Area Forecast Discussion
Issued by NWS Spokane, WA

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000 FXUS66 KOTX 202347 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 447 PM PDT Thu Sep 20 2018 .SYNOPSIS... A plume of moisture will remain near the Canadian border through Friday resulting in a small chance of showers. A better chance of precipitation will arrive Friday night into Saturday as a weakening cold front slides across the Inland Northwest. The cold front will also be accompanied by breezy west winds across the Columbia Basin and Palouse for much of Saturday. The last chance of showery and cool weather will occur on Sunday with the better chances near the Canadian border and the Blue mountains. Warmer and drier weather is then expected to take hold for the work week. && .DISCUSSION... Tonight through Friday night: Extremely low amplitude ridge which is cluttered with moisture and disturbances fluxing through it mark tonight with primarily clouds and spotty shower activity primarily near the British Columbia Border and over parts of the East Slopes of the North Cascades. A low pressure system approaching the coast Friday keeps a good amount of middle and high cloud cover over Eastern Washington and North Idaho. It also pumps up 500mb heights over the area with it coupled with warm southerly flow at low levels allowing for Friday to likely be one of the warmest days of the seven day forecast. Any precipitation changes for Friday are again relegated to the British Columbia Border and to a lesser extent over the East Slopes of the North Cascades. Friday night this low pressure system drags a cold front through the region allowing for winds to shift to the southwest and become breezy/gusty along with some increase of pops, however a good chunk of Southeast Washington and North Idaho is expected to remain dry due to the resulting downsloping in the lee of the Cascades. /Pelatti .Saturday and Sunday...Upper level low which is currently nearing 145w will provide the focus for this period. By Saturday this low will move onto the Washington coast which pushes a cold front through the Inland NW. Most of the moisture from the front will be intercepted by the Cascades, however there will be enough moisture, ascent and instability to bring a chance of precipitation to regions near the Canadian border as well as a small chance over extreme SE Washington into NC Idaho. The latter region is where the front is expected to lose its east-southeast progression and will likely remain fixed in this area through Saturday morning. It appears most of the precipitation will be light with any heavier amounts expected to occur over southern BC. The front will also deliver moderate west to southwest winds with gusts of 25-30 mph possible over the Columbia Basin, Palouse, and Spokane area. The precipitation threat from the front (and winds) will wane on Sunday, however then the focus will shift to the upper level trough pushing through the northern half of Washington. Model consistency is good that this trough will push a 500 mb cold pool across the northern portion of the forecast area. 500 mb temps are expected to drop to -21c or colder which results in some fairly impressive instability. The NAM is the most bullish on this notion and is showing MUCAPE values of 100-300 j/kg moving from the north Cascades early Saturday morning and then into the north Idaho Panhandle by afternoon. Dynamic forcing ahead of this trough should be strong enough to generate some showers and if the NAM is right we could see some nocturnal thunderstorms near the Canadian border late Saturday night/Sunday morning. The thunder threat would translate toward the ID/MT border by afternoon. Monday through Thursday...Upper level ridging is expected to build over the region with temperatures warming steadily through the week. Highs will warm into the 70s for most locations by Wednesday with cool night time lows. Whether or not Wednesday will be the warmest day of the week is questionable as a weak shortwave trough is forecast to dig through western Montana Wednesday night. If this comes to fruition, Thursday would be cooler by a bit, however that is far from certain at this point. fx && .AVIATION... 00Z TAFS: Clouds will steadily increase and gradually lower through the night as a weather disturbance scoots along the Canadian border. A cumulus deck and gusty winds across northeast Washington and north Idaho will dissipate early this evening, while the mid and high clouds increase from west to east. Any precipitation should remain north of the TAF sites in the mountains. High pressure will build into the region for Friday afternoon with winds less than 10kts. All TAF sites should remain VFR. /rfox. && .PRELIMINARY POINT TEMPS/POPS... Spokane 48 72 52 68 46 66 / 10 0 10 10 10 10 Coeur d`Alene 44 71 51 67 46 64 / 0 0 10 20 10 10 Pullman 44 73 50 66 44 63 / 0 0 10 10 10 10 Lewiston 48 79 56 72 52 69 / 0 0 0 20 10 10 Colville 45 70 46 69 44 69 / 20 20 20 10 20 20 Sandpoint 41 67 47 65 43 63 / 10 40 30 30 20 20 Kellogg 43 69 48 63 43 60 / 0 0 10 20 10 20 Moses Lake 46 76 51 74 45 71 / 0 0 10 0 10 0 Wenatchee 52 74 54 71 47 69 / 10 0 10 10 10 0 Omak 50 73 50 72 46 71 / 10 0 20 10 10 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$

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