000 FXUS66 KSEW 191111 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 311 AM PST Tue Jan 19 2021 .SYNOPSIS...High pressure aloft builds over the region and remains in place much of the first half of the week, though a weak front will clip the area late Tuesday. Another disturbance arrives Thursday. A stronger front likely arrives this weekend with cooler temperatures and lower snow levels. && .SHORT TERM /TODAY THROUGH THURSDAY/...High pressure and offshore flow will lead to dry conditions across western WA today. Expect patchy low clouds and fog in the interior this morning with skies becoming partly sunny this afternoon. Highs will be close to normal in the mid to upper 40s. The ridge will flatten over WA tonight while a weak trough cuts through B.C. This trough will clip western WA for a chance of light showers, mainly in the north interior and north Cascades. Weak high pressure then rebuilds on Wednesday for another dry day. We`ll see another round of showers on Thursday while a cool upper low tracks south down the coast. Precipitations amounts look light with just a few hundredths of an inch over the lowlands. However, snow levels will be low, around 1500-2000 ft, and could see a light rain/snow mix in areas near the Cascades (mainly Thursday night). 33 .LONG TERM /FRIDAY THROUGH MONDAY/...Cool (but dry) northerly flow will prevail Friday and Saturday with temperatures trending below normal - highs in the lower to mid 40s and lows in the 20s to lower 30s. The following system on Saturday night or Sunday shows some potential for lowland snow due to low snow levels (around 500-1000ft). Around half of the ECMWF and GFS ensemble members show snow but amounts look spotty and light. NBM at Sea-Tac has a 60% chance of snow with accumulations less than 1". The percentages are a little higher at Bellingham where snow levels will be lower due to N/NE flow. The coast will likely just see a rain/snow mix with no accumulations. So we`ll see how this continues to unfold as we get closer to the event. As always, snow amounts will depend on timing of snow levels, temperatures and moisture. The threat for more lowland snow continues into early next week as snow levels will remain low, with more systems headed our way. 33 && .AVIATION...West northwesterly flow aloft with front dissipating just to the north of the area tonight. Light flow in the lower levels. Mid and high level clouds over the area today. Areas of ceilings below 500 feet and visibility below a mile, tops 500-1000 feet, until 20z. KSEA...Ceilings below 200 feet and visibility below 1/2 of a mile until 18z. Mid and high level clouds after 18z. Light northerly winds becoming southerly by 20z. Felton && .MARINE...High pressure will remain over the waters through Wednesday. A front will dissipate just north of the area tonight. A weak system will arrive Thursday with high pressure rebuilding again Friday. Another system will approach the waters late Saturday. Outside of the possibility of some small craft northerly winds over the Northern Inland waters Friday no advisories are forecast through the end of the week. Felton && .HYDROLOGY...No river flooding is expected through the next seven days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$ www.weather.gov/seattle
NWS SEW Office Area Forecast Discussion
