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 2024-10-24.

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	16% 11% 4 9% 5% 5% 4 4 5% 6% 31%	101508
	Night	15% 12% 4 9% 5% 5% 4 3 5% 6% 31%	97261
Transparency	Day	51% 7% 11% 20% 10% 1	101266
	Night	53% 7% 12% 18% 9% 1	97123
Seeing	Day	23% 17% 31% 19% 8% 2	14363
	Night	21% 15% 31% 23% 8% 1	23505

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	15% 16% 5% 14% 8% 6% 5% 4 4 4 20%	2517
	11th to 20th	Day	12% 12% 8% 19% 8% 6% 4 3 4 6% 18%	2520
	21st to end	Day	15% 21% 9% 15% 6% 5% 3 2 3 3 17%	3026
February	1st to 10th	Day	11% 17% 6% 15% 8% 6% 4 4 5% 5% 20%	1710
	11th to 20th	Day	11% 16% 6% 14% 6% 4 5% 4 5% 5% 25%	1663
	21st to end	Day	16% 16% 4 9% 6% 6% 6% 5% 4 5% 23%	1505
March	1st to 10th	Day	16% 16% 5% 10% 5% 4 4 3 4 6% 27%	3262
	11th to 20th	Day	9% 18% 7% 13% 6% 4 4 3 4 5% 26%	3480
	21st to end	Day	11% 9% 3 9% 5% 4 4 3 4 5% 43%	3929
April	1st to 10th	Day	20% 16% 3 7% 5% 4 5% 3 4 6% 29%	2280
	11th to 20th	Day	22% 11% 3 6% 4 5% 3 3 3 4 36%	2254
	21st to end	Day	22% 11% 4 8% 4 3 3 3 4 5% 32%	2454
May	1st to 10th	Day	19% 9% 3 8% 5% 4 5% 4 5% 6% 32%	4389
	11th to 20th	Day	16% 10% 3 8% 5% 5% 5% 3 6% 8% 33%	4398
	21st to end	Day	16% 7% 2 7% 5% 4 4 4 4 7% 38%	4837
June	1st to 10th	Day	22% 9% 2 7% 6% 4 5% 4 5% 6% 30%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 5% 6% 8% 37%	2660
	21st to end	Day	17% 8% 3 6% 6% 5% 5% 5% 6% 8% 33%	2660
July	1st to 10th	Day	13% 8% 3 7% 5% 6% 5% 4 6% 10% 33%	4440
	11th to 20th	Day	13% 5% 2 6% 5% 5% 5% 4 6% 8% 40%	4440
	21st to end	Day	10% 6% 2 6% 4 4 4 4 6% 7% 45%	4814
August	1st to 10th	Day	15% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	4200
	11th to 20th	Day	18% 8% 2 7% 4 5% 5% 4 6% 8% 34%	4044
	21st to end	Day	10% 5% 2 7% 4 5% 5% 5% 8% 9% 39%	4247
September	1st to 10th	Day	16% 6% 3 6% 3 4 5% 4 5% 7% 40%	2280
	11th to 20th	Day	14% 6% 2 6% 5% 4 3 2 5% 7% 45%	2280
	21st to end	Day	18% 9% 2 8% 4 4 4 4 6% 7% 35%	1994
October	1st to 10th	Day	21% 10% 3 8% 4 4 4 2 4 6% 33%	1900
	11th to 20th	Day	21% 14% 4 8% 5% 4 5% 3 4 5% 27%	1900
	21st to end	Day	26% 12% 4 9% 5% 4 5% 4 4 6% 22%	1932
November	1st to 10th	Day	13% 13% 4 8% 5% 4 5% 4 4 6% 34%	1595
	11th to 20th	Day	16% 15% 6% 11% 6% 4 3 3 5% 7% 26%	1520
	21st to end	Day	18% 18% 6% 12% 6% 5% 4 4 4 5% 17%	1520
December	1st to 10th	Day	18% 22% 6% 13% 8% 5% 4 3 3 5% 14%	1520
	11th to 20th	Day	17% 17% 6% 11% 6% 4 4 3 5% 4 22%	1906
	21st to end	Day	22% 20% 6% 15% 5% 3 3 1 2 4 17%	2772
January	1st to 10th	Night	14% 17% 8% 14% 8% 5% 5% 4 4 5% 16%	4429
	11th to 20th	Night	10% 13% 5% 15% 9% 8% 6% 4 5% 6% 19%	4440
	21st to end	Night	14% 18% 8% 12% 6% 7% 4 3 4 3 18%	4628
February	1st to 10th	Night	12% 16% 6% 12% 8% 6% 5% 4 5% 5% 20%	2470
	11th to 20th	Night	11% 15% 6% 12% 7% 5% 5% 3 5% 5% 28%	2403
	21st to end	Night	12% 14% 4 12% 6% 5% 5% 3 5% 6% 28%	1947
March	1st to 10th	Night	18% 13% 4 10% 5% 5% 3 3 3 5% 31%	3574
	11th to 20th	Night	12% 17% 6% 12% 6% 5% 5% 3 5% 5% 23%	3479
	21st to end	Night	11% 10% 4 10% 6% 4 4 3 6% 6% 35%	3702
April	1st to 10th	Night	19% 13% 3 9% 5% 4 3 3 4 6% 31%	1900
	11th to 20th	Night	19% 10% 3 7% 4 5% 4 3 3 6% 36%	1875
	21st to end	Night	20% 11% 3 8% 5% 4 3 4 5% 6% 31%	1743
May	1st to 10th	Night	19% 10% 2 7% 4 4 4 4 5% 6% 34%	2549
	11th to 20th	Night	18% 7% 3 7% 4 4 4 4 5% 8% 36%	2495
	21st to end	Night	13% 6% 2 7% 5% 5% 5% 4 6% 7% 41%	2738
June	1st to 10th	Night	16% 7% 3 8% 4 4 5% 5% 6% 8% 33%	1520
	11th to 20th	Night	14% 6% 3 5% 4 4 4 4 5% 8% 43%	1520
	21st to end	Night	18% 7% 3 7% 5% 5% 4 4 6% 7% 36%	1520
July	1st to 10th	Night	11% 7% 3 8% 6% 6% 6% 5% 5% 7% 38%	2520
	11th to 20th	Night	13% 6% 2 6% 5% 4 4 4 6% 7% 43%	2520
	21st to end	Night	9% 6% 2 6% 4 4 4 4 6% 8% 46%	2739
August	1st to 10th	Night	12% 6% 2 7% 4 4 5% 4 6% 8% 43%	2726
	11th to 20th	Night	15% 7% 3 5% 4 3 4 3 6% 7% 44%	2785
	21st to end	Night	12% 6% 2 5% 4 4 5% 4 6% 8% 44%	3376
September	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 6% 6% 47%	1900
	11th to 20th	Night	14% 5% 2 5% 3 4 3 3 5% 5% 51%	1900
	21st to end	Night	16% 8% 2 5% 5% 4 3 4 5% 6% 41%	2180
October	1st to 10th	Night	19% 8% 2 7% 3 4 3 3 4 6% 39%	2280
	11th to 20th	Night	19% 12% 3 8% 5% 4 4 4 5% 5% 30%	2280
	21st to end	Night	22% 15% 3 8% 4 4 4 3 4 6% 25%	2490
November	1st to 10th	Night	15% 13% 4 8% 5% 4 4 3 5% 5% 32%	2481
	11th to 20th	Night	16% 14% 5% 10% 5% 5% 5% 3 5% 5% 26%	2660
	21st to end	Night	17% 17% 4 12% 6% 5% 4 4 5% 5% 20%	2660
December	1st to 10th	Night	17% 19% 7% 13% 7% 4 5% 3 4 4 16%	2660
	11th to 20th	Night	16% 19% 5% 13% 6% 4 4 3 3 4 23%	3288
	21st to end	Night	24% 19% 6% 16% 6% 4 3 2 3 4 14%	4884

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	66% 10% 10% 8% 6%	2518
	11th to 20th	Day	66% 8% 9% 10% 6% 1	2520
	21st to end	Day	72% 5% 7% 9% 5% 1	3026
February	1st to 10th	Day	65% 7% 8% 14% 5% 1	1710
	11th to 20th	Day	58% 7% 12% 13% 9% 1	1672
	21st to end	Day	61% 6% 9% 12% 10% 2	1505
March	1st to 10th	Day	59% 6% 10% 13% 11% 1	3265
	11th to 20th	Day	57% 8% 11% 14% 8% 1	3480
	21st to end	Day	40% 7% 10% 22% 16% 4	3929
April	1st to 10th	Day	56% 5% 8% 18% 11% 3	2280
	11th to 20th	Day	52% 4 7% 21% 14% 2	2254
	21st to end	Day	53% 5% 8% 15% 15% 3	2454
May	1st to 10th	Day	48% 9% 10% 19% 11% 2	4403
	11th to 20th	Day	44% 10% 15% 20% 10% 2	4402
	21st to end	Day	43% 8% 12% 18% 16% 2	4837
June	1st to 10th	Day	52% 7% 11% 18% 11% 1	2660
	11th to 20th	Day	43% 8% 11% 22% 13% 2	2660
	21st to end	Day	47% 8% 13% 19% 12% 1	2660
July	1st to 10th	Day	45% 5% 14% 25% 10% 1	4370
	11th to 20th	Day	39% 6% 16% 29% 10%	4365
	21st to end	Day	37% 6% 12% 33% 12%	4661
August	1st to 10th	Day	49% 5% 13% 23% 9%	4186
	11th to 20th	Day	47% 6% 15% 26% 6%	4083
	21st to end	Day	37% 7% 14% 32% 10% 1	4247
September	1st to 10th	Day	41% 8% 14% 26% 11% 1	2280
	11th to 20th	Day	38% 6% 12% 29% 14%	2280
	21st to end	Day	47% 7% 13% 23% 10%	1994
October	1st to 10th	Day	52% 6% 10% 20% 11% 1	1900
	11th to 20th	Day	59% 8% 12% 15% 6% 1	1900
	21st to end	Day	62% 7% 11% 13% 6% 1	1932
November	1st to 10th	Day	49% 8% 15% 20% 7%	1595
	11th to 20th	Day	58% 8% 12% 13% 8% 1	1520
	21st to end	Day	68% 8% 10% 9% 5% 1	1520
December	1st to 10th	Day	73% 6% 8% 9% 3	1520
	11th to 20th	Day	63% 9% 10% 11% 6%	1906
	21st to end	Day	74% 4 6% 14% 3	2772
January	1st to 10th	Night	68% 9% 11% 9% 2	4429
	11th to 20th	Night	62% 12% 12% 9% 4 1	4440
	21st to end	Night	70% 6% 9% 9% 6%	4628
February	1st to 10th	Night	64% 7% 10% 13% 6% 1	2470
	11th to 20th	Night	58% 7% 11% 18% 7% 1	2405
	21st to end	Night	55% 7% 10% 18% 9% 1	1947
March	1st to 10th	Night	55% 6% 12% 16% 9% 1	3584
	11th to 20th	Night	57% 9% 13% 14% 7% 1	3480
	21st to end	Night	44% 8% 11% 21% 13% 2	3702
April	1st to 10th	Night	55% 6% 8% 19% 12% 2	1900
	11th to 20th	Night	49% 6% 8% 22% 14% 1	1875
	21st to end	Night	53% 6% 8% 16% 15% 2	1743
May	1st to 10th	Night	45% 10% 12% 20% 10% 2	2555
	11th to 20th	Night	42% 13% 14% 21% 9% 1	2496
	21st to end	Night	37% 11% 13% 21% 16% 2	2739
June	1st to 10th	Night	44% 9% 15% 20% 11% 1	1520
	11th to 20th	Night	38% 8% 12% 25% 15% 2	1520
	21st to end	Night	45% 8% 14% 20% 12% 1	1520
July	1st to 10th	Night	44% 6% 15% 19% 14% 1	2480
	11th to 20th	Night	39% 4 14% 32% 10%	2472
	21st to end	Night	35% 7% 15% 29% 14%	2651
August	1st to 10th	Night	38% 6% 15% 27% 12% 2	2716
	11th to 20th	Night	40% 5% 16% 29% 9%	2812
	21st to end	Night	37% 5% 15% 30% 10% 2	3376
September	1st to 10th	Night	36% 8% 14% 28% 13% 1	1900
	11th to 20th	Night	35% 6% 15% 32% 11%	1900
	21st to end	Night	42% 7% 13% 28% 10%	2180
October	1st to 10th	Night	46% 6% 12% 21% 14%	2280
	11th to 20th	Night	54% 8% 14% 16% 8%	2280
	21st to end	Night	59% 7% 12% 14% 7%	2490
November	1st to 10th	Night	51% 7% 16% 18% 8%	2481
	11th to 20th	Night	58% 9% 11% 14% 7% 1	2660
	21st to end	Night	64% 7% 13% 13% 3	2660
December	1st to 10th	Night	70% 8% 9% 10% 3	2660
	11th to 20th	Night	64% 6% 9% 13% 7% 1	3288
	21st to end	Night	75% 5% 7% 10% 3	4884

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	21% 23% 36% 17% 3 1	180
	11th to 20th	Day	28% 17% 37% 14% 4 1	180
	21st to end	Day	22% 24% 32% 18% 4	270
February	1st to 10th	Day	26% 27% 35% 8% 3 1	270
	11th to 20th	Day	25% 30% 39% 6%	270
	21st to end	Day	34% 22% 32% 12%	317
March	1st to 10th	Day	24% 25% 33% 15% 3	460
	11th to 20th	Day	27% 19% 33% 17% 4	460
	21st to end	Day	29% 23% 31% 11% 5% 1	506
April	1st to 10th	Day	30% 20% 30% 13% 6%	460
	11th to 20th	Day	33% 21% 22% 14% 8% 2	452
	21st to end	Day	30% 21% 30% 12% 5% 1	460
May	1st to 10th	Day	25% 19% 30% 16% 8% 2	463
	11th to 20th	Day	21% 17% 31% 21% 7% 3	487
	21st to end	Day	19% 18% 33% 19% 10% 2	529
June	1st to 10th	Day	24% 13% 35% 20% 7%	490
	11th to 20th	Day	17% 16% 32% 22% 9% 3	490
	21st to end	Day	19% 15% 33% 21% 10% 2	490
July	1st to 10th	Day	12% 8% 33% 34% 10% 2	485
	11th to 20th	Day	14% 11% 35% 25% 13% 2	484
	21st to end	Day	13% 10% 35% 27% 11% 3	532
August	1st to 10th	Day	16% 8% 33% 28% 12% 4	486
	11th to 20th	Day	15% 8% 28% 26% 17% 5%	479
	21st to end	Day	14% 12% 32% 26% 10% 6%	539
September	1st to 10th	Day	18% 13% 29% 21% 14% 6%	490
	11th to 20th	Day	14% 11% 23% 24% 18% 10%	490
	21st to end	Day	20% 14% 28% 21% 13% 5%	490
October	1st to 10th	Day	26% 16% 24% 18% 12% 4	490
	11th to 20th	Day	30% 22% 27% 15% 6% 1	490
	21st to end	Day	31% 19% 29% 16% 4	467
November	1st to 10th	Day	25% 19% 33% 16% 6% 1	289
	11th to 20th	Day	31% 22% 32% 9% 4 1	180
	21st to end	Day	27% 30% 31% 8% 2 2	180
December	1st to 10th	Day	28% 17% 42% 9% 3	180
	11th to 20th	Day	31% 31% 25% 11% 1 1	180
	21st to end	Day	32% 21% 31% 13% 3 1	198
January	1st to 10th	Night	24% 20% 35% 17% 4	760
	11th to 20th	Night	24% 20% 30% 20% 5%	760
	21st to end	Night	16% 16% 38% 24% 6%	836
February	1st to 10th	Night	19% 21% 39% 18% 3	760
	11th to 20th	Night	20% 20% 42% 15% 3	743
	21st to end	Night	21% 22% 32% 21% 2	628
March	1st to 10th	Night	23% 20% 34% 20% 3	760
	11th to 20th	Night	23% 21% 33% 18% 4 1	760
	21st to end	Night	19% 19% 34% 21% 7%	836
April	1st to 10th	Night	28% 16% 32% 21% 3	760
	11th to 20th	Night	25% 19% 31% 17% 8%	751
	21st to end	Night	25% 15% 27% 23% 10%	603
May	1st to 10th	Night	22% 10% 31% 28% 9%	402
	11th to 20th	Night	20% 10% 34% 27% 8%	374
	21st to end	Night	15% 8% 38% 27% 11%	411
June	1st to 10th	Night	19% 8% 37% 30% 5% 1	380
	11th to 20th	Night	18% 8% 34% 29% 10%	380
	21st to end	Night	21% 10% 31% 27% 12%	380
July	1st to 10th	Night	9% 7% 36% 35% 12% 1	370
	11th to 20th	Night	12% 8% 29% 38% 14%	368
	21st to end	Night	8% 6% 35% 39% 11% 1	416
August	1st to 10th	Night	10% 5% 27% 39% 19% 1	507
	11th to 20th	Night	12% 4 24% 39% 18% 3	564
	21st to end	Night	12% 8% 30% 31% 17% 2	775
September	1st to 10th	Night	15% 8% 31% 27% 17% 1	760
	11th to 20th	Night	19% 6% 23% 29% 19% 4	760
	21st to end	Night	20% 12% 22% 26% 18% 2	760
October	1st to 10th	Night	24% 11% 30% 23% 12% 1	760
	11th to 20th	Night	25% 17% 32% 18% 8% 1	760
	21st to end	Night	30% 17% 27% 20% 5%	805
November	1st to 10th	Night	25% 17% 30% 21% 6% 1	740
	11th to 20th	Night	23% 21% 30% 17% 9% 1	760
	21st to end	Night	30% 18% 26% 22% 4	760
December	1st to 10th	Night	27% 20% 33% 16% 3	760
	11th to 20th	Night	26% 21% 31% 19% 3 1	760
	21st to end	Night	31% 18% 31% 17% 3	836

Page generated at 2024-10-21 02:20:04. Version ac07

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