Windsor
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Windsor clear sky chart from 2005-11-06 to 2024-12-06.

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	18% 12% 4 9% 5% 5% 4 3 5% 6% 28%	102420
	Night	18% 12% 4 10% 6% 4 4 3 5% 6% 27%	97378
Transparency	Day	56% 5% 11% 18% 9% 1	106015
	Night	58% 4 11% 18% 8% 1	101872
Seeing	Day	27% 20% 30% 16% 5% 1	17453
	Night	26% 18% 30% 21% 5%	24821

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	15% 19% 6% 13% 8% 5% 4 3 4 4 20%	2526
	11th to 20th	Day	13% 15% 7% 21% 7% 6% 5% 3 4 5% 14%	2627
	21st to end	Day	17% 13% 6% 14% 8% 6% 4 4 4 6% 19%	3124
February	1st to 10th	Day	17% 15% 6% 12% 9% 5% 5% 4 5% 5% 17%	1710
	11th to 20th	Day	17% 15% 6% 12% 8% 5% 3 4 5% 5% 19%	1663
	21st to end	Day	10% 15% 5% 9% 8% 6% 4 4 4 6% 29%	1430
March	1st to 10th	Day	23% 18% 4 8% 5% 5% 3 3 3 4 23%	3429
	11th to 20th	Day	12% 21% 7% 11% 7% 5% 4 3 4 5% 23%	3480
	21st to end	Day	24% 19% 6% 11% 5% 4 4 2 3 3 21%	3816
April	1st to 10th	Day	20% 17% 5% 9% 5% 4 4 3 5% 5% 25%	2266
	11th to 20th	Day	19% 13% 3 7% 4 4 4 3 5% 6% 33%	2333
	21st to end	Day	20% 14% 3 7% 5% 4 4 4 4 7% 28%	2470
May	1st to 10th	Day	24% 18% 3 7% 4 4 4 3 5% 7% 22%	4197
	11th to 20th	Day	20% 12% 3 7% 4 5% 4 3 5% 6% 31%	4398
	21st to end	Day	15% 9% 3 7% 5% 5% 4 4 7% 10% 31%	4836
June	1st to 10th	Day	26% 10% 3 7% 5% 4 5% 4 5% 7% 25%	2660
	11th to 20th	Day	21% 9% 3 6% 5% 4 4 3 5% 7% 33%	2802
	21st to end	Day	23% 11% 3 8% 6% 4 4 3 5% 6% 27%	2850
July	1st to 10th	Day	20% 9% 3 6% 5% 5% 5% 4 6% 8% 30%	4706
	11th to 20th	Day	14% 8% 3 8% 6% 5% 5% 5% 6% 8% 32%	4440
	21st to end	Day	14% 8% 3 8% 6% 6% 6% 4 7% 9% 30%	4666
August	1st to 10th	Day	18% 10% 3 9% 5% 5% 5% 4 6% 6% 28%	4105
	11th to 20th	Day	14% 7% 3 8% 6% 5% 5% 4 6% 7% 34%	4045
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 8% 44%	4372
September	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 5% 7% 42%	2280
	11th to 20th	Day	18% 6% 2 6% 4 3 3 3 5% 6% 43%	2199
	21st to end	Day	18% 7% 2 6% 4 3 3 3 5% 7% 41%	2033
October	1st to 10th	Day	17% 7% 3 7% 5% 4 4 3 6% 7% 37%	1900
	11th to 20th	Day	18% 9% 3 6% 4 4 5% 4 5% 7% 34%	1900
	21st to end	Day	19% 14% 4 8% 6% 4 4 3 4 5% 30%	2090
November	1st to 10th	Day	20% 15% 3 7% 5% 5% 5% 2 4 5% 28%	1618
	11th to 20th	Day	19% 20% 5% 8% 5% 4 5% 3 4 5% 22%	1600
	21st to end	Day	17% 18% 6% 11% 5% 5% 4 4 4 5% 20%	1600
December	1st to 10th	Day	23% 18% 7% 11% 5% 4 3 3 4 5% 16%	1560
	11th to 20th	Day	26% 17% 6% 12% 8% 4 4 3 4 3 13%	1906
	21st to end	Day	21% 15% 10% 14% 5% 4 3 3 4 5% 16%	2783
January	1st to 10th	Night	14% 13% 7% 18% 7% 4 4 3 5% 5% 19%	4429
	11th to 20th	Night	15% 16% 6% 19% 7% 6% 5% 3 4 4 15%	4339
	21st to end	Night	16% 13% 5% 16% 9% 5% 5% 4 5% 5% 17%	4532
February	1st to 10th	Night	18% 15% 5% 13% 9% 6% 5% 4 5% 5% 17%	2470
	11th to 20th	Night	16% 14% 5% 12% 9% 7% 5% 4 5% 5% 19%	2403
	21st to end	Night	10% 15% 6% 12% 7% 5% 4 3 5% 6% 28%	2021
March	1st to 10th	Night	22% 15% 4 11% 8% 5% 3 2 3 4 22%	3410
	11th to 20th	Night	17% 20% 7% 10% 5% 4 4 3 4 5% 21%	3479
	21st to end	Night	23% 15% 6% 13% 5% 3 3 2 3 3 23%	3816
April	1st to 10th	Night	21% 14% 5% 7% 5% 4 4 3 5% 4 28%	1914
	11th to 20th	Night	21% 12% 4 8% 3 4 4 3 4 5% 32%	1793
	21st to end	Night	22% 13% 2 6% 5% 4 4 4 5% 6% 30%	1710
May	1st to 10th	Night	21% 21% 3 6% 5% 4 4 3 5% 5% 23%	2745
	11th to 20th	Night	20% 11% 3 7% 4 5% 4 4 5% 6% 32%	2506
	21st to end	Night	15% 9% 4 9% 5% 4 5% 4 6% 8% 31%	2749
June	1st to 10th	Night	25% 9% 3 7% 4 4 4 3 6% 7% 28%	1520
	11th to 20th	Night	19% 9% 2 6% 5% 5% 4 3 6% 6% 35%	1391
	21st to end	Night	22% 8% 3 7% 6% 5% 5% 4 6% 7% 27%	1330
July	1st to 10th	Night	15% 10% 3 9% 6% 6% 5% 6% 6% 8% 28%	2228
	11th to 20th	Night	15% 7% 3 7% 3 5% 4 5% 7% 11% 34%	2530
	21st to end	Night	11% 7% 2 6% 4 4 4 4 7% 8% 42%	2891
August	1st to 10th	Night	17% 9% 3 8% 4 4 5% 4 5% 8% 34%	2825
	11th to 20th	Night	12% 8% 3 7% 6% 5% 5% 4 6% 8% 36%	2782
	21st to end	Night	13% 5% 2 5% 3 3 4 3 5% 8% 50%	3284
September	1st to 10th	Night	12% 7% 2 6% 5% 4 5% 3 5% 8% 44%	1900
	11th to 20th	Night	16% 7% 2 6% 3 3 3 3 5% 8% 44%	1978
	21st to end	Night	18% 6% 2 6% 4 4 5% 3 5% 6% 39%	2145
October	1st to 10th	Night	18% 7% 2 6% 4 4 5% 3 5% 7% 39%	2280
	11th to 20th	Night	18% 8% 2 5% 5% 4 5% 3 5% 8% 37%	2280
	21st to end	Night	23% 10% 3 7% 4 3 4 3 4 6% 32%	2508
November	1st to 10th	Night	20% 12% 4 7% 5% 4 4 3 5% 5% 31%	2676
	11th to 20th	Night	18% 19% 4 9% 5% 5% 4 3 5% 6% 22%	2800
	21st to end	Night	21% 15% 5% 9% 6% 5% 4 3 4 6% 22%	2800
December	1st to 10th	Night	21% 18% 4 12% 7% 6% 4 3 4 5% 16%	2737
	11th to 20th	Night	23% 19% 6% 12% 7% 4 3 3 4 3 15%	3293
	21st to end	Night	25% 15% 7% 11% 5% 4 3 2 4 4 20%	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	68% 5% 15% 10% 2	2527
	11th to 20th	Day	73% 4 7% 13% 2	2627
	21st to end	Day	67% 3 9% 12% 8%	3124
February	1st to 10th	Day	70% 4 8% 12% 6% 1	1710
	11th to 20th	Day	68% 4 9% 13% 6% 1	1671
	21st to end	Day	56% 4 10% 18% 10% 2	1430
March	1st to 10th	Day	66% 2 7% 16% 7% 1	3433
	11th to 20th	Day	65% 3 9% 15% 6% 1	3480
	21st to end	Day	72% 2 4 12% 8% 1	3816
April	1st to 10th	Day	63% 3 7% 14% 11% 2	2266
	11th to 20th	Day	53% 4 8% 21% 12% 1	2333
	21st to end	Day	56% 4 8% 18% 11% 2	2470
May	1st to 10th	Day	64% 3 10% 16% 7% 1	4211
	11th to 20th	Day	55% 5% 13% 20% 7%	4402
	21st to end	Day	50% 5% 16% 19% 10% 1	4836
June	1st to 10th	Day	59% 5% 11% 19% 7%	2660
	11th to 20th	Day	51% 4 12% 21% 11% 1	2802
	21st to end	Day	59% 5% 10% 16% 10% 1	2850
July	1st to 10th	Day	51% 5% 14% 18% 12% 1	4632
	11th to 20th	Day	49% 7% 14% 21% 8% 1	4364
	21st to end	Day	46% 9% 15% 21% 8%	4517
August	1st to 10th	Day	57% 6% 11% 18% 8%	4092
	11th to 20th	Day	47% 7% 14% 23% 9%	4084
	21st to end	Day	35% 8% 14% 26% 17% 1	4372
September	1st to 10th	Day	43% 4 12% 25% 14% 2	2280
	11th to 20th	Day	44% 4 11% 25% 15% 2	2199
	21st to end	Day	44% 4 9% 27% 16%	2033
October	1st to 10th	Day	44% 9% 13% 23% 11%	3160
	11th to 20th	Day	44% 6% 10% 27% 13%	3140
	21st to end	Day	48% 4 14% 22% 12%	3428
November	1st to 10th	Day	59% 5% 9% 19% 8% 1	1618
	11th to 20th	Day	64% 5% 11% 15% 5% 1	1600
	21st to end	Day	67% 6% 11% 13% 4	1600
December	1st to 10th	Day	71% 4 9% 13% 4	1560
	11th to 20th	Day	77% 3 7% 10% 3 1	1905
	21st to end	Day	73% 2 13% 9% 3	2783
January	1st to 10th	Night	66% 5% 11% 16% 2	4429
	11th to 20th	Night	74% 4 7% 10% 4	4339
	21st to end	Night	68% 4 9% 13% 5% 1	4532
February	1st to 10th	Night	70% 3 9% 11% 6% 1	2470
	11th to 20th	Night	67% 4 11% 12% 5% 1	2406
	21st to end	Night	59% 4 11% 18% 8% 1	2021
March	1st to 10th	Night	69% 2 6% 15% 7% 1	3419
	11th to 20th	Night	67% 3 9% 14% 7% 1	3480
	21st to end	Night	69% 2 7% 14% 7% 1	3816
April	1st to 10th	Night	61% 4 8% 14% 10% 3	1914
	11th to 20th	Night	55% 3 7% 21% 14% 1	1793
	21st to end	Night	57% 3 10% 16% 12% 2	1710
May	1st to 10th	Night	63% 3 13% 14% 6% 1	2751
	11th to 20th	Night	54% 3 13% 23% 7% 1	2507
	21st to end	Night	53% 5% 17% 19% 5% 1	2750
June	1st to 10th	Night	55% 5% 13% 21% 6%	1520
	11th to 20th	Night	50% 4 12% 22% 12% 1	1391
	21st to end	Night	56% 6% 12% 17% 8% 1	1330
July	1st to 10th	Night	52% 9% 15% 15% 9% 1	2193
	11th to 20th	Night	46% 7% 19% 18% 10%	2482
	21st to end	Night	41% 7% 16% 24% 12% 1	2800
August	1st to 10th	Night	50% 7% 15% 23% 6%	2813
	11th to 20th	Night	45% 7% 17% 23% 7%	2809
	21st to end	Night	32% 6% 18% 28% 16%	3283
September	1st to 10th	Night	39% 5% 12% 29% 14% 2	1900
	11th to 20th	Night	41% 4 11% 30% 14% 1	1978
	21st to end	Night	44% 6% 10% 26% 13% 1	2145
October	1st to 10th	Night	47% 6% 12% 24% 11%	3800
	11th to 20th	Night	40% 6% 12% 26% 15%	3779
	21st to end	Night	44% 4 14% 23% 14%	4120
November	1st to 10th	Night	55% 4 12% 19% 9% 1	2676
	11th to 20th	Night	65% 4 10% 15% 6%	2800
	21st to end	Night	65% 4 14% 14% 3	2800
December	1st to 10th	Night	71% 4 10% 13% 2	2737
	11th to 20th	Night	76% 3 7% 10% 4	3295
	21st to end	Night	70% 2 10% 14% 3	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	29% 27% 29% 14% 1	370
	11th to 20th	Day	35% 24% 27% 11% 3	370
	21st to end	Day	25% 28% 32% 12% 2	407
February	1st to 10th	Day	27% 29% 30% 11% 2	370
	11th to 20th	Day	33% 32% 24% 11% 1	366
	21st to end	Day	22% 30% 32% 12% 3 1	307
March	1st to 10th	Day	30% 27% 32% 9% 2	460
	11th to 20th	Day	27% 30% 28% 11% 4	460
	21st to end	Day	34% 30% 24% 9% 3	506
April	1st to 10th	Day	37% 26% 28% 6% 2	460
	11th to 20th	Day	30% 29% 29% 9% 2	452
	21st to end	Day	29% 25% 26% 15% 4	460
May	1st to 10th	Day	33% 26% 26% 9% 4 1	515
	11th to 20th	Day	26% 20% 30% 19% 5% 1	674
	21st to end	Day	28% 18% 33% 16% 4 1	735
June	1st to 10th	Day	34% 16% 30% 15% 6%	680
	11th to 20th	Day	26% 16% 31% 21% 6% 1	680
	21st to end	Day	31% 13% 30% 19% 6% 1	680
July	1st to 10th	Day	23% 10% 36% 23% 8% 1	670
	11th to 20th	Day	20% 9% 38% 23% 8% 1	668
	21st to end	Day	22% 11% 33% 26% 6% 1	653
August	1st to 10th	Day	17% 9% 37% 27% 7% 2	486
	11th to 20th	Day	21% 12% 34% 19% 11% 3	479
	21st to end	Day	14% 17% 33% 22% 11% 4	539
September	1st to 10th	Day	19% 14% 36% 23% 8% 1	490
	11th to 20th	Day	26% 14% 28% 21% 9% 2	490
	21st to end	Day	22% 18% 30% 19% 9% 2	460
October	1st to 10th	Day	21% 18% 32% 18% 8% 3	390
	11th to 20th	Day	25% 22% 31% 14% 6% 2	390
	21st to end	Day	28% 26% 27% 15% 4 1	429
November	1st to 10th	Day	27% 23% 30% 15% 5% 1	395
	11th to 20th	Day	38% 22% 27% 9% 5% 1	400
	21st to end	Day	33% 26% 27% 11% 3 1	400
December	1st to 10th	Day	36% 23% 28% 10% 2 1	385
	11th to 20th	Day	35% 29% 25% 9% 1	370
	21st to end	Day	30% 29% 29% 8% 3 1	407
January	1st to 10th	Night	28% 23% 33% 15% 1	850
	11th to 20th	Night	29% 24% 31% 14% 3	820
	21st to end	Night	24% 26% 31% 16% 3	836
February	1st to 10th	Night	28% 24% 31% 16% 2	760
	11th to 20th	Night	30% 28% 28% 12% 2	743
	21st to end	Night	20% 27% 30% 19% 4	628
March	1st to 10th	Night	27% 26% 30% 15% 2	760
	11th to 20th	Night	24% 21% 32% 18% 5%	760
	21st to end	Night	28% 20% 31% 16% 4	836
April	1st to 10th	Night	31% 21% 28% 17% 3	584
	11th to 20th	Night	29% 20% 31% 16% 4 1	564
	21st to end	Night	31% 18% 29% 16% 5%	570
May	1st to 10th	Night	29% 16% 31% 18% 5% 1	570
	11th to 20th	Night	28% 12% 31% 22% 6% 1	562
	21st to end	Night	20% 14% 41% 22% 2	616
June	1st to 10th	Night	28% 14% 33% 22% 4	570
	11th to 20th	Night	22% 10% 36% 26% 5%	441
	21st to end	Night	24% 8% 31% 28% 9%	380
July	1st to 10th	Night	19% 6% 33% 32% 10%	375
	11th to 20th	Night	17% 5% 35% 32% 9%	552
	21st to end	Night	17% 7% 31% 35% 9%	623
August	1st to 10th	Night	17% 5% 31% 36% 10% 1	568
	11th to 20th	Night	18% 8% 27% 35% 12% 1	562
	21st to end	Night	17% 7% 29% 33% 13% 1	627
September	1st to 10th	Night	15% 10% 33% 31% 10% 1	570
	11th to 20th	Night	21% 9% 26% 32% 12% 1	648
	21st to end	Night	22% 13% 30% 25% 9% 1	760
October	1st to 10th	Night	22% 11% 31% 26% 10% 1	760
	11th to 20th	Night	23% 16% 34% 19% 8% 1	760
	21st to end	Night	32% 17% 29% 18% 4	836
November	1st to 10th	Night	29% 18% 28% 19% 5% 1	867
	11th to 20th	Night	31% 21% 26% 18% 4 1	900
	21st to end	Night	33% 20% 26% 17% 3	900
December	1st to 10th	Night	33% 20% 29% 14% 3	878
	11th to 20th	Night	32% 26% 29% 11% 2	850
	21st to end	Night	30% 25% 27% 15% 3 1	935

Page generated at 2024-12-03 07:45:15. Version ac07

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