Long Point Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Long Point Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	101317
	Night	15% 10% 4 8% 5% 4 4 4 5% 7% 34%	97701
Transparency	Day	26% 48% 7% 12% 6% 1	104925
	Night	26% 48% 6% 12% 7% 1	102181
Seeing	Day	18% 8% 25% 28% 16% 6%	14499
	Night	21% 8% 27% 29% 14% 2	24024

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% 16% 8% 10% 7% 5% 5% 2 5% 5% 20%	2627
	11th to 20th	Day	12% 20% 7% 20% 9% 6% 5% 3 5% 4 11%	2840
	21st to end	Day	23% 18% 6% 13% 7% 5% 4 3 4 4 14%	3124
February	1st to 10th	Day	17% 15% 4 13% 8% 5% 5% 4 4 5% 19%	1710
	11th to 20th	Day	14% 13% 7% 12% 7% 6% 5% 5% 5% 5% 22%	1663
	21st to end	Day	19% 13% 5% 12% 6% 5% 4 3 6% 5% 23%	1520
March	1st to 10th	Day	21% 10% 4 9% 6% 5% 5% 4 4 6% 27%	3422
	11th to 20th	Day	10% 14% 5% 10% 6% 5% 4 4 5% 7% 30%	3480
	21st to end	Day	17% 9% 3 9% 6% 5% 4 3 4 5% 33%	3815
April	1st to 10th	Day	16% 12% 4 8% 6% 5% 4 4 5% 7% 31%	2195
	11th to 20th	Day	16% 11% 3 8% 4 4 4 3 5% 7% 35%	2358
	21st to end	Day	17% 9% 3 7% 5% 5% 5% 4 5% 6% 34%	2470
May	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	4108
	11th to 20th	Day	15% 9% 3 8% 6% 5% 5% 4 6% 8% 33%	4175
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 46%	4837
June	1st to 10th	Day	11% 6% 3 7% 5% 4 5% 4 7% 8% 41%	2660
	11th to 20th	Day	10% 6% 2 7% 5% 4 5% 5% 7% 8% 40%	2660
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 7% 10% 43%	2660
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 4 6% 10% 45%	4440
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 7% 10% 43%	4230
	21st to end	Day	6% 4 2 6% 5% 5% 5% 4 7% 10% 44%	4466
August	1st to 10th	Day	15% 5% 2 5% 4 4 5% 4 7% 9% 40%	4104
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 5% 8% 9% 36%	4044
	21st to end	Day	9% 5% 2 7% 4 5% 5% 4 7% 9% 42%	4389
September	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 3 6% 8% 44%	2280
	11th to 20th	Day	9% 5% 2 4 4 4 4 4 7% 8% 47%	2097
	21st to end	Day	15% 7% 3 6% 5% 5% 5% 4 6% 7% 37%	2090
October	1st to 10th	Day	15% 7% 2 7% 5% 4 5% 4 5% 7% 38%	1902
	11th to 20th	Day	18% 8% 4 8% 6% 5% 5% 3 6% 7% 30%	1900
	21st to end	Day	21% 11% 4 9% 6% 5% 4 4 6% 7% 24%	2090
November	1st to 10th	Day	14% 8% 2 8% 6% 5% 4 4 5% 7% 37%	1723
	11th to 20th	Day	15% 10% 4 8% 6% 6% 4 3 6% 8% 30%	1520
	21st to end	Day	20% 14% 3 8% 5% 5% 4 5% 7% 7% 21%	1520
December	1st to 10th	Day	18% 14% 5% 11% 7% 5% 5% 4 6% 6% 20%	1520
	11th to 20th	Day	19% 15% 6% 11% 6% 5% 4 4 7% 5% 18%	1906
	21st to end	Day	27% 19% 6% 10% 5% 4 4 3 4 5% 12%	2772
January	1st to 10th	Night	18% 16% 6% 10% 6% 5% 4 3 4 5% 22%	4301
	11th to 20th	Night	15% 15% 7% 13% 7% 5% 7% 5% 6% 7% 14%	4120
	21st to end	Night	24% 17% 6% 15% 6% 4 3 2 3 4 13%	4532
February	1st to 10th	Night	16% 16% 5% 9% 7% 5% 5% 4 5% 5% 23%	2470
	11th to 20th	Night	15% 13% 4 11% 6% 6% 5% 4 6% 7% 25%	2403
	21st to end	Night	17% 13% 4 11% 5% 5% 4 4 5% 8% 23%	1932
March	1st to 10th	Night	18% 9% 4 8% 6% 4 4 4 4 6% 33%	3418
	11th to 20th	Night	14% 11% 4 7% 4 3 4 4 5% 7% 38%	3479
	21st to end	Night	16% 9% 3 6% 4 4 4 3 5% 5% 40%	3817
April	1st to 10th	Night	19% 10% 3 6% 5% 5% 5% 4 5% 6% 32%	1983
	11th to 20th	Night	18% 7% 3 6% 5% 5% 4 5% 5% 7% 36%	1787
	21st to end	Night	15% 6% 3 7% 6% 6% 5% 4 5% 7% 36%	1710
May	1st to 10th	Night	19% 9% 3 7% 4 4 4 3 5% 6% 37%	2833
	11th to 20th	Night	11% 8% 4 8% 5% 5% 6% 4 6% 7% 36%	2717
	21st to end	Night	10% 5% 2 6% 4 3 4 4 6% 9% 48%	2738
June	1st to 10th	Night	11% 7% 2 6% 5% 5% 4 4 6% 8% 42%	1520
	11th to 20th	Night	9% 5% 2 7% 6% 5% 5% 5% 7% 9% 42%	1520
	21st to end	Night	11% 4 3 5% 4 4 5% 3 7% 8% 45%	1520
July	1st to 10th	Night	7% 6% 3 6% 4 4 4 3 6% 10% 48%	2520
	11th to 20th	Night	8% 5% 1 6% 4 4 4 4 6% 8% 49%	2726
	21st to end	Night	6% 5% 2 6% 4 4 5% 5% 7% 8% 49%	3087
August	1st to 10th	Night	11% 6% 2 7% 4 5% 4 4 5% 8% 43%	2825
	11th to 20th	Night	11% 5% 2 6% 4 4 4 3 6% 8% 46%	2785
	21st to end	Night	7% 4 1 5% 5% 4 4 4 6% 9% 49%	3220
September	1st to 10th	Night	12% 7% 2 6% 4 4 3 3 5% 7% 47%	1900
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 6% 6% 55%	2080
	21st to end	Night	16% 6% 3 7% 5% 4 5% 4 5% 6% 39%	2090
October	1st to 10th	Night	14% 7% 3 6% 4 3 4 4 6% 7% 43%	2276
	11th to 20th	Night	17% 9% 4 8% 4 5% 4 3 5% 6% 35%	2280
	21st to end	Night	21% 9% 3 7% 4 5% 4 4 5% 6% 33%	2508
November	1st to 10th	Night	15% 8% 2 6% 4 4 4 4 5% 7% 40%	2452
	11th to 20th	Night	15% 12% 3 7% 5% 6% 5% 5% 6% 8% 30%	2660
	21st to end	Night	19% 13% 4 7% 5% 5% 5% 3 5% 7% 26%	2660
December	1st to 10th	Night	20% 17% 4 9% 6% 4 5% 4 5% 5% 21%	2660
	11th to 20th	Night	16% 16% 5% 10% 6% 6% 4 4 5% 6% 21%	3288
	21st to end	Night	27% 17% 5% 10% 6% 5% 4 3 4 5% 14%	4884

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% 41% 4 4 7%	2628
	11th to 20th	Day	50% 42% 3 3 2	2840
	21st to end	Day	47% 43% 5% 3 1	3124
February	1st to 10th	Day	24% 65% 3 5% 2	1710
	11th to 20th	Day	23% 65% 2 7% 3	1672
	21st to end	Day	18% 66% 3 8% 3 1	1520
March	1st to 10th	Day	37% 42% 4 14% 3	3425
	11th to 20th	Day	31% 42% 12% 11% 3 1	3480
	21st to end	Day	29% 42% 6% 14% 8% 1	3815
April	1st to 10th	Day	23% 64% 3 6% 3	2195
	11th to 20th	Day	18% 66% 3 8% 4 1	2358
	21st to end	Day	19% 65% 5% 6% 4 1	2470
May	1st to 10th	Day	31% 43% 8% 11% 5% 1	4120
	11th to 20th	Day	31% 43% 10% 14% 2	4179
	21st to end	Day	21% 42% 7% 14% 12% 3	4837
June	1st to 10th	Day	15% 65% 3 9% 6% 1	2660
	11th to 20th	Day	15% 65% 6% 8% 6% 1	2660
	21st to end	Day	13% 64% 4 11% 8%	2660
July	1st to 10th	Day	23% 37% 9% 19% 10% 2	4370
	11th to 20th	Day	20% 38% 10% 22% 10%	4157
	21st to end	Day	20% 38% 12% 14% 15% 1	4324
August	1st to 10th	Day	26% 38% 10% 15% 9% 1	4091
	11th to 20th	Day	27% 41% 12% 17% 4	4083
	21st to end	Day	22% 40% 8% 21% 8%	4389
September	1st to 10th	Day	14% 60% 8% 12% 6%	2280
	11th to 20th	Day	12% 61% 5% 12% 10%	2097
	21st to end	Day	18% 60% 6% 10% 6%	2090
October	1st to 10th	Day	20% 39% 10% 18% 13% 1	3162
	11th to 20th	Day	21% 38% 10% 20% 11%	3140
	21st to end	Day	26% 38% 12% 19% 5%	3428
November	1st to 10th	Day	24% 58% 5% 9% 3 1	1723
	11th to 20th	Day	21% 60% 5% 8% 4	1520
	21st to end	Day	25% 61% 6% 5% 3	1520
December	1st to 10th	Day	28% 61% 4 6% 2	1520
	11th to 20th	Day	33% 52% 6% 5% 4	1906
	21st to end	Day	48% 39% 7% 5% 2	2772
January	1st to 10th	Night	39% 41% 7% 9% 4 1	4301
	11th to 20th	Night	42% 48% 4 4 2	4120
	21st to end	Night	51% 41% 2 3 2	4532
February	1st to 10th	Night	22% 65% 4 7% 3	2470
	11th to 20th	Night	20% 64% 3 8% 4	2405
	21st to end	Night	21% 64% 3 7% 4 1	1932
March	1st to 10th	Night	34% 41% 7% 14% 4	3428
	11th to 20th	Night	26% 43% 11% 10% 9% 1	3480
	21st to end	Night	25% 42% 6% 13% 13% 1	3817
April	1st to 10th	Night	22% 65% 3 7% 3	1983
	11th to 20th	Night	17% 66% 3 7% 5% 1	1787
	21st to end	Night	15% 65% 4 10% 5% 2	1710
May	1st to 10th	Night	29% 42% 7% 11% 8% 3	2840
	11th to 20th	Night	31% 42% 10% 14% 3	2718
	21st to end	Night	20% 42% 8% 14% 15% 1	2739
June	1st to 10th	Night	16% 65% 3 10% 6% 1	1520
	11th to 20th	Night	14% 65% 5% 10% 5% 1	1520
	21st to end	Night	14% 63% 5% 8% 8% 1	1520
July	1st to 10th	Night	22% 37% 8% 15% 13% 4	2480
	11th to 20th	Night	20% 37% 8% 23% 11%	2676
	21st to end	Night	22% 38% 10% 14% 14% 2	2988
August	1st to 10th	Night	25% 38% 8% 18% 9% 2	2814
	11th to 20th	Night	26% 39% 10% 20% 4	2812
	21st to end	Night	19% 39% 9% 23% 10%	3220
September	1st to 10th	Night	13% 60% 6% 11% 9%	1900
	11th to 20th	Night	11% 60% 5% 13% 11%	2080
	21st to end	Night	17% 60% 4 11% 6%	2090
October	1st to 10th	Night	17% 38% 4 21% 19% 1	3796
	11th to 20th	Night	25% 37% 8% 18% 12%	3779
	21st to end	Night	20% 38% 11% 19% 12%	4120
November	1st to 10th	Night	22% 59% 5% 8% 6% 1	2452
	11th to 20th	Night	19% 60% 4 11% 5%	2660
	21st to end	Night	25% 61% 6% 6% 2	2660
December	1st to 10th	Night	26% 60% 5% 7% 2	2660
	11th to 20th	Night	32% 52% 5% 8% 3	3288
	21st to end	Night	48% 39% 7% 4 1	4884

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% 16% 31% 16% 9% 2	213
	11th to 20th	Day	27% 12% 37% 18% 5% 2	270
	21st to end	Day	24% 13% 31% 25% 6%	297
February	1st to 10th	Day	22% 12% 41% 21% 3	270
	11th to 20th	Day	23% 18% 34% 22% 3	270
	21st to end	Day	24% 22% 34% 18% 3	225
March	1st to 10th	Day	22% 9% 30% 29% 9%	450
	11th to 20th	Day	19% 12% 33% 28% 7% 1	460
	21st to end	Day	27% 9% 33% 21% 9%	506
April	1st to 10th	Day	17% 10% 34% 29% 8% 2	460
	11th to 20th	Day	21% 11% 31% 23% 10% 4	452
	21st to end	Day	21% 6% 33% 29% 9% 2	460
May	1st to 10th	Day	25% 6% 25% 28% 11% 5%	463
	11th to 20th	Day	17% 4 22% 30% 21% 6%	487
	21st to end	Day	13% 3 21% 32% 22% 9%	529
June	1st to 10th	Day	13% 3 24% 38% 17% 4	490
	11th to 20th	Day	14% 4 20% 35% 22% 5%	490
	21st to end	Day	15% 2 24% 37% 18% 5%	490
July	1st to 10th	Day	9% 2 16% 33% 28% 12%	485
	11th to 20th	Day	16% 3 16% 33% 20% 12%	484
	21st to end	Day	8% 2 19% 37% 27% 7%	532
August	1st to 10th	Day	10% 2 14% 34% 28% 11%	486
	11th to 20th	Day	11% 4 14% 33% 27% 11%	479
	21st to end	Day	12% 3 18% 31% 27% 10%	539
September	1st to 10th	Day	13% 4 18% 29% 24% 12%	490
	11th to 20th	Day	9% 1 14% 25% 32% 19%	490
	21st to end	Day	17% 7% 21% 29% 19% 7%	490
October	1st to 10th	Day	18% 6% 24% 26% 18% 9%	490
	11th to 20th	Day	20% 13% 27% 27% 9% 4	490
	21st to end	Day	28% 11% 28% 23% 10%	539
November	1st to 10th	Day	18% 14% 32% 24% 10% 3	305
	11th to 20th	Day	23% 22% 26% 19% 8% 2	180
	21st to end	Day	28% 12% 36% 20% 3	180
December	1st to 10th	Day	27% 18% 27% 20% 7% 2	180
	11th to 20th	Day	26% 20% 32% 16% 6%	180
	21st to end	Day	28% 18% 30% 19% 6%	198
January	1st to 10th	Night	26% 16% 34% 18% 6%	760
	11th to 20th	Night	30% 13% 33% 19% 5%	760
	21st to end	Night	22% 11% 34% 27% 7%	836
February	1st to 10th	Night	26% 11% 36% 24% 3	760
	11th to 20th	Night	23% 11% 35% 27% 5%	743
	21st to end	Night	23% 12% 36% 24% 4	628
March	1st to 10th	Night	20% 8% 33% 31% 7%	760
	11th to 20th	Night	22% 6% 34% 28% 9% 1	760
	21st to end	Night	23% 7% 30% 29% 9% 1	836
April	1st to 10th	Night	23% 8% 32% 28% 8% 1	760
	11th to 20th	Night	22% 6% 31% 29% 10% 2	663
	21st to end	Night	19% 4 29% 37% 11% 1	570
May	1st to 10th	Night	21% 3 25% 32% 16% 2	570
	11th to 20th	Night	17% 4 20% 39% 17% 2	505
	21st to end	Night	14% 1 21% 33% 26% 5%	411
June	1st to 10th	Night	14% 1 22% 41% 19% 2	380
	11th to 20th	Night	12% 2 22% 38% 26% 1	380
	21st to end	Night	12% 4 18% 41% 23% 2	380
July	1st to 10th	Night	8% 1 16% 41% 26% 8%	370
	11th to 20th	Night	12% 1 16% 38% 27% 5%	481
	21st to end	Night	10% 1 15% 42% 28% 4	624
August	1st to 10th	Night	9% 2 12% 39% 32% 6%	567
	11th to 20th	Night	11% 2 15% 34% 33% 6%	564
	21st to end	Night	11% 2 17% 34% 28% 7%	684
September	1st to 10th	Night	16% 4 17% 31% 26% 7%	760
	11th to 20th	Night	12% 2 14% 30% 33% 8%	760
	21st to end	Night	19% 5% 18% 31% 21% 6%	760
October	1st to 10th	Night	19% 6% 22% 28% 21% 4	760
	11th to 20th	Night	22% 10% 28% 26% 11% 2	760
	21st to end	Night	26% 9% 32% 25% 7% 1	836
November	1st to 10th	Night	21% 10% 27% 28% 12% 2	760
	11th to 20th	Night	22% 17% 32% 20% 8% 2	760
	21st to end	Night	28% 14% 29% 22% 7%	760
December	1st to 10th	Night	32% 15% 30% 17% 5% 1	760
	11th to 20th	Night	27% 15% 34% 20% 5%	760
	21st to end	Night	31% 11% 32% 23% 3	836

Page generated at 2024-11-03 02:11:10. Version ac07

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