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 2024-11-05.

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	15% 11% 4 8% 5% 4 4 3 5% 6% 35%	101529
	Night	15% 13% 5% 11% 6% 5% 4 3 4 5% 28%	97578
Transparency	Day	50% 5% 12% 21% 11% 1	105072
	Night	58% 4 11% 17% 9% 1	102123
Seeing	Day	20% 5% 22% 30% 18% 4	15268
	Night	23% 8% 24% 27% 15% 3	24485

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% 12% 15% 6% 5% 3 3 2 3 9%	2217
	11th to 20th	Day	13% 21% 10% 27% 10% 5% 4 2 2 2 4	2530
	21st to end	Day	20% 22% 9% 14% 6% 6% 5% 3 4 4 8%	3061
February	1st to 10th	Day	13% 19% 7% 16% 9% 4 5% 3 3 5% 15%	1710
	11th to 20th	Day	12% 16% 6% 12% 8% 8% 5% 4 5% 4 20%	1663
	21st to end	Day	13% 17% 6% 11% 5% 5% 5% 4 5% 6% 23%	1542
March	1st to 10th	Day	16% 12% 4 8% 5% 4 4 4 5% 6% 32%	3295
	11th to 20th	Day	11% 16% 6% 12% 5% 5% 4 4 5% 6% 28%	3480
	21st to end	Day	14% 11% 5% 9% 5% 4 5% 3 4 5% 34%	3815
April	1st to 10th	Day	18% 11% 4 7% 5% 4 4 3 5% 5% 33%	2211
	11th to 20th	Day	18% 8% 2 6% 4 4 3 3 5% 6% 40%	2442
	21st to end	Day	18% 9% 4 6% 3 4 3 3 5% 7% 37%	2470
May	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 5% 6% 43%	4108
	11th to 20th	Day	13% 7% 2 5% 4 4 4 3 5% 8% 45%	4256
	21st to end	Day	14% 6% 2 5% 3 4 4 3 4 7% 48%	4891
June	1st to 10th	Day	13% 7% 2 7% 4 4 5% 4 6% 7% 41%	2850
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 4 6% 9% 44%	2850
	21st to end	Day	14% 6% 3 6% 5% 4 4 3 6% 8% 42%	2850
July	1st to 10th	Day	12% 7% 2 7% 4 5% 4 4 5% 8% 41%	4760
	11th to 20th	Day	9% 5% 2 5% 3 3 4 3 5% 8% 53%	4673
	21st to end	Day	9% 4 2 4 3 4 3 4 6% 8% 54%	4565
August	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 6% 10% 45%	4104
	11th to 20th	Day	15% 6% 2 5% 3 3 3 4 5% 8% 45%	4044
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 6% 8% 47%	4532
September	1st to 10th	Day	13% 7% 2 6% 5% 4 3 3 5% 7% 44%	2244
	11th to 20th	Day	12% 6% 2 5% 3 4 4 4 6% 7% 48%	2090
	21st to end	Day	18% 8% 2 6% 4 4 4 3 4 8% 37%	2090
October	1st to 10th	Day	17% 10% 3 8% 4 4 4 3 5% 8% 33%	1942
	11th to 20th	Day	26% 11% 4 8% 5% 3 5% 4 5% 6% 23%	1900
	21st to end	Day	26% 17% 4 10% 4 4 3 4 4 6% 19%	1978
November	1st to 10th	Day	18% 18% 4 9% 5% 4 5% 3 5% 7% 22%	1675
	11th to 20th	Day	18% 18% 5% 13% 6% 5% 4 4 4 5% 17%	1520
	21st to end	Day	23% 22% 6% 12% 7% 4 4 3 4 4 10%	1520
December	1st to 10th	Day	17% 30% 7% 15% 7% 4 3 3 3 3 8%	1520
	11th to 20th	Day	19% 24% 7% 16% 8% 4 3 2 4 3 10%	1700
	21st to end	Day	25% 24% 8% 17% 5% 4 3 3 3 3 4	2431
January	1st to 10th	Night	16% 24% 11% 19% 9% 5% 3 2 2 2 7%	4734
	11th to 20th	Night	14% 18% 10% 24% 10% 6% 4 2 3 3 6%	4440
	21st to end	Night	16% 18% 9% 17% 7% 6% 5% 3 4 4 12%	4595
February	1st to 10th	Night	12% 20% 7% 18% 8% 6% 4 3 4 4 16%	2470
	11th to 20th	Night	13% 18% 6% 14% 7% 5% 4 3 5% 5% 21%	2403
	21st to end	Night	14% 15% 5% 12% 6% 6% 5% 3 5% 5% 23%	1908
March	1st to 10th	Night	13% 10% 4 8% 5% 4 3 3 5% 5% 39%	3543
	11th to 20th	Night	10% 13% 5% 8% 5% 4 5% 4 5% 6% 36%	3479
	21st to end	Night	13% 10% 5% 11% 6% 5% 4 4 6% 5% 32%	3817
April	1st to 10th	Night	20% 12% 3 6% 4 4 4 3 5% 5% 33%	1983
	11th to 20th	Night	18% 8% 3 6% 4 4 3 4 6% 7% 37%	1687
	21st to end	Night	21% 8% 3 8% 5% 5% 4 3 5% 5% 33%	1710
May	1st to 10th	Night	15% 6% 3 8% 4 5% 4 4 5% 6% 39%	2833
	11th to 20th	Night	12% 7% 3 6% 5% 5% 3 4 6% 8% 42%	2637
	21st to end	Night	13% 6% 3 7% 4 4 4 4 5% 7% 43%	2683
June	1st to 10th	Night	13% 7% 3 7% 6% 4 5% 4 6% 7% 39%	1330
	11th to 20th	Night	9% 6% 2 5% 5% 4 5% 4 7% 8% 44%	1330
	21st to end	Night	12% 7% 1 7% 4 5% 5% 5% 6% 8% 41%	1330
July	1st to 10th	Night	10% 7% 2 6% 4 3 4 3 6% 7% 48%	2210
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 5% 8% 49%	2294
	21st to end	Night	8% 6% 2 5% 4 3 4 3 5% 7% 52%	2987
August	1st to 10th	Night	10% 7% 2 6% 4 4 4 4 6% 8% 45%	2825
	11th to 20th	Night	12% 7% 2 6% 4 4 5% 4 6% 8% 42%	2785
	21st to end	Night	9% 6% 2 6% 4 5% 5% 3 6% 7% 47%	3124
September	1st to 10th	Night	13% 4 2 5% 4 4 5% 3 6% 6% 47%	1914
	11th to 20th	Night	12% 5% 2 4 4 4 5% 3 6% 6% 48%	2090
	21st to end	Night	19% 7% 3 6% 4 4 4 3 5% 7% 38%	2090
October	1st to 10th	Night	20% 9% 3 7% 6% 5% 4 3 4 6% 33%	2237
	11th to 20th	Night	24% 12% 4 9% 5% 5% 4 3 4 6% 24%	2280
	21st to end	Night	25% 14% 5% 9% 5% 5% 4 3 5% 5% 19%	2617
November	1st to 10th	Night	21% 15% 4 8% 5% 5% 4 3 4 6% 25%	2503
	11th to 20th	Night	17% 21% 6% 11% 6% 5% 5% 4 4 5% 16%	2660
	21st to end	Night	23% 23% 5% 11% 7% 4 4 3 4 4 11%	2660
December	1st to 10th	Night	21% 27% 8% 15% 6% 4 3 3 2 3 8%	2660
	11th to 20th	Night	19% 22% 8% 15% 7% 5% 3 3 3 4 11%	3494
	21st to end	Night	25% 22% 8% 16% 7% 4 3 2 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	86% 4 7% 3	2218
	11th to 20th	Day	91% 2 3 3 1	2530
	21st to end	Day	81% 4 8% 6% 1	3061
February	1st to 10th	Day	75% 3 9% 12% 2	1710
	11th to 20th	Day	67% 4 11% 12% 5%	1672
	21st to end	Day	64% 4 11% 16% 5%	1542
March	1st to 10th	Day	54% 4 16% 16% 9% 1	3298
	11th to 20th	Day	56% 4 12% 20% 6% 1	3480
	21st to end	Day	48% 6% 14% 19% 11% 2	3815
April	1st to 10th	Day	52% 4 10% 22% 11% 1	2211
	11th to 20th	Day	45% 4 7% 26% 15% 2	2442
	21st to end	Day	46% 4 13% 21% 13% 3	2470
May	1st to 10th	Day	42% 4 11% 22% 20% 2	4120
	11th to 20th	Day	40% 5% 14% 25% 14% 1	4260
	21st to end	Day	39% 4 13% 19% 22% 4	4891
June	1st to 10th	Day	41% 6% 11% 27% 15% 1	2850
	11th to 20th	Day	38% 5% 10% 29% 18% 1	2850
	21st to end	Day	41% 6% 13% 25% 13% 2	2850
July	1st to 10th	Day	42% 7% 13% 22% 14% 1	4686
	11th to 20th	Day	30% 5% 15% 36% 13% 1	4592
	21st to end	Day	29% 6% 12% 32% 20% 1	4420
August	1st to 10th	Day	34% 6% 15% 30% 14% 1	4091
	11th to 20th	Day	38% 4 18% 28% 13%	4083
	21st to end	Day	35% 5% 15% 33% 11% 1	4531
September	1st to 10th	Day	39% 6% 13% 30% 11% 1	2244
	11th to 20th	Day	36% 4 16% 31% 12% 1	2090
	21st to end	Day	46% 5% 15% 25% 9%	2090
October	1st to 10th	Day	41% 4 12% 27% 16%	3228
	11th to 20th	Day	53% 4 12% 22% 9%	3140
	21st to end	Day	60% 4 13% 18% 5%	3241
November	1st to 10th	Day	63% 4 12% 15% 5%	1675
	11th to 20th	Day	69% 5% 11% 9% 5%	1520
	21st to end	Day	78% 4 9% 6% 2	1520
December	1st to 10th	Day	86% 2 5% 4 2	1520
	11th to 20th	Day	83% 2 9% 6%	1700
	21st to end	Day	88% 3 6% 3	2431
January	1st to 10th	Night	87% 2 6% 4	4734
	11th to 20th	Night	88% 2 5% 4 1	4440
	21st to end	Night	80% 3 9% 6% 2	4595
February	1st to 10th	Night	74% 3 9% 11% 3	2470
	11th to 20th	Night	69% 4 8% 14% 5%	2405
	21st to end	Night	63% 3 13% 14% 7%	1908
March	1st to 10th	Night	48% 4 17% 19% 11% 1	3553
	11th to 20th	Night	49% 3 14% 21% 10% 2	3480
	21st to end	Night	54% 5% 10% 19% 10% 1	3817
April	1st to 10th	Night	53% 4 8% 22% 12% 2	1983
	11th to 20th	Night	46% 4 7% 23% 17% 2	1687
	21st to end	Night	53% 4 8% 18% 16% 3	1710
May	1st to 10th	Night	45% 6% 9% 20% 19% 2	2840
	11th to 20th	Night	41% 4 10% 24% 18% 3	2638
	21st to end	Night	41% 4 12% 21% 17% 5%	2684
June	1st to 10th	Night	42% 5% 8% 24% 19% 2	1330
	11th to 20th	Night	35% 5% 12% 26% 20% 1	1330
	21st to end	Night	40% 5% 13% 24% 15% 2	1330
July	1st to 10th	Night	37% 5% 13% 24% 17% 5%	2175
	11th to 20th	Night	33% 4 10% 36% 16% 1	2252
	21st to end	Night	31% 5% 12% 25% 25% 1	2892
August	1st to 10th	Night	36% 5% 14% 30% 15% 1	2814
	11th to 20th	Night	39% 6% 17% 23% 14% 1	2812
	21st to end	Night	35% 5% 14% 32% 13% 1	3124
September	1st to 10th	Night	35% 5% 14% 28% 15% 2	1914
	11th to 20th	Night	36% 4 15% 31% 13% 1	2090
	21st to end	Night	48% 3 14% 24% 10%	2090
October	1st to 10th	Night	40% 5% 10% 29% 15%	3731
	11th to 20th	Night	53% 4 13% 22% 9%	3779
	21st to end	Night	58% 5% 14% 19% 4	4304
November	1st to 10th	Night	62% 4 10% 19% 5%	2503
	11th to 20th	Night	72% 3 11% 9% 4 1	2660
	21st to end	Night	79% 4 10% 6% 1	2660
December	1st to 10th	Night	86% 3 6% 4 1	2660
	11th to 20th	Night	81% 3 9% 6% 1	3493
	21st to end	Night	86% 3 8% 2 1	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% 25% 31% 12% 3	460
May	1st to 10th	Day	22% 3 22% 37% 13% 3	463
	11th to 20th	Day	18% 3 18% 34% 21% 6%	487
	21st to end	Day	13% 3 20% 34% 24% 7%	557
June	1st to 10th	Day	15% 2 18% 39% 22% 4	680
	11th to 20th	Day	14% 2 19% 35% 25% 5%	680
	21st to end	Day	17% 3 16% 38% 22% 4	680
July	1st to 10th	Day	10% 1 12% 42% 29% 5%	671
	11th to 20th	Day	12% 1 15% 37% 27% 8%	668
	21st to end	Day	11% 2 15% 35% 30% 6%	592
August	1st to 10th	Day	17% 1 13% 31% 30% 7%	486
	11th to 20th	Day	11% 2 10% 33% 34% 10%	479
	21st to end	Day	14% 3 17% 29% 28% 8%	539
September	1st to 10th	Day	15% 3 19% 27% 27% 8%	490
	11th to 20th	Day	11% 3 16% 30% 28% 11%	490
	21st to end	Day	19% 4 18% 27% 23% 8%	490
October	1st to 10th	Day	25% 6% 22% 22% 18% 6%	490
	11th to 20th	Day	32% 8% 25% 24% 9% 2	490
	21st to end	Day	32% 10% 28% 22% 7% 1	427
November	1st to 10th	Day	24% 11% 32% 23% 9% 1	267
	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% 4 21% 30% 16% 3	570
May	1st to 10th	Night	18% 2 19% 38% 21% 3	570
	11th to 20th	Night	17% 3 14% 40% 24% 3	464
	21st to end	Night	15% 3 16% 37% 25% 6%	411
June	1st to 10th	Night	17% 4 16% 39% 21% 3	380
	11th to 20th	Night	12% 3 17% 39% 25% 4	380
	21st to end	Night	14% 2 14% 37% 28% 5%	380
July	1st to 10th	Night	8% 2 12% 42% 30% 6%	370
	11th to 20th	Night	9% 3 15% 35% 34% 5%	413
	21st to end	Night	9% 3 12% 38% 33% 5%	624
August	1st to 10th	Night	12% 2 13% 35% 31% 7%	567
	11th to 20th	Night	12% 2 11% 30% 34% 11%	564
	21st to end	Night	14% 3 17% 31% 29% 6%	627
September	1st to 10th	Night	14% 5% 15% 31% 25% 10%	731
	11th to 20th	Night	16% 3 17% 29% 26% 10%	760
	21st to end	Night	22% 5% 17% 23% 24% 8%	760
October	1st to 10th	Night	26% 5% 22% 25% 19% 3	760
	11th to 20th	Night	31% 8% 22% 26% 11% 2	760
	21st to end	Night	36% 8% 24% 23% 7% 1	836
November	1st to 10th	Night	32% 11% 23% 23% 9% 2	760
	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 2024-11-03 02:11:10. Version ac07

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