FXUS66 KOTX 101812 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 1112 AM PDT Tue Sep 10 2024 .SYNOPSIS... The weather pattern will be changing. After one more mild day Tuesday, a larger low pressure system descends on the Pacific northwest. A cooler weather pattern, featuring the chance of showers, is expected Wednesday and Thursday. Temperatures will reach the 60s and 70s. The weekend looks to be on the drier side with seasonal temperatures. && .DISCUSSION... Today through Thursday: An upper-level trof is beginning to carve into the Northwestern US and will remain in place through the next few days. Confidence is high for a significant cooling trend with temperatures by Wednesday and Thursday only warming into the 60s-70s. These temperatures will be similar to those experienced with the deep low that moved through the region on Aug 23-24th however, odds are low that we will rebound back into the 90s again this year! The incoming system will bring rain chances to the Inland NW largely coming Wednesday and Thursday. Today will be dry with scattered to broken mid and high clouds. There is enough instability in the midlevels that a few clouds may squeeze out some sprinkles but the antecedent air mass is quite dry and will take time to saturate. Consequently, the HREF is advertising 0% chances for measurable precipitation (~ 0.01"). Additionally, the stronger dynamics with the incoming trof have just recently crossed 140W off the Northern BC coast and will not arrive until early Wednesday morning. During this time, showers will increase along the Cascades and along a ribbon of instability stretching from NE Oregon...through far southeastern WA...and into the lower Idaho Panhandle. Through the day Wednesday, showers will slowly fill across Central and Eastern WA with isolated to scattered coverage. Precipitation amounts will be light with most areas receiving less than a tenth of an inch. The ribbon of showers stretching from Kellogg to St Maries to Pullman and Anatone will carry the highest probabilities for tenth of rainfall with the latest HREF giving this corridor a 40-60% chance. Areas of the Cascades and Okanogan Highlands carry a 20-30% chance for a tenth or more but coverage will be spotty. Thinking, afternoon instability will likely need to play a role. Models do show pockets of CAPE from 200-600 J/kg; this will be highly dependent on afternoon sunshine. A majority of the Columbia Basin which could really use the rainfall, only carries a 5-10% chance for a tenth of rain. On Thursday, there is good agreement for the low to migrate eastward into southern Idaho/SW MT. Exact placement is still wavering but model trends have been slightly further east compared to 24 hours ago. A band of steady light to moderate rain wrapping around the low will make for a wet and cool day. The million dollar question is...does this reach North Idaho or remain just west in Montana. Several models placed this feature in North Idaho 24 hours ago and now, as mentioned above, have trend further east. Still looks like some of this moisture will reach the Idaho Panhandle but amounts are half of those projected yesterday. There will also be a sharp gradient from east to west from wet to dry conditions. The placement of this rain axis could continue to change over the next 24 hours but as it stands right now, the latest NBM probabilities for 12 hour rain amounts (5AM-5PM THU) in Idaho and extreme E WA are as follows: Probability for 0.10 or more" Bonners Ferry - 35% Sandpoint - 40% Coeur D Alene - 20% Kellogg - 50% St Maries - 40% Deary - 40% Lewiston - 25% Winchester - 40% Ione-Spokane-Pullman - 20% Probability for 0.25 or more" Bonners Ferry - 8% Sandpoint - 12% Coeur D Alene - 5% Kellogg - 20% St Maries - 10% Deary - 8% Lewiston - 4% Winchester - 5% Ione-Spokane-Pullman - 5% or less Central WA will be too far west and likely experience a day full of sunshine once morning clouds exit. Temperatures across the region will range from the 70s in Central WA to 60s-70s in Eastern WA and North Idaho. Communities along the Montana border may struggle to hit 60F if persistent light rains were to set up. Friday through Tuesday: Shortwave ridging returns on Friday as one system exits and the next one approaches. By Saturday, the region will become under the influence of southerly flow aloft as the next trof begins to swing onto the coast. The incoming system looks to undergo a good deal of meridional stretching which does not bode well for appreciable precipitation for the Inland NW. Showers are introduced into the forecast across the northern mountains Saturday and Sunday and expand into most areas Monday and Tuesday. Once again, confidence is highest for another bout of cooler temperatures but low for that season-ending precipitation event. Probabilities for a tenth for each Monday and Tuesday only range from 5-15% for most areas. Breezy winds will come at times but not seeing any significant impacts during this time-frame. /sb && .AVIATION... 18Z TAFS: Trof of low pressure working its way into the region will result in periods of mid-high clouds today. After 06z...light elevated showers to develop along with lowering cloud bases. Main chances for showers from 06-12Z will be from Ellensburg to Omak and also the Palouse to North Idaho. Better chances develop area- wide after 12Z. Also expect breezy to gusty winds through the Cascade Gaps impacting Wenatchee, Douglas, and Vantage area this afternoon and evening. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate to high confidence in VFR conditions. Low confidence for locally reduced visibilities in areas of smoke. /KD && .PRELIMINARY POINT TEMPS/POPS... Spokane 82 57 71 52 72 49 / 0 20 60 30 40 20 Coeur d'Alene 81 55 68 51 66 49 / 0 30 80 50 70 30 Pullman 79 55 66 50 65 45 / 0 40 80 50 70 20 Lewiston 88 60 73 56 71 54 / 0 50 80 70 70 20 Colville 81 56 71 50 74 38 / 10 20 50 40 40 10 Sandpoint 78 56 66 51 63 46 / 0 20 80 60 80 50 Kellogg 79 54 63 50 59 51 / 0 50 90 70 90 60 Moses Lake 83 57 73 52 77 46 / 0 10 30 10 10 0 Wenatchee 82 57 70 52 75 53 / 0 20 40 10 0 0 Omak 83 57 75 51 80 51 / 10 10 50 20 10 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$