White Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Mountain clear sky chart from 2005-11-06 to 2024-11-01.

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	3 6% 2 7% 5% 5% 5% 4 6% 8% 49%	101346
	Night	3 6% 3 7% 5% 5% 5% 4 6% 8% 49%	97872
Transparency	Day	29% 9% 13% 20% 18% 11%	101102
	Night	29% 9% 15% 22% 17% 8%	97706
Seeing	Day	7% 10% 25% 30% 20% 8%	15542
	Night	6% 7% 25% 42% 19% 1	25666

By Month

Percentage Cloud Cover SW (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	2 6% 3 14% 9% 8% 8% 6% 8% 8% 30%	2643
	11th to 20th	Day	2 7% 4 14% 9% 7% 5% 4 6% 7% 35%	2860
	21st to end	Day	2 9% 5% 19% 10% 8% 5% 3 5% 6% 27%	3146
February	1st to 10th	Day	2 8% 4 8% 6% 6% 5% 5% 6% 8% 41%	1710
	11th to 20th	Day	2 8% 4 9% 6% 5% 6% 4 7% 9% 40%	1665
	21st to end	Day	1 8% 4 9% 5% 5% 5% 6% 7% 7% 42%	1514
March	1st to 10th	Day	2 9% 4 9% 7% 5% 6% 6% 8% 10% 34%	3444
	11th to 20th	Day	1 8% 4 10% 7% 6% 6% 5% 7% 9% 37%	3490
	21st to end	Day	4 12% 5% 10% 6% 5% 6% 5% 8% 9% 31%	3825
April	1st to 10th	Day	5% 10% 2 6% 5% 5% 4 4 7% 9% 43%	2232
	11th to 20th	Day	5% 9% 3 8% 5% 5% 5% 5% 6% 7% 42%	2251
	21st to end	Day	5% 9% 2 7% 5% 5% 4 5% 6% 9% 43%	2466
May	1st to 10th	Day	5% 12% 3 8% 5% 5% 5% 4 6% 8% 38%	4110
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 7% 8% 50%	4197
	21st to end	Day	6% 6% 2 5% 5% 5% 5% 5% 6% 7% 49%	4825
June	1st to 10th	Day	5% 4 1 5% 4 4 4 5% 7% 8% 52%	2660
	11th to 20th	Day	5% 4 2 5% 4 3 4 3 6% 7% 58%	2660
	21st to end	Day	2 3 1 4 3 4 4 4 6% 7% 63%	2660
July	1st to 10th	Day	2 2 1 3 2 3 4 3 4 5% 72%	4430
	11th to 20th	Day	2 2 1 4 4 4 5% 4 6% 8% 58%	4243
	21st to end	Day	3 3 1 4 3 4 4 4 7% 7% 59%	4454
August	1st to 10th	Day	3 3 1 4 3 5% 5% 5% 7% 8% 56%	4092
	11th to 20th	Day	3 3 1 4 4 5% 6% 5% 6% 8% 56%	4028
	21st to end	Day	2 2 1 3 3 3 4 3 6% 8% 65%	4314
September	1st to 10th	Day	3 4 1 3 3 3 4 3 4 6% 65%	2280
	11th to 20th	Day	3 2 1 5% 4 3 3 4 6% 7% 61%	2157
	21st to end	Day	5% 5% 1 3 2 2 3 2 3 5% 68%	2071
October	1st to 10th	Day	6% 5% 2 5% 4 3 4 2 5% 6% 59%	1900
	11th to 20th	Day	5% 5% 2 4 3 3 3 4 5% 7% 59%	1900
	21st to end	Day	3 7% 2 5% 4 3 3 3 5% 8% 55%	2090
November	1st to 10th	Day	3 5% 2 5% 4 5% 4 4 8% 8% 51%	1749
	11th to 20th	Day	4 7% 3 6% 4 4 5% 3 7% 9% 50%	1520
	21st to end	Day	2 6% 3 7% 5% 6% 5% 4 6% 9% 48%	1520
December	1st to 10th	Day	3 8% 3 10% 6% 6% 5% 4 7% 8% 40%	1520
	11th to 20th	Day	2 9% 4 8% 6% 6% 7% 5% 7% 10% 37%	1926
	21st to end	Day	2 9% 4 11% 9% 7% 7% 6% 7% 8% 31%	2794
January	1st to 10th	Night	2 8% 4 11% 7% 6% 6% 4 7% 9% 36%	4342
	11th to 20th	Night	1 8% 5% 12% 7% 5% 5% 4 6% 9% 39%	4110
	21st to end	Night	2 9% 5% 16% 11% 6% 5% 3 5% 6% 31%	4521
February	1st to 10th	Night	2 6% 3 8% 6% 6% 6% 6% 7% 10% 42%	2470
	11th to 20th	Night	2 8% 3 8% 5% 5% 5% 5% 6% 9% 44%	2402
	21st to end	Night	2 7% 5% 8% 6% 5% 5% 5% 7% 9% 41%	1937
March	1st to 10th	Night	2 7% 3 9% 7% 6% 8% 6% 8% 8% 36%	3430
	11th to 20th	Night	2 8% 2 6% 5% 6% 7% 5% 6% 8% 44%	3490
	21st to end	Night	4 12% 4 9% 6% 5% 6% 5% 6% 7% 36%	3828
April	1st to 10th	Night	5% 10% 3 5% 4 4 6% 5% 5% 7% 48%	1948
	11th to 20th	Night	6% 9% 3 7% 5% 4 4 5% 6% 6% 44%	1877
	21st to end	Night	5% 7% 3 6% 4 5% 5% 5% 6% 8% 46%	1710
May	1st to 10th	Night	6% 11% 3 7% 5% 5% 4 4 6% 7% 42%	2860
	11th to 20th	Night	5% 5% 2 6% 5% 4 4 4 7% 8% 52%	2708
	21st to end	Night	5% 6% 2 6% 4 4 4 3 6% 7% 54%	2762
June	1st to 10th	Night	4 5% 2 3 3 4 4 6% 7% 8% 54%	1520
	11th to 20th	Night	5% 3 2 4 3 3 4 3 5% 7% 61%	1520
	21st to end	Night	3 2 1 3 2 3 3 4 5% 7% 67%	1520
July	1st to 10th	Night	3 2 1 3 3 3 4 3 5% 7% 65%	2540
	11th to 20th	Night	2 2 1 5% 5% 4 5% 5% 7% 9% 56%	2723
	21st to end	Night	2 2 1 4 3 4 5% 4 8% 9% 58%	3109
August	1st to 10th	Night	2 2 1 4 4 3 4 3 7% 8% 62%	2847
	11th to 20th	Night	3 3 1 5% 4 5% 4 3 5% 6% 60%	2811
	21st to end	Night	2 2 1 3 3 3 3 3 5% 7% 70%	3353
September	1st to 10th	Night	4 2 1 2 2 2 3 3 5% 6% 69%	1900
	11th to 20th	Night	3 3 1 3 3 3 3 3 5% 7% 66%	2021
	21st to end	Night	4 3 1 3 2 3 3 3 4 6% 68%	2108
October	1st to 10th	Night	5% 5% 2 4 3 4 4 3 5% 6% 59%	2280
	11th to 20th	Night	4 6% 2 5% 3 3 3 3 4 6% 62%	2280
	21st to end	Night	4 6% 2 5% 3 4 3 3 5% 8% 57%	2508
November	1st to 10th	Night	3 6% 2 5% 3 4 4 4 6% 8% 54%	2313
	11th to 20th	Night	4 6% 2 6% 4 4 4 4 6% 8% 51%	2660
	21st to end	Night	2 8% 3 6% 5% 4 4 3 5% 8% 51%	2660
December	1st to 10th	Night	2 9% 3 8% 6% 5% 5% 4 7% 8% 42%	2660
	11th to 20th	Night	4 9% 3 8% 5% 5% 6% 5% 7% 10% 38%	3271
	21st to end	Night	2 8% 4 10% 7% 7% 7% 5% 8% 8% 34%	4873

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	39% 19% 17% 16% 7% 1	2644
	11th to 20th	Day	40% 16% 19% 18% 6% 1	2860
	21st to end	Day	52% 14% 17% 12% 5% 1	3146
February	1st to 10th	Day	39% 11% 18% 21% 10% 1	1710
	11th to 20th	Day	38% 10% 18% 24% 9% 1	1674
	21st to end	Day	34% 10% 20% 21% 13% 1	1514
March	1st to 10th	Day	33% 14% 19% 25% 8% 1	3444
	11th to 20th	Day	36% 12% 20% 23% 9%	3490
	21st to end	Day	42% 12% 17% 22% 5% 1	3825
April	1st to 10th	Day	36% 8% 18% 22% 14% 3	2232
	11th to 20th	Day	37% 9% 16% 23% 14% 1	2254
	21st to end	Day	35% 9% 13% 24% 18% 1	2466
May	1st to 10th	Day	36% 11% 11% 20% 16% 6%	4110
	11th to 20th	Day	25% 9% 13% 30% 18% 5%	4201
	21st to end	Day	27% 10% 11% 25% 24% 3	4825
June	1st to 10th	Day	26% 8% 14% 23% 22% 7%	2660
	11th to 20th	Day	24% 7% 9% 19% 26% 15%	2660
	21st to end	Day	18% 5% 7% 18% 28% 24%	2660
July	1st to 10th	Day	15% 4 5% 11% 21% 43%	4361
	11th to 20th	Day	22% 5% 4 13% 23% 33%	4169
	21st to end	Day	22% 5% 6% 13% 25% 30%	4314
August	1st to 10th	Day	23% 6% 8% 18% 25% 21%	4078
	11th to 20th	Day	24% 5% 8% 18% 26% 18%	4067
	21st to end	Day	18% 4 8% 16% 30% 24%	4313
September	1st to 10th	Day	21% 4 8% 15% 28% 24%	2280
	11th to 20th	Day	21% 6% 8% 21% 28% 16%	2157
	21st to end	Day	20% 4 6% 24% 33% 13%	2071
October	1st to 10th	Day	25% 6% 12% 24% 26% 7%	1900
	11th to 20th	Day	23% 6% 14% 31% 21% 6%	1900
	21st to end	Day	26% 6% 17% 30% 19% 2	2090
November	1st to 10th	Day	28% 8% 17% 27% 18% 2	1749
	11th to 20th	Day	29% 8% 22% 26% 14% 1	1520
	21st to end	Day	31% 9% 17% 25% 16% 1	1520
December	1st to 10th	Day	38% 11% 21% 18% 11% 2	1520
	11th to 20th	Day	37% 12% 21% 22% 8%	1924
	21st to end	Day	43% 13% 16% 16% 9% 4	2794
January	1st to 10th	Night	38% 15% 20% 20% 7% 1	4342
	11th to 20th	Night	38% 15% 20% 18% 8% 1	4110
	21st to end	Night	48% 16% 17% 12% 5% 1	4521
February	1st to 10th	Night	35% 13% 21% 22% 8% 1	2470
	11th to 20th	Night	33% 10% 17% 26% 12% 2	2403
	21st to end	Night	35% 11% 21% 19% 13% 1	1937
March	1st to 10th	Night	32% 13% 19% 28% 7%	3430
	11th to 20th	Night	28% 16% 23% 24% 8% 1	3490
	21st to end	Night	40% 12% 16% 25% 5% 1	3828
April	1st to 10th	Night	34% 8% 18% 22% 15% 4	1948
	11th to 20th	Night	37% 8% 16% 24% 15% 1	1877
	21st to end	Night	32% 10% 15% 29% 13% 1	1710
May	1st to 10th	Night	35% 10% 12% 21% 20% 3	2860
	11th to 20th	Night	24% 10% 15% 29% 16% 5%	2709
	21st to end	Night	25% 7% 13% 33% 20% 2	2762
June	1st to 10th	Night	22% 7% 18% 25% 22% 6%	1520
	11th to 20th	Night	22% 5% 11% 20% 27% 16%	1520
	21st to end	Night	14% 5% 7% 17% 31% 26%	1520
July	1st to 10th	Night	16% 5% 6% 11% 20% 42%	2500
	11th to 20th	Night	20% 5% 6% 18% 24% 27%	2674
	21st to end	Night	17% 6% 8% 16% 31% 22%	3011
August	1st to 10th	Night	18% 5% 7% 22% 24% 24%	2838
	11th to 20th	Night	25% 4 7% 17% 30% 18%	2838
	21st to end	Night	14% 3 10% 20% 28% 25%	3353
September	1st to 10th	Night	15% 4 9% 19% 28% 25%	1900
	11th to 20th	Night	17% 5% 12% 21% 29% 16%	2021
	21st to end	Night	17% 4 9% 26% 35% 10%	2108
October	1st to 10th	Night	24% 6% 11% 27% 25% 8%	2280
	11th to 20th	Night	23% 4 10% 35% 23% 5%	2280
	21st to end	Night	24% 6% 17% 31% 18% 3	2508
November	1st to 10th	Night	26% 9% 14% 28% 20% 3	2313
	11th to 20th	Night	28% 7% 19% 31% 11% 2	2660
	21st to end	Night	31% 6% 16% 28% 17% 2	2660
December	1st to 10th	Night	36% 11% 21% 20% 11% 2	2660
	11th to 20th	Night	37% 12% 18% 24% 9%	3272
	21st to end	Night	41% 13% 16% 16% 13% 2	4873

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% 11% 13% 38% 22% 7%	270
	11th to 20th	Day	6% 11% 23% 36% 20% 4	270
	21st to end	Day	5% 7% 26% 36% 21% 7%	297
February	1st to 10th	Day	7% 17% 29% 36% 8% 3	270
	11th to 20th	Day	5% 12% 29% 31% 19% 4	270
	21st to end	Day	7% 11% 27% 40% 13% 3	275
March	1st to 10th	Day	8% 11% 32% 32% 13% 4	460
	11th to 20th	Day	6% 12% 26% 31% 22% 3	460
	21st to end	Day	11% 12% 26% 34% 15% 1	506
April	1st to 10th	Day	12% 12% 27% 27% 18% 4	460
	11th to 20th	Day	12% 19% 31% 24% 11% 3	452
	21st to end	Day	11% 20% 30% 17% 17% 6%	460
May	1st to 10th	Day	11% 20% 28% 21% 16% 4	463
	11th to 20th	Day	10% 12% 25% 28% 19% 6%	562
	21st to end	Day	10% 10% 24% 25% 21% 10%	734
June	1st to 10th	Day	6% 9% 22% 27% 25% 11%	680
	11th to 20th	Day	7% 12% 28% 31% 19% 3	680
	21st to end	Day	3 7% 27% 31% 27% 5%	680
July	1st to 10th	Day	4 3 20% 33% 32% 8%	671
	11th to 20th	Day	3 6% 25% 30% 28% 9%	560
	21st to end	Day	5% 3 22% 30% 26% 15%	531
August	1st to 10th	Day	6% 5% 22% 29% 26% 13%	487
	11th to 20th	Day	3 5% 25% 30% 25% 12%	477
	21st to end	Day	3 6% 25% 29% 19% 17%	539
September	1st to 10th	Day	5% 6% 25% 25% 24% 15%	490
	11th to 20th	Day	6% 8% 30% 24% 18% 14%	490
	21st to end	Day	7% 10% 24% 22% 24% 13%	471
October	1st to 10th	Day	7% 8% 19% 24% 24% 17%	300
	11th to 20th	Day	9% 12% 21% 25% 23% 10%	300
	21st to end	Day	8% 16% 27% 30% 16% 4	330
November	1st to 10th	Day	9% 14% 24% 32% 13% 8%	270
	11th to 20th	Day	8% 10% 22% 37% 19% 5%	270
	21st to end	Day	6% 9% 24% 34% 20% 7%	270
December	1st to 10th	Day	6% 8% 24% 40% 18% 5%	270
	11th to 20th	Day	6% 9% 19% 47% 16% 3	270
	21st to end	Day	8% 9% 30% 31% 13% 8%	297
January	1st to 10th	Night	5% 9% 26% 40% 19% 1	901
	11th to 20th	Night	5% 10% 28% 39% 16% 2	760
	21st to end	Night	4 6% 29% 44% 14% 2	836
February	1st to 10th	Night	4 10% 36% 39% 11% 1	760
	11th to 20th	Night	4 9% 32% 43% 11% 2	744
	21st to end	Night	5% 8% 33% 44% 10%	628
March	1st to 10th	Night	6% 7% 29% 45% 13% 1	760
	11th to 20th	Night	6% 5% 27% 46% 16% 1	760
	21st to end	Night	8% 6% 33% 41% 12%	836
April	1st to 10th	Night	9% 10% 31% 40% 11%	618
	11th to 20th	Night	10% 10% 30% 39% 9% 1	563
	21st to end	Night	7% 12% 29% 37% 15% 1	570
May	1st to 10th	Night	9% 10% 29% 35% 15% 1	570
	11th to 20th	Night	10% 6% 22% 40% 19% 2	561
	21st to end	Night	7% 8% 23% 39% 21% 2	617
June	1st to 10th	Night	6% 5% 24% 41% 23% 2	570
	11th to 20th	Night	6% 8% 26% 43% 16%	570
	21st to end	Night	3 2 21% 48% 25% 1	570
July	1st to 10th	Night	3 2 15% 45% 34% 1	555
	11th to 20th	Night	3 2 15% 46% 32% 1	552
	21st to end	Night	3 1 11% 47% 36% 2	624
August	1st to 10th	Night	3 2 12% 46% 36% 1	567
	11th to 20th	Night	2 2 13% 47% 34% 1	564
	21st to end	Night	3 3 13% 41% 36% 4	627
September	1st to 10th	Night	5% 4 16% 40% 32% 3	570
	11th to 20th	Night	3 3 19% 44% 27% 4	691
	21st to end	Night	4 5% 18% 37% 32% 4	760
October	1st to 10th	Night	7% 5% 25% 36% 24% 3	760
	11th to 20th	Night	7% 7% 22% 40% 23% 2	760
	21st to end	Night	6% 6% 25% 42% 18% 2	836
November	1st to 10th	Night	6% 7% 26% 42% 19% 1	761
	11th to 20th	Night	6% 9% 28% 42% 13% 1	950
	21st to end	Night	5% 10% 25% 43% 16% 1	950
December	1st to 10th	Night	6% 10% 29% 43% 12% 1	950
	11th to 20th	Night	9% 7% 27% 45% 12%	950
	21st to end	Night	6% 12% 30% 39% 12% 2	1045

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