Mount Forest
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Forest clear sky chart from 2005-11-06 to 2025-02-25.

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	15% 13% 5% 10% 6% 5% 5% 4 5% 6% 27%	108898
	Night	14% 14% 6% 12% 6% 5% 4 3 5% 5% 26%	109749
Transparency	Day	55% 6% 11% 17% 10% 1	112505
	Night	57% 6% 10% 16% 9% 1	114306
Seeing	Day	21% 13% 29% 22% 11% 4	15316
	Night	21% 12% 30% 26% 10% 1	24614

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	11% 16% 10% 20% 9% 6% 4 3 2 4 14%	3222
	11th to 20th	Day	9% 20% 11% 25% 11% 10% 4 2 2 2 5%	4007
	21st to end	Day	13% 20% 8% 22% 8% 6% 5% 2 3 3 9%	4466
February	1st to 10th	Day	13% 20% 7% 20% 10% 6% 4 3 3 3 11%	1800
	11th to 20th	Day	13% 15% 9% 19% 11% 4 4 3 4 4 13%	1753
	21st to end	Day	15% 19% 7% 13% 9% 4 5% 3 5% 5% 15%	1556
March	1st to 10th	Day	17% 15% 5% 13% 7% 4 4 2 3 4 26%	3368
	11th to 20th	Day	10% 17% 9% 14% 5% 5% 4 3 4 5% 25%	3480
	21st to end	Day	15% 15% 5% 11% 6% 5% 4 4 5% 6% 26%	3815
April	1st to 10th	Day	17% 16% 5% 10% 5% 5% 4 3 5% 5% 25%	2191
	11th to 20th	Day	19% 13% 3 6% 4 3 3 4 5% 5% 34%	2412
	21st to end	Day	21% 12% 5% 7% 4 3 4 2 5% 7% 31%	2470
May	1st to 10th	Day	18% 9% 3 7% 5% 5% 4 4 6% 7% 33%	4108
	11th to 20th	Day	17% 9% 3 7% 5% 4 5% 4 6% 8% 32%	4238
	21st to end	Day	15% 5% 2 5% 3 4 4 3 5% 7% 46%	4837
June	1st to 10th	Day	15% 7% 3 7% 4 5% 5% 4 6% 7% 36%	2685
	11th to 20th	Day	12% 6% 2 5% 5% 5% 4 4 7% 9% 40%	2850
	21st to end	Day	17% 7% 2 5% 4 5% 4 4 6% 8% 37%	2850
July	1st to 10th	Day	12% 7% 3 7% 5% 5% 6% 5% 7% 8% 34%	4760
	11th to 20th	Day	12% 7% 2 5% 5% 6% 5% 4 7% 7% 41%	4464
	21st to end	Day	9% 6% 3 7% 5% 5% 5% 5% 7% 9% 41%	4466
August	1st to 10th	Day	14% 7% 2 7% 6% 5% 7% 4 6% 9% 33%	4104
	11th to 20th	Day	14% 8% 3 8% 5% 5% 6% 5% 7% 9% 30%	4044
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 8% 40%	4450
September	1st to 10th	Day	13% 8% 3 7% 5% 4 4 4 6% 7% 38%	2275
	11th to 20th	Day	12% 6% 3 6% 4 4 4 3 6% 9% 42%	2090
	21st to end	Day	16% 9% 3 8% 5% 5% 4 4 7% 7% 33%	2090
October	1st to 10th	Day	20% 10% 3 8% 5% 3 4 4 5% 6% 32%	1914
	11th to 20th	Day	23% 14% 4 8% 5% 6% 5% 4 5% 5% 23%	1900
	21st to end	Day	25% 18% 4 8% 5% 5% 4 4 4 6% 17%	2057
November	1st to 10th	Day	17% 19% 4 8% 5% 5% 4 3 4 6% 25%	1720
	11th to 20th	Day	17% 19% 6% 11% 4 5% 5% 3 6% 6% 19%	1600
	21st to end	Day	18% 23% 9% 11% 6% 4 5% 4 4 5% 12%	1600
December	1st to 10th	Day	17% 27% 10% 16% 6% 5% 3 2 3 3 8%	2600
	11th to 20th	Day	20% 23% 8% 15% 6% 3 4 2 4 4 11%	2986
	21st to end	Day	24% 22% 7% 12% 6% 5% 4 3 4 4 10%	3670
January	1st to 10th	Night	12% 16% 8% 23% 10% 6% 5% 3 3 4 9%	6726
	11th to 20th	Night	11% 16% 9% 23% 15% 8% 5% 3 3 3 5%	5859
	21st to end	Night	13% 16% 9% 20% 9% 7% 6% 3 4 4 9%	6490
February	1st to 10th	Night	14% 20% 6% 15% 10% 5% 5% 3 4 4 13%	2600
	11th to 20th	Night	13% 16% 8% 15% 8% 6% 4 3 4 5% 17%	2533
	21st to end	Night	15% 14% 6% 14% 7% 5% 4 4 5% 5% 20%	1989
March	1st to 10th	Night	14% 13% 6% 9% 5% 5% 5% 3 5% 5% 31%	3471
	11th to 20th	Night	10% 14% 6% 11% 6% 5% 5% 3 5% 6% 30%	3479
	21st to end	Night	14% 11% 5% 11% 5% 5% 4 3 4 5% 33%	3817
April	1st to 10th	Night	20% 14% 4 8% 5% 3 4 3 4 6% 28%	1988
	11th to 20th	Night	18% 12% 4 6% 4 4 5% 3 4 6% 35%	1735
	21st to end	Night	15% 12% 4 9% 6% 5% 4 4 5% 5% 31%	1710
May	1st to 10th	Night	14% 8% 3 7% 5% 3 4 3 5% 7% 40%	2833
	11th to 20th	Night	15% 8% 3 7% 5% 5% 6% 4 5% 6% 38%	2639
	21st to end	Night	10% 6% 2 6% 4 4 3 3 5% 7% 49%	2738
June	1st to 10th	Night	14% 6% 3 8% 5% 3 4 4 5% 8% 40%	1490
	11th to 20th	Night	12% 5% 2 6% 5% 5% 5% 5% 6% 9% 39%	1330
	21st to end	Night	13% 7% 3 5% 3 3 4 4 6% 8% 43%	1330
July	1st to 10th	Night	6% 7% 2 7% 4 4 5% 3 5% 8% 49%	2210
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 5% 7% 50%	2493
	21st to end	Night	6% 7% 2 6% 5% 4 4 5% 6% 7% 47%	3087
August	1st to 10th	Night	13% 6% 3 6% 4 4 4 3 5% 7% 45%	2825
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 6% 7% 39%	2785
	21st to end	Night	12% 7% 2 6% 4 5% 4 3 5% 6% 46%	3173
September	1st to 10th	Night	11% 6% 3 6% 4 4 5% 4 5% 7% 45%	1903
	11th to 20th	Night	12% 5% 2 5% 4 4 3 3 6% 6% 50%	2090
	21st to end	Night	14% 9% 3 7% 5% 4 4 3 5% 7% 38%	2090
October	1st to 10th	Night	17% 9% 3 7% 5% 5% 3 3 5% 7% 36%	2266
	11th to 20th	Night	22% 12% 4 7% 4 4 5% 3 5% 6% 27%	2280
	21st to end	Night	23% 15% 4 8% 5% 5% 4 3 5% 6% 22%	2536
November	1st to 10th	Night	17% 13% 3 9% 5% 5% 5% 4 4 6% 28%	2576
	11th to 20th	Night	16% 18% 5% 10% 6% 4 5% 4 5% 6% 21%	2800
	21st to end	Night	20% 19% 6% 11% 6% 5% 5% 3 4 6% 15%	2800
December	1st to 10th	Night	15% 23% 8% 14% 6% 6% 5% 3 5% 4 9%	4580
	11th to 20th	Night	12% 23% 11% 17% 7% 4 4 3 3 4 13%	5208
	21st to end	Night	20% 22% 8% 15% 6% 5% 4 3 4 4 9%	7290

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	74% 4 7% 7% 7% 1	3223
	11th to 20th	Day	88% 3 4 2 2	4041
	21st to end	Day	81% 4 8% 5% 2	4466
February	1st to 10th	Day	78% 5% 5% 10% 2 1	1800
	11th to 20th	Day	73% 5% 7% 10% 5% 1	1762
	21st to end	Day	70% 5% 8% 11% 5% 1	1556
March	1st to 10th	Day	62% 4 11% 14% 8% 1	3371
	11th to 20th	Day	62% 4 11% 16% 6% 1	3480
	21st to end	Day	57% 5% 12% 15% 9% 2	3815
April	1st to 10th	Day	60% 5% 9% 17% 9%	2191
	11th to 20th	Day	51% 5% 10% 19% 13% 1	2412
	21st to end	Day	54% 5% 10% 17% 11% 2	2470
May	1st to 10th	Day	48% 6% 13% 19% 13% 1	4120
	11th to 20th	Day	48% 8% 13% 23% 7% 1	4242
	21st to end	Day	38% 6% 12% 21% 18% 5%	4837
June	1st to 10th	Day	45% 7% 11% 21% 14% 1	2685
	11th to 20th	Day	40% 7% 12% 24% 15% 1	2850
	21st to end	Day	42% 8% 13% 23% 13% 1	2850
July	1st to 10th	Day	43% 7% 14% 19% 15% 1	4686
	11th to 20th	Day	38% 7% 11% 31% 11% 1	4384
	21st to end	Day	38% 7% 13% 23% 17% 2	4324
August	1st to 10th	Day	46% 7% 12% 22% 12% 1	4091
	11th to 20th	Day	46% 8% 15% 22% 9%	4083
	21st to end	Day	38% 7% 13% 30% 11% 1	4450
September	1st to 10th	Day	43% 7% 13% 24% 11% 2	2275
	11th to 20th	Day	38% 6% 13% 29% 14%	2090
	21st to end	Day	48% 8% 13% 22% 9% 1	2090
October	1st to 10th	Day	47% 7% 11% 21% 13% 1	3174
	11th to 20th	Day	48% 6% 12% 19% 14% 1	3140
	21st to end	Day	59% 6% 13% 17% 5%	3371
November	1st to 10th	Day	59% 7% 10% 16% 8%	1720
	11th to 20th	Day	63% 7% 11% 11% 7% 1	1600
	21st to end	Day	71% 7% 9% 9% 3	1600
December	1st to 10th	Day	80% 6% 8% 5% 1	2600
	11th to 20th	Day	78% 4 7% 8% 3	2986
	21st to end	Day	79% 6% 5% 5% 5%	3670
January	1st to 10th	Night	75% 5% 7% 8% 5%	6726
	11th to 20th	Night	84% 4 5% 4 3	5900
	21st to end	Night	77% 6% 9% 5% 3	6490
February	1st to 10th	Night	72% 5% 8% 11% 3	2600
	11th to 20th	Night	68% 5% 9% 12% 6%	2535
	21st to end	Night	63% 6% 10% 12% 8%	1989
March	1st to 10th	Night	53% 7% 14% 19% 7% 1	3481
	11th to 20th	Night	52% 6% 15% 16% 10% 2	3480
	21st to end	Night	51% 4 12% 19% 12% 1	3817
April	1st to 10th	Night	58% 5% 8% 16% 12% 1	1988
	11th to 20th	Night	50% 5% 8% 20% 16% 2	1735
	21st to end	Night	52% 6% 9% 16% 15% 2	1710
May	1st to 10th	Night	43% 7% 11% 20% 15% 5%	2840
	11th to 20th	Night	44% 9% 12% 22% 11% 2	2640
	21st to end	Night	34% 7% 12% 23% 22% 3	2739
June	1st to 10th	Night	41% 6% 11% 25% 17% 2	1490
	11th to 20th	Night	38% 7% 12% 24% 17% 2	1330
	21st to end	Night	39% 7% 11% 27% 16% 1	1330
July	1st to 10th	Night	33% 6% 14% 23% 19% 5%	2175
	11th to 20th	Night	33% 6% 11% 33% 17% 1	2450
	21st to end	Night	34% 8% 14% 27% 16% 1	2988
August	1st to 10th	Night	38% 6% 12% 27% 16% 1	2814
	11th to 20th	Night	41% 6% 15% 25% 11% 1	2812
	21st to end	Night	37% 5% 11% 31% 14% 1	3173
September	1st to 10th	Night	37% 7% 12% 28% 15% 2	1903
	11th to 20th	Night	33% 5% 13% 29% 19% 1	2090
	21st to end	Night	45% 6% 13% 24% 11%	2090
October	1st to 10th	Night	38% 6% 10% 25% 21% 1	3786
	11th to 20th	Night	49% 5% 12% 18% 15%	3779
	21st to end	Night	50% 6% 16% 20% 7%	4172
November	1st to 10th	Night	54% 8% 12% 17% 9% 1	2576
	11th to 20th	Night	62% 7% 11% 13% 5% 2	2800
	21st to end	Night	67% 8% 11% 11% 3 1	2800
December	1st to 10th	Night	75% 7% 10% 7% 1	4580
	11th to 20th	Night	76% 4 8% 8% 3	5208
	21st to end	Night	77% 6% 6% 7% 3	7290

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	23% 19% 38% 15% 4 1	213
	11th to 20th	Day	19% 28% 35% 14% 3 1	300
	21st to end	Day	25% 18% 37% 17% 4	330
February	1st to 10th	Day	27% 22% 38% 11% 3	300
	11th to 20th	Day	24% 23% 41% 11% 1	300
	21st to end	Day	32% 28% 30% 9% 1	237
March	1st to 10th	Day	26% 16% 36% 15% 6%	418
	11th to 20th	Day	23% 18% 34% 18% 6% 1	460
	21st to end	Day	28% 14% 32% 18% 7% 1	506
April	1st to 10th	Day	23% 18% 34% 18% 6% 1	460
	11th to 20th	Day	29% 19% 25% 14% 9% 4	452
	21st to end	Day	28% 12% 31% 20% 7% 2	460
May	1st to 10th	Day	24% 11% 27% 24% 11% 3	463
	11th to 20th	Day	21% 10% 26% 24% 15% 4	487
	21st to end	Day	18% 7% 25% 29% 15% 6%	529
June	1st to 10th	Day	15% 14% 26% 29% 13% 3	515
	11th to 20th	Day	15% 9% 31% 29% 14% 3	680
	21st to end	Day	19% 9% 30% 28% 12% 3	680
July	1st to 10th	Day	11% 8% 25% 27% 22% 7%	671
	11th to 20th	Day	14% 8% 27% 27% 17% 7%	565
	21st to end	Day	11% 5% 28% 33% 17% 7%	532
August	1st to 10th	Day	13% 6% 23% 27% 20% 11%	486
	11th to 20th	Day	14% 5% 21% 26% 21% 13%	479
	21st to end	Day	14% 7% 23% 28% 19% 9%	539
September	1st to 10th	Day	14% 10% 26% 23% 17% 10%	490
	11th to 20th	Day	10% 6% 21% 27% 23% 14%	490
	21st to end	Day	15% 14% 26% 24% 14% 6%	490
October	1st to 10th	Day	22% 12% 26% 21% 13% 4	490
	11th to 20th	Day	27% 19% 29% 19% 5% 1	490
	21st to end	Day	33% 16% 28% 17% 5%	506
November	1st to 10th	Day	30% 18% 29% 17% 5%	278
	11th to 20th	Day	26% 23% 35% 11% 3 3	200
	21st to end	Day	29% 20% 37% 14% 2	200
December	1st to 10th	Day	30% 26% 28% 14% 3	200
	11th to 20th	Day	28% 28% 30% 12% 3	200
	21st to end	Day	36% 15% 35% 10% 3	220
January	1st to 10th	Night	22% 17% 38% 17% 5% 1	998
	11th to 20th	Night	27% 18% 31% 21% 4	800
	21st to end	Night	20% 13% 39% 23% 6%	880
February	1st to 10th	Night	23% 18% 37% 20% 2	800
	11th to 20th	Night	22% 15% 37% 22% 4	783
	21st to end	Night	24% 17% 36% 20% 3	647
March	1st to 10th	Night	19% 15% 40% 19% 6% 1	760
	11th to 20th	Night	20% 16% 37% 20% 6% 1	760
	21st to end	Night	23% 12% 32% 23% 9% 1	836
April	1st to 10th	Night	26% 13% 31% 26% 4	760
	11th to 20th	Night	23% 14% 29% 23% 10% 1	611
	21st to end	Night	21% 11% 32% 27% 8% 1	570
May	1st to 10th	Night	18% 7% 30% 31% 13% 1	570
	11th to 20th	Night	19% 5% 29% 33% 12% 1	466
	21st to end	Night	12% 5% 27% 37% 18%	411
June	1st to 10th	Night	16% 5% 29% 38% 12%	380
	11th to 20th	Night	14% 5% 30% 38% 13%	380
	21st to end	Night	16% 7% 24% 38% 14% 1	380
July	1st to 10th	Night	6% 4 18% 49% 22% 1	370
	11th to 20th	Night	11% 5% 22% 37% 23% 2	426
	21st to end	Night	11% 3 19% 45% 21% 1	624
August	1st to 10th	Night	13% 2 18% 38% 28% 1	567
	11th to 20th	Night	12% 2 19% 35% 28% 4	564
	21st to end	Night	14% 4 22% 33% 25% 2	650
September	1st to 10th	Night	13% 6% 24% 33% 19% 5%	760
	11th to 20th	Night	13% 4 21% 33% 23% 5%	760
	21st to end	Night	18% 8% 23% 33% 15% 4	760
October	1st to 10th	Night	22% 7% 27% 28% 14% 2	760
	11th to 20th	Night	26% 12% 26% 26% 8% 2	760
	21st to end	Night	30% 12% 31% 23% 4	836
November	1st to 10th	Night	25% 13% 29% 25% 7% 1	780
	11th to 20th	Night	24% 19% 32% 19% 6% 1	800
	21st to end	Night	27% 16% 33% 21% 3	800
December	1st to 10th	Night	29% 16% 34% 17% 4	800
	11th to 20th	Night	23% 19% 39% 16% 3 1	800
	21st to end	Night	30% 16% 34% 17% 2	1005

Page generated at 2025-02-22 06:51:37. Version ac07

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