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 2024-01-16.

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	19% 11% 4 7% 6% 3 5% 4 5% 6% 29%	75177
	Night	19% 11% 5% 8% 7% 3 5% 4 5% 6% 28%	74630
Transparency	Day	57% 4 10% 19% 9% 1	74881
	Night	58% 4 11% 18% 8% 1	74461
Seeing	Day	27% 21% 30% 16% 5% 1	16188
	Night	26% 18% 30% 20% 5%	23680

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	16% 19% 8% 12% 9% 4 5% 4 5% 4 13%	1516
	11th to 20th	Day	19% 17% 7% 12% 7% 6% 6% 4 4 5% 14%	1539
	21st to end	Day	13% 10% 6% 12% 12% 6% 7% 6% 4 5% 19%	1782
February	1st to 10th	Day	17% 13% 7% 12% 10% 5% 5% 5% 4 5% 17%	1620
	11th to 20th	Day	18% 14% 6% 11% 9% 4 4 4 5% 5% 19%	1573
	21st to end	Day	10% 13% 6% 10% 8% 5% 5% 4 4 7% 29%	1348
March	1st to 10th	Day	15% 19% 7% 10% 8% 3 4 3 4 3 24%	1975
	11th to 20th	Day	13% 11% 7% 11% 8% 5% 4 4 4 4 29%	1980
	21st to end	Day	16% 17% 7% 8% 5% 3 3 3 3 4 30%	2178
April	1st to 10th	Day	21% 15% 6% 8% 6% 3 4 4 5% 5% 24%	2146
	11th to 20th	Day	20% 12% 3 6% 4 3 4 4 5% 6% 34%	2208
	21st to end	Day	21% 13% 4 6% 6% 3 5% 5% 4 7% 27%	2340
May	1st to 10th	Day	23% 13% 4 7% 5% 3 4 4 5% 7% 25%	2389
	11th to 20th	Day	21% 10% 3 5% 5% 3 4 4 5% 6% 34%	2478
	21st to end	Day	19% 9% 4 6% 6% 3 4 4 5% 8% 31%	2724
June	1st to 10th	Day	27% 8% 4 6% 6% 4 5% 4 5% 7% 26%	2520
	11th to 20th	Day	22% 8% 3 6% 5% 3 4 4 5% 7% 32%	2654
	21st to end	Day	23% 10% 4 7% 6% 3 4 4 5% 7% 27%	2700
July	1st to 10th	Day	16% 6% 3 6% 5% 3 6% 5% 6% 10% 35%	2674
	11th to 20th	Day	14% 8% 3 5% 6% 4 6% 6% 6% 9% 34%	2520
	21st to end	Day	18% 8% 3 6% 6% 5% 6% 5% 6% 8% 28%	2663
August	1st to 10th	Day	16% 6% 2 6% 6% 3 6% 6% 6% 8% 36%	2327
	11th to 20th	Day	16% 8% 3 6% 7% 4 5% 6% 6% 7% 33%	2304
	21st to end	Day	14% 7% 3 5% 5% 3 3 4 6% 8% 43%	2484
September	1st to 10th	Day	17% 6% 3 5% 5% 3 4 4 5% 7% 42%	2160
	11th to 20th	Day	18% 6% 2 5% 5% 3 3 3 4 6% 43%	2084
	21st to end	Day	18% 7% 2 5% 4 3 3 4 5% 6% 42%	1926
October	1st to 10th	Day	18% 7% 2 6% 6% 3 5% 3 5% 7% 38%	1800
	11th to 20th	Day	19% 9% 3 6% 5% 3 5% 5% 5% 7% 33%	1800
	21st to end	Day	20% 13% 4 7% 7% 3 4 4 4 5% 29%	1980
November	1st to 10th	Day	21% 14% 4 6% 6% 5% 5% 3 4 6% 28%	1536
	11th to 20th	Day	19% 17% 6% 7% 5% 4 5% 4 4 6% 24%	1520
	21st to end	Day	17% 17% 6% 10% 6% 4 5% 5% 4 5% 21%	1520
December	1st to 10th	Day	24% 17% 8% 11% 6% 3 4 4 3 5% 16%	1520
	11th to 20th	Day	26% 15% 6% 11% 9% 3 5% 4 4 3 13%	1906
	21st to end	Day	22% 14% 10% 13% 6% 3 4 3 4 5% 16%	2783
January	1st to 10th	Night	16% 16% 8% 13% 8% 3 5% 4 5% 4 16%	2649
	11th to 20th	Night	17% 13% 7% 13% 9% 5% 7% 4 4 5% 16%	2542
	21st to end	Night	13% 12% 6% 12% 11% 4 7% 5% 5% 6% 19%	2574
February	1st to 10th	Night	18% 13% 5% 12% 10% 5% 6% 5% 5% 5% 17%	2340
	11th to 20th	Night	17% 13% 5% 11% 10% 5% 6% 5% 5% 5% 18%	2273
	21st to end	Night	10% 13% 7% 11% 8% 4 4 4 5% 6% 27%	1906
March	1st to 10th	Night	15% 15% 5% 8% 9% 4 4 4 4 5% 26%	1971
	11th to 20th	Night	17% 10% 6% 9% 7% 4 5% 5% 5% 6% 27%	1979
	21st to end	Night	17% 12% 6% 8% 6% 3 4 4 4 5% 31%	2178
April	1st to 10th	Night	22% 12% 5% 6% 6% 3 4 4 5% 5% 27%	1814
	11th to 20th	Night	22% 11% 4 7% 4 2 4 4 4 5% 32%	1698
	21st to end	Night	23% 13% 3 5% 5% 3 4 5% 5% 6% 29%	1620
May	1st to 10th	Night	22% 13% 3 6% 6% 3 5% 4 4 6% 28%	1570
	11th to 20th	Night	23% 8% 3 5% 5% 4 4 4 5% 6% 33%	1416
	21st to end	Night	15% 9% 3 7% 6% 3 5% 5% 6% 8% 33%	1550
June	1st to 10th	Night	25% 7% 3 5% 5% 3 4 4 6% 8% 29%	1440
	11th to 20th	Night	20% 8% 3 5% 6% 4 4 4 5% 6% 34%	1318
	21st to end	Night	22% 7% 4 6% 6% 5% 4 6% 5% 7% 28%	1260
July	1st to 10th	Night	14% 7% 3 5% 5% 3 4 6% 6% 10% 36%	1264
	11th to 20th	Night	15% 6% 3 5% 5% 4 5% 7% 7% 10% 34%	1440
	21st to end	Night	15% 7% 3 6% 5% 4 5% 6% 7% 9% 33%	1652
August	1st to 10th	Night	14% 6% 3 5% 5% 3 4 5% 5% 8% 41%	1612
	11th to 20th	Night	15% 8% 3 6% 6% 4 4 6% 6% 8% 34%	1596
	21st to end	Night	15% 6% 3 5% 4 2 4 4 4 9% 43%	1872
September	1st to 10th	Night	12% 6% 2 5% 6% 3 4 5% 5% 9% 43%	1800
	11th to 20th	Night	17% 7% 2 5% 4 2 3 4 5% 8% 43%	1873
	21st to end	Night	18% 6% 2 5% 5% 3 4 5% 5% 6% 40%	2032
October	1st to 10th	Night	18% 7% 2 5% 4 3 4 4 5% 8% 40%	2160
	11th to 20th	Night	19% 7% 2 5% 6% 3 5% 5% 5% 8% 36%	2160
	21st to end	Night	23% 10% 4 7% 5% 3 4 4 4 6% 30%	2376
November	1st to 10th	Night	21% 11% 4 6% 5% 3 4 4 5% 6% 31%	2538
	11th to 20th	Night	18% 16% 5% 8% 7% 3 5% 4 5% 6% 23%	2660
	21st to end	Night	19% 14% 6% 8% 7% 4 5% 4 4 6% 23%	2660
December	1st to 10th	Night	21% 16% 5% 11% 8% 4 5% 4 4 5% 16%	2660
	11th to 20th	Night	23% 18% 7% 11% 8% 3 4 3 4 3 16%	3293
	21st to end	Night	25% 14% 8% 10% 6% 3 4 3 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	75% 3 10% 8% 3	1517
	11th to 20th	Day	74% 4 9% 11% 2	1539
	21st to end	Day	68% 4 8% 13% 6%	1782
February	1st to 10th	Day	70% 4 8% 12% 5% 1	1620
	11th to 20th	Day	68% 4 9% 12% 6% 1	1581
	21st to end	Day	56% 4 11% 18% 9% 2	1348
March	1st to 10th	Day	67% 3 6% 15% 8% 1	1979
	11th to 20th	Day	60% 3 10% 17% 10% 1	1980
	21st to end	Day	60% 3 6% 18% 10% 2	2178
April	1st to 10th	Day	64% 3 7% 14% 10% 2	2146
	11th to 20th	Day	52% 4 8% 21% 13% 1	2208
	21st to end	Day	58% 4 8% 18% 9% 2	2340
May	1st to 10th	Day	60% 4 8% 17% 9% 1	2389
	11th to 20th	Day	51% 5% 9% 21% 13% 1	2482
	21st to end	Day	53% 6% 11% 21% 8% 1	2724
June	1st to 10th	Day	59% 5% 10% 19% 7% 1	2520
	11th to 20th	Day	53% 4 11% 21% 11% 1	2654
	21st to end	Day	58% 5% 10% 16% 10% 1	2700
July	1st to 10th	Day	44% 6% 16% 22% 11% 1	2600
	11th to 20th	Day	47% 5% 15% 24% 9% 1	2444
	21st to end	Day	52% 7% 13% 22% 5%	2514
August	1st to 10th	Day	46% 6% 14% 23% 10%	2314
	11th to 20th	Day	50% 6% 14% 22% 9%	2304
	21st to end	Day	40% 6% 12% 28% 13% 1	2484
September	1st to 10th	Day	43% 4 12% 25% 14% 2	2160
	11th to 20th	Day	44% 3 11% 24% 15% 2	2084
	21st to end	Day	43% 4 9% 27% 17%	1926
October	1st to 10th	Day	47% 5% 9% 27% 12%	1800
	11th to 20th	Day	51% 5% 12% 24% 7%	1800
	21st to end	Day	60% 4 8% 20% 8% 1	1980
November	1st to 10th	Day	59% 5% 8% 19% 8% 1	1536
	11th to 20th	Day	62% 5% 11% 15% 6% 1	1520
	21st to end	Day	66% 6% 11% 13% 4	1520
December	1st to 10th	Day	71% 4 9% 13% 4	1520
	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	72% 4 10% 12% 2	2649
	11th to 20th	Night	72% 5% 9% 10% 3	2542
	21st to end	Night	66% 5% 10% 14% 5% 1	2574
February	1st to 10th	Night	69% 4 9% 11% 6% 1	2340
	11th to 20th	Night	68% 4 12% 11% 5% 1	2276
	21st to end	Night	59% 4 11% 17% 8% 1	1906
March	1st to 10th	Night	62% 3 9% 16% 8% 1	1980
	11th to 20th	Night	58% 3 11% 15% 10% 2	1980
	21st to end	Night	58% 3 8% 19% 9% 2	2178
April	1st to 10th	Night	61% 4 8% 14% 10% 3	1814
	11th to 20th	Night	55% 3 7% 20% 14% 1	1698
	21st to end	Night	57% 3 10% 16% 11% 2	1620
May	1st to 10th	Night	57% 4 10% 19% 8% 1	1570
	11th to 20th	Night	53% 3 9% 24% 11% 1	1417
	21st to end	Night	49% 7% 14% 22% 6% 1	1551
June	1st to 10th	Night	54% 5% 13% 22% 6%	1440
	11th to 20th	Night	52% 4 11% 21% 12% 1	1318
	21st to end	Night	56% 6% 12% 17% 8% 1	1260
July	1st to 10th	Night	42% 8% 20% 21% 9%	1229
	11th to 20th	Night	45% 6% 17% 21% 9% 1	1392
	21st to end	Night	47% 6% 19% 20% 8% 1	1561
August	1st to 10th	Night	42% 5% 15% 29% 9%	1600
	11th to 20th	Night	49% 5% 18% 20% 8%	1596
	21st to end	Night	39% 5% 16% 29% 11%	1872
September	1st to 10th	Night	39% 5% 13% 29% 12% 2	1800
	11th to 20th	Night	42% 4 11% 29% 14% 1	1873
	21st to end	Night	44% 5% 10% 27% 14% 1	2032
October	1st to 10th	Night	45% 5% 10% 26% 13% 1	2160
	11th to 20th	Night	48% 4 12% 28% 7%	2160
	21st to end	Night	57% 3 11% 18% 10%	2376
November	1st to 10th	Night	55% 4 12% 19% 9% 1	2538
	11th to 20th	Night	63% 4 11% 15% 6%	2660
	21st to end	Night	64% 4 15% 14% 3	2660
December	1st to 10th	Night	71% 4 10% 12% 2	2660
	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	34% 25% 27% 11% 3	356
	21st to end	Day	24% 28% 33% 13% 2	374
February	1st to 10th	Day	27% 30% 31% 9% 2	340
	11th to 20th	Day	32% 32% 23% 11% 1	336
	21st to end	Day	21% 31% 33% 12% 3 1	280
March	1st to 10th	Day	27% 29% 32% 9% 2	420
	11th to 20th	Day	26% 30% 28% 11% 4	420
	21st to end	Day	31% 31% 24% 10% 3	462
April	1st to 10th	Day	37% 26% 29% 6% 2	420
	11th to 20th	Day	28% 30% 29% 9% 2	412
	21st to end	Day	28% 25% 27% 16% 4	420
May	1st to 10th	Day	33% 26% 26% 9% 4 1	472
	11th to 20th	Day	27% 20% 30% 18% 4	624
	21st to end	Day	29% 18% 33% 16% 4 1	680
June	1st to 10th	Day	33% 16% 30% 15% 6%	630
	11th to 20th	Day	27% 16% 30% 21% 5% 1	630
	21st to end	Day	29% 13% 31% 20% 6% 2	630
July	1st to 10th	Day	22% 10% 36% 23% 8% 1	620
	11th to 20th	Day	20% 8% 38% 24% 8% 1	618
	21st to end	Day	24% 10% 32% 26% 7% 1	603
August	1st to 10th	Day	17% 9% 38% 27% 8% 2	446
	11th to 20th	Day	22% 12% 33% 20% 12% 2	439
	21st to end	Day	14% 17% 32% 23% 12% 2	495
September	1st to 10th	Day	19% 13% 35% 24% 8% 1	450
	11th to 20th	Day	27% 15% 28% 21% 7% 2	450
	21st to end	Day	22% 18% 31% 17% 9% 2	423
October	1st to 10th	Day	22% 18% 32% 17% 8% 3	360
	11th to 20th	Day	25% 21% 31% 14% 7% 3	360
	21st to end	Day	29% 26% 26% 14% 4 1	396
November	1st to 10th	Day	26% 22% 30% 15% 5% 1	365
	11th to 20th	Day	35% 21% 29% 10% 5% 1	370
	21st to end	Day	31% 28% 28% 11% 3 1	370
December	1st to 10th	Day	37% 23% 27% 10% 2 1	370
	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	28% 23% 31% 14% 3	802
	21st to end	Night	24% 26% 31% 16% 3	792
February	1st to 10th	Night	28% 25% 31% 15% 1	720
	11th to 20th	Night	31% 28% 27% 12% 2	703
	21st to end	Night	20% 28% 30% 18% 4	592
March	1st to 10th	Night	26% 27% 30% 15% 2	720
	11th to 20th	Night	24% 21% 32% 18% 5%	720
	21st to end	Night	27% 19% 32% 17% 4	792
April	1st to 10th	Night	32% 20% 28% 17% 3	554
	11th to 20th	Night	29% 20% 31% 15% 4 1	534
	21st to end	Night	31% 18% 29% 17% 4	540
May	1st to 10th	Night	29% 17% 31% 18% 5% 1	540
	11th to 20th	Night	29% 13% 31% 21% 5%	532
	21st to end	Night	20% 14% 42% 22% 2	583
June	1st to 10th	Night	28% 13% 32% 23% 4	540
	11th to 20th	Night	23% 11% 36% 26% 4	418
	21st to end	Night	24% 8% 31% 28% 10%	360
July	1st to 10th	Night	18% 6% 33% 33% 10%	354
	11th to 20th	Night	18% 5% 36% 32% 9%	522
	21st to end	Night	18% 7% 31% 35% 9%	590
August	1st to 10th	Night	16% 5% 31% 36% 10% 1	538
	11th to 20th	Night	19% 8% 27% 34% 11% 1	532
	21st to end	Night	17% 7% 29% 33% 13% 1	594
September	1st to 10th	Night	15% 10% 32% 32% 10% 1	540
	11th to 20th	Night	22% 9% 27% 31% 11% 1	613
	21st to end	Night	21% 13% 31% 25% 9% 1	720
October	1st to 10th	Night	23% 11% 31% 25% 9% 1	720
	11th to 20th	Night	23% 15% 35% 19% 8% 1	720
	21st to end	Night	33% 17% 29% 18% 4	792
November	1st to 10th	Night	29% 17% 28% 20% 6% 1	818
	11th to 20th	Night	29% 21% 26% 18% 4 1	850
	21st to end	Night	31% 21% 27% 18% 4	850
December	1st to 10th	Night	34% 20% 29% 14% 3	850
	11th to 20th	Night	32% 26% 29% 11% 2	850
	21st to end	Night	30% 25% 27% 15% 3 1	935

Page generated at 2024-01-13 10:37:52. Version ac07

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