Mole Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mole Hill Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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	11% 6% 3 5% 5% 3 5% 5% 7% 9% 41%	74885
	Night	12% 5% 2 5% 4 3 4 5% 6% 8% 46%	74855
Transparency	Day	23% 39% 10% 14% 9% 4	74610
	Night	23% 38% 10% 14% 11% 5%	74650
Seeing	Day	11% 3 12% 25% 34% 15%	13512
	Night	14% 4 15% 30% 31% 7%	23550

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	19% 6% 3 4 5% 3 5% 5% 5% 5% 40%	1707
	11th to 20th	Day	21% 8% 3 4 4 2 4 4 5% 5% 41%	1634
	21st to end	Day	16% 6% 3 6% 5% 3 3 5% 5% 6% 41%	1845
February	1st to 10th	Day	20% 9% 4 6% 5% 2 3 3 4 6% 39%	1800
	11th to 20th	Day	18% 8% 4 6% 5% 2 4 4 5% 6% 39%	1749
	21st to end	Day	20% 7% 2 6% 4 2 3 4 5% 6% 41%	1580
March	1st to 10th	Day	19% 7% 3 5% 4 3 4 4 5% 8% 38%	1980
	11th to 20th	Day	14% 8% 4 6% 6% 2 5% 4 5% 7% 39%	1980
	21st to end	Day	13% 6% 2 5% 4 3 4 4 5% 6% 46%	2178
April	1st to 10th	Day	13% 7% 3 5% 5% 2 5% 5% 6% 9% 39%	1980
	11th to 20th	Day	16% 7% 4 5% 6% 4 5% 5% 4 7% 38%	1986
	21st to end	Day	11% 5% 3 5% 6% 3 5% 4 5% 8% 46%	2160
May	1st to 10th	Day	11% 5% 3 6% 6% 3 5% 5% 7% 9% 40%	2272
	11th to 20th	Day	9% 5% 2 6% 5% 3 6% 7% 8% 10% 40%	2302
	21st to end	Day	6% 5% 2 5% 6% 5% 6% 7% 9% 14% 35%	2531
June	1st to 10th	Day	4 3 2 4 5% 3 5% 6% 9% 14% 45%	2340
	11th to 20th	Day	5% 4 2 5% 6% 4 6% 7% 9% 12% 41%	2340
	21st to end	Day	7% 4 3 5% 7% 4 7% 7% 10% 13% 32%	2340
July	1st to 10th	Day	11% 6% 2 5% 5% 4 6% 7% 9% 12% 33%	2340
	11th to 20th	Day	4 3 3 4 5% 4 6% 7% 8% 13% 43%	2340
	21st to end	Day	4 3 2 4 5% 3 6% 6% 10% 14% 44%	2546
August	1st to 10th	Day	2 3 2 4 5% 3 6% 6% 8% 12% 51%	2328
	11th to 20th	Day	4 3 2 4 5% 3 6% 7% 9% 15% 43%	2204
	21st to end	Day	7% 5% 2 7% 6% 4 5% 7% 9% 12% 36%	2178
September	1st to 10th	Day	7% 7% 2 7% 6% 5% 6% 7% 9% 12% 32%	1980
	11th to 20th	Day	11% 6% 2 6% 7% 4 5% 6% 8% 9% 36%	1980
	21st to end	Day	8% 6% 2 4 5% 4 6% 6% 7% 9% 42%	1980
October	1st to 10th	Day	5% 4 2 3 4 3 6% 6% 7% 11% 50%	1960
	11th to 20th	Day	10% 5% 2 5% 5% 3 4 5% 5% 7% 49%	1800
	21st to end	Day	11% 4 2 5% 4 3 4 4 5% 7% 52%	1980
November	1st to 10th	Day	9% 5% 3 5% 5% 3 5% 6% 6% 10% 42%	1858
	11th to 20th	Day	14% 4 3 5% 5% 3 4 5% 4 7% 46%	1900
	21st to end	Day	17% 7% 2 5% 5% 5% 5% 4 4 6% 39%	1801
December	1st to 10th	Day	18% 7% 3 5% 5% 3 4 4 5% 8% 39%	1710
	11th to 20th	Day	13% 8% 3 6% 6% 3 4 5% 6% 7% 39%	2161
	21st to end	Day	16% 6% 3 5% 4 3 4 4 5% 7% 42%	3135
January	1st to 10th	Night	18% 7% 3 5% 5% 2 4 4 3 6% 43%	2458
	11th to 20th	Night	18% 6% 3 5% 4 2 3 3 4 6% 46%	2366
	21st to end	Night	18% 6% 3 5% 4 2 4 4 5% 6% 42%	2524
February	1st to 10th	Night	19% 9% 4 6% 4 2 4 3 4 5% 40%	2160
	11th to 20th	Night	18% 6% 3 4 4 2 3 5% 5% 7% 43%	2098
	21st to end	Night	18% 9% 3 5% 5% 3 4 4 5% 5% 40%	1673
March	1st to 10th	Night	16% 8% 3 4 4 3 4 4 4 8% 41%	1980
	11th to 20th	Night	14% 8% 3 6% 5% 4 4 4 4 7% 40%	1980
	21st to end	Night	14% 6% 3 4 3 2 3 4 5% 7% 48%	2178
April	1st to 10th	Night	14% 7% 4 5% 5% 2 4 5% 6% 9% 38%	1980
	11th to 20th	Night	17% 7% 3 5% 4 2 3 4 4 8% 43%	1920
	21st to end	Night	13% 6% 2 6% 5% 3 5% 5% 6% 7% 41%	1800
May	1st to 10th	Night	12% 6% 2 5% 4 3 5% 4 7% 8% 44%	1683
	11th to 20th	Night	9% 4 2 5% 5% 4 5% 6% 6% 9% 45%	1593
	21st to end	Night	8% 4 2 5% 5% 3 5% 7% 8% 13% 40%	1745
June	1st to 10th	Night	6% 3 1 4 3 2 3 6% 7% 11% 55%	1620
	11th to 20th	Night	5% 4 1 4 4 3 6% 6% 6% 12% 49%	1620
	21st to end	Night	5% 5% 3 5% 5% 3 6% 6% 10% 13% 40%	1620
July	1st to 10th	Night	7% 5% 3 5% 4 3 6% 6% 9% 14% 39%	1620
	11th to 20th	Night	2 3 2 2 5% 2 4 6% 7% 13% 54%	1620
	21st to end	Night	2 2 2 3 3 3 4 5% 8% 13% 54%	1772
August	1st to 10th	Night	1 1 1 2 3 2 3 4 6% 12% 64%	1611
	11th to 20th	Night	3 2 1 4 4 2 4 5% 8% 13% 53%	1687
	21st to end	Night	5% 3 2 4 5% 3 5% 5% 8% 12% 50%	2178
September	1st to 10th	Night	6% 4 3 5% 5% 3 5% 5% 9% 12% 43%	1980
	11th to 20th	Night	9% 6% 2 7% 5% 2 5% 5% 6% 10% 44%	1980
	21st to end	Night	7% 4 2 4 4 3 4 5% 6% 9% 50%	1980
October	1st to 10th	Night	4 3 2 4 5% 3 4 5% 6% 9% 55%	1980
	11th to 20th	Night	9% 4 2 4 3 2 3 3 4 7% 59%	2160
	21st to end	Night	9% 3 2 4 4 2 2 4 3 7% 61%	2376
November	1st to 10th	Night	8% 4 2 4 4 3 4 4 5% 7% 55%	2220
	11th to 20th	Night	15% 6% 2 5% 4 3 4 3 4 5% 49%	2280
	21st to end	Night	16% 6% 2 5% 4 3 6% 4 4 7% 43%	2375
December	1st to 10th	Night	18% 6% 3 5% 5% 3 3 4 5% 6% 43%	2470
	11th to 20th	Night	15% 8% 3 6% 5% 3 5% 5% 5% 7% 37%	3036
	21st to end	Night	14% 7% 3 7% 5% 3 4 4 5% 6% 42%	4532

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	25% 41% 5% 10% 12% 6%	1708
	11th to 20th	Day	28% 43% 5% 7% 10% 8%	1634
	21st to end	Day	33% 37% 4 9% 10% 7%	1845
February	1st to 10th	Day	29% 36% 5% 10% 12% 7%	1800
	11th to 20th	Day	33% 38% 6% 7% 11% 6%	1759
	21st to end	Day	27% 37% 7% 13% 10% 6%	1580
March	1st to 10th	Day	22% 37% 10% 13% 12% 6%	1980
	11th to 20th	Day	28% 38% 7% 9% 10% 8%	1980
	21st to end	Day	25% 40% 9% 9% 11% 6%	2178
April	1st to 10th	Day	26% 39% 10% 14% 8% 3	1980
	11th to 20th	Day	29% 38% 6% 12% 9% 6%	1986
	21st to end	Day	25% 38% 9% 15% 8% 6%	2160
May	1st to 10th	Day	26% 39% 12% 15% 6% 2	2272
	11th to 20th	Day	22% 40% 10% 17% 11% 1	2306
	21st to end	Day	19% 40% 14% 18% 9%	2531
June	1st to 10th	Day	16% 39% 15% 20% 10%	2340
	11th to 20th	Day	15% 39% 11% 24% 10% 1	2340
	21st to end	Day	22% 40% 14% 18% 5%	2340
July	1st to 10th	Day	29% 41% 11% 15% 3	2276
	11th to 20th	Day	19% 43% 16% 18% 4	2271
	21st to end	Day	18% 43% 21% 17% 1	2405
August	1st to 10th	Day	13% 39% 18% 23% 6%	2314
	11th to 20th	Day	20% 40% 18% 17% 5%	2204
	21st to end	Day	22% 42% 14% 16% 5% 1	2178
September	1st to 10th	Day	26% 42% 10% 12% 8% 2	1980
	11th to 20th	Day	27% 41% 9% 14% 8% 1	1980
	21st to end	Day	19% 39% 10% 12% 14% 6%	1980
October	1st to 10th	Day	20% 38% 7% 14% 16% 6%	1960
	11th to 20th	Day	21% 37% 7% 14% 12% 8%	1800
	21st to end	Day	18% 38% 7% 13% 14% 11%	1980
November	1st to 10th	Day	17% 43% 6% 14% 16% 5%	1858
	11th to 20th	Day	20% 40% 8% 13% 12% 7%	1900
	21st to end	Day	27% 41% 8% 10% 9% 6%	1801
December	1st to 10th	Day	28% 42% 8% 11% 7% 4	1710
	11th to 20th	Day	30% 34% 6% 8% 13% 9%	2159
	21st to end	Day	30% 26% 6% 16% 14% 9%	3135
January	1st to 10th	Night	24% 40% 5% 9% 14% 8%	2458
	11th to 20th	Night	24% 41% 4 11% 10% 9%	2366
	21st to end	Night	32% 38% 5% 8% 10% 7%	2524
February	1st to 10th	Night	29% 37% 7% 8% 10% 9%	2160
	11th to 20th	Night	29% 38% 6% 7% 14% 6%	2098
	21st to end	Night	31% 36% 6% 11% 12% 5%	1673
March	1st to 10th	Night	20% 38% 9% 12% 12% 8%	1980
	11th to 20th	Night	28% 38% 8% 9% 10% 7%	1980
	21st to end	Night	26% 37% 8% 10% 11% 7%	2178
April	1st to 10th	Night	29% 38% 8% 12% 9% 4	1980
	11th to 20th	Night	27% 36% 6% 12% 11% 8%	1920
	21st to end	Night	27% 39% 7% 12% 9% 6%	1800
May	1st to 10th	Night	23% 39% 11% 15% 9% 4	1683
	11th to 20th	Night	21% 39% 11% 15% 12% 2	1594
	21st to end	Night	21% 40% 13% 16% 9% 1	1746
June	1st to 10th	Night	16% 38% 15% 19% 11% 1	1620
	11th to 20th	Night	14% 37% 10% 25% 12% 1	1620
	21st to end	Night	18% 40% 17% 19% 6% 1	1620
July	1st to 10th	Night	27% 41% 13% 17% 3	1575
	11th to 20th	Night	15% 41% 20% 18% 5%	1566
	21st to end	Night	15% 42% 24% 18% 2	1673
August	1st to 10th	Night	8% 40% 20% 29% 4	1601
	11th to 20th	Night	15% 40% 22% 18% 4	1687
	21st to end	Night	18% 41% 18% 17% 6%	2178
September	1st to 10th	Night	24% 41% 12% 11% 9% 3	1980
	11th to 20th	Night	24% 40% 11% 15% 8% 2	1980
	21st to end	Night	17% 37% 10% 16% 15% 5%	1980
October	1st to 10th	Night	18% 39% 7% 13% 15% 8%	1980
	11th to 20th	Night	19% 36% 8% 16% 13% 8%	2160
	21st to end	Night	14% 38% 6% 14% 15% 12%	2376
November	1st to 10th	Night	13% 41% 7% 14% 18% 6%	2220
	11th to 20th	Night	19% 39% 8% 13% 14% 7%	2280
	21st to end	Night	24% 41% 7% 13% 9% 6%	2375
December	1st to 10th	Night	26% 41% 7% 14% 8% 4	2470
	11th to 20th	Night	31% 35% 6% 9% 9% 10%	3037
	21st to end	Night	30% 28% 6% 13% 17% 6%	4532

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	19% 6% 22% 37% 15%	270
	11th to 20th	Day	23% 7% 22% 29% 18% 1	245
	21st to end	Day	17% 6% 31% 31% 14%	264
February	1st to 10th	Day	27% 7% 21% 28% 16% 1	240
	11th to 20th	Day	24% 7% 20% 32% 16% 1	240
	21st to end	Day	20% 8% 27% 37% 8% 1	198
March	1st to 10th	Day	23% 5% 21% 37% 13%	240
	11th to 20th	Day	21% 4 27% 35% 12% 1	240
	21st to end	Day	13% 5% 27% 43% 11%	264
April	1st to 10th	Day	19% 4 27% 35% 15%	240
	11th to 20th	Day	13% 8% 27% 33% 17% 2	264
	21st to end	Day	13% 4 21% 44% 18% 1	420
May	1st to 10th	Day	10% 6% 19% 46% 17% 1	535
	11th to 20th	Day	12% 3 14% 42% 26% 3	625
	21st to end	Day	7% 2 11% 38% 37% 4	679
June	1st to 10th	Day	5% 1 7% 28% 49% 12%	630
	11th to 20th	Day	7% 3 31% 47% 12%	630
	21st to end	Day	8% 1 6% 17% 49% 19%	630
July	1st to 10th	Day	9% 1 3 14% 47% 27%	621
	11th to 20th	Day	4 2 7% 57% 31%	618
	21st to end	Day	5% 1 2 8% 51% 33%	684
August	1st to 10th	Day	1 1 9% 51% 38%	626
	11th to 20th	Day	3 2 6% 47% 42%	518
	21st to end	Day	9% 1 3 8% 31% 47%	297
September	1st to 10th	Day	9% 3 10% 45% 33%	270
	11th to 20th	Day	9% 1 3 13% 39% 37%	270
	21st to end	Day	7% 3 14% 48% 29%	270
October	1st to 10th	Day	7% 1 6% 20% 48% 20%	270
	11th to 20th	Day	10% 2 9% 23% 38% 18%	270
	21st to end	Day	16% 5% 17% 23% 34% 5%	297
November	1st to 10th	Day	16% 3 6% 24% 41% 10%	270
	11th to 20th	Day	20% 3 13% 30% 29% 6%	270
	21st to end	Day	23% 5% 21% 31% 14% 6%	270
December	1st to 10th	Day	21% 4 15% 30% 25% 5%	270
	11th to 20th	Day	20% 6% 25% 31% 17% 1	270
	21st to end	Day	20% 5% 17% 37% 18% 2	297
January	1st to 10th	Night	21% 7% 24% 32% 16% 1	950
	11th to 20th	Night	21% 7% 21% 38% 13% 1	910
	21st to end	Night	21% 7% 26% 34% 13%	940
February	1st to 10th	Night	25% 7% 23% 34% 11%	720
	11th to 20th	Night	23% 9% 19% 35% 14%	704
	21st to end	Night	22% 9% 25% 36% 8%	489
March	1st to 10th	Night	19% 6% 24% 36% 16%	540
	11th to 20th	Night	17% 7% 20% 43% 14%	540
	21st to end	Night	16% 6% 21% 41% 15% 1	594
April	1st to 10th	Night	15% 4 24% 44% 12%	540
	11th to 20th	Night	19% 6% 22% 36% 17%	533
	21st to end	Night	16% 6% 22% 40% 16% 1	540
May	1st to 10th	Night	14% 4 20% 47% 15%	540
	11th to 20th	Night	11% 3 14% 47% 23% 3	531
	21st to end	Night	7% 2 12% 39% 39% 3	584
June	1st to 10th	Night	5% 1 4 28% 56% 5%	540
	11th to 20th	Night	5% 1 4 34% 52% 4	540
	21st to end	Night	7% 1 6% 19% 51% 15%	540
July	1st to 10th	Night	6% 2 3 17% 52% 20%	525
	11th to 20th	Night	2 2 10% 58% 28%	522
	21st to end	Night	3 1 1 13% 59% 23%	591
August	1st to 10th	Night	1 1 8% 61% 28%	537
	11th to 20th	Night	4 1 6% 65% 24%	534
	21st to end	Night	6% 2 11% 50% 32%	594
September	1st to 10th	Night	9% 2 11% 55% 23%	540
	11th to 20th	Night	11% 1 3 14% 49% 20%	540
	21st to end	Night	8% 2 5% 19% 52% 14%	540
October	1st to 10th	Night	5% 1 5% 21% 52% 15%	540
	11th to 20th	Night	11% 2 8% 30% 42% 6%	720
	21st to end	Night	10% 3 15% 35% 32% 5%	792
November	1st to 10th	Night	11% 3 9% 31% 39% 7%	740
	11th to 20th	Night	17% 4 17% 30% 30% 3	760
	21st to end	Night	18% 5% 21% 34% 19% 3	855
December	1st to 10th	Night	21% 5% 19% 28% 24% 3	950
	11th to 20th	Night	20% 8% 21% 32% 17% 1	950
	21st to end	Night	22% 8% 22% 32% 15% 1	1045

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