Lowland Snow Potential tonight (Friday night) through Sunday
National Weather Service, Seattle WA
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A cold air mass remains in place over western Washington, cold enough so that any precipitation will fall as snow through Sunday morning. The slowly warming air mass will eventually moderate enough so that any precipitation will transition to rain Sunday afternoon or evening.
There are potentially three weak weather systems that are expected affect western Washington through Monday morning. It is very likely that the first weak system crossing Oregon will brush the south part of western Washington with a little snow tonight into Saturday morning.
A second weak system could possibly bring a little light snow to much of western Washington late Saturday night through Sunday morning.
A third weak warm front is expected to bring warmer temperatures and light rain to the area Sunday afternoon or evening through Monday morning. There is a small chance that there could be some spotty snow early on in the transition to warm conditions with this front.
No weather watches, warnings, or statements are in effect at this time.
System #1, Tonight-Saturday morning.
Confidence is high that the weak system crossing Oregon will brush the southwest interior of western Washington with a little light snow late this evening through early Saturday morning. Up to an inch of snow is expected over Lewis County, It is possible that neighboring counties – Thurston and Pierce – could see some light snow flurries with no accumulation. Areas to the north should be dry.
System #2. Saturday night-Sunday morning.
Confidence is low that the next weak system will cross western Washington late Saturday night through Sunday morning. Confidence is low because some computer models show this system and others do not. It is possible that nothing will happen and that it will be completely dry, or that a little light snow (with accumulations less than an inch) could fall over much of the western Washington interior.
System #3, Sunday night-Monday morning.
Confidence is moderate that a weak warm front will bring light rain to much of the area. For now, all the main computer models agree on the strength (weak), track and timing of this front, However, given the lead time associated with this system, the model guidance may still continue to evolve as we get closer to the event. Confidence is moderate that the lowland precipitation will be rain, however there continues to be some differences between models regarding how quickly temperatures will warm up enough to prevent snow. The warm-up could take longer than expected and the south to north transition means locations in the northwest interior (like Bellingham) could be last to transition to rain. Furthermore, the extended cold snap has put road surface temperatures near or below freezing so this could help keep some roads slippery even with light rain falling.
The main impact from these weather systems through this weekend will be potentially slippery roads and thus more locally hazardous travel conditions.
This is summary of the confidence associated with various aspects of the weather affecting the area over the next few days as we transition back to warmer and wetter weather.
Confidence is high that there will be a little light snow over the southwest interior late tonight and Saturday morning, and that snow accumulations will be an inch or less.
The most uncertainty lies with the possible second system Saturday night to Sunday morning. This weak system may not materialize, so there could be zero precipitation. There could be some light snow with spotty one inch accumulations over much of the area, and there could be some messy slop-over precipitation into Sunday afternoon.
Sunday is still a couple of days and several computer model runs away. This has been a weak low confidence pattern the past few days so it is highly likely that there will be changes to the forecast.
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National Weather Service, Seattle WA