Issaquah
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Issaquah clear sky chart from 2005-11-06 to 2024-11-01.

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	22% 10% 3 7% 5% 4 4 3 5% 6% 32%	102081
	Night	24% 10% 3 8% 4 4 4 3 4 5% 30%	96858
Transparency	Day	54% 6% 12% 17% 8% 2	101840
	Night	58% 6% 12% 16% 7% 1	96745
Seeing	Day	28% 8% 18% 26% 15% 4	15009
	Night	33% 6% 12% 26% 20% 3	23333

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	39% 17% 4 9% 5% 4 3 3 4 3 11%	2419
	11th to 20th	Day	26% 13% 4 10% 5% 4 4 3 4 6% 22%	2516
	21st to end	Day	38% 15% 4 10% 4 4 3 2 4 5% 11%	2858
February	1st to 10th	Day	34% 12% 4 8% 5% 4 4 3 4 6% 15%	1710
	11th to 20th	Day	32% 14% 4 9% 5% 4 3 3 4 5% 19%	1665
	21st to end	Day	29% 15% 4 9% 5% 5% 4 3 3 4 19%	1489
March	1st to 10th	Day	20% 13% 5% 10% 7% 6% 5% 4 5% 6% 19%	3192
	11th to 20th	Day	22% 11% 3 7% 5% 3 3 3 4 5% 35%	3490
	21st to end	Day	26% 15% 4 10% 6% 5% 6% 4 5% 5% 15%	3969
April	1st to 10th	Day	27% 14% 4 8% 6% 4 5% 4 6% 5% 16%	2280
	11th to 20th	Day	24% 12% 3 8% 6% 5% 5% 4 5% 6% 24%	2258
	21st to end	Day	24% 11% 4 10% 5% 5% 4 4 6% 7% 19%	2522
May	1st to 10th	Day	19% 9% 2 6% 5% 4 5% 3 5% 6% 34%	4420
	11th to 20th	Day	20% 7% 2 6% 4 4 3 4 5% 9% 36%	4377
	21st to end	Day	30% 11% 3 10% 5% 5% 4 3 5% 6% 18%	4813
June	1st to 10th	Day	23% 9% 3 7% 6% 5% 4 4 6% 6% 26%	2661
	11th to 20th	Day	25% 11% 4 8% 6% 5% 5% 4 6% 6% 20%	2850
	21st to end	Day	14% 8% 3 7% 5% 4 5% 4 6% 6% 37%	2850
July	1st to 10th	Day	8% 5% 2 4 3 3 3 3 3 4 62%	4740
	11th to 20th	Day	7% 3 1 3 3 2 3 3 4 5% 66%	4462
	21st to end	Day	12% 5% 2 5% 3 3 3 3 4 6% 55%	4790
August	1st to 10th	Day	7% 3 2 4 3 3 3 3 5% 7% 61%	4347
	11th to 20th	Day	10% 7% 3 8% 5% 5% 5% 4 7% 8% 38%	4026
	21st to end	Day	18% 9% 3 6% 4 4 3 3 4 6% 40%	4313
September	1st to 10th	Day	12% 6% 2 6% 3 4 3 3 5% 6% 49%	2280
	11th to 20th	Day	16% 9% 3 7% 5% 4 5% 4 5% 7% 37%	2280
	21st to end	Day	19% 9% 2 8% 4 4 4 3 5% 5% 37%	2015
October	1st to 10th	Day	21% 9% 3 7% 4 5% 5% 4 6% 7% 30%	1900
	11th to 20th	Day	27% 9% 3 7% 3 4 4 4 5% 6% 27%	1900
	21st to end	Day	32% 9% 3 8% 3 4 4 3 5% 5% 23%	1966
November	1st to 10th	Day	38% 10% 3 7% 4 4 3 4 4 6% 17%	1543
	11th to 20th	Day	34% 12% 3 8% 5% 4 3 3 4 4 22%	1520
	21st to end	Day	35% 11% 3 8% 5% 4 3 2 4 5% 21%	1520
December	1st to 10th	Day	31% 10% 3 7% 4 4 5% 3 3 5% 23%	1520
	11th to 20th	Day	34% 12% 4 8% 4 5% 3 2 5% 5% 18%	1925
	21st to end	Day	28% 13% 5% 10% 7% 5% 5% 4 4 5% 15%	2695
January	1st to 10th	Night	39% 16% 4 9% 5% 4 4 3 3 3 11%	4479
	11th to 20th	Night	28% 13% 5% 8% 4 4 3 3 4 6% 22%	4382
	21st to end	Night	36% 13% 4 9% 6% 4 4 3 4 5% 13%	4796
February	1st to 10th	Night	33% 12% 4 8% 6% 4 4 3 3 5% 17%	2470
	11th to 20th	Night	30% 13% 3 8% 4 3 3 3 5% 5% 22%	2402
	21st to end	Night	31% 15% 3 8% 4 4 4 2 5% 5% 19%	1965
March	1st to 10th	Night	19% 15% 4 9% 6% 5% 6% 5% 5% 7% 18%	3679
	11th to 20th	Night	20% 10% 3 6% 3 3 3 2 4 6% 39%	3489
	21st to end	Night	30% 15% 4 9% 5% 5% 5% 3 5% 5% 15%	3684
April	1st to 10th	Night	26% 11% 3 9% 6% 5% 5% 5% 5% 6% 18%	1900
	11th to 20th	Night	21% 11% 3 8% 5% 5% 5% 3 5% 6% 27%	1870
	21st to end	Night	25% 13% 3 9% 5% 5% 4 3 5% 6% 22%	1658
May	1st to 10th	Night	21% 9% 3 7% 5% 3 3 3 4 4 38%	2540
	11th to 20th	Night	17% 9% 3 7% 5% 4 5% 4 5% 8% 34%	2516
	21st to end	Night	26% 14% 4 10% 5% 5% 5% 3 4 4 20%	2762
June	1st to 10th	Night	19% 9% 4 9% 6% 5% 4 3 4 6% 30%	1514
	11th to 20th	Night	21% 12% 3 10% 6% 5% 4 3 5% 6% 25%	1330
	21st to end	Night	14% 6% 3 8% 4 4 4 3 6% 6% 43%	1330
July	1st to 10th	Night	8% 5% 2 5% 3 3 2 3 3 4 61%	2220
	11th to 20th	Night	5% 3 1 3 2 2 2 2 3 4 72%	2494
	21st to end	Night	12% 5% 2 4 3 3 3 2 4 5% 58%	2762
August	1st to 10th	Night	5% 3 2 3 2 2 2 2 5% 6% 68%	2582
	11th to 20th	Night	12% 6% 3 6% 3 4 4 3 4 7% 49%	2812
	21st to end	Night	20% 7% 2 5% 3 3 2 2 3 5% 48%	3360
September	1st to 10th	Night	10% 5% 2 6% 4 3 4 2 4 6% 53%	1900
	11th to 20th	Night	18% 8% 3 6% 3 3 4 4 4 5% 41%	1900
	21st to end	Night	19% 8% 3 7% 4 4 3 3 5% 5% 40%	2161
October	1st to 10th	Night	20% 8% 3 8% 5% 4 4 3 5% 6% 35%	2280
	11th to 20th	Night	26% 9% 3 7% 4 4 4 3 5% 5% 31%	2280
	21st to end	Night	30% 10% 2 7% 3 4 3 3 4 5% 27%	2631
November	1st to 10th	Night	34% 10% 3 8% 4 4 4 3 4 6% 20%	2537
	11th to 20th	Night	34% 10% 3 8% 5% 3 4 3 4 4 22%	2660
	21st to end	Night	33% 11% 3 8% 4 3 4 3 4 5% 22%	2660
December	1st to 10th	Night	31% 11% 2 8% 6% 4 3 3 4 5% 24%	2660
	11th to 20th	Night	32% 12% 4 9% 4 5% 4 3 4 5% 17%	3280
	21st to end	Night	29% 13% 4 11% 6% 5% 5% 4 4 4 15%	4913

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	79% 5% 5% 8% 3 1	2419
	11th to 20th	Day	64% 5% 11% 13% 6% 1	2540
	21st to end	Day	78% 4 6% 8% 3	2858
February	1st to 10th	Day	72% 4 10% 9% 4 1	1710
	11th to 20th	Day	70% 5% 8% 10% 6% 1	1674
	21st to end	Day	72% 3 9% 11% 4	1489
March	1st to 10th	Day	64% 5% 14% 13% 4	3192
	11th to 20th	Day	53% 5% 14% 25% 2 1	3490
	21st to end	Day	70% 8% 11% 10% 1	3969
April	1st to 10th	Day	71% 7% 14% 8% 1	2280
	11th to 20th	Day	63% 6% 11% 12% 6% 1	2258
	21st to end	Day	68% 6% 11% 10% 4 1	2522
May	1st to 10th	Day	52% 5% 15% 18% 10%	4420
	11th to 20th	Day	48% 7% 24% 18% 3	4380
	21st to end	Day	68% 7% 16% 8% 1	4814
June	1st to 10th	Day	61% 7% 15% 12% 5%	2661
	11th to 20th	Day	66% 6% 14% 11% 3	2850
	21st to end	Day	47% 8% 17% 19% 8% 1	2850
July	1st to 10th	Day	27% 6% 8% 21% 22% 15%	4666
	11th to 20th	Day	24% 4 7% 28% 35% 3	4385
	21st to end	Day	30% 6% 14% 33% 14% 2	4639
August	1st to 10th	Day	23% 6% 11% 40% 18% 2	4330
	11th to 20th	Day	41% 10% 19% 20% 7% 2	4065
	21st to end	Day	45% 5% 12% 26% 11% 1	4312
September	1st to 10th	Day	36% 6% 14% 26% 12% 5%	2280
	11th to 20th	Day	48% 7% 11% 18% 14% 2	2280
	21st to end	Day	50% 5% 16% 18% 10% 2	2015
October	1st to 10th	Day	53% 6% 11% 22% 7% 1	1900
	11th to 20th	Day	58% 5% 12% 18% 6% 1	1900
	21st to end	Day	63% 6% 9% 12% 10%	1966
November	1st to 10th	Day	70% 5% 10% 10% 4	1543
	11th to 20th	Day	70% 5% 8% 9% 7% 2	1520
	21st to end	Day	69% 5% 5% 11% 9% 2	1520
December	1st to 10th	Day	66% 5% 8% 13% 8% 1	1520
	11th to 20th	Day	70% 4 11% 12% 2 1	1928
	21st to end	Day	71% 6% 10% 10% 3	2695
January	1st to 10th	Night	79% 6% 5% 7% 2 1	4479
	11th to 20th	Night	63% 4 9% 16% 6% 1	4420
	21st to end	Night	75% 5% 7% 8% 4 1	4796
February	1st to 10th	Night	71% 5% 10% 9% 5% 1	2470
	11th to 20th	Night	65% 7% 10% 10% 6% 2	2404
	21st to end	Night	69% 5% 10% 11% 4	1965
March	1st to 10th	Night	63% 6% 13% 13% 5%	3679
	11th to 20th	Night	50% 5% 19% 23% 3 1	3490
	21st to end	Night	71% 8% 12% 9% 1	3684
April	1st to 10th	Night	67% 8% 13% 10% 2	1900
	11th to 20th	Night	60% 6% 12% 13% 8% 1	1870
	21st to end	Night	65% 7% 12% 11% 5% 1	1658
May	1st to 10th	Night	51% 5% 12% 24% 8%	2540
	11th to 20th	Night	49% 8% 21% 18% 4 1	2516
	21st to end	Night	70% 7% 14% 8% 1	2762
June	1st to 10th	Night	59% 5% 16% 15% 5%	1514
	11th to 20th	Night	64% 6% 15% 12% 2	1330
	21st to end	Night	44% 7% 20% 20% 7% 2	1330
July	1st to 10th	Night	29% 6% 10% 19% 16% 20%	2185
	11th to 20th	Night	20% 3 8% 27% 40% 1	2448
	21st to end	Night	30% 6% 13% 30% 18% 2	2674
August	1st to 10th	Night	20% 4 11% 40% 22% 2	2574
	11th to 20th	Night	37% 10% 21% 22% 8% 2	2839
	21st to end	Night	42% 4 13% 30% 9% 1	3360
September	1st to 10th	Night	34% 6% 16% 27% 14% 4	1900
	11th to 20th	Night	47% 7% 10% 19% 13% 4	1900
	21st to end	Night	48% 7% 13% 20% 11% 2	2161
October	1st to 10th	Night	50% 5% 13% 23% 7% 1	2280
	11th to 20th	Night	58% 5% 10% 19% 7% 1	2280
	21st to end	Night	60% 5% 10% 13% 10%	2631
November	1st to 10th	Night	68% 6% 12% 11% 4 1	2537
	11th to 20th	Night	68% 5% 9% 10% 5% 3	2660
	21st to end	Night	67% 6% 6% 10% 9% 1	2660
December	1st to 10th	Night	66% 4 9% 12% 8% 1	2660
	11th to 20th	Night	70% 5% 10% 11% 3 1	3276
	21st to end	Night	71% 7% 10% 9% 3	4913

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% 9% 12% 18% 11% 6%	180
	11th to 20th	Day	34% 14% 14% 21% 13% 4	180
	21st to end	Day	47% 11% 11% 14% 12% 4	236
February	1st to 10th	Day	44% 8% 20% 17% 9% 2	370
	11th to 20th	Day	46% 9% 19% 16% 8% 2	365
	21st to end	Day	40% 12% 20% 21% 6% 1	343
March	1st to 10th	Day	36% 15% 19% 19% 10% 2	460
	11th to 20th	Day	34% 12% 17% 21% 12% 4	460
	21st to end	Day	39% 11% 21% 19% 9% 1	506
April	1st to 10th	Day	38% 12% 20% 16% 12% 2	460
	11th to 20th	Day	30% 14% 24% 18% 9% 4	452
	21st to end	Day	33% 11% 23% 22% 10% 1	460
May	1st to 10th	Day	23% 10% 21% 31% 12% 2	463
	11th to 20th	Day	30% 8% 16% 25% 15% 6%	488
	21st to end	Day	30% 8% 21% 25% 13% 3	529
June	1st to 10th	Day	30% 7% 21% 25% 14% 4	491
	11th to 20th	Day	30% 10% 20% 26% 11% 2	680
	21st to end	Day	15% 5% 23% 33% 19% 4	680
July	1st to 10th	Day	15% 5% 18% 35% 23% 3	671
	11th to 20th	Day	11% 4 17% 38% 25% 4	511
	21st to end	Day	10% 5% 15% 40% 25% 5%	531
August	1st to 10th	Day	13% 5% 15% 36% 23% 9%	487
	11th to 20th	Day	9% 3 15% 38% 28% 8%	477
	21st to end	Day	18% 6% 20% 32% 17% 7%	539
September	1st to 10th	Day	15% 7% 20% 38% 16% 4	490
	11th to 20th	Day	21% 7% 17% 31% 19% 5%	490
	21st to end	Day	22% 8% 19% 30% 17% 4	490
October	1st to 10th	Day	27% 7% 18% 21% 20% 6%	490
	11th to 20th	Day	34% 8% 13% 24% 14% 6%	490
	21st to end	Day	37% 10% 18% 20% 11% 4	415
November	1st to 10th	Day	43% 9% 13% 18% 14% 2	207
	11th to 20th	Day	43% 9% 13% 9% 19% 7%	180
	21st to end	Day	39% 9% 13% 18% 12% 9%	180
December	1st to 10th	Day	46% 7% 12% 16% 9% 11%	180
	11th to 20th	Day	46% 9% 14% 21% 9% 1	180
	21st to end	Day	40% 11% 11% 23% 13% 3	198
January	1st to 10th	Night	51% 7% 14% 16% 11% 1	780
	11th to 20th	Night	42% 9% 12% 23% 13% 2	760
	21st to end	Night	40% 6% 12% 28% 12%	836
February	1st to 10th	Night	42% 6% 17% 24% 10% 1	760
	11th to 20th	Night	40% 6% 13% 26% 14% 1	744
	21st to end	Night	42% 8% 14% 24% 11% 2	628
March	1st to 10th	Night	36% 8% 15% 24% 14% 2	760
	11th to 20th	Night	35% 8% 17% 27% 12% 2	760
	21st to end	Night	38% 8% 16% 25% 10% 2	836
April	1st to 10th	Night	35% 8% 16% 25% 14% 3	760
	11th to 20th	Night	30% 7% 16% 30% 14% 3	742
	21st to end	Night	35% 9% 13% 26% 15% 3	518
May	1st to 10th	Night	25% 7% 14% 29% 22% 2	380
	11th to 20th	Night	24% 5% 8% 30% 27% 5%	374
	21st to end	Night	30% 4 11% 23% 25% 6%	411
June	1st to 10th	Night	26% 5% 12% 27% 27% 3	380
	11th to 20th	Night	31% 8% 12% 27% 19% 3	380
	21st to end	Night	17% 4 11% 29% 34% 5%	380
July	1st to 10th	Night	15% 4 8% 30% 38% 5%	370
	11th to 20th	Night	12% 2 6% 30% 44% 5%	368
	21st to end	Night	10% 1 7% 26% 47% 8%	416
August	1st to 10th	Night	13% 3 4 23% 46% 11%	405
	11th to 20th	Night	11% 2 5% 24% 43% 14%	564
	21st to end	Night	20% 4 6% 25% 39% 7%	750
September	1st to 10th	Night	14% 3 7% 35% 34% 6%	760
	11th to 20th	Night	24% 3 7% 25% 33% 8%	760
	21st to end	Night	24% 5% 10% 28% 29% 4	760
October	1st to 10th	Night	26% 4 8% 30% 28% 4	760
	11th to 20th	Night	33% 6% 11% 25% 19% 6%	760
	21st to end	Night	37% 8% 12% 28% 12% 3	836
November	1st to 10th	Night	41% 7% 16% 27% 9%	742
	11th to 20th	Night	42% 8% 14% 23% 12% 1	760
	21st to end	Night	41% 8% 13% 23% 13% 1	760
December	1st to 10th	Night	38% 5% 15% 27% 14% 2	760
	11th to 20th	Night	46% 8% 15% 23% 8% 2	760
	21st to end	Night	50% 8% 15% 20% 6%	853

Page generated at 2024-10-29 08:20:50. Version ac07

Copyright © 2024 Attilla Danko.