Scientific Forecaster Discussion
000 FXUS66 KPDT 212040 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 1240 PM PST Thu Nov 21 2019 .SHORT TERM...Tonight through Sunday night...The upper level ridge will remain over the region through Saturday but begin flattening as a shortwave passes through Canada overnight and Friday. There will be some fog and stratus development mainly around the Columbia Basin overnight, some of which will persist through Friday and into Saturday. The ridge will eventually flatten enough that by late Saturday night and Sunday a cold front will sweep across the region under a northwest flow. This will favor the Cascades and Blue mountains for precipitation but not so much along the east slopes of the Cascades or Columbia Basin. Snow levels will lower late Sunday and overnight getting down to 2000 to 3000 feet. As mentioned, the northwest flow will favor the Cascades and Blue Mountains with precipitation and with lowering snow levels there will be some snow accumulations to deal with Sunday night for travelers over the mountains. .LONG TERM...Monday through Thanksgiving...Initial shortwave/cold front will have shifted south and east of the CWA by Monday, but expect mountain unsloped snow showers to continue through Monday night as the region falls under moist northwest flow aloft. Locally breezy winds behind the front on Monday will diminish Monday night. A couple of weak waves passing through the flow could help to enhance precip, but only expect a slight chance in the basin. Snow levels will start off around 2-3kft. More uncertainty exists with the second stronger system as model solutions differ. Potent trough expected to dig south along the BC coast, moving into the PacNW on Tuesday. Upper low/long wave trough then expected to develop somewhere over the western US. Initial front expected to pass through Tue/Tue night and bring a chance of precip. Snow levels start off low (1500-2500ft) with cold air in place in wake of initial system. Models differ quite a bit towards Wednesday in placement and strength of upper low. GFS has been more consistent and more in line with the ensembles and has been dropping the low further south into NorCal. That would mean heavier precip for southern and far eastern Oregon. If surface and upper low track further north, then expect better threat of impactful precip amounts over most of our area. This could bring moderate to heavy snow for the mountains with the potential of snow for lower elevations, possibly down to around 500-1000ft. Trended towards drier GFS solution but still bring a decent shot of impactful snow for the central and northeast mountains with a chance of snow elsewhere. The brunt of the system should push east by Thanksgiving with drier conditions expected ahead of another potential potent system towards the weekend. Either way, temps expected to continue their downward trend as cold Canadian air filters into the Inland Northwest. Highs Monday in the mid 30s to mid 40s, and only reaching he mid 20s to mid 30s on Thanksgiving. && .AVIATION...00Z TAFs...Lingering strato-cu over central/northeast Oregon will dissipate this afternoon. Otherwise expect VFR conditions through this evening with a few passing high clouds and light winds. Late tonight into tomorrow morning expect haze and possible fog to develop, especially near ALW and PSC, which could lead to MVFR or lower conditions. && .PRELIMINARY POINT TEMPS/POPS... PDT 27 44 30 51 / 0 0 0 0 ALW 28 44 32 49 / 0 0 0 0 PSC 26 43 29 46 / 0 0 0 0 YKM 23 46 27 47 / 0 0 0 0 HRI 26 44 28 48 / 0 0 0 0 ELN 22 47 29 47 / 0 0 0 0 RDM 19 53 24 56 / 0 0 0 0 LGD 26 48 29 49 / 0 0 0 0 GCD 27 50 29 53 / 0 0 0 0 DLS 29 48 32 49 / 0 0 0 0 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None.