518 FXUS66 KOTX 022152 AFDOTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SPOKANE WA 252 PM PDT Sun Jun 2 2013 .SYNOPSIS... An area of low pressure over the region will promote widely scattered showers and thunderstorms across the eastern third of Washington and the majority of the Idaho Panhandle this evening. On Monday, the precipitation threat will migrate north and east mainly into the Idaho Panhandle. High pressure strengthen over the region on Tuesday and persist through much of the week delivering mostly dry conditions and above normal temperatures. && .DISCUSSION... Tonight...Closed low over the Central Panhandle Mountains this afternoon will move east into western Montana this evening...pulling away from the Inland Northwest tonight. Afternoon heating combined with the cold pool aloft associated with this system will continue to produce showers and isolated thunderstorms through early this evening mainly east of a line from Republic to Ritzville. A lack of sheer will keep these storms of the pulse type that last only 10-15 minutes with brief heavy rain and small hail the main threats. Drier air over north central Washington with dew points in the mid 30s will result in only isolated showers mainly over the higher terrain. As the low pulls east the main threat for precipitation in the late evening and overnight will shift east of the area. However a few showers may linger over North Idaho and southeast Washington. With the boundary layer moist over northeast Washington from showers today and some clearing expected overnight...patchy valley fog may late tonight mainly near rivers and lakes. JW .Monday through Wednesday...Model guidance is in good agreement that today's deep and unstable 500 mb low will migrate into central Montana by early Monday morning and into the eastern half of the state by afternoon. Meanwhile a much weaker upper level low currently over NW is expected to weaken even farther as it moves into SE BC by afternoon. The instability associated with the approach of this low will pale in comparison to today, however there will likely be just enough extending from the NE corner of WA toward the central ID Panhandle to trigger another round of showers...and possibly a thunderstorm. CAPE values suggest the best threat of thunderstorms will be confined to a small portion of NE Washington and most of the Idaho Panhandle north of Shoshone County. This secondary upper level disturbance will weaken even further Monday evening and the convection should wind down rapidly as shortwave ridge begins to build overhead. The ridge will then remain over the region for both Tuesday and Wednesday. This should dry out the entire forecast area and bring a gradual warming trend. 850 mb temps should warm to 13-15c on Tuesday and into the 16-18z range for Wednesday. This equates to some of the warmest high temperatures in a few weeks with widespread valley readings in the 80s...with lower 90s possible over the lowest portions of the Columbia Basin and L-C Valley. fx Wednesday night through Monday: Models remain in decent agreement that a flat jet stream (aka zonal flow) will be common during the period. The main forecast challenges will be determining exactly where the jet axis will setup. A few runs of the GFS and older ECMWF solutions carved the polar jet into Washington (wetter) starting around Thursday and lingering through Saturday while the remaining model consensus generally keep the jet north across southern BC (drier). This will have rather big ramifications on precipitation chances because each guidance agrees the jet will steer a rich fetch of subtropical moisture toward the Pac NW but whether the deep moisture remains fixed into the region (ECMWF) or sags south (GFS) could mean the difference between precipitation or not. Given the better agreement with the ECMWF solutions and stronger westerly flow in this regime...we have kept much of the Basin and lowlands dry at this time but did introduce some mountain PoPs across the north. This forecast does not carry a lot of confidence due to the flip-flopping in model guidance and could change within the upcoming days. Temperatures will generally be above seasonal normals but could be on the warm side if the jet stream was to carve deeper into Washington per GFS. /sb && .AVIATION... 18Z TAFS: An upper level trough over the area will promote numerous showers and isolated thunderstorms mainly east of KMWH. A thunderstorm can not be ruled out at the KGEG/KSFF/KCOE/KPUW/KLWS TAF sites but with isolated coverage will go with a CB cloud group and monitor for possible updates if any storms approach the TAF sites. The main threat from thunderstorms will be brief heavy rain and small hail. Ceiling with this activity are expected to remain VFR...but brief MVFR CIGS is possible through 20z due to persistent rainfall this morning around KGEG/KSFF/KPUW that has moistened the boundary layer. As the low pulls away this evening and daytime heating is lost...showers/thunderstorms will begin to wind down. JW && .PRELIMINARY POINT TEMPS/POPS... Spokane 47 71 50 77 54 81 / 50 20 10 0 0 0 Coeur d'Alene 45 70 46 76 48 81 / 70 20 20 0 0 0 Pullman 44 70 45 76 48 81 / 60 20 10 0 0 0 Lewiston 50 76 51 83 55 89 / 50 10 10 0 0 0 Colville 45 77 47 82 49 86 / 50 20 20 10 0 0 Sandpoint 43 69 43 74 45 80 / 70 40 30 10 0 0 Kellogg 45 66 47 73 50 79 / 70 50 40 10 0 0 Moses Lake 48 81 50 85 54 89 / 10 0 0 0 0 0 Wenatchee 52 80 54 84 58 86 / 10 0 0 0 0 0 Omak 46 77 48 82 51 85 / 20 10 10 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$