Foymount
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Foymount clear sky chart from 2005-11-06 to 2026-08-15.

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% 11% 4 9% 5% 5% 5% 4 5% 7% 31%	144503
	Night	14% 12% 4 10% 6% 5% 4 3 5% 6% 30%	137376
Transparency	Day	52% 5% 11% 21% 10% 1	148022
	Night	54% 6% 11% 19% 10% 1	141946
Seeing	Day	23% 17% 31% 18% 8% 2	16607
	Night	21% 15% 32% 23% 8% 1	25719

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	10% 15% 5% 15% 11% 8% 6% 4 5% 5% 17%	4661
	11th to 20th	Day	9% 17% 9% 19% 8% 6% 5% 3 5% 5% 15%	4650
	21st to end	Day	9% 15% 8% 18% 9% 7% 6% 3 3 4 18%	5598
February	1st to 10th	Day	11% 16% 6% 15% 8% 6% 4 4 5% 4 21%	1890
	11th to 20th	Day	11% 15% 6% 14% 7% 5% 5% 4 5% 5% 24%	1843
	21st to end	Day	16% 16% 5% 10% 7% 6% 5% 5% 4 4 22%	1659
March	1st to 10th	Day	16% 14% 5% 12% 6% 4 4 3 4 6% 25%	4796
	11th to 20th	Day	9% 14% 6% 12% 7% 5% 5% 4 6% 7% 26%	5090
	21st to end	Day	14% 14% 4 10% 4 4 3 3 4 4 37%	5759
April	1st to 10th	Day	19% 15% 4 7% 5% 4 5% 3 4 6% 28%	2520
	11th to 20th	Day	22% 13% 3 7% 4 4 3 3 3 4 35%	2494
	21st to end	Day	21% 11% 4 8% 4 4 4 3 4 5% 33%	2712
May	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 4 5% 6% 30%	8172
	11th to 20th	Day	15% 10% 3 8% 5% 5% 5% 4 5% 7% 33%	8221
	21st to end	Day	19% 9% 3 7% 5% 4 4 3 4 6% 36%	9060
June	1st to 10th	Day	21% 9% 3 7% 5% 4 5% 3 5% 6% 31%	2940
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 5% 6% 8% 36%	2940
	21st to end	Day	15% 8% 3 6% 6% 5% 5% 5% 6% 8% 33%	2940
July	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 4 7% 10% 37%	8280
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 46%	8280
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 6% 9% 41%	8993
August	1st to 10th	Day	15% 8% 3 8% 6% 5% 5% 4 6% 7% 33%	4466
	11th to 20th	Day	18% 7% 2 7% 4 5% 5% 4 6% 8% 35%	4226
	21st to end	Day	10% 5% 2 7% 4 5% 5% 5% 8% 9% 39%	4381
September	1st to 10th	Day	16% 6% 3 6% 4 4 5% 4 5% 7% 40%	2400
	11th to 20th	Day	14% 6% 2 6% 5% 4 3 2 5% 7% 45%	2400
	21st to end	Day	18% 9% 2 8% 4 4 4 4 6% 7% 35%	2099
October	1st to 10th	Day	20% 10% 3 7% 4 4 4 2 4 6% 35%	2000
	11th to 20th	Day	20% 13% 5% 8% 5% 4 5% 4 4 6% 27%	2000
	21st to end	Day	25% 12% 4 10% 5% 4 5% 4 4 5% 22%	2112
November	1st to 10th	Day	14% 13% 4 9% 5% 4 5% 3 4 6% 33%	1767
	11th to 20th	Day	15% 15% 7% 11% 6% 4 3 3 5% 6% 25%	1680
	21st to end	Day	19% 19% 6% 12% 6% 5% 4 3 4 5% 17%	1680
December	1st to 10th	Day	16% 25% 8% 14% 8% 6% 3 3 3 5% 11%	2680
	11th to 20th	Day	15% 17% 8% 15% 7% 5% 4 2 4 3 22%	3066
	21st to end	Day	19% 18% 7% 15% 7% 3 4 2 3 4 19%	4048
January	1st to 10th	Night	11% 14% 9% 18% 10% 6% 5% 3 4 4 17%	8234
	11th to 20th	Night	8% 15% 6% 17% 9% 8% 6% 3 5% 6% 17%	8235
	21st to end	Night	9% 14% 7% 14% 8% 9% 6% 4 5% 5% 19%	8581
February	1st to 10th	Night	11% 16% 6% 12% 8% 6% 5% 4 5% 5% 21%	2730
	11th to 20th	Night	11% 14% 6% 12% 7% 5% 5% 3 5% 5% 26%	2663
	21st to end	Night	12% 15% 5% 12% 6% 5% 5% 3 5% 6% 26%	2145
March	1st to 10th	Night	17% 15% 4 11% 6% 5% 4 3 3 4 28%	5260
	11th to 20th	Night	9% 13% 5% 10% 6% 6% 6% 5% 7% 7% 26%	5089
	21st to end	Night	14% 12% 4 11% 6% 4 4 3 5% 6% 30%	5414
April	1st to 10th	Night	19% 13% 4 9% 5% 4 3 3 4 6% 30%	2100
	11th to 20th	Night	19% 11% 4 7% 4 5% 4 3 3 6% 35%	2075
	21st to end	Night	20% 11% 3 7% 5% 4 4 4 5% 6% 32%	1927
May	1st to 10th	Night	18% 10% 3 8% 4 4 4 4 5% 7% 31%	4723
	11th to 20th	Night	14% 8% 3 6% 4 4 4 4 5% 8% 40%	4639
	21st to end	Night	19% 7% 3 6% 4 4 4 4 6% 7% 36%	5114
June	1st to 10th	Night	16% 8% 3 7% 4 4 5% 5% 6% 8% 35%	1680
	11th to 20th	Night	15% 6% 3 5% 4 4 4 4 5% 8% 43%	1680
	21st to end	Night	17% 7% 3 7% 5% 5% 4 4 6% 8% 36%	1680
July	1st to 10th	Night	11% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	4680
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 6% 7% 49%	4680
	21st to end	Night	10% 6% 3 7% 4 4 4 4 5% 8% 44%	5084
August	1st to 10th	Night	11% 6% 2 7% 4 4 5% 4 6% 8% 43%	2900
	11th to 20th	Night	15% 7% 3 5% 4 3 4 3 5% 7% 44%	2911
	21st to end	Night	12% 6% 2 5% 4 4 5% 5% 6% 8% 44%	3483
September	1st to 10th	Night	12% 6% 2 6% 5% 4 4 3 6% 6% 47%	2000
	11th to 20th	Night	14% 5% 2 5% 3 4 3 2 5% 6% 52%	2000
	21st to end	Night	16% 8% 2 5% 5% 4 3 4 5% 6% 41%	2295
October	1st to 10th	Night	19% 8% 2 7% 3 4 3 3 4 6% 40%	2400
	11th to 20th	Night	19% 12% 3 8% 5% 5% 4 4 5% 5% 31%	2400
	21st to end	Night	21% 14% 3 8% 4 4 4 3 5% 7% 26%	2727
November	1st to 10th	Night	15% 14% 4 9% 6% 4 4 3 5% 5% 31%	2749
	11th to 20th	Night	16% 14% 5% 10% 6% 5% 5% 3 5% 5% 27%	2940
	21st to end	Night	17% 17% 5% 12% 6% 5% 4 4 5% 5% 19%	2940
December	1st to 10th	Night	15% 19% 7% 14% 8% 5% 5% 4 5% 5% 14%	4720
	11th to 20th	Night	16% 18% 6% 14% 6% 5% 4 3 3 4 22%	5348
	21st to end	Night	20% 18% 5% 15% 7% 4 3 2 3 4 18%	7150

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	68% 6% 9% 11% 5%	4662
	11th to 20th	Day	69% 6% 7% 8% 9% 1	4680
	21st to end	Day	70% 4 6% 11% 8% 1	5598
February	1st to 10th	Day	64% 6% 8% 15% 6% 1	1890
	11th to 20th	Day	59% 6% 11% 14% 8% 1	1852
	21st to end	Day	63% 6% 8% 12% 9% 1	1659
March	1st to 10th	Day	60% 5% 9% 11% 14% 2	4799
	11th to 20th	Day	55% 6% 14% 15% 8% 2	5090
	21st to end	Day	50% 5% 7% 18% 16% 3	5759
April	1st to 10th	Day	57% 4 8% 18% 11% 3	2520
	11th to 20th	Day	53% 4 7% 20% 14% 2	2494
	21st to end	Day	53% 5% 8% 16% 15% 3	2712
May	1st to 10th	Day	51% 6% 9% 21% 10% 3	8184
	11th to 20th	Day	48% 6% 11% 21% 12% 1	8225
	21st to end	Day	49% 5% 10% 21% 13% 2	9061
June	1st to 10th	Day	51% 6% 10% 19% 12% 1	2940
	11th to 20th	Day	44% 7% 11% 23% 13% 2	2940
	21st to end	Day	46% 8% 13% 20% 11% 1	2940
July	1st to 10th	Day	42% 4 16% 26% 11%	8210
	11th to 20th	Day	34% 4 13% 35% 13% 1	8205
	21st to end	Day	39% 4 15% 33% 9%	8795
August	1st to 10th	Day	49% 5% 14% 23% 9%	4452
	11th to 20th	Day	46% 6% 15% 26% 7%	4265
	21st to end	Day	37% 6% 14% 32% 9% 1	4381
September	1st to 10th	Day	41% 8% 14% 26% 11% 1	2400
	11th to 20th	Day	38% 6% 12% 30% 14%	2400
	21st to end	Day	48% 7% 12% 22% 11%	2099
October	1st to 10th	Day	51% 4 8% 28% 8%	3260
	11th to 20th	Day	52% 5% 11% 20% 11% 1	3240
	21st to end	Day	58% 5% 15% 16% 5% 1	3389
November	1st to 10th	Day	51% 7% 14% 20% 7%	1767
	11th to 20th	Day	59% 7% 12% 13% 8% 1	1680
	21st to end	Day	69% 7% 10% 9% 5% 1	1680
December	1st to 10th	Day	78% 4 9% 7% 2	2680
	11th to 20th	Day	66% 6% 7% 13% 8%	3066
	21st to end	Day	71% 3 6% 14% 4	4048
January	1st to 10th	Night	71% 5% 9% 11% 4	8234
	11th to 20th	Night	66% 7% 8% 11% 7%	8280
	21st to end	Night	66% 5% 6% 13% 11%	8581
February	1st to 10th	Night	63% 6% 10% 15% 6% 1	2730
	11th to 20th	Night	59% 6% 10% 18% 6%	2665
	21st to end	Night	57% 7% 9% 17% 9% 1	2145
March	1st to 10th	Night	60% 4 9% 14% 9% 4	5270
	11th to 20th	Night	52% 8% 16% 15% 7% 1	5090
	21st to end	Night	52% 6% 10% 19% 11% 2	5414
April	1st to 10th	Night	55% 5% 7% 19% 11% 2	2100
	11th to 20th	Night	50% 5% 7% 23% 13% 1	2075
	21st to end	Night	52% 6% 8% 17% 15% 2	1927
May	1st to 10th	Night	50% 7% 9% 21% 9% 3	4729
	11th to 20th	Night	41% 8% 13% 22% 14% 2	4640
	21st to end	Night	45% 6% 12% 22% 14% 1	5115
June	1st to 10th	Night	43% 9% 14% 21% 13% 1	1680
	11th to 20th	Night	38% 8% 12% 26% 15% 2	1680
	21st to end	Night	45% 7% 14% 21% 12% 1	1680
July	1st to 10th	Night	41% 4 18% 23% 13% 1	4640
	11th to 20th	Night	35% 3 15% 33% 14%	4632
	21st to end	Night	39% 4 13% 31% 13%	4967
August	1st to 10th	Night	38% 6% 15% 27% 12% 1	2890
	11th to 20th	Night	40% 5% 16% 29% 9%	2938
	21st to end	Night	38% 5% 14% 31% 10% 2	3483
September	1st to 10th	Night	36% 8% 14% 29% 13% 1	2000
	11th to 20th	Night	34% 6% 15% 34% 11%	2000
	21st to end	Night	42% 7% 12% 27% 11%	2295
October	1st to 10th	Night	39% 4 12% 30% 14%	3920
	11th to 20th	Night	49% 5% 15% 19% 11%	3899
	21st to end	Night	53% 5% 17% 19% 6%	4400
November	1st to 10th	Night	53% 6% 15% 18% 7%	2749
	11th to 20th	Night	58% 8% 11% 16% 7% 1	2940
	21st to end	Night	65% 6% 12% 13% 3	2940
December	1st to 10th	Night	72% 4 12% 9% 2	4720
	11th to 20th	Night	65% 5% 7% 12% 10% 1	5348
	21st to end	Night	71% 4 6% 11% 8%	7150

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	20% 22% 40% 16% 3	220
	11th to 20th	Day	28% 18% 37% 12% 3 1	220
	21st to end	Day	22% 26% 32% 17% 3	330
February	1st to 10th	Day	27% 27% 33% 8% 4 1	330
	11th to 20th	Day	26% 29% 38% 6%	330
	21st to end	Day	34% 21% 33% 12%	375
March	1st to 10th	Day	25% 25% 34% 14% 2	540
	11th to 20th	Day	30% 19% 31% 15% 3	540
	21st to end	Day	31% 23% 30% 11% 4 1	594
April	1st to 10th	Day	32% 22% 29% 12% 6%	540
	11th to 20th	Day	34% 20% 23% 14% 7% 2	532
	21st to end	Day	29% 21% 32% 12% 5% 1	540
May	1st to 10th	Day	26% 20% 30% 15% 7% 2	543
	11th to 20th	Day	22% 17% 32% 19% 7% 2	567
	21st to end	Day	21% 19% 32% 17% 9% 2	617
June	1st to 10th	Day	24% 13% 36% 19% 8%	570
	11th to 20th	Day	17% 17% 34% 21% 9% 3	570
	21st to end	Day	17% 15% 35% 21% 10% 2	570
July	1st to 10th	Day	12% 9% 35% 33% 9% 2	565
	11th to 20th	Day	14% 13% 35% 25% 11% 2	564
	21st to end	Day	14% 11% 35% 26% 11% 3	620
August	1st to 10th	Day	15% 7% 33% 29% 12% 4	566
	11th to 20th	Day	16% 8% 28% 27% 16% 5%	535
	21st to end	Day	15% 11% 32% 26% 11% 5%	583
September	1st to 10th	Day	18% 12% 28% 21% 14% 5%	530
	11th to 20th	Day	13% 10% 22% 26% 19% 11%	530
	21st to end	Day	20% 14% 29% 21% 12% 5%	530
October	1st to 10th	Day	25% 15% 24% 19% 12% 4	530
	11th to 20th	Day	29% 22% 28% 15% 5% 1	530
	21st to end	Day	30% 18% 30% 17% 4	533
November	1st to 10th	Day	28% 19% 31% 16% 5% 1	341
	11th to 20th	Day	29% 23% 33% 10% 5% 1	220
	21st to end	Day	32% 28% 30% 8% 2 1	220
December	1st to 10th	Day	29% 18% 40% 10% 3	220
	11th to 20th	Day	30% 31% 26% 10% 1 1	220
	21st to end	Day	31% 21% 29% 14% 3 1	242
January	1st to 10th	Night	23% 20% 37% 17% 3	840
	11th to 20th	Night	24% 20% 31% 20% 5%	840
	21st to end	Night	16% 17% 38% 23% 6%	924
February	1st to 10th	Night	19% 21% 38% 19% 3	840
	11th to 20th	Night	20% 19% 43% 15% 3	823
	21st to end	Night	22% 22% 33% 21% 2	692
March	1st to 10th	Night	24% 21% 35% 18% 3	840
	11th to 20th	Night	24% 20% 33% 18% 4 1	840
	21st to end	Night	21% 19% 33% 20% 6%	924
April	1st to 10th	Night	28% 16% 32% 20% 3	840
	11th to 20th	Night	25% 19% 30% 18% 8%	831
	21st to end	Night	24% 15% 28% 23% 9%	667
May	1st to 10th	Night	23% 10% 30% 27% 9% 1	444
	11th to 20th	Night	20% 11% 36% 26% 7%	414
	21st to end	Night	17% 8% 38% 26% 10%	455
June	1st to 10th	Night	19% 7% 37% 30% 6%	420
	11th to 20th	Night	18% 10% 34% 29% 9%	420
	21st to end	Night	20% 9% 30% 29% 12%	420
July	1st to 10th	Night	9% 7% 37% 35% 11% 1	410
	11th to 20th	Night	12% 8% 29% 38% 13%	408
	21st to end	Night	9% 6% 35% 39% 10% 1	460
August	1st to 10th	Night	10% 4 25% 40% 19% 1	561
	11th to 20th	Night	12% 4 23% 41% 18% 3	606
	21st to end	Night	13% 8% 30% 31% 16% 2	816
September	1st to 10th	Night	15% 8% 32% 27% 17% 1	800
	11th to 20th	Night	18% 6% 22% 30% 21% 4	800
	21st to end	Night	19% 12% 23% 26% 18% 2	800
October	1st to 10th	Night	23% 10% 30% 24% 12% 1	800
	11th to 20th	Night	25% 17% 32% 18% 8% 1	800
	21st to end	Night	29% 17% 27% 21% 5%	880
November	1st to 10th	Night	27% 18% 29% 21% 5% 1	820
	11th to 20th	Night	23% 21% 30% 17% 8% 1	840
	21st to end	Night	31% 19% 25% 21% 3	840
December	1st to 10th	Night	27% 20% 34% 17% 3	840
	11th to 20th	Night	25% 22% 31% 18% 2	840
	21st to end	Night	31% 18% 30% 18% 3	924

Page generated at 2026-08-12 03:37:20. Version ac07

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