Metcalf Nature Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Metcalf Nature Center clear sky chart from 2005-11-06 to 2026-08-30.

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	12% 9% 3 8% 5% 4 4 4 5% 7% 39%	144801
	Night	11% 9% 4 9% 5% 4 4 4 5% 6% 38%	137779
Transparency	Day	43% 5% 13% 26% 12% 1	148353
	Night	45% 5% 12% 23% 13% 1	142307
Seeing	Day	16% 11% 31% 26% 13% 3	18592
	Night	16% 9% 32% 32% 10% 1	28371

By Month

Percentage Cloud Cover SE (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	9% 13% 6% 20% 8% 5% 5% 3 4 6% 21%	4691
	11th to 20th	Day	5% 13% 7% 14% 7% 6% 8% 8% 7% 4 21%	4710
	21st to end	Day	5% 13% 6% 10% 5% 5% 6% 4 6% 7% 33%	5789
February	1st to 10th	Day	8% 11% 5% 11% 7% 6% 6% 5% 6% 6% 29%	1890
	11th to 20th	Day	8% 10% 6% 10% 5% 6% 4 4 5% 6% 35%	1844
	21st to end	Day	11% 11% 4 10% 6% 5% 5% 4 6% 7% 32%	1642
March	1st to 10th	Day	12% 8% 3 6% 4 3 3 3 5% 7% 46%	4879
	11th to 20th	Day	10% 9% 3 7% 4 4 4 4 6% 8% 40%	5090
	21st to end	Day	22% 11% 3 9% 5% 4 4 3 5% 6% 27%	5692
April	1st to 10th	Day	17% 11% 4 7% 5% 4 4 3 5% 7% 33%	2520
	11th to 20th	Day	19% 12% 4 8% 4 4 4 3 4 5% 31%	2494
	21st to end	Day	20% 11% 4 7% 5% 4 5% 4 5% 6% 30%	2711
May	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 5% 7% 49%	8025
	11th to 20th	Day	15% 8% 2 6% 3 3 4 3 4 7% 45%	8222
	21st to end	Day	15% 8% 2 7% 4 4 4 3 5% 7% 39%	9047
June	1st to 10th	Day	12% 6% 2 4 4 4 5% 4 6% 9% 45%	2940
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 4 7% 8% 36%	2940
	21st to end	Day	11% 5% 2 6% 6% 5% 6% 4 7% 9% 39%	2940
July	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 7% 11% 39%	8280
	11th to 20th	Day	7% 3 2 3 3 3 3 3 5% 8% 60%	8280
	21st to end	Day	8% 4 2 6% 4 4 4 4 6% 9% 48%	8977
August	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 9% 43%	4364
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 6% 8% 44%	4301
	21st to end	Day	9% 6% 2 7% 4 4 5% 4 5% 7% 47%	4538
September	1st to 10th	Day	12% 6% 2 5% 5% 4 4 3 5% 8% 46%	2400
	11th to 20th	Day	12% 6% 1 6% 4 4 4 4 6% 8% 44%	2400
	21st to end	Day	13% 6% 3 6% 4 4 3 4 6% 7% 45%	2085
October	1st to 10th	Day	15% 7% 2 5% 4 3 4 3 5% 6% 46%	2000
	11th to 20th	Day	14% 11% 2 6% 5% 4 5% 4 4 7% 38%	2000
	21st to end	Day	17% 13% 3 7% 3 4 4 3 4 6% 37%	2150
November	1st to 10th	Day	12% 13% 3 9% 5% 4 4 3 5% 6% 35%	1752
	11th to 20th	Day	12% 14% 6% 10% 7% 3 4 3 5% 6% 29%	1680
	21st to end	Day	13% 13% 4 9% 6% 3 3 3 5% 7% 33%	1680
December	1st to 10th	Day	8% 11% 5% 16% 12% 6% 5% 5% 5% 6% 23%	2690
	11th to 20th	Day	11% 15% 7% 10% 8% 4 5% 3 5% 5% 27%	3088
	21st to end	Day	19% 21% 8% 18% 5% 4 3 2 3 3 14%	4070
January	1st to 10th	Night	8% 13% 6% 15% 8% 5% 4 3 5% 6% 27%	8232
	11th to 20th	Night	6% 13% 5% 13% 8% 7% 9% 8% 6% 4 20%	8280
	21st to end	Night	7% 14% 6% 10% 5% 5% 5% 3 6% 6% 34%	8422
February	1st to 10th	Night	6% 12% 5% 11% 7% 6% 5% 4 5% 6% 33%	2730
	11th to 20th	Night	8% 9% 4 8% 6% 6% 5% 4 5% 7% 39%	2663
	21st to end	Night	11% 11% 3 9% 6% 5% 4 4 5% 6% 36%	2162
March	1st to 10th	Night	10% 6% 3 7% 4 4 4 4 5% 7% 46%	5226
	11th to 20th	Night	10% 7% 3 7% 5% 4 5% 4 7% 8% 39%	5090
	21st to end	Night	24% 11% 4 10% 4 3 3 3 4 4 29%	5477
April	1st to 10th	Night	17% 12% 3 7% 3 4 4 3 6% 6% 36%	2100
	11th to 20th	Night	20% 10% 2 7% 4 4 4 3 5% 5% 36%	2075
	21st to end	Night	18% 10% 3 7% 4 4 4 3 5% 7% 36%	1906
May	1st to 10th	Night	10% 7% 2 6% 4 4 4 4 5% 6% 50%	4855
	11th to 20th	Night	17% 5% 2 4 4 3 3 3 5% 6% 49%	4670
	21st to end	Night	14% 9% 3 8% 5% 4 4 3 5% 7% 38%	5139
June	1st to 10th	Night	11% 5% 2 4 4 4 4 5% 6% 8% 46%	1680
	11th to 20th	Night	10% 6% 2 5% 5% 5% 5% 4 7% 8% 45%	1680
	21st to end	Night	7% 5% 2 5% 4 4 5% 5% 6% 8% 50%	1680
July	1st to 10th	Night	10% 4 1 5% 4 5% 5% 4 6% 10% 46%	4708
	11th to 20th	Night	5% 3 1 4 3 3 4 3 7% 10% 57%	4707
	21st to end	Night	8% 4 2 5% 4 4 4 4 6% 7% 51%	5117
August	1st to 10th	Night	12% 7% 3 7% 4 3 4 4 5% 7% 47%	3014
	11th to 20th	Night	14% 5% 2 4 3 3 4 4 6% 8% 49%	2978
	21st to end	Night	9% 6% 2 6% 4 5% 4 3 5% 7% 48%	3559
September	1st to 10th	Night	10% 5% 2 5% 3 4 4 4 5% 6% 53%	2000
	11th to 20th	Night	9% 5% 2 5% 3 4 4 4 6% 8% 52%	2000
	21st to end	Night	13% 4 2 4 4 4 3 2 5% 6% 52%	2291
October	1st to 10th	Night	14% 6% 2 6% 4 3 3 3 4 6% 51%	2400
	11th to 20th	Night	17% 9% 3 6% 4 3 3 3 5% 7% 41%	2400
	21st to end	Night	18% 11% 3 7% 3 3 4 2 4 7% 37%	2688
November	1st to 10th	Night	13% 11% 3 7% 4 4 3 4 5% 7% 41%	2761
	11th to 20th	Night	13% 12% 5% 10% 5% 4 4 4 4 5% 34%	2940
	21st to end	Night	13% 11% 4 10% 5% 4 4 3 4 7% 36%	2940
December	1st to 10th	Night	7% 10% 5% 15% 8% 8% 4 3 5% 6% 29%	4720
	11th to 20th	Night	10% 17% 7% 14% 6% 5% 5% 4 4 5% 23%	5339
	21st to end	Night	21% 16% 9% 16% 5% 3 4 2 4 4 17%	7150

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	66% 4 10% 16% 4	4692
	11th to 20th	Day	62% 4 7% 16% 10%	4710
	21st to end	Day	50% 5% 14% 21% 9%	5789
February	1st to 10th	Day	53% 6% 14% 17% 8% 1	1890
	11th to 20th	Day	50% 5% 12% 26% 8%	1853
	21st to end	Day	50% 6% 13% 20% 10% 1	1642
March	1st to 10th	Day	38% 5% 18% 25% 12% 3	4879
	11th to 20th	Day	42% 4 16% 28% 10% 1	5090
	21st to end	Day	59% 5% 10% 18% 8% 1	5694
April	1st to 10th	Day	50% 5% 12% 21% 12% 1	2520
	11th to 20th	Day	54% 5% 11% 17% 11% 2	2494
	21st to end	Day	54% 6% 12% 19% 9%	2711
May	1st to 10th	Day	34% 5% 11% 30% 18% 2	8064
	11th to 20th	Day	39% 4 9% 25% 18% 4	8226
	21st to end	Day	44% 6% 10% 28% 11% 1	9061
June	1st to 10th	Day	35% 8% 14% 29% 13% 1	2940
	11th to 20th	Day	43% 8% 14% 22% 12% 1	2940
	21st to end	Day	39% 9% 15% 26% 10% 1	2940
July	1st to 10th	Day	36% 7% 17% 31% 7%	8211
	11th to 20th	Day	23% 5% 14% 40% 18% 1	8205
	21st to end	Day	31% 7% 14% 30% 17% 1	8781
August	1st to 10th	Day	37% 7% 13% 28% 13% 1	4350
	11th to 20th	Day	36% 6% 14% 33% 10%	4340
	21st to end	Day	36% 6% 16% 28% 13% 1	4537
September	1st to 10th	Day	35% 6% 15% 31% 13%	2400
	11th to 20th	Day	36% 8% 17% 31% 8%	2400
	21st to end	Day	38% 7% 11% 32% 11%	2085
October	1st to 10th	Day	29% 4 8% 35% 23% 1	3260
	11th to 20th	Day	39% 4 12% 26% 17% 1	3240
	21st to end	Day	44% 4 15% 28% 9%	3452
November	1st to 10th	Day	49% 5% 13% 18% 12% 2	1752
	11th to 20th	Day	56% 6% 12% 17% 8% 1	1680
	21st to end	Day	51% 6% 17% 19% 6% 1	1680
December	1st to 10th	Day	62% 6% 15% 13% 5%	2690
	11th to 20th	Day	59% 4 13% 18% 6%	3085
	21st to end	Day	76% 4 8% 8% 4	4070
January	1st to 10th	Night	58% 4 14% 17% 6%	8233
	11th to 20th	Night	63% 5% 10% 14% 8%	8280
	21st to end	Night	50% 4 11% 24% 11%	8422
February	1st to 10th	Night	52% 5% 12% 21% 9% 1	2730
	11th to 20th	Night	44% 5% 15% 26% 9% 1	2664
	21st to end	Night	48% 5% 12% 22% 11% 1	2162
March	1st to 10th	Night	38% 4 15% 24% 17% 3	5226
	11th to 20th	Night	40% 5% 16% 24% 14% 1	5090
	21st to end	Night	59% 4 10% 17% 10%	5477
April	1st to 10th	Night	49% 5% 9% 22% 15% 1	2100
	11th to 20th	Night	49% 5% 10% 19% 14% 2	2075
	21st to end	Night	48% 5% 9% 21% 14% 2	1906
May	1st to 10th	Night	34% 5% 9% 30% 20% 1	4881
	11th to 20th	Night	37% 4 10% 21% 22% 6%	4671
	21st to end	Night	45% 6% 10% 25% 13% 2	5149
June	1st to 10th	Night	34% 6% 14% 28% 17% 2	1680
	11th to 20th	Night	36% 7% 14% 23% 18% 2	1680
	21st to end	Night	30% 7% 16% 29% 15% 3	1680
July	1st to 10th	Night	33% 7% 19% 29% 11% 1	4670
	11th to 20th	Night	22% 6% 13% 38% 20% 1	4662
	21st to end	Night	31% 6% 14% 30% 18% 2	5002
August	1st to 10th	Night	37% 6% 12% 28% 14% 3	3005
	11th to 20th	Night	33% 7% 14% 31% 14% 1	3005
	21st to end	Night	35% 7% 16% 28% 12% 2	3559
September	1st to 10th	Night	31% 6% 13% 34% 16% 1	2000
	11th to 20th	Night	30% 6% 18% 30% 16%	2000
	21st to end	Night	33% 5% 14% 31% 15% 1	2291
October	1st to 10th	Night	25% 3 7% 35% 26% 4	3920
	11th to 20th	Night	34% 5% 12% 24% 22% 2	3899
	21st to end	Night	45% 5% 11% 27% 13%	4336
November	1st to 10th	Night	43% 6% 12% 24% 14% 1	2761
	11th to 20th	Night	53% 6% 12% 18% 10% 1	2940
	21st to end	Night	50% 5% 16% 22% 7% 1	2940
December	1st to 10th	Night	55% 6% 16% 18% 4	4720
	11th to 20th	Night	64% 5% 11% 15% 5% 1	5341
	21st to end	Night	72% 4 9% 12% 4	7150

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	15% 12% 35% 27% 10% 2	330
	11th to 20th	Day	16% 14% 43% 22% 5%	330
	21st to end	Day	13% 12% 41% 23% 8% 2	363
February	1st to 10th	Day	14% 18% 42% 19% 4 2	330
	11th to 20th	Day	13% 16% 42% 22% 7% 1	330
	21st to end	Day	17% 14% 41% 25% 3	273
March	1st to 10th	Day	18% 13% 44% 19% 6%	330
	11th to 20th	Day	20% 15% 37% 21% 6% 1	330
	21st to end	Day	27% 16% 27% 22% 6% 3	408
April	1st to 10th	Day	23% 18% 33% 21% 5%	540
	11th to 20th	Day	27% 17% 24% 24% 7% 1	532
	21st to end	Day	26% 14% 30% 21% 8% 1	731
May	1st to 10th	Day	18% 16% 29% 24% 11% 2	753
	11th to 20th	Day	20% 14% 29% 23% 12% 3	775
	21st to end	Day	18% 10% 30% 24% 16% 3	844
June	1st to 10th	Day	11% 10% 26% 33% 18% 3	780
	11th to 20th	Day	15% 13% 34% 26% 10% 2	780
	21st to end	Day	13% 9% 32% 27% 15% 4	780
July	1st to 10th	Day	9% 4 21% 33% 24% 10%	771
	11th to 20th	Day	8% 5% 28% 30% 21% 7%	768
	21st to end	Day	6% 4 27% 38% 18% 7%	849
August	1st to 10th	Day	10% 6% 24% 34% 21% 6%	776
	11th to 20th	Day	14% 5% 21% 33% 23% 5%	765
	21st to end	Day	10% 7% 24% 34% 19% 5%	698
September	1st to 10th	Day	14% 8% 29% 28% 17% 5%	530
	11th to 20th	Day	13% 5% 28% 30% 21% 3	530
	21st to end	Day	14% 17% 26% 22% 16% 6%	330
October	1st to 10th	Day	15% 15% 28% 27% 11% 4	330
	11th to 20th	Day	20% 20% 36% 18% 7%	330
	21st to end	Day	23% 15% 38% 17% 6% 1	363
November	1st to 10th	Day	21% 17% 34% 19% 8% 1	330
	11th to 20th	Day	18% 19% 42% 18% 3	330
	21st to end	Day	24% 16% 36% 20% 4	330
December	1st to 10th	Day	14% 12% 40% 25% 8% 1	330
	11th to 20th	Day	20% 18% 38% 19% 5%	330
	21st to end	Day	27% 15% 40% 15% 2 1	363
January	1st to 10th	Night	11% 13% 36% 31% 8% 1	1050
	11th to 20th	Night	17% 11% 37% 29% 5% 1	1050
	21st to end	Night	17% 11% 35% 30% 6% 1	1155
February	1st to 10th	Night	13% 12% 40% 28% 7%	1050
	11th to 20th	Night	13% 11% 43% 26% 7% 1	1029
	21st to end	Night	17% 14% 34% 28% 7%	778
March	1st to 10th	Night	15% 11% 37% 28% 7% 1	729
	11th to 20th	Night	19% 12% 38% 26% 5%	630
	21st to end	Night	22% 13% 30% 24% 10% 1	693
April	1st to 10th	Night	22% 13% 35% 26% 4	630
	11th to 20th	Night	25% 9% 32% 28% 6%	623
	21st to end	Night	21% 10% 33% 27% 8% 1	630
May	1st to 10th	Night	18% 10% 32% 31% 7% 1	630
	11th to 20th	Night	18% 10% 29% 33% 10% 1	621
	21st to end	Night	14% 8% 25% 38% 13%	683
June	1st to 10th	Night	13% 5% 28% 41% 12% 1	630
	11th to 20th	Night	12% 5% 33% 42% 8%	630
	21st to end	Night	9% 4 24% 46% 15% 1	630
July	1st to 10th	Night	5% 3 20% 43% 27% 2	615
	11th to 20th	Night	5% 4 25% 44% 21% 1	612
	21st to end	Night	6% 3 22% 46% 20% 2	690
August	1st to 10th	Night	7% 4 17% 51% 21% 1	627
	11th to 20th	Night	13% 4 19% 37% 26% 2	624
	21st to end	Night	8% 4 25% 38% 23% 2	687
September	1st to 10th	Night	11% 6% 22% 42% 16% 4	600
	11th to 20th	Night	10% 7% 29% 35% 18% 2	600
	21st to end	Night	14% 9% 29% 31% 17% 1	695
October	1st to 10th	Night	17% 8% 28% 33% 13% 1	800
	11th to 20th	Night	21% 11% 33% 28% 6% 1	800
	21st to end	Night	24% 12% 27% 30% 7%	880
November	1st to 10th	Night	18% 11% 34% 30% 7% 1	915
	11th to 20th	Night	19% 13% 35% 26% 7%	1050
	21st to end	Night	19% 14% 35% 25% 6%	1050
December	1st to 10th	Night	15% 9% 39% 29% 7% 1	1050
	11th to 20th	Night	19% 10% 38% 27% 6%	1050
	21st to end	Night	25% 11% 34% 25% 5%	1155

Page generated at 2026-08-27 03:07:10. Version ac07

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