695 FXUS66 KOTX 130455 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 955 PM PDT Thu May 12 2022 .SYNOPSIS... A cold front this evening into tonight will produce widespread showers and isolated thunderstorms across much of the region. Winds will also shift westerly and become gusty overnight with frontal passage. Mountain passes will also see the potential for light snow accumulations through early Friday morning. There will be chances for rain this weekend as temperatures trend warmer into Monday. Next week temps cool down once again with mountains showers most afternoons. && .DISCUSSION... Evening update (945 pm): First band of showers has moved through eastern/southeastern Washington and stretches now from the Colville to Grangeville vicinity and will continue northeast. Widespread wetting rains occurred with this band. A second band has moved into central Washington and produced several gusts of 35 to 45 mph and isolated lightning strikes as it moved through the eastern Cascades and adjacent Waterville Plateau and lower Columbia Basin. This band appears to have weakened as it has moved into north-central/northeast Washington. However, its southern extension (currently near/east of the Tri-Cities), has been noticeably stronger, with heavier instantaneous rain rates and occasional lightning. Latest convection-allowing models suggest this band may hold together as it moves into/through southeastern Washington and adjacent portions of the central/southern Idaho Panhandle. As temperatures drop overnight, may see some mixture with snow in the higher terrain of northern Idaho, though with minimal or negligible impacts. Main change to the forecast overnight was the addition of some thunder mention in eastern Washington and northern Idaho through 09z, though lightning should be rather isolated. Did also lower hourly temperatures for much of the overnight, with hi-res guidance performing much better than the rest of the model suite. Otherwise, current forecast is in good shape. /CMS Tonight into Friday: A cold front will sweep across the Inland Northwest this evening into tonight. The front will be supported by strong upper level dynamics with the trough pushing across with a negative tilt. This negative will help support strong divergence aloft and feed the converging motions occurring along the frontal band. The moisture plume in the warm sector is modest at best, but the strong dynamical forcing will squeeze out much of the moisture that is available to precipitate. Showers will be widespread along the front and radar is already showing the band of precipitation impinging on to the northern Washington Cascades at 2:00 PM this afternoon. There will also be a convective component with model soundings indicating skinny CAPE with equilibrium levels up to around 18-20 kft possible. This may not be sufficient to achieve the necessary charge separation for lightning; however, dynamics on the synoptic level are strong enough that it may be the difference to overcome these deficiencies in the thermal profile. Model soundings also are saturated throughout the vertical column. Thunderstorms notwithstanding, it's likely that this instability at low to mid levels in the atmosphere will produce pockets of moderate to potential heavy rainfall, especially if and where any thunderstorms do happen to develop. Small stream flooding is unlikely though with with the relatively paltry P-Wat values near 0.50 inches. Cold front passage across the Columbia Basin will occur later on in the evening and punch into the Panhandle between 1:00 AM and 3:00 AM tonight. The bulk of the showers will move off to the east with the front, as well as the best potential for convection. A low pressure circulation will track across the northern mountains behind the front. The center of the low will track from around Lake Chelan at 2:00 AM to the Okanogan Highlands and Northeast Mountains by around 5:00 AM overnight. Moisture looks to wrap in around this low pressure circulation and a healthy dose of cold air tracking in behind the front will result in snow levels crashing down to valley floors. Decreasing snow levels will result in snow accumulations for the Cascade passes, as well as Sherman Pass in the Okanogan Highlands. Road temperatures should start out above freezing, but those road temperatures do cool down to around freezing overnight. Snow intensities may be heavy enough for up to around 3 inches of snow for those mountain passes. The mountain valleys, such as Republic, Colville, Northport, Metaline Falls also will see the potential for snow behind the front; these lower elevation locations though are unlikely to snow stick to roadways -- maybe on grassy surfaces if snow comes down heavy enough. Winds will pick up with frontal passage tonight across the exposed areas of the basin. Winds will shift westerly with gusts to between 20-30 mph possible. Winds will then continue to be breezy and gusty into Friday. Gusts also look to tick up slightly as mixing increases with daylight hours. Showers will mainly form across the higher terrain of northeast Washington and the Idaho Panhandle on Friday. Westerly flow into the Central Panhandle Mountains with dropping snow levels may result in some light snow at Lookout Pass with little to no impacts expected. Temperatures will drop down into mid 30s for many areas. I think it will be tough to see freezing temperatures though with winds remaining breezy through the night. We could see near freezing temperatures along the Highway 2 corridor in the northern portions of the Columbia Basin and and more sheltered northern mountain valleys. Friday night into Saturday: A second low pressure system will spread light precipitation across the region Friday night into Saturday morning. The surface low will remain offshore and track up towards Vancouver Island. The Inland Northwest will see increasing isentropic ascent with a warm front. This will result in lighter intensity precipitation compared to our cold front passage that will push through tonight. The strongest isentropic ascent will occur across southeast Washington and into the southern to central portions of the Idaho Panhandle. Snow levels will increase to between 3,000 and 4,000 feet with light snow of up to about an inch for Stevens Pass, Washington Pass, Blewett Pass, and Lookout Pass. Otherwise, we are looking at 0.05 up to 0.20 inches of rainfall for the lowlands across the Palouse, into the Lewiston-Clarkston Valley, Camas Prairie, to St. Maries and the Silver Valley. Temperatures will warm up a bit Friday into Saturday with the warm air advection. High temperatures on Saturday will be in the mid 50s to mid 60s. /SVH Sunday through Thursday: After a quick break from the precipitation chances on Saturday, another round of moisture is anticipated to stream into the Inland Northwest on Sunday with more showers likely. As typical, lesser chances are expected across the Columbia Basin than in the mountains and elsewhere. We're looking at more mild conditions for Sunday, perhaps even near normal! For Monday and Tuesday, slight chances for precip are expected to generally be confined to the mountains. Daytime temps should be near normal again on Monday, before yet another burst of cooler temps shifts into the region. Unusually low snow levels and moist onshore flow may lead to periods of accumulating snow in the mountains Wednesday and Thursday, with rain showers expected across the more populated locales. /KD && .AVIATION... 06z TAFs: First rain band has moved to the east of the eastern WA/northern ID terminals this evening, but residual/brief MVFR/IFR is expected through 09z, especially as another band of showers approaches PUW/LWS between 06z and 08z. Anticipating VFR to dominate after 09z or so, as southwest winds increase to 10 to 20 kt with gusts to 30 kt, with precipitation quickly ending for all but COE, which may see some lingering showers through much of the day. VFR and breezy conditions should continue through Friday afternoon, before slowly diminishing after 00z Saturday. /CMS && .PRELIMINARY POINT TEMPS/POPS... Spokane 34 55 38 58 43 68 / 70 10 20 40 10 20 Coeur d'Alene 35 53 36 54 43 67 / 90 10 20 50 10 20 Pullman 34 53 40 59 45 69 / 80 0 40 60 10 20 Lewiston 40 61 46 66 50 76 / 70 10 40 60 10 30 Colville 36 56 35 58 40 65 / 80 30 10 20 10 40 Sandpoint 37 50 35 52 41 63 / 90 40 10 40 10 30 Kellogg 34 49 36 52 44 67 / 90 20 30 60 10 20 Moses Lake 36 61 42 67 46 73 / 10 0 10 10 0 10 Wenatchee 37 59 42 64 48 66 / 20 0 30 30 10 50 Omak 36 61 40 61 45 66 / 70 10 10 20 10 50 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$