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 2024-10-24.

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%	101099
	Night	5% 5% 2 5% 4 4 4 3 5% 6% 58%	97857
Transparency	Day	22% 2 6% 19% 24% 27%	100840
	Night	28% 2 8% 21% 22% 20%	97706
Seeing	Day	6% 6% 15% 28% 29% 16%	14929
	Night	7% 3 15% 45% 27% 4	24307

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 11% 3 8% 5% 6% 6% 5% 7% 9% 36%	2539
	11th to 20th	Day	7% 10% 4 9% 6% 5% 5% 4 6% 7% 38%	2540
	21st to end	Day	7% 10% 3 8% 6% 6% 6% 4 7% 8% 35%	3054
February	1st to 10th	Day	4 7% 2 5% 4 4 5% 4 7% 8% 50%	1795
	11th to 20th	Day	4 6% 2 6% 5% 4 4 4 6% 9% 50%	1850
	21st to end	Day	4 7% 2 5% 4 3 4 3 5% 6% 55%	1570
March	1st to 10th	Day	4 8% 3 8% 6% 6% 5% 5% 7% 10% 39%	3138
	11th to 20th	Day	2 5% 1 4 3 2 4 3 4 6% 64%	3287
	21st to end	Day	5% 8% 3 7% 5% 4 5% 4 7% 8% 44%	4165
April	1st to 10th	Day	4 6% 2 6% 5% 4 4 4 5% 8% 52%	2280
	11th to 20th	Day	4 6% 1 4 4 3 3 3 5% 7% 58%	2249
	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	4 3 1 4 2 3 2 2 4 4 71%	2033
	11th to 20th	Day	3 2 1 3 1 2 3 2 5% 5% 73%	1900
	21st to end	Day	3 2 1 3 2 2 2 3 5% 7% 70%	1887
November	1st to 10th	Day	4 5% 2 5% 3 3 3 3 6% 8% 58%	1674
	11th to 20th	Day	3 3 2 3 3 3 3 4 6% 8% 63%	1710
	21st to end	Day	3 6% 2 5% 4 4 3 3 6% 8% 55%	1710
December	1st to 10th	Day	4 6% 1 5% 4 4 6% 4 6% 8% 52%	1549
	11th to 20th	Day	6% 10% 3 9% 7% 5% 6% 6% 7% 7% 33%	1928
	21st to end	Day	5% 9% 3 10% 6% 7% 6% 5% 8% 9% 32%	2794
January	1st to 10th	Night	4 8% 3 7% 5% 5% 5% 4 6% 7% 46%	4406
	11th to 20th	Night	8% 11% 4 10% 6% 5% 4 4 6% 7% 36%	4420
	21st to end	Night	7% 9% 3 8% 6% 5% 5% 4 6% 8% 39%	4610
February	1st to 10th	Night	4 7% 3 6% 4 4 5% 3 5% 6% 52%	2383
	11th to 20th	Night	3 8% 2 5% 3 5% 3 3 6% 7% 54%	2218
	21st to end	Night	3 7% 3 7% 3 4 5% 4 6% 7% 51%	1884
March	1st to 10th	Night	4 11% 3 8% 5% 5% 4 4 4 6% 45%	3736
	11th to 20th	Night	4 6% 2 5% 3 3 3 4 5% 6% 59%	3676
	21st to end	Night	8% 8% 3 6% 5% 4 4 4 6% 8% 45%	3488
April	1st to 10th	Night	5% 6% 2 5% 5% 4 4 4 7% 6% 52%	1900
	11th to 20th	Night	6% 6% 2 5% 4 2 4 3 4 6% 58%	1879
	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	5% 3 2 4 3 3 2 3 4 4 68%	2144
	11th to 20th	Night	3 2 2 3 2 2 2 2 3 6% 73%	2280
	21st to end	Night	3 2 1 2 2 2 3 2 4 7% 72%	2534
November	1st to 10th	Night	5% 5% 2 5% 2 3 3 3 4 8% 60%	2405
	11th to 20th	Night	5% 4 2 3 3 3 3 3 5% 7% 63%	2470
	21st to end	Night	5% 6% 3 5% 3 3 4 3 5% 7% 56%	2470
December	1st to 10th	Night	5% 7% 3 7% 4 4 3 2 6% 6% 53%	2627
	11th to 20th	Night	7% 9% 3 8% 5% 5% 5% 5% 6% 9% 39%	3276
	21st to end	Night	7% 9% 3 10% 7% 6% 6% 4 7% 8% 32%	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	43% 3 17% 32% 4	2539
	11th to 20th	Day	46% 2 18% 25% 8% 1	2540
	21st to end	Day	46% 2 19% 26% 7%	3054
February	1st to 10th	Day	31% 3 13% 33% 15% 5%	1795
	11th to 20th	Day	31% 2 12% 30% 21% 3	1860
	21st to end	Day	30% 2 11% 31% 21% 4	1570
March	1st to 10th	Day	41% 1 6% 31% 18% 3	3138
	11th to 20th	Day	23% 1 10% 36% 25% 5%	3287
	21st to end	Day	39% 2 8% 25% 21% 5%	4165
April	1st to 10th	Day	31% 2 8% 25% 25% 9%	2280
	11th to 20th	Day	27% 2 7% 24% 28% 11%	2252
	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	18% 2 6% 17% 34% 23%	2033
	11th to 20th	Day	14% 1 4 26% 36% 18%	1900
	21st to end	Day	16% 2 6% 32% 33% 11%	1887
November	1st to 10th	Day	25% 2 10% 27% 30% 7%	1674
	11th to 20th	Day	20% 2 14% 34% 27% 3	1710
	21st to end	Day	28% 2 11% 33% 23% 3	1710
December	1st to 10th	Day	30% 3 16% 31% 18% 3	1549
	11th to 20th	Day	48% 3 15% 25% 9%	1928
	21st to end	Day	46% 3 22% 23% 6%	2794
January	1st to 10th	Night	37% 2 23% 30% 7% 1	4406
	11th to 20th	Night	48% 2 17% 21% 11% 1	4420
	21st to end	Night	43% 2 17% 29% 9%	4610
February	1st to 10th	Night	33% 3 12% 31% 18% 4	2383
	11th to 20th	Night	30% 2 11% 33% 21% 4	2219
	21st to end	Night	31% 3 11% 31% 18% 6%	1884
March	1st to 10th	Night	41% 2 6% 28% 20% 4	3736
	11th to 20th	Night	27% 1 8% 37% 23% 4	3676
	21st to end	Night	39% 1 10% 30% 18% 3	3488
April	1st to 10th	Night	30% 3 10% 26% 24% 8%	1900
	11th to 20th	Night	28% 3 6% 28% 24% 11%	1879
	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	22% 2 3 16% 28% 29%	2144
	11th to 20th	Night	16% 1 3 21% 33% 25%	2280
	21st to end	Night	14% 1 4 27% 37% 17%	2534
November	1st to 10th	Night	25% 2 8% 24% 29% 10%	2405
	11th to 20th	Night	22% 2 9% 32% 29% 5%	2470
	21st to end	Night	28% 2 8% 31% 28% 3	2470
December	1st to 10th	Night	32% 3 13% 29% 20% 3	2627
	11th to 20th	Night	41% 3 15% 29% 11% 1	3276
	21st to end	Night	49% 2 15% 24% 10%	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	8% 4 22% 35% 23% 8%	180
	11th to 20th	Day	11% 6% 12% 29% 28% 14%	180
	21st to end	Day	10% 5% 9% 30% 32% 13%	354
February	1st to 10th	Day	8% 10% 15% 30% 26% 11%	410
	11th to 20th	Day	7% 8% 19% 35% 23% 7%	455
	21st to end	Day	9% 11% 20% 32% 24% 4	382
March	1st to 10th	Day	13% 11% 18% 33% 20% 6%	460
	11th to 20th	Day	8% 12% 24% 25% 20% 11%	460
	21st to end	Day	10% 12% 21% 32% 17% 7%	506
April	1st to 10th	Day	8% 12% 22% 29% 20% 10%	460
	11th to 20th	Day	9% 12% 20% 28% 22% 10%	452
	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 11% 31% 32% 21%	384
November	1st to 10th	Day	6% 2 13% 33% 33% 13%	270
	11th to 20th	Day	3 2 12% 34% 31% 17%	270
	21st to end	Day	7% 3 13% 29% 34% 13%	270
December	1st to 10th	Day	6% 5% 11% 34% 28% 16%	194
	11th to 20th	Day	8% 4 12% 33% 28% 14%	180
	21st to end	Day	9% 7% 15% 27% 32% 10%	198
January	1st to 10th	Night	10% 2 17% 42% 23% 6%	760
	11th to 20th	Night	8% 2 17% 43% 25% 5%	760
	21st to end	Night	8% 3 13% 46% 25% 4	836
February	1st to 10th	Night	7% 4 16% 45% 23% 5%	760
	11th to 20th	Night	8% 3 18% 45% 24% 2	744
	21st to end	Night	7% 5% 19% 51% 17% 2	628
March	1st to 10th	Night	9% 6% 19% 44% 20% 1	760
	11th to 20th	Night	7% 4 19% 42% 25% 3	760
	21st to end	Night	10% 6% 22% 42% 18% 1	836
April	1st to 10th	Night	8% 6% 21% 44% 21% 1	760
	11th to 20th	Night	9% 6% 21% 40% 20% 4	751
	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% 1 12% 41% 32% 9%	804
November	1st to 10th	Night	8% 2 10% 42% 30% 8%	740
	11th to 20th	Night	6% 1 11% 52% 25% 5%	760
	21st to end	Night	8% 2 12% 47% 26% 5%	760
December	1st to 10th	Night	8% 2 17% 45% 22% 5%	760
	11th to 20th	Night	10% 3 15% 43% 24% 4	760
	21st to end	Night	13% 5% 18% 44% 18% 2	836

Page generated at 2024-10-20 23:20:02. Version ac07

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