*I have been experiencing a ton of connection difficulties over the last few days. This post was for yesterday’s weather.*
In Seattle this morning, the weather was stereotypically Pacific Northwest. It was overcast, cool and mostly still. However, this afternoon, the skies have cleared considerably. We now have scattered L1 cumulus clouds and H1 cirrus clouds, but only covering about half of the sky.
The National Weather Service (NWS) in Seattle, WA, forecasts a mostly sunny day today, with a high temperature of 73 F and light west winds. This evening will have a 20% chance of rain, increasing cloudiness and a low temperature of 56 F. North-northeast winds of 5-11 mph will shift to the east after midnight.
The visible satellite imagery shows that much of the state has cleared up this afternoon.
The enhanced infrared satellite imagery shows no thick clouds. This image has been excluded from today’s post.
The water vapor satellite imagery shows that there is still plenty of deep moisture over the region. There is a compact low off the coast of British Columbia that is helping to draw moisture through the state.
The 12Z upper air sounding from UIL shows a damp, nearly saturated boundary layer, followed by much drier midlevels. There was 1.05 inches of precipitable water present in the column this morning, and no Convective Available Potential Energy (CAPE). There was a slight but deep thermal inversion through the dry layers, and the 0-3 km average lapse rate was only 3.3 C/km.
The deep-layer shear was 28 kts (speed shear), and the low-level shear was 3 kts (directional shear).
The surface observations (from the SPC Mesoscale Analysis Map) show that east of Seattle, clouds and higher dewpoints were recorded. West of Seattle, the skies clear.
The surface pressure map shows high pressure over the water, and low pressure over the land, setting up a sea breeze. This could be expected for a typical warm summer day. The RAP shows that this will not change much over the next six hours.
Synoptically speaking, the 300 mb NAM chart (from Unisys) shows that a jetstreak will nose its way into the Seattle area by tomorrow. This will likely increase the chances of clouds and rain tomorrow as compared to today.
The 500 mb NAM chart shows no significant vorticity advection over the state throughout the rest of the afternoon. Tomorrow, there may be some Positive Vorticity Advection (PVA), just ahead of that jetstreak.
The 700 mb NAM chart shows no rapidly-rising air over the state today. This chart has been excluded from today’s post.
The 850 mb NAM chart shows some Cold Air Advection (CAA) pushing its way into the state this afternoon ahead of the jetstreak. Temperatures will cool, causing some of the moisture to condense out and perhaps fall as rain.
Overall, I expect that the clouds and chances of precipitation will increase overnight. However, I think the remainder of the daylight hours will remain pleasant and mostly sunny today.
Thank you for reading my forecast.
The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from TwisterData.com.
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC