GrandIsland Sky Watchers
Clear Sky Chart
History

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

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	16% 11% 4 8% 5% 5% 4 4 5% 7% 32%	101494
	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 31%	97666
Transparency	Day	49% 8% 13% 19% 10% 1	105098
	Night	52% 8% 12% 18% 9% 1	102150
Seeing	Day	21% 16% 28% 21% 10% 4	14536
	Night	22% 14% 28% 25% 10% 1	23930

By Month

Percentage Cloud Cover NE (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	17% 20% 7% 12% 6% 4 4 3 4 4 19%	2517
	11th to 20th	Day	13% 22% 8% 19% 9% 6% 4 3 3 3 9%	2758
	21st to end	Day	23% 19% 8% 11% 8% 6% 4 3 4 4 10%	3124
February	1st to 10th	Day	18% 20% 4 13% 7% 7% 4 3 5% 5% 16%	1710
	11th to 20th	Day	14% 18% 7% 16% 9% 5% 5% 3 3 4 16%	1663
	21st to end	Day	20% 15% 5% 12% 7% 5% 4 4 4 5% 19%	1482
March	1st to 10th	Day	19% 12% 5% 11% 6% 5% 4 3 4 4 29%	3432
	11th to 20th	Day	11% 21% 4 8% 5% 5% 4 3 5% 5% 29%	3480
	21st to end	Day	17% 11% 3 9% 4 4 4 3 5% 7% 33%	3815
April	1st to 10th	Day	18% 14% 4 8% 4 4 4 3 5% 6% 31%	2261
	11th to 20th	Day	20% 10% 2 7% 4 4 4 3 4 6% 36%	2278
	21st to end	Day	20% 10% 3 8% 5% 3 4 3 5% 5% 34%	2470
May	1st to 10th	Day	19% 9% 3 7% 5% 5% 4 3 5% 7% 33%	4108
	11th to 20th	Day	15% 11% 3 9% 5% 5% 5% 4 5% 7% 31%	4384
	21st to end	Day	11% 7% 2 6% 4 3 4 3 6% 7% 46%	4837
June	1st to 10th	Day	16% 6% 2 6% 4 4 4 5% 6% 7% 39%	2660
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	2660
	21st to end	Day	15% 5% 2 5% 4 4 4 4 7% 8% 41%	2660
July	1st to 10th	Day	8% 5% 2 5% 4 4 6% 4 7% 10% 45%	4440
	11th to 20th	Day	11% 5% 3 5% 4 4 5% 4 7% 10% 42%	4440
	21st to end	Day	8% 5% 2 6% 5% 4 5% 5% 7% 9% 43%	4503
August	1st to 10th	Day	18% 6% 2 6% 4 4 4 4 6% 8% 38%	4104
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 5% 7% 11% 35%	4044
	21st to end	Day	11% 5% 2 5% 4 4 4 4 6% 9% 45%	4290
September	1st to 10th	Day	14% 7% 2 5% 4 4 4 3 7% 8% 42%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 6% 7% 45%	2198
	21st to end	Day	15% 8% 3 6% 6% 6% 5% 4 7% 8% 33%	2032
October	1st to 10th	Day	20% 7% 2 6% 5% 4 4 3 6% 7% 35%	1900
	11th to 20th	Day	21% 10% 4 9% 4 4 5% 3 5% 6% 29%	1900
	21st to end	Day	25% 13% 4 10% 5% 4 4 3 4 5% 23%	2090
November	1st to 10th	Day	14% 11% 3 9% 7% 5% 5% 4 5% 6% 31%	1736
	11th to 20th	Day	15% 14% 5% 9% 5% 4 4 3 5% 7% 29%	1520
	21st to end	Day	20% 18% 4 10% 6% 5% 4 3 4 6% 21%	1520
December	1st to 10th	Day	20% 19% 6% 11% 7% 6% 3 4 4 5% 15%	1520
	11th to 20th	Day	20% 18% 7% 12% 6% 4 4 3 5% 6% 15%	1906
	21st to end	Day	27% 23% 5% 12% 5% 4 4 3 3 3 12%	2772
January	1st to 10th	Night	18% 20% 5% 11% 6% 5% 4 3 4 5% 19%	4429
	11th to 20th	Night	14% 20% 8% 16% 7% 5% 4 3 4 5% 14%	4187
	21st to end	Night	25% 20% 5% 13% 8% 5% 4 3 3 3 12%	4532
February	1st to 10th	Night	17% 17% 6% 13% 6% 4 4 3 5% 4 20%	2470
	11th to 20th	Night	15% 16% 5% 12% 7% 5% 5% 4 5% 5% 21%	2403
	21st to end	Night	18% 15% 4 14% 6% 4 4 3 4 7% 20%	1967
March	1st to 10th	Night	21% 13% 3 9% 6% 4 4 3 3 5% 31%	3408
	11th to 20th	Night	18% 16% 3 8% 4 4 4 4 5% 6% 29%	3479
	21st to end	Night	16% 8% 2 8% 5% 4 3 3 5% 6% 41%	3817
April	1st to 10th	Night	20% 12% 4 7% 6% 4 3 3 4 5% 31%	1919
	11th to 20th	Night	19% 8% 3 6% 5% 4 4 4 5% 6% 35%	1868
	21st to end	Night	18% 9% 4 6% 4 4 6% 5% 5% 6% 35%	1710
May	1st to 10th	Night	22% 10% 4 7% 4 4 3 3 5% 5% 33%	2833
	11th to 20th	Night	13% 8% 2 7% 6% 5% 6% 4 7% 8% 34%	2509
	21st to end	Night	12% 6% 2 5% 4 4 4 5% 6% 8% 46%	2738
June	1st to 10th	Night	13% 6% 3 7% 6% 5% 6% 5% 7% 7% 35%	1520
	11th to 20th	Night	10% 5% 2 6% 6% 5% 5% 4 6% 7% 43%	1520
	21st to end	Night	13% 6% 3 6% 4 5% 5% 4 5% 9% 40%	1520
July	1st to 10th	Night	8% 6% 2 7% 4 5% 5% 4 6% 8% 44%	2520
	11th to 20th	Night	11% 5% 2 6% 4 4 4 3 6% 9% 47%	2520
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 7% 7% 48%	3046
August	1st to 10th	Night	11% 6% 2 6% 5% 5% 4 4 7% 8% 43%	2825
	11th to 20th	Night	14% 6% 3 7% 4 4 5% 3 6% 7% 40%	2785
	21st to end	Night	8% 5% 2 6% 4 4 4 4 7% 10% 45%	3332
September	1st to 10th	Night	14% 6% 2 6% 3 4 4 3 5% 6% 46%	1900
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 5% 7% 51%	1979
	21st to end	Night	17% 7% 3 7% 4 5% 5% 4 5% 7% 36%	2147
October	1st to 10th	Night	16% 8% 3 7% 4 4 4 4 5% 6% 39%	2280
	11th to 20th	Night	23% 10% 2 7% 5% 4 4 3 5% 6% 31%	2280
	21st to end	Night	25% 10% 3 8% 4 4 4 4 5% 5% 27%	2508
November	1st to 10th	Night	16% 11% 2 6% 5% 4 4 3 4 6% 38%	2556
	11th to 20th	Night	15% 13% 4 9% 6% 5% 4 3 5% 6% 29%	2667
	21st to end	Night	19% 15% 5% 9% 5% 4 5% 4 5% 6% 23%	2660
December	1st to 10th	Night	21% 20% 6% 11% 5% 4 4 3 4 5% 17%	2660
	11th to 20th	Night	17% 21% 6% 11% 5% 5% 4 3 4 5% 19%	3288
	21st to end	Night	30% 17% 5% 9% 5% 5% 5% 3 5% 5% 12%	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	70% 10% 8% 8% 4	2518
	11th to 20th	Day	79% 8% 6% 5% 1	2758
	21st to end	Day	78% 7% 11% 3 1	3124
February	1st to 10th	Day	72% 7% 10% 9% 1	1710
	11th to 20th	Day	70% 7% 9% 11% 2	1672
	21st to end	Day	67% 8% 11% 9% 5%	1482
March	1st to 10th	Day	56% 7% 11% 20% 6%	3435
	11th to 20th	Day	53% 8% 18% 13% 6% 1	3480
	21st to end	Day	50% 10% 10% 22% 7% 1	3815
April	1st to 10th	Day	55% 5% 12% 17% 9% 1	2261
	11th to 20th	Day	50% 6% 11% 18% 13% 2	2278
	21st to end	Day	52% 6% 11% 17% 12% 2	2470
May	1st to 10th	Day	50% 7% 13% 17% 12% 2	4120
	11th to 20th	Day	49% 11% 13% 19% 7% 1	4388
	21st to end	Day	35% 9% 13% 25% 15% 3	4837
June	1st to 10th	Day	42% 8% 14% 19% 15% 2	2660
	11th to 20th	Day	39% 8% 15% 24% 14% 1	2660
	21st to end	Day	38% 9% 14% 25% 14% 1	2660
July	1st to 10th	Day	33% 7% 14% 27% 17% 2	4370
	11th to 20th	Day	35% 9% 13% 29% 13%	4365
	21st to end	Day	34% 10% 17% 21% 17% 1	4359
August	1st to 10th	Day	43% 8% 15% 22% 12% 1	4091
	11th to 20th	Day	42% 9% 16% 24% 9% 1	4083
	21st to end	Day	34% 7% 12% 34% 12% 1	4290
September	1st to 10th	Day	39% 9% 15% 24% 12% 1	2280
	11th to 20th	Day	35% 8% 12% 29% 14% 1	2198
	21st to end	Day	47% 7% 15% 21% 9% 1	2032
October	1st to 10th	Day	38% 7% 14% 27% 14% 1	3160
	11th to 20th	Day	46% 6% 16% 20% 11%	3140
	21st to end	Day	51% 5% 15% 21% 7%	3428
November	1st to 10th	Day	53% 7% 12% 18% 8% 1	1736
	11th to 20th	Day	55% 8% 16% 14% 6% 1	1520
	21st to end	Day	64% 8% 14% 11% 4	1520
December	1st to 10th	Day	71% 6% 14% 8% 1	1520
	11th to 20th	Day	70% 10% 10% 8% 2	1906
	21st to end	Day	78% 7% 9% 6% 1	2772
January	1st to 10th	Night	67% 11% 11% 8% 2	4429
	11th to 20th	Night	71% 13% 8% 5% 2	4187
	21st to end	Night	76% 8% 8% 6% 2	4532
February	1st to 10th	Night	68% 8% 9% 11% 3	2470
	11th to 20th	Night	64% 7% 12% 13% 4	2405
	21st to end	Night	65% 7% 10% 12% 5%	1967
March	1st to 10th	Night	56% 6% 11% 21% 6%	3418
	11th to 20th	Night	54% 9% 14% 14% 7% 1	3480
	21st to end	Night	42% 7% 11% 23% 15% 1	3817
April	1st to 10th	Night	56% 6% 9% 18% 10% 1	1919
	11th to 20th	Night	49% 6% 10% 19% 14% 2	1868
	21st to end	Night	48% 8% 10% 17% 14% 2	1710
May	1st to 10th	Night	51% 8% 10% 17% 11% 3	2840
	11th to 20th	Night	44% 11% 15% 20% 8% 1	2510
	21st to end	Night	34% 9% 11% 23% 20% 2	2739
June	1st to 10th	Night	44% 9% 10% 20% 16% 1	1520
	11th to 20th	Night	38% 9% 12% 21% 18% 2	1520
	21st to end	Night	41% 8% 13% 21% 15% 2	1520
July	1st to 10th	Night	37% 6% 12% 23% 19% 3	2480
	11th to 20th	Night	35% 6% 15% 30% 13% 1	2472
	21st to end	Night	34% 8% 17% 22% 17% 2	2949
August	1st to 10th	Night	38% 7% 15% 26% 12% 2	2814
	11th to 20th	Night	42% 8% 14% 27% 10%	2812
	21st to end	Night	32% 8% 14% 32% 14% 1	3332
September	1st to 10th	Night	37% 7% 15% 25% 15% 2	1900
	11th to 20th	Night	32% 6% 13% 30% 18% 1	1979
	21st to end	Night	45% 8% 12% 20% 13% 1	2147
October	1st to 10th	Night	41% 6% 9% 25% 19% 1	3800
	11th to 20th	Night	49% 5% 13% 21% 12% 1	3779
	21st to end	Night	45% 5% 17% 24% 8% 1	4120
November	1st to 10th	Night	47% 7% 12% 22% 11% 2	2556
	11th to 20th	Night	54% 7% 14% 16% 7% 1	2667
	21st to end	Night	61% 9% 13% 14% 3	2660
December	1st to 10th	Night	69% 8% 12% 9% 2	2660
	11th to 20th	Night	68% 9% 9% 11% 3	3288
	21st to end	Night	74% 8% 11% 6% 1	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	28% 27% 27% 12% 4 2	180
	11th to 20th	Day	27% 29% 29% 12% 3 1	249
	21st to end	Day	24% 25% 28% 19% 4	297
February	1st to 10th	Day	30% 27% 30% 11% 2	270
	11th to 20th	Day	27% 31% 33% 8% 1	270
	21st to end	Day	40% 16% 31% 13% 1	275
March	1st to 10th	Day	26% 19% 33% 16% 5% 1	460
	11th to 20th	Day	28% 16% 35% 17% 3 1	460
	21st to end	Day	29% 17% 29% 19% 5% 1	506
April	1st to 10th	Day	24% 22% 30% 17% 5% 1	460
	11th to 20th	Day	29% 21% 23% 17% 8% 3	452
	21st to end	Day	25% 19% 31% 17% 7% 2	460
May	1st to 10th	Day	25% 14% 29% 19% 9% 3	463
	11th to 20th	Day	18% 12% 29% 25% 13% 3	487
	21st to end	Day	14% 12% 30% 26% 13% 5%	529
June	1st to 10th	Day	19% 16% 32% 23% 9% 1	490
	11th to 20th	Day	13% 15% 28% 28% 13% 3	490
	21st to end	Day	17% 12% 31% 28% 9% 2	490
July	1st to 10th	Day	9% 9% 25% 31% 21% 5%	485
	11th to 20th	Day	14% 10% 28% 27% 15% 6%	484
	21st to end	Day	11% 8% 31% 31% 14% 5%	532
August	1st to 10th	Day	14% 7% 23% 29% 18% 8%	486
	11th to 20th	Day	13% 9% 24% 29% 18% 9%	479
	21st to end	Day	12% 7% 30% 25% 17% 8%	539
September	1st to 10th	Day	14% 12% 24% 25% 18% 8%	490
	11th to 20th	Day	11% 8% 20% 24% 25% 13%	490
	21st to end	Day	18% 14% 29% 21% 12% 6%	490
October	1st to 10th	Day	22% 14% 25% 18% 16% 5%	490
	11th to 20th	Day	22% 20% 31% 19% 6% 2	490
	21st to end	Day	35% 20% 23% 17% 6%	539
November	1st to 10th	Day	24% 21% 31% 16% 6% 2	336
	11th to 20th	Day	28% 29% 23% 13% 3 3	180
	21st to end	Day	30% 28% 27% 12% 3	180
December	1st to 10th	Day	28% 26% 31% 10% 4 1	180
	11th to 20th	Day	32% 27% 26% 13% 2	180
	21st to end	Day	31% 34% 23% 9% 2 1	198
January	1st to 10th	Night	29% 23% 30% 13% 5%	760
	11th to 20th	Night	32% 23% 27% 16% 3	760
	21st to end	Night	24% 19% 33% 19% 5%	836
February	1st to 10th	Night	27% 24% 31% 15% 3	760
	11th to 20th	Night	25% 21% 33% 17% 3	743
	21st to end	Night	28% 20% 31% 18% 2	628
March	1st to 10th	Night	23% 16% 34% 22% 6%	760
	11th to 20th	Night	25% 18% 31% 20% 5% 1	760
	21st to end	Night	22% 13% 32% 23% 8% 1	836
April	1st to 10th	Night	25% 17% 33% 22% 4	760
	11th to 20th	Night	23% 15% 32% 22% 7% 1	744
	21st to end	Night	22% 10% 31% 28% 9%	570
May	1st to 10th	Night	21% 9% 25% 31% 13% 2	570
	11th to 20th	Night	14% 7% 30% 40% 8%	388
	21st to end	Night	13% 7% 27% 35% 15% 2	411
June	1st to 10th	Night	13% 7% 33% 34% 13%	380
	11th to 20th	Night	14% 7% 31% 34% 14%	380
	21st to end	Night	16% 7% 31% 37% 10%	380
July	1st to 10th	Night	7% 6% 25% 41% 19% 1	370
	11th to 20th	Night	10% 5% 30% 36% 18% 1	368
	21st to end	Night	11% 3 25% 39% 20% 2	596
August	1st to 10th	Night	9% 5% 19% 41% 24% 2	567
	11th to 20th	Night	10% 5% 21% 33% 29% 3	564
	21st to end	Night	12% 5% 23% 35% 23% 2	744
September	1st to 10th	Night	16% 7% 23% 33% 19% 3	760
	11th to 20th	Night	13% 5% 21% 28% 28% 5%	760
	21st to end	Night	17% 11% 23% 29% 16% 4	760
October	1st to 10th	Night	19% 10% 28% 26% 16% 2	760
	11th to 20th	Night	26% 16% 25% 23% 8% 1	760
	21st to end	Night	31% 15% 27% 23% 4	836
November	1st to 10th	Night	24% 15% 29% 23% 10% 1	780
	11th to 20th	Night	23% 20% 32% 17% 8% 1	763
	21st to end	Night	26% 21% 31% 17% 6%	760
December	1st to 10th	Night	33% 22% 25% 17% 4	760
	11th to 20th	Night	26% 25% 29% 16% 4	760
	21st to end	Night	33% 19% 31% 15% 2	836

Page generated at 2024-11-08 06:44:47. Version ac07

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