Grayson Lake State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grayson Lake State Park clear sky chart from 2005-11-06 to 2024-01-17.

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% 8% 3 6% 6% 3 5% 5% 5% 7% 37%	74926
	Night	14% 8% 3 6% 5% 3 4 5% 5% 7% 39%	74914
Transparency	Day	45% 7% 11% 21% 13% 2	74649
	Night	44% 6% 11% 21% 15% 3	74710
Seeing	Day	21% 12% 26% 22% 14% 6%	13771
	Night	19% 10% 24% 28% 16% 2	23912

By Month

Percentage Cloud Cover SE (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	16% 12% 5% 10% 7% 3 4 4 5% 6% 28%	1706
	11th to 20th	Day	19% 14% 5% 11% 7% 3 5% 4 4 5% 24%	1674
	21st to end	Day	18% 13% 5% 7% 5% 2 4 4 5% 6% 30%	1782
February	1st to 10th	Day	19% 13% 6% 9% 6% 3 4 3 3 5% 28%	1654
	11th to 20th	Day	21% 11% 6% 7% 5% 3 4 4 5% 5% 29%	1748
	21st to end	Day	19% 13% 4 7% 5% 3 5% 4 3 6% 30%	1480
March	1st to 10th	Day	19% 10% 3 5% 4 2 4 5% 4 7% 36%	1886
	11th to 20th	Day	20% 9% 4 6% 6% 3 4 4 5% 6% 32%	1980
	21st to end	Day	20% 9% 4 6% 6% 3 5% 5% 4 6% 33%	2178
April	1st to 10th	Day	13% 8% 4 6% 6% 4 4 5% 5% 8% 39%	1998
	11th to 20th	Day	15% 8% 4 5% 6% 3 4 4 5% 6% 41%	2240
	21st to end	Day	17% 8% 3 6% 6% 3 4 5% 5% 6% 37%	2340
May	1st to 10th	Day	17% 7% 4 6% 6% 3 5% 5% 6% 8% 33%	2340
	11th to 20th	Day	17% 8% 3 7% 6% 4 5% 5% 4 6% 34%	2301
	21st to end	Day	9% 5% 3 5% 8% 4 7% 7% 7% 9% 37%	2531
June	1st to 10th	Day	11% 6% 2 5% 6% 3 4 7% 7% 8% 41%	2340
	11th to 20th	Day	9% 5% 2 6% 6% 5% 6% 5% 7% 9% 41%	2340
	21st to end	Day	9% 6% 2 6% 6% 3 6% 6% 7% 10% 40%	2340
July	1st to 10th	Day	12% 5% 3 6% 6% 4 5% 6% 8% 10% 36%	2340
	11th to 20th	Day	10% 5% 3 5% 6% 3 7% 8% 7% 10% 36%	2340
	21st to end	Day	12% 6% 2 5% 6% 3 7% 4 7% 10% 37%	2547
August	1st to 10th	Day	10% 6% 2 6% 6% 4 6% 6% 7% 11% 36%	2327
	11th to 20th	Day	11% 7% 2 5% 7% 5% 6% 6% 7% 10% 34%	2303
	21st to end	Day	8% 5% 3 4 6% 3 5% 6% 7% 10% 43%	2476
September	1st to 10th	Day	13% 6% 2 5% 4 3 4 4 5% 8% 46%	1980
	11th to 20th	Day	11% 5% 3 5% 5% 2 4 5% 5% 7% 48%	1980
	21st to end	Day	17% 7% 2 5% 5% 2 4 4 4 6% 45%	1980
October	1st to 10th	Day	12% 5% 2 4 3 4 3 4 5% 8% 50%	1949
	11th to 20th	Day	14% 5% 3 5% 5% 2 4 4 5% 6% 47%	1800
	21st to end	Day	20% 7% 3 7% 4 2 3 3 4 6% 42%	1967
November	1st to 10th	Day	11% 6% 2 4 4 3 4 3 4 6% 52%	1672
	11th to 20th	Day	14% 9% 4 7% 5% 2 4 5% 4 7% 41%	1710
	21st to end	Day	16% 9% 4 6% 5% 3 4 4 4 5% 40%	1710
December	1st to 10th	Day	23% 12% 4 6% 4 3 5% 5% 5% 5% 27%	1710
	11th to 20th	Day	18% 12% 5% 8% 6% 3 4 4 4 6% 32%	2153
	21st to end	Day	17% 16% 4 8% 8% 5% 6% 5% 4 6% 21%	3124
January	1st to 10th	Night	15% 11% 5% 10% 7% 3 4 5% 5% 5% 29%	2459
	11th to 20th	Night	21% 14% 5% 7% 6% 3 4 4 4 4 26%	2430
	21st to end	Night	17% 10% 4 9% 6% 3 5% 4 4 5% 32%	2574
February	1st to 10th	Night	19% 11% 4 8% 7% 3 4 4 5% 6% 28%	2304
	11th to 20th	Night	21% 11% 4 8% 5% 3 5% 4 5% 5% 29%	2098
	21st to end	Night	22% 13% 4 8% 6% 2 4 3 3 6% 28%	1776
March	1st to 10th	Night	17% 10% 4 6% 6% 2 3 4 4 5% 39%	2072
	11th to 20th	Night	20% 9% 3 7% 5% 3 4 5% 4 6% 35%	1980
	21st to end	Night	14% 9% 4 7% 6% 4 6% 4 5% 7% 35%	2178
April	1st to 10th	Night	13% 7% 3 6% 5% 3 4 5% 6% 7% 41%	1976
	11th to 20th	Night	14% 6% 3 4 5% 3 4 4 5% 8% 42%	1669
	21st to end	Night	17% 7% 3 5% 6% 4 4 5% 4 6% 39%	1620
May	1st to 10th	Night	17% 8% 2 6% 5% 3 4 6% 6% 7% 36%	1620
	11th to 20th	Night	14% 6% 3 6% 5% 4 5% 5% 6% 10% 35%	1592
	21st to end	Night	8% 5% 2 5% 6% 4 6% 5% 7% 11% 42%	1744
June	1st to 10th	Night	8% 5% 2 4 5% 3 6% 6% 7% 10% 44%	1620
	11th to 20th	Night	6% 4 2 5% 5% 3 5% 5% 8% 11% 46%	1620
	21st to end	Night	8% 5% 2 4 5% 2 5% 6% 8% 12% 44%	1620
July	1st to 10th	Night	10% 7% 2 5% 4 4 5% 6% 6% 8% 43%	1620
	11th to 20th	Night	6% 3 2 5% 5% 4 5% 5% 6% 11% 47%	1620
	21st to end	Night	8% 6% 2 6% 7% 4 5% 6% 7% 10% 41%	1771
August	1st to 10th	Night	8% 5% 2 5% 5% 3 5% 5% 7% 10% 45%	1611
	11th to 20th	Night	8% 5% 2 6% 5% 3 5% 5% 7% 9% 44%	1598
	21st to end	Night	8% 4 2 5% 5% 3 4 5% 6% 8% 51%	1868
September	1st to 10th	Night	10% 5% 2 4 5% 3 5% 5% 5% 7% 48%	1970
	11th to 20th	Night	10% 5% 2 5% 4 2 4 4 5% 7% 51%	1980
	21st to end	Night	11% 6% 3 5% 5% 4 4 4 5% 6% 48%	1980
October	1st to 10th	Night	11% 5% 2 5% 4 3 3 4 5% 7% 52%	2010
	11th to 20th	Night	14% 5% 3 5% 5% 2 4 4 4 7% 46%	2160
	21st to end	Night	18% 7% 3 5% 5% 2 4 4 4 5% 43%	2384
November	1st to 10th	Night	12% 7% 2 4 4 3 4 4 4 5% 51%	2406
	11th to 20th	Night	14% 7% 3 6% 5% 3 4 4 4 6% 43%	2470
	21st to end	Night	17% 10% 3 5% 5% 3 4 4 4 6% 40%	2470
December	1st to 10th	Night	19% 14% 5% 7% 6% 2 4 4 5% 5% 30%	2470
	11th to 20th	Night	17% 11% 6% 7% 5% 3 4 4 4 6% 31%	3042
	21st to end	Night	17% 15% 4 8% 7% 4 6% 5% 5% 6% 22%	4532

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	58% 5% 10% 17% 9% 1	1707
	11th to 20th	Day	63% 6% 8% 16% 6% 1	1674
	21st to end	Day	54% 5% 10% 21% 8% 2	1782
February	1st to 10th	Day	59% 5% 8% 18% 9% 1	1654
	11th to 20th	Day	57% 5% 7% 19% 9% 2	1758
	21st to end	Day	56% 4 8% 18% 11% 3	1480
March	1st to 10th	Day	49% 4 10% 23% 12% 2	1886
	11th to 20th	Day	53% 5% 9% 19% 11% 3	1980
	21st to end	Day	52% 6% 9% 22% 10% 2	2178
April	1st to 10th	Day	44% 5% 11% 23% 14% 3	1998
	11th to 20th	Day	44% 5% 9% 20% 18% 5%	2240
	21st to end	Day	46% 6% 13% 21% 11% 3	2340
May	1st to 10th	Day	48% 7% 12% 22% 10% 2	2340
	11th to 20th	Day	52% 6% 11% 19% 10% 1	2305
	21st to end	Day	40% 11% 13% 22% 13% 1	2531
June	1st to 10th	Day	37% 10% 12% 25% 15% 1	2340
	11th to 20th	Day	37% 10% 13% 21% 17% 2	2340
	21st to end	Day	38% 10% 14% 20% 15% 4	2340
July	1st to 10th	Day	41% 10% 16% 17% 16% 1	2275
	11th to 20th	Day	38% 11% 14% 20% 14% 3	2271
	21st to end	Day	41% 7% 14% 25% 12% 2	2405
August	1st to 10th	Day	39% 10% 18% 21% 11% 1	2314
	11th to 20th	Day	42% 9% 15% 22% 12% 1	2303
	21st to end	Day	34% 8% 15% 25% 15% 3	2476
September	1st to 10th	Day	36% 6% 13% 22% 17% 5%	1980
	11th to 20th	Day	35% 7% 11% 26% 21% 1	1980
	21st to end	Day	41% 5% 8% 23% 21% 2	1980
October	1st to 10th	Day	34% 6% 13% 24% 21% 3	1949
	11th to 20th	Day	37% 5% 10% 25% 20% 3	1800
	21st to end	Day	45% 3 9% 24% 16% 2	1967
November	1st to 10th	Day	35% 4 8% 26% 23% 4	1672
	11th to 20th	Day	44% 4 9% 22% 19% 3	1710
	21st to end	Day	47% 4 10% 21% 18% 1	1710
December	1st to 10th	Day	58% 6% 9% 19% 7% 1	1710
	11th to 20th	Day	54% 4 11% 16% 13% 1	2150
	21st to end	Day	61% 8% 10% 16% 5% 1	3124
January	1st to 10th	Night	57% 7% 8% 16% 11% 1	2459
	11th to 20th	Night	61% 4 9% 16% 9% 2	2430
	21st to end	Night	55% 4 9% 21% 8% 2	2574
February	1st to 10th	Night	57% 5% 9% 19% 9% 1	2304
	11th to 20th	Night	58% 4 8% 18% 11% 1	2099
	21st to end	Night	60% 4 9% 15% 9% 3	1776
March	1st to 10th	Night	49% 4 7% 21% 17% 3	2072
	11th to 20th	Night	50% 6% 10% 21% 11% 2	1980
	21st to end	Night	49% 5% 11% 19% 13% 2	2178
April	1st to 10th	Night	39% 7% 11% 22% 17% 2	1976
	11th to 20th	Night	39% 6% 11% 19% 18% 7%	1669
	21st to end	Night	45% 6% 12% 20% 15% 2	1620
May	1st to 10th	Night	46% 7% 11% 20% 12% 3	1620
	11th to 20th	Night	44% 9% 13% 20% 12% 2	1593
	21st to end	Night	35% 8% 17% 22% 17% 2	1745
June	1st to 10th	Night	32% 9% 15% 24% 16% 4	1620
	11th to 20th	Night	30% 10% 16% 19% 20% 4	1620
	21st to end	Night	31% 10% 15% 25% 15% 4	1620
July	1st to 10th	Night	36% 10% 16% 18% 17% 4	1575
	11th to 20th	Night	30% 10% 16% 23% 17% 4	1566
	21st to end	Night	36% 9% 14% 27% 13% 1	1672
August	1st to 10th	Night	33% 9% 15% 26% 15% 2	1600
	11th to 20th	Night	34% 8% 14% 27% 15% 1	1598
	21st to end	Night	30% 7% 13% 27% 18% 5%	1868
September	1st to 10th	Night	33% 8% 13% 21% 18% 8%	1970
	11th to 20th	Night	32% 6% 12% 22% 24% 3	1980
	21st to end	Night	36% 6% 11% 21% 24% 2	1980
October	1st to 10th	Night	32% 6% 11% 26% 21% 5%	2010
	11th to 20th	Night	38% 5% 9% 23% 21% 4	2160
	21st to end	Night	44% 5% 7% 23% 18% 4	2384
November	1st to 10th	Night	36% 4 8% 23% 23% 5%	2406
	11th to 20th	Night	42% 4 9% 19% 21% 5%	2470
	21st to end	Night	46% 4 9% 24% 15% 2	2470
December	1st to 10th	Night	56% 5% 9% 19% 9% 1	2470
	11th to 20th	Night	54% 4 9% 22% 11% 1	3044
	21st to end	Night	60% 7% 9% 16% 7%	4532

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	27% 20% 34% 14% 4 1	270
	11th to 20th	Day	34% 20% 33% 12%	258
	21st to end	Day	31% 30% 25% 13% 2	264
February	1st to 10th	Day	34% 22% 30% 10% 4	240
	11th to 20th	Day	43% 24% 26% 6%	240
	21st to end	Day	37% 21% 34% 6% 2	198
March	1st to 10th	Day	33% 20% 31% 11% 5%	326
	11th to 20th	Day	26% 20% 33% 16% 5% 1	420
	21st to end	Day	32% 16% 30% 16% 6%	462
April	1st to 10th	Day	22% 18% 30% 21% 8% 1	420
	11th to 20th	Day	22% 17% 31% 18% 9% 3	412
	21st to end	Day	27% 15% 33% 18% 5% 2	420
May	1st to 10th	Day	24% 17% 31% 14% 10% 4	423
	11th to 20th	Day	20% 12% 31% 21% 12% 4	447
	21st to end	Day	14% 9% 22% 27% 17% 11%	485
June	1st to 10th	Day	14% 6% 24% 27% 21% 9%	450
	11th to 20th	Day	13% 7% 25% 28% 18% 9%	450
	21st to end	Day	13% 6% 28% 23% 20% 10%	450
July	1st to 10th	Day	16% 4 15% 24% 20% 21%	445
	11th to 20th	Day	8% 4 23% 30% 20% 14%	444
	21st to end	Day	15% 4 18% 28% 21% 13%	488
August	1st to 10th	Day	14% 3 19% 26% 24% 14%	446
	11th to 20th	Day	15% 5% 15% 33% 23% 10%	439
	21st to end	Day	9% 4 15% 31% 26% 14%	495
September	1st to 10th	Day	14% 4 16% 24% 30% 12%	450
	11th to 20th	Day	13% 4 13% 30% 27% 14%	450
	21st to end	Day	19% 9% 19% 26% 20% 6%	450
October	1st to 10th	Day	14% 6% 26% 27% 20% 7%	450
	11th to 20th	Day	17% 13% 30% 24% 13% 4	450
	21st to end	Day	25% 11% 31% 21% 10% 1	482
November	1st to 10th	Day	17% 13% 33% 26% 9% 2	270
	11th to 20th	Day	24% 17% 29% 20% 8% 2	270
	21st to end	Day	26% 16% 33% 17% 7% 1	270
December	1st to 10th	Day	31% 19% 28% 16% 6% 1	270
	11th to 20th	Day	29% 18% 30% 15% 6% 1	270
	21st to end	Day	31% 21% 32% 14% 2	297
January	1st to 10th	Night	26% 18% 31% 20% 5%	760
	11th to 20th	Night	32% 17% 27% 20% 3	748
	21st to end	Night	24% 19% 33% 20% 3	792
February	1st to 10th	Night	29% 14% 33% 22% 2	720
	11th to 20th	Night	32% 18% 30% 18% 1	703
	21st to end	Night	32% 17% 32% 17% 2	592
March	1st to 10th	Night	25% 17% 31% 23% 5%	720
	11th to 20th	Night	26% 14% 30% 22% 7%	720
	21st to end	Night	20% 15% 32% 26% 8%	792
April	1st to 10th	Night	19% 14% 31% 26% 9%	716
	11th to 20th	Night	16% 11% 31% 27% 13% 1	533
	21st to end	Night	19% 9% 37% 28% 7%	540
May	1st to 10th	Night	19% 10% 28% 27% 14% 2	540
	11th to 20th	Night	18% 7% 22% 34% 18% 1	531
	21st to end	Night	9% 4 20% 35% 29% 4	584
June	1st to 10th	Night	9% 4 21% 41% 22% 3	540
	11th to 20th	Night	8% 3 18% 38% 28% 5%	540
	21st to end	Night	9% 4 21% 36% 28% 2	540
July	1st to 10th	Night	13% 3 13% 32% 30% 9%	525
	11th to 20th	Night	7% 2 14% 36% 36% 5%	522
	21st to end	Night	11% 2 12% 35% 34% 6%	591
August	1st to 10th	Night	10% 1 11% 34% 38% 6%	537
	11th to 20th	Night	10% 3 9% 37% 34% 7%	534
	21st to end	Night	10% 2 10% 35% 34% 9%	594
September	1st to 10th	Night	11% 2 13% 33% 35% 6%	710
	11th to 20th	Night	12% 2 15% 28% 37% 6%	720
	21st to end	Night	15% 4 20% 30% 29% 2	720
October	1st to 10th	Night	14% 5% 17% 32% 28% 4	720
	11th to 20th	Night	18% 8% 27% 28% 17% 2	720
	21st to end	Night	23% 9% 25% 28% 14% 1	792
November	1st to 10th	Night	16% 8% 25% 32% 17% 1	740
	11th to 20th	Night	19% 15% 27% 28% 10% 1	760
	21st to end	Night	23% 12% 25% 29% 10% 1	760
December	1st to 10th	Night	29% 15% 26% 25% 5%	760
	11th to 20th	Night	24% 13% 31% 25% 6% 1	760
	21st to end	Night	29% 16% 27% 25% 4	836

Page generated at 2024-01-14 09:54:59. Version ac07

Copyright 2024 Attilla Danko