Shot Rock
Clear Sky Chart
History

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

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	5% 8% 2 4 2 2 3 2 4 5% 63%	105257
	Night	6% 8% 2 4 3 3 3 3 4 5% 59%	102947
Transparency	Day	25% 3 7% 19% 26% 20%	105005
	Night	27% 4 6% 18% 26% 19%	102788
Seeing	Day	16% 17% 33% 22% 10% 3	15201
	Night	13% 9% 23% 33% 19% 4	24574

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	7% 18% 4 7% 3 3 3 2 4 5% 43%	2539
	11th to 20th	Day	10% 16% 3 8% 5% 4 4 3 5% 7% 37%	2679
	21st to end	Day	11% 16% 4 7% 3 4 4 4 5% 7% 36%	3146
February	1st to 10th	Day	11% 12% 4 7% 3 3 3 3 4 5% 46%	1710
	11th to 20th	Day	7% 14% 5% 6% 3 4 4 3 4 6% 45%	1850
	21st to end	Day	9% 16% 5% 8% 3 3 3 3 3 5% 42%	1570
March	1st to 10th	Day	7% 20% 9% 12% 4 4 3 3 5% 6% 28%	3138
	11th to 20th	Day	6% 13% 3 4 3 2 3 2 4 5% 55%	3480
	21st to end	Day	7% 23% 7% 7% 4 3 3 2 4 6% 34%	4041
April	1st to 10th	Day	9% 14% 3 5% 3 3 3 3 5% 6% 45%	2280
	11th to 20th	Day	8% 14% 3 5% 3 3 3 3 4 6% 49%	2249
	21st to end	Day	9% 10% 1 4 2 2 3 3 6% 7% 54%	2280
May	1st to 10th	Day	6% 7% 2 3 2 2 2 2 3 5% 67%	3919
	11th to 20th	Day	4 5% 1 3 2 2 2 2 3 5% 71%	4302
	21st to end	Day	6% 5% 1 3 2 2 3 2 4 4 66%	4813
June	1st to 10th	Day	6% 5% 2 4 3 3 3 3 5% 6% 60%	2660
	11th to 20th	Day	3 3 1 2 2 2 2 2 4 5% 75%	2660
	21st to end	Day	3 2 1 2 1 2 2 2 3 3 78%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 1 2 91%	4420
	11th to 20th	Day	2 2 3 2 2 2 2 4 5% 76%	4420
	21st to end	Day	1 2 1 2 1 1 1 2 3 3 84%	4590
August	1st to 10th	Day	2 2 1 2 2 2 2 2 3 4 78%	4042
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 86%	3724
	21st to end	Day	2 1 2 1 1 1 1 2 2 86%	4180
September	1st to 10th	Day	1 1 2 2 2 1 1 3 3 84%	2280
	11th to 20th	Day	4 2 1 3 2 2 3 2 5% 5% 71%	2261
	21st to end	Day	5% 3 1 3 1 2 2 2 2 4 75%	2090
October	1st to 10th	Day	4 4 1 3 2 2 2 3 4 5% 70%	3194
	11th to 20th	Day	6% 2 1 2 2 2 2 2 3 3 76%	3161
	21st to end	Day	4 6% 1 4 3 3 3 3 4 6% 64%	3419
November	1st to 10th	Day	8% 9% 3 3 3 4 3 3 5% 6% 53%	1764
	11th to 20th	Day	7% 7% 2 4 3 3 4 3 5% 7% 55%	1800
	21st to end	Day	7% 10% 3 5% 3 2 3 4 6% 6% 52%	1694
December	1st to 10th	Day	11% 8% 2 5% 3 4 4 4 4 6% 49%	1520
	11th to 20th	Day	15% 14% 5% 8% 5% 5% 4 3 5% 5% 33%	1928
	21st to end	Day	8% 10% 4 6% 4 4 4 4 6% 9% 41%	2794
January	1st to 10th	Night	6% 11% 4 6% 4 4 3 4 5% 6% 45%	4406
	11th to 20th	Night	12% 14% 4 7% 5% 5% 5% 4 5% 6% 34%	4282
	21st to end	Night	8% 19% 4 7% 5% 5% 4 3 5% 7% 34%	4521
February	1st to 10th	Night	9% 11% 4 6% 3 3 3 3 4 7% 47%	2469
	11th to 20th	Night	6% 13% 4 6% 3 3 4 3 6% 7% 44%	2218
	21st to end	Night	8% 13% 4 8% 3 3 3 3 4 4 47%	1884
March	1st to 10th	Night	6% 19% 9% 10% 3 3 3 3 5% 5% 34%	3736
	11th to 20th	Night	7% 13% 2 4 2 2 2 2 4 5% 56%	3496
	21st to end	Night	7% 21% 5% 7% 4 4 4 3 5% 7% 32%	3599
April	1st to 10th	Night	8% 11% 3 6% 3 3 4 3 4 7% 47%	1900
	11th to 20th	Night	6% 11% 3 5% 3 2 3 3 4 6% 52%	1879
	21st to end	Night	6% 9% 2 3 2 3 4 4 4 8% 57%	1900
May	1st to 10th	Night	3 4 2 4 2 2 3 3 4 5% 67%	3055
	11th to 20th	Night	2 4 1 2 2 2 2 2 3 6% 73%	2590
	21st to end	Night	4 4 1 2 2 2 2 2 4 6% 71%	2762
June	1st to 10th	Night	6% 5% 1 3 3 3 3 3 3 5% 65%	1520
	11th to 20th	Night	2 2 1 2 1 2 2 3 3 82%	1520
	21st to end	Night	3 2 1 2 2 2 2 1 3 3 80%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 1 92%	2540
	11th to 20th	Night	4 4 1 3 2 2 2 2 2 4 74%	2540
	21st to end	Night	2 2 2 2 2 2 2 3 3 82%	2966
August	1st to 10th	Night	2 3 1 2 2 2 3 3 3 4 75%	2897
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 2 87%	3126
	21st to end	Night	1 1 1 2 2 2 1 1 1 2 87%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 4 87%	1900
	11th to 20th	Night	3 3 1 1 2 2 2 3 5% 78%	1919
	21st to end	Night	3 2 1 3 2 2 2 2 2 5% 76%	2090
October	1st to 10th	Night	3 3 1 2 2 2 2 2 3 3 77%	3782
	11th to 20th	Night	3 2 1 3 2 2 2 2 3 4 77%	3777
	21st to end	Night	5% 5% 1 2 3 3 3 3 4 6% 64%	4147
November	1st to 10th	Night	7% 9% 3 3 2 2 3 3 5% 7% 56%	2535
	11th to 20th	Night	6% 6% 1 3 3 4 4 3 5% 8% 56%	2600
	21st to end	Night	7% 9% 3 5% 3 3 4 2 4 6% 54%	2575
December	1st to 10th	Night	12% 10% 3 4 3 3 3 3 4 6% 49%	2660
	11th to 20th	Night	14% 17% 3 6% 4 4 4 3 5% 7% 33%	3276
	21st to end	Night	8% 11% 5% 8% 5% 4 4 4 6% 7% 38%	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	44% 5% 9% 19% 19% 5%	2539
	11th to 20th	Day	48% 3 8% 17% 15% 8%	2679
	21st to end	Day	48% 5% 7% 19% 14% 6%	3146
February	1st to 10th	Day	40% 3 8% 18% 18% 12%	1710
	11th to 20th	Day	40% 4 7% 19% 23% 8%	1860
	21st to end	Day	46% 3 6% 19% 19% 6%	1570
March	1st to 10th	Day	56% 5% 9% 14% 10% 6%	3138
	11th to 20th	Day	33% 3 10% 29% 21% 4	3480
	21st to end	Day	52% 5% 11% 21% 10% 2	4041
April	1st to 10th	Day	39% 5% 13% 21% 18% 4	2280
	11th to 20th	Day	37% 5% 12% 24% 17% 6%	2252
	21st to end	Day	28% 4 15% 30% 19% 3	2280
May	1st to 10th	Day	21% 3 11% 29% 23% 12%	3919
	11th to 20th	Day	17% 3 8% 34% 31% 8%	4305
	21st to end	Day	21% 5% 10% 40% 21% 3	4814
June	1st to 10th	Day	24% 4 11% 26% 27% 7%	2660
	11th to 20th	Day	13% 3 9% 25% 34% 16%	2660
	21st to end	Day	12% 3 3 16% 35% 31%	2660
July	1st to 10th	Day	4 1 1 7% 18% 70%	4351
	11th to 20th	Day	11% 2 3 11% 20% 53%	4345
	21st to end	Day	8% 1 3 10% 31% 47%	4445
August	1st to 10th	Day	11% 2 3 9% 32% 43%	4027
	11th to 20th	Day	6% 2 2 7% 36% 48%	3760
	21st to end	Day	8% 1 2 12% 43% 34%	4179
September	1st to 10th	Day	9% 1 2 11% 39% 38%	2280
	11th to 20th	Day	16% 3 4 22% 36% 18%	2261
	21st to end	Day	16% 2 3 21% 36% 21%	2090
October	1st to 10th	Day	17% 2 4 11% 38% 28%	3194
	11th to 20th	Day	16% 2 4 20% 43% 16%	3161
	21st to end	Day	21% 3 6% 23% 34% 13%	3419
November	1st to 10th	Day	32% 3 7% 22% 23% 13%	1764
	11th to 20th	Day	29% 5% 9% 19% 26% 12%	1800
	21st to end	Day	31% 4 7% 20% 26% 12%	1694
December	1st to 10th	Day	36% 5% 8% 19% 20% 12%	1520
	11th to 20th	Day	54% 4 5% 14% 15% 9%	1928
	21st to end	Day	38% 5% 11% 21% 17% 8%	2794
January	1st to 10th	Night	38% 5% 11% 25% 17% 5%	4406
	11th to 20th	Night	49% 6% 7% 13% 16% 9%	4282
	21st to end	Night	49% 6% 7% 15% 15% 8%	4521
February	1st to 10th	Night	39% 4 7% 18% 19% 14%	2469
	11th to 20th	Night	37% 4 8% 20% 21% 10%	2219
	21st to end	Night	40% 4 7% 21% 21% 8%	1884
March	1st to 10th	Night	52% 4 8% 14% 16% 6%	3736
	11th to 20th	Night	32% 4 6% 26% 27% 5%	3496
	21st to end	Night	50% 6% 8% 21% 12% 3	3599
April	1st to 10th	Night	36% 5% 12% 22% 19% 6%	1900
	11th to 20th	Night	32% 6% 12% 24% 19% 7%	1879
	21st to end	Night	26% 5% 11% 34% 19% 4	1900
May	1st to 10th	Night	18% 4 11% 30% 26% 10%	3055
	11th to 20th	Night	14% 2 7% 24% 40% 13%	2590
	21st to end	Night	14% 5% 11% 38% 30% 3	2762
June	1st to 10th	Night	21% 5% 10% 25% 30% 10%	1520
	11th to 20th	Night	9% 3 6% 29% 34% 19%	1520
	21st to end	Night	11% 2 3 16% 34% 34%	1520
July	1st to 10th	Night	4 1 2 6% 18% 70%	2500
	11th to 20th	Night	16% 2 3 8% 16% 54%	2492
	21st to end	Night	9% 1 3 10% 27% 50%	2873
August	1st to 10th	Night	13% 2 2 9% 32% 41%	2888
	11th to 20th	Night	6% 2 2 7% 30% 53%	3156
	21st to end	Night	9% 1 1 11% 41% 37%	3498
September	1st to 10th	Night	6% 1 2 10% 39% 41%	1900
	11th to 20th	Night	12% 3 4 23% 38% 21%	1919
	21st to end	Night	13% 3 3 24% 34% 23%	2090
October	1st to 10th	Night	14% 2 3 11% 37% 32%	3782
	11th to 20th	Night	12% 2 3 19% 43% 20%	3777
	21st to end	Night	21% 3 5% 20% 34% 17%	4147
November	1st to 10th	Night	28% 4 7% 22% 23% 17%	2535
	11th to 20th	Night	26% 5% 7% 21% 28% 12%	2600
	21st to end	Night	32% 4 5% 21% 25% 14%	2575
December	1st to 10th	Night	36% 3 7% 17% 22% 14%	2660
	11th to 20th	Night	50% 5% 5% 13% 19% 9%	3276
	21st to end	Night	44% 5% 8% 15% 19% 8%	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	37% 17% 23% 17% 6% 1	180
	11th to 20th	Day	26% 15% 27% 17% 11% 4	267
	21st to end	Day	24% 16% 24% 22% 12% 2	407
February	1st to 10th	Day	29% 18% 24% 18% 8% 3	370
	11th to 20th	Day	25% 21% 30% 17% 7% 1	455
	21st to end	Day	24% 22% 32% 17% 4 1	382
March	1st to 10th	Day	33% 24% 24% 13% 4 2	460
	11th to 20th	Day	30% 20% 23% 16% 10% 2	460
	21st to end	Day	29% 24% 29% 14% 4	506
April	1st to 10th	Day	21% 23% 30% 17% 8% 1	460
	11th to 20th	Day	29% 19% 26% 20% 6% 1	452
	21st to end	Day	17% 18% 28% 22% 10% 4	460
May	1st to 10th	Day	21% 20% 30% 18% 8% 3	463
	11th to 20th	Day	19% 19% 26% 21% 11% 3	488
	21st to end	Day	20% 14% 26% 22% 15% 4	529
June	1st to 10th	Day	12% 17% 34% 20% 12% 5%	490
	11th to 20th	Day	10% 22% 34% 21% 9% 4	490
	21st to end	Day	4 18% 38% 25% 11% 5%	490
July	1st to 10th	Day	3 10% 51% 20% 12% 4	486
	11th to 20th	Day	2 11% 44% 27% 12% 4	484
	21st to end	Day	3 10% 44% 24% 12% 6%	531
August	1st to 10th	Day	3 15% 43% 23% 12% 4	487
	11th to 20th	Day	4 15% 41% 25% 10% 5%	477
	21st to end	Day	5% 9% 46% 24% 12% 2	539
September	1st to 10th	Day	4 14% 43% 24% 13% 1	490
	11th to 20th	Day	10% 17% 37% 26% 8% 2	490
	21st to end	Day	9% 15% 37% 32% 6% 2	490
October	1st to 10th	Day	9% 19% 29% 32% 9% 2	490
	11th to 20th	Day	11% 14% 32% 28% 12% 3	490
	21st to end	Day	14% 18% 30% 25% 11% 3	522
November	1st to 10th	Day	20% 14% 22% 23% 16% 4	300
	11th to 20th	Day	17% 13% 29% 23% 12% 6%	300
	21st to end	Day	20% 14% 29% 21% 14% 3	258
December	1st to 10th	Day	23% 14% 22% 20% 13% 7%	180
	11th to 20th	Day	19% 22% 27% 15% 14% 3	180
	21st to end	Day	27% 13% 26% 20% 12% 2	198
January	1st to 10th	Night	21% 13% 24% 23% 14% 6%	760
	11th to 20th	Night	18% 13% 29% 28% 9% 3	760
	21st to end	Night	19% 14% 25% 25% 14% 3	836
February	1st to 10th	Night	19% 15% 24% 25% 15% 2	760
	11th to 20th	Night	19% 13% 24% 27% 13% 5%	744
	21st to end	Night	22% 11% 26% 29% 10% 2	628
March	1st to 10th	Night	24% 13% 27% 23% 11% 2	760
	11th to 20th	Night	20% 12% 25% 22% 19% 3	760
	21st to end	Night	19% 12% 29% 28% 10% 1	836
April	1st to 10th	Night	16% 10% 26% 34% 12% 2	760
	11th to 20th	Night	14% 13% 27% 30% 13% 3	751
	21st to end	Night	12% 10% 25% 30% 18% 4	760
May	1st to 10th	Night	10% 11% 26% 31% 18% 3	687
	11th to 20th	Night	5% 9% 20% 40% 22% 3	422
	21st to end	Night	10% 4 22% 34% 26% 4	411
June	1st to 10th	Night	8% 4 21% 40% 22% 4	380
	11th to 20th	Night	3 6% 23% 43% 24% 2	380
	21st to end	Night	4 4 18% 44% 28% 2	380
July	1st to 10th	Night	1 13% 47% 36% 3	370
	11th to 20th	Night	2 3 14% 45% 33% 3	368
	21st to end	Night	3 1 11% 35% 42% 8%	533
August	1st to 10th	Night	4 1 14% 47% 30% 4	590
	11th to 20th	Night	2 2 20% 44% 27% 5%	752
	21st to end	Night	3 2 14% 49% 30% 2	836
September	1st to 10th	Night	2 2 17% 46% 29% 4	760
	11th to 20th	Night	5% 3 20% 36% 28% 7%	760
	21st to end	Night	4 6% 23% 36% 24% 7%	760
October	1st to 10th	Night	8% 8% 20% 39% 20% 6%	760
	11th to 20th	Night	9% 9% 21% 36% 21% 5%	760
	21st to end	Night	11% 8% 24% 29% 20% 9%	836
November	1st to 10th	Night	13% 9% 19% 34% 19% 5%	780
	11th to 20th	Night	12% 11% 28% 30% 14% 4	800
	21st to end	Night	16% 13% 25% 27% 15% 3	778
December	1st to 10th	Night	21% 11% 25% 28% 12% 3	760
	11th to 20th	Night	22% 12% 24% 27% 12% 3	760
	21st to end	Night	24% 15% 24% 25% 10% 2	836

Page generated at 2024-11-22 05:02:23. Version ac07

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