Wetand News

Weather prediction technology has come a huge way over the past decades and yesterday's localized snow event is a great example of how far we have come. The most difficult Northwest forecasting problem is snow prediction. And there is no harder snow problem than a situation marginal for snow and where there are very localized weather effects. Yesterday (Tuesday) was such a difficult snow situation and the high-resolution models did very well. The Forecast As I described in this blog, cold air was in place and an approaching frontal system brought general very light snow, with heavier snow over North Seattle and Snohomish counties.  The models also predicted heavy snow in the Cascades, including its lower western slopes. Below is the high-resolution WRF model forecast of snowfall through 4 AM today (Wednesday) made 4 PM Monday. Light snow from downtown through Tacoma (about 3/4 inch), with heavier snowfall (peaking at 5-7 inches) from Lynwood to Everett.  Heavy snow in the mountains

As expected, some light snow came in this morning....a dusting for most and as much as .5-1 inches for favored locations (see below).  The roads were warm enough and the air temperatures marginal enough that the snow rapidly melted on most roadway surfaces.  Ironically, the snow is associated with warming aloft. The weather radar this morning around 11 AM  showed very light precipitation over the region (blue colors), with heavier precipitation offshore). Warm air is streaming in aloft as shown by temperature sensors on aircraft taking off and leaving Seattle.  And surface temperatures are being warmed by the (weak) sun.   Don't expect any low-level snow accumulation during the day. This warm air aloft is leading a surface warm front, which will get to the coast around 6 PM, with a cold front a few hours behind. So there will be a few light flakes in the air today, but nothing that will be substantial. As precipitation increases on the coast later this afternoon, the higher intensi

I will have an update at noon....  Some light snow showers are over western WA right now.... __________________________ The most powerful high-resolution meteorological tools are now available for the snow event tomorrow night.   Parts of the lowlands will get snow--up to several inches in places. But it won't last. And the situation tomorrow is not a good one for accumulating lowland snow in our region. The Golden Rule of Snow Snowfall is NOT snow depth.    This is going to be very important for the upcoming event.   And this subtlety is often missing from the analyses of some amateur weather websites. A key issue is the temperature of the ground and particularly roadway surfaces.  Below are this morning's values from the city of Seattle's Snowwatch website, with the temperatures in the boxes showing the roadway surface temperature.   Most are in the upper 30s to near 40F. The air above us right now has a freezing level  of about 1300 ft (see below from SnowWatch below fo

  We are much closer to the potential events this week:  close enough in time to have the higher-resolution models available. As I will explain, the upcoming situation has the potential for lowland snow but is not optimal.  Heavy snow in the mountains is a sure thing. The SnowTrick Let me remind you, i t is hard to get lowland snow west of Cascade crest.  Moist air coming off the Pacific is too warm for lowland snow, and it is difficult for cold air in the continental region to reach us because of the blocking effects of the Rockies and Cascades. So to get snow we need something exotic to occur.   The most popular trick is to get a low center off the southern Washington coast and cold high pressure over the BC interior. The difference in pressure causes cold air to be drawn southwestward through the Fraser River Valley or across low terrain into NW Washington, which then spreads southward.  The low on the Washington coast and an accompanying upper-level trough of low-pressure results i

We enjoyed an unusually dry, temperate mid-November, and Thanksgiving Day was a pleasure, but now the brass knuckles of a La Nina winter are about to be revealed. Cold air and a hard freeze will hit the entire state next week, with massive mountain snowfalls that will delight the ski community.   All of us should take steps to deal with the upcoming cold, from unscrewing outdoor hoses, and protecting pets, to ensuring that the region's large homeless population is brought inside or protected. The upcoming situation is a classic for a La Nina winter, in which the central and eastern tropical Pacific is colder than normal.   During such winters, we typically observed a large ridge of high pressure developing over the northeast Pacific, with cool, northerly (from the north) flow on its eastern side (see the forecast upper-level map for Saturday at 10 PM as an illustration). If there are disturbances in that northerly flow, moving south out of Alaska, we can get bouts of mountain snow,

It seems like there is another strident climate "tipping point" headline every other day.   Threats of irreversible catastrophic climate change just around the corner. The truth is that such claims by some media outlets and climate activists are contrary to the best science. An attempt to sow worry and panic, with the motivation to motivate people to "do the right thing."  And it is both unethical and counterproductive. What is a climate tipping point?   According to the  Merriam-Webster dictionary, a tipping point is defined as the critical point in a situation, process, or system beyond which a significant and often unstoppable effect or change takes place And a climate tipping point can be defined as   a critical threshold that, when crossed, leads to large and often irreversible changes in the climate system. Specifically, the idea is that increasing greenhouse gases (like CO2) will result in warming that will produce large, irreversible changes in the climat

Climatologically, the Northwest is now in the wettest time of the year.   But that is no guarantee of cloudy, dripping skies. Today will represent the 13th day without measurable rain at Seattle Tacoma Airport (measurable rain is 0.01 inches of rain or more).      Another sunny day in western Washington and Oregon And in doing so we tied the record string of 13 dry days in November at SEA that occurred in 2000. Tomorrow will be dry as well , and thus we will break the November record for consecutive dry days..   But to deflate your excitement a bit, this only ties the record that crosses over into December (November 20-December 3). As noted, in earlier blogs, the origin of this dry bounty is a ridge of high pressure over the West Coast (see below), ironically resulting in headlines of cold/wet weather in the western U.S. Upper level (500 hPa pressure) at 10 PM Saturday night.  Red indicates ridging (high pressure) and green/blue indicates troughing (low pressure). A front will break th