Mahoney State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mahoney State Park clear sky chart from 2005-11-06 to 2026-10-14.

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	10% 7% 3 7% 4 4 4 3 5% 7% 45%	148884
	Night	10% 7% 2 6% 4 4 4 3 5% 7% 48%	143236
Transparency	Day	38% 5% 13% 25% 16% 2	152522
	Night	35% 5% 13% 26% 19% 3	147665
Seeing	Day	14% 9% 30% 29% 14% 3	18497
	Night	13% 9% 33% 34% 10% 1	28259

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	10% 11% 5% 14% 7% 5% 4 3 4 5% 31%	5289
	11th to 20th	Day	5% 8% 4 10% 6% 6% 6% 4 5% 5% 41%	5310
	21st to end	Day	5% 11% 5% 11% 5% 5% 4 3 5% 6% 40%	5812
February	1st to 10th	Day	9% 12% 5% 8% 6% 5% 4 3 6% 7% 34%	1890
	11th to 20th	Day	10% 10% 3 9% 5% 3 5% 4 4 7% 41%	1893
	21st to end	Day	10% 7% 3 6% 4 4 4 3 5% 7% 46%	1730
March	1st to 10th	Day	14% 8% 3 6% 3 2 2 2 3 4 52%	4959
	11th to 20th	Day	11% 7% 2 5% 3 3 3 3 4 7% 52%	5090
	21st to end	Day	17% 11% 4 8% 4 4 5% 4 6% 7% 31%	5583
April	1st to 10th	Day	16% 9% 2 6% 4 4 4 3 4 6% 43%	2362
	11th to 20th	Day	15% 9% 3 5% 3 4 4 4 4 7% 41%	2623
	21st to end	Day	19% 7% 3 6% 4 4 4 3 5% 6% 38%	2730
May	1st to 10th	Day	11% 7% 3 6% 4 4 4 4 5% 7% 45%	7617
	11th to 20th	Day	12% 7% 2 6% 3 3 4 3 5% 6% 48%	7627
	21st to end	Day	17% 8% 3 7% 4 4 4 4 5% 6% 37%	8509
June	1st to 10th	Day	7% 5% 2 5% 4 4 5% 4 6% 9% 48%	2940
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 7% 9% 48%	2940
	21st to end	Day	7% 6% 2 6% 5% 5% 4 4 6% 8% 48%	2928
July	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 7% 10% 45%	7680
	11th to 20th	Day	5% 4 2 5% 4 4 4 3 6% 8% 56%	7680
	21st to end	Day	9% 6% 2 6% 4 4 4 4 6% 10% 45%	8337
August	1st to 10th	Day	7% 4 2 5% 4 4 4 4 7% 10% 48%	6014
	11th to 20th	Day	10% 6% 3 8% 5% 5% 5% 4 7% 8% 39%	5948
	21st to end	Day	7% 5% 2 7% 4 4 5% 4 6% 8% 48%	6499
September	1st to 10th	Day	12% 5% 2 5% 4 3 3 3 4 7% 52%	2423
	11th to 20th	Day	11% 5% 2 5% 3 4 3 3 5% 7% 51%	2310
	21st to end	Day	11% 5% 1 4 3 3 3 3 4 6% 55%	2310
October	1st to 10th	Day	13% 6% 2 4 3 3 3 3 4 6% 54%	2158
	11th to 20th	Day	11% 6% 1 5% 4 2 3 3 3 4 57%	2030
	21st to end	Day	13% 9% 2 6% 3 3 4 3 5% 6% 47%	2200
November	1st to 10th	Day	9% 7% 2 5% 3 3 4 2 5% 6% 54%	1870
	11th to 20th	Day	10% 6% 3 7% 5% 4 4 3 4 5% 49%	1853
	21st to end	Day	12% 9% 3 6% 4 3 3 4 4 7% 44%	1680
December	1st to 10th	Day	5% 6% 2 6% 5% 5% 4 4 4 6% 53%	2690
	11th to 20th	Day	8% 9% 3 10% 5% 5% 4 3 6% 6% 42%	3088
	21st to end	Day	16% 11% 5% 13% 4 4 3 3 4 6% 32%	4282
January	1st to 10th	Night	10% 9% 4 15% 7% 5% 4 4 5% 6% 31%	7634
	11th to 20th	Night	5% 7% 3 7% 5% 5% 6% 4 7% 8% 44%	7680
	21st to end	Night	8% 11% 5% 10% 5% 4 4 3 4 5% 42%	8402
February	1st to 10th	Night	10% 11% 4 8% 5% 4 5% 3 5% 5% 40%	2730
	11th to 20th	Night	9% 9% 3 8% 5% 5% 5% 4 6% 7% 42%	2631
	21st to end	Night	9% 8% 2 6% 3 4 3 3 5% 6% 52%	2076
March	1st to 10th	Night	13% 6% 2 6% 3 3 3 3 4 5% 51%	5107
	11th to 20th	Night	10% 6% 2 4 2 3 3 3 4 6% 57%	5090
	21st to end	Night	14% 10% 2 7% 4 4 4 4 5% 8% 36%	5588
April	1st to 10th	Night	13% 8% 2 5% 4 4 3 3 5% 6% 46%	2258
	11th to 20th	Night	11% 7% 2 6% 4 3 4 3 5% 7% 48%	1942
	21st to end	Night	16% 7% 2 6% 3 3 4 3 4 5% 46%	1890
May	1st to 10th	Night	11% 6% 2 5% 4 4 4 3 5% 6% 51%	5266
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 5% 6% 53%	5265
	21st to end	Night	17% 7% 2 6% 4 3 3 3 5% 7% 42%	5658
June	1st to 10th	Night	6% 4 2 5% 5% 4 4 4 6% 8% 52%	1680
	11th to 20th	Night	7% 4 2 4 3 4 4 4 7% 9% 51%	1680
	21st to end	Night	5% 4 2 4 3 4 4 3 7% 8% 56%	1684
July	1st to 10th	Night	6% 6% 2 6% 4 4 5% 4 6% 9% 50%	5308
	11th to 20th	Night	4 3 2 4 3 3 4 3 5% 7% 62%	5307
	21st to end	Night	6% 4 2 5% 4 4 5% 5% 7% 10% 46%	5770
August	1st to 10th	Night	4 4 1 4 4 3 4 3 5% 9% 59%	4156
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 3 6% 9% 47%	4118
	21st to end	Night	6% 4 2 5% 3 3 4 3 6% 11% 54%	4645
September	1st to 10th	Night	8% 4 2 4 3 2 3 3 5% 7% 59%	2193
	11th to 20th	Night	9% 4 1 4 3 3 4 3 5% 8% 56%	2310
	21st to end	Night	10% 5% 1 5% 3 3 4 2 5% 5% 57%	2310
October	1st to 10th	Night	13% 4 2 4 3 3 4 4 5% 6% 52%	2440
	11th to 20th	Night	12% 5% 2 4 3 3 3 2 3 6% 56%	2437
	21st to end	Night	14% 7% 2 4 3 3 3 3 4 5% 51%	2640
November	1st to 10th	Night	8% 4 2 4 3 3 3 4 5% 7% 57%	2645
	11th to 20th	Night	9% 7% 2 6% 4 3 3 3 5% 6% 53%	2764
	21st to end	Night	11% 8% 3 6% 3 3 3 3 4 6% 51%	2940
December	1st to 10th	Night	5% 5% 2 6% 4 4 4 3 5% 7% 54%	4720
	11th to 20th	Night	9% 8% 3 7% 4 3 4 3 5% 7% 46%	5339
	21st to end	Night	16% 13% 5% 10% 4 3 3 3 4 5% 34%	6933

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	54% 5% 12% 19% 10% 1	5290
	11th to 20th	Day	44% 4 13% 20% 17% 2	5310
	21st to end	Day	45% 5% 15% 24% 11%	5812
February	1st to 10th	Day	48% 7% 16% 19% 10% 1	1890
	11th to 20th	Day	44% 6% 11% 23% 14% 3	1902
	21st to end	Day	36% 6% 14% 25% 16% 3	1730
March	1st to 10th	Day	38% 4 8% 27% 18% 6%	4959
	11th to 20th	Day	33% 5% 9% 26% 23% 5%	5090
	21st to end	Day	50% 8% 20% 16% 5% 2	5585
April	1st to 10th	Day	42% 5% 13% 25% 13% 2	2362
	11th to 20th	Day	41% 7% 13% 23% 14% 3	2623
	21st to end	Day	46% 7% 11% 23% 13% 1	2730
May	1st to 10th	Day	37% 6% 10% 26% 19% 2	7655
	11th to 20th	Day	37% 5% 9% 23% 23% 3	7631
	21st to end	Day	45% 6% 12% 22% 15% 1	8523
June	1st to 10th	Day	31% 8% 17% 29% 13% 2	2940
	11th to 20th	Day	32% 7% 13% 30% 17% 1	2940
	21st to end	Day	33% 8% 15% 27% 14% 4	2928
July	1st to 10th	Day	35% 3 17% 31% 13% 1	7616
	11th to 20th	Day	27% 4 14% 30% 21% 4	7611
	21st to end	Day	35% 4 18% 28% 13% 1	8155
August	1st to 10th	Day	31% 6% 15% 28% 19% 2	6000
	11th to 20th	Day	42% 5% 18% 24% 11%	5987
	21st to end	Day	34% 5% 17% 28% 12% 4	6498
September	1st to 10th	Day	32% 4 12% 29% 18% 5%	2423
	11th to 20th	Day	32% 5% 13% 31% 17% 1	2310
	21st to end	Day	31% 5% 10% 29% 24% 2	2310
October	1st to 10th	Day	21% 3 7% 20% 46% 3	3444
	11th to 20th	Day	21% 3 13% 30% 26% 7%	3270
	21st to end	Day	36% 4 9% 27% 21% 2	3538
November	1st to 10th	Day	32% 4 14% 28% 20% 3	1870
	11th to 20th	Day	36% 6% 13% 25% 19% 1	1853
	21st to end	Day	40% 4 12% 29% 13% 1	1680
December	1st to 10th	Day	33% 4 17% 28% 17% 1	2690
	11th to 20th	Day	43% 5% 17% 25% 10%	3085
	21st to end	Day	54% 5% 12% 21% 6% 1	4282
January	1st to 10th	Night	52% 6% 13% 16% 12% 1	7635
	11th to 20th	Night	36% 5% 13% 26% 18% 1	7680
	21st to end	Night	44% 4 15% 19% 16% 2	8402
February	1st to 10th	Night	45% 5% 15% 21% 12% 2	2730
	11th to 20th	Night	41% 5% 14% 22% 15% 3	2632
	21st to end	Night	33% 6% 11% 26% 21% 4	2076
March	1st to 10th	Night	34% 5% 8% 28% 23% 3	5107
	11th to 20th	Night	29% 4 7% 25% 27% 7%	5090
	21st to end	Night	44% 8% 18% 22% 7% 1	5588
April	1st to 10th	Night	37% 6% 11% 26% 17% 3	2258
	11th to 20th	Night	35% 6% 12% 25% 18% 3	1942
	21st to end	Night	40% 6% 13% 23% 17% 1	1890
May	1st to 10th	Night	34% 5% 8% 25% 24% 3	5293
	11th to 20th	Night	32% 5% 10% 22% 26% 5%	5266
	21st to end	Night	42% 6% 11% 24% 15% 1	5669
June	1st to 10th	Night	27% 8% 15% 32% 16% 3	1680
	11th to 20th	Night	26% 8% 14% 26% 20% 5%	1680
	21st to end	Night	23% 8% 15% 30% 21% 3	1684
July	1st to 10th	Night	32% 3 15% 32% 15% 2	5265
	11th to 20th	Night	22% 4 13% 31% 24% 5%	5256
	21st to end	Night	32% 5% 19% 26% 17% 1	5641
August	1st to 10th	Night	23% 4 15% 35% 20% 2	4146
	11th to 20th	Night	35% 3 21% 26% 13% 1	4145
	21st to end	Night	27% 4 17% 33% 13% 6%	4645
September	1st to 10th	Night	25% 4 13% 29% 23% 7%	2193
	11th to 20th	Night	26% 6% 14% 32% 19% 4	2310
	21st to end	Night	30% 4 9% 26% 27% 4	2310
October	1st to 10th	Night	20% 4 7% 17% 47% 5%	3921
	11th to 20th	Night	22% 2 8% 29% 30% 9%	3936
	21st to end	Night	34% 3 9% 30% 22% 2	4252
November	1st to 10th	Night	27% 6% 14% 26% 23% 4	2645
	11th to 20th	Night	32% 4 12% 30% 19% 3	2764
	21st to end	Night	36% 4 12% 28% 18% 2	2940
December	1st to 10th	Night	30% 4 16% 34% 16% 1	4720
	11th to 20th	Night	38% 5% 15% 29% 13%	5341
	21st to end	Night	53% 5% 11% 23% 8% 1	6933

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	18% 13% 37% 24% 7% 2	330
	11th to 20th	Day	18% 15% 36% 23% 5% 1	330
	21st to end	Day	12% 14% 45% 21% 7% 1	363
February	1st to 10th	Day	16% 16% 44% 21% 3	330
	11th to 20th	Day	17% 15% 39% 22% 6% 1	330
	21st to end	Day	14% 20% 38% 23% 5%	273
March	1st to 10th	Day	18% 14% 41% 22% 4 1	330
	11th to 20th	Day	27% 10% 34% 20% 7% 2	330
	21st to end	Day	29% 17% 35% 17% 2	363
April	1st to 10th	Day	21% 18% 41% 16% 4	382
	11th to 20th	Day	21% 16% 38% 20% 6%	661
	21st to end	Day	22% 17% 31% 21% 7% 2	750
May	1st to 10th	Day	17% 12% 33% 26% 11% 1	753
	11th to 20th	Day	17% 10% 32% 27% 12% 2	775
	21st to end	Day	18% 9% 29% 28% 14% 2	844
June	1st to 10th	Day	7% 5% 24% 36% 23% 5%	780
	11th to 20th	Day	10% 6% 29% 35% 17% 3	780
	21st to end	Day	8% 7% 33% 35% 14% 2	780
July	1st to 10th	Day	8% 4 16% 34% 27% 10%	771
	11th to 20th	Day	4 4 21% 38% 25% 8%	768
	21st to end	Day	7% 2 19% 41% 28% 4	849
August	1st to 10th	Day	6% 2 22% 42% 23% 4	776
	11th to 20th	Day	9% 2 17% 42% 24% 4	765
	21st to end	Day	10% 2 23% 36% 25% 5%	816
September	1st to 10th	Day	11% 5% 27% 35% 17% 4	473
	11th to 20th	Day	10% 3 30% 34% 18% 5%	360
	21st to end	Day	17% 7% 29% 27% 15% 5%	360
October	1st to 10th	Day	19% 5% 26% 31% 14% 5%	360
	11th to 20th	Day	12% 15% 43% 21% 9% 1	339
	21st to end	Day	19% 14% 37% 19% 8% 2	363
November	1st to 10th	Day	15% 14% 37% 25% 8% 2	330
	11th to 20th	Day	15% 15% 39% 23% 7%	330
	21st to end	Day	22% 13% 32% 24% 8% 1	330
December	1st to 10th	Day	9% 14% 41% 29% 5% 2	330
	11th to 20th	Day	16% 16% 33% 28% 7%	330
	21st to end	Day	20% 13% 41% 21% 4 1	363
January	1st to 10th	Night	12% 11% 37% 34% 6%	1050
	11th to 20th	Night	14% 13% 38% 29% 6%	1050
	21st to end	Night	16% 8% 40% 31% 5%	1155
February	1st to 10th	Night	15% 10% 41% 29% 4	1050
	11th to 20th	Night	13% 11% 43% 29% 4	997
	21st to end	Night	13% 13% 45% 25% 4	692
March	1st to 10th	Night	14% 14% 39% 27% 7%	671
	11th to 20th	Night	18% 10% 39% 27% 6%	630
	21st to end	Night	20% 11% 41% 23% 5%	693
April	1st to 10th	Night	16% 16% 40% 24% 4	630
	11th to 20th	Night	14% 15% 39% 28% 3	623
	21st to end	Night	19% 11% 36% 27% 7%	630
May	1st to 10th	Night	16% 10% 34% 32% 9%	630
	11th to 20th	Night	15% 9% 31% 35% 9%	621
	21st to end	Night	18% 7% 30% 31% 13% 1	683
June	1st to 10th	Night	8% 3 25% 46% 17%	630
	11th to 20th	Night	8% 4 32% 42% 14%	630
	21st to end	Night	6% 3 33% 45% 13%	630
July	1st to 10th	Night	7% 2 17% 43% 29% 1	615
	11th to 20th	Night	3 2 17% 50% 27% 1	612
	21st to end	Night	4 1 16% 55% 24% 1	690
August	1st to 10th	Night	5% 2 21% 48% 22% 2	627
	11th to 20th	Night	8% 2 17% 48% 25% 1	624
	21st to end	Night	8% 2 21% 42% 24% 2	693
September	1st to 10th	Night	10% 3 24% 43% 18% 1	630
	11th to 20th	Night	11% 1 30% 40% 16% 1	630
	21st to end	Night	12% 5% 30% 36% 16% 1	630
October	1st to 10th	Night	14% 8% 29% 36% 12% 2	760
	11th to 20th	Night	14% 10% 37% 31% 7%	813
	21st to end	Night	19% 10% 31% 32% 9%	880
November	1st to 10th	Night	10% 10% 35% 36% 9% 1	1005
	11th to 20th	Night	13% 11% 40% 30% 6%	1050
	21st to end	Night	16% 11% 34% 30% 8% 1	1050
December	1st to 10th	Night	13% 10% 39% 32% 6%	1050
	11th to 20th	Night	16% 10% 35% 33% 5%	1050
	21st to end	Night	19% 11% 34% 31% 4	1155

Page generated at 2026-10-11 04:06:28. Version ac07

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