okanogan Valley-Upper Columbia Basin- Waterville Plateau-Wenatchee Area. && $$