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 2024-02-25.

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	13% 9% 4 7% 6% 3 5% 5% 5% 7% 36%	78360
	Night	12% 10% 4 8% 6% 3 4 4 5% 6% 37%	80989
Transparency	Day	47% 7% 14% 22% 10% 1	78061
	Night	47% 6% 13% 22% 11% 1	80809
Seeing	Day	16% 11% 30% 26% 13% 3	14962
	Night	16% 9% 32% 32% 11% 1	25071

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	12% 15% 7% 17% 6% 3 4 4 4 5% 21%	2527
	11th to 20th	Day	6% 12% 6% 13% 11% 6% 8% 9% 5% 4 20%	2530
	21st to end	Day	9% 20% 7% 11% 6% 3 4 4 5% 7% 24%	3112
February	1st to 10th	Day	8% 10% 6% 10% 7% 4 7% 6% 6% 6% 31%	1710
	11th to 20th	Day	9% 9% 7% 9% 7% 4 6% 5% 5% 6% 34%	1664
	21st to end	Day	12% 10% 5% 9% 7% 4 5% 5% 6% 7% 30%	1440
March	1st to 10th	Day	14% 12% 5% 9% 7% 3 4 3 5% 7% 32%	1911
	11th to 20th	Day	15% 9% 5% 7% 5% 3 4 5% 5% 7% 36%	1980
	21st to end	Day	20% 12% 4 5% 6% 3 5% 4 5% 7% 30%	2216
April	1st to 10th	Day	17% 10% 4 6% 6% 2 4 4 5% 7% 34%	2160
	11th to 20th	Day	21% 11% 4 7% 5% 3 4 4 4 6% 32%	2134
	21st to end	Day	21% 11% 4 6% 5% 3 5% 5% 5% 6% 29%	2323
May	1st to 10th	Day	17% 8% 3 8% 6% 4 5% 5% 5% 7% 33%	2457
	11th to 20th	Day	17% 8% 3 4 5% 3 4 5% 5% 7% 39%	2479
	21st to end	Day	14% 7% 2 6% 7% 4 6% 4 6% 8% 37%	2725
June	1st to 10th	Day	12% 5% 2 4 4 3 5% 5% 6% 9% 45%	2520
	11th to 20th	Day	12% 7% 3 5% 5% 3 5% 5% 7% 9% 38%	2520
	21st to end	Day	10% 4 2 6% 6% 3 6% 5% 7% 9% 41%	2520
July	1st to 10th	Day	7% 4 2 4 4 3 5% 5% 7% 11% 47%	2520
	11th to 20th	Day	9% 4 2 4 4 3 5% 5% 6% 7% 52%	2520
	21st to end	Day	6% 3 2 4 5% 3 5% 7% 6% 10% 48%	2743
August	1st to 10th	Day	9% 5% 3 5% 6% 4 5% 6% 7% 9% 40%	2328
	11th to 20th	Day	13% 6% 2 5% 4 3 4 5% 6% 7% 44%	2301
	21st to end	Day	10% 5% 2 5% 4 2 5% 5% 5% 6% 52%	2444
September	1st to 10th	Day	13% 6% 2 5% 5% 3 4 4 5% 8% 45%	2160
	11th to 20th	Day	13% 6% 1 4 4 3 4 5% 6% 8% 45%	2160
	21st to end	Day	14% 6% 3 6% 6% 3 4 5% 5% 7% 42%	1877
October	1st to 10th	Day	17% 7% 3 4 5% 3 4 4 5% 6% 44%	1800
	11th to 20th	Day	15% 11% 3 5% 6% 3 5% 4 4 7% 37%	1800
	21st to end	Day	18% 12% 4 7% 4 3 3 4 4 5% 36%	1936
November	1st to 10th	Day	11% 12% 5% 8% 6% 3 4 4 5% 6% 36%	1582
	11th to 20th	Day	13% 12% 8% 10% 8% 3 4 4 5% 7% 27%	1520
	21st to end	Day	13% 11% 5% 7% 7% 2 3 4 5% 7% 35%	1520
December	1st to 10th	Day	12% 12% 6% 12% 9% 4 4 5% 5% 6% 25%	1520
	11th to 20th	Day	11% 11% 9% 9% 9% 3 5% 5% 5% 6% 28%	1918
	21st to end	Day	19% 18% 7% 14% 7% 3 4 3 3 4 18%	2783
January	1st to 10th	Night	9% 15% 9% 14% 8% 3 4 4 4 4 25%	4428
	11th to 20th	Night	8% 11% 5% 12% 9% 5% 8% 9% 6% 5% 21%	4440
	21st to end	Night	11% 19% 8% 12% 6% 3 4 4 3 4 25%	4552
February	1st to 10th	Night	6% 11% 5% 10% 8% 5% 6% 5% 4 6% 34%	2470
	11th to 20th	Night	7% 8% 5% 7% 6% 5% 5% 5% 5% 7% 39%	2403
	21st to end	Night	12% 11% 4 7% 7% 4 5% 5% 5% 5% 35%	1909
March	1st to 10th	Night	13% 9% 5% 7% 6% 4 5% 4 5% 5% 37%	2066
	11th to 20th	Night	12% 11% 5% 7% 5% 2 4 4 5% 6% 39%	1980
	21st to end	Night	18% 8% 4 7% 5% 3 4 4 5% 7% 35%	2138
April	1st to 10th	Night	16% 11% 4 6% 4 3 4 5% 6% 6% 37%	1800
	11th to 20th	Night	22% 10% 3 6% 5% 3 4 4 4 5% 34%	1775
	21st to end	Night	18% 10% 3 6% 5% 3 4 4 5% 7% 35%	1634
May	1st to 10th	Night	17% 7% 4 6% 4 3 5% 4 5% 6% 38%	1500
	11th to 20th	Night	16% 5% 2 4 5% 4 4 5% 6% 7% 42%	1416
	21st to end	Night	10% 7% 3 6% 6% 3 5% 5% 6% 7% 42%	1551
June	1st to 10th	Night	11% 5% 2 3 4 3 5% 5% 7% 8% 48%	1440
	11th to 20th	Night	9% 5% 2 5% 5% 3 6% 4 6% 9% 46%	1440
	21st to end	Night	6% 4 2 4 4 3 5% 6% 6% 8% 52%	1440
July	1st to 10th	Night	6% 3 1 4 4 2 4 5% 6% 10% 57%	1440
	11th to 20th	Night	5% 2 2 3 5% 2 5% 4 6% 10% 55%	1440
	21st to end	Night	4 3 2 3 3 3 4 4 6% 9% 59%	1575
August	1st to 10th	Night	5% 5% 3 6% 4 3 5% 5% 6% 9% 48%	1609
	11th to 20th	Night	13% 4 2 3 4 2 4 4 6% 8% 52%	1600
	21st to end	Night	8% 5% 2 4 4 3 4 4 5% 7% 54%	1910
September	1st to 10th	Night	10% 5% 2 4 4 3 4 5% 4 7% 53%	1800
	11th to 20th	Night	10% 4 2 4 3 3 4 4 5% 7% 53%	1800
	21st to end	Night	14% 4 2 4 4 3 4 3 5% 7% 49%	2061
October	1st to 10th	Night	15% 6% 3 5% 5% 2 3 4 4 6% 49%	2160
	11th to 20th	Night	17% 9% 3 5% 4 2 3 4 5% 7% 41%	2160
	21st to end	Night	18% 11% 3 6% 3 2 4 4 4 6% 37%	2418
November	1st to 10th	Night	13% 10% 4 5% 5% 3 3 4 5% 6% 42%	2491
	11th to 20th	Night	13% 11% 5% 9% 7% 3 4 5% 5% 5% 33%	2660
	21st to end	Night	13% 10% 4 8% 6% 3 4 4 4 7% 37%	2660
December	1st to 10th	Night	11% 12% 5% 11% 8% 4 4 4 4 6% 30%	2660
	11th to 20th	Night	11% 15% 5% 10% 8% 4 6% 4 5% 6% 26%	3279
	21st to end	Night	22% 14% 7% 11% 7% 3 4 4 4 4 21%	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	66% 5% 10% 16% 3	2528
	11th to 20th	Day	64% 6% 10% 15% 6%	2530
	21st to end	Day	61% 7% 14% 15% 4	3112
February	1st to 10th	Day	51% 6% 15% 18% 9% 1	1710
	11th to 20th	Day	50% 5% 12% 24% 8% 1	1673
	21st to end	Day	52% 7% 11% 19% 10%	1440
March	1st to 10th	Day	53% 5% 14% 18% 7% 1	1911
	11th to 20th	Day	48% 5% 14% 23% 8% 1	1980
	21st to end	Day	54% 6% 12% 20% 7% 1	2216
April	1st to 10th	Day	49% 5% 12% 21% 11% 1	2160
	11th to 20th	Day	54% 5% 10% 18% 11% 2	2134
	21st to end	Day	55% 6% 12% 18% 8%	2323
May	1st to 10th	Day	49% 6% 13% 21% 9% 2	2457
	11th to 20th	Day	45% 6% 14% 23% 11% 1	2483
	21st to end	Day	45% 8% 11% 23% 13% 1	2725
June	1st to 10th	Day	35% 8% 15% 29% 12% 1	2520
	11th to 20th	Day	40% 8% 15% 22% 14% 1	2520
	21st to end	Day	37% 9% 16% 26% 10% 2	2520
July	1st to 10th	Day	29% 9% 17% 31% 13% 1	2451
	11th to 20th	Day	29% 9% 16% 26% 19% 2	2445
	21st to end	Day	29% 9% 17% 28% 15% 2	2591
August	1st to 10th	Day	37% 9% 16% 27% 8% 3	2314
	11th to 20th	Day	37% 8% 15% 29% 11%	2301
	21st to end	Day	30% 7% 15% 30% 17% 1	2444
September	1st to 10th	Day	37% 6% 14% 29% 13%	2160
	11th to 20th	Day	36% 8% 16% 32% 9%	2160
	21st to end	Day	41% 7% 12% 31% 9%	1877
October	1st to 10th	Day	41% 6% 13% 28% 12% 1	1800
	11th to 20th	Day	45% 6% 14% 23% 11% 1	1800
	21st to end	Day	50% 5% 13% 22% 9%	1936
November	1st to 10th	Day	49% 5% 12% 18% 13% 2	1582
	11th to 20th	Day	57% 7% 13% 15% 8% 1	1520
	21st to end	Day	49% 6% 18% 20% 7% 1	1520
December	1st to 10th	Day	60% 7% 15% 13% 5%	1520
	11th to 20th	Day	57% 6% 17% 15% 5%	1915
	21st to end	Day	70% 5% 9% 10% 5%	2783
January	1st to 10th	Night	62% 5% 11% 18% 5% 1	4428
	11th to 20th	Night	60% 7% 13% 14% 5%	4440
	21st to end	Night	63% 4 9% 18% 5% 1	4552
February	1st to 10th	Night	51% 6% 11% 22% 9% 1	2470
	11th to 20th	Night	44% 5% 16% 25% 8% 1	2404
	21st to end	Night	50% 6% 10% 21% 11% 1	1909
March	1st to 10th	Night	49% 6% 14% 21% 9%	2066
	11th to 20th	Night	46% 5% 12% 21% 14% 1	1980
	21st to end	Night	49% 6% 11% 22% 11% 1	2138
April	1st to 10th	Night	48% 5% 9% 22% 15% 1	1800
	11th to 20th	Night	52% 5% 9% 18% 13% 2	1775
	21st to end	Night	49% 5% 9% 21% 14% 2	1634
May	1st to 10th	Night	46% 6% 14% 19% 14% 1	1500
	11th to 20th	Night	40% 7% 14% 23% 14% 2	1417
	21st to end	Night	41% 8% 12% 21% 17% 1	1552
June	1st to 10th	Night	33% 6% 14% 28% 17% 2	1440
	11th to 20th	Night	34% 8% 14% 23% 18% 3	1440
	21st to end	Night	28% 8% 16% 30% 15% 3	1440
July	1st to 10th	Night	23% 6% 15% 35% 19% 2	1400
	11th to 20th	Night	23% 8% 16% 31% 18% 4	1392
	21st to end	Night	20% 6% 17% 33% 18% 5%	1487
August	1st to 10th	Night	31% 8% 14% 29% 15% 4	1600
	11th to 20th	Night	31% 7% 15% 29% 16% 2	1600
	21st to end	Night	29% 7% 14% 29% 17% 4	1910
September	1st to 10th	Night	31% 6% 13% 33% 17% 1	1800
	11th to 20th	Night	31% 6% 16% 30% 17%	1800
	21st to end	Night	35% 5% 14% 31% 14% 1	2061
October	1st to 10th	Night	37% 5% 11% 31% 14% 2	2160
	11th to 20th	Night	43% 6% 14% 23% 13% 1	2160
	21st to end	Night	48% 6% 12% 22% 12% 1	2418
November	1st to 10th	Night	43% 6% 13% 23% 15% 1	2491
	11th to 20th	Night	54% 6% 12% 17% 10% 1	2660
	21st to end	Night	48% 5% 16% 23% 7% 1	2660
December	1st to 10th	Night	55% 6% 14% 19% 6%	2660
	11th to 20th	Night	58% 6% 13% 16% 5% 1	3281
	21st to end	Night	66% 5% 12% 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	14% 12% 34% 28% 10% 2	270
	11th to 20th	Day	17% 13% 42% 21% 6%	270
	21st to end	Day	14% 10% 41% 25% 8% 2	297
February	1st to 10th	Day	13% 16% 44% 20% 4 1	270
	11th to 20th	Day	14% 17% 41% 21% 6% 1	270
	21st to end	Day	19% 13% 37% 29% 2	210
March	1st to 10th	Day	18% 14% 41% 20% 7%	240
	11th to 20th	Day	20% 12% 37% 22% 8% 1	240
	21st to end	Day	29% 15% 24% 22% 8% 4	302
April	1st to 10th	Day	24% 17% 32% 21% 6%	420
	11th to 20th	Day	29% 13% 23% 27% 8% 1	412
	21st to end	Day	27% 13% 29% 21% 9% 2	583
May	1st to 10th	Day	20% 15% 31% 24% 9% 1	603
	11th to 20th	Day	20% 13% 30% 22% 13% 3	625
	21st to end	Day	17% 9% 29% 25% 16% 3	679
June	1st to 10th	Day	10% 8% 27% 33% 18% 4	630
	11th to 20th	Day	13% 11% 34% 29% 12% 2	630
	21st to end	Day	10% 8% 31% 28% 17% 5%	630
July	1st to 10th	Day	9% 3 21% 32% 24% 10%	621
	11th to 20th	Day	9% 5% 29% 29% 21% 7%	618
	21st to end	Day	5% 4 26% 37% 21% 7%	684
August	1st to 10th	Day	11% 5% 22% 35% 23% 6%	626
	11th to 20th	Day	14% 5% 20% 32% 24% 6%	615
	21st to end	Day	11% 6% 24% 33% 20% 5%	563
September	1st to 10th	Day	15% 7% 29% 28% 17% 4	450
	11th to 20th	Day	13% 5% 28% 29% 21% 3	450
	21st to end	Day	17% 20% 28% 22% 9% 4	270
October	1st to 10th	Day	17% 15% 26% 26% 12% 4	270
	11th to 20th	Day	17% 21% 33% 20% 8%	270
	21st to end	Day	25% 17% 38% 14% 6% 1	297
November	1st to 10th	Day	19% 17% 33% 21% 9% 1	270
	11th to 20th	Day	17% 19% 40% 20% 3	270
	21st to end	Day	23% 16% 38% 19% 4	270
December	1st to 10th	Day	13% 12% 39% 26% 9% 1	270
	11th to 20th	Day	19% 16% 38% 20% 6%	270
	21st to end	Day	29% 14% 39% 16% 2	297
January	1st to 10th	Night	11% 13% 37% 31% 8% 1	950
	11th to 20th	Night	17% 10% 37% 30% 6% 1	950
	21st to end	Night	18% 10% 35% 30% 6% 1	1045
February	1st to 10th	Night	13% 11% 40% 29% 7% 1	950
	11th to 20th	Night	13% 11% 43% 26% 7% 1	929
	21st to end	Night	17% 13% 33% 28% 8%	689
March	1st to 10th	Night	16% 11% 36% 28% 8% 1	626
	11th to 20th	Night	19% 10% 37% 28% 6%	540
	21st to end	Night	21% 13% 28% 25% 12% 2	594
April	1st to 10th	Night	21% 12% 37% 26% 5%	540
	11th to 20th	Night	26% 8% 31% 28% 6%	533
	21st to end	Night	21% 9% 32% 28% 9% 1	540
May	1st to 10th	Night	21% 10% 32% 31% 6% 1	540
	11th to 20th	Night	18% 8% 29% 33% 11% 1	531
	21st to end	Night	14% 8% 25% 38% 14% 1	584
June	1st to 10th	Night	12% 5% 27% 42% 13% 1	540
	11th to 20th	Night	11% 4 33% 42% 9%	540
	21st to end	Night	8% 4 23% 48% 16% 2	540
July	1st to 10th	Night	5% 2 22% 42% 28% 2	525
	11th to 20th	Night	5% 4 25% 44% 20% 2	522
	21st to end	Night	6% 3 22% 46% 21% 2	591
August	1st to 10th	Night	6% 3 17% 51% 22% 1	537
	11th to 20th	Night	13% 3 19% 35% 27% 3	534
	21st to end	Night	9% 3 26% 36% 23% 2	594
September	1st to 10th	Night	10% 6% 23% 42% 16% 4	540
	11th to 20th	Night	11% 7% 29% 34% 18% 2	540
	21st to end	Night	15% 9% 31% 30% 14% 1	625
October	1st to 10th	Night	18% 8% 27% 32% 14% 1	720
	11th to 20th	Night	21% 11% 32% 28% 7% 1	720
	21st to end	Night	25% 12% 25% 31% 7%	792
November	1st to 10th	Night	19% 10% 33% 30% 8% 1	825
	11th to 20th	Night	19% 12% 35% 26% 7% 1	950
	21st to end	Night	18% 14% 35% 25% 7%	950
December	1st to 10th	Night	16% 9% 37% 30% 7% 1	950
	11th to 20th	Night	19% 8% 39% 28% 6%	950
	21st to end	Night	24% 11% 35% 25% 5%	1045

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