West Haven Pass Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Haven Pass Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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%	101403
	Night	17% 11% 4 9% 5% 5% 4 3 5% 6% 31%	97648
Transparency	Day	26% 48% 7% 12% 6%	104902
	Night	28% 48% 7% 11% 5% 1	102238
Seeing	Day	23% 16% 30% 20% 8% 2	14772
	Night	22% 13% 29% 27% 9% 1	23747

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	13% 13% 5% 11% 7% 6% 6% 3 6% 5% 26%	2517
	11th to 20th	Day	17% 12% 6% 16% 7% 5% 4 3 4 4 21%	2520
	21st to end	Day	17% 15% 5% 9% 6% 6% 5% 4 5% 5% 22%	2772
February	1st to 10th	Day	12% 14% 5% 10% 7% 6% 5% 4 6% 6% 24%	1709
	11th to 20th	Day	12% 13% 6% 10% 7% 5% 5% 3 5% 6% 28%	1824
	21st to end	Day	17% 13% 3 8% 7% 5% 4 4 4 6% 28%	1570
March	1st to 10th	Day	22% 15% 4 11% 5% 5% 3 3 4 3 25%	3116
	11th to 20th	Day	14% 17% 4 8% 5% 4 4 4 6% 5% 28%	3273
	21st to end	Day	17% 11% 3 10% 6% 4 4 3 4 5% 34%	4166
April	1st to 10th	Day	20% 11% 4 7% 4 3 3 3 4 6% 34%	2280
	11th to 20th	Day	17% 10% 2 7% 5% 4 5% 4 5% 5% 36%	2254
	21st to end	Day	21% 9% 4 7% 4 5% 4 3 5% 6% 31%	2412
May	1st to 10th	Day	24% 8% 3 8% 5% 5% 4 4 5% 6% 28%	4197
	11th to 20th	Day	16% 8% 3 8% 5% 5% 6% 4 6% 7% 32%	4398
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 6% 9% 42%	4837
June	1st to 10th	Day	17% 8% 3 7% 6% 5% 5% 4 7% 8% 29%	2660
	11th to 20th	Day	17% 7% 2 6% 6% 5% 5% 5% 5% 8% 35%	2660
	21st to end	Day	16% 8% 3 8% 5% 6% 5% 5% 6% 7% 32%	2660
July	1st to 10th	Day	11% 6% 2 6% 4 5% 6% 5% 7% 11% 37%	4440
	11th to 20th	Day	10% 6% 2 7% 5% 6% 5% 5% 9% 11% 35%	4440
	21st to end	Day	13% 6% 2 6% 4 5% 6% 5% 7% 8% 38%	4814
August	1st to 10th	Day	13% 7% 2 7% 5% 5% 7% 5% 7% 8% 34%	4410
	11th to 20th	Day	13% 7% 3 7% 6% 5% 5% 5% 7% 10% 32%	3826
	21st to end	Day	11% 5% 2 6% 4 5% 5% 5% 7% 9% 40%	4180
September	1st to 10th	Day	12% 6% 2 5% 4 4 5% 3 6% 8% 45%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 5% 7% 50%	2176
	21st to end	Day	14% 6% 2 7% 3 4 5% 4 7% 8% 40%	2090
October	1st to 10th	Day	20% 9% 2 8% 5% 4 5% 4 5% 6% 33%	2005
	11th to 20th	Day	16% 8% 3 9% 4 4 4 3 5% 8% 36%	1871
	21st to end	Day	23% 10% 3 7% 4 5% 4 4 5% 6% 29%	1881
November	1st to 10th	Day	13% 10% 3 8% 5% 4 5% 4 5% 7% 36%	1708
	11th to 20th	Day	17% 11% 2 8% 4 4 5% 4 6% 6% 33%	1710
	21st to end	Day	17% 10% 5% 8% 5% 5% 6% 4 6% 6% 29%	1549
December	1st to 10th	Day	20% 14% 4 10% 7% 4 4 3 6% 7% 22%	1520
	11th to 20th	Day	21% 13% 4 7% 4 4 4 3 6% 6% 27%	1906
	21st to end	Day	26% 15% 4 11% 5% 4 4 3 4 4 21%	2772
January	1st to 10th	Night	15% 14% 5% 11% 6% 4 5% 3 4 5% 27%	4429
	11th to 20th	Night	12% 14% 6% 15% 8% 5% 4 4 5% 6% 19%	4440
	21st to end	Night	21% 13% 5% 13% 6% 5% 4 3 4 4 22%	4884
February	1st to 10th	Night	14% 14% 4 13% 7% 7% 5% 4 5% 4 24%	2470
	11th to 20th	Night	12% 12% 4 10% 8% 6% 5% 4 6% 6% 28%	2242
	21st to end	Night	15% 14% 4 10% 7% 4 4 3 4 5% 31%	1884
March	1st to 10th	Night	24% 12% 4 10% 4 4 4 3 4 5% 26%	3724
	11th to 20th	Night	14% 15% 4 9% 6% 5% 4 3 4 5% 30%	3685
	21st to end	Night	17% 13% 4 9% 5% 4 4 3 3 4 34%	3466
April	1st to 10th	Night	19% 10% 3 8% 5% 5% 5% 3 5% 5% 32%	1900
	11th to 20th	Night	20% 10% 4 7% 4 4 4 3 4 6% 34%	1875
	21st to end	Night	20% 9% 3 8% 5% 4 3 3 5% 5% 35%	1767
May	1st to 10th	Night	25% 11% 3 7% 5% 3 4 4 5% 6% 26%	2772
	11th to 20th	Night	19% 11% 3 11% 5% 4 4 3 5% 5% 30%	2495
	21st to end	Night	14% 6% 3 7% 4 4 5% 4 7% 8% 39%	2738
June	1st to 10th	Night	18% 8% 2 7% 5% 4 5% 3 6% 7% 35%	1520
	11th to 20th	Night	17% 8% 3 6% 5% 3 4 4 5% 8% 38%	1520
	21st to end	Night	17% 7% 3 7% 6% 5% 4 4 5% 7% 36%	1520
July	1st to 10th	Night	12% 6% 2 7% 6% 6% 6% 5% 7% 8% 35%	2520
	11th to 20th	Night	15% 6% 3 6% 5% 5% 4 4 6% 8% 38%	2520
	21st to end	Night	12% 7% 3 6% 5% 5% 5% 5% 6% 7% 39%	2739
August	1st to 10th	Night	17% 8% 3 8% 5% 4 4 3 4 7% 36%	2506
	11th to 20th	Night	13% 8% 2 7% 5% 4 5% 4 5% 8% 37%	2966
	21st to end	Night	9% 4 2 6% 5% 5% 6% 5% 7% 9% 41%	3476
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 46%	1900
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 4 5% 52%	2003
	21st to end	Night	15% 6% 2 5% 4 4 6% 4 5% 6% 44%	2090
October	1st to 10th	Night	19% 9% 3 8% 6% 4 3 4 4 6% 32%	2171
	11th to 20th	Night	17% 8% 3 7% 5% 4 5% 3 5% 5% 37%	2308
	21st to end	Night	24% 9% 3 8% 5% 4 5% 3 5% 6% 28%	2717
November	1st to 10th	Night	14% 11% 3 8% 5% 4 4 3 5% 5% 36%	2470
	11th to 20th	Night	19% 9% 3 8% 4 4 4 3 6% 6% 34%	2470
	21st to end	Night	17% 11% 4 7% 6% 5% 5% 4 5% 6% 30%	2629
December	1st to 10th	Night	18% 15% 5% 12% 7% 5% 5% 4 4 6% 20%	2660
	11th to 20th	Night	21% 11% 3 9% 5% 5% 4 3 5% 6% 28%	3288
	21st to end	Night	25% 17% 5% 9% 4 4 4 3 4 4 19%	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	35% 41% 10% 11% 3	2518
	11th to 20th	Day	44% 39% 5% 9% 2	2520
	21st to end	Day	42% 42% 7% 7% 2	2772
February	1st to 10th	Day	21% 66% 5% 5% 3 1	1709
	11th to 20th	Day	20% 64% 4 7% 5%	1833
	21st to end	Day	18% 66% 4 6% 6% 1	1570
March	1st to 10th	Day	41% 43% 4 5% 5% 1	3119
	11th to 20th	Day	33% 45% 10% 7% 5% 1	3273
	21st to end	Day	32% 43% 4 8% 11% 1	4166
April	1st to 10th	Day	21% 65% 3 6% 4 1	2280
	11th to 20th	Day	17% 66% 4 7% 6% 1	2254
	21st to end	Day	20% 66% 3 6% 5%	2412
May	1st to 10th	Day	36% 43% 7% 11% 3	4211
	11th to 20th	Day	30% 45% 11% 10% 4	4402
	21st to end	Day	22% 44% 9% 17% 8%	4837
June	1st to 10th	Day	18% 66% 4 7% 5% 1	2660
	11th to 20th	Day	17% 65% 4 8% 6% 1	2660
	21st to end	Day	17% 64% 4 9% 5% 1	2660
July	1st to 10th	Day	24% 39% 11% 17% 10%	4370
	11th to 20th	Day	24% 40% 11% 20% 5%	4365
	21st to end	Day	27% 38% 10% 18% 7%	4661
August	1st to 10th	Day	31% 40% 9% 14% 7%	4396
	11th to 20th	Day	31% 41% 10% 16% 3	3865
	21st to end	Day	22% 39% 13% 17% 7% 1	4180
September	1st to 10th	Day	13% 62% 5% 14% 7%	2280
	11th to 20th	Day	13% 60% 5% 11% 10% 1	2176
	21st to end	Day	16% 61% 6% 11% 5% 1	2090
October	1st to 10th	Day	28% 39% 6% 18% 9%	3330
	11th to 20th	Day	25% 38% 9% 15% 13%	3087
	21st to end	Day	20% 39% 8% 25% 7%	3081
November	1st to 10th	Day	23% 58% 6% 9% 4	1708
	11th to 20th	Day	20% 60% 4 8% 8% 1	1710
	21st to end	Day	21% 60% 8% 6% 3 1	1549
December	1st to 10th	Day	26% 60% 5% 6% 3	1520
	11th to 20th	Day	30% 48% 10% 8% 3	1906
	21st to end	Day	42% 39% 5% 10% 4	2772
January	1st to 10th	Night	35% 40% 11% 9% 4	4429
	11th to 20th	Night	40% 41% 7% 9% 4	4440
	21st to end	Night	43% 43% 6% 5% 3	4884
February	1st to 10th	Night	22% 66% 5% 5% 2	2470
	11th to 20th	Night	20% 64% 3 7% 6%	2244
	21st to end	Night	18% 65% 4 8% 4 2	1884
March	1st to 10th	Night	33% 46% 6% 8% 6% 1	3734
	11th to 20th	Night	31% 44% 8% 9% 6% 1	3686
	21st to end	Night	35% 41% 4 7% 11% 1	3466
April	1st to 10th	Night	21% 65% 3 6% 5%	1900
	11th to 20th	Night	18% 66% 3 7% 5% 1	1875
	21st to end	Night	19% 65% 3 5% 6% 1	1767
May	1st to 10th	Night	35% 45% 8% 9% 3	2778
	11th to 20th	Night	36% 44% 7% 9% 3	2496
	21st to end	Night	24% 43% 9% 12% 10% 1	2739
June	1st to 10th	Night	16% 65% 4 7% 6% 1	1520
	11th to 20th	Night	16% 65% 5% 6% 7%	1520
	21st to end	Night	17% 63% 3 11% 4 1	1520
July	1st to 10th	Night	30% 38% 10% 12% 9% 1	2480
	11th to 20th	Night	30% 39% 8% 16% 7%	2472
	21st to end	Night	30% 38% 7% 19% 7%	2651
August	1st to 10th	Night	35% 39% 7% 13% 6%	2496
	11th to 20th	Night	29% 40% 12% 14% 4	2993
	21st to end	Night	21% 40% 12% 18% 7%	3476
September	1st to 10th	Night	12% 62% 6% 13% 6% 1	1900
	11th to 20th	Night	12% 60% 6% 12% 10% 1	2003
	21st to end	Night	13% 60% 6% 13% 6% 1	2090
October	1st to 10th	Night	34% 39% 7% 15% 5%	3626
	11th to 20th	Night	24% 38% 8% 17% 12%	3831
	21st to end	Night	27% 38% 7% 23% 4	4467
November	1st to 10th	Night	22% 58% 6% 9% 4 1	2470
	11th to 20th	Night	20% 60% 5% 8% 6% 1	2470
	21st to end	Night	22% 62% 6% 7% 3	2629
December	1st to 10th	Night	27% 61% 4 6% 1	2660
	11th to 20th	Night	30% 50% 7% 6% 6%	3288
	21st to end	Night	42% 41% 5% 10% 2	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	24% 26% 24% 22% 3 1	180
	11th to 20th	Day	27% 28% 28% 12% 3 1	180
	21st to end	Day	20% 29% 31% 16% 4	198
February	1st to 10th	Day	29% 31% 30% 8% 1	270
	11th to 20th	Day	26% 26% 34% 12% 2	432
	21st to end	Day	30% 20% 32% 15% 3	382
March	1st to 10th	Day	28% 17% 34% 18% 3	460
	11th to 20th	Day	28% 24% 31% 14% 3	460
	21st to end	Day	29% 23% 26% 13% 6% 2	506
April	1st to 10th	Day	35% 18% 24% 17% 6% 1	460
	11th to 20th	Day	35% 20% 25% 12% 6% 2	452
	21st to end	Day	30% 20% 29% 14% 6% 2	460
May	1st to 10th	Day	30% 19% 26% 15% 8% 1	463
	11th to 20th	Day	19% 16% 33% 25% 6% 2	487
	21st to end	Day	19% 16% 32% 22% 10% 1	529
June	1st to 10th	Day	21% 16% 32% 22% 8% 1	490
	11th to 20th	Day	19% 14% 33% 23% 9% 2	490
	21st to end	Day	19% 15% 35% 21% 8% 1	490
July	1st to 10th	Day	14% 10% 32% 28% 14% 2	485
	11th to 20th	Day	14% 9% 35% 28% 13% 2	484
	21st to end	Day	14% 9% 38% 28% 9% 2	532
August	1st to 10th	Day	14% 8% 31% 28% 16% 3	486
	11th to 20th	Day	16% 7% 28% 31% 14% 5%	479
	21st to end	Day	14% 13% 26% 29% 15% 4	539
September	1st to 10th	Day	13% 12% 29% 26% 14% 6%	490
	11th to 20th	Day	14% 11% 27% 20% 18% 10%	490
	21st to end	Day	18% 12% 30% 21% 13% 6%	490
October	1st to 10th	Day	25% 14% 26% 20% 11% 4	490
	11th to 20th	Day	20% 17% 29% 22% 10% 1	474
	21st to end	Day	31% 15% 29% 20% 4	429
November	1st to 10th	Day	25% 20% 26% 21% 9%	378
	11th to 20th	Day	29% 17% 28% 19% 6% 1	370
	21st to end	Day	27% 18% 33% 19% 3	209
December	1st to 10th	Day	29% 23% 27% 18% 1 1	180
	11th to 20th	Day	28% 25% 36% 11%	180
	21st to end	Day	32% 16% 38% 11% 3 1	198
January	1st to 10th	Night	24% 18% 34% 22% 2	760
	11th to 20th	Night	26% 19% 30% 22% 3	760
	21st to end	Night	19% 15% 36% 26% 3	836
February	1st to 10th	Night	22% 18% 39% 20% 2	760
	11th to 20th	Night	19% 20% 38% 20% 2	743
	21st to end	Night	24% 18% 34% 21% 3	628
March	1st to 10th	Night	24% 15% 32% 25% 4	760
	11th to 20th	Night	23% 19% 32% 21% 4	760
	21st to end	Night	25% 18% 29% 21% 7%	836
April	1st to 10th	Night	26% 16% 29% 26% 3	760
	11th to 20th	Night	26% 19% 28% 20% 7%	751
	21st to end	Night	28% 14% 26% 27% 6%	627
May	1st to 10th	Night	31% 12% 24% 25% 8%	534
	11th to 20th	Night	19% 12% 31% 31% 6% 1	374
	21st to end	Night	19% 8% 27% 36% 10%	411
June	1st to 10th	Night	20% 7% 28% 33% 12%	380
	11th to 20th	Night	19% 7% 27% 36% 12%	380
	21st to end	Night	18% 8% 25% 38% 10% 1	380
July	1st to 10th	Night	14% 4 20% 45% 16% 1	370
	11th to 20th	Night	14% 2 24% 40% 17% 1	368
	21st to end	Night	11% 4 22% 47% 15% 1	416
August	1st to 10th	Night	12% 3 20% 44% 20% 1	378
	11th to 20th	Night	15% 4 19% 40% 19% 2	667
	21st to end	Night	14% 5% 21% 38% 20% 1	836
September	1st to 10th	Night	15% 6% 26% 35% 16% 2	760
	11th to 20th	Night	17% 7% 21% 29% 22% 4	760
	21st to end	Night	18% 7% 28% 28% 18% 2	760
October	1st to 10th	Night	25% 11% 20% 28% 14% 1	760
	11th to 20th	Night	21% 14% 24% 29% 10% 1	760
	21st to end	Night	28% 12% 30% 24% 6%	836
November	1st to 10th	Night	22% 14% 33% 25% 7%	760
	11th to 20th	Night	23% 15% 30% 24% 8% 1	760
	21st to end	Night	22% 16% 33% 22% 6%	760
December	1st to 10th	Night	28% 18% 30% 20% 4	760
	11th to 20th	Night	25% 15% 34% 22% 4	760
	21st to end	Night	32% 12% 34% 19% 2	836

Page generated at 2024-11-03 02:11:08. Version ac07

Copyright © 2024 Attilla Danko.