216 FXUS66 KSEW 081642 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 842 AM PST Sun Dec 8 2019 .UPDATE...An upper level ridge will build into the region today and persist into early Tuesday. Radar indicates a few light showers across portions of the Cascades this morning and satellite shows plenty of low cloud cover across Western Washington. With ample low level moisture still in place across the region, expect clearing to be slow and for most areas to remain mostly cloudy throughout the day-with the exception of some clearing in the mountains. Afternoon highs will be in the upper 40s to near 50. The previous discussion below applies, with updates made to the marine and aviation sections. 14 && .PREV DISCUSSION... /issued 330 AM PST Sun Dec 8 2019/ .SYNOPSIS...An upper ridge will build offshore today for dry weather through early Tuesday with the best chances for sunshine being on Monday. The next system should slide through later Tuesday with unsettled conditions persisting thereafter. .SHORT TERM /TODAY THROUGH TUESDAY/...Current satellite and radar imagery show that system responsible for precip yesterday is out of the area with W WA now falling under the jurisdiction of an incoming upper level ridge still out over the offshore waters. Current obs show sufficient low level moisture is in place to keep low clouds over much of the area with areas of fog/reduced visibilities in some locations. This upper level ridge will keep conditions dry today...but any sort of clearing is going to be slow work at best. Given the widespread low clouds/fog this morning...expecting cloudiness to linger most of the day...although the mountains may see some clearing as the day progresses. This ridge will be the main weather factor throughout the short term as dry conditions persist into Monday and early Tuesday. Clouds should give way to some breaks of sunshine during the day Monday...mostly for locations east of Puget Sound. The western half of the CWA will start to see clouds associated with the next weather system start to roll in which may limit the amount of sun they get. The next system makes its way to the coast by mid to late Tuesday morning but really doesn`t make its way inland until Tuesday afternoon. Both ECMWF and GFS do not show this front being of any particular note and the ensemble mean leans toward that conclusion as well showing pretty minimal QPF values associated with its passage. Neither model has the system holding together very well and has a weak shortwave ridge in place over W WA by Tuesday night. Lowland high temps throughout the short term will remain pretty static...generally in the upper 40s. Overnight lows will not see very much variation either...sitting in the upper 30s to around 40. .LONG TERM /WEDNESDAY THROUGH SATURDAY/...Models agree on a shortwave ridge for early Wednesday...although the ECMWF is more progressive on kicking it out and getting the next system onto the coast by late Wednesday morning...inland by Wednesday evening. The GFS is slower with the system hitting the coast in the afternoon and pushing inland overnight. Most of the ensemble members fall somewhere in between causing any forecast solution to get lost in the spaghetti. Beyond this initial disagreement...models come back in line regarding the active pattern for the remainder of the forecast period as a broad upper level trough sets up over the Pac NW. This will shuttle in a series of systems and while both deterministic and ensemble models show some dry breaks...the overall pattern will be wet. Temps in the long term do not waver much from those in the short term with the lowlands generally seeing high temps in the upper 40s to around 50 while overnight lows will sit generally in the upper 30s to lower 40s. SMR && .AVIATION...North northwesterly flow aloft into Monday with upper level ridge offshore. Light flow in the lower levels with flat surface gradients. The air is moist and cloudy across most of Western Washington but some of the higher mountains are sticking up out of the clouds and there are some breaks in the clouds so that bodes well for some improvement today--cigs will set up and lower again tonight however. There is likely to be areas of fog and rather low cigs Monday morning. KSEA...Improvement into the afternoon is likely--but then low stratus will set up tonight and persist through midday Monday. Light and variable winds. && .MARINE...Weak low pressure today will give way to high pressure by Monday with light winds. A front will approach the area on Tuesday and weaken over the area Tuesday night. Another stronger front should reach the area Wednesday night and push inland on Thursday. && .HYDROLOGY...River flooding is unlikely for the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$ www.weather.gov/seattle
NWS SEW Office Area Forecast Discussion
