Grimes Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grimes Point clear sky chart from 2005-11-06 to 2025-04-11.

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	3 4 1 4 3 3 3 3 5% 6% 64%	117296
	Night	4 5% 2 5% 3 3 4 3 5% 6% 59%	119831
Transparency	Day	22% 2 7% 20% 25% 24%	117037
	Night	27% 2 8% 22% 23% 18%	119680
Seeing	Day	6% 6% 15% 28% 28% 16%	15449
	Night	7% 3 15% 45% 27% 4	24985

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	3 8% 2 6% 5% 5% 6% 5% 7% 8% 45%	3639
	11th to 20th	Day	5% 7% 3 6% 5% 4 4 3 4 5% 55%	3640
	21st to end	Day	6% 8% 3 6% 5% 5% 5% 4 6% 7% 45%	4390
February	1st to 10th	Day	4 7% 1 5% 4 4 5% 4 7% 7% 51%	1890
	11th to 20th	Day	4 6% 2 6% 5% 4 4 4 6% 9% 50%	1950
	21st to end	Day	4 7% 2 5% 4 3 4 3 5% 6% 56%	1650
March	1st to 10th	Day	5% 10% 3 7% 5% 5% 5% 5% 7% 9% 39%	4518
	11th to 20th	Day	3 6% 2 5% 4 3 4 3 5% 7% 58%	4706
	21st to end	Day	4 6% 3 7% 4 4 5% 4 6% 7% 50%	5969
April	1st to 10th	Day	4 6% 2 6% 4 4 4 4 5% 8% 53%	2400
	11th to 20th	Day	4 6% 1 4 4 3 3 3 5% 7% 58%	2251
	21st to end	Day	6% 5% 1 5% 3 2 3 4 5% 7% 60%	2290
May	1st to 10th	Day	5% 3 1 3 2 2 3 2 5% 6% 68%	4110
	11th to 20th	Day	3 2 1 3 2 2 2 3 4 5% 73%	4151
	21st to end	Day	4 3 1 4 2 3 3 3 4 6% 67%	4813
June	1st to 10th	Day	4 3 1 3 3 4 3 4 5% 8% 62%	2660
	11th to 20th	Day	3 2 1 2 2 2 3 2 4 5% 74%	2660
	21st to end	Day	2 2 1 2 2 2 2 3 3 4 77%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 3 87%	4420
	11th to 20th	Day	2 1 1 2 2 2 2 2 4 5% 76%	4420
	21st to end	Day	2 1 1 2 2 2 3 3 4 5% 74%	4790
August	1st to 10th	Day	3 2 1 2 2 2 2 3 4 5% 75%	4009
	11th to 20th	Day	1 1 1 1 2 1 1 2 4 86%	3724
	21st to end	Day	2 1 1 2 1 1 2 1 2 3 85%	4180
September	1st to 10th	Day	1 1 2 2 1 2 2 3 3 83%	2280
	11th to 20th	Day	3 2 1 3 3 2 2 2 3 4 75%	2190
	21st to end	Day	3 2 1 2 1 2 2 2 3 4 79%	2090
October	1st to 10th	Day	2 2 1 3 2 2 2 2 3 5% 76%	3397
	11th to 20th	Day	4 3 1 2 1 2 2 2 3 4 76%	3161
	21st to end	Day	2 1 1 3 2 3 3 3 5% 8% 69%	3229
November	1st to 10th	Day	4 5% 2 5% 3 3 3 3 6% 8% 59%	1764
	11th to 20th	Day	3 3 2 3 3 3 4 4 6% 8% 62%	1800
	21st to end	Day	3 6% 2 5% 4 4 3 3 5% 8% 55%	1800
December	1st to 10th	Day	3 3 1 4 3 4 4 3 5% 7% 64%	2663
	11th to 20th	Day	5% 8% 3 7% 6% 5% 6% 6% 8% 9% 38%	3028
	21st to end	Day	5% 8% 3 8% 5% 6% 5% 5% 7% 10% 38%	4004
January	1st to 10th	Night	4 6% 2 6% 4 4 5% 4 6% 8% 50%	6306
	11th to 20th	Night	5% 8% 3 7% 4 4 3 3 5% 6% 52%	6320
	21st to end	Night	6% 9% 3 7% 5% 4 4 3 5% 6% 51%	6583
February	1st to 10th	Night	4 7% 3 6% 4 4 5% 4 5% 6% 52%	2508
	11th to 20th	Night	3 8% 2 6% 3 5% 4 3 6% 7% 53%	2338
	21st to end	Night	3 7% 3 7% 4 4 5% 4 7% 6% 52%	1980
March	1st to 10th	Night	5% 12% 3 7% 4 4 4 3 4 6% 47%	5376
	11th to 20th	Night	4 6% 2 5% 4 3 4 4 6% 8% 55%	5277
	21st to end	Night	6% 7% 3 6% 5% 4 5% 4 6% 8% 48%	5006
April	1st to 10th	Night	5% 6% 2 5% 5% 4 4 4 7% 6% 52%	2000
	11th to 20th	Night	6% 6% 2 5% 4 2 4 3 4 6% 58%	1883
	21st to end	Night	6% 6% 2 3 2 4 4 3 5% 6% 59%	1887
May	1st to 10th	Night	6% 4 1 4 3 2 3 2 4 6% 64%	2860
	11th to 20th	Night	4 3 1 3 2 2 3 2 4 5% 71%	2747
	21st to end	Night	5% 4 2 6% 3 3 3 3 4 5% 62%	2762
June	1st to 10th	Night	4 3 1 4 4 4 4 3 6% 6% 62%	1520
	11th to 20th	Night	3 3 1 4 2 2 2 3 4 6% 71%	1520
	21st to end	Night	2 1 1 3 2 2 2 2 4 4 76%	1520
July	1st to 10th	Night	1 1 1 1 2 1 2 2 2 4 84%	2540
	11th to 20th	Night	3 3 1 5% 3 4 4 3 4 6% 63%	2540
	21st to end	Night	3 2 1 3 3 4 4 3 6% 7% 63%	2761
August	1st to 10th	Night	4 2 1 3 2 3 4 3 5% 7% 66%	2928
	11th to 20th	Night	2 1 1 2 2 2 2 2 3 4 79%	3126
	21st to end	Night	4 1 2 1 2 1 2 2 3 82%	3498
September	1st to 10th	Night	2 1 1 3 2 2 2 2 3 4 76%	1900
	11th to 20th	Night	4 3 1 3 2 3 3 2 4 5% 70%	1990
	21st to end	Night	4 1 1 2 2 2 3 1 3 5% 76%	2090
October	1st to 10th	Night	4 3 2 4 3 3 2 2 3 4 71%	3580
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 5% 76%	3777
	21st to end	Night	3 3 1 3 2 3 3 2 4 6% 72%	4331
November	1st to 10th	Night	5% 5% 2 5% 2 3 3 3 5% 8% 60%	2535
	11th to 20th	Night	4 4 2 3 3 3 3 3 5% 7% 63%	2600
	21st to end	Night	5% 6% 3 5% 3 3 4 3 5% 7% 57%	2600
December	1st to 10th	Night	3 4 2 5% 3 3 4 3 6% 5% 63%	4514
	11th to 20th	Night	5% 8% 3 7% 4 4 5% 5% 6% 11% 41%	5176
	21st to end	Night	6% 10% 4 10% 7% 6% 6% 4 7% 8% 33%	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	35% 3 22% 32% 8%	3639
	11th to 20th	Day	32% 2 13% 31% 20% 2	3640
	21st to end	Day	38% 2 14% 23% 20% 3	4390
February	1st to 10th	Day	31% 3 12% 32% 15% 7%	1890
	11th to 20th	Day	31% 3 12% 30% 21% 3	1960
	21st to end	Day	29% 2 11% 30% 21% 6%	1650
March	1st to 10th	Day	41% 1 5% 27% 21% 5%	4518
	11th to 20th	Day	27% 1 10% 32% 26% 4	4706
	21st to end	Day	33% 2 9% 24% 25% 7%	5969
April	1st to 10th	Day	31% 2 8% 25% 26% 9%	2400
	11th to 20th	Day	27% 2 7% 24% 28% 11%	2254
	21st to end	Day	25% 2 6% 28% 30% 9%	2290
May	1st to 10th	Day	20% 1 4 25% 38% 12%	4110
	11th to 20th	Day	16% 1 3 16% 36% 27%	4154
	21st to end	Day	21% 2 4 17% 40% 16%	4814
June	1st to 10th	Day	22% 2 5% 18% 31% 23%	2660
	11th to 20th	Day	13% 2 2 14% 33% 36%	2660
	21st to end	Day	12% 1 1 6% 27% 52%	2660
July	1st to 10th	Day	7% 1 1 4 12% 76%	4351
	11th to 20th	Day	11% 2 1 5% 14% 66%	4345
	21st to end	Day	13% 2 2 7% 22% 55%	4639
August	1st to 10th	Day	14% 1 1 7% 22% 56%	3993
	11th to 20th	Day	7% 1 1 4 16% 72%	3760
	21st to end	Day	9% 1 1 6% 27% 56%	4179
September	1st to 10th	Day	9% 1 1 6% 26% 57%	2280
	11th to 20th	Day	15% 1 2 13% 33% 35%	2190
	21st to end	Day	12% 1 1 17% 34% 35%	2090
October	1st to 10th	Day	13% 1 4 11% 33% 37%	3397
	11th to 20th	Day	15% 1 3 22% 42% 17%	3161
	21st to end	Day	15% 2 5% 30% 38% 11%	3229
November	1st to 10th	Day	24% 2 11% 28% 29% 7%	1764
	11th to 20th	Day	20% 2 14% 34% 27% 3	1800
	21st to end	Day	28% 2 11% 34% 23% 3	1800
December	1st to 10th	Day	20% 2 11% 36% 27% 3	2663
	11th to 20th	Day	40% 4 18% 29% 9% 1	3028
	21st to end	Day	40% 4 24% 26% 6%	4004
January	1st to 10th	Night	32% 3 23% 32% 10% 1	6306
	11th to 20th	Night	34% 2 13% 26% 23% 2	6320
	21st to end	Night	36% 1 12% 26% 23% 2	6583
February	1st to 10th	Night	33% 3 11% 30% 18% 5%	2508
	11th to 20th	Night	30% 2 11% 32% 22% 4	2339
	21st to end	Night	30% 3 11% 30% 18% 8%	1980
March	1st to 10th	Night	40% 1 5% 25% 23% 7%	5376
	11th to 20th	Night	28% 2 8% 36% 24% 3	5277
	21st to end	Night	35% 2 11% 29% 20% 3	5006
April	1st to 10th	Night	30% 3 10% 25% 25% 7%	2000
	11th to 20th	Night	28% 3 6% 28% 24% 11%	1883
	21st to end	Night	27% 2 7% 28% 29% 8%	1887
May	1st to 10th	Night	24% 2 3 22% 36% 13%	2860
	11th to 20th	Night	18% 1 3 14% 35% 28%	2748
	21st to end	Night	27% 1 4 16% 40% 11%	2762
June	1st to 10th	Night	23% 2 6% 20% 28% 22%	1520
	11th to 20th	Night	17% 2 3 12% 32% 35%	1520
	21st to end	Night	13% 2 1 9% 26% 49%	1520
July	1st to 10th	Night	9% 1 1 4 12% 74%	2500
	11th to 20th	Night	22% 2 2 5% 12% 58%	2492
	21st to end	Night	20% 2 3 10% 16% 49%	2674
August	1st to 10th	Night	19% 2 2 8% 18% 51%	2920
	11th to 20th	Night	12% 1 1 4 18% 64%	3156
	21st to end	Night	11% 1 1 5% 26% 56%	3498
September	1st to 10th	Night	14% 2 2 6% 22% 54%	1900
	11th to 20th	Night	18% 1 3 11% 28% 38%	1990
	21st to end	Night	13% 2 1 11% 32% 40%	2090
October	1st to 10th	Night	19% 1 3 10% 27% 39%	3580
	11th to 20th	Night	14% 2 3 17% 43% 22%	3777
	21st to end	Night	16% 2 3 24% 42% 14%	4331
November	1st to 10th	Night	25% 2 8% 25% 29% 10%	2535
	11th to 20th	Night	22% 2 9% 32% 29% 5%	2600
	21st to end	Night	28% 2 8% 31% 29% 3	2600
December	1st to 10th	Night	22% 3 9% 32% 27% 7%	4514
	11th to 20th	Night	35% 4 17% 33% 11%	5176
	21st to end	Night	48% 3 15% 24% 10%	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	8% 4 21% 37% 23% 8%	200
	11th to 20th	Day	10% 6% 11% 32% 28% 14%	200
	21st to end	Day	10% 5% 9% 32% 30% 14%	385
February	1st to 10th	Day	9% 11% 17% 29% 24% 11%	445
	11th to 20th	Day	7% 9% 19% 36% 22% 7%	495
	21st to end	Day	8% 11% 20% 34% 24% 4	414
March	1st to 10th	Day	14% 10% 18% 32% 19% 7%	500
	11th to 20th	Day	9% 13% 24% 25% 19% 11%	500
	21st to end	Day	11% 12% 20% 32% 17% 9%	550
April	1st to 10th	Day	8% 11% 21% 29% 21% 10%	500
	11th to 20th	Day	9% 11% 20% 28% 22% 10%	453
	21st to end	Day	7% 10% 20% 27% 24% 13%	460
May	1st to 10th	Day	6% 8% 25% 28% 22% 10%	463
	11th to 20th	Day	6% 10% 20% 24% 25% 15%	488
	21st to end	Day	8% 9% 13% 25% 25% 20%	529
June	1st to 10th	Day	4 8% 16% 22% 29% 21%	490
	11th to 20th	Day	6% 7% 21% 26% 25% 15%	490
	21st to end	Day	2 5% 15% 27% 33% 18%	490
July	1st to 10th	Day	2 1 14% 26% 33% 24%	486
	11th to 20th	Day	2 2 10% 25% 35% 27%	484
	21st to end	Day	3 2 9% 26% 36% 25%	531
August	1st to 10th	Day	5% 2 13% 24% 34% 23%	487
	11th to 20th	Day	2 3 15% 25% 32% 23%	477
	21st to end	Day	2 2 10% 27% 35% 24%	539
September	1st to 10th	Day	2 2 10% 24% 37% 24%	490
	11th to 20th	Day	4 4 10% 32% 31% 19%	490
	21st to end	Day	4 3 11% 24% 38% 19%	490
October	1st to 10th	Day	3 5% 13% 25% 31% 24%	490
	11th to 20th	Day	5% 3 13% 23% 36% 20%	490
	21st to end	Day	3 3 12% 31% 31% 20%	408
November	1st to 10th	Day	6% 2 12% 34% 33% 13%	300
	11th to 20th	Day	3 3 14% 35% 29% 17%	300
	21st to end	Day	7% 4 15% 28% 34% 12%	300
December	1st to 10th	Day	5% 4 10% 33% 28% 20%	215
	11th to 20th	Day	9% 5% 12% 33% 30% 13%	200
	21st to end	Day	10% 8% 16% 26% 31% 9%	220
January	1st to 10th	Night	10% 2 18% 43% 22% 6%	800
	11th to 20th	Night	7% 2 18% 44% 25% 5%	800
	21st to end	Night	8% 3 13% 47% 24% 4	880
February	1st to 10th	Night	7% 5% 18% 44% 22% 5%	800
	11th to 20th	Night	7% 3 20% 46% 23% 2	784
	21st to end	Night	7% 4 19% 51% 17% 2	660
March	1st to 10th	Night	9% 6% 20% 44% 20% 1	800
	11th to 20th	Night	7% 5% 20% 42% 24% 3	800
	21st to end	Night	10% 6% 23% 41% 18% 1	880
April	1st to 10th	Night	8% 5% 21% 45% 21% 1	800
	11th to 20th	Night	9% 6% 21% 40% 20% 4	753
	21st to end	Night	10% 6% 18% 40% 23% 4	747
May	1st to 10th	Night	7% 7% 25% 42% 17% 1	570
	11th to 20th	Night	8% 4 20% 38% 27% 2	514
	21st to end	Night	10% 4 12% 45% 28% 2	411
June	1st to 10th	Night	6% 2 19% 42% 30% 2	380
	11th to 20th	Night	4 4 17% 48% 26% 1	380
	21st to end	Night	3 2 17% 52% 26% 1	380
July	1st to 10th	Night	2 1 11% 61% 25% 1	370
	11th to 20th	Night	2 1 9% 58% 29% 1	368
	21st to end	Night	4 1 8% 53% 32% 1	416
August	1st to 10th	Night	4 1 10% 50% 33% 2	608
	11th to 20th	Night	3 1 12% 46% 36% 2	752
	21st to end	Night	3 1 8% 47% 38% 3	836
September	1st to 10th	Night	3 2 9% 42% 39% 5%	760
	11th to 20th	Night	5% 2 8% 40% 39% 5%	760
	21st to end	Night	4 3 9% 40% 37% 7%	760
October	1st to 10th	Night	7% 2 10% 44% 32% 5%	760
	11th to 20th	Night	4 2 13% 42% 33% 6%	760
	21st to end	Night	5% 2 13% 41% 32% 9%	836
November	1st to 10th	Night	8% 2 11% 42% 30% 8%	780
	11th to 20th	Night	6% 1 13% 52% 24% 5%	800
	21st to end	Night	8% 2 14% 46% 25% 5%	800
December	1st to 10th	Night	7% 2 17% 44% 24% 6%	800
	11th to 20th	Night	10% 4 16% 43% 24% 4	800
	21st to end	Night	13% 5% 19% 44% 17% 2	880

Page generated at 2025-04-08 06:17:29. Version ac07

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