Bolton Landing
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bolton Landing 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	16% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	101371
	Night	17% 10% 3 8% 5% 4 4 4 5% 6% 33%	97584
Transparency	Day	48% 8% 13% 19% 10% 1	101127
	Night	50% 7% 13% 18% 10% 1	97447
Seeing	Day	21% 16% 30% 21% 9% 2	14746
	Night	20% 11% 31% 28% 9% 1	23746

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	12% 15% 4 11% 6% 5% 5% 4 5% 5% 27%	2517
	11th to 20th	Day	15% 14% 7% 13% 8% 5% 4 3 5% 4 22%	2520
	21st to end	Day	16% 13% 4 11% 7% 6% 5% 4 6% 6% 22%	2804
February	1st to 10th	Day	13% 14% 4 9% 7% 6% 5% 4 6% 6% 26%	1710
	11th to 20th	Day	10% 13% 6% 11% 6% 5% 5% 3 6% 6% 29%	1809
	21st to end	Day	18% 12% 3 9% 6% 5% 4 3 4 6% 31%	1570
March	1st to 10th	Day	22% 16% 4 10% 5% 4 3 3 4 5% 26%	3116
	11th to 20th	Day	13% 13% 3 9% 6% 5% 5% 4 6% 6% 29%	3278
	21st to end	Day	17% 11% 3 8% 4 5% 4 3 4 5% 36%	4166
April	1st to 10th	Day	20% 11% 3 7% 5% 4 3 3 5% 5% 35%	2280
	11th to 20th	Day	18% 8% 3 7% 6% 4 4 3 5% 6% 36%	2254
	21st to end	Day	21% 9% 3 7% 5% 6% 4 3 6% 6% 30%	2393
May	1st to 10th	Day	23% 9% 3 7% 5% 4 4 3 5% 6% 29%	4227
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 5% 7% 33%	4398
	21st to end	Day	13% 5% 2 6% 5% 4 4 5% 7% 8% 41%	4837
June	1st to 10th	Day	17% 7% 2 7% 6% 6% 6% 5% 7% 8% 30%	2660
	11th to 20th	Day	16% 7% 3 6% 5% 5% 5% 5% 6% 8% 34%	2660
	21st to end	Day	17% 7% 2 8% 6% 5% 5% 4 7% 8% 30%	2660
July	1st to 10th	Day	11% 6% 2 6% 5% 6% 5% 5% 7% 10% 36%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 8% 11% 35%	4440
	21st to end	Day	13% 6% 2 6% 5% 6% 6% 5% 7% 8% 35%	4814
August	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 4 6% 8% 36%	4423
	11th to 20th	Day	15% 6% 3 7% 5% 6% 6% 5% 7% 10% 30%	3789
	21st to end	Day	12% 5% 2 5% 5% 5% 6% 5% 7% 9% 38%	4180
September	1st to 10th	Day	13% 5% 2 4 4 4 5% 4 7% 9% 43%	2280
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 5% 7% 49%	2190
	21st to end	Day	16% 7% 2 5% 4 5% 4 4 5% 8% 40%	2090
October	1st to 10th	Day	21% 9% 3 7% 5% 4 4 4 4 5% 33%	1986
	11th to 20th	Day	16% 8% 2 7% 5% 4 4 3 6% 8% 36%	1887
	21st to end	Day	23% 10% 3 8% 5% 4 5% 3 4 7% 28%	1881
November	1st to 10th	Day	14% 9% 3 7% 5% 4 4 4 6% 9% 35%	1671
	11th to 20th	Day	17% 9% 3 7% 5% 5% 4 3 6% 7% 33%	1710
	21st to end	Day	17% 10% 3 8% 5% 4 5% 4 6% 7% 31%	1533
December	1st to 10th	Day	21% 14% 4 10% 6% 4 5% 3 5% 6% 22%	1520
	11th to 20th	Day	23% 11% 4 9% 5% 4 4 3 4 6% 28%	1906
	21st to end	Day	24% 18% 6% 9% 5% 4 3 2 3 4 22%	2772
January	1st to 10th	Night	15% 15% 5% 9% 5% 4 4 3 5% 5% 30%	4429
	11th to 20th	Night	11% 13% 7% 14% 7% 6% 5% 3 5% 6% 22%	4440
	21st to end	Night	20% 15% 5% 9% 5% 4 4 3 4 5% 26%	4848
February	1st to 10th	Night	12% 13% 5% 11% 7% 6% 5% 4 5% 6% 25%	2470
	11th to 20th	Night	11% 11% 4 10% 8% 5% 5% 4 5% 6% 31%	2256
	21st to end	Night	15% 11% 4 8% 6% 5% 5% 3 5% 6% 32%	1884
March	1st to 10th	Night	24% 12% 3 8% 4 4 4 4 4 5% 28%	3724
	11th to 20th	Night	14% 13% 4 7% 6% 5% 4 4 5% 5% 33%	3677
	21st to end	Night	17% 12% 3 9% 4 4 4 3 4 4 34%	3466
April	1st to 10th	Night	19% 9% 3 7% 5% 5% 4 4 5% 6% 34%	1900
	11th to 20th	Night	20% 8% 3 8% 4 4 4 3 5% 6% 35%	1875
	21st to end	Night	20% 9% 3 7% 4 3 4 4 5% 6% 35%	1786
May	1st to 10th	Night	26% 9% 3 7% 4 4 4 3 5% 7% 28%	2741
	11th to 20th	Night	21% 10% 4 9% 5% 4 4 3 4 5% 30%	2495
	21st to end	Night	14% 6% 2 6% 4 4 5% 5% 7% 8% 39%	2738
June	1st to 10th	Night	19% 6% 2 6% 4 3 5% 5% 7% 7% 36%	1520
	11th to 20th	Night	18% 7% 3 6% 5% 3 4 4 6% 8% 39%	1520
	21st to end	Night	17% 6% 2 6% 6% 5% 5% 4 5% 7% 37%	1520
July	1st to 10th	Night	12% 6% 2 7% 6% 6% 5% 5% 6% 8% 37%	2520
	11th to 20th	Night	15% 6% 2 6% 4 5% 5% 3 5% 8% 42%	2520
	21st to end	Night	13% 7% 2 6% 4 4 5% 4 5% 7% 41%	2739
August	1st to 10th	Night	18% 7% 3 7% 5% 4 5% 3 5% 7% 36%	2506
	11th to 20th	Night	15% 7% 3 8% 5% 5% 4 4 6% 7% 38%	2993
	21st to end	Night	9% 5% 2 5% 5% 5% 6% 5% 6% 9% 43%	3476
September	1st to 10th	Night	13% 5% 2 5% 3 4 4 3 6% 7% 47%	1900
	11th to 20th	Night	13% 5% 1 5% 3 3 4 2 4 6% 52%	1990
	21st to end	Night	16% 6% 2 4 4 3 5% 4 5% 6% 44%	2090
October	1st to 10th	Night	20% 9% 3 8% 5% 4 5% 4 5% 5% 33%	2192
	11th to 20th	Night	17% 7% 2 7% 5% 5% 5% 3 6% 6% 37%	2291
	21st to end	Night	23% 10% 3 7% 5% 4 4 3 5% 6% 29%	2717
November	1st to 10th	Night	14% 9% 3 7% 5% 4 4 3 5% 6% 38%	2414
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 3 6% 7% 36%	2470
	21st to end	Night	17% 10% 3 7% 5% 4 4 4 6% 7% 33%	2645
December	1st to 10th	Night	19% 15% 5% 9% 5% 5% 4 3 5% 7% 23%	2660
	11th to 20th	Night	21% 12% 3 7% 5% 4 4 3 6% 6% 29%	3288
	21st to end	Night	25% 15% 6% 9% 4 4 4 3 4 5% 22%	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	53% 8% 14% 19% 5% 1	2518
	11th to 20th	Day	65% 6% 10% 13% 5% 1	2520
	21st to end	Day	62% 7% 12% 12% 6% 1	2804
February	1st to 10th	Day	55% 8% 13% 16% 6% 1	1710
	11th to 20th	Day	55% 7% 11% 15% 11% 1	1818
	21st to end	Day	55% 6% 12% 14% 13% 2	1570
March	1st to 10th	Day	62% 6% 10% 12% 9% 2	3119
	11th to 20th	Day	51% 9% 15% 13% 10% 2	3278
	21st to end	Day	49% 5% 7% 17% 19% 3	4166
April	1st to 10th	Day	51% 5% 11% 19% 11% 3	2280
	11th to 20th	Day	48% 6% 11% 18% 15% 2	2254
	21st to end	Day	52% 7% 10% 16% 12% 3	2393
May	1st to 10th	Day	54% 8% 10% 18% 9% 1	4241
	11th to 20th	Day	48% 9% 14% 19% 9% 1	4402
	21st to end	Day	36% 9% 14% 27% 13% 1	4837
June	1st to 10th	Day	49% 9% 15% 16% 10% 1	2660
	11th to 20th	Day	45% 8% 15% 18% 13% 1	2660
	21st to end	Day	49% 9% 12% 18% 11% 1	2660
July	1st to 10th	Day	40% 9% 15% 23% 13%	4370
	11th to 20th	Day	39% 9% 17% 28% 8%	4365
	21st to end	Day	43% 9% 16% 23% 9%	4661
August	1st to 10th	Day	44% 8% 16% 19% 12% 1	4409
	11th to 20th	Day	45% 9% 17% 24% 5%	3826
	21st to end	Day	37% 8% 18% 25% 11% 1	4180
September	1st to 10th	Day	36% 9% 13% 29% 13% 1	2280
	11th to 20th	Day	34% 5% 13% 29% 18% 1	2190
	21st to end	Day	40% 8% 15% 24% 12% 1	2090
October	1st to 10th	Day	52% 6% 10% 20% 11% 1	1986
	11th to 20th	Day	44% 8% 16% 22% 8% 1	1887
	21st to end	Day	56% 6% 13% 16% 8% 1	1881
November	1st to 10th	Day	45% 8% 15% 21% 11%	1671
	11th to 20th	Day	48% 7% 13% 17% 13% 2	1710
	21st to end	Day	51% 8% 17% 17% 7% 1	1533
December	1st to 10th	Day	60% 7% 14% 12% 6%	1520
	11th to 20th	Day	56% 8% 15% 15% 6% 1	1906
	21st to end	Day	67% 5% 8% 13% 7%	2772
January	1st to 10th	Night	54% 9% 15% 14% 8% 1	4429
	11th to 20th	Night	61% 7% 13% 12% 7% 1	4440
	21st to end	Night	61% 6% 12% 13% 7% 1	4848
February	1st to 10th	Night	57% 9% 12% 14% 7% 1	2470
	11th to 20th	Night	52% 7% 11% 19% 11% 1	2258
	21st to end	Night	51% 6% 13% 18% 8% 2	1884
March	1st to 10th	Night	57% 5% 10% 17% 9% 1	3734
	11th to 20th	Night	51% 7% 14% 16% 10% 1	3678
	21st to end	Night	51% 5% 8% 15% 17% 3	3466
April	1st to 10th	Night	50% 5% 11% 19% 13% 2	1900
	11th to 20th	Night	50% 5% 10% 21% 13% 1	1875
	21st to end	Night	48% 6% 11% 18% 14% 4	1786
May	1st to 10th	Night	55% 8% 10% 15% 10% 1	2747
	11th to 20th	Night	55% 8% 11% 17% 9% 1	2496
	21st to end	Night	39% 9% 14% 21% 15% 2	2739
June	1st to 10th	Night	45% 8% 14% 19% 12% 1	1520
	11th to 20th	Night	43% 6% 16% 20% 13% 1	1520
	21st to end	Night	45% 8% 13% 22% 11% 1	1520
July	1st to 10th	Night	42% 8% 16% 20% 13% 1	2480
	11th to 20th	Night	40% 8% 15% 24% 13%	2472
	21st to end	Night	41% 7% 12% 28% 10% 1	2651
August	1st to 10th	Night	46% 8% 15% 21% 10%	2496
	11th to 20th	Night	43% 7% 18% 23% 8%	3021
	21st to end	Night	33% 9% 19% 27% 11% 1	3476
September	1st to 10th	Night	36% 7% 15% 28% 13% 1	1900
	11th to 20th	Night	34% 5% 13% 30% 17% 1	1990
	21st to end	Night	38% 7% 13% 25% 15% 2	2090
October	1st to 10th	Night	51% 7% 11% 19% 12% 1	2192
	11th to 20th	Night	46% 6% 15% 22% 10% 1	2291
	21st to end	Night	56% 6% 12% 16% 9% 1	2717
November	1st to 10th	Night	47% 6% 14% 19% 12% 2	2414
	11th to 20th	Night	47% 7% 13% 19% 12% 2	2470
	21st to end	Night	49% 8% 16% 18% 8%	2645
December	1st to 10th	Night	60% 8% 14% 14% 4	2660
	11th to 20th	Night	54% 8% 14% 14% 9% 1	3288
	21st to end	Night	64% 7% 10% 14% 4	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% 27% 26% 22% 5%	180
	11th to 20th	Day	27% 27% 27% 16% 2 1	180
	21st to end	Day	17% 26% 35% 17% 4	207
February	1st to 10th	Day	28% 32% 29% 9% 1	270
	11th to 20th	Day	24% 27% 34% 13% 2	417
	21st to end	Day	29% 19% 33% 17% 3	382
March	1st to 10th	Day	27% 15% 34% 20% 4	460
	11th to 20th	Day	27% 22% 31% 16% 3 1	460
	21st to end	Day	29% 22% 26% 15% 6% 2	506
April	1st to 10th	Day	33% 18% 25% 16% 7%	460
	11th to 20th	Day	31% 21% 27% 12% 7% 2	452
	21st to end	Day	28% 18% 33% 13% 6% 2	460
May	1st to 10th	Day	28% 18% 28% 16% 8% 2	463
	11th to 20th	Day	19% 15% 35% 23% 6% 2	487
	21st to end	Day	18% 14% 32% 24% 11% 2	529
June	1st to 10th	Day	18% 17% 32% 22% 10% 1	490
	11th to 20th	Day	18% 14% 33% 24% 9% 2	490
	21st to end	Day	20% 13% 35% 22% 8% 2	490
July	1st to 10th	Day	15% 9% 31% 28% 15% 2	485
	11th to 20th	Day	13% 10% 32% 29% 14% 3	484
	21st to end	Day	14% 8% 36% 30% 11% 2	532
August	1st to 10th	Day	13% 8% 29% 30% 15% 4	486
	11th to 20th	Day	17% 7% 27% 29% 16% 5%	479
	21st to end	Day	11% 13% 29% 27% 16% 4	539
September	1st to 10th	Day	14% 9% 28% 27% 15% 7%	490
	11th to 20th	Day	13% 9% 28% 23% 18% 9%	490
	21st to end	Day	18% 9% 31% 23% 11% 7%	490
October	1st to 10th	Day	24% 15% 25% 20% 12% 4	490
	11th to 20th	Day	19% 16% 30% 24% 9% 2	483
	21st to end	Day	31% 13% 28% 22% 6%	429
November	1st to 10th	Day	22% 17% 27% 21% 12% 1	365
	11th to 20th	Day	24% 20% 31% 17% 6% 1	370
	21st to end	Day	23% 18% 35% 20% 4	193
December	1st to 10th	Day	26% 23% 29% 17% 5%	180
	11th to 20th	Day	29% 22% 36% 12% 1	180
	21st to end	Day	28% 21% 33% 15% 3 1	198
January	1st to 10th	Night	20% 15% 37% 25% 3	760
	11th to 20th	Night	23% 16% 34% 24% 3	760
	21st to end	Night	16% 15% 37% 28% 4	836
February	1st to 10th	Night	19% 16% 42% 22% 2	760
	11th to 20th	Night	17% 17% 42% 22% 2	743
	21st to end	Night	22% 16% 39% 21% 3	628
March	1st to 10th	Night	21% 15% 34% 27% 3	760
	11th to 20th	Night	22% 17% 33% 24% 4	760
	21st to end	Night	21% 18% 31% 23% 7%	836
April	1st to 10th	Night	25% 14% 32% 26% 4	760
	11th to 20th	Night	25% 16% 32% 20% 7%	751
	21st to end	Night	25% 15% 30% 25% 6%	646
May	1st to 10th	Night	27% 13% 25% 25% 9%	516
	11th to 20th	Night	21% 8% 36% 29% 6%	374
	21st to end	Night	16% 7% 28% 36% 12%	411
June	1st to 10th	Night	19% 5% 29% 34% 13%	380
	11th to 20th	Night	18% 8% 26% 37% 10%	380
	21st to end	Night	17% 4 29% 38% 11% 1	380
July	1st to 10th	Night	14% 4 21% 44% 16% 2	370
	11th to 20th	Night	13% 4 22% 42% 18% 1	368
	21st to end	Night	11% 4 23% 46% 15% 1	416
August	1st to 10th	Night	12% 2 21% 44% 21% 1	378
	11th to 20th	Night	16% 3 20% 39% 20% 3	682
	21st to end	Night	14% 5% 21% 38% 21% 1	836
September	1st to 10th	Night	15% 6% 23% 37% 17% 2	760
	11th to 20th	Night	16% 6% 22% 31% 21% 4	760
	21st to end	Night	18% 7% 27% 29% 18% 2	760
October	1st to 10th	Night	23% 11% 23% 28% 14% 1	760
	11th to 20th	Night	20% 10% 29% 31% 10% 1	760
	21st to end	Night	28% 10% 30% 26% 6%	836
November	1st to 10th	Night	20% 13% 32% 28% 7%	743
	11th to 20th	Night	23% 13% 31% 26% 7% 1	760
	21st to end	Night	22% 13% 34% 25% 6%	760
December	1st to 10th	Night	26% 13% 35% 22% 4	760
	11th to 20th	Night	25% 12% 34% 25% 4	760
	21st to end	Night	28% 13% 36% 21% 2	836

Page generated at 2024-10-29 11:20:49. Version ac07

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