Dorcas Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dorcas Bay clear sky chart from 2005-11-06 to 2024-04-25.

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	15% 11% 5% 8% 6% 3 4 4 5% 6% 32%	83037
	Night	16% 13% 6% 10% 7% 3 4 4 4 5% 26%	86088
Transparency	Day	39% 32% 8% 14% 7% 1	82741
	Night	45% 31% 7% 11% 5% 1	85919
Seeing	Day	20% 5% 22% 30% 18% 4	14448
	Night	24% 8% 24% 27% 14% 3	23902

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	17% 25% 13% 14% 7% 3 4 4 2 3 9%	2217
	11th to 20th	Day	13% 20% 10% 23% 14% 4 5% 3 2 2 4	2530
	21st to end	Day	20% 21% 10% 12% 7% 4 5% 5% 4 4 9%	3061
February	1st to 10th	Day	14% 18% 8% 13% 12% 3 5% 4 3 5% 15%	1710
	11th to 20th	Day	12% 14% 7% 11% 9% 6% 7% 5% 4 5% 20%	1663
	21st to end	Day	14% 16% 7% 10% 6% 4 6% 4 5% 6% 23%	1542
March	1st to 10th	Day	16% 12% 4 7% 6% 3 4 5% 5% 6% 33%	3295
	11th to 20th	Day	11% 15% 6% 10% 6% 3 5% 4 5% 6% 28%	3480
	21st to end	Day	14% 11% 5% 8% 6% 3 4 4 4 6% 34%	3815
April	1st to 10th	Day	19% 10% 4 6% 6% 3 5% 4 5% 6% 33%	2211
	11th to 20th	Day	19% 8% 3 6% 5% 3 3 4 4 6% 40%	2442
	21st to end	Day	18% 8% 4 6% 4 3 4 4 5% 8% 38%	2394
May	1st to 10th	Day	18% 6% 2 5% 5% 3 3 5% 6% 7% 39%	2340
	11th to 20th	Day	15% 7% 3 4 4 3 4 4 5% 7% 44%	2392
	21st to end	Day	11% 5% 2 5% 4 3 5% 4 5% 8% 49%	2751
June	1st to 10th	Day	13% 5% 3 6% 5% 3 5% 6% 6% 7% 42%	2700
	11th to 20th	Day	11% 6% 3 5% 5% 3 4 5% 6% 9% 44%	2700
	21st to end	Day	13% 6% 3 5% 5% 3 5% 4 5% 9% 43%	2700
July	1st to 10th	Day	7% 4 2 4 4 3 4 4 6% 9% 53%	2700
	11th to 20th	Day	9% 5% 2 4 5% 3 5% 5% 6% 8% 48%	2655
	21st to end	Day	10% 4 2 4 4 3 4 5% 6% 9% 49%	2604
August	1st to 10th	Day	13% 4 2 4 4 3 4 4 6% 8% 49%	2327
	11th to 20th	Day	10% 5% 2 4 5% 3 4 5% 5% 9% 49%	2303
	21st to end	Day	12% 7% 2 5% 6% 3 4 5% 6% 8% 44%	2574
September	1st to 10th	Day	13% 6% 2 5% 5% 3 4 4 5% 7% 43%	2127
	11th to 20th	Day	13% 6% 2 4 4 3 4 5% 6% 8% 46%	1980
	21st to end	Day	18% 7% 3 6% 5% 3 5% 5% 4 8% 36%	1980
October	1st to 10th	Day	18% 10% 4 7% 5% 4 4 4 5% 8% 32%	1840
	11th to 20th	Day	27% 11% 4 7% 6% 3 5% 5% 4 6% 22%	1800
	21st to end	Day	26% 16% 4 8% 6% 3 3 4 4 6% 19%	1874
November	1st to 10th	Day	18% 17% 5% 8% 6% 3 5% 4 5% 7% 22%	1639
	11th to 20th	Day	19% 17% 6% 11% 7% 3 6% 5% 4 6% 17%	1520
	21st to end	Day	24% 21% 6% 11% 7% 3 5% 3 3 5% 11%	1520
December	1st to 10th	Day	17% 28% 9% 13% 9% 5% 3 3 3 3 8%	1520
	11th to 20th	Day	19% 23% 7% 14% 9% 4 4 3 4 4 10%	1700
	21st to end	Day	26% 23% 9% 16% 7% 3 4 3 3 3 4	2431
January	1st to 10th	Night	17% 23% 11% 17% 11% 4 3 3 2 2 7%	4734
	11th to 20th	Night	14% 17% 11% 19% 15% 4 5% 3 3 3 6%	4440
	21st to end	Night	16% 18% 9% 15% 9% 5% 6% 4 3 4 12%	4595
February	1st to 10th	Night	12% 19% 7% 15% 10% 4 5% 4 4 4 16%	2470
	11th to 20th	Night	13% 16% 8% 12% 8% 4 5% 5% 5% 5% 21%	2403
	21st to end	Night	15% 14% 6% 10% 7% 4 6% 4 5% 5% 23%	1908
March	1st to 10th	Night	13% 9% 5% 7% 6% 3 4 4 5% 5% 39%	3543
	11th to 20th	Night	10% 13% 5% 7% 6% 3 5% 5% 5% 6% 36%	3479
	21st to end	Night	13% 9% 5% 9% 8% 4 4 4 5% 6% 32%	3817
April	1st to 10th	Night	21% 11% 4 5% 5% 3 4 4 5% 5% 33%	1983
	11th to 20th	Night	18% 8% 3 6% 5% 2 4 4 6% 7% 37%	1687
	21st to end	Night	20% 8% 3 7% 6% 4 5% 4 5% 6% 34%	1665
May	1st to 10th	Night	15% 7% 4 6% 5% 4 5% 6% 5% 6% 37%	1620
	11th to 20th	Night	14% 7% 3 5% 5% 3 5% 5% 5% 6% 41%	1501
	21st to end	Night	11% 6% 3 5% 4 3 5% 4 5% 8% 45%	1521
June	1st to 10th	Night	13% 6% 3 6% 6% 4 5% 5% 5% 7% 40%	1260
	11th to 20th	Night	9% 6% 2 4 6% 3 5% 5% 6% 9% 44%	1260
	21st to end	Night	11% 7% 2 6% 5% 4 5% 6% 6% 8% 41%	1260
July	1st to 10th	Night	7% 4 2 5% 5% 2 4 4 5% 8% 55%	1260
	11th to 20th	Night	8% 5% 2 4 6% 3 4 5% 7% 10% 45%	1302
	21st to end	Night	8% 5% 2 4 5% 3 4 5% 5% 8% 51%	1710
August	1st to 10th	Night	9% 5% 2 5% 4 3 4 4 6% 9% 50%	1611
	11th to 20th	Night	9% 5% 2 5% 5% 3 5% 5% 6% 8% 48%	1598
	21st to end	Night	11% 7% 2 6% 5% 3 5% 5% 5% 7% 44%	1782
September	1st to 10th	Night	12% 4 2 5% 5% 3 4 5% 6% 7% 47%	1812
	11th to 20th	Night	13% 5% 2 4 5% 3 4 5% 6% 6% 46%	1980
	21st to end	Night	19% 7% 3 5% 5% 3 4 3 6% 7% 38%	1980
October	1st to 10th	Night	21% 9% 3 7% 6% 4 4 4 4 6% 32%	2119
	11th to 20th	Night	26% 11% 4 8% 7% 4 4 5% 4 6% 23%	2160
	21st to end	Night	27% 15% 5% 8% 6% 3 4 4 4 5% 19%	2479
November	1st to 10th	Night	21% 14% 5% 7% 6% 4 4 4 4 6% 25%	2439
	11th to 20th	Night	18% 19% 6% 10% 7% 3 6% 4 4 5% 17%	2660
	21st to end	Night	24% 22% 6% 10% 8% 3 4 4 4 4 12%	2660
December	1st to 10th	Night	21% 24% 9% 14% 7% 3 4 3 2 3 8%	2660
	11th to 20th	Night	19% 21% 9% 14% 9% 3 4 3 3 4 11%	3494
	21st to end	Night	25% 21% 9% 15% 8% 3 4 3 3 3 7%	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	66% 24% 5% 5%	2218
	11th to 20th	Day	73% 23% 1 2	2530
	21st to end	Day	67% 21% 6% 5% 1	3061
February	1st to 10th	Day	51% 33% 5% 9% 1	1710
	11th to 20th	Day	48% 35% 5% 8% 4	1672
	21st to end	Day	46% 32% 6% 13% 2	1542
March	1st to 10th	Day	46% 20% 14% 12% 8% 1	3298
	11th to 20th	Day	48% 20% 9% 18% 4 1	3480
	21st to end	Day	42% 20% 11% 16% 9% 1	3815
April	1st to 10th	Day	35% 33% 7% 15% 8% 1	2211
	11th to 20th	Day	31% 33% 5% 18% 12% 1	2442
	21st to end	Day	32% 35% 8% 15% 9% 2	2394
May	1st to 10th	Day	30% 35% 5% 17% 11% 2	2340
	11th to 20th	Day	28% 36% 5% 17% 13% 1	2396
	21st to end	Day	24% 36% 10% 16% 12% 2	2751
June	1st to 10th	Day	29% 36% 8% 18% 10%	2700
	11th to 20th	Day	23% 36% 7% 21% 12%	2700
	21st to end	Day	29% 36% 9% 18% 7% 1	2700
July	1st to 10th	Day	22% 36% 12% 19% 10% 1	2626
	11th to 20th	Day	23% 37% 10% 20% 8% 1	2574
	21st to end	Day	24% 37% 11% 19% 10%	2459
August	1st to 10th	Day	25% 36% 11% 20% 7% 1	2314
	11th to 20th	Day	21% 34% 13% 21% 10%	2303
	21st to end	Day	27% 35% 9% 18% 9% 1	2574
September	1st to 10th	Day	26% 36% 8% 21% 8% 1	2127
	11th to 20th	Day	28% 35% 13% 18% 6%	1980
	21st to end	Day	34% 35% 9% 16% 5%	1980
October	1st to 10th	Day	34% 36% 8% 14% 7%	1840
	11th to 20th	Day	45% 35% 7% 8% 4	1800
	21st to end	Day	46% 36% 7% 8% 3	1874
November	1st to 10th	Day	38% 39% 8% 12% 3	1639
	11th to 20th	Day	43% 39% 7% 7% 4	1520
	21st to end	Day	51% 38% 6% 5%	1520
December	1st to 10th	Day	55% 38% 4 3 1	1520
	11th to 20th	Day	58% 31% 4 7%	1700
	21st to end	Day	69% 23% 6% 2	2431
January	1st to 10th	Night	68% 23% 5% 4 1	4734
	11th to 20th	Night	71% 23% 3 3 1	4440
	21st to end	Night	65% 21% 5% 7% 2	4595
February	1st to 10th	Night	50% 33% 5% 9% 2	2470
	11th to 20th	Night	51% 35% 4 7% 3	2405
	21st to end	Night	44% 33% 8% 11% 4	1908
March	1st to 10th	Night	39% 21% 16% 16% 8%	3553
	11th to 20th	Night	41% 20% 11% 19% 8% 1	3480
	21st to end	Night	46% 22% 7% 17% 7% 1	3817
April	1st to 10th	Night	34% 33% 6% 17% 8% 2	1983
	11th to 20th	Night	32% 33% 4 17% 12% 1	1687
	21st to end	Night	35% 34% 5% 12% 12% 2	1665
May	1st to 10th	Night	32% 35% 6% 15% 10% 2	1620
	11th to 20th	Night	28% 36% 4 18% 13% 2	1502
	21st to end	Night	23% 36% 10% 16% 11% 4	1522
June	1st to 10th	Night	33% 35% 6% 14% 10% 1	1260
	11th to 20th	Night	25% 35% 7% 18% 13% 1	1260
	21st to end	Night	30% 36% 9% 16% 8% 1	1260
July	1st to 10th	Night	19% 36% 8% 21% 13% 2	1225
	11th to 20th	Night	24% 37% 8% 18% 11% 1	1260
	21st to end	Night	22% 38% 10% 20% 10%	1615
August	1st to 10th	Night	26% 36% 10% 19% 8% 1	1600
	11th to 20th	Night	21% 35% 12% 19% 13% 1	1598
	21st to end	Night	26% 36% 10% 18% 8% 2	1782
September	1st to 10th	Night	25% 36% 8% 19% 11% 2	1812
	11th to 20th	Night	27% 36% 11% 22% 5%	1980
	21st to end	Night	33% 35% 9% 17% 6%	1980
October	1st to 10th	Night	35% 35% 7% 15% 8%	2119
	11th to 20th	Night	45% 36% 6% 10% 3	2160
	21st to end	Night	47% 37% 5% 8% 3	2479
November	1st to 10th	Night	36% 40% 6% 14% 4	2439
	11th to 20th	Night	45% 39% 6% 6% 3 1	2660
	21st to end	Night	49% 39% 7% 5%	2660
December	1st to 10th	Night	56% 38% 3 3	2660
	11th to 20th	Night	56% 31% 8% 4 1	3493
	21st to end	Night	68% 23% 7% 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	28% 13% 26% 23% 8% 2	184
	11th to 20th	Day	22% 7% 36% 24% 10% 1	270
	21st to end	Day	30% 5% 25% 28% 11% 1	297
February	1st to 10th	Day	25% 14% 30% 22% 8% 1	270
	11th to 20th	Day	17% 14% 35% 29% 6%	270
	21st to end	Day	23% 16% 36% 21% 4	225
March	1st to 10th	Day	21% 6% 34% 30% 8% 1	370
	11th to 20th	Day	20% 10% 28% 31% 9% 2	460
	21st to end	Day	23% 6% 27% 33% 10% 2	506
April	1st to 10th	Day	23% 6% 28% 30% 10% 3	460
	11th to 20th	Day	27% 5% 28% 23% 13% 5%	452
	21st to end	Day	24% 5% 26% 31% 12% 2	437
May	1st to 10th	Day	23% 3 22% 37% 12% 4	423
	11th to 20th	Day	19% 3 19% 32% 21% 6%	447
	21st to end	Day	13% 3 19% 35% 23% 7%	511
June	1st to 10th	Day	14% 2 19% 40% 21% 4	630
	11th to 20th	Day	15% 2 19% 34% 24% 5%	630
	21st to end	Day	17% 2 15% 38% 23% 5%	630
July	1st to 10th	Day	10% 1 12% 41% 30% 5%	621
	11th to 20th	Day	13% 1 16% 36% 27% 8%	618
	21st to end	Day	12% 2 16% 37% 29% 6%	545
August	1st to 10th	Day	18% 1 13% 31% 30% 7%	446
	11th to 20th	Day	11% 1 10% 33% 35% 10%	439
	21st to end	Day	15% 3 18% 29% 26% 8%	495
September	1st to 10th	Day	15% 3 19% 27% 27% 9%	450
	11th to 20th	Day	12% 4 18% 32% 27% 8%	450
	21st to end	Day	20% 5% 19% 26% 22% 8%	450
October	1st to 10th	Day	26% 6% 21% 23% 18% 6%	450
	11th to 20th	Day	34% 8% 25% 24% 8% 2	450
	21st to end	Day	34% 9% 28% 21% 7% 1	389
November	1st to 10th	Day	25% 10% 32% 23% 9% 1	255
	11th to 20th	Day	31% 11% 35% 16% 7%	180
	21st to end	Day	33% 13% 33% 18% 2	180
December	1st to 10th	Day	31% 14% 30% 20% 4 1	180
	11th to 20th	Day	32% 18% 27% 18% 5%	180
	21st to end	Day	35% 13% 35% 12% 3 1	198
January	1st to 10th	Night	27% 17% 27% 21% 7% 1	950
	11th to 20th	Night	28% 13% 27% 23% 8% 1	950
	21st to end	Night	23% 8% 31% 27% 10% 2	873
February	1st to 10th	Night	22% 15% 33% 23% 6% 1	760
	11th to 20th	Night	22% 10% 31% 28% 8% 1	743
	21st to end	Night	22% 10% 35% 26% 6% 1	628
March	1st to 10th	Night	19% 8% 32% 31% 8% 1	760
	11th to 20th	Night	19% 11% 31% 27% 10% 1	760
	21st to end	Night	19% 6% 28% 31% 13% 2	836
April	1st to 10th	Night	26% 7% 27% 31% 9% 1	732
	11th to 20th	Night	24% 6% 23% 31% 14% 3	563
	21st to end	Night	25% 5% 21% 30% 16% 3	555
May	1st to 10th	Night	18% 2 19% 37% 21% 3	540
	11th to 20th	Night	17% 3 14% 40% 23% 3	440
	21st to end	Night	14% 3 16% 37% 25% 6%	389
June	1st to 10th	Night	17% 4 16% 39% 21% 3	360
	11th to 20th	Night	12% 3 16% 39% 25% 4	360
	21st to end	Night	13% 2 14% 37% 29% 5%	360
July	1st to 10th	Night	8% 2 12% 42% 30% 6%	350
	11th to 20th	Night	9% 3 15% 35% 33% 5%	390
	21st to end	Night	9% 3 13% 39% 32% 4	591
August	1st to 10th	Night	11% 2 13% 36% 31% 7%	537
	11th to 20th	Night	12% 2 12% 29% 34% 10%	534
	21st to end	Night	15% 3 18% 32% 27% 6%	594
September	1st to 10th	Night	14% 4 15% 32% 24% 11%	692
	11th to 20th	Night	17% 3 18% 30% 23% 9%	720
	21st to end	Night	22% 5% 17% 24% 23% 9%	720
October	1st to 10th	Night	27% 5% 20% 25% 20% 3	720
	11th to 20th	Night	33% 8% 22% 25% 10% 2	720
	21st to end	Night	38% 8% 23% 23% 7% 1	792
November	1st to 10th	Night	32% 10% 24% 22% 9% 2	740
	11th to 20th	Night	31% 16% 26% 19% 8% 1	760
	21st to end	Night	39% 12% 26% 17% 5%	760
December	1st to 10th	Night	38% 14% 27% 14% 7%	760
	11th to 20th	Night	31% 18% 32% 14% 5%	918
	21st to end	Night	35% 13% 30% 16% 4	1045

Page generated at 2024-04-22 09:25:44. Version ac07

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