Hancock Field Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hancock Field Station 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	7% 7% 2 6% 5% 4 4 4 5% 7% 49%	105348
	Night	8% 9% 3 7% 5% 4 4 4 5% 7% 43%	102353
Transparency	Day	36% 2 10% 23% 18% 10%	105091
	Night	41% 3 12% 23% 15% 6%	102199
Seeing	Day	12% 9% 21% 28% 20% 10%	14558
	Night	12% 4 13% 43% 24% 3	23599

By Month

Percentage Cloud Cover SW (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	12% 14% 6% 14% 11% 7% 6% 4 6% 7% 11%	2539
	11th to 20th	Day	16% 19% 6% 12% 6% 4 5% 4 5% 6% 16%	2540
	21st to end	Day	14% 14% 4 11% 7% 6% 6% 6% 8% 8% 16%	2872
February	1st to 10th	Day	10% 14% 4 9% 6% 6% 5% 4 7% 7% 27%	1710
	11th to 20th	Day	12% 11% 4 8% 6% 5% 5% 4 7% 7% 30%	1698
	21st to end	Day	9% 13% 4 9% 7% 7% 6% 5% 7% 7% 26%	1570
March	1st to 10th	Day	6% 11% 5% 9% 6% 6% 6% 5% 8% 9% 29%	3138
	11th to 20th	Day	6% 9% 2 7% 5% 5% 5% 3 5% 8% 45%	3428
	21st to end	Day	8% 13% 4 10% 8% 7% 6% 5% 7% 8% 24%	4059
April	1st to 10th	Day	10% 12% 4 8% 6% 5% 6% 5% 7% 6% 31%	2280
	11th to 20th	Day	8% 12% 3 8% 6% 5% 5% 4 5% 7% 38%	2249
	21st to end	Day	7% 9% 2 7% 5% 4 5% 4 7% 8% 42%	2369
May	1st to 10th	Day	11% 7% 2 6% 4 4 4 4 6% 7% 44%	4420
	11th to 20th	Day	5% 4 2 4 4 3 4 3 4 6% 63%	4377
	21st to end	Day	9% 8% 2 6% 4 4 5% 4 6% 8% 44%	4813
June	1st to 10th	Day	10% 7% 3 6% 5% 5% 4 4 5% 8% 43%	2660
	11th to 20th	Day	8% 5% 2 5% 4 4 4 4 5% 6% 52%	2660
	21st to end	Day	4 4 1 2 3 3 3 3 4 6% 68%	2660
July	1st to 10th	Day	1 1 1 1 1 2 1 3 4 85%	4420
	11th to 20th	Day	2 1 1 1 2 2 2 2 3 3 82%	4420
	21st to end	Day	2 1 1 2 1 1 2 2 3 4 81%	4790
August	1st to 10th	Day	3 3 1 3 2 2 2 2 3 5% 73%	4344
	11th to 20th	Day	2 2 3 2 2 3 2 3 5% 75%	3964
	21st to end	Day	3 3 1 4 2 2 2 2 4 5% 72%	4180
September	1st to 10th	Day	2 2 1 3 2 2 2 2 3 5% 76%	2280
	11th to 20th	Day	4 4 1 5% 4 4 4 4 4 7% 59%	2280
	21st to end	Day	8% 5% 1 4 3 3 3 3 5% 6% 57%	2051
October	1st to 10th	Day	6% 5% 1 4 3 3 4 3 5% 6% 61%	3180
	11th to 20th	Day	5% 5% 2 7% 5% 5% 5% 4 7% 9% 46%	3161
	21st to end	Day	9% 11% 4 9% 5% 4 4 4 7% 8% 35%	3201
November	1st to 10th	Day	12% 11% 4 7% 5% 6% 6% 5% 6% 9% 30%	1710
	11th to 20th	Day	11% 12% 4 10% 7% 6% 7% 5% 6% 7% 25%	1563
	21st to end	Day	9% 12% 3 9% 7% 5% 5% 4 7% 10% 29%	1520
December	1st to 10th	Day	9% 12% 3 8% 7% 7% 7% 4 7% 7% 29%	1520
	11th to 20th	Day	10% 12% 5% 14% 10% 9% 7% 6% 7% 6% 14%	1928
	21st to end	Day	12% 15% 5% 14% 9% 7% 7% 5% 8% 7% 11%	2794
January	1st to 10th	Night	10% 16% 6% 19% 9% 6% 5% 4 5% 6% 12%	4406
	11th to 20th	Night	19% 17% 6% 10% 6% 5% 5% 4 7% 6% 15%	4420
	21st to end	Night	12% 14% 5% 12% 8% 6% 6% 5% 7% 9% 16%	4771
February	1st to 10th	Night	12% 13% 4 10% 6% 6% 4 4 7% 8% 27%	2470
	11th to 20th	Night	9% 13% 5% 9% 5% 5% 5% 4 5% 7% 32%	2369
	21st to end	Night	9% 16% 5% 8% 6% 5% 6% 5% 6% 7% 27%	1884
March	1st to 10th	Night	5% 10% 4 9% 5% 6% 6% 5% 7% 11% 32%	3736
	11th to 20th	Night	6% 7% 3 6% 5% 4 5% 3 5% 11% 46%	3537
	21st to end	Night	9% 12% 4 10% 6% 7% 7% 6% 7% 8% 24%	3593
April	1st to 10th	Night	9% 11% 4 8% 7% 5% 4 3 6% 7% 36%	1900
	11th to 20th	Night	9% 11% 3 7% 4 5% 5% 4 6% 6% 41%	1879
	21st to end	Night	8% 9% 3 6% 5% 5% 5% 5% 5% 8% 42%	1808
May	1st to 10th	Night	10% 9% 3 7% 4 4 3 3 4 6% 46%	2540
	11th to 20th	Night	6% 3 1 4 2 3 3 3 3 6% 67%	2516
	21st to end	Night	9% 7% 2 5% 3 3 3 3 5% 7% 52%	2762
June	1st to 10th	Night	10% 6% 3 5% 4 4 3 4 5% 8% 48%	1520
	11th to 20th	Night	7% 6% 2 5% 4 2 4 3 6% 6% 55%	1520
	21st to end	Night	5% 3 1 3 2 2 3 3 4 6% 68%	1520
July	1st to 10th	Night	1 1 1 1 1 2 2 3 3 85%	2540
	11th to 20th	Night	1 1 1 2 2 2 2 2 3 3 82%	2540
	21st to end	Night	1 1 1 2 1 2 1 2 3 4 82%	2761
August	1st to 10th	Night	2 2 1 3 2 3 3 3 5% 6% 70%	2584
	11th to 20th	Night	1 1 1 3 2 2 3 3 5% 5% 75%	2876
	21st to end	Night	1 2 1 3 2 2 3 2 4 5% 75%	3498
September	1st to 10th	Night	2 2 1 2 1 1 2 2 4 5% 77%	1900
	11th to 20th	Night	4 4 1 4 4 3 4 3 5% 6% 62%	1900
	21st to end	Night	7% 5% 2 4 2 3 3 3 4 7% 60%	2125
October	1st to 10th	Night	5% 5% 2 4 3 2 2 2 4 6% 65%	3800
	11th to 20th	Night	7% 5% 2 5% 5% 4 4 3 7% 9% 48%	3777
	21st to end	Night	8% 7% 3 8% 5% 6% 5% 4 7% 8% 38%	4358
November	1st to 10th	Night	12% 11% 4 8% 6% 5% 5% 4 5% 9% 32%	2469
	11th to 20th	Night	13% 12% 3 9% 6% 5% 6% 5% 8% 8% 26%	2616
	21st to end	Night	9% 11% 3 7% 6% 5% 5% 5% 7% 10% 31%	2660
December	1st to 10th	Night	11% 14% 3 8% 7% 6% 5% 5% 7% 7% 27%	2660
	11th to 20th	Night	11% 15% 6% 13% 8% 7% 7% 4 7% 8% 15%	3276
	21st to end	Night	10% 14% 5% 14% 10% 7% 7% 5% 5% 7% 16%	4862

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	69% 4 11% 14% 3	2539
	11th to 20th	Day	69% 3 12% 11% 4 1	2540
	21st to end	Day	69% 2 13% 12% 4 1	2872
February	1st to 10th	Day	54% 5% 15% 20% 6%	1710
	11th to 20th	Day	50% 5% 16% 21% 8% 1	1707
	21st to end	Day	53% 4 16% 18% 8% 1	1570
March	1st to 10th	Day	50% 2 9% 24% 15% 1	3138
	11th to 20th	Day	40% 2 13% 34% 11%	3428
	21st to end	Day	57% 2 13% 21% 6%	4059
April	1st to 10th	Day	50% 3 14% 21% 12% 1	2280
	11th to 20th	Day	45% 3 14% 21% 15% 3	2252
	21st to end	Day	38% 3 13% 30% 12% 2	2369
May	1st to 10th	Day	39% 1 7% 32% 20% 1	4420
	11th to 20th	Day	24% 1 9% 32% 29% 5%	4380
	21st to end	Day	38% 2 17% 30% 12% 1	4814
June	1st to 10th	Day	40% 3 10% 29% 16% 3	2660
	11th to 20th	Day	33% 2 9% 31% 21% 4	2660
	21st to end	Day	19% 2 9% 32% 28% 10%	2660
July	1st to 10th	Day	8% 1 4 13% 25% 50%	4351
	11th to 20th	Day	9% 1 4 8% 23% 55%	4345
	21st to end	Day	9% 1 4 17% 36% 32%	4639
August	1st to 10th	Day	16% 2 3 14% 36% 29%	4328
	11th to 20th	Day	13% 2 6% 31% 32% 16%	4003
	21st to end	Day	16% 2 7% 28% 30% 16%	4179
September	1st to 10th	Day	13% 2 5% 28% 34% 18%	2280
	11th to 20th	Day	26% 2 9% 25% 26% 11%	2280
	21st to end	Day	29% 2 11% 28% 22% 7%	2051
October	1st to 10th	Day	25% 2 10% 27% 27% 9%	3180
	11th to 20th	Day	31% 4 21% 26% 16% 2	3161
	21st to end	Day	43% 4 10% 27% 14% 2	3201
November	1st to 10th	Day	48% 4 12% 26% 9% 1	1710
	11th to 20th	Day	55% 5% 16% 18% 6%	1563
	21st to end	Day	49% 5% 16% 21% 8%	1520
December	1st to 10th	Day	50% 7% 14% 21% 7%	1520
	11th to 20th	Day	67% 4 14% 14% 1	1928
	21st to end	Day	72% 2 11% 12% 3	2794
January	1st to 10th	Night	73% 4 11% 10% 3	4406
	11th to 20th	Night	68% 3 12% 11% 4 1	4420
	21st to end	Night	71% 2 11% 12% 3	4771
February	1st to 10th	Night	54% 4 18% 17% 6%	2470
	11th to 20th	Night	50% 5% 15% 23% 7% 1	2371
	21st to end	Night	55% 4 12% 19% 8% 1	1884
March	1st to 10th	Night	46% 3 9% 26% 14% 1	3736
	11th to 20th	Night	37% 3 14% 37% 9%	3537
	21st to end	Night	56% 4 18% 19% 4	3593
April	1st to 10th	Night	46% 4 16% 25% 9%	1900
	11th to 20th	Night	43% 4 17% 24% 11% 2	1879
	21st to end	Night	39% 5% 14% 27% 13% 2	1808
May	1st to 10th	Night	40% 1 8% 31% 19%	2540
	11th to 20th	Night	21% 2 11% 40% 26% 1	2516
	21st to end	Night	32% 2 30% 28% 7% 1	2762
June	1st to 10th	Night	34% 5% 13% 31% 15% 2	1520
	11th to 20th	Night	29% 3 12% 38% 14% 3	1520
	21st to end	Night	19% 2 11% 34% 26% 8%	1520
July	1st to 10th	Night	7% 1 6% 16% 28% 43%	2500
	11th to 20th	Night	10% 2 5% 13% 20% 50%	2492
	21st to end	Night	9% 1 3 20% 38% 29%	2674
August	1st to 10th	Night	15% 2 5% 16% 38% 24%	2576
	11th to 20th	Night	11% 2 9% 41% 27% 10%	2903
	21st to end	Night	12% 2 11% 31% 31% 12%	3498
September	1st to 10th	Night	11% 1 9% 30% 31% 18%	1900
	11th to 20th	Night	23% 3 10% 27% 25% 13%	1900
	21st to end	Night	26% 2 9% 30% 26% 8%	2125
October	1st to 10th	Night	23% 3 9% 29% 32% 4	3800
	11th to 20th	Night	31% 4 21% 24% 17% 2	3777
	21st to end	Night	39% 5% 14% 28% 13% 1	4358
November	1st to 10th	Night	49% 4 11% 25% 10% 1	2469
	11th to 20th	Night	54% 5% 14% 22% 5%	2616
	21st to end	Night	47% 5% 16% 24% 8%	2660
December	1st to 10th	Night	54% 8% 14% 19% 6%	2660
	11th to 20th	Night	68% 4 12% 13% 3	3276
	21st to end	Night	70% 3 10% 13% 5%	4862

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	23% 5% 16% 31% 16% 9%	180
	11th to 20th	Day	17% 4 17% 36% 19% 7%	180
	21st to end	Day	13% 8% 16% 31% 25% 8%	250
February	1st to 10th	Day	19% 9% 15% 30% 20% 7%	370
	11th to 20th	Day	19% 8% 21% 27% 19% 6%	380
	21st to end	Day	18% 10% 21% 29% 18% 4	382
March	1st to 10th	Day	16% 12% 23% 32% 13% 4	460
	11th to 20th	Day	17% 10% 18% 30% 17% 7%	460
	21st to end	Day	20% 13% 21% 28% 17% 1	506
April	1st to 10th	Day	20% 12% 23% 25% 15% 6%	460
	11th to 20th	Day	15% 14% 27% 25% 13% 6%	452
	21st to end	Day	14% 17% 21% 27% 13% 8%	460
May	1st to 10th	Day	15% 10% 26% 26% 15% 7%	463
	11th to 20th	Day	17% 10% 19% 28% 15% 10%	488
	21st to end	Day	14% 10% 18% 28% 19% 12%	529
June	1st to 10th	Day	14% 10% 22% 25% 18% 10%	490
	11th to 20th	Day	15% 17% 21% 25% 15% 6%	490
	21st to end	Day	5% 12% 20% 32% 20% 12%	490
July	1st to 10th	Day	2 7% 27% 31% 24% 9%	486
	11th to 20th	Day	4 10% 27% 22% 26% 11%	484
	21st to end	Day	3 6% 26% 27% 24% 14%	531
August	1st to 10th	Day	4 8% 23% 28% 22% 15%	487
	11th to 20th	Day	4 6% 20% 27% 24% 20%	477
	21st to end	Day	5% 7% 23% 25% 26% 13%	539
September	1st to 10th	Day	3 7% 20% 28% 26% 17%	490
	11th to 20th	Day	7% 7% 18% 33% 26% 10%	490
	21st to end	Day	12% 7% 18% 27% 26% 11%	490
October	1st to 10th	Day	13% 7% 19% 24% 21% 15%	490
	11th to 20th	Day	13% 9% 17% 22% 27% 13%	490
	21st to end	Day	16% 8% 19% 28% 20% 9%	393
November	1st to 10th	Day	17% 8% 16% 36% 17% 6%	282
	11th to 20th	Day	15% 7% 14% 29% 25% 9%	201
	21st to end	Day	13% 3 19% 32% 25% 8%	180
December	1st to 10th	Day	17% 6% 12% 24% 26% 16%	180
	11th to 20th	Day	19% 1 14% 43% 18% 4	180
	21st to end	Day	20% 5% 15% 36% 18% 6%	198
January	1st to 10th	Night	19% 6% 17% 37% 18% 3	760
	11th to 20th	Night	18% 6% 14% 36% 24% 3	760
	21st to end	Night	18% 4 11% 41% 24% 3	836
February	1st to 10th	Night	18% 4 16% 42% 18% 2	760
	11th to 20th	Night	15% 5% 16% 43% 20% 2	744
	21st to end	Night	20% 6% 17% 39% 16% 1	628
March	1st to 10th	Night	14% 7% 14% 46% 17% 1	760
	11th to 20th	Night	12% 5% 13% 47% 20% 3	760
	21st to end	Night	14% 6% 19% 42% 16% 2	836
April	1st to 10th	Night	16% 4 17% 41% 20% 1	760
	11th to 20th	Night	13% 7% 19% 40% 18% 3	751
	21st to end	Night	14% 7% 19% 37% 21% 2	668
May	1st to 10th	Night	11% 3 18% 45% 21% 2	380
	11th to 20th	Night	11% 6% 13% 38% 31% 2	374
	21st to end	Night	10% 2 11% 43% 31% 3	411
June	1st to 10th	Night	13% 3 12% 46% 24% 1	380
	11th to 20th	Night	9% 4 18% 47% 20% 2	380
	21st to end	Night	6% 2 9% 53% 28% 1	380
July	1st to 10th	Night	3 1 11% 49% 35% 1	370
	11th to 20th	Night	1 13% 53% 32% 1	368
	21st to end	Night	1 1 6% 54% 36% 2	416
August	1st to 10th	Night	2 5% 49% 41% 2	407
	11th to 20th	Night	3 1 6% 37% 44% 9%	602
	21st to end	Night	2 3 13% 46% 31% 5%	836
September	1st to 10th	Night	3 3 10% 40% 40% 4	760
	11th to 20th	Night	5% 2 9% 41% 35% 9%	760
	21st to end	Night	10% 3 8% 41% 32% 6%	760
October	1st to 10th	Night	10% 3 9% 44% 30% 4	760
	11th to 20th	Night	11% 3 12% 40% 29% 5%	760
	21st to end	Night	13% 3 16% 41% 22% 5%	836
November	1st to 10th	Night	16% 4 12% 47% 20% 1	760
	11th to 20th	Night	18% 6% 13% 42% 18% 3	760
	21st to end	Night	13% 7% 14% 42% 21% 4	760
December	1st to 10th	Night	17% 4 13% 43% 19% 4	760
	11th to 20th	Night	17% 5% 14% 43% 20% 2	760
	21st to end	Night	21% 6% 19% 40% 13% 1	836

Page generated at 2024-11-02 23:11:28. Version ac07

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