Greenwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greenwood clear sky chart from 2005-11-06 to 2024-11-04.

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% 13% 4 9% 5% 4 4 3 5% 6% 29%	101800
	Night	19% 14% 5% 10% 6% 4 4 3 4 5% 26%	97260
Transparency	Day	56% 6% 11% 17% 9% 1	105381
	Night	59% 6% 11% 16% 7% 1	101768
Seeing	Day	27% 20% 31% 16% 5% 1	16938
	Night	26% 19% 31% 19% 5%	24502

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% 21% 6% 14% 12% 5% 3 2 3 4 15%	2207
	11th to 20th	Day	16% 19% 7% 26% 6% 5% 4 2 3 3 9%	2672
	21st to end	Day	17% 16% 7% 17% 9% 6% 4 3 3 4 16%	3124
February	1st to 10th	Day	18% 18% 7% 14% 11% 6% 4 3 3 4 13%	1710
	11th to 20th	Day	16% 18% 6% 14% 11% 6% 3 3 3 3 16%	1663
	21st to end	Day	11% 16% 7% 10% 8% 5% 4 3 4 5% 28%	1456
March	1st to 10th	Day	24% 19% 5% 9% 6% 6% 3 2 3 4 20%	3412
	11th to 20th	Day	13% 23% 5% 10% 7% 4 4 2 4 4 24%	3480
	21st to end	Day	26% 17% 5% 12% 5% 4 3 3 2 3 20%	3816
April	1st to 10th	Day	22% 17% 4 7% 4 4 3 3 5% 4 27%	2232
	11th to 20th	Day	19% 13% 3 6% 3 3 3 3 4 7% 36%	2381
	21st to end	Day	21% 13% 3 6% 4 5% 3 3 4 6% 32%	2470
May	1st to 10th	Day	23% 19% 3 7% 4 3 4 3 5% 6% 23%	4124
	11th to 20th	Day	19% 10% 3 8% 4 5% 4 3 5% 6% 33%	4398
	21st to end	Day	15% 9% 3 6% 5% 4 5% 4 6% 9% 35%	4836
June	1st to 10th	Day	24% 10% 3 6% 4 4 4 4 6% 6% 28%	2717
	11th to 20th	Day	21% 7% 2 6% 5% 4 4 4 5% 7% 35%	2850
	21st to end	Day	23% 11% 3 7% 5% 5% 4 4 5% 5% 28%	2850
July	1st to 10th	Day	21% 8% 2 6% 4 4 4 4 5% 7% 34%	4760
	11th to 20th	Day	21% 8% 2 5% 4 4 4 4 6% 7% 35%	4550
	21st to end	Day	14% 7% 3 7% 5% 5% 6% 4 7% 9% 34%	4568
August	1st to 10th	Day	21% 10% 3 8% 5% 4 4 3 5% 6% 30%	4105
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 7% 39%	4045
	21st to end	Day	11% 5% 2 5% 3 4 4 3 5% 8% 49%	4418
September	1st to 10th	Day	18% 6% 2 4 4 2 3 3 5% 6% 45%	2280
	11th to 20th	Day	16% 7% 3 6% 4 4 3 3 4 5% 46%	2147
	21st to end	Day	19% 7% 2 6% 4 3 3 3 5% 6% 43%	2066
October	1st to 10th	Day	19% 8% 2 6% 4 3 3 3 5% 7% 38%	1900
	11th to 20th	Day	20% 10% 2 7% 5% 3 4 3 4 7% 34%	1900
	21st to end	Day	21% 14% 3 7% 5% 4 3 3 4 5% 30%	2076
November	1st to 10th	Day	21% 14% 4 8% 5% 4 4 4 3 6% 27%	1576
	11th to 20th	Day	18% 19% 7% 9% 6% 4 4 3 3 5% 22%	1520
	21st to end	Day	19% 21% 7% 12% 5% 5% 3 3 3 4 18%	1520
December	1st to 10th	Day	23% 22% 7% 14% 5% 3 4 2 3 4 14%	1520
	11th to 20th	Day	25% 19% 6% 15% 9% 4 3 3 3 2 11%	1906
	21st to end	Day	21% 19% 10% 16% 7% 3 2 3 3 3 12%	2545
January	1st to 10th	Night	15% 17% 8% 20% 9% 5% 3 3 3 3 15%	4748
	11th to 20th	Night	16% 19% 7% 21% 7% 5% 4 2 4 4 12%	4271
	21st to end	Night	16% 14% 7% 16% 11% 5% 4 3 5% 5% 15%	4532
February	1st to 10th	Night	18% 17% 6% 17% 9% 6% 4 3 3 4 14%	2470
	11th to 20th	Night	18% 15% 6% 14% 10% 5% 4 3 4 4 16%	2403
	21st to end	Night	11% 16% 7% 11% 8% 5% 4 3 4 5% 26%	1994
March	1st to 10th	Night	21% 17% 5% 13% 8% 5% 3 2 3 3 20%	3426
	11th to 20th	Night	16% 21% 9% 11% 6% 5% 5% 2 4 4 17%	3479
	21st to end	Night	25% 15% 7% 10% 6% 3 3 2 3 2 24%	3816
April	1st to 10th	Night	23% 17% 3 7% 5% 4 4 3 3 4 27%	1948
	11th to 20th	Night	21% 13% 4 6% 3 4 3 3 4 7% 31%	1745
	21st to end	Night	22% 14% 3 6% 5% 4 3 2 4 6% 30%	1710
May	1st to 10th	Night	21% 20% 3 6% 4 4 4 3 4 6% 25%	2817
	11th to 20th	Night	20% 9% 3 7% 4 4 5% 4 6% 8% 30%	2506
	21st to end	Night	15% 10% 3 9% 5% 5% 5% 4 6% 7% 31%	2749
June	1st to 10th	Night	26% 8% 3 6% 3 5% 5% 3 6% 8% 27%	1477
	11th to 20th	Night	21% 8% 2 7% 5% 4 5% 3 5% 6% 35%	1330
	21st to end	Night	21% 9% 2 5% 6% 6% 4 4 5% 8% 29%	1330
July	1st to 10th	Night	19% 11% 4 8% 4 5% 5% 4 5% 7% 28%	2210
	11th to 20th	Night	20% 7% 2 6% 4 5% 5% 5% 7% 8% 30%	2384
	21st to end	Night	14% 7% 2 6% 4 5% 5% 4 7% 9% 38%	2985
August	1st to 10th	Night	21% 11% 3 7% 4 4 4 3 6% 7% 31%	2825
	11th to 20th	Night	15% 8% 2 7% 5% 5% 5% 5% 6% 9% 33%	2782
	21st to end	Night	13% 6% 2 5% 4 3 4 4 6% 8% 46%	3238
September	1st to 10th	Night	15% 6% 2 4 4 4 3 4 5% 7% 44%	1900
	11th to 20th	Night	19% 7% 2 5% 3 3 3 3 4 7% 45%	2029
	21st to end	Night	17% 8% 2 6% 4 3 4 4 6% 7% 39%	2114
October	1st to 10th	Night	19% 7% 3 6% 4 4 4 3 5% 6% 40%	2280
	11th to 20th	Night	18% 10% 3 6% 4 5% 4 4 4 6% 35%	2280
	21st to end	Night	25% 12% 3 8% 3 3 4 3 4 5% 30%	2518
November	1st to 10th	Night	21% 14% 3 8% 5% 4 3 3 4 5% 30%	2574
	11th to 20th	Night	18% 21% 6% 10% 5% 4 3 3 4 5% 21%	2660
	21st to end	Night	19% 21% 6% 10% 5% 4 3 3 4 5% 21%	2660
December	1st to 10th	Night	23% 21% 7% 14% 5% 3 4 3 4 4 14%	2660
	11th to 20th	Night	22% 19% 7% 17% 7% 4 3 2 2 3 14%	3293
	21st to end	Night	25% 20% 7% 12% 5% 2 3 2 3 3 18%	5117

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	72% 6% 14% 7% 1	2208
	11th to 20th	Day	79% 5% 6% 8% 2	2672
	21st to end	Day	71% 5% 11% 10% 3	3124
February	1st to 10th	Day	77% 4 7% 8% 4	1710
	11th to 20th	Day	73% 6% 8% 8% 4	1671
	21st to end	Day	60% 5% 10% 17% 8% 1	1456
March	1st to 10th	Day	69% 4 7% 14% 5% 1	3416
	11th to 20th	Day	63% 7% 11% 12% 7% 1	3480
	21st to end	Day	72% 3 5% 11% 7% 1	3816
April	1st to 10th	Day	62% 5% 7% 13% 11% 2	2232
	11th to 20th	Day	51% 6% 8% 21% 13% 1	2381
	21st to end	Day	54% 5% 10% 16% 12% 3	2470
May	1st to 10th	Day	60% 6% 11% 16% 6% 1	4138
	11th to 20th	Day	50% 8% 14% 19% 8% 1	4402
	21st to end	Day	46% 8% 16% 17% 13% 1	4836
June	1st to 10th	Day	55% 7% 10% 20% 8%	2717
	11th to 20th	Day	49% 6% 14% 19% 11% 1	2850
	21st to end	Day	59% 6% 9% 15% 10% 1	2850
July	1st to 10th	Day	50% 5% 13% 19% 12% 1	4685
	11th to 20th	Day	49% 6% 13% 24% 9%	4470
	21st to end	Day	47% 6% 15% 22% 9%	4422
August	1st to 10th	Day	56% 6% 10% 18% 9%	4092
	11th to 20th	Day	45% 6% 14% 23% 11%	4084
	21st to end	Day	36% 4 14% 27% 18% 1	4418
September	1st to 10th	Day	40% 6% 12% 25% 14% 2	2280
	11th to 20th	Day	42% 5% 11% 24% 17% 1	2147
	21st to end	Day	43% 4 10% 26% 16% 1	2066
October	1st to 10th	Day	47% 4 11% 26% 12%	3160
	11th to 20th	Day	47% 4 9% 26% 14%	3140
	21st to end	Day	49% 3 13% 22% 13% 1	3402
November	1st to 10th	Day	60% 6% 9% 16% 8% 1	1576
	11th to 20th	Day	65% 6% 11% 13% 4 1	1520
	21st to end	Day	71% 7% 10% 10% 2	1520
December	1st to 10th	Day	77% 4 8% 8% 3	1520
	11th to 20th	Day	78% 6% 6% 7% 3	1905
	21st to end	Day	77% 5% 10% 6% 2	2545
January	1st to 10th	Night	73% 6% 9% 11% 1	4748
	11th to 20th	Night	75% 7% 8% 8% 3	4271
	21st to end	Night	71% 6% 10% 11% 2	4532
February	1st to 10th	Night	75% 5% 8% 7% 4 1	2470
	11th to 20th	Night	72% 6% 8% 10% 4 1	2406
	21st to end	Night	61% 7% 10% 13% 8% 1	1994
March	1st to 10th	Night	71% 3 7% 12% 6% 1	3435
	11th to 20th	Night	67% 7% 10% 10% 5% 1	3480
	21st to end	Night	68% 4 7% 13% 7% 1	3816
April	1st to 10th	Night	62% 4 9% 12% 10% 3	1948
	11th to 20th	Night	53% 5% 9% 19% 13% 1	1745
	21st to end	Night	57% 5% 9% 15% 12% 2	1710
May	1st to 10th	Night	59% 7% 12% 15% 6% 1	2823
	11th to 20th	Night	50% 9% 15% 21% 5%	2507
	21st to end	Night	49% 10% 17% 18% 5% 1	2750
June	1st to 10th	Night	53% 7% 14% 20% 6%	1477
	11th to 20th	Night	50% 6% 11% 23% 9% 1	1330
	21st to end	Night	54% 8% 11% 18% 8% 1	1330
July	1st to 10th	Night	54% 7% 13% 16% 10%	2175
	11th to 20th	Night	50% 5% 19% 16% 10%	2341
	21st to end	Night	41% 7% 16% 24% 12% 1	2891
August	1st to 10th	Night	52% 7% 13% 22% 7%	2813
	11th to 20th	Night	46% 7% 17% 24% 7%	2809
	21st to end	Night	36% 4 16% 28% 16% 1	3237
September	1st to 10th	Night	39% 8% 10% 28% 14% 2	1900
	11th to 20th	Night	41% 4 12% 28% 15% 1	2029
	21st to end	Night	45% 7% 9% 23% 14% 1	2114
October	1st to 10th	Night	49% 4 11% 24% 11% 1	3800
	11th to 20th	Night	44% 5% 12% 24% 15%	3779
	21st to end	Night	49% 4 11% 23% 13% 1	4142
November	1st to 10th	Night	56% 7% 11% 17% 8%	2574
	11th to 20th	Night	66% 6% 10% 13% 5% 1	2660
	21st to end	Night	66% 6% 14% 11% 2	2660
December	1st to 10th	Night	75% 5% 8% 9% 2	2660
	11th to 20th	Night	76% 5% 7% 9% 2	3295
	21st to end	Night	72% 5% 8% 12% 2	5117

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	33% 31% 26% 10%	180
	11th to 20th	Day	36% 26% 25% 11% 2	356
	21st to end	Day	24% 27% 37% 11% 1	407
February	1st to 10th	Day	30% 27% 29% 12% 1 1	370
	11th to 20th	Day	32% 31% 26% 9% 2	366
	21st to end	Day	23% 31% 32% 12% 3	328
March	1st to 10th	Day	30% 27% 31% 10% 2	460
	11th to 20th	Day	27% 31% 28% 11% 3	460
	21st to end	Day	33% 27% 25% 11% 3	506
April	1st to 10th	Day	37% 28% 26% 6% 3	460
	11th to 20th	Day	29% 31% 27% 11% 2	452
	21st to end	Day	29% 22% 29% 15% 5%	460
May	1st to 10th	Day	30% 25% 30% 12% 3	468
	11th to 20th	Day	26% 19% 28% 20% 6% 1	674
	21st to end	Day	28% 19% 35% 15% 3 1	735
June	1st to 10th	Day	31% 17% 30% 16% 5%	680
	11th to 20th	Day	24% 15% 34% 20% 6% 1	680
	21st to end	Day	26% 16% 32% 19% 6% 1	680
July	1st to 10th	Day	21% 10% 38% 21% 8% 1	670
	11th to 20th	Day	21% 8% 38% 24% 9%	668
	21st to end	Day	20% 10% 36% 26% 7% 1	594
August	1st to 10th	Day	17% 9% 40% 26% 8%	486
	11th to 20th	Day	20% 11% 33% 24% 10% 2	479
	21st to end	Day	18% 15% 30% 25% 9% 3	539
September	1st to 10th	Day	19% 14% 35% 24% 7% 1	490
	11th to 20th	Day	23% 14% 32% 20% 9% 2	490
	21st to end	Day	20% 19% 29% 21% 9% 1	477
October	1st to 10th	Day	23% 16% 28% 22% 8% 3	390
	11th to 20th	Day	28% 20% 28% 16% 6% 2	390
	21st to end	Day	28% 26% 26% 16% 3 1	429
November	1st to 10th	Day	28% 22% 32% 14% 3 1	374
	11th to 20th	Day	35% 23% 25% 11% 4 1	370
	21st to end	Day	31% 26% 33% 7% 2	370
December	1st to 10th	Day	34% 27% 27% 10% 2	370
	11th to 20th	Day	39% 31% 21% 8% 1	370
	21st to end	Day	32% 30% 30% 6% 1 1	260
January	1st to 10th	Night	29% 26% 31% 13% 1	850
	11th to 20th	Night	31% 26% 28% 13% 3	796
	21st to end	Night	23% 27% 33% 14% 3	836
February	1st to 10th	Night	31% 26% 27% 14% 1	760
	11th to 20th	Night	31% 28% 27% 12% 2	743
	21st to end	Night	21% 25% 34% 17% 2	628
March	1st to 10th	Night	27% 25% 32% 14% 2	760
	11th to 20th	Night	24% 23% 32% 16% 4	760
	21st to end	Night	26% 24% 32% 14% 4	836
April	1st to 10th	Night	35% 21% 28% 14% 2	618
	11th to 20th	Night	26% 24% 31% 17% 3	564
	21st to end	Night	27% 20% 30% 19% 4	570
May	1st to 10th	Night	28% 15% 32% 20% 5% 1	570
	11th to 20th	Night	27% 14% 32% 24% 3	562
	21st to end	Night	22% 13% 42% 19% 4	616
June	1st to 10th	Night	29% 12% 34% 21% 5%	527
	11th to 20th	Night	24% 10% 34% 27% 5% 1	380
	21st to end	Night	23% 8% 36% 26% 6% 1	380
July	1st to 10th	Night	19% 5% 42% 28% 6%	370
	11th to 20th	Night	16% 10% 36% 27% 10%	463
	21st to end	Night	17% 8% 31% 38% 6%	623
August	1st to 10th	Night	20% 7% 31% 34% 7%	568
	11th to 20th	Night	17% 9% 30% 32% 12% 1	562
	21st to end	Night	17% 7% 32% 31% 12% 1	627
September	1st to 10th	Night	19% 10% 32% 30% 9% 1	570
	11th to 20th	Night	21% 11% 28% 28% 10% 1	699
	21st to end	Night	21% 14% 32% 24% 9% 1	760
October	1st to 10th	Night	21% 11% 32% 26% 8% 1	760
	11th to 20th	Night	24% 17% 33% 19% 6% 1	760
	21st to end	Night	33% 21% 25% 17% 3	836
November	1st to 10th	Night	31% 17% 29% 17% 5% 1	813
	11th to 20th	Night	27% 27% 26% 15% 4	850
	21st to end	Night	31% 24% 27% 16% 3	850
December	1st to 10th	Night	33% 22% 31% 12% 2	850
	11th to 20th	Night	32% 29% 27% 10% 2	850
	21st to end	Night	33% 25% 27% 13% 2	935

Page generated at 2024-11-01 23:47:42. Version ac07

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