Spirit Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spirit Lake clear sky chart from 2005-11-06 to 2024-11-28.

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	10% 10% 3 7% 5% 4 5% 4 5% 6% 42%	105417
	Night	12% 11% 3 7% 5% 4 4 4 5% 6% 39%	102707
Transparency	Day	43% 5% 13% 21% 13% 5%	105185
	Night	45% 6% 12% 20% 12% 5%	102585
Seeing	Day	17% 12% 24% 25% 17% 5%	14975
	Night	20% 7% 17% 33% 22% 3	24125

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	16% 27% 9% 12% 5% 5% 5% 3 5% 4 9%	2539
	11th to 20th	Day	19% 16% 4 9% 7% 6% 5% 4 4 5% 22%	2516
	21st to end	Day	24% 22% 6% 12% 6% 4 4 3 4 4 12%	2794
February	1st to 10th	Day	18% 23% 5% 9% 5% 3 6% 4 4 4 19%	1520
	11th to 20th	Day	15% 19% 5% 11% 5% 4 4 4 5% 4 23%	1761
	21st to end	Day	15% 21% 5% 10% 6% 4 5% 4 3 6% 22%	1570
March	1st to 10th	Day	10% 16% 5% 9% 5% 6% 6% 4 6% 6% 29%	3138
	11th to 20th	Day	9% 11% 3 6% 5% 4 5% 3 4 5% 44%	3297
	21st to end	Day	15% 17% 4 11% 7% 6% 6% 4 5% 5% 19%	4090
April	1st to 10th	Day	15% 15% 4 8% 6% 5% 5% 5% 7% 6% 23%	2280
	11th to 20th	Day	12% 13% 4 9% 6% 5% 6% 4 5% 7% 30%	2340
	21st to end	Day	12% 11% 4 9% 7% 6% 6% 3 6% 6% 32%	2470
May	1st to 10th	Day	10% 8% 3 8% 6% 5% 6% 5% 6% 7% 35%	4313
	11th to 20th	Day	7% 6% 2 7% 4 5% 5% 4 8% 11% 41%	4377
	21st to end	Day	10% 8% 4 8% 7% 6% 6% 4 6% 8% 31%	4961
June	1st to 10th	Day	17% 7% 3 6% 6% 4 4 4 5% 7% 36%	2850
	11th to 20th	Day	16% 6% 2 7% 5% 5% 5% 5% 6% 7% 35%	2850
	21st to end	Day	7% 4 1 5% 4 4 5% 4 6% 6% 54%	2850
July	1st to 10th	Day	3 2 1 2 2 2 3 3 4 4 74%	4588
	11th to 20th	Day	2 2 1 2 2 2 2 3 3 4 79%	4420
	21st to end	Day	1 1 1 2 2 2 3 3 4 5% 76%	4790
August	1st to 10th	Day	3 2 1 3 2 3 4 3 5% 6% 68%	4401
	11th to 20th	Day	3 3 1 3 2 3 3 3 5% 7% 65%	4124
	21st to end	Day	3 2 1 4 3 4 4 4 6% 8% 61%	4315
September	1st to 10th	Day	5% 4 2 4 3 3 4 3 5% 7% 63%	2280
	11th to 20th	Day	8% 6% 2 5% 5% 4 4 4 6% 7% 49%	2157
	21st to end	Day	9% 6% 2 6% 5% 4 5% 4 7% 8% 46%	2090
October	1st to 10th	Day	9% 5% 1 5% 4 3 4 2 4 7% 55%	3402
	11th to 20th	Day	8% 7% 3 7% 5% 6% 4 4 6% 7% 42%	2922
	21st to end	Day	17% 10% 4 8% 5% 6% 6% 5% 6% 6% 28%	3101
November	1st to 10th	Day	22% 18% 4 7% 5% 4 4 3 4 6% 22%	1764
	11th to 20th	Day	21% 17% 6% 9% 5% 4 5% 4 4 5% 21%	1710
	21st to end	Day	15% 21% 7% 14% 6% 4 5% 3 4 4 19%	1379
December	1st to 10th	Day	16% 18% 5% 13% 4 5% 5% 3 5% 6% 20%	1330
	11th to 20th	Day	20% 25% 8% 13% 8% 5% 4 2 3 3 11%	1682
	21st to end	Day	15% 22% 6% 14% 6% 5% 5% 3 4 5% 15%	2446
January	1st to 10th	Night	19% 24% 7% 12% 6% 5% 5% 3 4 4 13%	4429
	11th to 20th	Night	17% 16% 5% 10% 5% 4 3 2 4 6% 26%	4382
	21st to end	Night	22% 25% 5% 10% 5% 4 4 3 4 4 14%	4862
February	1st to 10th	Night	18% 20% 4 8% 4 4 3 3 5% 5% 24%	2660
	11th to 20th	Night	13% 16% 5% 10% 5% 5% 5% 3 4 6% 29%	2303
	21st to end	Night	12% 17% 4 9% 5% 5% 5% 4 6% 7% 28%	1884
March	1st to 10th	Night	8% 11% 3 10% 5% 5% 5% 4 6% 6% 36%	3736
	11th to 20th	Night	10% 10% 3 6% 4 4 3 3 4 4 49%	3681
	21st to end	Night	14% 12% 3 9% 7% 6% 7% 5% 7% 7% 23%	3560
April	1st to 10th	Night	10% 11% 3 7% 6% 5% 6% 5% 7% 7% 34%	1900
	11th to 20th	Night	11% 10% 3 8% 6% 5% 5% 4 4 6% 38%	1790
	21st to end	Night	9% 8% 3 8% 5% 5% 6% 5% 5% 7% 38%	1710
May	1st to 10th	Night	11% 7% 3 7% 6% 6% 6% 5% 7% 8% 34%	2648
	11th to 20th	Night	6% 5% 2 6% 4 4 5% 4 7% 9% 48%	2516
	21st to end	Night	11% 8% 3 7% 6% 6% 6% 5% 8% 9% 32%	2612
June	1st to 10th	Night	14% 6% 3 7% 4 4 4 5% 5% 7% 41%	1330
	11th to 20th	Night	10% 6% 2 8% 4 6% 5% 5% 7% 8% 40%	1330
	21st to end	Night	6% 4 2 5% 3 4 5% 3 6% 7% 54%	1330
July	1st to 10th	Night	2 1 1 2 3 2 3 3 4 5% 74%	2368
	11th to 20th	Night	1 1 1 2 2 2 2 2 3 3 81%	2540
	21st to end	Night	1 2 1 2 2 2 2 2 3 5% 78%	2762
August	1st to 10th	Night	3 2 1 3 2 2 2 3 4 7% 72%	2529
	11th to 20th	Night	3 3 2 5% 2 4 4 4 6% 7% 61%	2710
	21st to end	Night	2 2 1 4 3 6% 4 4 4 6% 63%	3356
September	1st to 10th	Night	4 2 1 4 2 3 3 3 6% 6% 65%	1900
	11th to 20th	Night	5% 5% 2 7% 5% 5% 4 3 6% 8% 50%	2023
	21st to end	Night	10% 4 2 5% 3 4 4 3 6% 8% 51%	2090
October	1st to 10th	Night	6% 3 2 3 3 3 3 3 5% 7% 60%	3575
	11th to 20th	Night	9% 5% 2 6% 5% 4 4 4 5% 7% 49%	4007
	21st to end	Night	11% 7% 2 6% 4 4 5% 5% 7% 7% 42%	4457
November	1st to 10th	Night	22% 13% 3 7% 5% 4 6% 4 5% 7% 25%	2535
	11th to 20th	Night	18% 15% 4 8% 6% 5% 5% 4 5% 5% 24%	2681
	21st to end	Night	20% 14% 4 10% 6% 5% 4 3 5% 5% 24%	2937
December	1st to 10th	Night	16% 15% 6% 10% 6% 5% 3 4 5% 5% 24%	2850
	11th to 20th	Night	21% 22% 6% 11% 6% 5% 5% 3 4 4 13%	3510
	21st to end	Night	18% 17% 6% 13% 7% 6% 5% 4 5% 4 14%	5214

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	78% 6% 9% 5% 2	2539
	11th to 20th	Day	64% 7% 11% 12% 3 3	2540
	21st to end	Day	76% 5% 11% 6% 2 1	2794
February	1st to 10th	Day	69% 6% 12% 8% 4 1	1520
	11th to 20th	Day	63% 8% 12% 11% 6%	1771
	21st to end	Day	64% 8% 9% 13% 6%	1570
March	1st to 10th	Day	55% 7% 11% 16% 10%	3138
	11th to 20th	Day	42% 6% 20% 29% 3	3298
	21st to end	Day	67% 7% 12% 11% 4	4090
April	1st to 10th	Day	58% 8% 15% 15% 4	2280
	11th to 20th	Day	52% 7% 14% 18% 9% 1	2340
	21st to end	Day	52% 7% 14% 19% 7% 1	2470
May	1st to 10th	Day	45% 7% 13% 27% 7%	4313
	11th to 20th	Day	33% 7% 21% 31% 8%	4380
	21st to end	Day	48% 7% 19% 21% 4	4962
June	1st to 10th	Day	47% 6% 14% 22% 11% 1	2850
	11th to 20th	Day	45% 7% 15% 22% 9% 2	2850
	21st to end	Day	28% 6% 15% 29% 18% 3	2850
July	1st to 10th	Day	14% 3 6% 22% 33% 21%	4518
	11th to 20th	Day	11% 3 6% 14% 29% 38%	4345
	21st to end	Day	12% 2 6% 23% 36% 20%	4639
August	1st to 10th	Day	17% 3 6% 28% 34% 12%	4384
	11th to 20th	Day	18% 4 9% 43% 24% 3	4165
	21st to end	Day	21% 4 11% 36% 24% 3	4314
September	1st to 10th	Day	22% 4 12% 32% 21% 9%	2280
	11th to 20th	Day	32% 6% 13% 25% 20% 3	2157
	21st to end	Day	36% 6% 20% 24% 11% 3	2090
October	1st to 10th	Day	29% 3 14% 37% 16%	3402
	11th to 20th	Day	41% 4 21% 23% 11% 1	2922
	21st to end	Day	54% 6% 14% 19% 6%	3101
November	1st to 10th	Day	63% 7% 14% 12% 3 1	1764
	11th to 20th	Day	66% 8% 11% 10% 4 1	1710
	21st to end	Day	68% 5% 13% 11% 3	1379
December	1st to 10th	Day	66% 6% 12% 12% 4	1330
	11th to 20th	Day	80% 5% 8% 6% 1	1684
	21st to end	Day	71% 5% 12% 8% 4	2446
January	1st to 10th	Night	76% 4 10% 8% 1	4429
	11th to 20th	Night	59% 6% 13% 16% 4 3	4420
	21st to end	Night	73% 5% 13% 7% 2 1	4862
February	1st to 10th	Night	62% 7% 13% 12% 4 1	2660
	11th to 20th	Night	57% 7% 16% 13% 7%	2304
	21st to end	Night	55% 8% 12% 17% 8% 1	1884
March	1st to 10th	Night	45% 8% 14% 23% 10% 1	3736
	11th to 20th	Night	39% 6% 18% 30% 7%	3681
	21st to end	Night	58% 9% 14% 15% 4	3560
April	1st to 10th	Night	46% 7% 17% 23% 7%	1900
	11th to 20th	Night	47% 5% 12% 21% 13% 1	1790
	21st to end	Night	44% 7% 12% 25% 11% 1	1710
May	1st to 10th	Night	44% 7% 13% 24% 11% 1	2648
	11th to 20th	Night	28% 7% 13% 36% 16%	2516
	21st to end	Night	46% 8% 15% 22% 9%	2612
June	1st to 10th	Night	41% 7% 11% 23% 16% 2	1330
	11th to 20th	Night	39% 6% 13% 24% 14% 4	1330
	21st to end	Night	26% 6% 11% 28% 23% 6%	1330
July	1st to 10th	Night	13% 3 5% 17% 35% 27%	2329
	11th to 20th	Night	9% 2 4 13% 21% 51%	2492
	21st to end	Night	10% 2 3 18% 35% 32%	2674
August	1st to 10th	Night	14% 3 5% 23% 37% 19%	2521
	11th to 20th	Night	22% 4 6% 35% 27% 7%	2735
	21st to end	Night	22% 3 10% 29% 28% 7%	3356
September	1st to 10th	Night	18% 5% 9% 28% 28% 12%	1900
	11th to 20th	Night	32% 6% 10% 24% 22% 7%	2023
	21st to end	Night	31% 5% 17% 27% 15% 5%	2090
October	1st to 10th	Night	24% 3 12% 44% 17%	3575
	11th to 20th	Night	35% 4 15% 25% 19% 1	4007
	21st to end	Night	40% 6% 16% 28% 8% 1	4457
November	1st to 10th	Night	58% 7% 16% 14% 4 1	2535
	11th to 20th	Night	61% 7% 14% 11% 5% 1	2681
	21st to end	Night	61% 6% 15% 14% 4	2937
December	1st to 10th	Night	62% 9% 11% 15% 3	2850
	11th to 20th	Night	72% 7% 11% 8% 2	3507
	21st to end	Night	70% 6% 13% 8% 3	5214

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	30% 17% 19% 18% 12% 4	180
	11th to 20th	Day	34% 12% 21% 18% 7% 8%	180
	21st to end	Day	33% 8% 24% 23% 11% 1	198
February	1st to 10th	Day	30% 19% 27% 14% 8% 2	180
	11th to 20th	Day	29% 16% 22% 22% 10% 1	395
	21st to end	Day	29% 18% 20% 21% 11% 1	382
March	1st to 10th	Day	23% 22% 24% 18% 10% 2	460
	11th to 20th	Day	22% 15% 21% 20% 20% 2	460
	21st to end	Day	26% 17% 25% 21% 9% 1	506
April	1st to 10th	Day	24% 16% 29% 18% 11% 3	460
	11th to 20th	Day	18% 22% 25% 19% 13% 3	452
	21st to end	Day	16% 17% 29% 25% 10% 3	460
May	1st to 10th	Day	14% 13% 27% 30% 12% 4	463
	11th to 20th	Day	16% 13% 25% 26% 14% 6%	488
	21st to end	Day	13% 12% 21% 29% 19% 6%	612
June	1st to 10th	Day	17% 10% 24% 25% 19% 5%	680
	11th to 20th	Day	16% 15% 28% 23% 14% 4	680
	21st to end	Day	7% 9% 24% 28% 25% 6%	680
July	1st to 10th	Day	5% 7% 26% 34% 26% 4	588
	11th to 20th	Day	5% 8% 27% 34% 20% 6%	484
	21st to end	Day	3 7% 25% 37% 19% 9%	531
August	1st to 10th	Day	7% 5% 22% 33% 24% 9%	487
	11th to 20th	Day	4 4 21% 35% 25% 10%	477
	21st to end	Day	6% 10% 25% 27% 21% 11%	539
September	1st to 10th	Day	8% 7% 27% 26% 23% 10%	490
	11th to 20th	Day	12% 10% 23% 27% 20% 8%	490
	21st to end	Day	12% 13% 26% 23% 20% 6%	490
October	1st to 10th	Day	14% 9% 26% 27% 18% 7%	490
	11th to 20th	Day	18% 13% 22% 25% 14% 8%	354
	21st to end	Day	28% 11% 22% 25% 10% 3	330
November	1st to 10th	Day	32% 11% 20% 23% 13% 1	300
	11th to 20th	Day	31% 13% 20% 19% 16% 1	257
	21st to end	Day	24% 11% 25% 24% 15% 2	194
December	1st to 10th	Day	28% 13% 21% 20% 13% 4	180
	11th to 20th	Day	31% 14% 24% 18% 11% 3	180
	21st to end	Day	35% 11% 19% 21% 12% 2	198
January	1st to 10th	Night	38% 9% 17% 23% 11% 2	770
	11th to 20th	Night	31% 8% 17% 28% 14% 2	760
	21st to end	Night	26% 7% 19% 31% 15% 2	836
February	1st to 10th	Night	31% 8% 21% 28% 10% 2	760
	11th to 20th	Night	25% 9% 18% 31% 15% 1	744
	21st to end	Night	22% 11% 19% 29% 17% 3	628
March	1st to 10th	Night	19% 9% 20% 33% 17% 2	760
	11th to 20th	Night	20% 9% 16% 33% 20% 1	760
	21st to end	Night	20% 9% 21% 34% 14% 2	836
April	1st to 10th	Night	17% 7% 18% 38% 20% 1	760
	11th to 20th	Night	15% 8% 26% 33% 16% 2	662
	21st to end	Night	13% 9% 23% 34% 19% 2	570
May	1st to 10th	Night	10% 6% 20% 35% 27% 2	449
	11th to 20th	Night	11% 5% 16% 27% 32% 8%	374
	21st to end	Night	13% 6% 14% 32% 29% 5%	411
June	1st to 10th	Night	17% 5% 13% 38% 24% 4	380
	11th to 20th	Night	12% 5% 22% 36% 22% 3	380
	21st to end	Night	7% 2 12% 40% 35% 3	380
July	1st to 10th	Night	2 2 10% 42% 41% 3	370
	11th to 20th	Night	3 1 13% 45% 35% 3	368
	21st to end	Night	1 2 10% 40% 43% 4	416
August	1st to 10th	Night	4 2 10% 37% 42% 6%	378
	11th to 20th	Night	5% 3 6% 33% 43% 9%	499
	21st to end	Night	4 3 13% 38% 39% 3	746
September	1st to 10th	Night	5% 2 13% 39% 34% 7%	760
	11th to 20th	Night	8% 4 14% 32% 36% 7%	760
	21st to end	Night	12% 5% 17% 33% 28% 5%	760
October	1st to 10th	Night	13% 6% 13% 39% 27% 3	760
	11th to 20th	Night	17% 6% 16% 31% 27% 3	760
	21st to end	Night	20% 5% 21% 33% 18% 3	836
November	1st to 10th	Night	31% 7% 15% 33% 13% 1	780
	11th to 20th	Night	29% 9% 18% 28% 14% 1	800
	21st to end	Night	30% 9% 15% 28% 17% 2	967
December	1st to 10th	Night	26% 8% 18% 32% 15% 1	950
	11th to 20th	Night	35% 6% 19% 30% 10%	950
	21st to end	Night	34% 9% 19% 27% 10%	1045

Page generated at 2024-11-24 21:22:18. Version ac07

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