246 FXUS66 KOTX 101030 AFDOTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SPOKANE WA 330 AM PDT Sun Mar 10 2013 .SYNOPSIS... High clouds will increase and thicken today as the next Pacific Storm system approaches. Wet, mild and breezy weather will return to the Inland Northwest Monday through much of next week with several rounds of rain and high mountain snow transitioning mostly to all rain. The warming, rain and snow melt has the potential to cause rises along many of the area rivers. && .DISCUSSION... Today through Monday...An upper level ridge currently resides over the forecast area. Satellite indicates an incoming fetch of Pacific moisture beginning to over-ride this ridge...promising an increase in high clouds available to filter the sun. The increase in these clouds should serve to keep fog less prevalent this morning than previous days. Latest models are in good agreement and depict a general deterioration over the next 24 to 36 hours into a generally rainy period for the beginning of the new week. The incoming moisture fetch will slowly moisten the air mass from top down through today. This will lead to a general increase and thickening of clouds...but there will be little chance of any precipitation yet. High temperatures will once again crest at or slightly above normal. Tonight brings the first increasing chance of precipitation as the moisture feed becomes more favorable and the air mass becomes increasingly saturated...still...other than weakly developing isentropic ascent mainly over the eastern high terrain...dynamic forcing and frontal lift is weak and ill defined so the main threat of very light precipitation will mainly be confined to the rising terrain of the Idaho Panhandle. Heavy clouds will likely retard any widespread cool down to freezing over most of the region by dawn Monday. On Monday the main sub-tropical moisture feed will become even more favorably directed into the region...and a better defined warm front...now discernible even in the surface pressure field...will begin to form over the forecast area roughly from west to east during the day. All of these elements...the imminent saturation of the low level air mass and increasingly strong isentropic ascent along the burgeoning warm front will lead to high confidecne of an increasing likelihood of light valley rain and mountain snow during the afternoon hours over most zones...with the lowest chance in the deep basin/Cascades Lee and highest chance over the Idaho Panhandle. /Fugazzi ...Wet and mild weather pattern will result in an extended period of rainfall across the Cascade crest and in the Idaho Panhandle next week with moderate accumulations possible... Monday night through Thursday night: The story will continue to be the possibility for some moderate to heavy rain accumulations across the region as a very wet weather pattern sets up. Medium range model guidance has been very consistent with an atmospheric river setting up through this period and continuing into the weekend. Low pressure in the eastern Pacific located at roughly 150W longitude will act to draw up a sub-tropical moisture plume that will originate from the Hawaiian Islands. As mentioned, models have remained consistent and confidence is high that this atmospheric river will set up across the eastern Pacific. What continues to pose the most uncertainty is where the axis of this moisture plume will set up and how long will it remain over any one area. Models have generally narrowed down the this moisture axis between southern WA and the norther portion of Vancouver Island. This zone between these two points will see a high probability of the highest moisture content associated with this plume. This will likely result in some hefty precip amounts over the Cascade crest. Exact amounts are still a bit uncertain still at this time as the much wetter GFS and NAM indicate 48 hour accumulations upwards of 5 inches and even localized amounts near 6 inches near the crest of central to northern Cascades for Monday through Wednesday. The ECMWF model is slightly more north with its maximum precip accumulations with the very northern portions of the Cascade crest hit the hardest, but is much drier than the GFS and NAM with a 48 hour total closer to 2.5 inches at the crest for this same time period. The GFS and NAM have had a wet bias and the reality of these accumulations over this period is somewhere in the middle of the drier ECMWF and wetter GFS and NAM solutions. Although we will see a pretty good rain shadow just east of the Cascade Mountains across the western basin, we will see a secondary maximum of precip amounts occurring across the ID Panhandle. The ECMWF has been the more consistent model, although differences have been slight with the latest runs. However, the ECMWF model has been showing more of a northward progression of the first and wettest warm front that moves through on Monday into Tuesday. The GFS is still a bit slower, and as a result, produces significantly more precip in the Idaho Panhandle compared to the ECMWF. I cut precip amounts in half over the Northeast Blue Mountains over into the Camas Prairie and these areas look to dry out quicker than previously though. I did not make many changes to the precip amounts across the Central Panhandle Mountains up into the Northern Panhandle in case the ECMWF is too fast with the warm front. Snow levels will be on the increase from about 3500 to 4000 ft in the north to around 5500 to 6000 ft further south on Monday night to 6000 ft in the north and 7000 ft across the southern zones by Thursday. This will result in much of the precip falling as rain, especially at mid slopes down into the valleys. Some low land flooding, rises to small streams and possible some debris flows will be possible with the combination of rainfall and some snow melt. The area of greatest concern will be in the east slopes of the Cascades, especially near the crest. A secondary concern will be across the Idaho Panhandle, especially in the wetter GFS and NAM models verify. Temperatures are expected to be much more mild through this period as we remain in the warm sector. We will see a warming trend with above normal temperatures. By Wednesday and Thursday, valleys will likely be in the mid 50s and in the 60s for some locations. /SVH Friday through Sunday...Various solutions exist in the extended with the latest solutions in little agreement. Have decided to stick with the status quo as far as the weather pattern goes, meaning the active west-southwest flow over the Inland Northwest will continue. The anchoring low that sits over the Gulf of Alaska may begin to migrate south toward the latter portion of the extended, which may bring some colder air with it and lowering snow levels. Have trended that way every so slightly during the day 8 time frame, but for the most part there was little deviation from previous thinking. The temperatures should not get too far out of hand, as the forecast afternoon temperatures are not too far from normal, so we can probably keep any potential snow-melt and associated flooding at an extreme local level. ty && .AVIATION... 06Z TAFS: VFR conditions continue at TAF sites for next 24 hrs. High clouds invade sky, thicken, and lower from west to east tonight then generally lower to mid clouds by morning. /Pelatti && .PRELIMINARY POINT TEMPS/POPS... Spokane 50 35 48 39 53 42 / 0 10 50 70 70 40 Coeur d'Alene 51 34 48 38 50 41 / 0 10 60 70 80 50 Pullman 53 37 49 42 54 43 / 0 20 60 80 70 30 Lewiston 63 42 55 46 61 46 / 0 20 40 70 60 20 Colville 50 33 49 36 51 40 / 10 10 50 60 80 60 Sandpoint 49 32 46 36 45 41 / 10 20 60 70 90 100 Kellogg 48 33 45 37 47 39 / 10 50 90 100 100 80 Moses Lake 58 39 55 43 62 45 / 0 10 20 20 20 10 Wenatchee 58 36 55 40 59 43 / 0 10 20 20 20 10 Omak 54 34 49 36 54 38 / 10 10 30 30 20 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$