Point Clark
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Point Clark clear sky chart from 2005-11-06 to 2024-11-12.

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	15% 12% 4 9% 5% 4 4 3 5% 6% 32%	101498
	Night	17% 15% 5% 11% 5% 4 4 3 4 5% 27%	97720
Transparency	Day	50% 8% 13% 18% 10% 1	105059
	Night	57% 7% 11% 16% 9% 1	102247
Seeing	Day	18% 9% 25% 28% 16% 4	15247
	Night	23% 10% 26% 27% 13% 2	24533

By Month

Percentage Cloud Cover NE (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	17% 28% 10% 21% 6% 4 2 1 2 2 8%	2349
	11th to 20th	Day	11% 23% 11% 26% 14% 3 2 2 2 2 4	2569
	21st to end	Day	19% 21% 11% 17% 8% 5% 4 2 2 3 7%	3124
February	1st to 10th	Day	14% 21% 8% 17% 10% 4 3 3 3 4 13%	1710
	11th to 20th	Day	13% 16% 9% 20% 11% 4 5% 2 3 4 14%	1667
	21st to end	Day	15% 18% 6% 12% 8% 4 4 3 4 4 22%	1570
March	1st to 10th	Day	17% 15% 5% 10% 6% 3 3 3 4 5% 28%	3299
	11th to 20th	Day	12% 16% 8% 11% 4 4 4 4 5% 6% 26%	3480
	21st to end	Day	15% 12% 5% 11% 5% 5% 4 3 5% 6% 28%	3815
April	1st to 10th	Day	17% 14% 5% 8% 4 5% 4 4 5% 5% 30%	2183
	11th to 20th	Day	18% 10% 3 6% 4 4 4 3 5% 7% 36%	2442
	21st to end	Day	18% 9% 4 7% 4 4 4 3 5% 7% 37%	2470
May	1st to 10th	Day	16% 8% 2 7% 5% 4 4 4 5% 7% 38%	4108
	11th to 20th	Day	16% 8% 2 7% 4 4 3 3 5% 8% 40%	4130
	21st to end	Day	14% 6% 2 5% 4 3 3 3 5% 7% 48%	4837
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 4 4 6% 9% 40%	2803
	11th to 20th	Day	11% 5% 2 6% 4 5% 4 4 7% 9% 44%	2850
	21st to end	Day	15% 6% 2 5% 4 4 3 3 6% 8% 44%	2850
July	1st to 10th	Day	12% 5% 2 6% 4 4 5% 5% 8% 8% 42%	4760
	11th to 20th	Day	11% 4 2 4 3 4 4 4 6% 8% 50%	4514
	21st to end	Day	9% 5% 2 5% 4 3 4 4 7% 9% 48%	4471
August	1st to 10th	Day	13% 5% 2 5% 4 5% 5% 4 7% 8% 42%	4104
	11th to 20th	Day	14% 5% 3 6% 4 4 5% 4 6% 8% 41%	4044
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 9% 46%	4532
September	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 6% 8% 40%	2211
	11th to 20th	Day	15% 5% 2 5% 3 4 4 4 6% 7% 46%	2090
	21st to end	Day	17% 8% 2 7% 5% 4 4 4 6% 7% 35%	2090
October	1st to 10th	Day	21% 9% 2 6% 5% 4 4 3 5% 6% 34%	1954
	11th to 20th	Day	26% 12% 3 8% 6% 4 5% 3 5% 6% 22%	1900
	21st to end	Day	30% 17% 4 8% 4 4 3 3 4 5% 18%	1997
November	1st to 10th	Day	19% 21% 3 8% 5% 5% 4 2 4 5% 23%	1762
	11th to 20th	Day	18% 24% 5% 10% 5% 4 4 3 5% 5% 18%	1553
	21st to end	Day	21% 30% 7% 10% 6% 4 3 2 3 4 11%	1520
December	1st to 10th	Day	19% 34% 12% 12% 4 3 3 2 2 3 5%	1520
	11th to 20th	Day	19% 23% 10% 19% 6% 4 4 2 3 3 8%	1789
	21st to end	Day	28% 25% 10% 10% 5% 3 2 2 3 3 8%	2431
January	1st to 10th	Night	17% 26% 12% 20% 6% 4 3 1 2 2 6%	4592
	11th to 20th	Night	15% 22% 10% 25% 12% 3 2 2 2 2 4	4397
	21st to end	Night	19% 21% 10% 20% 7% 5% 3 2 3 3 7%	4532
February	1st to 10th	Night	14% 22% 6% 18% 11% 4 3 3 5% 3 11%	2470
	11th to 20th	Night	14% 18% 8% 17% 9% 5% 4 2 4 4 14%	2396
	21st to end	Night	16% 16% 7% 13% 7% 4 4 3 4 4 21%	1884
March	1st to 10th	Night	13% 13% 6% 10% 5% 3 3 3 4 7% 34%	3541
	11th to 20th	Night	11% 16% 6% 9% 5% 4 3 3 5% 6% 32%	3479
	21st to end	Night	16% 11% 6% 12% 6% 4 4 3 4 5% 29%	3817
April	1st to 10th	Night	21% 13% 4 7% 4 4 4 3 4 6% 31%	2011
	11th to 20th	Night	19% 10% 1 6% 5% 4 4 3 4 7% 37%	1687
	21st to end	Night	19% 11% 4 7% 6% 4 4 3 4 6% 32%	1710
May	1st to 10th	Night	16% 8% 3 7% 5% 4 4 3 4 7% 39%	2833
	11th to 20th	Night	14% 10% 3 7% 5% 4 4 3 4 6% 40%	2761
	21st to end	Night	11% 5% 2 6% 5% 4 4 3 5% 7% 48%	2738
June	1st to 10th	Night	16% 6% 2 6% 4 5% 4 4 7% 8% 40%	1372
	11th to 20th	Night	12% 5% 3 6% 5% 4 4 4 8% 10% 40%	1330
	21st to end	Night	14% 6% 2 7% 4 5% 4 4 5% 9% 41%	1330
July	1st to 10th	Night	8% 6% 3 8% 5% 4 4 3 5% 8% 47%	2210
	11th to 20th	Night	12% 4 2 4 4 4 4 3 5% 7% 51%	2453
	21st to end	Night	8% 6% 2 6% 4 4 4 3 6% 8% 49%	3081
August	1st to 10th	Night	11% 6% 2 7% 5% 4 4 3 6% 7% 44%	2825
	11th to 20th	Night	13% 7% 3 6% 3 4 4 3 5% 8% 42%	2785
	21st to end	Night	10% 6% 2 6% 4 4 4 3 5% 7% 49%	3124
September	1st to 10th	Night	12% 6% 2 6% 4 4 5% 3 5% 7% 45%	1944
	11th to 20th	Night	14% 4 2 5% 3 3 4 3 4 8% 50%	2090
	21st to end	Night	19% 8% 2 8% 5% 4 4 4 5% 7% 36%	2090
October	1st to 10th	Night	20% 7% 3 7% 4 4 4 3 5% 6% 37%	2225
	11th to 20th	Night	28% 12% 3 10% 4 5% 4 2 4 6% 22%	2280
	21st to end	Night	29% 15% 4 8% 5% 4 4 3 4 5% 19%	2598
November	1st to 10th	Night	21% 18% 3 7% 5% 3 4 3 5% 6% 25%	2536
	11th to 20th	Night	20% 23% 5% 10% 4 4 4 3 4 5% 15%	2647
	21st to end	Night	24% 27% 8% 11% 5% 3 3 2 3 3 13%	2660
December	1st to 10th	Night	22% 33% 10% 11% 4 3 2 2 2 2 8%	2660
	11th to 20th	Night	15% 27% 10% 16% 5% 4 4 3 3 3 10%	3396
	21st to end	Night	27% 25% 10% 12% 5% 4 3 2 3 3 6%	5236

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	85% 5% 6% 3	2350
	11th to 20th	Day	90% 4 3 1 1	2569
	21st to end	Day	84% 7% 6% 2 1	3124
February	1st to 10th	Day	75% 8% 7% 9% 1	1710
	11th to 20th	Day	74% 8% 7% 8% 3 1	1676
	21st to end	Day	64% 9% 11% 12% 5%	1570
March	1st to 10th	Day	57% 8% 14% 15% 6%	3302
	11th to 20th	Day	54% 10% 13% 16% 6% 1	3480
	21st to end	Day	51% 11% 14% 14% 9% 1	3815
April	1st to 10th	Day	54% 7% 13% 17% 9%	2183
	11th to 20th	Day	45% 7% 12% 21% 13% 1	2442
	21st to end	Day	46% 7% 14% 18% 12% 2	2470
May	1st to 10th	Day	41% 10% 13% 18% 16% 2	4120
	11th to 20th	Day	40% 12% 17% 20% 9% 1	4134
	21st to end	Day	34% 8% 12% 20% 19% 6%	4837
June	1st to 10th	Day	38% 9% 13% 24% 14% 1	2803
	11th to 20th	Day	35% 8% 14% 25% 17% 1	2850
	21st to end	Day	38% 9% 14% 23% 15% 1	2850
July	1st to 10th	Day	36% 10% 16% 20% 16% 2	4686
	11th to 20th	Day	30% 8% 15% 35% 12% 1	4436
	21st to end	Day	30% 9% 16% 26% 17% 2	4329
August	1st to 10th	Day	36% 9% 16% 24% 14% 1	4091
	11th to 20th	Day	39% 8% 18% 25% 10% 1	4083
	21st to end	Day	33% 9% 16% 29% 13%	4531
September	1st to 10th	Day	38% 9% 17% 24% 11% 2	2211
	11th to 20th	Day	36% 8% 16% 27% 13%	2090
	21st to end	Day	46% 9% 13% 22% 8% 1	2090
October	1st to 10th	Day	42% 8% 14% 25% 10% 1	3240
	11th to 20th	Day	50% 8% 11% 21% 9%	3140
	21st to end	Day	60% 8% 13% 16% 4	3273
November	1st to 10th	Day	62% 7% 8% 15% 6%	1762
	11th to 20th	Day	68% 7% 12% 8% 5%	1553
	21st to end	Day	79% 6% 8% 7% 1	1520
December	1st to 10th	Day	88% 4 4 3 1	1520
	11th to 20th	Day	82% 7% 6% 4	1788
	21st to end	Day	83% 6% 8% 3	2431
January	1st to 10th	Night	86% 6% 5% 3	4592
	11th to 20th	Night	89% 5% 4 2 1	4397
	21st to end	Night	83% 7% 7% 2 1	4532
February	1st to 10th	Night	77% 7% 7% 7% 1	2470
	11th to 20th	Night	73% 7% 9% 9% 2	2398
	21st to end	Night	64% 8% 11% 10% 7%	1884
March	1st to 10th	Night	49% 8% 15% 20% 6%	3551
	11th to 20th	Night	49% 9% 14% 19% 8% 1	3480
	21st to end	Night	52% 10% 12% 17% 8% 1	3817
April	1st to 10th	Night	55% 5% 10% 18% 12% 1	2011
	11th to 20th	Night	47% 6% 9% 19% 17% 2	1687
	21st to end	Night	52% 7% 9% 15% 15% 2	1710
May	1st to 10th	Night	43% 8% 11% 18% 16% 4	2840
	11th to 20th	Night	43% 8% 13% 20% 15% 2	2762
	21st to end	Night	34% 8% 12% 22% 20% 4	2739
June	1st to 10th	Night	40% 8% 10% 24% 16% 3	1372
	11th to 20th	Night	38% 8% 13% 22% 17% 2	1330
	21st to end	Night	40% 6% 12% 23% 16% 2	1330
July	1st to 10th	Night	35% 6% 12% 25% 17% 5%	2175
	11th to 20th	Night	30% 7% 13% 32% 17% 1	2408
	21st to end	Night	32% 9% 15% 23% 20% 2	2983
August	1st to 10th	Night	38% 8% 11% 28% 14% 1	2814
	11th to 20th	Night	38% 9% 16% 22% 15% 1	2812
	21st to end	Night	35% 7% 13% 32% 12% 1	3124
September	1st to 10th	Night	38% 6% 13% 25% 15% 2	1944
	11th to 20th	Night	35% 6% 16% 27% 16% 1	2090
	21st to end	Night	47% 8% 12% 23% 10%	2090
October	1st to 10th	Night	39% 8% 12% 25% 16% 1	3719
	11th to 20th	Night	53% 5% 14% 18% 9%	3779
	21st to end	Night	55% 6% 15% 18% 6%	4272
November	1st to 10th	Night	60% 7% 11% 15% 6%	2536
	11th to 20th	Night	70% 7% 11% 8% 3 1	2647
	21st to end	Night	78% 5% 9% 7% 1	2660
December	1st to 10th	Night	85% 5% 6% 3 1	2660
	11th to 20th	Night	80% 7% 9% 4 1	3396
	21st to end	Night	85% 7% 6% 3	5236

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	24% 17% 35% 18% 6% 1	222
	11th to 20th	Day	19% 19% 39% 18% 6%	270
	21st to end	Day	30% 12% 30% 24% 4	297
February	1st to 10th	Day	21% 20% 37% 17% 3	270
	11th to 20th	Day	20% 15% 44% 20% 2	270
	21st to end	Day	21% 27% 35% 16% 1	225
March	1st to 10th	Day	20% 14% 39% 20% 7%	374
	11th to 20th	Day	20% 13% 30% 28% 8% 1	460
	21st to end	Day	23% 10% 32% 27% 7% 1	506
April	1st to 10th	Day	20% 13% 32% 26% 9%	460
	11th to 20th	Day	25% 13% 24% 24% 11% 4	452
	21st to end	Day	23% 7% 28% 29% 12% 1	460
May	1st to 10th	Day	20% 7% 25% 30% 16% 2	463
	11th to 20th	Day	17% 5% 23% 30% 20% 5%	487
	21st to end	Day	15% 5% 20% 29% 26% 5%	529
June	1st to 10th	Day	12% 3 25% 35% 23% 2	633
	11th to 20th	Day	11% 4 22% 38% 21% 4	680
	21st to end	Day	16% 5% 19% 39% 19% 3	680
July	1st to 10th	Day	9% 3 17% 36% 28% 7%	671
	11th to 20th	Day	13% 4 18% 35% 23% 7%	668
	21st to end	Day	10% 3 14% 39% 27% 7%	537
August	1st to 10th	Day	12% 3 15% 35% 24% 10%	486
	11th to 20th	Day	14% 3 13% 34% 25% 12%	479
	21st to end	Day	12% 4 17% 34% 26% 6%	539
September	1st to 10th	Day	14% 7% 19% 29% 22% 8%	490
	11th to 20th	Day	11% 4 17% 28% 29% 11%	490
	21st to end	Day	17% 8% 23% 24% 19% 8%	490
October	1st to 10th	Day	22% 10% 23% 22% 17% 6%	490
	11th to 20th	Day	27% 14% 30% 22% 6% 1	490
	21st to end	Day	33% 16% 27% 17% 6% 1	446
November	1st to 10th	Day	26% 15% 29% 20% 9%	300
	11th to 20th	Day	30% 18% 30% 15% 5% 2	195
	21st to end	Day	32% 18% 32% 17% 1	180
December	1st to 10th	Day	36% 19% 28% 14% 2 1	180
	11th to 20th	Day	27% 24% 31% 14% 3	180
	21st to end	Day	35% 19% 33% 10% 2 1	198
January	1st to 10th	Night	27% 17% 32% 16% 6% 1	950
	11th to 20th	Night	29% 17% 32% 18% 4 1	920
	21st to end	Night	22% 12% 35% 25% 6%	836
February	1st to 10th	Night	26% 14% 32% 24% 4	760
	11th to 20th	Night	25% 13% 33% 23% 5%	743
	21st to end	Night	23% 14% 37% 23% 4	628
March	1st to 10th	Night	20% 12% 35% 24% 9%	760
	11th to 20th	Night	19% 12% 34% 27% 6% 2	760
	21st to end	Night	23% 9% 27% 29% 11% 2	836
April	1st to 10th	Night	25% 11% 26% 31% 6% 1	741
	11th to 20th	Night	22% 9% 25% 30% 12% 2	563
	21st to end	Night	21% 9% 24% 31% 13% 1	570
May	1st to 10th	Night	18% 4 23% 38% 16% 2	570
	11th to 20th	Night	19% 3 22% 35% 20% 1	536
	21st to end	Night	12% 1 20% 39% 26% 2	411
June	1st to 10th	Night	17% 4 17% 40% 21% 2	380
	11th to 20th	Night	13% 6% 19% 37% 24% 1	380
	21st to end	Night	13% 4 18% 38% 25% 2	380
July	1st to 10th	Night	10% 1 14% 42% 29% 4	370
	11th to 20th	Night	10% 1 17% 38% 28% 6%	504
	21st to end	Night	11% 3 12% 42% 29% 3	624
August	1st to 10th	Night	12% 2 13% 40% 29% 4	567
	11th to 20th	Night	10% 3 16% 31% 32% 7%	564
	21st to end	Night	12% 3 19% 36% 27% 4	627
September	1st to 10th	Night	14% 4 20% 34% 20% 8%	736
	11th to 20th	Night	13% 3 15% 35% 28% 6%	760
	21st to end	Night	19% 7% 21% 30% 19% 5%	760
October	1st to 10th	Night	22% 6% 25% 27% 17% 2	760
	11th to 20th	Night	31% 11% 25% 24% 8% 1	760
	21st to end	Night	36% 12% 26% 22% 4	836
November	1st to 10th	Night	30% 13% 24% 24% 8%	780
	11th to 20th	Night	31% 17% 28% 17% 6%	765
	21st to end	Night	36% 15% 26% 19% 3 1	760
December	1st to 10th	Night	37% 18% 27% 14% 4	760
	11th to 20th	Night	27% 21% 36% 15% 2	831
	21st to end	Night	35% 15% 32% 15% 2	1045

Page generated at 2024-11-08 22:45:37. Version ac07

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