Scientific Forecaster Discussion

000 fxus66 kotx 220015 afdotx Area forecast discussion National Weather Service Spokane Washington 515 PM PDT Thu Mar 21 2019 Synopsis... Friday will be a few degrees cooler as clouds increase ahead of a weak cold front. The chance for showers will increase Friday night as the front moves across the region. The weekend will feature temperatures near average with rain and mountain snow showers over the Idaho Panhandle and portions of eastern Washington. Typical cool and showery weather is expected much of next week with high temperatures mainly in the 50s. && Discussion... Tonight: tonight will be another chilly one with light winds and mainly clear skies. Bands of high clouds will wrap around low pressure over the Great Basin, but the high level moisture shouldn't hinder radiational cooling much. Most lowland communities across the inland northwest will experience overnight temperatures in the 30s. Friday: a slow moving trough will reach the Washington/or coast Friday afternoon spreading increasing mid and high clouds across Washington and north Idaho on Friday. Most of our region should be 2 to 5 degrees cooler on Friday than today. Showers associated with the incoming trough will mainly be limited to western Washington and the high terrain of the Cascades. Friday night and saturday: a weak cold frontal passage will occur Fri night as the upper level trough shears and stretches apart. The strongest moisture advection and upper level support will dig into California and Nevada Fri night into Saturday. The models have been pretty consistent very little measurable precipitation across the Columbia Basin and north central Washington Fri night. The help of orographic forcing should yield some rain and snow showers over the Idaho Panhandle on Saturday. With snow levels expected to be around 4500 feet, skiers may witness periods of light snow. Saturday night and sunday: up through Saturday night, precipitation amounts look to be showery and light. We will be watching Saturday night and Sunday for the potential of some more significant amounts as a shortwave pivots northeast out of northern Nevada. The potential for wet snow accumulations (above 4000 ft) and the potential for rain onto fields soaked by melting snow are reasons to monitor this wave. Model agreement isn't good with the track and timing of this wave. The GFS lifts the wave far enough north Saturday night to produce a quarter to half inch of liquid equivalent across the southern Idaho Panhandle and clips the Camas Prairie with enough moisture for accumulating snow above 4000 feet. The NAM is slower with the majority of the precipitation arriving during the day Sunday. The European model (ecmwf) drags the trough far enough south yielding much lighter and spottier precipitation. The National Weather Service blend of models seems to favor the track further south similar to the European model (ecmwf) which is reflected in our forecast. /Gkoch Monday to thursday: the inland northwest will be in a more active pattern, with periodic opportunities for precipitation. Looking at the big picture a broad trough sets up off the coast and sends occasional shortwaves inland. There are timing disagreements regarding these individual features, which basically means there are modest chances for precipitation but we are still pinning down when chances will be highest. One wave exits early Monday and a second comes through sometime between Monday night and Tuesday. So Monday looks mostly dry, save for limited shower chances in the north early and then in the Cascades and far western basin later in the day. Then Monday evening into Tuesday broader chances expand across the region, with some suggestion that the threat will lift toward the mountains into Tuesday afternoon. This is accompanied by some breezy conditions. Additional impulses will bring additional shower chances going into Wednesday and Thursday. As for precipitation-type: overall it looks like valley rain and mountain snow, with snow levels averaging 3-4kft. However nighttime temperatures will be near freezing in spots, enough to allow for some mix down to valley floors. As for precipitation amounts: some moderate amounts are possible closer to the Cascades and far western Columbia Basin and northern mountains with the Monday/Tuesday front. Where this falls as snow will largely be in the mountains, but we will have to monitor the Cascades passes and places like Sherman Pass for travel impacts. Overall afternoon temperatures are expected to be near seasonal norms, while overnight lows are expected to be near to slightly below normal. /Cote' && Hydrology... A Flood Watch has been issued for areas in and around Moscow Idaho. Paradise creek rose sharply last evening in response to lowland snow melt. It crested a foot shy of flood stage (9.2 feet) before dropping this morning. Another rise will occur this afternoon and evening as our diurnal melting cycle begins. The Paradise creek basin still has ripe snow. If a similar amount of water (roughly 110 cubic feet per second) reaches the river gauge tonight, the river will be close to flood stage. Tomorrow afternoon looks 3 to 5 degrees cooler. The basin will also be gradually losing snow the next few days. By the weekend, cooler temps and less runoff should lead to lower flows into Paradise creek. For the remainder of the Palouse, West Plains, and upper Columbia Basin, snow cover will become increasingly patchy the next few days. As the snow disappears, we expect some more minor field flooding. Snow is ripening in The Lowlands of Bonner and boundary counties, so small streams are expected to experience rises the next few days. At this time, the precipitation moving into the region for the weekend looks to be showery with light basin average amounts. This is generally good news, along with the arrival of cooler daytime temperatures over the weekend into early next week. /Gkoch && Aviation... 00z tafs: high level clouds will move across the region from the southeast tonight. The clouds will thickin overnight and towards morning. Winds will remain light. && Preliminary point temps/pops... Spokane 34 57 38 54 35 53 / 0 0 10 20 20 20 Coeur D'Alene 33 55 38 51 34 50 / 0 10 20 20 30 30 Pullman 34 55 38 47 33 47 / 0 0 20 20 20 20 Lewiston 38 59 43 53 37 54 / 0 0 30 30 20 20 Colville 27 58 37 54 33 54 / 0 10 20 30 20 30 Sandpoint 31 53 36 50 34 48 / 0 10 20 30 30 40 Kellogg 37 56 37 51 34 50 / 0 10 20 30 30 50 Moses Lake 35 63 39 59 34 58 / 0 0 10 0 10 0 Wenatchee 38 58 41 54 36 54 / 0 0 30 0 10 10 Omak 34 62 39 56 36 54 / 0 0 30 10 20 20 && Otx watches/warnings/advisories... Idaho...none.

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