784 FXUS66 KOTX 250912 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 212 AM PDT Tue Jun 25 2019 .SYNOPSIS... Cool and showery weather is expected this week with the arrival of a slow moving low pressure system. Wednesday has the potential to be our most active day with a good chance for showers and thunderstorms region wide. Some thunderstorms may produce hail and gusty winds over the Idaho Panhandle and southeast Washington Wednesday afternoon. Scattered showers and thunderstorms are expected to linger Thursday into Friday before a warming and drying trend arrives over the weekend. && .DISCUSSION... ...WIDESPREAD THUNDERSTORMS WEDNESDAY/WEDNESDAY NIGHT. ISOLATED STRONG STORMS POSSIBLE OVER SOUTHEAST WASHINGTON AND IDAHO PANHANDLE... Today through Wednesday: A large closed low off Vancouver Island will drop southeast and be positioned just off the central Oregon coast Wednesday afternoon. For today there is a weak mid level wave over NW Oregon that will track up along the East Slopes of the Washington Cascades this afternoon. This will help trigger scattered showers with a chance of a few thunderstorms as well. The other area of concern is the Blue Mountains, Camas Prairie, and Lewiston area where models continue to show convection firing over NE Oregon this afternoon with uncapped CAPE of 600-1000 J/KG. This combined with 0-6km shear values near 50-60 kts may result in a strong thunderstorm. The best threat of thunderstorms will be early evening for the Lewiston area. This activity should weaken after sunset but another mid level wave ahead of the low will track into Central and Eastern WA overnight into Wednesday morning possibly producing a few showers. As this wave exits the focus of afternoon convection should again be in the Cascades, SE Washington, and NE Oregon as a strong short wave comes moves north ahead of the low. Models show even greater instability over the eastern third of Washington and north Idaho with CAPE as high as 1000-1500 J/KG and 0-6km shear around 50 kts. Strong thunderstorm outflow wind gusts to 50 mph and isolated large hail are not of the question. Thunderstorms should expand north into the Spokane area, Columbia Basin, NE Washington, and the N Idaho Panhandle Wednesday evening with more details in discussion below. JW Wednesday night through Friday...Wednesday evening is increasingly looking like a very active thunderstorm period for the forecast area. By this time the region will be under deep moist and diffluent southerly flow just ahead of the incoming upper low. This is a recognized climatological pattern for thunderstorms during this time of year with pretty much the entire forecast area subject to a thunderstorm or two with all of the latest deterministic model runs suggesting a short wave transiting this southerly flow and through the forecast area from southwest to northeast between 5 pm and 10 pm Wednesday evening. Instability parameters and shear profiles suggest the area south of a line from about Walla Walla to Kellogg will be most favorable for strong organized thunderstorms with heavy rain...hail and gusty winds...with the Columbia Basin subject to gusty outflow winds followed by or concurrent with a line of brief thunderstorms followed by a period of showers with a few isolated embedded thunderstorms as the night wears on. The Cascades and mountains north of the basin will also be subject to scattered early evening pulse type storms capable of brief heavy rain and small hail probably evolving into periods of rain showers overnight. The incoming upper low will be slow to transit the region with the Idaho panhandle in particular remaining under or near a mid level frontal boundary on the eastern flank of this low through Friday and subject to periods of thunderstorms again on Thursday afternoon/evening and Friday afternoon/evening. The remainder of the forecast area closer to the center of the low will experience more of a hit-and-miss spring time cool showery regime with a few weak pulse type thunderstorms salted among the showers each afternoon...concentrated over the northern mountains and Cascades. By Saturday model agreement begins to deteriorate with synoptic details...however a general weakening of the upper low is expected into more of a baggy trough over the northwestern US through the weekend. This would suggest a continuing chance of showers and maybe a stray thunderstorms during the afternoon and evening hours over the mountains ringing the basin with largely dry conditions albeit with plenty of flat cumulus over the basin. Also this will allow a slow recovery of temperatures back toward normal through the weekend and into next week after an anomalously cool period as the upper low sits over the region for the next few days. /Fugazzi && .AVIATION... 06Z TAFS: Dry weather and VFR conditions are expected at all TAF sites through 00z Wednesday. Spotty showers, with an infrequent thunderstorm or two away from TAF sites and close to the British Columbia Border will linger overnight there and again after 21Z tomorrow in the same general locations away from TAF sites. However after 04Z Wednesday thunderstorms may impact KLWS and be within the vicinity of KPUW at the extreme southern edge. /Pelatti && .PRELIMINARY POINT TEMPS/POPS... Spokane 75 50 77 51 70 48 / 0 20 20 60 40 10 Coeur d'Alene 75 49 78 51 69 47 / 0 20 20 60 40 20 Pullman 73 48 74 48 67 44 / 0 20 40 60 30 30 Lewiston 80 56 81 56 73 52 / 10 30 60 60 40 40 Colville 82 40 83 43 75 39 / 10 10 20 60 60 30 Sandpoint 74 48 76 51 67 46 / 10 10 30 70 60 40 Kellogg 73 52 76 53 67 49 / 10 20 30 60 50 40 Moses Lake 82 51 79 50 75 48 / 0 20 20 50 30 10 Wenatchee 79 55 77 55 71 52 / 10 10 60 50 40 10 Omak 79 53 78 53 72 50 / 10 10 40 60 70 40 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$