Broad Creek
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Broad Creek clear sky chart from 2005-11-06 to 2024-11-10.

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% 6% 2 6% 4 4 4 4 6% 7% 40%	101307
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	97756
Transparency	Day	42% 4 11% 24% 16% 3	104939
	Night	42% 3 11% 25% 17% 3	102264
Seeing	Day	20% 15% 28% 22% 11% 3	14991
	Night	19% 14% 29% 26% 11% 1	24355

By Month

Percentage Cloud Cover SE (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	15% 7% 2 5% 4 3 4 3 5% 6% 46%	2517
	11th to 20th	Day	14% 11% 3 10% 5% 4 4 2 4 5% 37%	2726
	21st to end	Day	20% 8% 2 7% 4 5% 4 3 5% 5% 36%	3124
February	1st to 10th	Day	15% 9% 2 6% 4 4 4 3 7% 7% 39%	1710
	11th to 20th	Day	16% 8% 2 6% 4 4 4 3 5% 7% 41%	1756
	21st to end	Day	18% 12% 2 7% 4 3 4 2 3 5% 40%	1570
March	1st to 10th	Day	24% 6% 2 5% 4 3 4 3 4 6% 41%	3247
	11th to 20th	Day	10% 6% 2 6% 5% 5% 4 3 6% 7% 47%	3480
	21st to end	Day	21% 8% 2 5% 4 3 3 3 4 5% 43%	3963
April	1st to 10th	Day	15% 7% 2 6% 5% 4 5% 3 6% 7% 40%	2280
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 5% 7% 44%	2254
	21st to end	Day	18% 6% 2 5% 4 4 4 4 6% 7% 41%	2280
May	1st to 10th	Day	29% 6% 2 6% 4 4 4 3 5% 7% 30%	4002
	11th to 20th	Day	25% 7% 3 7% 6% 4 5% 4 5% 7% 28%	4398
	21st to end	Day	12% 4 2 5% 4 4 5% 4 7% 9% 45%	4823
June	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 7% 10% 39%	2660
	11th to 20th	Day	12% 5% 2 6% 6% 5% 5% 5% 7% 8% 39%	2660
	21st to end	Day	10% 5% 2 5% 5% 4 5% 4 8% 10% 43%	2660
July	1st to 10th	Day	6% 5% 2 6% 5% 5% 6% 6% 8% 11% 40%	4440
	11th to 20th	Day	9% 5% 1 6% 5% 5% 6% 5% 8% 11% 38%	4440
	21st to end	Day	10% 7% 3 8% 5% 6% 6% 5% 8% 8% 34%	4547
August	1st to 10th	Day	19% 5% 2 6% 5% 5% 5% 5% 7% 8% 33%	4104
	11th to 20th	Day	11% 5% 2 7% 4 5% 5% 5% 6% 9% 40%	3804
	21st to end	Day	11% 4 2 5% 3 4 4 4 6% 7% 49%	4180
September	1st to 10th	Day	15% 5% 2 6% 4 4 4 3 5% 6% 45%	2280
	11th to 20th	Day	12% 5% 1 5% 4 4 4 3 4 7% 51%	2280
	21st to end	Day	21% 7% 2 7% 4 4 4 3 6% 7% 36%	2028
October	1st to 10th	Day	17% 7% 2 5% 3 3 4 3 4 6% 45%	1900
	11th to 20th	Day	17% 4 2 4 3 4 4 4 4 6% 48%	1900
	21st to end	Day	16% 6% 2 6% 3 3 3 3 5% 5% 48%	2090
November	1st to 10th	Day	12% 5% 2 4 3 4 4 3 4 6% 52%	1757
	11th to 20th	Day	16% 6% 1 4 3 3 4 4 5% 6% 48%	1710
	21st to end	Day	16% 6% 2 5% 4 4 4 3 4 6% 45%	1535
December	1st to 10th	Day	17% 8% 2 5% 4 5% 5% 3 5% 7% 39%	1520
	11th to 20th	Day	19% 8% 3 5% 3 4 3 3 5% 7% 41%	1910
	21st to end	Day	16% 7% 3 7% 5% 5% 5% 4 5% 6% 36%	2772
January	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 4 7% 43%	4429
	11th to 20th	Night	19% 8% 2 6% 3 3 4 3 4 5% 43%	4216
	21st to end	Night	22% 9% 2 6% 4 3 3 3 4 5% 39%	4532
February	1st to 10th	Night	16% 9% 2 6% 5% 4 3 4 4 6% 41%	2470
	11th to 20th	Night	17% 8% 2 6% 3 4 4 4 5% 4 43%	2309
	21st to end	Night	16% 8% 3 6% 4 5% 4 3 4 5% 41%	1884
March	1st to 10th	Night	22% 8% 3 6% 4 2 3 3 4 5% 40%	3590
	11th to 20th	Night	11% 6% 2 5% 4 3 4 3 5% 6% 51%	3480
	21st to end	Night	16% 9% 2 5% 3 4 3 2 3 5% 47%	3668
April	1st to 10th	Night	16% 8% 3 5% 6% 3 4 4 6% 7% 40%	1900
	11th to 20th	Night	16% 5% 2 5% 3 4 3 3 6% 8% 43%	1875
	21st to end	Night	18% 6% 2 5% 4 3 4 2 6% 6% 43%	1900
May	1st to 10th	Night	25% 8% 3 7% 4 3 3 3 5% 8% 31%	2918
	11th to 20th	Night	27% 10% 3 7% 4 4 4 3 5% 6% 28%	2495
	21st to end	Night	14% 5% 2 5% 4 4 4 4 6% 9% 43%	2732
June	1st to 10th	Night	13% 4 2 5% 5% 4 4 3 6% 9% 45%	1520
	11th to 20th	Night	12% 6% 2 7% 5% 5% 4 4 7% 9% 41%	1520
	21st to end	Night	10% 4 2 5% 6% 4 4 5% 6% 10% 43%	1520
July	1st to 10th	Night	7% 5% 3 8% 6% 5% 5% 5% 8% 9% 40%	2520
	11th to 20th	Night	10% 6% 2 7% 5% 5% 6% 5% 7% 10% 38%	2520
	21st to end	Night	13% 8% 3 7% 5% 5% 5% 4 6% 7% 39%	2989
August	1st to 10th	Night	20% 5% 2 6% 5% 4 4 4 6% 9% 35%	2825
	11th to 20th	Night	13% 8% 2 6% 5% 5% 4 3 5% 8% 41%	2991
	21st to end	Night	12% 5% 2 5% 4 4 4 4 5% 7% 48%	3476
September	1st to 10th	Night	15% 6% 2 6% 4 3 4 3 4 6% 47%	1900
	11th to 20th	Night	12% 6% 2 5% 3 3 3 2 4 7% 53%	1900
	21st to end	Night	20% 7% 2 5% 4 4 4 3 4 7% 40%	2145
October	1st to 10th	Night	19% 7% 2 6% 4 4 3 2 4 5% 43%	2280
	11th to 20th	Night	16% 5% 1 5% 3 3 3 3 4 7% 51%	2280
	21st to end	Night	17% 5% 1 5% 3 3 3 2 5% 6% 49%	2508
November	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 5% 6% 54%	2524
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 4 6% 48%	2470
	21st to end	Night	13% 5% 2 5% 4 4 4 3 5% 7% 47%	2641
December	1st to 10th	Night	18% 8% 2 5% 5% 4 4 3 4 6% 39%	2660
	11th to 20th	Night	18% 6% 2 5% 4 4 4 3 5% 6% 42%	3285
	21st to end	Night	16% 8% 2 6% 4 5% 5% 5% 6% 8% 35%	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	40% 3 10% 29% 14% 4	2518
	11th to 20th	Day	52% 2 9% 20% 14% 4	2726
	21st to end	Day	52% 2 10% 24% 11% 2	3124
February	1st to 10th	Day	44% 3 13% 26% 12% 2	1710
	11th to 20th	Day	44% 3 9% 26% 15% 3	1765
	21st to end	Day	48% 3 9% 22% 13% 5%	1570
March	1st to 10th	Day	47% 2 8% 28% 11% 4	3247
	11th to 20th	Day	38% 2 7% 30% 19% 4	3480
	21st to end	Day	47% 2 8% 21% 18% 4	3963
April	1st to 10th	Day	43% 3 11% 20% 17% 5%	2280
	11th to 20th	Day	40% 5% 11% 22% 17% 5%	2254
	21st to end	Day	43% 3 10% 21% 19% 4	2280
May	1st to 10th	Day	55% 2 10% 19% 12% 2	4037
	11th to 20th	Day	57% 3 12% 19% 8% 2	4402
	21st to end	Day	37% 4 13% 27% 17% 2	4837
June	1st to 10th	Day	40% 5% 11% 25% 16% 2	2660
	11th to 20th	Day	41% 6% 13% 26% 13% 3	2660
	21st to end	Day	34% 6% 15% 26% 17% 1	2660
July	1st to 10th	Day	36% 8% 18% 20% 14% 4	4370
	11th to 20th	Day	38% 6% 17% 26% 11% 2	4365
	21st to end	Day	44% 6% 12% 20% 16% 1	4402
August	1st to 10th	Day	46% 7% 13% 25% 9%	4091
	11th to 20th	Day	37% 7% 11% 29% 15% 1	3842
	21st to end	Day	33% 5% 12% 29% 18% 2	4180
September	1st to 10th	Day	40% 5% 10% 21% 20% 4	2280
	11th to 20th	Day	34% 4 8% 28% 22% 4	2280
	21st to end	Day	47% 4 6% 20% 20% 2	2028
October	1st to 10th	Day	37% 3 7% 19% 28% 5%	3160
	11th to 20th	Day	27% 3 10% 25% 26% 9%	3140
	21st to end	Day	25% 2 10% 31% 28% 5%	3428
November	1st to 10th	Day	33% 3 13% 25% 21% 4	1757
	11th to 20th	Day	38% 3 9% 25% 22% 3	1710
	21st to end	Day	40% 3 10% 31% 13% 3	1535
December	1st to 10th	Day	45% 4 15% 23% 12% 1	1520
	11th to 20th	Day	44% 3 10% 31% 11% 2	1906
	21st to end	Day	49% 3 13% 22% 13% 1	2772
January	1st to 10th	Night	44% 2 9% 29% 14% 3	4429
	11th to 20th	Night	45% 2 10% 27% 15% 2	4216
	21st to end	Night	49% 1 6% 30% 12% 2	4532
February	1st to 10th	Night	45% 3 12% 25% 13% 2	2470
	11th to 20th	Night	44% 3 8% 22% 18% 4	2311
	21st to end	Night	46% 3 9% 21% 16% 5%	1884
March	1st to 10th	Night	49% 2 8% 27% 13% 2	3590
	11th to 20th	Night	36% 2 10% 32% 17% 3	3480
	21st to end	Night	43% 2 7% 21% 23% 5%	3668
April	1st to 10th	Night	44% 3 9% 20% 19% 4	1900
	11th to 20th	Night	39% 3 12% 22% 19% 5%	1875
	21st to end	Night	41% 4 9% 23% 19% 5%	1900
May	1st to 10th	Night	53% 3 9% 19% 13% 2	2948
	11th to 20th	Night	59% 3 12% 15% 11% 1	2496
	21st to end	Night	38% 5% 16% 24% 14% 4	2739
June	1st to 10th	Night	38% 5% 11% 26% 18% 2	1520
	11th to 20th	Night	41% 4 14% 24% 16% 1	1520
	21st to end	Night	35% 6% 13% 28% 16% 3	1520
July	1st to 10th	Night	39% 7% 19% 18% 12% 4	2480
	11th to 20th	Night	39% 7% 18% 23% 12% 1	2472
	21st to end	Night	44% 5% 13% 21% 16% 1	2894
August	1st to 10th	Night	46% 5% 18% 21% 9% 1	2814
	11th to 20th	Night	41% 5% 10% 29% 14% 1	3019
	21st to end	Night	35% 4 11% 31% 17% 2	3476
September	1st to 10th	Night	40% 3 11% 21% 21% 5%	1900
	11th to 20th	Night	33% 3 8% 26% 26% 4	1900
	21st to end	Night	45% 3 8% 21% 20% 3	2145
October	1st to 10th	Night	45% 3 9% 20% 21% 2	3800
	11th to 20th	Night	25% 2 10% 27% 29% 6%	3779
	21st to end	Night	25% 2 11% 33% 24% 5%	4120
November	1st to 10th	Night	33% 3 10% 27% 22% 5%	2524
	11th to 20th	Night	39% 3 8% 24% 20% 5%	2470
	21st to end	Night	38% 3 11% 29% 18% 2	2641
December	1st to 10th	Night	46% 3 11% 24% 15% 1	2660
	11th to 20th	Night	42% 3 11% 22% 17% 4	3288
	21st to end	Night	47% 3 14% 23% 12% 1	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	28% 27% 28% 13% 2 1	180
	11th to 20th	Day	32% 30% 24% 14% 1	240
	21st to end	Day	22% 35% 28% 11% 4 1	297
February	1st to 10th	Day	27% 27% 35% 9% 2 1	270
	11th to 20th	Day	33% 25% 36% 5% 1	363
	21st to end	Day	35% 23% 27% 12% 2	382
March	1st to 10th	Day	27% 23% 31% 16% 3	460
	11th to 20th	Day	28% 24% 32% 11% 4 1	460
	21st to end	Day	26% 24% 32% 13% 4 1	506
April	1st to 10th	Day	23% 25% 35% 12% 5% 1	460
	11th to 20th	Day	22% 19% 30% 18% 8% 2	452
	21st to end	Day	26% 18% 35% 14% 5% 2	460
May	1st to 10th	Day	28% 17% 30% 16% 8% 2	463
	11th to 20th	Day	23% 16% 29% 23% 8% 2	487
	21st to end	Day	19% 9% 26% 26% 17% 4	529
June	1st to 10th	Day	15% 12% 31% 24% 14% 3	490
	11th to 20th	Day	15% 11% 27% 30% 13% 4	490
	21st to end	Day	13% 9% 33% 29% 11% 4	490
July	1st to 10th	Day	12% 3 22% 33% 24% 6%	485
	11th to 20th	Day	5% 4 23% 37% 23% 7%	484
	21st to end	Day	13% 6% 27% 32% 19% 4	532
August	1st to 10th	Day	13% 5% 24% 31% 21% 7%	486
	11th to 20th	Day	11% 6% 20% 35% 19% 9%	479
	21st to end	Day	12% 4 27% 30% 18% 9%	539
September	1st to 10th	Day	18% 8% 19% 27% 19% 8%	490
	11th to 20th	Day	16% 5% 25% 28% 18% 8%	490
	21st to end	Day	28% 10% 24% 22% 13% 3	490
October	1st to 10th	Day	24% 9% 23% 23% 14% 6%	490
	11th to 20th	Day	18% 16% 28% 23% 12% 2	490
	21st to end	Day	19% 16% 35% 19% 9% 3	539
November	1st to 10th	Day	16% 16% 33% 22% 10% 3	395
	11th to 20th	Day	20% 22% 32% 18% 8% 1	370
	21st to end	Day	23% 20% 30% 21% 6% 1	195
December	1st to 10th	Day	24% 26% 33% 12% 3 1	180
	11th to 20th	Day	31% 27% 27% 12% 4	180
	21st to end	Day	24% 20% 33% 16% 7%	198
January	1st to 10th	Night	20% 21% 39% 17% 3	760
	11th to 20th	Night	25% 18% 32% 22% 3	760
	21st to end	Night	20% 22% 37% 20% 1	836
February	1st to 10th	Night	22% 21% 34% 21% 3	760
	11th to 20th	Night	24% 26% 35% 14% 1	743
	21st to end	Night	22% 24% 33% 17% 3	628
March	1st to 10th	Night	22% 23% 34% 17% 4	760
	11th to 20th	Night	23% 23% 32% 18% 5%	760
	21st to end	Night	21% 17% 38% 18% 5%	836
April	1st to 10th	Night	22% 23% 33% 18% 4	760
	11th to 20th	Night	20% 15% 35% 25% 6%	751
	21st to end	Night	22% 15% 32% 24% 7%	760
May	1st to 10th	Night	21% 12% 29% 30% 7%	639
	11th to 20th	Night	21% 10% 32% 28% 9%	374
	21st to end	Night	17% 6% 21% 39% 16% 1	411
June	1st to 10th	Night	14% 5% 27% 39% 15% 1	380
	11th to 20th	Night	14% 6% 24% 41% 15% 1	380
	21st to end	Night	10% 3 25% 43% 18%	380
July	1st to 10th	Night	12% 4 19% 39% 24% 3	370
	11th to 20th	Night	8% 3 19% 38% 29% 4	368
	21st to end	Night	10% 3 18% 44% 23% 2	565
August	1st to 10th	Night	12% 3 16% 40% 26% 2	567
	11th to 20th	Night	14% 4 15% 35% 29% 2	680
	21st to end	Night	14% 4 16% 38% 24% 3	836
September	1st to 10th	Night	17% 4 21% 33% 22% 3	760
	11th to 20th	Night	14% 6% 16% 35% 25% 5%	760
	21st to end	Night	23% 4 23% 30% 19% 2	760
October	1st to 10th	Night	21% 8% 23% 24% 19% 4	760
	11th to 20th	Night	19% 11% 26% 30% 12% 1	760
	21st to end	Night	20% 12% 31% 24% 13%	836
November	1st to 10th	Night	14% 12% 34% 28% 11% 1	779
	11th to 20th	Night	20% 18% 30% 25% 7% 1	760
	21st to end	Night	16% 20% 31% 25% 8%	760
December	1st to 10th	Night	24% 18% 33% 17% 7% 1	760
	11th to 20th	Night	20% 18% 38% 20% 5%	760
	21st to end	Night	20% 19% 33% 25% 3	836

Page generated at 2024-11-07 06:55:42. Version ac07

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