Brockport State Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brockport State Observatory clear sky chart from 2005-11-06 to 2025-02-21.

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	15% 11% 4 9% 6% 5% 5% 4 5% 7% 30%	108765
	Night	16% 13% 5% 11% 6% 5% 4 4 5% 6% 27%	109787
Transparency	Day	52% 7% 12% 19% 9% 1	112396
	Night	55% 7% 11% 17% 9% 1	114318
Seeing	Day	22% 19% 30% 18% 8% 3	14811
	Night	22% 18% 29% 21% 9% 1	24282

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	12% 21% 9% 18% 8% 4 4 3 4 4 13%	3597
	11th to 20th	Day	11% 25% 9% 19% 9% 5% 5% 3 3 3 8%	3753
	21st to end	Day	17% 19% 9% 14% 7% 6% 5% 3 4 4 11%	4466
February	1st to 10th	Day	16% 18% 6% 14% 8% 5% 4 4 5% 5% 15%	1800
	11th to 20th	Day	13% 16% 9% 18% 9% 5% 4 3 4 4 16%	1753
	21st to end	Day	19% 16% 5% 15% 8% 5% 4 3 4 5% 16%	1508
March	1st to 10th	Day	18% 13% 5% 10% 5% 4 4 3 4 5% 28%	3365
	11th to 20th	Day	11% 19% 5% 10% 6% 5% 4 4 5% 5% 28%	3480
	21st to end	Day	14% 12% 5% 11% 5% 4 4 4 5% 7% 29%	3864
April	1st to 10th	Day	17% 14% 5% 8% 5% 4 4 3 5% 5% 31%	2280
	11th to 20th	Day	19% 11% 2 6% 4 4 4 4 4 6% 36%	2254
	21st to end	Day	20% 12% 3 8% 4 4 4 3 4 6% 32%	2432
May	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 3 5% 6% 33%	4203
	11th to 20th	Day	16% 11% 2 8% 5% 4 5% 4 6% 6% 33%	4398
	21st to end	Day	10% 5% 2 6% 5% 4 5% 4 6% 8% 44%	4837
June	1st to 10th	Day	15% 7% 2 7% 6% 5% 4 4 6% 8% 36%	2660
	11th to 20th	Day	13% 5% 2 5% 5% 5% 6% 5% 7% 10% 38%	2660
	21st to end	Day	13% 6% 2 5% 5% 5% 5% 4 6% 9% 40%	2660
July	1st to 10th	Day	10% 5% 2 6% 5% 4 4 5% 6% 10% 43%	4440
	11th to 20th	Day	9% 6% 2 7% 5% 4 5% 5% 7% 10% 41%	4440
	21st to end	Day	8% 4 3 6% 6% 5% 6% 5% 7% 10% 39%	4640
August	1st to 10th	Day	16% 7% 2 6% 4 4 5% 3 6% 8% 38%	4104
	11th to 20th	Day	14% 6% 3 8% 6% 5% 5% 4 6% 10% 34%	4044
	21st to end	Day	14% 6% 2 5% 4 4 4 4 6% 9% 42%	4222
September	1st to 10th	Day	14% 7% 2 5% 3 5% 5% 4 5% 8% 42%	2280
	11th to 20th	Day	15% 5% 2 6% 4 4 5% 3 6% 8% 43%	2268
	21st to end	Day	16% 7% 3 8% 5% 5% 5% 4 5% 7% 34%	1990
October	1st to 10th	Day	21% 7% 3 7% 5% 4 4 3 6% 5% 33%	1900
	11th to 20th	Day	20% 9% 3 9% 6% 4 4 3 6% 7% 29%	1900
	21st to end	Day	24% 13% 4 9% 6% 5% 4 3 5% 5% 23%	2090
November	1st to 10th	Day	14% 12% 4 9% 6% 5% 5% 4 4 6% 31%	1731
	11th to 20th	Day	12% 17% 5% 11% 7% 5% 3 3 5% 6% 25%	1600
	21st to end	Day	19% 18% 5% 10% 6% 5% 5% 2 5% 8% 18%	1600
December	1st to 10th	Day	18% 20% 7% 14% 7% 5% 5% 3 5% 5% 12%	2600
	11th to 20th	Day	20% 21% 6% 12% 5% 3 4 2 4 4 18%	2986
	21st to end	Day	21% 20% 7% 14% 8% 5% 3 3 4 4 11%	3960
January	1st to 10th	Night	15% 18% 7% 22% 8% 5% 4 2 3 3 12%	6349
	11th to 20th	Night	9% 19% 9% 19% 10% 7% 5% 4 5% 4 9%	6118
	21st to end	Night	17% 19% 7% 14% 7% 6% 5% 3 4 4 13%	6490
February	1st to 10th	Night	16% 19% 5% 13% 7% 5% 5% 3 4 5% 19%	2600
	11th to 20th	Night	13% 14% 7% 15% 8% 6% 5% 3 5% 5% 19%	2533
	21st to end	Night	17% 14% 4 15% 7% 5% 3 3 6% 6% 20%	1946
March	1st to 10th	Night	19% 12% 4 9% 6% 5% 3 3 4 4 30%	3473
	11th to 20th	Night	16% 16% 4 9% 5% 5% 5% 4 5% 6% 25%	3479
	21st to end	Night	16% 9% 4 11% 5% 4 3 3 4 6% 35%	3768
April	1st to 10th	Night	18% 14% 4 8% 5% 4 4 3 5% 5% 30%	1900
	11th to 20th	Night	17% 9% 3 6% 6% 5% 4 3 5% 6% 35%	1875
	21st to end	Night	19% 9% 2 7% 4 4 5% 4 6% 7% 33%	1762
May	1st to 10th	Night	23% 9% 2 8% 5% 4 4 3 4 5% 32%	2737
	11th to 20th	Night	18% 7% 3 7% 4 4 4 3 6% 8% 36%	2495
	21st to end	Night	11% 5% 2 6% 4 4 4 4 6% 9% 45%	2738
June	1st to 10th	Night	14% 6% 2 7% 5% 4 5% 4 8% 9% 36%	1520
	11th to 20th	Night	11% 6% 2 5% 5% 5% 5% 4 7% 9% 40%	1520
	21st to end	Night	11% 7% 3 7% 4 5% 5% 4 6% 8% 40%	1520
July	1st to 10th	Night	10% 7% 2 6% 5% 4 4 4 6% 9% 42%	2520
	11th to 20th	Night	9% 7% 2 6% 4 4 5% 4 6% 8% 45%	2520
	21st to end	Night	9% 5% 2 5% 4 4 5% 4 7% 9% 47%	2896
August	1st to 10th	Night	12% 6% 2 6% 4 5% 4 3 6% 10% 42%	2825
	11th to 20th	Night	14% 6% 2 7% 5% 4 5% 3 7% 8% 39%	2785
	21st to end	Night	7% 5% 2 6% 5% 4 5% 4 7% 9% 46%	3401
September	1st to 10th	Night	14% 6% 2 5% 4 3 4 3 5% 7% 46%	1900
	11th to 20th	Night	13% 4 3 6% 4 4 3 3 6% 7% 47%	1909
	21st to end	Night	16% 7% 2 6% 4 4 5% 5% 7% 6% 37%	2190
October	1st to 10th	Night	18% 8% 3 8% 5% 4 5% 3 5% 7% 35%	2280
	11th to 20th	Night	20% 10% 3 7% 5% 5% 4 3 5% 6% 30%	2280
	21st to end	Night	26% 11% 3 7% 5% 4 3 4 5% 6% 26%	2508
November	1st to 10th	Night	15% 11% 3 7% 5% 5% 4 4 5% 7% 34%	2566
	11th to 20th	Night	15% 12% 4 9% 7% 5% 5% 4 6% 6% 26%	2800
	21st to end	Night	19% 15% 5% 8% 6% 5% 5% 3 6% 7% 21%	2800
December	1st to 10th	Night	16% 19% 7% 16% 7% 6% 5% 4 5% 5% 11%	4580
	11th to 20th	Night	18% 21% 6% 11% 6% 5% 4 3 4 4 18%	5208
	21st to end	Night	24% 17% 7% 13% 7% 5% 4 3 4 4 12%	6996

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	75% 5% 8% 9% 3	3598
	11th to 20th	Day	79% 7% 6% 4 3 1	3784
	21st to end	Day	77% 5% 11% 5% 2	4466
February	1st to 10th	Day	72% 6% 10% 11% 2	1800
	11th to 20th	Day	73% 5% 7% 12% 3	1762
	21st to end	Day	70% 5% 8% 11% 5%	1508
March	1st to 10th	Day	59% 4 9% 20% 7%	3368
	11th to 20th	Day	57% 7% 14% 14% 8% 1	3480
	21st to end	Day	53% 5% 11% 22% 8% 1	3864
April	1st to 10th	Day	55% 6% 9% 18% 11% 1	2280
	11th to 20th	Day	49% 6% 9% 20% 14% 2	2254
	21st to end	Day	54% 5% 8% 18% 13% 2	2432
May	1st to 10th	Day	50% 6% 11% 20% 12% 2	4215
	11th to 20th	Day	49% 9% 13% 21% 8% 1	4402
	21st to end	Day	36% 8% 12% 26% 16% 3	4837
June	1st to 10th	Day	44% 7% 12% 19% 17% 1	2660
	11th to 20th	Day	40% 6% 14% 24% 15% 1	2660
	21st to end	Day	39% 8% 14% 23% 16% 1	2660
July	1st to 10th	Day	35% 7% 13% 30% 15% 1	4370
	11th to 20th	Day	35% 8% 14% 28% 13%	4365
	21st to end	Day	37% 10% 17% 24% 13%	4492
August	1st to 10th	Day	44% 7% 14% 22% 12% 1	4091
	11th to 20th	Day	45% 7% 15% 25% 7%	4083
	21st to end	Day	38% 7% 13% 32% 9% 1	4222
September	1st to 10th	Day	40% 7% 13% 27% 12% 1	2280
	11th to 20th	Day	38% 6% 12% 28% 15%	2268
	21st to end	Day	47% 7% 13% 22% 10% 1	1990
October	1st to 10th	Day	40% 8% 16% 24% 12%	3160
	11th to 20th	Day	47% 5% 15% 20% 13%	3140
	21st to end	Day	50% 7% 14% 23% 6% 1	3428
November	1st to 10th	Day	54% 7% 11% 18% 9% 1	1731
	11th to 20th	Day	59% 7% 13% 14% 7% 1	1600
	21st to end	Day	66% 6% 12% 13% 3	1600
December	1st to 10th	Day	72% 7% 13% 7% 2	2600
	11th to 20th	Day	70% 6% 9% 8% 7%	2986
	21st to end	Day	77% 5% 10% 6% 2	3960
January	1st to 10th	Night	75% 7% 8% 7% 2	6349
	11th to 20th	Night	74% 7% 9% 6% 4	6161
	21st to end	Night	74% 5% 9% 6% 5%	6490
February	1st to 10th	Night	67% 5% 10% 13% 5%	2600
	11th to 20th	Night	67% 6% 9% 14% 5%	2535
	21st to end	Night	63% 6% 12% 14% 5%	1946
March	1st to 10th	Night	58% 5% 10% 22% 6%	3483
	11th to 20th	Night	58% 7% 13% 15% 7%	3480
	21st to end	Night	49% 6% 9% 22% 13% 1	3768
April	1st to 10th	Night	56% 5% 9% 19% 10% 1	1900
	11th to 20th	Night	49% 7% 11% 18% 13% 2	1875
	21st to end	Night	48% 6% 11% 19% 14% 2	1762
May	1st to 10th	Night	53% 6% 10% 17% 12% 2	2744
	11th to 20th	Night	45% 8% 15% 21% 9% 1	2496
	21st to end	Night	34% 7% 13% 23% 21% 2	2739
June	1st to 10th	Night	41% 8% 12% 22% 15% 2	1520
	11th to 20th	Night	37% 7% 11% 23% 18% 2	1520
	21st to end	Night	41% 8% 12% 22% 17% 1	1520
July	1st to 10th	Night	38% 7% 13% 23% 17% 2	2480
	11th to 20th	Night	35% 7% 13% 30% 15% 1	2472
	21st to end	Night	33% 7% 15% 28% 16% 1	2803
August	1st to 10th	Night	37% 6% 15% 28% 13% 1	2814
	11th to 20th	Night	41% 8% 16% 26% 9%	2812
	21st to end	Night	32% 8% 12% 34% 13% 1	3401
September	1st to 10th	Night	36% 6% 13% 29% 14% 2	1900
	11th to 20th	Night	36% 6% 12% 28% 17% 1	1909
	21st to end	Night	43% 8% 12% 24% 12%	2190
October	1st to 10th	Night	44% 6% 10% 25% 14% 1	3800
	11th to 20th	Night	48% 6% 13% 19% 12% 1	3779
	21st to end	Night	46% 7% 12% 26% 8% 1	4120
November	1st to 10th	Night	48% 7% 11% 21% 10% 2	2566
	11th to 20th	Night	55% 7% 13% 16% 8% 1	2800
	21st to end	Night	61% 7% 14% 14% 3	2800
December	1st to 10th	Night	74% 8% 10% 7% 1	4580
	11th to 20th	Night	68% 6% 7% 11% 7% 1	5208
	21st to end	Night	75% 6% 8% 8% 3	6996

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	29% 33% 26% 9% 3 1	200
	11th to 20th	Day	31% 33% 25% 9% 1	240
	21st to end	Day	25% 32% 30% 10% 3	330
February	1st to 10th	Day	32% 36% 24% 7% 1	300
	11th to 20th	Day	32% 37% 25% 5%	300
	21st to end	Day	40% 24% 28% 7% 1	320
March	1st to 10th	Day	24% 28% 31% 14% 3	460
	11th to 20th	Day	28% 26% 30% 12% 3 1	460
	21st to end	Day	32% 24% 25% 14% 4 1	506
April	1st to 10th	Day	29% 22% 33% 11% 4	460
	11th to 20th	Day	33% 22% 25% 12% 6% 2	452
	21st to end	Day	28% 23% 28% 15% 5% 1	460
May	1st to 10th	Day	27% 15% 31% 17% 6% 3	463
	11th to 20th	Day	17% 16% 34% 23% 8% 2	487
	21st to end	Day	15% 16% 33% 23% 10% 3	529
June	1st to 10th	Day	20% 16% 35% 21% 7% 1	490
	11th to 20th	Day	16% 14% 32% 27% 9% 2	490
	21st to end	Day	15% 15% 38% 21% 9% 1	490
July	1st to 10th	Day	10% 12% 30% 29% 16% 3	485
	11th to 20th	Day	14% 11% 30% 29% 12% 4	484
	21st to end	Day	11% 10% 40% 28% 9% 3	532
August	1st to 10th	Day	12% 10% 30% 28% 14% 6%	486
	11th to 20th	Day	13% 10% 30% 28% 14% 6%	479
	21st to end	Day	14% 10% 31% 25% 14% 6%	539
September	1st to 10th	Day	16% 13% 26% 26% 12% 7%	490
	11th to 20th	Day	13% 10% 21% 25% 20% 10%	490
	21st to end	Day	18% 16% 29% 21% 11% 5%	490
October	1st to 10th	Day	23% 17% 26% 19% 11% 4	490
	11th to 20th	Day	24% 23% 29% 16% 6% 2	490
	21st to end	Day	31% 21% 30% 14% 4	539
November	1st to 10th	Day	23% 22% 30% 16% 7% 1	360
	11th to 20th	Day	26% 29% 30% 11% 3 2	200
	21st to end	Day	31% 27% 34% 8% 2	200
December	1st to 10th	Day	33% 25% 27% 12% 3 1	200
	11th to 20th	Day	32% 32% 27% 8% 3	200
	21st to end	Day	33% 30% 25% 10% 2	220
January	1st to 10th	Night	25% 32% 28% 12% 3	800
	11th to 20th	Night	27% 29% 30% 13% 2	800
	21st to end	Night	21% 30% 32% 14% 4	880
February	1st to 10th	Night	30% 28% 29% 12% 2	800
	11th to 20th	Night	26% 29% 30% 13% 2	783
	21st to end	Night	27% 28% 30% 14% 1	629
March	1st to 10th	Night	26% 21% 34% 16% 4	760
	11th to 20th	Night	28% 21% 31% 16% 3	760
	21st to end	Night	24% 17% 34% 19% 7% 1	836
April	1st to 10th	Night	27% 19% 34% 18% 3	760
	11th to 20th	Night	25% 17% 31% 21% 5% 1	751
	21st to end	Night	24% 13% 31% 25% 7%	622
May	1st to 10th	Night	22% 12% 27% 26% 12% 1	513
	11th to 20th	Night	16% 9% 32% 34% 9%	374
	21st to end	Night	11% 11% 31% 30% 16% 1	411
June	1st to 10th	Night	14% 9% 35% 31% 11% 1	380
	11th to 20th	Night	13% 10% 31% 35% 11%	380
	21st to end	Night	12% 9% 37% 34% 7%	380
July	1st to 10th	Night	8% 5% 30% 37% 18% 2	370
	11th to 20th	Night	10% 8% 31% 32% 19% 1	368
	21st to end	Night	11% 5% 28% 38% 15% 3	511
August	1st to 10th	Night	11% 4 26% 35% 21% 3	567
	11th to 20th	Night	11% 5% 24% 34% 24% 2	564
	21st to end	Night	11% 7% 26% 33% 22% 2	787
September	1st to 10th	Night	16% 8% 25% 31% 18% 3	760
	11th to 20th	Night	15% 6% 21% 28% 25% 5%	760
	21st to end	Night	18% 12% 23% 28% 16% 3	760
October	1st to 10th	Night	21% 13% 26% 23% 14% 2	760
	11th to 20th	Night	24% 19% 29% 21% 6% 1	760
	21st to end	Night	33% 15% 29% 20% 3	836
November	1st to 10th	Night	24% 17% 29% 23% 6% 1	780
	11th to 20th	Night	24% 23% 29% 17% 7% 1	800
	21st to end	Night	28% 23% 30% 14% 5%	800
December	1st to 10th	Night	33% 25% 27% 11% 4	800
	11th to 20th	Night	27% 28% 29% 14% 3	800
	21st to end	Night	33% 23% 29% 13% 2	880

Page generated at 2025-02-18 03:26:27. Version ac07

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