10 Day Weather Outlook

Now just 10 days away from the nuptials and we continue to get a better look at the September 3rd forecast. We continue to get data from only one model, the GFS model. The GFS offers a look much further into the future than it's main counterpart NAM. However, GFS sacrifices a higher resolution in favor of time. The NAM only goes out roughly 4 days into the future but has a much higher resolution so broken down in more detail. Once the two models overlap, it is a great way to compare biases. So we continue to look at the GFS data. Here is what we are looking at 10 days out!

Let's peak at the numerical data first:

FCST Hour	Valid Time	Max Temp	Min Temp	Td	10m Wind mph	850mb Wind mph	Total Precip(")	Conv. Precip(")	500-1000 THKNS	500mb Height	850mb Temp °C	500mb Temp °C	MSLP mb	Total Cloud Cover
192	Sat 09/01 06Z	61 °	58 °	58 °	N 18	N 7	0.00	0.00	563	578	12 °	-11 °	1016	0 %
204	Sat 09/01 18Z	60 °	56 °	57 °	N 13	NNE 13	0.00	0.00	562	577	12 °	-11 °	1017	5 %
216	Sun 09/02 06Z	61 °	57 °	55 °	N 18	NNE 13	0.00	0.00	563	577	13 °	-12 °	1016	35 %
228	Sun 09/02 18Z	60 °	56 °	46 °	N 11	N 11	0.01	0.00	561	576	12 °	-13 °	1016	46 %
240	Mon 09/03 06Z	61 °	56 °	34 °	NNW 13	N 7	0.02	0.00	561	575	12 °	-13 °	1016	74 %
252	Mon 09/03 18Z	59 °	56 °	32 °	NW 7	NNW 4	0.02	0.00	559	574	11 °	-14 °	1017	76 %
264	Tue 09/04 06Z	60 °	57 °	48 °	NNW 13	NNW 9	0.02	0.00	557	573	10 °	-15 °	1018	81 %

Highlighted are the times for September 3rd. Our mid-level air temperatures are right around 10 degrees Celsius. This should translate to a surface temperature in the mid-70s. The big change from the last post shows that we have a precipitation chance through the day, calling for 0.02". September 3rd actually averages 0.03", so rain isn't unusual. What you can't see is that with each model run (GFS runs 4 times per day), the precipitation forecast changes. The waffling of the runs tells me that the GFS is trying to pick up something on the maps, so lets take a look.

The 500mb map offers a pretty good hint as to why we are seeing some precipitation in the forecast. Notice the large bump over the middle part of the country. A nice ridge of high pressure dominates a good chunk of the U.S. and that causes a kink in the weather pattern on both coasts. This setup is known as the "Omega Block" named after the Greek letter Omega. Generally, fair conditions dominate over the central U.S. and both coasts would see some potentially unsettled weather. This would explain the cooler than average temperatures as well as the hint of precipitation that numerical data has been showing at times. Coincidentally and totally unrelated, a tropical storm/hurricane is the big feature on the east coast. 

So, the forecast 10 days out goes something like this: I'd expect partly to mostly cloudy conditions with a slight chance for a shower. If I saw this setup on September 2nd, I would not put a rain icon on the forecast, but it is definitely worth a mention. With 10 days to go and the flip-flopping of the model output, there are still no concrete details. Stay tuned, only three more days until September 3rd hits the seven-day forecast!

No End In Sight

The Pacific Northwest continues to be mired in a Spring-like run of weather in the middle of Summer. Today marks the first day that average temperatures should reach 80 degrees, yet we are currently in a stretch of 8 consecutive days below 80 degrees. And then comes even worse news: there isn't an end on the horizon. Let's see why:


Above is our trusty 500mb chart. This is a set up known as the "Omega Block" because the graph resembles the Greek letter Omega. It is caused by a large ridge of high pressure over the Central U.S. and troughs on either side of the ridge. Under a ridge this big, hot air is sinking to the ground, resulting in scorching temperatures that have brought several days of triple digits. All we are stuck with is cool, gray conditions and some rain this week. That huge ridge blocks systems that typically track north into Canada but are now forced down into our backyard. This Omega Block has been set up for the better part of a week now and things aren't changing a whole lot.
This map is an anomaly chart that shows the average 500 mb lines from multiple model runs with different starting parameters. It basically gives us a an idea of where ridges and troughs will be 8-14 days in the future. Notice the big ridge over the Central U.S. has subsided a bit but the general trough in the NW/ridge in the East pattern still exists. That's not a welcoming sign for a return to Summer!
Here is a temperature probability map that correlates with the 500mb map 8-14 days out. I think this is pretty self-explanatory. Blues mean below average, red above. Yadda yadda yadda. Summer appears to be on hold until further notice. Maybe it's time to take a vacation...