Robert and Elisabeth Moore Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robert and Elisabeth Moore Observatory clear sky chart from 2005-11-06 to 2025-01-07.

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% 3 6% 4 4 4 3 5% 6% 50%	109015
	Night	9% 8% 3 7% 5% 4 4 4 5% 6% 43%	108686
Transparency	Day	36% 3 10% 23% 19% 10%	108761
	Night	41% 3 11% 22% 15% 7%	108529
Seeing	Day	10% 8% 20% 26% 24% 13%	14523
	Night	12% 6% 19% 36% 23% 3	23689

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	14% 20% 6% 13% 6% 6% 4 4 5% 6% 15%	2587
	11th to 20th	Day	21% 18% 7% 9% 5% 4 4 4 5% 6% 18%	2540
	21st to end	Day	22% 19% 9% 14% 6% 5% 4 3 3 3 11%	2794
February	1st to 10th	Day	14% 13% 6% 12% 8% 5% 5% 4 4 5% 24%	1648
	11th to 20th	Day	11% 12% 4 9% 5% 6% 5% 5% 4 7% 32%	1732
	21st to end	Day	9% 9% 3 9% 7% 6% 6% 5% 7% 8% 31%	1570
March	1st to 10th	Day	7% 8% 3 6% 5% 5% 5% 5% 8% 10% 38%	3138
	11th to 20th	Day	5% 6% 2 6% 4 4 3 3 5% 6% 55%	3299
	21st to end	Day	9% 8% 3 9% 6% 7% 7% 6% 7% 8% 31%	4151
April	1st to 10th	Day	8% 8% 3 7% 5% 6% 5% 5% 7% 8% 39%	2280
	11th to 20th	Day	6% 7% 2 6% 4 5% 5% 4 6% 8% 46%	2249
	21st to end	Day	6% 6% 2 6% 4 5% 4 4 6% 9% 48%	2432
May	1st to 10th	Day	8% 5% 1 4 3 4 4 3 6% 8% 53%	4415
	11th to 20th	Day	4 3 1 4 3 3 4 3 5% 6% 63%	4377
	21st to end	Day	5% 6% 2 6% 5% 5% 6% 5% 6% 8% 46%	4813
June	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 3 5% 8% 48%	2660
	11th to 20th	Day	6% 4 2 4 4 4 5% 4 5% 7% 55%	2660
	21st to end	Day	3 3 1 3 3 3 3 3 4 6% 68%	2660
July	1st to 10th	Day	1 1 2 2 1 2 2 3 3 83%	4420
	11th to 20th	Day	1 1 1 2 2 1 2 2 3 3 83%	4420
	21st to end	Day	1 1 1 1 2 2 2 2 3 4 81%	4790
August	1st to 10th	Day	3 2 1 3 2 2 2 2 4 5% 74%	4400
	11th to 20th	Day	1 1 1 2 2 2 2 3 4 6% 75%	4063
	21st to end	Day	3 3 1 4 3 2 3 2 4 5% 70%	4180
September	1st to 10th	Day	2 1 2 2 2 3 2 5% 6% 74%	2280
	11th to 20th	Day	4 4 1 4 4 4 4 4 6% 7% 59%	2234
	21st to end	Day	7% 4 1 5% 4 4 3 3 5% 7% 58%	2090
October	1st to 10th	Day	5% 3 1 4 3 3 3 3 4 7% 64%	3221
	11th to 20th	Day	5% 4 2 5% 4 4 6% 5% 7% 11% 47%	3130
	21st to end	Day	10% 7% 2 8% 5% 6% 5% 4 6% 7% 40%	3101
November	1st to 10th	Day	13% 9% 3 9% 6% 5% 5% 5% 6% 7% 33%	1764
	11th to 20th	Day	12% 16% 4 10% 7% 6% 6% 4 6% 6% 25%	1665
	21st to end	Day	11% 14% 6% 14% 8% 7% 5% 5% 5% 6% 20%	1600
December	1st to 10th	Day	8% 11% 7% 14% 10% 9% 6% 4 5% 5% 20%	2620
	11th to 20th	Day	17% 21% 8% 14% 7% 6% 4 3 4 4 14%	3028
	21st to end	Day	15% 16% 7% 17% 8% 6% 5% 3 3 4 16%	4004
January	1st to 10th	Night	17% 19% 5% 11% 7% 5% 5% 4 5% 6% 16%	4490
	11th to 20th	Night	18% 16% 5% 9% 5% 4 4 4 7% 7% 20%	4420
	21st to end	Night	17% 17% 8% 14% 6% 5% 4 4 5% 5% 14%	4862
February	1st to 10th	Night	13% 13% 4 8% 5% 5% 6% 5% 5% 7% 30%	2528
	11th to 20th	Night	9% 12% 3 8% 6% 5% 5% 4 6% 7% 35%	2334
	21st to end	Night	9% 10% 4 7% 7% 5% 6% 4 6% 6% 35%	1884
March	1st to 10th	Night	8% 7% 2 6% 4 5% 6% 5% 8% 10% 39%	3736
	11th to 20th	Night	6% 6% 2 5% 4 3 3 4 5% 6% 55%	3677
	21st to end	Night	7% 8% 3 8% 7% 6% 7% 6% 9% 9% 30%	3502
April	1st to 10th	Night	11% 10% 3 7% 5% 4 5% 4 5% 8% 38%	1900
	11th to 20th	Night	9% 6% 3 6% 5% 5% 4 4 5% 6% 48%	1879
	21st to end	Night	6% 5% 2 7% 6% 5% 5% 4 7% 7% 44%	1746
May	1st to 10th	Night	7% 6% 2 5% 4 4 5% 4 6% 7% 51%	2543
	11th to 20th	Night	6% 4 1 3 3 3 4 3 5% 7% 61%	2516
	21st to end	Night	6% 4 2 6% 4 5% 5% 4 7% 9% 49%	2762
June	1st to 10th	Night	8% 5% 1 5% 4 4 6% 4 7% 9% 48%	1520
	11th to 20th	Night	7% 6% 3 5% 5% 4 3 3 5% 6% 54%	1520
	21st to end	Night	3 3 1 4 4 3 4 4 4 5% 64%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 2 3 4 82%	2540
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 5% 82%	2540
	21st to end	Night	1 1 1 2 1 1 2 2 3 4 82%	2761
August	1st to 10th	Night	4 3 1 3 2 2 2 2 4 5% 71%	2529
	11th to 20th	Night	1 2 1 2 2 3 3 2 4 5% 75%	2770
	21st to end	Night	2 2 1 3 3 3 4 3 4 6% 72%	3498
September	1st to 10th	Night	3 2 1 2 2 2 3 3 3 5% 75%	1900
	11th to 20th	Night	4 3 1 4 4 3 4 3 6% 7% 61%	1945
	21st to end	Night	6% 3 1 4 3 3 5% 2 5% 9% 59%	2090
October	1st to 10th	Night	5% 3 1 3 3 3 3 3 4 5% 67%	3755
	11th to 20th	Night	7% 3 1 5% 3 4 4 4 6% 8% 53%	3807
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 4 7% 8% 45%	4457
November	1st to 10th	Night	14% 8% 3 8% 5% 5% 4 3 5% 6% 37%	2535
	11th to 20th	Night	14% 11% 3 9% 6% 5% 5% 5% 5% 6% 30%	2732
	21st to end	Night	12% 11% 4 8% 6% 7% 6% 4 6% 8% 29%	2800
December	1st to 10th	Night	7% 11% 7% 9% 7% 7% 6% 5% 6% 8% 27%	4560
	11th to 20th	Night	18% 19% 7% 13% 7% 6% 6% 4 5% 5% 11%	5176
	21st to end	Night	15% 17% 5% 11% 7% 7% 5% 4 4 6% 20%	6952

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	72% 4 9% 11% 4	2587
	11th to 20th	Day	69% 3 16% 10% 2	2540
	21st to end	Day	81% 2 9% 6% 2	2794
February	1st to 10th	Day	61% 5% 18% 12% 4	1648
	11th to 20th	Day	53% 5% 15% 20% 7%	1741
	21st to end	Day	49% 6% 14% 20% 10% 1	1570
March	1st to 10th	Day	41% 3 10% 28% 18% 1	3138
	11th to 20th	Day	31% 2 15% 38% 13% 1	3299
	21st to end	Day	49% 3 16% 21% 10% 1	4151
April	1st to 10th	Day	41% 4 13% 25% 15% 2	2280
	11th to 20th	Day	34% 3 13% 27% 16% 6%	2252
	21st to end	Day	33% 3 12% 29% 19% 3	2432
May	1st to 10th	Day	31% 2 5% 31% 25% 6%	4415
	11th to 20th	Day	22% 3 6% 30% 29% 10%	4380
	21st to end	Day	35% 2 15% 30% 15% 3	4814
June	1st to 10th	Day	35% 3 8% 28% 21% 5%	2660
	11th to 20th	Day	28% 2 9% 31% 25% 5%	2660
	21st to end	Day	19% 2 6% 31% 29% 13%	2660
July	1st to 10th	Day	9% 1 3 13% 27% 47%	4351
	11th to 20th	Day	9% 1 3 8% 25% 53%	4345
	21st to end	Day	9% 2 3 16% 36% 33%	4639
August	1st to 10th	Day	15% 2 3 14% 37% 29%	4384
	11th to 20th	Day	11% 2 4 35% 35% 13%	4105
	21st to end	Day	19% 2 6% 28% 33% 12%	4179
September	1st to 10th	Day	12% 2 8% 29% 33% 16%	2280
	11th to 20th	Day	25% 3 10% 26% 27% 8%	2234
	21st to end	Day	27% 3 13% 35% 17% 4	2090
October	1st to 10th	Day	22% 2 11% 38% 24% 3	3221
	11th to 20th	Day	29% 5% 23% 29% 13% 1	3130
	21st to end	Day	41% 5% 14% 27% 11% 1	3101
November	1st to 10th	Day	50% 5% 15% 21% 7% 1	1764
	11th to 20th	Day	59% 5% 15% 16% 5% 1	1665
	21st to end	Day	65% 4 15% 11% 4	1600
December	1st to 10th	Day	65% 6% 13% 13% 2	2620
	11th to 20th	Day	76% 4 10% 9% 2	3028
	21st to end	Day	73% 3 9% 12% 2	4004
January	1st to 10th	Night	70% 3 12% 11% 3	4490
	11th to 20th	Night	63% 3 16% 15% 2	4420
	21st to end	Night	72% 4 14% 9% 1	4862
February	1st to 10th	Night	54% 5% 20% 17% 4 1	2528
	11th to 20th	Night	48% 5% 15% 24% 8%	2336
	21st to end	Night	49% 4 14% 22% 9% 2	1884
March	1st to 10th	Night	40% 3 9% 32% 16% 1	3736
	11th to 20th	Night	30% 2 12% 38% 18%	3677
	21st to end	Night	48% 3 14% 27% 7% 1	3502
April	1st to 10th	Night	45% 3 13% 25% 13% 2	1900
	11th to 20th	Night	37% 3 9% 27% 18% 6%	1879
	21st to end	Night	37% 4 11% 26% 18% 5%	1746
May	1st to 10th	Night	34% 1 4 28% 28% 4	2543
	11th to 20th	Night	25% 2 6% 30% 32% 6%	2516
	21st to end	Night	32% 2 15% 37% 12% 2	2762
June	1st to 10th	Night	32% 4 9% 27% 23% 6%	1520
	11th to 20th	Night	33% 3 5% 30% 25% 5%	1520
	21st to end	Night	21% 3 5% 26% 29% 15%	1520
July	1st to 10th	Night	8% 1 2 14% 25% 50%	2500
	11th to 20th	Night	7% 2 3 10% 22% 56%	2492
	21st to end	Night	9% 2 2 13% 31% 44%	2674
August	1st to 10th	Night	17% 2 2 9% 33% 37%	2521
	11th to 20th	Night	13% 2 4 31% 33% 17%	2794
	21st to end	Night	15% 3 5% 27% 31% 19%	3498
September	1st to 10th	Night	15% 2 6% 23% 33% 21%	1900
	11th to 20th	Night	23% 3 9% 26% 26% 14%	1945
	21st to end	Night	24% 3 8% 32% 26% 8%	2090
October	1st to 10th	Night	21% 2 8% 34% 32% 2	3755
	11th to 20th	Night	29% 3 16% 27% 22% 2	3807
	21st to end	Night	37% 4 11% 31% 15% 2	4457
November	1st to 10th	Night	48% 5% 14% 24% 10%	2535
	11th to 20th	Night	54% 4 15% 21% 6% 1	2732
	21st to end	Night	54% 4 18% 17% 6% 1	2800
December	1st to 10th	Night	54% 9% 18% 16% 4	4560
	11th to 20th	Night	75% 5% 12% 6% 2	5176
	21st to end	Night	66% 4 13% 12% 5%	6952

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	27% 7% 22% 26% 15% 3	192
	11th to 20th	Day	25% 9% 17% 28% 17% 4	180
	21st to end	Day	18% 8% 21% 27% 23% 3	198
February	1st to 10th	Day	18% 12% 24% 27% 15% 5%	308
	11th to 20th	Day	18% 10% 21% 26% 19% 6%	397
	21st to end	Day	14% 11% 25% 27% 19% 4	382
March	1st to 10th	Day	16% 13% 28% 23% 15% 5%	460
	11th to 20th	Day	11% 10% 19% 29% 22% 10%	460
	21st to end	Day	15% 11% 26% 28% 16% 3	506
April	1st to 10th	Day	13% 15% 24% 24% 14% 10%	460
	11th to 20th	Day	9% 13% 30% 25% 14% 8%	452
	21st to end	Day	7% 11% 28% 27% 19% 8%	460
May	1st to 10th	Day	6% 9% 25% 28% 21% 11%	463
	11th to 20th	Day	10% 8% 21% 24% 24% 14%	488
	21st to end	Day	10% 5% 19% 26% 25% 16%	529
June	1st to 10th	Day	9% 8% 19% 22% 26% 16%	490
	11th to 20th	Day	7% 11% 25% 29% 19% 9%	490
	21st to end	Day	2 5% 19% 25% 31% 18%	490
July	1st to 10th	Day	2 2 12% 28% 41% 16%	486
	11th to 20th	Day	1 3 14% 30% 33% 20%	484
	21st to end	Day	1 2 12% 23% 33% 29%	531
August	1st to 10th	Day	3 3 9% 23% 34% 27%	487
	11th to 20th	Day	1 2 10% 23% 30% 32%	477
	21st to end	Day	4 6% 15% 26% 27% 22%	539
September	1st to 10th	Day	3 2 12% 26% 32% 24%	490
	11th to 20th	Day	5% 5% 16% 26% 27% 22%	490
	21st to end	Day	7% 7% 16% 28% 28% 14%	490
October	1st to 10th	Day	10% 5% 20% 25% 24% 16%	490
	11th to 20th	Day	10% 9% 15% 25% 26% 15%	471
	21st to end	Day	18% 8% 21% 30% 14% 8%	330
November	1st to 10th	Day	18% 9% 23% 29% 18% 3	300
	11th to 20th	Day	24% 10% 21% 23% 20% 3	233
	21st to end	Day	9% 12% 20% 28% 27% 6%	200
December	1st to 10th	Day	10% 10% 24% 27% 17% 13%	200
	11th to 20th	Day	18% 11% 22% 33% 15% 2	200
	21st to end	Day	17% 5% 32% 29% 13% 3	220
January	1st to 10th	Night	26% 9% 18% 28% 16% 2	784
	11th to 20th	Night	20% 7% 17% 35% 19% 3	760
	21st to end	Night	18% 6% 14% 37% 23% 3	836
February	1st to 10th	Night	17% 9% 19% 33% 20% 2	760
	11th to 20th	Night	13% 10% 21% 34% 20% 3	744
	21st to end	Night	13% 14% 20% 35% 17% 1	628
March	1st to 10th	Night	13% 8% 23% 35% 19% 3	760
	11th to 20th	Night	10% 9% 19% 35% 23% 3	760
	21st to end	Night	12% 8% 30% 34% 14% 1	836
April	1st to 10th	Night	16% 7% 20% 37% 17% 2	760
	11th to 20th	Night	10% 9% 29% 30% 18% 4	751
	21st to end	Night	8% 8% 27% 35% 20% 2	606
May	1st to 10th	Night	7% 6% 24% 38% 23% 3	383
	11th to 20th	Night	10% 5% 15% 36% 31% 3	374
	21st to end	Night	8% 3 20% 39% 26% 4	411
June	1st to 10th	Night	9% 5% 25% 35% 23% 3	380
	11th to 20th	Night	9% 6% 32% 34% 17% 2	380
	21st to end	Night	2 4 23% 39% 29% 3	380
July	1st to 10th	Night	4 2 18% 45% 29% 2	370
	11th to 20th	Night	4 2 20% 46% 26% 2	368
	21st to end	Night	1 2 17% 41% 35% 4	416
August	1st to 10th	Night	4 2 12% 42% 37% 4	378
	11th to 20th	Night	4 1 13% 35% 38% 10%	532
	21st to end	Night	3 2 14% 41% 34% 6%	836
September	1st to 10th	Night	3 3 15% 39% 36% 5%	760
	11th to 20th	Night	5% 2 12% 34% 38% 8%	760
	21st to end	Night	6% 3 17% 33% 34% 7%	760
October	1st to 10th	Night	10% 3 15% 38% 30% 4	760
	11th to 20th	Night	10% 7% 16% 33% 27% 7%	760
	21st to end	Night	11% 7% 23% 33% 21% 5%	836
November	1st to 10th	Night	16% 7% 20% 36% 19% 1	780
	11th to 20th	Night	18% 10% 21% 32% 17% 2	800
	21st to end	Night	16% 6% 17% 38% 20% 4	800
December	1st to 10th	Night	15% 7% 18% 35% 22% 4	800
	11th to 20th	Night	22% 8% 18% 35% 16% 1	800
	21st to end	Night	24% 7% 19% 35% 13% 1	880

Page generated at 2025-01-04 00:23:58. Version ac07

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