Telegraph City
Clear Sky Chart
History

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

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% 3 1 3 2 2 2 2 4 5% 67%	105046
	Night	10% 4 1 3 2 2 3 2 4 5% 64%	102692
Transparency	Day	21% 3 7% 17% 24% 28%	104799
	Night	24% 4 8% 18% 22% 23%	102528
Seeing	Day	8% 5% 20% 35% 24% 7%	15254
	Night	10% 3 14% 41% 27% 5%	24620

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	20% 9% 2 6% 4 3 4 3 5% 7% 36%	2539
	11th to 20th	Day	20% 8% 4 9% 5% 5% 4 3 4 5% 32%	2805
	21st to end	Day	21% 8% 3 8% 5% 4 4 5% 5% 8% 29%	3146
February	1st to 10th	Day	18% 6% 2 4 4 2 4 4 4 5% 47%	1710
	11th to 20th	Day	14% 5% 2 5% 4 3 3 4 5% 8% 47%	1831
	21st to end	Day	17% 5% 2 5% 4 4 3 4 4 6% 47%	1570
March	1st to 10th	Day	13% 9% 3 9% 5% 5% 5% 5% 7% 7% 31%	3200
	11th to 20th	Day	12% 4 1 3 2 2 3 3 5% 7% 58%	3490
	21st to end	Day	13% 7% 2 6% 4 4 5% 4 7% 8% 40%	4000
April	1st to 10th	Day	12% 5% 2 3 3 3 4 4 5% 7% 52%	2280
	11th to 20th	Day	10% 4 1 4 2 2 3 3 5% 6% 59%	2249
	21st to end	Day	7% 3 1 2 2 2 3 3 3 6% 66%	2280
May	1st to 10th	Day	6% 3 1 2 2 2 2 2 3 5% 75%	3816
	11th to 20th	Day	2 2 2 1 1 1 2 2 4 82%	4328
	21st to end	Day	3 1 1 1 1 1 2 2 3 4 80%	4813
June	1st to 10th	Day	3 2 1 3 2 2 3 3 4 6% 72%	2660
	11th to 20th	Day	1 1 1 1 2 2 1 3 5% 84%	2660
	21st to end	Day	2 1 1 1 1 1 1 3 2 86%	2660
July	1st to 10th	Day	1 1 1 1 94%	4420
	11th to 20th	Day	1 1 2 1 1 2 2 2 4 84%	4403
	21st to end	Day	1 1 1 1 1 1 2 2 90%	4455
August	1st to 10th	Day	2 1 1 2 1 2 1 1 3 3 83%	4068
	11th to 20th	Day	1 1 1 1 1 1 2 3 90%	3724
	21st to end	Day	1 1 1 1 1 1 1 2 2 89%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 1 3 90%	2280
	11th to 20th	Day	2 1 1 2 1 2 2 2 3 4 79%	2280
	21st to end	Day	2 1 1 2 1 1 2 2 2 4 82%	2067
October	1st to 10th	Day	2 1 1 2 2 2 2 2 3 5% 78%	3180
	11th to 20th	Day	3 1 1 2 1 2 2 1 3 3 80%	3161
	21st to end	Day	5% 2 1 3 2 3 3 3 5% 6% 68%	3448
November	1st to 10th	Day	7% 4 2 4 4 4 3 3 6% 7% 56%	1739
	11th to 20th	Day	9% 4 2 4 4 2 3 3 5% 6% 57%	1710
	21st to end	Day	11% 4 2 4 3 4 3 3 5% 8% 53%	1652
December	1st to 10th	Day	13% 6% 2 5% 5% 3 4 2 4 7% 48%	1520
	11th to 20th	Day	26% 9% 3 6% 5% 3 4 2 4 6% 32%	1928
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 5% 8% 9% 32%	2794
January	1st to 10th	Night	16% 7% 3 6% 3 3 3 3 5% 7% 44%	4406
	11th to 20th	Night	21% 8% 2 6% 4 4 4 4 5% 6% 35%	4158
	21st to end	Night	23% 8% 2 6% 4 4 4 4 4 7% 34%	4521
February	1st to 10th	Night	17% 5% 1 4 3 3 3 3 4 5% 52%	2470
	11th to 20th	Night	15% 4 1 4 3 3 4 3 5% 8% 51%	2235
	21st to end	Night	18% 5% 1 3 3 3 3 3 4 5% 53%	1884
March	1st to 10th	Night	18% 9% 3 7% 4 4 4 4 5% 5% 36%	3657
	11th to 20th	Night	14% 5% 1 4 3 2 2 2 3 5% 59%	3490
	21st to end	Night	20% 7% 2 5% 4 3 4 3 5% 6% 41%	3653
April	1st to 10th	Night	12% 4 2 3 3 3 3 4 5% 7% 54%	1900
	11th to 20th	Night	9% 4 2 3 3 3 3 3 3 7% 60%	1879
	21st to end	Night	5% 4 1 2 2 2 3 3 4 7% 66%	1900
May	1st to 10th	Night	3 3 1 2 2 2 1 2 3 5% 77%	3162
	11th to 20th	Night	3 1 1 1 1 1 2 3 5% 82%	2562
	21st to end	Night	2 1 2 2 2 2 2 2 4 82%	2762
June	1st to 10th	Night	4 2 1 2 2 1 2 2 3 5% 76%	1520
	11th to 20th	Night	1 1 1 1 2 1 3 4 86%	1520
	21st to end	Night	1 1 1 2 1 1 1 1 2 3 86%	1520
July	1st to 10th	Night	1 1 1 1 1 1 95%	2540
	11th to 20th	Night	2 2 1 2 2 1 2 2 2 3 82%	2540
	21st to end	Night	1 1 1 1 1 1 1 3 3 86%	3109
August	1st to 10th	Night	2 1 1 2 1 1 2 2 3 4 81%	2870
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 89%	3126
	21st to end	Night	3 1 1 1 1 1 1 1 1 90%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 1 2 90%	1900
	11th to 20th	Night	2 2 1 2 1 2 1 1 3 4 82%	1900
	21st to end	Night	2 1 1 1 1 1 1 1 2 3 85%	2107
October	1st to 10th	Night	3 1 1 2 1 2 2 2 3 3 80%	3800
	11th to 20th	Night	3 1 1 2 1 2 2 1 3 4 81%	3777
	21st to end	Night	6% 2 1 3 2 2 3 2 4 5% 70%	4121
November	1st to 10th	Night	10% 4 1 4 3 1 2 3 4 7% 62%	2410
	11th to 20th	Night	9% 4 1 3 3 2 3 3 6% 7% 59%	2470
	21st to end	Night	11% 4 2 3 3 3 3 3 4 6% 59%	2527
December	1st to 10th	Night	15% 4 2 5% 3 4 3 3 5% 6% 51%	2660
	11th to 20th	Night	25% 8% 3 5% 4 3 3 3 5% 6% 36%	3276
	21st to end	Night	17% 7% 3 8% 5% 5% 4 4 6% 7% 34%	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	51% 5% 14% 22% 7% 1	2539
	11th to 20th	Day	54% 8% 9% 14% 11% 5%	2805
	21st to end	Day	53% 7% 12% 17% 10% 2	3146
February	1st to 10th	Day	39% 6% 11% 23% 15% 6%	1710
	11th to 20th	Day	35% 5% 11% 22% 21% 6%	1841
	21st to end	Day	37% 5% 11% 24% 20% 4	1570
March	1st to 10th	Day	45% 10% 12% 18% 14% 2	3200
	11th to 20th	Day	25% 5% 11% 30% 17% 11%	3490
	21st to end	Day	38% 7% 15% 25% 13% 2	4000
April	1st to 10th	Day	30% 6% 11% 26% 17% 8%	2280
	11th to 20th	Day	25% 4 13% 28% 22% 8%	2252
	21st to end	Day	20% 3 11% 29% 30% 7%	2280
May	1st to 10th	Day	14% 2 7% 28% 29% 19%	3816
	11th to 20th	Day	9% 2 4 25% 42% 18%	4331
	21st to end	Day	9% 2 8% 26% 40% 14%	4814
June	1st to 10th	Day	15% 3 9% 24% 31% 18%	2660
	11th to 20th	Day	6% 1 6% 20% 34% 33%	2660
	21st to end	Day	8% 1 2 9% 31% 49%	2660
July	1st to 10th	Day	2 1 1 4 13% 80%	4351
	11th to 20th	Day	7% 2 2 5% 14% 70%	4328
	21st to end	Day	5% 1 1 3 21% 69%	4315
August	1st to 10th	Day	9% 1 2 5% 19% 65%	4053
	11th to 20th	Day	4 1 1 5% 27% 62%	3760
	21st to end	Day	6% 1 3 6% 32% 53%	4179
September	1st to 10th	Day	5% 1 2 6% 26% 60%	2280
	11th to 20th	Day	10% 2 4 18% 39% 26%	2280
	21st to end	Day	9% 1 4 17% 38% 32%	2067
October	1st to 10th	Day	10% 2 4 11% 22% 51%	3180
	11th to 20th	Day	11% 2 5% 23% 37% 22%	3161
	21st to end	Day	18% 3 5% 20% 40% 15%	3448
November	1st to 10th	Day	27% 3 9% 26% 24% 11%	1739
	11th to 20th	Day	28% 5% 12% 26% 24% 4	1710
	21st to end	Day	30% 5% 11% 24% 23% 7%	1652
December	1st to 10th	Day	38% 6% 12% 20% 17% 7%	1520
	11th to 20th	Day	55% 5% 10% 15% 11% 3	1928
	21st to end	Day	47% 10% 19% 14% 8% 2	2794
January	1st to 10th	Night	40% 8% 17% 24% 9% 2	4406
	11th to 20th	Night	49% 6% 13% 16% 9% 7%	4158
	21st to end	Night	49% 5% 12% 18% 12% 4	4521
February	1st to 10th	Night	35% 3 10% 24% 19% 8%	2470
	11th to 20th	Night	31% 5% 10% 24% 24% 7%	2236
	21st to end	Night	34% 4 10% 28% 19% 5%	1884
March	1st to 10th	Night	45% 9% 12% 15% 16% 4	3657
	11th to 20th	Night	29% 4 10% 26% 19% 12%	3490
	21st to end	Night	41% 6% 12% 25% 11% 4	3653
April	1st to 10th	Night	29% 6% 14% 24% 21% 7%	1900
	11th to 20th	Night	25% 4 13% 28% 20% 10%	1879
	21st to end	Night	19% 4 13% 28% 29% 7%	1900
May	1st to 10th	Night	11% 3 12% 26% 31% 17%	3162
	11th to 20th	Night	8% 2 5% 25% 41% 20%	2562
	21st to end	Night	8% 2 8% 31% 39% 11%	2762
June	1st to 10th	Night	13% 3 11% 23% 33% 16%	1520
	11th to 20th	Night	4 2 6% 19% 36% 33%	1520
	21st to end	Night	7% 1 2 12% 29% 49%	1520
July	1st to 10th	Night	2 1 5% 11% 80%	2500
	11th to 20th	Night	9% 2 2 4 13% 69%	2492
	21st to end	Night	6% 1 2 3 22% 65%	3011
August	1st to 10th	Night	9% 1 2 7% 19% 63%	2861
	11th to 20th	Night	4 1 1 5% 28% 59%	3156
	21st to end	Night	6% 1 1 8% 30% 54%	3498
September	1st to 10th	Night	5% 3 5% 27% 59%	1900
	11th to 20th	Night	9% 1 4 19% 39% 28%	1900
	21st to end	Night	8% 1 3 16% 38% 34%	2107
October	1st to 10th	Night	11% 2 4 11% 18% 55%	3800
	11th to 20th	Night	10% 2 5% 25% 34% 24%	3777
	21st to end	Night	17% 2 5% 18% 36% 22%	4121
November	1st to 10th	Night	23% 3 9% 24% 24% 17%	2410
	11th to 20th	Night	24% 4 10% 25% 27% 9%	2470
	21st to end	Night	27% 4 9% 23% 29% 8%	2527
December	1st to 10th	Night	34% 5% 10% 22% 19% 10%	2660
	11th to 20th	Night	48% 6% 10% 18% 14% 4	3276
	21st to end	Night	48% 9% 15% 18% 8% 4	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	32% 9% 18% 23% 13% 5%	180
	11th to 20th	Day	18% 6% 20% 28% 20% 8%	341
	21st to end	Day	19% 4 18% 29% 23% 8%	407
February	1st to 10th	Day	21% 8% 16% 25% 21% 9%	370
	11th to 20th	Day	17% 8% 27% 25% 17% 6%	446
	21st to end	Day	16% 7% 23% 34% 18% 3	382
March	1st to 10th	Day	19% 8% 23% 33% 13% 3	460
	11th to 20th	Day	21% 8% 22% 26% 17% 6%	460
	21st to end	Day	17% 9% 24% 30% 17% 2	506
April	1st to 10th	Day	15% 9% 31% 23% 16% 6%	460
	11th to 20th	Day	12% 10% 28% 28% 15% 6%	452
	21st to end	Day	6% 10% 27% 31% 19% 8%	460
May	1st to 10th	Day	6% 12% 27% 34% 16% 5%	463
	11th to 20th	Day	6% 9% 26% 32% 23% 4	488
	21st to end	Day	5% 7% 21% 36% 26% 5%	529
June	1st to 10th	Day	4 8% 22% 38% 23% 5%	490
	11th to 20th	Day	1 7% 29% 40% 21% 3	490
	21st to end	Day	2 2 22% 43% 26% 5%	490
July	1st to 10th	Day	1 16% 46% 33% 5%	486
	11th to 20th	Day	1 1 12% 46% 36% 5%	484
	21st to end	Day	1 1 10% 47% 34% 7%	531
August	1st to 10th	Day	3 1 14% 45% 29% 7%	487
	11th to 20th	Day	2 1 21% 43% 26% 7%	477
	21st to end	Day	1 1 18% 43% 32% 6%	539
September	1st to 10th	Day	2 1 14% 48% 27% 8%	490
	11th to 20th	Day	3 3 26% 37% 25% 7%	490
	21st to end	Day	3 4 15% 40% 29% 8%	490
October	1st to 10th	Day	3 7% 19% 32% 28% 11%	490
	11th to 20th	Day	6% 6% 17% 28% 32% 13%	490
	21st to end	Day	7% 4 17% 34% 27% 10%	539
November	1st to 10th	Day	9% 6% 13% 28% 30% 14%	317
	11th to 20th	Day	7% 6% 13% 37% 26% 11%	270
	21st to end	Day	10% 2 17% 32% 33% 7%	242
December	1st to 10th	Day	17% 3 18% 32% 21% 9%	180
	11th to 20th	Day	16% 7% 19% 28% 22% 8%	180
	21st to end	Day	19% 8% 22% 28% 17% 6%	198
January	1st to 10th	Night	21% 5% 14% 30% 24% 7%	760
	11th to 20th	Night	16% 3 11% 38% 24% 9%	760
	21st to end	Night	20% 4 9% 33% 27% 6%	836
February	1st to 10th	Night	18% 3 14% 36% 24% 5%	760
	11th to 20th	Night	17% 5% 15% 33% 24% 6%	744
	21st to end	Night	20% 4 14% 43% 16% 4	628
March	1st to 10th	Night	21% 4 16% 35% 20% 3	760
	11th to 20th	Night	18% 4 15% 34% 23% 6%	760
	21st to end	Night	18% 4 18% 39% 20% 2	836
April	1st to 10th	Night	14% 3 22% 36% 23% 2	760
	11th to 20th	Night	9% 6% 20% 40% 21% 5%	751
	21st to end	Night	7% 3 19% 44% 23% 5%	760
May	1st to 10th	Night	6% 3 22% 44% 21% 4	755
	11th to 20th	Night	4 3 19% 46% 25% 2	407
	21st to end	Night	3 2 20% 46% 27% 1	411
June	1st to 10th	Night	4 2 23% 44% 25% 2	380
	11th to 20th	Night	2 19% 52% 25% 2	380
	21st to end	Night	2 2 15% 52% 28% 2	380
July	1st to 10th	Night	9% 58% 31% 1	370
	11th to 20th	Night	2 1 12% 59% 26% 1	368
	21st to end	Night	1 1 10% 46% 37% 5%	624
August	1st to 10th	Night	2 11% 46% 36% 3	576
	11th to 20th	Night	1 15% 49% 30% 4	752
	21st to end	Night	2 11% 49% 34% 3	836
September	1st to 10th	Night	1 1 10% 49% 35% 5%	760
	11th to 20th	Night	3 2 14% 44% 32% 5%	760
	21st to end	Night	2 1 12% 39% 37% 8%	760
October	1st to 10th	Night	5% 2 11% 42% 32% 7%	760
	11th to 20th	Night	5% 3 12% 37% 35% 8%	760
	21st to end	Night	5% 2 12% 39% 29% 12%	836
November	1st to 10th	Night	11% 2 10% 38% 29% 10%	754
	11th to 20th	Night	11% 3 11% 41% 29% 7%	760
	21st to end	Night	13% 2 12% 38% 29% 6%	760
December	1st to 10th	Night	17% 3 11% 40% 22% 7%	760
	11th to 20th	Night	23% 2 12% 36% 23% 4	760
	21st to end	Night	21% 4 14% 36% 20% 4	836

Page generated at 2024-11-01 19:47:39. Version ac07

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