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550 FXUS66 KOTX 231141 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 440 AM PDT WED JUL 23 2014 .SYNOPSIS... A strong storm system will move through the region today, bringing the potential for thunderstorms and heavy rain. Cool and windy weather is expected for Thursday. Temperatures will rebound by the weekend and be accompanied by dry conditions. Hot weather will return to the area on Sunday and early next week. && .DISCUSSION... Today and tonight: A strong storm system comes into the region, with a good chance of showers and thunderstorms. Low pressure is centered off the Washington coast this morning and is forecast to reach NE WA/SE BC by Thursday morning. Ahead of it is a moist southwest flow, with PWATs around 1 inch (or about 180% of normal) and surface dew points in the 50s to low 60s. This morning showers and thunderstorms, associated with a mid-level disturbance and slug of mid-level instability that came in from Oregon, will continue to lift northward and out into BC and MT. This will leave some lull in the bigger precipitation threat from around 15-20Z for a good chunk of the region. However other showers are expected to continue near the Cascades with the offshore low approaching and the next shortwave pivoting around it. Then this afternoon and evening the next round of showers and thunderstorms develops. As temperatures warm into the 70s and 80s the convective instability blossoms: SBCAPE values from 18 and 00Z rise to between 200 and 1000 J/kg. The best of it centered along and north and east of a line from Mazama to Othello. In that region models paint the core of it across the northeast mountains south into the Palouse and across the north and central Panhandle. So going into the afternoon a theta-e ridge slips in from the south, while the cold front and supporting upper low push into the Cascades and east toward the Idaho Panhandle by this evening. These latter several features would be enough to bring a good threat of showers and thunderstorms. But the coupling of one jet streak tracking up from the Great Basin into central Idaho and second jet streak rounding the upper low, with a fair amount of diffluence over eastern Washington and north Idaho, makes me even more confident there is enough lift out there to bring showers and thunderstorms. Models still paint some of the higher precipitation amounts along the cold front and upper low over the Cascades, supporting the potential for flooding. Hence the flash flood watch remains in place, especially with concerns in the burn scar areas from this and the past few summers. The threat of strong to locally severe thunderstorms also remains over much of eastern WA and north ID too given the forces of lift, moisture and instability coming together. With 0-6km bulk shear between 30 to 50kts, storms will have the potential to be more organized. Looking at forecast soundings, the CAPE appears to be relatively thin and tall, with a relatively dry sub-cloud layer. This lends thinking that the main threat from storms will be hail and gusty winds. Going into the late evening and overnight the cold front is pushed east of the region, with the upper low near the WA/BC border. Some elevated instability lingers across the Canadian border, petering out southwest toward the Waterville Plateau. Some weak instability lingers near the Clearwaters too. Thus the primary shower chances will continue near the Cascade crest, northern mountains and across Idaho, especially through the early overnight. The remainder of the area should see things drying out, with some clearing from the southwest. The other issue will be winds. Outside of those generated with thunderstorms, synoptic winds are expected to pick up from the west-southwest this afternoon and tonight along and behind the front. By mid to later afternoon winds in the 10 to 20 mph range will be possible, especially over the east Chelan county, across the Basin into the Spokane/C`dA area, Palouse and L-C Valley. Gusts near 30 mph or so will also be possible. Speeds abate some overnight, but still remain relatively breezy for the time of day. /J. Cote` Thursday through Sunday...Model guidance indicates the cold pool aloft associated with the anomalous upper low will be centered over the northern reaches of the forecast area as Thursday dawns. This should promote continued showers...but given the time of day before appreciable surface based instability can be generated these lingering showers will be primarily left over rain showers from the previous evening`s convective activity with only a few isolated thunderstorms centered mainly over the mountainous terrain north of the Columbia Basin. Thursday overall will be a day of general improvement as the offending upper low begins to move out of the region to the northeast during the afternoon. The cooler maritime air mass in the wake of the upper low will manifest itself as much cooler than normal temperatures on Thursday with generally breezy conditions with gusts to near 30 mph over the exposed terrain of the basin and Cascade gaps. Friday through Sunday will feature a drying and warming trend as a mid-summer 4 corners upper level ridge builds into the region. A general warming trend to back above normal will become noticeable starting Friday and continuing through the weekend with lighter winds and a dry and stable air mass precluding any precipitation. /Fugazzi Monday through Wednesday: A ridging pattern is expected to be over the region for this period. This will lead to a dry and warming trend in the temperatures. The models are in good agreement for this period with the exception of the GFS showing a shortwave on Monday morning. The lack of moisture kept the chance of showers out the forecast. Temperatures are expected to be in the 90s for the region during this period. /JDC && .AVIATION... 12Z TAFS: Low pressure off the coast this Wednesday morning will move inland over the next 24 hours. Isolated showers will be possible around the TAF sites this morning, but a better threat of showers and thunderstorms develops this afternoon, first around EAT near 18-21Z and elsewhere starting between 20-23Z, before the threat begins to wane after 00Z-06Z from west to east. Some of the thunderstorms may be strong and isolated severe thunderstorms are not out of the question. Predominantly VFR conditions are forecast. Yet heavier storms may produce brief MVFR/IFR cigs/vis, with the potential for heavy downpours, gusty winds and hail. Aside from possible winds with thunderstorms, general winds will increase for this afternoon and evening with sustained speeds between 10-20kts and gusts up to 30kts, before decreasing after 03-06Z. /J. Cote` && .PRELIMINARY POINT TEMPS/POPS... Spokane 83 52 71 51 77 55 / 50 80 20 10 0 0 Coeur d`Alene 84 53 67 52 76 51 / 50 80 40 10 0 0 Pullman 84 49 69 46 76 44 / 40 70 10 0 0 0 Lewiston 90 58 78 57 84 56 / 40 60 10 0 0 0 Colville 81 51 71 51 80 50 / 60 80 50 10 0 0 Sandpoint 85 51 66 49 73 49 / 50 80 50 10 0 0 Kellogg 85 52 65 50 73 51 / 40 80 40 10 0 0 Moses Lake 83 56 75 57 84 57 / 50 40 10 0 0 0 Wenatchee 75 58 73 59 83 61 / 70 40 20 0 0 0 Omak 77 55 74 53 84 54 / 80 60 20 10 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...Flash Flood Watch from 8 AM PDT this morning through this evening for East Slopes Northern Cascades-Okanogan Valley- Wenatchee Area. && $$