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 2026-07-01.

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% 12% 5% 10% 6% 5% 4 3 5% 6% 29%	138203
	Night	14% 13% 5% 12% 6% 5% 4 3 5% 5% 26%	134132
Transparency	Day	54% 6% 10% 18% 10% 1	141767
	Night	57% 6% 10% 16% 10% 1	138657
Seeing	Day	21% 14% 29% 22% 11% 4	17146
	Night	21% 12% 30% 26% 10% 1	26263

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	14% 17% 10% 19% 9% 6% 4 3 3 4 12%	4172
	11th to 20th	Day	9% 22% 12% 24% 11% 9% 3 2 2 2 4	5227
	21st to end	Day	11% 18% 7% 20% 10% 10% 7% 3 3 3 8%	5780
February	1st to 10th	Day	13% 19% 7% 19% 10% 6% 4 3 3 3 12%	1890
	11th to 20th	Day	13% 14% 9% 20% 11% 4 5% 3 4 4 13%	1843
	21st to end	Day	14% 20% 7% 13% 9% 4 5% 3 5% 5% 15%	1674
March	1st to 10th	Day	16% 13% 5% 15% 8% 5% 4 2 3 4 24%	4948
	11th to 20th	Day	12% 15% 7% 13% 4 4 4 4 5% 7% 26%	5090
	21st to end	Day	17% 16% 7% 11% 5% 4 4 3 4 5% 24%	5586
April	1st to 10th	Day	17% 16% 5% 10% 5% 5% 4 3 5% 5% 25%	2422
	11th to 20th	Day	19% 13% 3 6% 4 3 3 4 5% 5% 34%	2669
	21st to end	Day	19% 12% 5% 7% 4 3 4 3 5% 7% 31%	2730
May	1st to 10th	Day	15% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	7642
	11th to 20th	Day	14% 12% 3 7% 5% 4 5% 4 5% 7% 33%	7923
	21st to end	Day	18% 8% 2 5% 3 4 4 3 5% 6% 42%	9060
June	1st to 10th	Day	14% 7% 3 7% 4 5% 5% 4 6% 7% 37%	2968
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 7% 8% 39%	3150
	21st to end	Day	16% 7% 2 5% 4 5% 4 4 6% 8% 37%	3150
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 5% 5% 7% 9% 37%	6820
	11th to 20th	Day	11% 7% 2 6% 4 5% 4 4 6% 7% 44%	6398
	21st to end	Day	8% 6% 3 6% 4 4 5% 4 6% 9% 46%	6424
August	1st to 10th	Day	13% 7% 2 7% 6% 5% 7% 4 6% 9% 34%	4234
	11th to 20th	Day	13% 8% 3 8% 5% 5% 6% 5% 7% 9% 30%	4174
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 4 8% 8% 40%	4591
September	1st to 10th	Day	13% 8% 3 7% 5% 4 4 4 6% 7% 38%	2394
	11th to 20th	Day	12% 6% 2 6% 4 4 4 3 6% 9% 44%	2200
	21st to end	Day	16% 9% 3 8% 5% 5% 4 4 6% 7% 33%	2200
October	1st to 10th	Day	20% 9% 3 8% 5% 3 4 4 5% 6% 33%	2014
	11th to 20th	Day	22% 14% 4 8% 5% 5% 5% 4 5% 5% 23%	2000
	21st to end	Day	24% 17% 4 8% 5% 4 4 4 4 6% 17%	2165
November	1st to 10th	Day	17% 19% 4 8% 5% 5% 4 3 4 6% 25%	1808
	11th to 20th	Day	16% 19% 6% 11% 5% 5% 5% 3 6% 6% 19%	1680
	21st to end	Day	17% 24% 9% 11% 6% 4 4 4 4 5% 12%	1680
December	1st to 10th	Day	17% 26% 11% 16% 6% 5% 3 2 3 3 8%	2680
	11th to 20th	Day	19% 23% 8% 16% 6% 3 4 2 4 4 11%	3066
	21st to end	Day	23% 22% 7% 12% 6% 5% 4 3 4 4 10%	3751
January	1st to 10th	Night	13% 16% 9% 24% 10% 6% 5% 3 3 4 8%	8721
	11th to 20th	Night	9% 19% 10% 24% 14% 7% 4 3 2 3 4	7639
	21st to end	Night	10% 15% 8% 19% 12% 8% 7% 4 4 4 8%	8401
February	1st to 10th	Night	14% 20% 6% 15% 10% 5% 5% 3 4 5% 14%	2730
	11th to 20th	Night	13% 16% 8% 15% 8% 6% 4 3 4 5% 18%	2663
	21st to end	Night	14% 15% 6% 14% 7% 5% 5% 4 5% 5% 19%	2128
March	1st to 10th	Night	14% 13% 6% 11% 7% 5% 5% 3 5% 5% 26%	5111
	11th to 20th	Night	9% 12% 6% 11% 5% 5% 5% 4 6% 7% 29%	5089
	21st to end	Night	19% 12% 5% 12% 6% 4 4 3 3 4 29%	5588
April	1st to 10th	Night	19% 14% 5% 10% 5% 3 4 3 4 6% 27%	2197
	11th to 20th	Night	17% 12% 3 7% 4 4 5% 3 4 6% 34%	1919
	21st to end	Night	14% 12% 4 9% 6% 5% 4 4 5% 5% 32%	1890
May	1st to 10th	Night	16% 9% 3 7% 5% 3 4 3 5% 7% 38%	5257
	11th to 20th	Night	15% 9% 3 7% 4 4 5% 3 4 6% 40%	4921
	21st to end	Night	17% 7% 2 5% 4 3 3 3 4 6% 46%	5114
June	1st to 10th	Night	14% 6% 2 7% 5% 3 4 3 5% 8% 42%	1646
	11th to 20th	Night	12% 5% 2 6% 5% 5% 5% 5% 6% 9% 38%	1470
	21st to end	Night	13% 8% 3 5% 3 4 4 4 6% 8% 42%	1470
July	1st to 10th	Night	8% 8% 2 6% 4 4 5% 3 5% 8% 45%	3160
	11th to 20th	Night	13% 7% 2 5% 3 3 4 3 5% 6% 48%	3563
	21st to end	Night	9% 7% 2 6% 4 3 4 4 5% 7% 49%	4428
August	1st to 10th	Night	12% 6% 3 6% 4 4 4 3 5% 7% 45%	2915
	11th to 20th	Night	15% 8% 3 6% 4 4 5% 3 6% 7% 39%	2875
	21st to end	Night	12% 7% 2 6% 4 5% 5% 3 5% 6% 46%	3273
September	1st to 10th	Night	11% 6% 3 6% 4 4 5% 4 5% 7% 45%	2003
	11th to 20th	Night	12% 5% 2 4 4 4 3 3 6% 6% 51%	2200
	21st to end	Night	15% 10% 3 7% 5% 4 4 3 5% 6% 38%	2200
October	1st to 10th	Night	16% 8% 3 7% 5% 5% 3 3 5% 7% 38%	2385
	11th to 20th	Night	22% 12% 4 7% 4 4 5% 3 5% 6% 28%	2400
	21st to end	Night	22% 14% 4 8% 5% 5% 4 3 5% 6% 23%	2670
November	1st to 10th	Night	17% 14% 4 9% 5% 5% 5% 4 4 6% 28%	2708
	11th to 20th	Night	16% 18% 5% 10% 6% 4 5% 4 5% 6% 20%	2940
	21st to end	Night	19% 20% 7% 11% 6% 5% 4 3 4 6% 15%	2940
December	1st to 10th	Night	15% 23% 8% 14% 6% 5% 5% 3 6% 4 9%	4720
	11th to 20th	Night	12% 23% 10% 18% 7% 4 4 3 3 4 13%	5348
	21st to end	Night	20% 22% 8% 15% 6% 5% 4 3 4 4 9%	7450

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	75% 4 8% 6% 6% 1	4173
	11th to 20th	Day	90% 3 3 2 2	5261
	21st to end	Day	81% 4 7% 5% 3	5780
February	1st to 10th	Day	77% 5% 4 10% 3 1	1890
	11th to 20th	Day	73% 5% 7% 10% 4 1	1852
	21st to end	Day	70% 5% 8% 11% 5%	1674
March	1st to 10th	Day	63% 4 14% 11% 8% 1	4951
	11th to 20th	Day	58% 4 13% 17% 6% 2	5090
	21st to end	Day	61% 4 10% 15% 8% 2	5586
April	1st to 10th	Day	60% 5% 8% 17% 9%	2422
	11th to 20th	Day	52% 5% 10% 20% 13% 1	2669
	21st to end	Day	53% 6% 10% 18% 11% 2	2730
May	1st to 10th	Day	48% 5% 13% 18% 11% 4	7651
	11th to 20th	Day	48% 6% 10% 20% 15% 1	7927
	21st to end	Day	43% 4 9% 25% 15% 3	9061
June	1st to 10th	Day	44% 7% 11% 21% 16% 1	2968
	11th to 20th	Day	41% 7% 12% 24% 14% 1	3150
	21st to end	Day	42% 8% 13% 24% 12% 1	3150
July	1st to 10th	Day	41% 7% 13% 22% 16% 1	6747
	11th to 20th	Day	36% 6% 11% 30% 16% 1	6318
	21st to end	Day	34% 6% 13% 28% 18% 1	6240
August	1st to 10th	Day	45% 7% 12% 22% 12% 1	4221
	11th to 20th	Day	46% 8% 15% 23% 9%	4213
	21st to end	Day	38% 7% 14% 31% 10% 1	4591
September	1st to 10th	Day	43% 7% 13% 24% 11% 2	2394
	11th to 20th	Day	36% 6% 13% 30% 14%	2200
	21st to end	Day	48% 8% 13% 22% 9% 1	2200
October	1st to 10th	Day	46% 7% 10% 22% 13% 1	3274
	11th to 20th	Day	48% 6% 12% 20% 14% 1	3240
	21st to end	Day	59% 6% 13% 17% 6%	3479
November	1st to 10th	Day	59% 7% 10% 17% 7%	1808
	11th to 20th	Day	63% 7% 11% 11% 7% 1	1680
	21st to end	Day	72% 7% 9% 9% 3	1680
December	1st to 10th	Day	80% 5% 8% 6% 1	2680
	11th to 20th	Day	78% 4 7% 8% 3	3066
	21st to end	Day	79% 6% 5% 5% 5%	3751
January	1st to 10th	Night	77% 5% 7% 7% 4	8721
	11th to 20th	Night	85% 4 4 4 3	7680
	21st to end	Night	77% 6% 8% 5% 5%	8401
February	1st to 10th	Night	71% 5% 8% 12% 4	2730
	11th to 20th	Night	67% 5% 9% 12% 6%	2665
	21st to end	Night	63% 6% 10% 13% 8%	2128
March	1st to 10th	Night	57% 6% 12% 15% 9% 1	5121
	11th to 20th	Night	51% 5% 17% 17% 9% 1	5090
	21st to end	Night	57% 4 10% 15% 12% 2	5588
April	1st to 10th	Night	58% 5% 8% 15% 12% 1	2197
	11th to 20th	Night	51% 5% 8% 20% 16% 1	1919
	21st to end	Night	51% 6% 10% 17% 14% 2	1890
May	1st to 10th	Night	45% 5% 9% 20% 14% 6%	5264
	11th to 20th	Night	45% 8% 10% 21% 15% 2	4922
	21st to end	Night	40% 5% 9% 26% 18% 2	5115
June	1st to 10th	Night	40% 5% 10% 25% 19% 2	1646
	11th to 20th	Night	39% 7% 12% 24% 16% 1	1470
	21st to end	Night	39% 6% 11% 27% 16% 1	1470
July	1st to 10th	Night	35% 6% 14% 23% 19% 3	3125
	11th to 20th	Night	35% 6% 10% 29% 19% 2	3520
	21st to end	Night	34% 6% 11% 30% 17% 2	4297
August	1st to 10th	Night	37% 6% 12% 27% 16% 1	2904
	11th to 20th	Night	41% 6% 15% 25% 11% 1	2902
	21st to end	Night	37% 6% 12% 31% 13% 1	3273
September	1st to 10th	Night	37% 7% 12% 29% 14% 2	2003
	11th to 20th	Night	32% 5% 13% 31% 19% 1	2200
	21st to end	Night	45% 6% 12% 24% 12% 1	2200
October	1st to 10th	Night	37% 6% 9% 26% 21% 1	3905
	11th to 20th	Night	49% 5% 12% 19% 15%	3899
	21st to end	Night	50% 6% 16% 20% 8%	4306
November	1st to 10th	Night	55% 7% 12% 17% 8% 1	2708
	11th to 20th	Night	62% 6% 11% 13% 5% 2	2940
	21st to end	Night	68% 7% 11% 11% 2 1	2940
December	1st to 10th	Night	74% 7% 10% 7% 2	4720
	11th to 20th	Night	75% 4 8% 8% 4	5348
	21st to end	Night	77% 6% 6% 7% 3	7450

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	24% 20% 38% 14% 3 1	234
	11th to 20th	Day	21% 29% 34% 12% 3 1	330
	21st to end	Day	25% 18% 36% 17% 3	363
February	1st to 10th	Day	27% 21% 37% 13% 3	330
	11th to 20th	Day	25% 22% 40% 12% 1	330
	21st to end	Day	32% 27% 30% 9% 1	273
March	1st to 10th	Day	27% 17% 37% 14% 5%	494
	11th to 20th	Day	26% 19% 32% 17% 5% 1	540
	21st to end	Day	29% 16% 32% 16% 6% 1	594
April	1st to 10th	Day	26% 20% 32% 17% 5% 1	540
	11th to 20th	Day	30% 19% 23% 14% 9% 4	532
	21st to end	Day	27% 13% 32% 20% 6% 2	540
May	1st to 10th	Day	23% 13% 31% 22% 10% 2	543
	11th to 20th	Day	21% 11% 26% 23% 14% 4	567
	21st to end	Day	19% 8% 27% 26% 14% 5%	617
June	1st to 10th	Day	14% 14% 29% 28% 12% 3	598
	11th to 20th	Day	15% 10% 32% 27% 12% 2	780
	21st to end	Day	18% 9% 31% 29% 11% 2	780
July	1st to 10th	Day	11% 8% 26% 28% 21% 7%	722
	11th to 20th	Day	14% 8% 26% 28% 16% 7%	609
	21st to end	Day	10% 5% 30% 32% 17% 6%	576
August	1st to 10th	Day	12% 6% 23% 29% 20% 11%	526
	11th to 20th	Day	14% 5% 21% 27% 21% 12%	519
	21st to end	Day	14% 7% 23% 28% 18% 10%	583
September	1st to 10th	Day	14% 10% 26% 23% 17% 10%	530
	11th to 20th	Day	9% 6% 20% 27% 24% 14%	530
	21st to end	Day	15% 13% 25% 25% 15% 6%	530
October	1st to 10th	Day	22% 12% 25% 23% 15% 4	530
	11th to 20th	Day	26% 19% 31% 18% 4 1	530
	21st to end	Day	32% 16% 28% 18% 5%	548
November	1st to 10th	Day	32% 19% 28% 16% 5%	306
	11th to 20th	Day	27% 23% 34% 12% 3 2	220
	21st to end	Day	30% 19% 35% 14% 1	220
December	1st to 10th	Day	30% 24% 28% 15% 3	220
	11th to 20th	Day	30% 27% 30% 11% 2	220
	21st to end	Day	37% 15% 35% 10% 3	242
January	1st to 10th	Night	22% 17% 39% 17% 4 1	1048
	11th to 20th	Night	27% 18% 31% 20% 4	840
	21st to end	Night	19% 14% 39% 23% 6%	924
February	1st to 10th	Night	22% 18% 36% 20% 3	840
	11th to 20th	Night	22% 15% 36% 22% 4	823
	21st to end	Night	24% 18% 36% 20% 3	692
March	1st to 10th	Night	20% 16% 40% 18% 6% 1	840
	11th to 20th	Night	22% 16% 37% 20% 5%	840
	21st to end	Night	23% 13% 32% 22% 9% 1	924
April	1st to 10th	Night	26% 15% 31% 24% 4	840
	11th to 20th	Night	22% 15% 30% 22% 10% 1	675
	21st to end	Night	21% 12% 31% 27% 8% 1	630
May	1st to 10th	Night	18% 8% 30% 30% 13% 1	630
	11th to 20th	Night	19% 5% 30% 32% 12% 1	516
	21st to end	Night	14% 6% 27% 37% 16%	455
June	1st to 10th	Night	15% 5% 30% 37% 12%	420
	11th to 20th	Night	14% 6% 32% 36% 12%	420
	21st to end	Night	16% 7% 24% 40% 13% 1	420
July	1st to 10th	Night	7% 4 18% 51% 21% 1	390
	11th to 20th	Night	12% 5% 22% 37% 23% 2	449
	21st to end	Night	11% 3 20% 45% 20% 1	657
August	1st to 10th	Night	12% 2 18% 39% 29% 1	597
	11th to 20th	Night	12% 2 19% 35% 28% 4	594
	21st to end	Night	14% 4 22% 33% 25% 2	684
September	1st to 10th	Night	12% 7% 24% 32% 20% 5%	800
	11th to 20th	Night	13% 4 21% 34% 24% 5%	800
	21st to end	Night	18% 8% 23% 32% 15% 4	800
October	1st to 10th	Night	21% 7% 26% 29% 15% 2	800
	11th to 20th	Night	26% 12% 27% 26% 8% 2	800
	21st to end	Night	29% 12% 31% 23% 4	880
November	1st to 10th	Night	25% 14% 29% 25% 7% 1	820
	11th to 20th	Night	24% 19% 31% 19% 6% 1	840
	21st to end	Night	28% 16% 33% 21% 3	840
December	1st to 10th	Night	29% 17% 34% 17% 4	840
	11th to 20th	Night	22% 19% 40% 16% 3	840
	21st to end	Night	31% 16% 34% 17% 2	1055

Page generated at 2026-06-28 02:10:44. Version ac07

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