Spider Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spider Lake clear sky chart from 2005-11-06 to 2024-11-10.

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	13% 11% 4 10% 5% 4 5% 4 5% 7% 32%	101658
	Night	12% 12% 4 10% 5% 5% 4 4 5% 6% 32%	97592
Transparency	Day	50% 6% 12% 22% 10% 1	105176
	Night	51% 5% 11% 21% 10% 1	102214
Seeing	Day	21% 16% 34% 20% 8% 2	16102
	Night	20% 14% 33% 24% 8% 1	25971

By Month

Percentage Cloud Cover SE (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	10% 17% 7% 22% 6% 5% 4 3 4 5% 16%	2527
	11th to 20th	Day	7% 16% 7% 17% 11% 8% 9% 5% 6% 5% 11%	2530
	21st to end	Day	8% 18% 11% 20% 6% 5% 5% 3 5% 5% 15%	2852
February	1st to 10th	Day	8% 14% 5% 14% 6% 5% 5% 5% 6% 4 28%	1710
	11th to 20th	Day	8% 14% 5% 12% 7% 6% 5% 5% 5% 5% 28%	1664
	21st to end	Day	11% 14% 6% 13% 8% 5% 4 4 5% 6% 24%	1557
March	1st to 10th	Day	9% 11% 3 12% 6% 4 5% 3 5% 6% 36%	3120
	11th to 20th	Day	7% 14% 4 14% 6% 4 4 4 5% 8% 30%	3475
	21st to end	Day	18% 15% 4 14% 5% 3 3 3 4 5% 24%	4027
April	1st to 10th	Day	15% 17% 5% 9% 5% 4 4 3 5% 6% 27%	2280
	11th to 20th	Day	19% 15% 6% 8% 3 4 3 3 4 6% 29%	2254
	21st to end	Day	19% 12% 4 8% 5% 5% 4 3 4 5% 31%	2445
May	1st to 10th	Day	17% 10% 3 7% 4 4 4 3 4 6% 39%	4399
	11th to 20th	Day	15% 8% 2 7% 4 4 5% 4 5% 7% 38%	4399
	21st to end	Day	19% 9% 3 7% 5% 4 4 4 5% 6% 33%	4824
June	1st to 10th	Day	14% 6% 3 7% 5% 4 6% 4 7% 7% 38%	2660
	11th to 20th	Day	14% 7% 3 8% 6% 4 5% 4 6% 7% 35%	2660
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 4 7% 8% 36%	2660
July	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 4 6% 10% 40%	4440
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 5% 7% 10% 46%	4440
	21st to end	Day	8% 6% 2 6% 4 4 5% 4 6% 8% 47%	4813
August	1st to 10th	Day	13% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	4401
	11th to 20th	Day	14% 6% 2 5% 4 4 4 3 5% 7% 47%	4041
	21st to end	Day	13% 8% 3 7% 5% 4 4 4 6% 7% 39%	4191
September	1st to 10th	Day	14% 7% 2 7% 5% 4 4 4 5% 9% 40%	2280
	11th to 20th	Day	14% 6% 2 6% 5% 4 5% 4 6% 9% 40%	2280
	21st to end	Day	20% 9% 3 6% 3 4 4 3 4 6% 37%	2023
October	1st to 10th	Day	17% 11% 3 7% 3 3 4 3 5% 7% 35%	1900
	11th to 20th	Day	18% 18% 5% 9% 4 4 4 3 4 4 27%	1900
	21st to end	Day	21% 16% 4 7% 4 4 5% 3 4 5% 27%	1921
November	1st to 10th	Day	12% 19% 5% 9% 5% 3 4 4 5% 5% 30%	1724
	11th to 20th	Day	14% 19% 10% 13% 7% 5% 3 2 4 5% 18%	1520
	21st to end	Day	14% 14% 5% 16% 7% 5% 4 3 4 6% 21%	1520
December	1st to 10th	Day	10% 17% 8% 17% 9% 6% 5% 3 4 6% 15%	1520
	11th to 20th	Day	10% 16% 8% 13% 12% 7% 6% 3 4 4 16%	1918
	21st to end	Day	18% 20% 8% 20% 6% 5% 3 2 3 3 13%	2783
January	1st to 10th	Night	10% 14% 7% 18% 7% 5% 5% 4 4 5% 20%	4428
	11th to 20th	Night	7% 14% 6% 17% 10% 8% 7% 6% 6% 5% 13%	4440
	21st to end	Night	8% 20% 9% 16% 8% 5% 4 4 4 4 17%	4811
February	1st to 10th	Night	6% 15% 5% 13% 7% 7% 5% 4 5% 5% 27%	2470
	11th to 20th	Night	7% 11% 4 11% 7% 8% 6% 6% 5% 6% 28%	2403
	21st to end	Night	11% 16% 4 10% 6% 5% 5% 4 5% 6% 28%	1896
March	1st to 10th	Night	8% 9% 3 8% 5% 4 5% 4 7% 8% 40%	3733
	11th to 20th	Night	8% 11% 5% 16% 5% 4 5% 5% 4 6% 31%	3513
	21st to end	Night	19% 15% 6% 11% 5% 4 3 3 4 3 26%	3603
April	1st to 10th	Night	18% 14% 4 8% 5% 5% 4 4 5% 5% 28%	1900
	11th to 20th	Night	21% 11% 5% 6% 3 3 5% 3 5% 5% 32%	1875
	21st to end	Night	19% 13% 3 7% 4 3 4 3 5% 5% 33%	1733
May	1st to 10th	Night	16% 10% 3 7% 4 4 5% 3 5% 7% 37%	2506
	11th to 20th	Night	13% 8% 3 6% 3 4 4 3 4 7% 46%	2506
	21st to end	Night	13% 8% 3 8% 6% 5% 5% 4 6% 7% 35%	2743
June	1st to 10th	Night	12% 6% 2 6% 4 5% 4 4 7% 9% 42%	1520
	11th to 20th	Night	10% 6% 3 7% 6% 5% 5% 5% 6% 7% 40%	1520
	21st to end	Night	11% 7% 3 6% 4 5% 5% 4 6% 8% 41%	1520
July	1st to 10th	Night	10% 5% 2 6% 4 3 5% 4 6% 9% 48%	2530
	11th to 20th	Night	6% 4 1 5% 3 3 4 4 6% 9% 55%	2530
	21st to end	Night	7% 6% 2 6% 4 3 4 3 5% 7% 53%	2750
August	1st to 10th	Night	12% 7% 2 5% 5% 3 4 3 6% 8% 44%	2536
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 5% 7% 51%	2798
	21st to end	Night	15% 9% 3 6% 3 3 3 3 4 6% 44%	3464
September	1st to 10th	Night	10% 6% 2 6% 3 4 4 3 5% 8% 50%	1900
	11th to 20th	Night	10% 5% 1 5% 4 4 5% 3 6% 7% 48%	1900
	21st to end	Night	16% 8% 3 5% 4 4 4 3 5% 7% 40%	2132
October	1st to 10th	Night	16% 10% 2 5% 5% 3 4 3 4 6% 42%	2280
	11th to 20th	Night	17% 13% 5% 8% 5% 4 4 3 5% 6% 31%	2280
	21st to end	Night	19% 15% 4 8% 4 4 4 3 5% 5% 28%	2675
November	1st to 10th	Night	14% 14% 5% 9% 5% 4 3 3 5% 6% 31%	2554
	11th to 20th	Night	12% 16% 7% 13% 7% 5% 4 3 5% 5% 24%	2660
	21st to end	Night	13% 15% 5% 13% 6% 6% 4 4 5% 5% 24%	2660
December	1st to 10th	Night	9% 16% 8% 16% 8% 6% 6% 4 4 5% 19%	2660
	11th to 20th	Night	11% 16% 6% 14% 8% 7% 5% 5% 5% 5% 19%	3279
	21st to end	Night	21% 22% 6% 12% 6% 5% 3 3 3 4 16%	4884

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	71% 3 6% 16% 4	2528
	11th to 20th	Day	74% 5% 7% 11% 3	2530
	21st to end	Day	71% 4 9% 11% 4	2852
February	1st to 10th	Day	57% 4 10% 17% 11%	1710
	11th to 20th	Day	56% 5% 10% 21% 8%	1673
	21st to end	Day	59% 5% 9% 16% 10% 1	1557
March	1st to 10th	Day	48% 6% 13% 20% 13% 1	3120
	11th to 20th	Day	52% 4 13% 20% 10% 1	3475
	21st to end	Day	63% 4 9% 18% 5% 1	4027
April	1st to 10th	Day	58% 5% 10% 17% 10% 1	2280
	11th to 20th	Day	58% 3 8% 21% 8% 1	2254
	21st to end	Day	57% 4 8% 19% 11% 1	2445
May	1st to 10th	Day	47% 6% 9% 23% 14% 1	4440
	11th to 20th	Day	43% 8% 12% 26% 10% 1	4403
	21st to end	Day	50% 7% 10% 18% 14% 1	4837
June	1st to 10th	Day	41% 8% 13% 26% 12% 1	2660
	11th to 20th	Day	46% 6% 12% 21% 14% 1	2660
	21st to end	Day	42% 8% 15% 25% 9% 1	2660
July	1st to 10th	Day	38% 7% 17% 25% 12% 1	4371
	11th to 20th	Day	30% 7% 17% 32% 13% 1	4365
	21st to end	Day	33% 7% 13% 31% 16%	4662
August	1st to 10th	Day	44% 6% 15% 23% 11% 1	4386
	11th to 20th	Day	37% 6% 16% 31% 10%	4080
	21st to end	Day	44% 6% 16% 24% 10% 1	4190
September	1st to 10th	Day	40% 6% 15% 28% 11%	2280
	11th to 20th	Day	41% 7% 18% 26% 7%	2280
	21st to end	Day	47% 6% 12% 26% 9%	2023
October	1st to 10th	Day	37% 4 14% 29% 15% 1	3160
	11th to 20th	Day	54% 4 8% 22% 11%	3140
	21st to end	Day	53% 5% 16% 20% 6%	3146
November	1st to 10th	Day	56% 5% 12% 19% 7% 1	1724
	11th to 20th	Day	69% 4 9% 12% 5%	1520
	21st to end	Day	66% 5% 12% 13% 4 1	1520
December	1st to 10th	Day	72% 5% 9% 11% 3	1520
	11th to 20th	Day	72% 4 10% 10% 3	1915
	21st to end	Day	78% 4 5% 10% 3	2783
January	1st to 10th	Night	67% 5% 8% 16% 3	4428
	11th to 20th	Night	69% 6% 10% 11% 3	4440
	21st to end	Night	70% 4 7% 16% 3	4811
February	1st to 10th	Night	57% 4 9% 18% 11% 1	2470
	11th to 20th	Night	54% 6% 12% 19% 8% 1	2404
	21st to end	Night	56% 5% 10% 19% 8% 2	1896
March	1st to 10th	Night	39% 6% 16% 21% 15% 2	3733
	11th to 20th	Night	53% 5% 10% 23% 8% 1	3513
	21st to end	Night	62% 5% 7% 16% 9% 1	3603
April	1st to 10th	Night	55% 6% 7% 17% 13% 1	1900
	11th to 20th	Night	53% 5% 8% 21% 11% 2	1875
	21st to end	Night	52% 4 8% 23% 13% 1	1733
May	1st to 10th	Night	46% 6% 13% 21% 13% 1	2530
	11th to 20th	Night	39% 5% 10% 27% 17% 3	2507
	21st to end	Night	45% 9% 13% 20% 12% 1	2751
June	1st to 10th	Night	37% 7% 15% 27% 12% 1	1520
	11th to 20th	Night	41% 7% 11% 21% 17% 2	1520
	21st to end	Night	39% 7% 14% 26% 13% 1	1520
July	1st to 10th	Night	33% 7% 19% 26% 12% 3	2490
	11th to 20th	Night	24% 7% 15% 39% 13% 1	2482
	21st to end	Night	30% 6% 12% 31% 21% 2	2662
August	1st to 10th	Night	38% 5% 15% 26% 14% 2	2527
	11th to 20th	Night	33% 6% 15% 35% 10% 1	2825
	21st to end	Night	42% 5% 16% 26% 10% 2	3464
September	1st to 10th	Night	32% 6% 15% 33% 13% 1	1900
	11th to 20th	Night	33% 7% 17% 34% 9%	1900
	21st to end	Night	43% 6% 14% 27% 10% 1	2132
October	1st to 10th	Night	32% 4 8% 33% 21% 2	3800
	11th to 20th	Night	47% 5% 11% 22% 15%	3779
	21st to end	Night	57% 4 11% 21% 8%	4400
November	1st to 10th	Night	53% 5% 12% 21% 9%	2554
	11th to 20th	Night	61% 5% 13% 12% 8%	2660
	21st to end	Night	60% 5% 13% 16% 4 1	2660
December	1st to 10th	Night	67% 6% 9% 14% 3	2660
	11th to 20th	Night	66% 6% 11% 14% 3	3281
	21st to end	Night	75% 3 6% 11% 5%	4884

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	22% 20% 33% 19% 4 2	270
	11th to 20th	Day	24% 18% 35% 20% 3	270
	21st to end	Day	22% 14% 40% 22% 3	297
February	1st to 10th	Day	21% 24% 39% 12% 3	270
	11th to 20th	Day	20% 29% 37% 10% 4	270
	21st to end	Day	24% 26% 43% 7%	225
March	1st to 10th	Day	17% 21% 44% 13% 4	270
	11th to 20th	Day	23% 20% 39% 14% 5%	270
	21st to end	Day	27% 17% 34% 15% 5% 2	420
April	1st to 10th	Day	28% 15% 38% 13% 5% 1	460
	11th to 20th	Day	31% 16% 30% 17% 6%	452
	21st to end	Day	30% 15% 30% 18% 6% 1	554
May	1st to 10th	Day	25% 18% 35% 16% 5% 1	653
	11th to 20th	Day	23% 17% 31% 21% 6% 2	675
	21st to end	Day	23% 15% 34% 19% 7% 1	734
June	1st to 10th	Day	16% 18% 36% 22% 7% 2	680
	11th to 20th	Day	19% 14% 40% 19% 5% 1	680
	21st to end	Day	20% 12% 36% 20% 9% 3	680
July	1st to 10th	Day	10% 10% 34% 26% 15% 6%	671
	11th to 20th	Day	12% 12% 33% 26% 12% 5%	668
	21st to end	Day	9% 10% 39% 23% 15% 4	739
August	1st to 10th	Day	16% 8% 31% 28% 14% 3	676
	11th to 20th	Day	17% 6% 29% 30% 14% 4	665
	21st to end	Day	19% 11% 28% 26% 13% 3	550
September	1st to 10th	Day	18% 12% 29% 26% 12% 2	490
	11th to 20th	Day	15% 13% 32% 30% 9% 2	490
	21st to end	Day	25% 16% 28% 20% 11% 1	419
October	1st to 10th	Day	27% 17% 29% 18% 8% 1	300
	11th to 20th	Day	31% 21% 34% 11% 2	300
	21st to end	Day	32% 22% 37% 7% 2	330
November	1st to 10th	Day	25% 20% 39% 14% 3	297
	11th to 20th	Day	26% 26% 36% 8% 4	270
	21st to end	Day	26% 23% 37% 11% 2	270
December	1st to 10th	Day	18% 22% 41% 16% 3	270
	11th to 20th	Day	27% 21% 36% 13% 3	270
	21st to end	Day	28% 22% 37% 9% 3	297
January	1st to 10th	Night	17% 19% 38% 21% 5%	950
	11th to 20th	Night	20% 15% 40% 18% 6% 1	950
	21st to end	Night	20% 15% 40% 21% 4	1045
February	1st to 10th	Night	16% 19% 37% 21% 6%	950
	11th to 20th	Night	15% 23% 37% 18% 7% 1	929
	21st to end	Night	19% 17% 40% 21% 4	640
March	1st to 10th	Night	18% 18% 36% 22% 6% 1	760
	11th to 20th	Night	19% 18% 36% 20% 7%	590
	21st to end	Night	25% 11% 30% 22% 10% 2	627
April	1st to 10th	Night	27% 12% 35% 20% 5% 1	570
	11th to 20th	Night	29% 11% 29% 22% 8%	563
	21st to end	Night	28% 9% 29% 26% 7% 1	570
May	1st to 10th	Night	23% 12% 32% 26% 5% 1	570
	11th to 20th	Night	19% 9% 34% 29% 7% 2	561
	21st to end	Night	15% 10% 31% 32% 10% 1	617
June	1st to 10th	Night	16% 8% 31% 34% 10% 1	570
	11th to 20th	Night	15% 7% 33% 34% 10%	570
	21st to end	Night	14% 8% 29% 35% 12% 2	570
July	1st to 10th	Night	8% 5% 30% 36% 20% 2	555
	11th to 20th	Night	10% 7% 33% 32% 18% 1	552
	21st to end	Night	8% 5% 30% 38% 17% 2	624
August	1st to 10th	Night	12% 4 24% 43% 16% 1	567
	11th to 20th	Night	16% 4 23% 35% 20% 3	564
	21st to end	Night	15% 6% 29% 29% 18% 3	627
September	1st to 10th	Night	12% 9% 26% 35% 14% 3	570
	11th to 20th	Night	12% 8% 34% 29% 15% 2	570
	21st to end	Night	20% 12% 29% 26% 10% 1	736
October	1st to 10th	Night	24% 12% 29% 24% 10% 1	760
	11th to 20th	Night	27% 14% 35% 17% 6% 1	760
	21st to end	Night	28% 12% 31% 22% 6%	836
November	1st to 10th	Night	24% 15% 36% 19% 5%	803
	11th to 20th	Night	22% 22% 34% 17% 5% 1	950
	21st to end	Night	24% 21% 35% 17% 4	950
December	1st to 10th	Night	20% 19% 38% 19% 5% 1	950
	11th to 20th	Night	21% 19% 34% 19% 5% 1	950
	21st to end	Night	31% 17% 33% 14% 4	1045

Page generated at 2024-11-07 05:55:44. Version ac07

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