Scientific Forecaster Discussion
000 FXUS66 KOTX 201135 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 435 AM PDT Sun Aug 20 2017 .SYNOPSIS... Bands of mid and high clouds are expected to move over the Pacific Northwest today, but we will see clearing overnight. Skies should be favorable for viewing the eclipse Monday morning, however there may be some smoke in the northern valleys. Tuesday and Wednesday will be quite warm with afternoon temperatures in the upper 80s to mid 90s. A vigorous cold front on Wednesday night will have the potential to produce thunderstorms, with strong winds expected on Thursday. && .DISCUSSION... Today through Monday night: A dry northwest flow will continue today before weak high pressure begins building on Monday. A weak wave embedded within the northwest flow will track across southern BC today clipping northern Washington and the north Idaho Panhandle. Main impact from this will be mid and high level cloud cover. This wave exits tonight bringing clearing skies. For Monday (Eclipse Day), the 00z GFS and ECMWF model progs show a band of cirrus moving into Central Washington in the morning reaching the Idaho Panhandle during the late morning or early afternoon. Satellite imagery shows quite a bit of high clouds to our west-northwest so this idea is accepted. This moisture is very high up (above 300 mb) and shouldn't have much of an impact on eclipse viewing. The other issue of note is smoke and haze which moved into NE Washington and the N Idaho Panhandle yesterday. Southwest winds this afternoon is expected to improve the smoke/haze situation for the Spokane/Coeur d'Alene area but isn't expected to bring much improvement to the northern valleys and N Idaho Panhandle where lighter winds are expected. Still...the smoke/haze isn't as bad as what occurred during the first 10 days of August and probably won't have to much of an impact on the eclipse. Mostly clear skies and the weak ridge will allow for the beginning of a warming trend with highs in the mid to upper 80s for most towns with the warmest spots in the lower 90s. JW Tuesday and Wednesday: Our forecast for Tuesday and Wednesday has changed little. The models continue to forecast the amplification of a broad high pressure ridge on Tuesday leading to above average temperatures. Tuesday should be our warmest day with high temperatures in the upper 80s to mid 90s. We will have light winds in the lowest 8 to 10 thousand feet of the atmosphere on Tuesday under our 500mb ridge. With smoke being produced by fires in BC, Oregon, central Idaho, and north central Washington, it may be tough to escape the haze and smoke. With fires all around, our only "clean" wind direction is out of the west. On Wednesday, the 500mb ridge axis will migrate into Montana allowing increasing on-shore flow to bleed a bit of marine air into our region. Look for our temperatures to be a couple degrees cooler Wednesday afternoon with afternoon winds of 5 to 15 mph. Thursday: The evening runs of the GFS, ECMWF, and Canadian models continue to suggest that Thursday will be our most volatile weather day of the week. It is still possible that the timing and intensity of this storm could change, but at this time it looks like it could be one of our most noteworthy events of the summer. A vigorous cold front is expected to push through the Inland Northwest during the early morning hours. *Thunderstorms: A ribbon of mid-level moisture and instability is forecast along and ahead of the cold front suggesting scattered showers and thunderstorms over the Idaho Panhandle and southeast Washington early in the day Thursday. Model soundings suggest high cloud bases and fast storm motion. It is too early to tell how much lightning may accompany storms early on Thursday, but it does not appear that fast moving, high-based cells will produce much wetting rain. Given the extreme dryness of July and August, our fuels are critically dry. Any lightning at this stage is a potentially significant wildfire concern. *Wind: A negatively tilted 500mb trough tracking along the Washington/BC border is notorious wind producing pattern. Strong cold advection will occur Thursday into Thursday evening. Steep lapse rates from the surface to 700mb will allow efficient downward momentum transfer from late morning through early evening. Fortunately, model winds aren't stronger in the layer around 800-850mb (30-35kts), or our gust potential would be higher. At this time, it looks like sustained 20 to 25 mph winds with gusts of 30 mph or more across the Columbia Basin, Palouse, and West Plains from late morning through early evening. Localized gusts up to 40 mph will be a good bet through the Cascade gaps around Wenatchee, Entiat, Chelan, and Vantage. *Blowing Dust: The magnitude of the wind and the duration of the wind through the afternoon into the evening will heighten the risk of blowing dust. We have had little to no measurable precipitation across the dryland wheat country since late June...leaving the region susceptible to blowing dust. Friday and Saturday: Temperatures on Friday will be noticeably cooler in the wake of Thursday's strong front. Much of the Inland Northwest will only top out in the 70s to around 80. Our temps will rebound a bit on Saturday...close to seasonal normals. /GKoch && .AVIATION... 12Z TAFS: Main aviation concern will be smoke settling into the valleys of NE WA and N ID with the overnight inversions. Overall, confidence remains low for restrictions at the main terminals but is MVFR visibilities are possible at Colville, Deer Park, Bonners Ferry, and Sandpoint. Otherwise...expect generally light winds with afternoon gusts around 15 mph. JW && .PRELIMINARY POINT TEMPS/POPS... Spokane 81 57 85 61 90 63 / 0 0 0 0 0 0 Coeur d'Alene 81 53 86 55 91 58 / 0 0 0 0 0 0 Pullman 79 52 85 54 91 59 / 0 0 0 0 0 0 Lewiston 87 60 92 62 97 66 / 0 0 0 0 0 10 Colville 82 51 86 52 91 54 / 0 0 0 0 0 0 Sandpoint 81 46 84 48 87 51 / 0 0 0 0 0 0 Kellogg 77 50 84 54 89 55 / 0 0 0 0 0 0 Moses Lake 86 55 90 57 94 60 / 0 0 0 0 0 0 Wenatchee 86 62 89 64 93 65 / 0 0 0 0 0 0 Omak 86 59 90 60 94 62 / 0 0 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None.