Fermont
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fermont clear sky chart from 2005-11-06 to 2024-12-06.

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	17% 15% 5% 12% 7% 6% 5% 4 5% 6% 18%	102330
	Night	13% 15% 6% 12% 8% 6% 6% 4 6% 7% 18%	97523
Transparency	Day	36% 47% 6% 9% 3	105683
	Night	35% 47% 6% 8% 4 1	102263
Seeing	Day	24% 9% 25% 24% 14% 4	16206
	Night	21% 9% 28% 29% 12% 2	23788

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	7% 12% 5% 15% 11% 8% 4 5% 11% 11% 12%	2207
	11th to 20th	Day	6% 15% 7% 18% 7% 6% 8% 4 5% 11% 13%	2210
	21st to end	Day	3 8% 5% 15% 9% 8% 6% 6% 8% 12% 21%	2557
February	1st to 10th	Day	4 12% 5% 12% 7% 7% 7% 7% 10% 11% 19%	1536
	11th to 20th	Day	3 16% 8% 14% 9% 7% 6% 5% 8% 11% 13%	1663
	21st to end	Day	5% 16% 5% 10% 8% 7% 7% 5% 10% 10% 16%	1437
March	1st to 10th	Day	8% 15% 6% 14% 7% 10% 6% 6% 6% 8% 14%	3166
	11th to 20th	Day	9% 27% 11% 18% 6% 5% 5% 3 4 4 10%	3480
	21st to end	Day	14% 21% 7% 13% 6% 6% 8% 4 4 4 12%	3816
April	1st to 10th	Day	13% 19% 6% 15% 9% 7% 6% 3 4 3 13%	2392
	11th to 20th	Day	11% 17% 5% 13% 8% 5% 5% 3 5% 5% 23%	2442
	21st to end	Day	17% 18% 5% 12% 7% 5% 5% 3 4 5% 18%	2470
May	1st to 10th	Day	17% 24% 7% 12% 5% 4 4 2 3 3 18%	4564
	11th to 20th	Day	19% 13% 5% 9% 6% 5% 4 3 5% 6% 24%	4715
	21st to end	Day	31% 17% 6% 10% 5% 4 4 3 3 4 14%	5185
June	1st to 10th	Day	22% 14% 4 9% 5% 4 4 2 4 5% 25%	2850
	11th to 20th	Day	22% 14% 4 9% 5% 5% 4 4 6% 7% 21%	2850
	21st to end	Day	25% 10% 4 9% 6% 4 5% 4 6% 6% 19%	2850
July	1st to 10th	Day	19% 10% 3 8% 5% 5% 5% 4 6% 7% 29%	4760
	11th to 20th	Day	23% 10% 3 9% 5% 5% 5% 4 5% 5% 24%	4760
	21st to end	Day	16% 10% 3 11% 8% 8% 8% 6% 7% 6% 17%	5162
August	1st to 10th	Day	17% 10% 4 11% 7% 7% 6% 5% 6% 6% 21%	4576
	11th to 20th	Day	21% 10% 3 11% 6% 6% 6% 4 6% 7% 20%	4045
	21st to end	Day	19% 8% 3 8% 5% 5% 5% 4 6% 7% 31%	4532
September	1st to 10th	Day	22% 13% 4 10% 6% 6% 5% 3 6% 6% 20%	2391
	11th to 20th	Day	23% 14% 5% 12% 6% 5% 4 3 4 5% 18%	2104
	21st to end	Day	21% 20% 5% 10% 5% 5% 4 2 5% 5% 19%	2090
October	1st to 10th	Day	21% 21% 6% 9% 6% 5% 4 3 4 4 17%	1919
	11th to 20th	Day	25% 20% 8% 11% 6% 4 3 3 3 5% 14%	1813
	21st to end	Day	22% 22% 7% 14% 7% 4 4 2 3 4 11%	1824
November	1st to 10th	Day	19% 19% 6% 20% 9% 6% 5% 3 3 3 7%	1565
	11th to 20th	Day	15% 21% 8% 18% 9% 7% 4 4 3 4 7%	1535
	21st to end	Day	14% 19% 7% 16% 10% 8% 7% 4 4 4 7%	1400
December	1st to 10th	Day	7% 17% 6% 18% 9% 10% 7% 5% 5% 6% 9%	1365
	11th to 20th	Day	10% 17% 6% 14% 10% 9% 7% 5% 6% 8% 8%	1668
	21st to end	Day	7% 13% 7% 15% 10% 12% 7% 5% 6% 7% 11%	2431
January	1st to 10th	Night	5% 12% 4 14% 10% 8% 7% 5% 11% 12% 11%	4748
	11th to 20th	Night	8% 16% 6% 16% 8% 8% 7% 5% 7% 10% 9%	4760
	21st to end	Night	3 7% 4 14% 11% 8% 7% 6% 10% 10% 20%	5104
February	1st to 10th	Night	3 12% 4 11% 10% 9% 7% 7% 8% 12% 16%	2643
	11th to 20th	Night	5% 16% 7% 14% 9% 6% 5% 5% 8% 10% 14%	2403
	21st to end	Night	6% 14% 5% 13% 8% 7% 6% 7% 8% 9% 18%	2017
March	1st to 10th	Night	7% 15% 6% 11% 5% 7% 7% 6% 8% 8% 20%	3673
	11th to 20th	Night	11% 28% 10% 15% 6% 4 4 3 4 4 12%	3479
	21st to end	Night	12% 22% 8% 13% 6% 5% 5% 3 4 3 18%	3816
April	1st to 10th	Night	13% 17% 7% 15% 7% 5% 5% 3 5% 5% 18%	1785
	11th to 20th	Night	14% 14% 4 11% 6% 6% 4 4 4 6% 28%	1688
	21st to end	Night	15% 15% 6% 10% 7% 5% 5% 4 4 5% 24%	1710
May	1st to 10th	Night	18% 23% 8% 12% 5% 3 3 2 4 3 18%	2414
	11th to 20th	Night	21% 11% 4 7% 4 4 5% 3 5% 5% 30%	2188
	21st to end	Night	29% 16% 6% 8% 6% 4 4 3 4 4 16%	2401
June	1st to 10th	Night	18% 11% 4 9% 5% 5% 5% 3 6% 5% 29%	1330
	11th to 20th	Night	22% 11% 3 8% 6% 5% 5% 4 5% 6% 24%	1330
	21st to end	Night	23% 9% 2 9% 5% 5% 5% 4 6% 6% 25%	1330
July	1st to 10th	Night	17% 8% 3 6% 5% 5% 4 3 7% 6% 36%	2210
	11th to 20th	Night	19% 8% 3 9% 6% 5% 5% 4 6% 6% 29%	2210
	21st to end	Night	12% 9% 3 9% 6% 6% 6% 4 7% 9% 27%	2402
August	1st to 10th	Night	14% 7% 3 10% 7% 7% 7% 5% 8% 8% 26%	2334
	11th to 20th	Night	19% 10% 4 11% 8% 7% 6% 4 6% 8% 18%	2773
	21st to end	Night	14% 7% 3 6% 4 5% 5% 4 7% 9% 36%	3124
September	1st to 10th	Night	19% 12% 4 9% 7% 5% 5% 3 5% 5% 26%	1789
	11th to 20th	Night	21% 12% 4 10% 6% 5% 4 4 5% 6% 23%	2075
	21st to end	Night	20% 14% 3 11% 6% 5% 5% 3 6% 6% 22%	2090
October	1st to 10th	Night	20% 17% 4 8% 5% 4 4 4 4 6% 23%	2261
	11th to 20th	Night	23% 19% 8% 11% 5% 4 4 3 4 4 15%	2365
	21st to end	Night	22% 18% 6% 12% 6% 4 5% 4 5% 4 13%	2774
November	1st to 10th	Night	17% 21% 7% 18% 10% 5% 5% 3 4 4 8%	2733
	11th to 20th	Night	17% 22% 7% 16% 10% 7% 4 3 4 4 8%	2865
	21st to end	Night	15% 21% 6% 17% 8% 7% 7% 4 5% 5% 7%	3000
December	1st to 10th	Night	9% 17% 8% 16% 11% 10% 7% 5% 5% 6% 7%	2932
	11th to 20th	Night	12% 17% 6% 14% 11% 8% 6% 4 6% 8% 8%	3531
	21st to end	Night	7% 16% 9% 14% 10% 12% 7% 5% 5% 6% 9%	5236

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	36% 37% 5% 14% 8%	2208
	11th to 20th	Day	46% 37% 9% 6% 2	2210
	21st to end	Day	29% 39% 5% 6% 17% 3	2557
February	1st to 10th	Day	16% 66% 4 8% 6%	1536
	11th to 20th	Day	21% 66% 4 6% 4	1671
	21st to end	Day	22% 66% 3 5% 4	1437
March	1st to 10th	Day	39% 40% 4 10% 6%	3170
	11th to 20th	Day	55% 39% 2 2 1 1	3480
	21st to end	Day	47% 40% 3 4 4 1	3816
April	1st to 10th	Day	24% 66% 4 3 3	2392
	11th to 20th	Day	23% 65% 2 4 6% 1	2442
	21st to end	Day	27% 66% 3 2 2	2470
May	1st to 10th	Day	44% 41% 4 9% 1	4579
	11th to 20th	Day	34% 42% 6% 14% 4	4719
	21st to end	Day	48% 40% 4 6% 2	5185
June	1st to 10th	Day	22% 65% 4 8% 1	2850
	11th to 20th	Day	23% 65% 4 6% 2	2850
	21st to end	Day	23% 65% 4 7% 1	2850
July	1st to 10th	Day	30% 38% 7% 19% 6%	4685
	11th to 20th	Day	39% 37% 8% 10% 6%	4679
	21st to end	Day	41% 39% 8% 11% 1	4998
August	1st to 10th	Day	37% 40% 8% 13% 3	4561
	11th to 20th	Day	39% 39% 9% 10% 2	4084
	21st to end	Day	26% 39% 14% 17% 4	4532
September	1st to 10th	Day	27% 62% 5% 5% 1	2391
	11th to 20th	Day	27% 61% 5% 6% 1	2104
	21st to end	Day	26% 60% 5% 7% 1	2090
October	1st to 10th	Day	36% 38% 9% 15% 1	3192
	11th to 20th	Day	51% 39% 3 6% 1	2990
	21st to end	Day	48% 38% 5% 8% 1	2991
November	1st to 10th	Day	39% 57% 2 1 1	1565
	11th to 20th	Day	35% 58% 4 1 2 1	1535
	21st to end	Day	35% 58% 3 3 1	1400
December	1st to 10th	Day	30% 60% 3 5% 1 1	1365
	11th to 20th	Day	38% 50% 6% 4 3	1668
	21st to end	Day	44% 38% 5% 8% 5% 1	2431
January	1st to 10th	Night	34% 38% 7% 12% 8% 1	4748
	11th to 20th	Night	46% 39% 8% 6% 1	4760
	21st to end	Night	32% 40% 7% 7% 11% 4	5104
February	1st to 10th	Night	17% 67% 4 5% 7% 1	2643
	11th to 20th	Night	23% 65% 3 6% 4	2406
	21st to end	Night	23% 66% 3 3 4 1	2017
March	1st to 10th	Night	34% 42% 4 10% 9% 1	3682
	11th to 20th	Night	53% 40% 3 2 2	3480
	21st to end	Night	44% 40% 4 4 9% 1	3816
April	1st to 10th	Night	22% 65% 3 4 5% 1	1785
	11th to 20th	Night	19% 65% 3 7% 5% 1	1688
	21st to end	Night	28% 65% 2 3 2	1710
May	1st to 10th	Night	45% 41% 4 10% 1	2419
	11th to 20th	Night	33% 42% 4 17% 4	2189
	21st to end	Night	47% 40% 3 8% 2	2402
June	1st to 10th	Night	18% 67% 5% 9% 2	1330
	11th to 20th	Night	23% 65% 3 8% 2	1330
	21st to end	Night	20% 65% 4 10% 1	1330
July	1st to 10th	Night	27% 39% 11% 20% 4	2175
	11th to 20th	Night	35% 38% 8% 11% 8%	2168
	21st to end	Night	31% 39% 10% 17% 2	2325
August	1st to 10th	Night	32% 41% 12% 14% 2	2325
	11th to 20th	Night	41% 40% 10% 7% 1	2800
	21st to end	Night	20% 40% 12% 23% 4	3124
September	1st to 10th	Night	25% 61% 6% 7% 1	1789
	11th to 20th	Night	23% 61% 7% 8% 1	2075
	21st to end	Night	20% 62% 6% 9% 2	2090
October	1st to 10th	Night	35% 38% 10% 15% 2	3768
	11th to 20th	Night	47% 39% 6% 5% 2	3927
	21st to end	Night	48% 39% 4 8% 2	4560
November	1st to 10th	Night	36% 56% 5% 2 1	2733
	11th to 20th	Night	35% 58% 3 2 1	2865
	21st to end	Night	34% 59% 4 2 1	3000
December	1st to 10th	Night	32% 59% 3 4 2	2932
	11th to 20th	Night	39% 50% 5% 4 3	3532
	21st to end	Night	47% 37% 5% 5% 4 2	5236

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	8% 7% 28% 31% 20% 7%	180
	11th to 20th	Day	12% 9% 31% 29% 15% 3	180
	21st to end	Day	9% 9% 35% 29% 15% 3	198
February	1st to 10th	Day	8% 10% 33% 26% 15% 9%	196
	11th to 20th	Day	9% 8% 36% 29% 15% 3	366
	21st to end	Day	11% 10% 34% 26% 15% 3	319
March	1st to 10th	Day	13% 11% 29% 27% 16% 5%	460
	11th to 20th	Day	14% 11% 27% 28% 15% 5%	460
	21st to end	Day	17% 13% 33% 24% 11% 2	506
April	1st to 10th	Day	20% 12% 32% 21% 12% 3	460
	11th to 20th	Day	17% 11% 26% 26% 14% 6%	452
	21st to end	Day	23% 11% 23% 25% 12% 7%	460
May	1st to 10th	Day	31% 7% 21% 24% 11% 5%	642
	11th to 20th	Day	20% 9% 23% 22% 18% 8%	674
	21st to end	Day	30% 10% 22% 23% 13% 3	735
June	1st to 10th	Day	28% 5% 20% 27% 17% 4	680
	11th to 20th	Day	29% 8% 22% 21% 15% 5%	680
	21st to end	Day	27% 8% 25% 20% 15% 5%	680
July	1st to 10th	Day	25% 6% 23% 23% 17% 6%	670
	11th to 20th	Day	28% 7% 22% 26% 13% 4	668
	21st to end	Day	27% 6% 15% 27% 19% 6%	740
August	1st to 10th	Day	31% 7% 17% 24% 16% 5%	595
	11th to 20th	Day	24% 6% 15% 26% 20% 9%	479
	21st to end	Day	26% 6% 21% 24% 18% 6%	539
September	1st to 10th	Day	30% 13% 26% 20% 8% 3	490
	11th to 20th	Day	27% 10% 30% 21% 9% 3	490
	21st to end	Day	27% 15% 29% 18% 8% 3	490
October	1st to 10th	Day	26% 17% 30% 19% 8% 2	400
	11th to 20th	Day	36% 9% 24% 19% 8% 4	390
	21st to end	Day	29% 13% 26% 18% 12% 3	429
November	1st to 10th	Day	28% 14% 31% 20% 6% 1	395
	11th to 20th	Day	23% 11% 29% 24% 12% 1	335
	21st to end	Day	18% 13% 37% 21% 9% 3	200
December	1st to 10th	Day	13% 7% 27% 28% 19% 7%	190
	11th to 20th	Day	13% 14% 36% 25% 10% 2	180
	21st to end	Day	15% 10% 34% 24% 14% 4	198
January	1st to 10th	Night	14% 7% 29% 31% 16% 3	850
	11th to 20th	Night	15% 9% 33% 32% 10% 2	850
	21st to end	Night	10% 8% 32% 34% 14% 2	897
February	1st to 10th	Night	7% 10% 30% 33% 17% 3	760
	11th to 20th	Night	12% 10% 32% 30% 13% 3	743
	21st to end	Night	12% 9% 31% 30% 14% 3	628
March	1st to 10th	Night	11% 8% 31% 32% 15% 3	760
	11th to 20th	Night	16% 9% 31% 28% 15% 1	760
	21st to end	Night	17% 11% 33% 28% 9% 2	836
April	1st to 10th	Night	22% 8% 31% 31% 7% 1	628
	11th to 20th	Night	19% 8% 31% 28% 10% 4	564
	21st to end	Night	25% 8% 26% 31% 8% 2	570
May	1st to 10th	Night	28% 8% 23% 29% 11% 2	501
	11th to 20th	Night	25% 7% 25% 25% 16% 3	374
	21st to end	Night	26% 10% 25% 28% 10% 1	411
June	1st to 10th	Night	23% 4 26% 37% 9% 1	380
	11th to 20th	Night	27% 7% 22% 30% 13%	380
	21st to end	Night	26% 6% 23% 28% 16% 1	380
July	1st to 10th	Night	23% 6% 21% 33% 16% 1	370
	11th to 20th	Night	24% 6% 24% 35% 11% 1	368
	21st to end	Night	21% 6% 18% 33% 20% 2	416
August	1st to 10th	Night	24% 6% 14% 36% 19% 1	378
	11th to 20th	Night	24% 5% 18% 33% 19% 1	553
	21st to end	Night	26% 6% 21% 33% 12% 2	627
September	1st to 10th	Night	27% 9% 29% 27% 8% 1	570
	11th to 20th	Night	26% 9% 28% 28% 8% 1	745
	21st to end	Night	25% 10% 33% 24% 8%	760
October	1st to 10th	Night	30% 12% 28% 23% 6%	760
	11th to 20th	Night	33% 9% 22% 24% 10% 2	760
	21st to end	Night	32% 12% 23% 23% 9% 2	866
November	1st to 10th	Night	27% 15% 29% 22% 6% 2	880
	11th to 20th	Night	27% 11% 28% 23% 10% 1	900
	21st to end	Night	24% 10% 30% 26% 9% 1	900
December	1st to 10th	Night	16% 10% 32% 28% 11% 3	878
	11th to 20th	Night	15% 10% 34% 29% 11% 1	850
	21st to end	Night	16% 11% 27% 28% 15% 3	935

Page generated at 2024-12-03 06:45:08. Version ac07

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