Whiskey Bay Observatory
Clear Sky Chart
History

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

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	13% 9% 3 8% 5% 4 4 4 5% 7% 36%	101525
	Night	15% 12% 4 9% 5% 4 4 3 5% 6% 32%	97749
Transparency	Day	25% 48% 7% 13% 6% 1	105015
	Night	27% 48% 7% 11% 5% 1	102347
Seeing	Day	16% 9% 29% 30% 13% 3	15560
	Night	20% 9% 29% 28% 12% 2	24936

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% 17% 6% 11% 7% 6% 6% 5% 7% 6% 16%	2399
	11th to 20th	Day	12% 17% 5% 12% 10% 7% 6% 4 6% 5% 16%	2530
	21st to end	Day	13% 20% 9% 15% 8% 6% 5% 3 3 5% 13%	2783
February	1st to 10th	Day	8% 14% 5% 13% 8% 6% 6% 4 6% 7% 24%	1671
	11th to 20th	Day	11% 12% 4 11% 7% 6% 5% 4 6% 5% 29%	1739
	21st to end	Day	10% 13% 5% 10% 6% 6% 5% 4 5% 6% 28%	1570
March	1st to 10th	Day	10% 12% 4 9% 4 4 4 3 6% 7% 37%	3118
	11th to 20th	Day	8% 12% 4 9% 7% 5% 5% 4 5% 7% 33%	3479
	21st to end	Day	13% 10% 6% 9% 7% 6% 5% 4 5% 6% 29%	3829
April	1st to 10th	Day	16% 12% 4 7% 5% 4 4 4 6% 6% 32%	2280
	11th to 20th	Day	18% 10% 3 7% 4 4 5% 4 5% 5% 36%	2433
	21st to end	Day	17% 8% 3 8% 4 5% 5% 4 5% 7% 34%	2470
May	1st to 10th	Day	15% 7% 2 7% 5% 4 4 4 6% 7% 39%	4108
	11th to 20th	Day	12% 7% 3 6% 5% 4 4 4 5% 7% 43%	4167
	21st to end	Day	13% 6% 2 6% 4 3 4 3 6% 7% 47%	5154
June	1st to 10th	Day	13% 5% 2 6% 5% 4 5% 4 7% 8% 42%	2850
	11th to 20th	Day	12% 6% 2 6% 4 5% 4 5% 5% 8% 41%	2850
	21st to end	Day	14% 7% 3 5% 4 4 4 3 6% 8% 42%	2850
July	1st to 10th	Day	15% 8% 3 6% 3 4 4 4 6% 8% 41%	4760
	11th to 20th	Day	7% 4 2 6% 4 4 4 3 6% 8% 51%	4455
	21st to end	Day	10% 4 2 5% 3 3 4 4 6% 9% 51%	4814
August	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 4 6% 10% 45%	4177
	11th to 20th	Day	12% 6% 2 6% 4 5% 4 4 6% 8% 45%	4044
	21st to end	Day	12% 6% 3 6% 4 3 3 3 5% 8% 47%	4532
September	1st to 10th	Day	13% 7% 3 5% 4 4 4 3 5% 7% 44%	2218
	11th to 20th	Day	13% 4 2 6% 4 4 4 3 6% 9% 44%	2090
	21st to end	Day	15% 8% 3 7% 4 4 4 3 6% 8% 38%	2090
October	1st to 10th	Day	19% 7% 2 7% 5% 3 4 3 5% 7% 37%	2028
	11th to 20th	Day	20% 9% 4 8% 7% 6% 5% 4 6% 8% 22%	1848
	21st to end	Day	22% 10% 4 9% 6% 6% 6% 4 5% 7% 22%	1881
November	1st to 10th	Day	19% 11% 4 9% 6% 4 6% 3 5% 8% 25%	1762
	11th to 20th	Day	13% 17% 6% 11% 8% 6% 5% 4 6% 6% 19%	1608
	21st to end	Day	21% 18% 6% 11% 6% 5% 4 3 4 7% 16%	1506
December	1st to 10th	Day	14% 19% 5% 11% 7% 5% 5% 5% 5% 5% 20%	1330
	11th to 20th	Day	16% 18% 5% 13% 8% 5% 4 4 4 6% 18%	1671
	21st to end	Day	25% 23% 5% 13% 5% 4 3 3 3 3 13%	2431
January	1st to 10th	Night	17% 14% 5% 11% 5% 5% 5% 4 6% 6% 22%	4555
	11th to 20th	Night	11% 16% 6% 15% 8% 7% 6% 4 5% 6% 16%	4440
	21st to end	Night	14% 20% 8% 14% 7% 5% 4 3 4 5% 15%	4884
February	1st to 10th	Night	10% 16% 5% 11% 8% 7% 5% 5% 6% 6% 22%	2508
	11th to 20th	Night	11% 13% 4 11% 8% 5% 5% 5% 6% 6% 27%	2323
	21st to end	Night	12% 14% 5% 10% 7% 6% 5% 5% 5% 6% 25%	1884
March	1st to 10th	Night	16% 11% 2 6% 4 4 3 3 4 6% 41%	3722
	11th to 20th	Night	9% 12% 4 8% 5% 4 5% 4 5% 7% 37%	3479
	21st to end	Night	13% 8% 5% 9% 5% 5% 5% 3 6% 6% 34%	3817
April	1st to 10th	Night	18% 10% 4 8% 5% 5% 5% 4 5% 6% 31%	1914
	11th to 20th	Night	19% 8% 4 6% 4 3 5% 3 5% 6% 37%	1695
	21st to end	Night	19% 8% 3 6% 4 4 4 4 5% 6% 35%	1710
May	1st to 10th	Night	17% 8% 2 7% 6% 5% 5% 4 4 6% 36%	2833
	11th to 20th	Night	12% 9% 3 9% 6% 4 4 4 5% 6% 37%	2728
	21st to end	Night	16% 7% 2 6% 3 4 4 4 5% 7% 41%	2419
June	1st to 10th	Night	13% 6% 2 5% 4 4 5% 4 7% 9% 40%	1330
	11th to 20th	Night	10% 7% 3 6% 4 4 6% 4 7% 9% 42%	1330
	21st to end	Night	13% 8% 2 6% 4 4 4 3 6% 8% 42%	1330
July	1st to 10th	Night	14% 6% 2 5% 4 4 5% 3 6% 8% 42%	2210
	11th to 20th	Night	7% 4 2 6% 4 4 4 4 5% 7% 52%	2498
	21st to end	Night	9% 6% 2 5% 4 3 4 3 5% 9% 50%	2750
August	1st to 10th	Night	8% 6% 3 7% 4 4 5% 4 6% 8% 45%	2752
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 5% 10% 45%	2785
	21st to end	Night	10% 5% 3 6% 4 4 4 3 5% 6% 52%	3124
September	1st to 10th	Night	13% 7% 2 5% 4 5% 4 3 5% 6% 45%	1942
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 6% 8% 48%	2090
	21st to end	Night	17% 9% 3 7% 4 4 4 5% 5% 5% 37%	2090
October	1st to 10th	Night	18% 8% 2 7% 5% 3 4 2 6% 7% 38%	2152
	11th to 20th	Night	20% 11% 3 8% 5% 5% 5% 3 5% 7% 28%	2327
	21st to end	Night	27% 12% 3 7% 5% 5% 4 3 5% 6% 24%	2717
November	1st to 10th	Night	17% 11% 3 8% 6% 4 5% 3 6% 7% 29%	2536
	11th to 20th	Night	18% 16% 4 10% 7% 5% 5% 4 5% 6% 20%	2593
	21st to end	Night	19% 19% 6% 10% 6% 4 4 3 4 5% 19%	2670
December	1st to 10th	Night	15% 19% 5% 10% 6% 5% 5% 4 5% 5% 20%	2850
	11th to 20th	Night	18% 16% 5% 10% 6% 5% 5% 3 5% 5% 22%	3526
	21st to end	Night	25% 24% 6% 11% 4 3 3 2 3 3 14%	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	41% 47% 5% 5% 2	2400
	11th to 20th	Day	44% 42% 8% 5% 1 1	2530
	21st to end	Day	49% 43% 3 2 2	2783
February	1st to 10th	Day	20% 67% 4 7% 2	1671
	11th to 20th	Day	20% 66% 3 6% 5%	1748
	21st to end	Day	20% 66% 4 7% 4	1570
March	1st to 10th	Day	27% 44% 10% 11% 7% 1	3120
	11th to 20th	Day	32% 42% 8% 13% 4 1	3479
	21st to end	Day	32% 46% 7% 7% 7% 1	3829
April	1st to 10th	Day	20% 66% 4 7% 4	2280
	11th to 20th	Day	17% 66% 3 8% 5% 1	2433
	21st to end	Day	16% 65% 4 8% 5% 1	2470
May	1st to 10th	Day	23% 46% 6% 15% 9% 1	4120
	11th to 20th	Day	22% 46% 7% 17% 8%	4171
	21st to end	Day	22% 42% 8% 13% 13% 2	5154
June	1st to 10th	Day	14% 66% 4 10% 5% 2	2850
	11th to 20th	Day	16% 66% 4 8% 5% 1	2850
	21st to end	Day	14% 64% 5% 11% 6% 1	2850
July	1st to 10th	Day	30% 38% 9% 14% 8% 1	4686
	11th to 20th	Day	18% 38% 10% 28% 5% 1	4379
	21st to end	Day	18% 37% 6% 24% 14%	4662
August	1st to 10th	Day	20% 40% 9% 24% 8%	4162
	11th to 20th	Day	26% 39% 9% 19% 7%	4083
	21st to end	Day	24% 38% 12% 21% 4	4531
September	1st to 10th	Day	17% 62% 6% 11% 4	2218
	11th to 20th	Day	13% 61% 6% 15% 5%	2090
	21st to end	Day	17% 62% 7% 10% 4	2090
October	1st to 10th	Day	19% 38% 9% 21% 13%	3366
	11th to 20th	Day	27% 39% 7% 23% 3	3051
	21st to end	Day	37% 39% 7% 12% 4	3081
November	1st to 10th	Day	26% 57% 6% 8% 3	1762
	11th to 20th	Day	27% 61% 5% 4 2	1608
	21st to end	Day	29% 61% 4 3 2	1506
December	1st to 10th	Day	27% 62% 4 4 3	1330
	11th to 20th	Day	33% 53% 5% 7% 2	1671
	21st to end	Day	51% 39% 4 3 4	2431
January	1st to 10th	Night	39% 43% 7% 6% 5%	4555
	11th to 20th	Night	42% 43% 8% 5% 2	4440
	21st to end	Night	46% 44% 5% 3 1	4884
February	1st to 10th	Night	19% 67% 4 7% 2	2508
	11th to 20th	Night	17% 66% 4 9% 3	2325
	21st to end	Night	20% 66% 4 6% 5%	1884
March	1st to 10th	Night	26% 43% 11% 13% 7%	3733
	11th to 20th	Night	25% 42% 10% 15% 6% 1	3480
	21st to end	Night	28% 46% 8% 12% 6% 1	3817
April	1st to 10th	Night	21% 65% 3 7% 4	1914
	11th to 20th	Night	18% 65% 2 8% 5% 2	1695
	21st to end	Night	19% 65% 3 7% 5% 1	1710
May	1st to 10th	Night	28% 44% 6% 15% 6% 1	2840
	11th to 20th	Night	26% 43% 4 18% 9%	2729
	21st to end	Night	27% 43% 7% 10% 8% 5%	2420
June	1st to 10th	Night	13% 65% 5% 9% 6% 1	1330
	11th to 20th	Night	16% 66% 3 8% 5% 2	1330
	21st to end	Night	15% 64% 4 10% 6% 1	1330
July	1st to 10th	Night	29% 37% 8% 15% 9% 1	2175
	11th to 20th	Night	19% 37% 11% 22% 11%	2451
	21st to end	Night	18% 37% 8% 21% 15% 1	2662
August	1st to 10th	Night	23% 39% 8% 20% 10% 1	2743
	11th to 20th	Night	24% 40% 9% 19% 7% 1	2812
	21st to end	Night	21% 38% 7% 24% 9%	3124
September	1st to 10th	Night	15% 62% 6% 11% 6%	1942
	11th to 20th	Night	12% 61% 7% 15% 5%	2090
	21st to end	Night	18% 61% 7% 10% 4	2090
October	1st to 10th	Night	25% 39% 9% 20% 7%	3594
	11th to 20th	Night	22% 38% 14% 18% 8%	3863
	21st to end	Night	34% 39% 11% 14% 2	4467
November	1st to 10th	Night	26% 57% 6% 8% 3	2536
	11th to 20th	Night	24% 61% 6% 6% 3	2593
	21st to end	Night	30% 61% 3 4 2	2670
December	1st to 10th	Night	26% 61% 6% 6% 1	2850
	11th to 20th	Night	30% 53% 5% 5% 4 2	3525
	21st to end	Night	51% 38% 4 5% 3	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	20% 16% 30% 23% 11% 1	234
	11th to 20th	Day	21% 9% 35% 27% 7% 1	270
	21st to end	Day	22% 10% 30% 28% 9% 1	297
February	1st to 10th	Day	16% 18% 40% 19% 7% 1	270
	11th to 20th	Day	16% 14% 43% 24% 2 1	270
	21st to end	Day	16% 21% 40% 21% 2	225
March	1st to 10th	Day	16% 16% 34% 27% 7% 1	270
	11th to 20th	Day	15% 13% 35% 28% 8% 1	459
	21st to end	Day	21% 11% 32% 26% 9% 1	506
April	1st to 10th	Day	20% 11% 32% 27% 8% 1	460
	11th to 20th	Day	23% 14% 30% 22% 10% 2	452
	21st to end	Day	21% 11% 33% 22% 11% 2	460
May	1st to 10th	Day	19% 9% 30% 28% 12% 1	463
	11th to 20th	Day	17% 5% 32% 31% 12% 4	534
	21st to end	Day	12% 6% 29% 35% 14% 3	734
June	1st to 10th	Day	12% 6% 32% 36% 13% 2	680
	11th to 20th	Day	13% 6% 30% 36% 12% 3	680
	21st to end	Day	18% 8% 23% 36% 13% 2	680
July	1st to 10th	Day	9% 4 24% 41% 17% 4	671
	11th to 20th	Day	11% 5% 24% 37% 20% 3	668
	21st to end	Day	11% 4 22% 37% 23% 4	739
August	1st to 10th	Day	13% 3 19% 36% 25% 4	534
	11th to 20th	Day	12% 3 17% 33% 25% 10%	479
	21st to end	Day	12% 7% 24% 32% 22% 4	539
September	1st to 10th	Day	15% 5% 24% 29% 21% 5%	490
	11th to 20th	Day	13% 5% 18% 34% 22% 7%	490
	21st to end	Day	18% 8% 20% 31% 18% 4	490
October	1st to 10th	Day	21% 13% 27% 20% 15% 3	490
	11th to 20th	Day	19% 16% 30% 28% 6% 1	438
	21st to end	Day	27% 14% 34% 20% 5%	330
November	1st to 10th	Day	21% 15% 33% 24% 6% 1	300
	11th to 20th	Day	20% 17% 40% 18% 4	220
	21st to end	Day	22% 22% 36% 17% 3	180
December	1st to 10th	Day	24% 14% 32% 21% 7% 1	180
	11th to 20th	Day	25% 22% 33% 14% 6% 1	180
	21st to end	Day	29% 19% 35% 14% 3	198
January	1st to 10th	Night	22% 13% 33% 24% 7%	950
	11th to 20th	Night	23% 13% 32% 24% 8% 1	950
	21st to end	Night	21% 8% 33% 30% 7% 1	1045
February	1st to 10th	Night	16% 12% 40% 25% 8%	798
	11th to 20th	Night	16% 12% 36% 27% 8% 1	743
	21st to end	Night	19% 12% 35% 28% 6%	628
March	1st to 10th	Night	17% 9% 36% 29% 8% 1	760
	11th to 20th	Night	18% 11% 35% 28% 8% 1	760
	21st to end	Night	18% 8% 33% 31% 9% 1	836
April	1st to 10th	Night	22% 9% 31% 31% 6% 1	584
	11th to 20th	Night	22% 8% 27% 31% 11% 1	563
	21st to end	Night	23% 5% 30% 28% 13% 1	570
May	1st to 10th	Night	14% 7% 28% 37% 13% 2	570
	11th to 20th	Night	18% 6% 24% 34% 18% 1	561
	21st to end	Night	13% 5% 27% 36% 18% 1	429
June	1st to 10th	Night	14% 4 26% 39% 17%	380
	11th to 20th	Night	11% 4 27% 37% 19% 2	380
	21st to end	Night	15% 4 22% 38% 19% 2	380
July	1st to 10th	Night	12% 1 19% 47% 20% 1	370
	11th to 20th	Night	7% 2 19% 40% 26% 5%	534
	21st to end	Night	11% 3 18% 38% 27% 3	624
August	1st to 10th	Night	11% 3 19% 40% 24% 3	567
	11th to 20th	Night	11% 3 18% 31% 31% 6%	564
	21st to end	Night	13% 3 19% 36% 26% 3	627
September	1st to 10th	Night	14% 5% 23% 31% 23% 5%	627
	11th to 20th	Night	15% 4 23% 32% 21% 5%	760
	21st to end	Night	20% 5% 23% 26% 21% 4	760
October	1st to 10th	Night	20% 9% 26% 27% 15% 2	760
	11th to 20th	Night	24% 14% 28% 26% 7% 1	760
	21st to end	Night	33% 10% 28% 22% 6% 1	836
November	1st to 10th	Night	23% 14% 31% 24% 8%	780
	11th to 20th	Night	24% 16% 32% 21% 6% 1	765
	21st to end	Night	30% 17% 29% 19% 4	770
December	1st to 10th	Night	23% 17% 33% 20% 6% 1	950
	11th to 20th	Night	26% 14% 38% 15% 6% 1	950
	21st to end	Night	31% 13% 31% 19% 6%	1045

Page generated at 2024-11-08 22:45:35. Version ac07

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