772 FXUS66 KOTX 262356 AFDOTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SPOKANE WA 356 PM PST Tue Feb 26 2013 .SYNOPSIS...Another quick moving, weak storm system will affect the region tonight and Wednesday...with yet another system due for Thursday. Warmer weather will make an appearance late this week, with spring-like temperatures expected by this weekend. && .DISCUSSION... Tonight into Wednesday...Today's brief shortwave ridging will be pushing off toward the east as our next weak weather system moves onshore. Water vapor satellite imagery this afternoon shows a weakening trough approaching western Washington and British Columbia. Models in fairly good agreement in bringing this trough and associated elevated front through the Inland Northwest tonight into tomorrow. Main affects for this feature will only skirt the region, with the Cascades, northern Washington, into the Idaho panhandle being the best areas to receive measurable precipitation. The models agree that this precipitation is driven by weak warm advection and upslope affects. The moisture content is not near as high as previous systems, so kept qpf amounts very low. This does look like an all snow (shower) event given the forecasted wet bulb temperatures, but amounts will be well below advisory amounts. ty Wednesday Night through Saturday...The cool and unstable trough pattern of the past week or so will be replaced by a much warmer more moisture laden one as strong zonal jet...currently extending from the Gulf of Alaska to the western Pacific...begins to amplify into a strong upper level ridge. The model solutions are all consistent in amplifying this ridge. While ridges typically deliver dry weather...this one will be a dirty one which means it will bring considerable cloudiness as well as varying amounts of precipitation. Just where the precipitation falls and how much will occur is where this forecast becomes quite difficult. While all the models depict some precipitation the variations are quite remarkable considering the event is not that far into the future. Looks like the threat of precipitation will begin late Wednesday night. The NAM12 is quite wet and it produces precipitation over most of the forecast area...while the ECMWF only brings precipitation to locations near the Cascade crest...and portions of the Idaho Panhandle. Isentropic ascent from all the models is fairly weak...so we will lean toward the drier EC solution. That notion is also backed by the models containing a wet bias of late. Precipitation chances will likely improve markedly on Thursday afternoon through Friday as a strong warm front moves in from the southwest. Precipitable water levels rise from .40 inches ahead of the front to nearly .70 inches or 170% of normal by Friday. This moisture increase will be accompanied by strong warm air advection and isentropic ascent which will undoubtedly produce some precipitation. Given the prevailing S-SW flow the most significant amounts should fall at the Cascade Crest...northern WA mountains and Idaho Panhandle. Most of the precipitation will fall as rain...however there will be a tricky transition period over the northern valleys on Thursday night as the snow levels rise from the valley floors on Thursday to nearly 6000 feet by Friday morning. We expect the transition to be a smooth one with not much valley snow accumulation expected before it all changes to rain. In the mountains we expect to see anywhere from 3 to 6 inches of snow...with most occurring near the Canadian border. By late Friday night and Saturday the front will push into BC with the threat of precipitation waning substantially...except for locations near the Canadian Border. 850 mb temps climb to some of their warmest readings this winter and with ample mixing anticipated we expect to see highs in the 50s to lower 60s. fx Saturday night through Tuesday: The Inland Northwest will be in a progressive pattern, with a couple opportunities for precipitation and moderating temperatures. A ridge of high pressure continues to reign Saturday, but it'll be shifting east. A plume of moisture riding over the ridge and the onshore flow will provide mostly cloudy conditions, with the primary precipitation threat laying near the Cascades and Canadian border. A mild southwest flow and 850mb temperatures in the lower to mid- single digits support above normal temperatures and snow levels above 5000 feet. Between Saturday night and Sunday a storm system comes into the region. The cold front reaches the Cascades Saturday evening and pushes toward Montana by Sunday morning. The supporting 500mb shortwave trough comes on its heels. These features are relatively sharp and the mid-level shortwave takes on a slight negative-tilt as it moves through. Combined with the modest moisture plume this will bring a good chance of precipitation to the region Saturday night and Sunday morning. The exception will be in the typical locations, including the lee of the Cascades, deeper basin and L-C valley due to some downsloping. Chances remain high Sunday afternoon and evening with an inverted surface trough/deformation axis trailing into the region, before shortwave ridging develops later Sunday night into Monday. Look for a drying trend by this period. Cooler air comes in from the west through this period, dropping snow levels toward 2000-3000 feet by late Sunday morning through the afternoon, before falling toward valley floors at night. So the precipitation that comes late Saturday into Sunday morning should be a case of valley rain and mountain snow. However a snow threat mixes into the valleys by late morning. Temperatures drop closer to seasonal norms. Between Monday night into Tuesday another systems come to the region. Models disagree over its evolution, including how directly it passes through the region. Regardless of this, the system appears weaker than the Saturday night/Sunday system and does not have the same deep moisture tap. Look for a relative increase in precipitation chances but overall PoPs remain low. Snow levels rise to between 2500-4000 feet. /J. Cote' && .AVIATION... 00Z TAFS: A weak weather system will skirt eastern Washington and the ID panhandle tonight. Ceilings will lower but remain VFR at the TAF sites...with the best chances for light snow north of the KGEG-KSFF-KCOE corridor. && .PRELIMINARY POINT TEMPS/POPS... Spokane 27 42 30 43 34 48 / 10 20 10 40 50 40 Coeur d'Alene 26 40 29 43 32 45 / 20 30 10 50 50 40 Pullman 28 44 31 45 35 50 / 0 20 10 40 50 20 Lewiston 31 52 35 53 38 57 / 0 10 0 30 40 20 Colville 26 47 27 46 31 48 / 30 40 30 60 60 50 Sandpoint 25 41 29 41 33 43 / 20 50 30 50 60 50 Kellogg 24 39 28 43 31 44 / 20 60 30 60 60 40 Moses Lake 29 50 30 50 34 57 / 10 10 10 40 20 10 Wenatchee 30 50 30 49 34 54 / 20 10 10 30 20 10 Omak 25 44 23 41 29 47 / 50 20 10 40 20 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$