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 2024-01-13.

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	16% 11% 5% 8% 6% 3 4 4 5% 6% 32%	74674
	Night	18% 14% 6% 9% 6% 3 4 4 4 5% 26%	75053
Transparency	Day	52% 8% 12% 18% 9% 1	74383
	Night	60% 7% 10% 14% 8% 1	74879
Seeing	Day	19% 8% 24% 28% 16% 4	14053
	Night	23% 10% 26% 27% 13% 2	23514

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	18% 21% 10% 16% 11% 5% 3 2 2 3 9%	1417
	11th to 20th	Day	15% 21% 11% 18% 10% 3 5% 3 3 4 7%	1487
	21st to end	Day	16% 18% 11% 15% 13% 5% 4 4 3 3 9%	1782
February	1st to 10th	Day	15% 19% 9% 17% 12% 4 3 4 3 4 11%	1620
	11th to 20th	Day	14% 14% 10% 17% 14% 2 5% 3 3 4 13%	1577
	21st to end	Day	16% 17% 7% 10% 10% 3 4 4 3 4 22%	1480
March	1st to 10th	Day	14% 12% 6% 13% 8% 3 4 4 4 5% 27%	1895
	11th to 20th	Day	14% 12% 7% 10% 5% 2 5% 5% 5% 5% 29%	1980
	21st to end	Day	17% 10% 4 8% 7% 3 4 4 5% 6% 32%	2178
April	1st to 10th	Day	18% 13% 5% 7% 5% 3 4 5% 5% 5% 30%	2067
	11th to 20th	Day	17% 10% 3 6% 5% 3 4 4 5% 8% 36%	2312
	21st to end	Day	19% 8% 4 6% 4 3 4 4 5% 7% 36%	2340
May	1st to 10th	Day	17% 7% 3 7% 5% 2 5% 4 5% 8% 38%	2340
	11th to 20th	Day	16% 7% 3 5% 4 3 4 4 4 6% 44%	2322
	21st to end	Day	13% 6% 2 5% 5% 3 4 4 5% 8% 46%	2725
June	1st to 10th	Day	12% 6% 3 5% 5% 3 4 5% 5% 9% 42%	2655
	11th to 20th	Day	11% 5% 2 5% 5% 3 5% 4 7% 9% 44%	2700
	21st to end	Day	14% 5% 2 4 5% 3 4 3 5% 8% 45%	2700
July	1st to 10th	Day	8% 4 2 3 4 2 4 5% 7% 8% 52%	2700
	11th to 20th	Day	11% 5% 2 4 4 3 5% 5% 6% 8% 47%	2566
	21st to end	Day	10% 5% 3 5% 5% 2 5% 5% 7% 9% 46%	2552
August	1st to 10th	Day	11% 5% 2 4 5% 3 5% 4 6% 8% 46%	2327
	11th to 20th	Day	12% 4 3 5% 4 3 5% 5% 6% 8% 45%	2303
	21st to end	Day	13% 5% 2 5% 5% 3 5% 5% 6% 8% 44%	2574
September	1st to 10th	Day	13% 6% 2 5% 5% 3 4 5% 6% 8% 40%	2095
	11th to 20th	Day	16% 4 2 5% 4 3 4 5% 6% 7% 44%	1980
	21st to end	Day	18% 8% 3 6% 6% 3 4 5% 6% 8% 35%	1980
October	1st to 10th	Day	22% 8% 3 6% 6% 3 4 4 5% 6% 33%	1852
	11th to 20th	Day	27% 12% 4 7% 7% 4 4 4 5% 6% 20%	1800
	21st to end	Day	32% 16% 4 7% 6% 3 4 3 4 4 18%	1892
November	1st to 10th	Day	19% 20% 4 7% 6% 3 4 3 4 5% 24%	1672
	11th to 20th	Day	19% 22% 6% 9% 6% 3 4 4 4 5% 18%	1544
	21st to end	Day	21% 29% 8% 9% 6% 3 3 3 3 4 11%	1520
December	1st to 10th	Day	19% 30% 16% 12% 5% 3 3 3 2 3 5%	1520
	11th to 20th	Day	19% 22% 11% 17% 7% 3 4 3 3 4 8%	1789
	21st to end	Day	28% 25% 11% 9% 6% 2 2 3 3 4 8%	2431
January	1st to 10th	Night	19% 21% 11% 18% 9% 4 3 2 3 2 7%	2747
	11th to 20th	Night	21% 20% 10% 16% 9% 3 3 4 3 3 7%	2532
	21st to end	Night	14% 18% 10% 18% 12% 5% 4 3 3 4 9%	2574
February	1st to 10th	Night	16% 20% 8% 17% 12% 4 3 3 4 3 10%	2340
	11th to 20th	Night	15% 16% 9% 15% 11% 4 4 3 4 4 14%	2266
	21st to end	Night	17% 15% 8% 12% 9% 3 4 4 4 5% 21%	1776
March	1st to 10th	Night	14% 12% 7% 12% 7% 3 5% 3 4 6% 27%	2052
	11th to 20th	Night	14% 13% 7% 8% 7% 3 4 3 5% 5% 30%	1979
	21st to end	Night	20% 12% 4 7% 6% 3 4 4 4 4 32%	2178
April	1st to 10th	Night	22% 11% 5% 6% 5% 3 4 4 4 6% 31%	1906
	11th to 20th	Night	18% 9% 2 5% 6% 3 5% 3 4 7% 37%	1597
	21st to end	Night	20% 10% 4 6% 7% 3 5% 4 4 6% 32%	1620
May	1st to 10th	Night	16% 8% 3 7% 5% 3 4 4 4 8% 36%	1620
	11th to 20th	Night	15% 9% 3 5% 5% 4 4 4 5% 7% 40%	1569
	21st to end	Night	10% 5% 2 5% 6% 3 4 5% 5% 7% 47%	1550
June	1st to 10th	Night	15% 5% 3 4 5% 3 4 4 7% 8% 41%	1300
	11th to 20th	Night	13% 5% 3 5% 5% 3 5% 4 7% 10% 41%	1260
	21st to end	Night	13% 5% 3 6% 5% 3 5% 4 5% 9% 42%	1260
July	1st to 10th	Night	8% 3 2 4 5% 3 4 4 6% 8% 55%	1260
	11th to 20th	Night	10% 3 3 4 5% 4 5% 4 6% 9% 48%	1391
	21st to end	Night	10% 5% 2 5% 4 3 4 4 5% 8% 49%	1765
August	1st to 10th	Night	9% 5% 2 5% 5% 4 4 4 7% 9% 45%	1611
	11th to 20th	Night	10% 5% 2 4 4 3 3 5% 6% 9% 48%	1598
	21st to end	Night	10% 7% 2 6% 6% 4 4 5% 5% 7% 45%	1782
September	1st to 10th	Night	12% 5% 3 5% 5% 3 5% 5% 5% 7% 44%	1841
	11th to 20th	Night	14% 4 3 5% 4 3 4 4 4 8% 48%	1980
	21st to end	Night	19% 7% 3 7% 5% 3 4 4 4 7% 36%	1980
October	1st to 10th	Night	21% 7% 3 6% 6% 3 4 4 5% 6% 36%	2107
	11th to 20th	Night	29% 11% 4 9% 6% 3 4 3 4 6% 21%	2160
	21st to end	Night	31% 15% 4 7% 6% 3 3 4 4 4 18%	2461
November	1st to 10th	Night	21% 17% 4 6% 6% 3 4 5% 4 6% 25%	2406
	11th to 20th	Night	21% 22% 6% 9% 5% 3 4 4 4 5% 16%	2633
	21st to end	Night	24% 25% 9% 9% 6% 2 3 3 2 3 13%	2660
December	1st to 10th	Night	23% 29% 14% 10% 5% 2 3 2 2 2 8%	2660
	11th to 20th	Night	15% 26% 12% 14% 7% 3 4 4 3 4 10%	3396
	21st to end	Night	27% 24% 11% 11% 6% 3 3 3 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	83% 6% 6% 5% 1	1418
	11th to 20th	Day	84% 7% 5% 3 1	1487
	21st to end	Day	81% 7% 8% 3 1	1782
February	1st to 10th	Day	77% 7% 6% 8% 1	1620
	11th to 20th	Day	75% 7% 7% 8% 3 1	1586
	21st to end	Day	65% 8% 10% 11% 5%	1480
March	1st to 10th	Day	59% 7% 13% 13% 7% 1	1898
	11th to 20th	Day	54% 8% 11% 16% 8% 2	1980
	21st to end	Day	52% 7% 13% 18% 9% 1	2178
April	1st to 10th	Day	54% 7% 13% 17% 9%	2067
	11th to 20th	Day	46% 7% 12% 21% 14% 2	2312
	21st to end	Day	47% 7% 14% 18% 11% 2	2340
May	1st to 10th	Day	45% 7% 10% 22% 14% 1	2340
	11th to 20th	Day	42% 7% 10% 23% 15% 2	2326
	21st to end	Day	37% 8% 14% 23% 15% 3	2725
June	1st to 10th	Day	37% 9% 13% 24% 15% 1	2655
	11th to 20th	Day	35% 8% 14% 25% 17% 1	2700
	21st to end	Day	37% 9% 14% 24% 15% 1	2700
July	1st to 10th	Day	26% 9% 16% 26% 20% 3	2626
	11th to 20th	Day	32% 9% 16% 28% 13% 2	2488
	21st to end	Day	33% 9% 15% 27% 14% 2	2410
August	1st to 10th	Day	33% 10% 18% 26% 11% 2	2314
	11th to 20th	Day	35% 9% 19% 25% 11% 1	2303
	21st to end	Day	37% 9% 16% 25% 13% 1	2574
September	1st to 10th	Day	39% 9% 17% 23% 11% 2	2095
	11th to 20th	Day	37% 8% 16% 27% 11%	1980
	21st to end	Day	46% 10% 14% 22% 8% 1	1980
October	1st to 10th	Day	50% 8% 12% 19% 10% 1	1852
	11th to 20th	Day	64% 8% 11% 12% 5% 1	1800
	21st to end	Day	70% 8% 9% 11% 3	1892
November	1st to 10th	Day	62% 7% 8% 15% 6%	1672
	11th to 20th	Day	68% 7% 12% 8% 6%	1544
	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	85% 5% 6% 3	2747
	11th to 20th	Night	83% 6% 6% 3 1	2532
	21st to end	Night	80% 7% 8% 3 2	2574
February	1st to 10th	Night	80% 7% 6% 7% 1	2340
	11th to 20th	Night	74% 6% 9% 9% 2	2268
	21st to end	Night	65% 7% 11% 10% 7%	1776
March	1st to 10th	Night	58% 7% 11% 15% 7%	2062
	11th to 20th	Night	55% 7% 9% 17% 10% 2	1980
	21st to end	Night	55% 5% 10% 17% 10% 2	2178
April	1st to 10th	Night	54% 5% 10% 18% 12% 1	1906
	11th to 20th	Night	46% 6% 9% 19% 17% 2	1597
	21st to end	Night	52% 7% 9% 16% 15% 2	1620
May	1st to 10th	Night	47% 6% 9% 21% 15% 2	1620
	11th to 20th	Night	43% 5% 10% 21% 17% 4	1570
	21st to end	Night	35% 7% 14% 25% 15% 4	1551
June	1st to 10th	Night	39% 7% 11% 24% 16% 3	1300
	11th to 20th	Night	38% 8% 13% 22% 17% 2	1260
	21st to end	Night	39% 6% 13% 23% 17% 2	1260
July	1st to 10th	Night	27% 7% 12% 27% 25% 3	1225
	11th to 20th	Night	32% 8% 14% 27% 17% 2	1346
	21st to end	Night	33% 10% 16% 25% 15% 2	1667
August	1st to 10th	Night	33% 9% 14% 29% 13% 1	1600
	11th to 20th	Night	30% 10% 16% 26% 16% 2	1598
	21st to end	Night	38% 7% 14% 27% 12% 2	1782
September	1st to 10th	Night	38% 7% 14% 24% 15% 2	1841
	11th to 20th	Night	37% 6% 16% 27% 14% 1	1980
	21st to end	Night	46% 8% 12% 23% 10%	1980
October	1st to 10th	Night	50% 8% 10% 19% 12% 1	2107
	11th to 20th	Night	64% 7% 11% 13% 5%	2160
	21st to end	Night	70% 6% 9% 9% 5%	2461
November	1st to 10th	Night	60% 8% 11% 15% 6%	2406
	11th to 20th	Night	70% 7% 11% 8% 3 1	2633
	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	21% 14% 40% 18% 6%	248
	21st to end	Day	30% 13% 31% 21% 5%	264
February	1st to 10th	Day	24% 22% 37% 15% 2	240
	11th to 20th	Day	20% 14% 46% 18% 1	240
	21st to end	Day	23% 26% 35% 15% 2	198
March	1st to 10th	Day	20% 14% 39% 19% 7%	338
	11th to 20th	Day	20% 11% 31% 28% 8% 1	420
	21st to end	Day	24% 9% 31% 27% 7% 1	462
April	1st to 10th	Day	21% 11% 31% 27% 9%	420
	11th to 20th	Day	24% 11% 24% 24% 12% 5%	412
	21st to end	Day	24% 6% 29% 28% 13% 1	420
May	1st to 10th	Day	22% 6% 25% 30% 16% 2	423
	11th to 20th	Day	17% 4 24% 31% 19% 5%	447
	21st to end	Day	16% 4 19% 28% 27% 6%	485
June	1st to 10th	Day	12% 2 24% 36% 23% 3	585
	11th to 20th	Day	12% 3 21% 37% 22% 5%	630
	21st to end	Day	15% 3 18% 40% 20% 3	630
July	1st to 10th	Day	8% 3 16% 36% 30% 7%	621
	11th to 20th	Day	13% 4 16% 37% 23% 7%	618
	21st to end	Day	10% 3 15% 40% 27% 6%	493
August	1st to 10th	Day	12% 3 14% 35% 25% 11%	446
	11th to 20th	Day	13% 2 11% 34% 27% 13%	439
	21st to end	Day	13% 4 17% 33% 26% 7%	495
September	1st to 10th	Day	14% 5% 20% 31% 22% 8%	450
	11th to 20th	Day	12% 4 18% 29% 28% 9%	450
	21st to end	Day	18% 8% 24% 23% 20% 8%	450
October	1st to 10th	Day	23% 10% 22% 22% 17% 6%	450
	11th to 20th	Day	29% 14% 31% 20% 5% 1	450
	21st to end	Day	35% 15% 27% 18% 5% 1	407
November	1st to 10th	Day	25% 15% 29% 20% 10%	270
	11th to 20th	Day	30% 18% 30% 15% 5% 2	192
	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	30% 15% 32% 19% 4 1	886
	21st to end	Night	21% 12% 35% 24% 7% 1	792
February	1st to 10th	Night	27% 14% 32% 23% 4	720
	11th to 20th	Night	26% 13% 33% 23% 5%	703
	21st to end	Night	24% 13% 36% 23% 4	592
March	1st to 10th	Night	20% 11% 35% 25% 9%	720
	11th to 20th	Night	20% 11% 34% 27% 6% 2	720
	21st to end	Night	24% 8% 27% 28% 12% 2	792
April	1st to 10th	Night	25% 11% 26% 31% 6% 1	702
	11th to 20th	Night	21% 8% 25% 31% 12% 2	533
	21st to end	Night	22% 9% 23% 31% 14% 1	540
May	1st to 10th	Night	18% 4 24% 37% 16% 2	540
	11th to 20th	Night	19% 3 21% 36% 20% 1	508
	21st to end	Night	12% 1 20% 38% 26% 2	389
June	1st to 10th	Night	17% 3 16% 41% 21% 3	360
	11th to 20th	Night	14% 5% 19% 36% 25% 1	360
	21st to end	Night	13% 4 18% 38% 26% 2	360
July	1st to 10th	Night	9% 1 13% 43% 30% 4	350
	11th to 20th	Night	9% 1 16% 39% 28% 7%	476
	21st to end	Night	11% 3 13% 42% 28% 3	591
August	1st to 10th	Night	12% 2 13% 40% 30% 4	537
	11th to 20th	Night	10% 3 16% 32% 33% 7%	534
	21st to end	Night	12% 2 19% 35% 27% 4	594
September	1st to 10th	Night	14% 4 19% 35% 20% 8%	697
	11th to 20th	Night	14% 3 16% 36% 26% 5%	720
	21st to end	Night	20% 6% 21% 28% 19% 5%	720
October	1st to 10th	Night	23% 7% 23% 27% 18% 2	720
	11th to 20th	Night	33% 10% 25% 23% 8% 1	720
	21st to end	Night	38% 12% 25% 21% 4	792
November	1st to 10th	Night	30% 12% 24% 24% 8%	740
	11th to 20th	Night	31% 17% 29% 17% 6%	760
	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 2024-01-10 19:35:21. Version ac07

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