Scientific Forecaster Discussion

000 fxus66 kotx 162138 afdotx Area forecast discussion National Weather Service Spokane Washington 238 PM PDT Thu Aug 16 2018 Synopsis... haze and smoke will continue through next week with temperatures remaining above average. There will be thunderstorms over southeast Washington and the Idaho Panhandle tonight and Friday. Northerly winds will develop on Monday and could bring an additional surge of Canadian smoke into the region. && Discussion... tonight through Saturday...this period will see the transit of an splitting upper level trough. Most of the energy of this wave will be focused south of the region...with a weakening northern branch wave ambling through eastern Washington tonight and tomorrow. Meanwhile mid level monsoonal moisture is once again surging up from the south ahead of the trough. With moisture a sure bet...mid level instability likely...and some weak dynamic forcing overnight in the cyclonic diffluent region just ahead of the trough confidence is high enough to forecast isolated high based thunderstorms late overnight and into Friday morning for extreme eastern Washington and the Idaho Panhandle. To the west over the deep basin and northeast Washington mountains expect a lot of altocumulus castellanus with a few sprinkles and maybe a rogue lightning strike or two but the main axis will lay to the east in the Panhandle. On Friday the activity will be mainly confined to the Idaho Panhandle...with surface based instability promoting an increase in coverage to scattered thunderstorms mainly south of Interstate 90 and these storms will become wetter as the day wears on. The rest of the region...the Washington zones will need to deal with breezy winds with another warm day promoting low relative humidity in the afternoon as a weak cold front crosses the basin during the morning. By afternoon the cross Cascades gradient tightens and with the continued warm temperatures in the wake of the underachieving cold front...a few degrees cooler that today but not really noticeable without a thermometer...this will create the potential for wind and low relative humidity red flag conditions in the Cascade Gap areas in and near the Cascades. Friday night and Saturday things settle down to simply warm and dry with decreasing winds as a Post trough short wave rideg builds back over the area. Fridays cold front may marginally improve improve air quality and smoke layers around the region...but it is expected that the calming and stabilizing conditions on Saturday will simply promote another deterioration. /Fugazzi Saturday night through thursday: temperatures are expected to remain on the warm/hot side and above normal as the weather pattern undergoes a number of changes during this time interval. The weather pattern changes will have a substantial impact on what smoke gets pushed into the region and affecting air quality. Per the latest GFS the expectation is Saturday night on thru the weekend will be marked with the positioning of an upper level area of low pressure just off the Washington and Oregon coast which wobbles about a bit in that general location until it opens up and ejects to the northeast and across Washington and north Idaho Tuesday evening into Wednesday. This positioning of the low allows for minor pops for thunderstorm mention that appear every now and then between Sunday and Tuesday night with the highest pops for thunderstorms associated with a wave rotating up ahead of the low from the south Monday night into Tuesday morning and with the ejection of the low Tuesday evening into Wednesday. Of additional concern with this pattern change is resulting breezy/gusty northerly winds Sunday night into Monday which is expected to push down substantial smoke from wildfires in British Columbia while also elevating fire danger due to the gusty winds occurring with low relative humidity. Sunday and Monday will likely be the coolest days of the seven day forecast followed by a warming trend thru the rest of the next workweek as the flow following the Tuesday night/Wednesday ejection of the offshore low favors a warmer southwest one. With fires location on all quadrants outside of the forecast area its doubtful there will be any long term improvement to air quality. Indeed available smoke models, some that go out 240 hours, suggest smoke will stick around awhile. /Pelatti && Aviation... 18z tafs: haze and smoke will remain the biggest impact to taf sites, with MVFR/isolated VFR visibility. Periods of IFR vis at keat is expected. Trended towards a persistence forecast with moderate uncertainty in details. Middle to high clouds continue to stream overhead as the move up from the south, sometimes resulting in ceilings near 15-20kft. Expectation is that best potential for any thunderstorms will be overnight between 08z and 18z Friday. /Pelatti && Preliminary point temps/pops... Spokane 67 90 61 88 61 89 / 10 20 0 0 0 0 Coeur D'Alene 62 88 58 87 57 89 / 10 20 10 0 0 0 Pullman 63 86 55 86 54 89 / 20 30 10 0 0 0 Lewiston 69 92 63 92 62 95 / 20 30 10 0 0 0 Colville 56 93 54 91 54 91 / 0 10 0 0 0 0 Sandpoint 53 87 51 86 52 86 / 0 20 0 0 0 0 Kellogg 58 84 55 83 54 86 / 10 30 10 0 0 0 Moses Lake 62 95 58 92 58 93 / 10 10 0 0 0 0 Wenatchee 66 92 64 91 64 92 / 10 10 0 0 0 0 Omak 63 94 63 92 62 93 / 0 10 0 0 0 0 && Otx watches/warnings/advisories... flag warning from 7 PM this evening to 5 PM PDT Friday for northern and central Idaho Panhandle (zone 101). Washington...Fire Weather Watch from Friday afternoon through Friday evening for East Washington central Cascade mountains (zone 682)- East Washington central Cascade valleys (zone 677)-East Washington south central Cascade valleys (zone 676). Red flag warning from 7 PM this evening to 11 am PDT Friday for East Washington Palouse and Spokane area (zone 674).

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