Everett Astro SP
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Everett Astro SP clear sky chart from 2005-11-06 to 2024-11-04.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	23% 9% 3 7% 4 4 4 3 5% 6% 32%	105666
	Night	27% 10% 3 7% 4 4 4 3 4 5% 30%	101919
Transparency	Day	54% 6% 13% 17% 8% 1	105423
	Night	58% 6% 12% 16% 7% 1	101808
Seeing	Day	28% 8% 20% 25% 14% 3	15073
	Night	35% 6% 14% 26% 17% 2	23416

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	43% 17% 3 7% 4 4 3 2 2 3 11%	2252
	11th to 20th	Day	27% 12% 4 8% 5% 4 3 3 4 6% 24%	2516
	21st to end	Day	43% 14% 4 8% 4 3 3 2 3 4 12%	2830
February	1st to 10th	Day	36% 12% 4 7% 5% 4 4 3 4 5% 16%	1710
	11th to 20th	Day	31% 14% 4 8% 5% 4 3 3 4 4 21%	1665
	21st to end	Day	32% 14% 4 8% 5% 4 4 2 3 4 21%	1484
March	1st to 10th	Day	22% 14% 3 9% 6% 5% 4 4 5% 6% 20%	3188
	11th to 20th	Day	22% 11% 3 6% 5% 4 4 3 3 5% 35%	3490
	21st to end	Day	29% 12% 3 10% 6% 5% 4 4 5% 5% 16%	3972
April	1st to 10th	Day	27% 13% 4 9% 5% 5% 5% 4 5% 6% 17%	2280
	11th to 20th	Day	27% 11% 3 9% 5% 5% 5% 3 4 5% 23%	2267
	21st to end	Day	25% 11% 3 10% 6% 5% 5% 4 6% 5% 20%	2534
May	1st to 10th	Day	20% 8% 2 6% 4 4 4 3 5% 5% 37%	4420
	11th to 20th	Day	18% 7% 2 6% 4 4 4 4 7% 9% 34%	4377
	21st to end	Day	32% 11% 3 9% 5% 4 4 3 4 5% 20%	4813
June	1st to 10th	Day	26% 8% 3 7% 5% 5% 4 3 5% 7% 27%	2708
	11th to 20th	Day	27% 10% 3 8% 6% 5% 5% 4 5% 6% 22%	2850
	21st to end	Day	16% 7% 3 8% 4 4 4 4 6% 7% 37%	2850
July	1st to 10th	Day	9% 4 2 4 3 2 3 2 4 5% 62%	4740
	11th to 20th	Day	7% 3 1 3 3 2 3 2 3 4 68%	4530
	21st to end	Day	12% 4 2 5% 3 3 3 3 4 5% 55%	4790
August	1st to 10th	Day	7% 3 1 3 3 3 4 3 5% 8% 61%	4376
	11th to 20th	Day	10% 7% 3 8% 5% 5% 4 4 6% 8% 40%	4026
	21st to end	Day	16% 8% 3 8% 4 4 4 4 5% 6% 40%	4318
September	1st to 10th	Day	13% 5% 3 7% 4 4 3 3 4 6% 48%	2280
	11th to 20th	Day	16% 8% 3 8% 4 5% 4 3 5% 6% 38%	2280
	21st to end	Day	21% 7% 2 6% 5% 4 4 4 4 6% 38%	2015
October	1st to 10th	Day	19% 7% 2 6% 4 4 5% 4 6% 10% 33%	3180
	11th to 20th	Day	37% 9% 2 6% 4 3 3 2 3 6% 23%	3161
	21st to end	Day	30% 11% 4 9% 6% 5% 4 3 4 5% 18%	3213
November	1st to 10th	Day	40% 10% 3 6% 4 3 4 4 4 5% 16%	1560
	11th to 20th	Day	37% 10% 3 7% 4 4 4 2 4 4 22%	1520
	21st to end	Day	37% 12% 3 6% 4 3 2 3 4 5% 20%	1520
December	1st to 10th	Day	33% 13% 4 6% 5% 3 3 3 4 4 23%	1520
	11th to 20th	Day	36% 12% 4 7% 4 4 4 3 4 6% 17%	1925
	21st to end	Day	30% 15% 5% 11% 6% 3 4 3 4 5% 14%	2506
January	1st to 10th	Night	41% 15% 3 9% 4 4 4 3 3 3 11%	4688
	11th to 20th	Night	31% 11% 4 7% 4 4 3 3 4 6% 23%	4382
	21st to end	Night	40% 12% 3 9% 5% 4 3 3 3 4 13%	4826
February	1st to 10th	Night	35% 12% 3 7% 5% 4 4 3 4 5% 19%	2470
	11th to 20th	Night	32% 14% 3 7% 5% 3 4 3 3 4 22%	2402
	21st to end	Night	31% 14% 3 7% 4 4 4 3 5% 5% 22%	1970
March	1st to 10th	Night	22% 16% 4 9% 6% 6% 5% 4 6% 5% 18%	3684
	11th to 20th	Night	25% 10% 2 6% 3 3 3 2 4 6% 37%	3489
	21st to end	Night	33% 16% 4 8% 5% 4 4 3 4 4 16%	3680
April	1st to 10th	Night	29% 13% 3 8% 4 5% 5% 3 5% 6% 18%	1900
	11th to 20th	Night	26% 10% 3 7% 5% 5% 4 4 5% 5% 27%	1860
	21st to end	Night	27% 10% 4 8% 7% 5% 4 4 5% 6% 21%	1644
May	1st to 10th	Night	21% 10% 3 6% 3 3 3 2 4 4 42%	2540
	11th to 20th	Night	20% 8% 3 6% 4 3 3 3 4 6% 40%	2516
	21st to end	Night	31% 10% 4 8% 5% 5% 3 3 4 5% 22%	2762
June	1st to 10th	Night	24% 8% 3 7% 5% 5% 4 3 5% 6% 31%	1467
	11th to 20th	Night	29% 10% 3 7% 6% 5% 3 2 5% 5% 24%	1330
	21st to end	Night	16% 7% 2 5% 4 4 5% 4 6% 6% 41%	1330
July	1st to 10th	Night	10% 5% 1 4 3 3 2 2 3 2 63%	2220
	11th to 20th	Night	6% 2 1 2 2 2 2 2 4 5% 72%	2427
	21st to end	Night	13% 5% 2 4 3 3 3 2 4 5% 56%	2762
August	1st to 10th	Night	5% 2 1 3 3 3 2 2 5% 5% 69%	2552
	11th to 20th	Night	15% 7% 3 5% 3 3 3 3 4 5% 50%	2812
	21st to end	Night	19% 6% 3 6% 3 3 3 2 3 5% 47%	3356
September	1st to 10th	Night	12% 6% 2 6% 3 3 3 3 4 5% 54%	1900
	11th to 20th	Night	19% 7% 3 6% 4 4 3 3 4 5% 40%	1900
	21st to end	Night	21% 9% 3 7% 4 3 3 3 4 5% 40%	2161
October	1st to 10th	Night	17% 7% 2 7% 5% 5% 4 4 5% 7% 35%	3800
	11th to 20th	Night	31% 9% 2 6% 3 3 3 3 5% 6% 29%	3777
	21st to end	Night	35% 12% 3 7% 5% 4 3 2 3 5% 20%	4335
November	1st to 10th	Night	39% 10% 2 7% 4 3 4 3 4 5% 19%	2590
	11th to 20th	Night	39% 8% 3 6% 4 3 3 2 4 4 23%	2660
	21st to end	Night	37% 11% 3 5% 4 4 4 3 3 4 21%	2660
December	1st to 10th	Night	33% 11% 3 6% 4 3 4 3 5% 4 24%	2660
	11th to 20th	Night	33% 15% 4 8% 4 4 3 3 4 5% 16%	3280
	21st to end	Night	31% 15% 4 10% 5% 5% 5% 3 4 4 13%	5127

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	81% 4 5% 8% 2 1	2252
	11th to 20th	Day	62% 6% 9% 15% 6% 1	2540
	21st to end	Day	78% 5% 7% 7% 3	2830
February	1st to 10th	Day	71% 7% 9% 8% 3 1	1710
	11th to 20th	Day	70% 4 9% 8% 8%	1674
	21st to end	Day	69% 5% 10% 11% 5%	1484
March	1st to 10th	Day	63% 6% 15% 12% 4	3188
	11th to 20th	Day	54% 7% 13% 23% 2 1	3490
	21st to end	Day	71% 8% 11% 9%	3972
April	1st to 10th	Day	70% 7% 15% 7% 1	2280
	11th to 20th	Day	65% 5% 12% 11% 6% 1	2267
	21st to end	Day	68% 7% 11% 9% 4	2534
May	1st to 10th	Day	49% 6% 16% 20% 9%	4420
	11th to 20th	Day	47% 8% 25% 16% 3	4380
	21st to end	Day	69% 9% 14% 7% 1	4814
June	1st to 10th	Day	59% 7% 17% 12% 5% 1	2708
	11th to 20th	Day	64% 8% 15% 10% 2	2850
	21st to end	Day	47% 9% 19% 18% 6% 1	2850
July	1st to 10th	Day	27% 5% 9% 22% 25% 11%	4666
	11th to 20th	Day	22% 5% 9% 30% 32% 2	4451
	21st to end	Day	31% 5% 17% 32% 13% 2	4639
August	1st to 10th	Day	24% 7% 14% 39% 16% 1	4359
	11th to 20th	Day	42% 10% 19% 21% 7% 2	4065
	21st to end	Day	44% 5% 14% 25% 11% 1	4317
September	1st to 10th	Day	39% 5% 16% 23% 12% 5%	2280
	11th to 20th	Day	48% 7% 12% 17% 14% 2	2280
	21st to end	Day	49% 7% 17% 15% 10% 2	2015
October	1st to 10th	Day	44% 7% 17% 26% 5%	3180
	11th to 20th	Day	63% 4 9% 15% 8%	3161
	21st to end	Day	68% 5% 10% 8% 8%	3213
November	1st to 10th	Day	72% 5% 12% 8% 4	1560
	11th to 20th	Day	70% 5% 8% 8% 7% 2	1520
	21st to end	Day	70% 4 6% 10% 8% 1	1520
December	1st to 10th	Day	67% 5% 7% 12% 9% 1	1520
	11th to 20th	Day	71% 6% 10% 11% 1 1	1928
	21st to end	Day	72% 8% 9% 8% 2	2506
January	1st to 10th	Night	79% 6% 6% 6% 2 1	4688
	11th to 20th	Night	63% 4 8% 17% 7% 1	4420
	21st to end	Night	77% 5% 7% 8% 3	4826
February	1st to 10th	Night	70% 5% 10% 10% 4 1	2470
	11th to 20th	Night	67% 6% 10% 9% 7% 1	2404
	21st to end	Night	66% 6% 10% 13% 4 1	1970
March	1st to 10th	Night	64% 9% 12% 10% 5%	3684
	11th to 20th	Night	51% 5% 19% 22% 2 1	3490
	21st to end	Night	72% 8% 11% 9% 1	3680
April	1st to 10th	Night	67% 8% 13% 11% 1	1900
	11th to 20th	Night	60% 7% 13% 10% 8% 2	1860
	21st to end	Night	65% 7% 11% 11% 5% 1	1644
May	1st to 10th	Night	48% 4 14% 26% 8%	2540
	11th to 20th	Night	47% 7% 21% 21% 4	2516
	21st to end	Night	66% 11% 15% 8% 1	2762
June	1st to 10th	Night	56% 6% 17% 15% 6%	1467
	11th to 20th	Night	62% 7% 16% 12% 3	1330
	21st to end	Night	43% 9% 20% 20% 5% 3	1330
July	1st to 10th	Night	27% 4 10% 22% 20% 17%	2185
	11th to 20th	Night	18% 3 11% 26% 39% 2	2383
	21st to end	Night	32% 5% 14% 28% 20% 2	2674
August	1st to 10th	Night	18% 5% 16% 41% 18% 2	2544
	11th to 20th	Night	37% 9% 21% 22% 9% 2	2839
	21st to end	Night	42% 5% 15% 29% 9%	3356
September	1st to 10th	Night	34% 6% 15% 27% 14% 4	1900
	11th to 20th	Night	48% 5% 11% 18% 14% 3	1900
	21st to end	Night	48% 7% 14% 20% 10% 2	2161
October	1st to 10th	Night	46% 7% 16% 27% 4	3800
	11th to 20th	Night	58% 4 12% 16% 9%	3777
	21st to end	Night	67% 5% 10% 11% 6%	4335
November	1st to 10th	Night	70% 5% 12% 9% 3 1	2590
	11th to 20th	Night	69% 4 10% 10% 5% 2	2660
	21st to end	Night	69% 4 8% 10% 9% 1	2660
December	1st to 10th	Night	65% 5% 10% 11% 8% 1	2660
	11th to 20th	Night	71% 7% 8% 9% 3 1	3276
	21st to end	Night	74% 8% 9% 8% 3	5127

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	43% 7% 16% 16% 11% 7%	180
	11th to 20th	Day	39% 12% 14% 16% 16% 2	180
	21st to end	Day	49% 9% 13% 15% 11% 3	221
February	1st to 10th	Day	46% 9% 20% 17% 7% 1	370
	11th to 20th	Day	44% 11% 21% 16% 7% 1	365
	21st to end	Day	40% 10% 19% 23% 8%	341
March	1st to 10th	Day	35% 12% 26% 16% 10% 1	460
	11th to 20th	Day	35% 12% 16% 23% 11% 3	460
	21st to end	Day	41% 14% 22% 15% 8% 1	506
April	1st to 10th	Day	36% 12% 24% 17% 9% 2	460
	11th to 20th	Day	30% 17% 24% 17% 10% 3	452
	21st to end	Day	30% 13% 26% 19% 11% 1	460
May	1st to 10th	Day	22% 12% 25% 28% 12% 1	463
	11th to 20th	Day	28% 9% 20% 25% 14% 4	488
	21st to end	Day	33% 9% 16% 27% 13% 3	529
June	1st to 10th	Day	26% 9% 25% 26% 12% 3	538
	11th to 20th	Day	26% 9% 26% 26% 11% 2	680
	21st to end	Day	18% 6% 22% 33% 18% 4	680
July	1st to 10th	Day	15% 3 22% 38% 19% 3	671
	11th to 20th	Day	11% 6% 20% 38% 21% 4	551
	21st to end	Day	10% 4 18% 39% 23% 5%	531
August	1st to 10th	Day	12% 4 14% 38% 22% 9%	487
	11th to 20th	Day	12% 3 17% 35% 25% 8%	477
	21st to end	Day	15% 8% 23% 32% 15% 7%	539
September	1st to 10th	Day	18% 6% 22% 34% 15% 5%	490
	11th to 20th	Day	20% 8% 20% 28% 21% 3	490
	21st to end	Day	22% 8% 22% 29% 14% 4	490
October	1st to 10th	Day	28% 7% 20% 23% 18% 4	490
	11th to 20th	Day	37% 5% 16% 21% 18% 4	490
	21st to end	Day	38% 11% 17% 20% 11% 4	405
November	1st to 10th	Day	46% 10% 18% 15% 10% 1	211
	11th to 20th	Day	46% 8% 10% 15% 15% 6%	180
	21st to end	Day	42% 8% 17% 13% 9% 11%	180
December	1st to 10th	Day	52% 6% 11% 11% 13% 8%	180
	11th to 20th	Day	46% 8% 19% 16% 10% 1	180
	21st to end	Day	43% 8% 18% 21% 9% 2	198
January	1st to 10th	Night	51% 7% 13% 17% 11% 1	837
	11th to 20th	Night	43% 7% 13% 23% 12% 1	760
	21st to end	Night	44% 5% 13% 26% 12% 1	836
February	1st to 10th	Night	42% 7% 15% 26% 8% 1	760
	11th to 20th	Night	41% 6% 13% 28% 10% 1	744
	21st to end	Night	40% 7% 16% 26% 11% 1	628
March	1st to 10th	Night	37% 10% 17% 23% 12% 1	760
	11th to 20th	Night	41% 8% 14% 23% 13% 1	760
	21st to end	Night	42% 9% 17% 22% 9% 1	836
April	1st to 10th	Night	37% 7% 16% 27% 12% 1	760
	11th to 20th	Night	33% 6% 19% 27% 13% 1	732
	21st to end	Night	35% 7% 20% 25% 12% 2	504
May	1st to 10th	Night	26% 5% 15% 33% 21%	380
	11th to 20th	Night	26% 4 12% 34% 23% 2	374
	21st to end	Night	29% 5% 13% 29% 21% 3	411
June	1st to 10th	Night	28% 5% 17% 32% 14% 3	380
	11th to 20th	Night	35% 6% 12% 28% 17% 1	380
	21st to end	Night	21% 4 12% 35% 25% 3	380
July	1st to 10th	Night	15% 4 10% 35% 34% 3	370
	11th to 20th	Night	12% 1 14% 34% 36% 3	368
	21st to end	Night	12% 3 9% 31% 41% 4	416
August	1st to 10th	Night	10% 2 6% 29% 46% 8%	388
	11th to 20th	Night	12% 2 6% 29% 40% 10%	564
	21st to end	Night	18% 3 12% 31% 33% 5%	746
September	1st to 10th	Night	17% 2 11% 35% 30% 6%	760
	11th to 20th	Night	24% 3 11% 25% 30% 6%	760
	21st to end	Night	27% 6% 10% 28% 26% 4	760
October	1st to 10th	Night	26% 4 13% 28% 25% 3	760
	11th to 20th	Night	35% 4 15% 25% 18% 3	760
	21st to end	Night	40% 6% 15% 25% 12% 2	836
November	1st to 10th	Night	46% 7% 17% 22% 8%	754
	11th to 20th	Night	46% 4 20% 19% 9% 2	760
	21st to end	Night	44% 5% 16% 20% 13% 1	760
December	1st to 10th	Night	38% 6% 17% 25% 12% 2	760
	11th to 20th	Night	49% 7% 13% 24% 6% 1	760
	21st to end	Night	50% 7% 16% 20% 7%	912

Page generated at 2024-11-01 19:47:32. Version ac07

Copyright © 2024 Attilla Danko.