McElroy Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McElroy Mountain clear sky chart from 2005-11-06 to 2024-01-14.

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% 6% 3 5% 5% 3 5% 5% 6% 7% 39%	74879
	Night	14% 6% 3 5% 5% 3 4 5% 5% 7% 43%	74897
Transparency	Day	42% 8% 12% 18% 17% 4	74602
	Night	38% 7% 12% 19% 18% 5%	74693
Seeing	Day	19% 11% 23% 23% 16% 8%	13734
	Night	17% 10% 23% 28% 19% 3	23833

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	22% 7% 3 5% 4 2 4 3 3 5% 41%	1706
	11th to 20th	Day	22% 7% 3 5% 4 3 4 4 4 5% 41%	1647
	21st to end	Day	18% 7% 3 6% 4 3 3 3 4 4 45%	1839
February	1st to 10th	Day	21% 8% 3 5% 5% 3 4 5% 5% 5% 37%	1800
	11th to 20th	Day	26% 6% 2 4 4 2 3 4 4 6% 39%	1748
	21st to end	Day	25% 8% 3 5% 4 2 3 4 4 5% 37%	1480
March	1st to 10th	Day	17% 4 2 5% 5% 3 5% 4 5% 6% 43%	1845
	11th to 20th	Day	20% 7% 3 5% 6% 3 4 5% 6% 6% 36%	1980
	21st to end	Day	15% 7% 4 6% 6% 3 5% 5% 6% 7% 37%	2178
April	1st to 10th	Day	13% 6% 2 5% 4 3 6% 6% 6% 7% 42%	2042
	11th to 20th	Day	14% 6% 3 6% 6% 3 4 4 5% 5% 45%	2134
	21st to end	Day	13% 4 2 4 4 3 5% 5% 6% 8% 46%	2311
May	1st to 10th	Day	12% 5% 3 4 5% 4 5% 4 5% 9% 44%	2340
	11th to 20th	Day	12% 6% 3 7% 6% 4 5% 5% 6% 8% 37%	2301
	21st to end	Day	12% 5% 2 5% 7% 4 6% 6% 7% 8% 38%	2531
June	1st to 10th	Day	12% 6% 3 6% 6% 4 7% 6% 7% 10% 32%	2340
	11th to 20th	Day	6% 4 2 6% 6% 4 7% 8% 8% 11% 38%	2340
	21st to end	Day	8% 5% 2 5% 7% 5% 7% 8% 8% 10% 34%	2340
July	1st to 10th	Day	9% 7% 4 6% 7% 5% 8% 8% 7% 10% 29%	2340
	11th to 20th	Day	9% 6% 4 6% 8% 7% 8% 8% 9% 11% 25%	2340
	21st to end	Day	7% 6% 3 8% 8% 5% 8% 8% 8% 10% 28%	2547
August	1st to 10th	Day	8% 6% 3 7% 8% 5% 8% 8% 8% 10% 29%	2327
	11th to 20th	Day	12% 6% 3 7% 7% 5% 7% 6% 7% 9% 31%	2177
	21st to end	Day	14% 7% 3 7% 8% 5% 6% 7% 7% 8% 28%	2376
September	1st to 10th	Day	11% 7% 3 6% 6% 3 6% 6% 7% 8% 37%	1994
	11th to 20th	Day	14% 5% 3 6% 5% 3 5% 6% 6% 7% 40%	1980
	21st to end	Day	13% 5% 2 5% 5% 3 5% 4 5% 7% 46%	1980
October	1st to 10th	Day	12% 5% 2 4 4 3 4 4 5% 6% 53%	1980
	11th to 20th	Day	13% 5% 2 3 4 2 3 4 4 6% 54%	1877
	21st to end	Day	15% 5% 2 4 3 2 3 3 4 5% 53%	1980
November	1st to 10th	Day	14% 4 2 4 3 2 3 3 4 6% 55%	1672
	11th to 20th	Day	15% 5% 2 4 3 3 4 3 5% 5% 51%	1710
	21st to end	Day	17% 6% 2 5% 5% 3 4 4 4 7% 44%	1710
December	1st to 10th	Day	25% 7% 3 3 4 2 5% 3 5% 6% 36%	1710
	11th to 20th	Day	18% 6% 3 5% 5% 3 4 3 4 5% 43%	2153
	21st to end	Day	22% 7% 6% 4 4 3 5% 5% 5% 6% 33%	3124
January	1st to 10th	Night	21% 6% 3 4 4 2 4 4 4 5% 42%	2459
	11th to 20th	Night	19% 7% 4 5% 4 2 5% 4 5% 6% 37%	2391
	21st to end	Night	18% 7% 4 5% 4 2 3 3 4 5% 45%	2516
February	1st to 10th	Night	17% 6% 4 5% 5% 2 4 4 5% 6% 42%	2160
	11th to 20th	Night	22% 7% 3 6% 4 2 3 4 4 5% 40%	2098
	21st to end	Night	24% 7% 3 5% 5% 2 4 4 5% 5% 36%	1776
March	1st to 10th	Night	16% 5% 2 4 4 2 4 6% 4 6% 47%	2113
	11th to 20th	Night	16% 6% 3 5% 5% 3 4 5% 6% 6% 41%	1980
	21st to end	Night	15% 6% 3 5% 6% 3 5% 4 5% 6% 43%	2178
April	1st to 10th	Night	13% 4 2 5% 3 3 4 5% 6% 7% 48%	1931
	11th to 20th	Night	14% 7% 2 5% 3 2 3 5% 4 7% 49%	1775
	21st to end	Night	11% 6% 2 4 4 3 4 4 6% 7% 50%	1648
May	1st to 10th	Night	12% 3 2 4 5% 2 4 5% 5% 8% 50%	1620
	11th to 20th	Night	11% 6% 2 6% 5% 3 5% 5% 5% 9% 41%	1592
	21st to end	Night	11% 6% 2 6% 5% 2 6% 5% 5% 10% 43%	1744
June	1st to 10th	Night	9% 5% 3 6% 8% 4 6% 6% 7% 9% 37%	1620
	11th to 20th	Night	6% 3 2 4 5% 3 5% 7% 7% 13% 43%	1620
	21st to end	Night	6% 4 2 5% 6% 3 7% 5% 8% 11% 43%	1620
July	1st to 10th	Night	9% 6% 2 5% 6% 5% 6% 7% 9% 10% 35%	1620
	11th to 20th	Night	8% 4 2 5% 6% 4 7% 8% 8% 12% 36%	1620
	21st to end	Night	7% 5% 2 6% 6% 5% 7% 6% 10% 11% 36%	1771
August	1st to 10th	Night	9% 4 2 5% 7% 4 6% 6% 8% 12% 37%	1611
	11th to 20th	Night	10% 6% 3 7% 7% 3 4 6% 5% 10% 39%	1720
	21st to end	Night	14% 7% 3 5% 5% 4 5% 5% 7% 9% 34%	1980
September	1st to 10th	Night	9% 6% 3 6% 6% 4 6% 6% 6% 8% 42%	1948
	11th to 20th	Night	13% 5% 2 4 4 3 5% 5% 7% 8% 44%	1980
	21st to end	Night	11% 6% 2 4 4 2 3 5% 5% 6% 52%	1980
October	1st to 10th	Night	13% 4 2 4 3 2 3 3 4 5% 59%	1980
	11th to 20th	Night	12% 4 2 5% 4 2 4 4 4 5% 54%	2082
	21st to end	Night	14% 5% 2 4 4 2 3 3 4 6% 54%	2376
November	1st to 10th	Night	13% 5% 2 3 4 2 3 3 4 6% 56%	2404
	11th to 20th	Night	14% 5% 3 4 3 2 3 4 4 6% 52%	2470
	21st to end	Night	17% 6% 2 4 4 3 4 4 6% 6% 44%	2470
December	1st to 10th	Night	21% 8% 3 6% 3 3 4 4 5% 6% 37%	2470
	11th to 20th	Night	17% 8% 3 5% 3 3 3 3 4 5% 46%	3042
	21st to end	Night	21% 7% 4 6% 5% 3 4 5% 5% 7% 32%	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	45% 5% 7% 18% 21% 5%	1707
	11th to 20th	Day	45% 4 8% 18% 20% 5%	1647
	21st to end	Day	42% 4 6% 21% 20% 7%	1839
February	1st to 10th	Day	48% 4 9% 16% 18% 4	1800
	11th to 20th	Day	47% 4 8% 18% 18% 5%	1758
	21st to end	Day	49% 4 7% 14% 19% 7%	1480
March	1st to 10th	Day	39% 6% 10% 15% 21% 9%	1845
	11th to 20th	Day	48% 5% 10% 15% 17% 5%	1980
	21st to end	Day	46% 6% 10% 20% 16% 3	2178
April	1st to 10th	Day	39% 7% 10% 21% 18% 5%	2042
	11th to 20th	Day	40% 5% 8% 17% 23% 7%	2134
	21st to end	Day	34% 7% 12% 26% 18% 3	2311
May	1st to 10th	Day	37% 6% 13% 22% 18% 4	2340
	11th to 20th	Day	42% 10% 13% 20% 13% 1	2305
	21st to end	Day	39% 10% 14% 21% 15% 2	2531
June	1st to 10th	Day	44% 11% 16% 19% 9% 1	2340
	11th to 20th	Day	35% 13% 19% 21% 10% 1	2340
	21st to end	Day	39% 12% 17% 18% 11% 2	2340
July	1st to 10th	Day	45% 13% 18% 16% 7% 1	2275
	11th to 20th	Day	46% 15% 18% 11% 7% 3	2271
	21st to end	Day	44% 15% 19% 15% 7%	2405
August	1st to 10th	Day	44% 14% 18% 18% 4 1	2314
	11th to 20th	Day	46% 11% 16% 16% 9% 1	2177
	21st to end	Day	50% 12% 14% 14% 8% 2	2376
September	1st to 10th	Day	42% 9% 14% 15% 15% 4	1994
	11th to 20th	Day	42% 8% 12% 16% 19% 1	1980
	21st to end	Day	37% 6% 12% 17% 21% 7%	1980
October	1st to 10th	Day	33% 7% 9% 16% 27% 8%	1980
	11th to 20th	Day	30% 5% 10% 22% 22% 10%	1877
	21st to end	Day	34% 4 6% 19% 27% 10%	1980
November	1st to 10th	Day	32% 3 7% 15% 33% 10%	1672
	11th to 20th	Day	35% 4 8% 18% 25% 11%	1710
	21st to end	Day	40% 4 7% 16% 25% 7%	1710
December	1st to 10th	Day	49% 4 8% 17% 17% 6%	1710
	11th to 20th	Day	43% 4 7% 15% 23% 7%	2150
	21st to end	Day	45% 8% 9% 19% 16% 3	3124
January	1st to 10th	Night	44% 5% 8% 17% 22% 5%	2459
	11th to 20th	Night	46% 6% 10% 16% 17% 5%	2391
	21st to end	Night	42% 4 5% 21% 24% 5%	2516
February	1st to 10th	Night	42% 5% 9% 19% 19% 6%	2160
	11th to 20th	Night	46% 5% 7% 17% 19% 6%	2099
	21st to end	Night	49% 5% 8% 14% 17% 7%	1776
March	1st to 10th	Night	38% 6% 8% 17% 20% 11%	2113
	11th to 20th	Night	41% 8% 11% 17% 19% 5%	1980
	21st to end	Night	43% 5% 9% 22% 18% 3	2178
April	1st to 10th	Night	33% 6% 12% 19% 24% 6%	1931
	11th to 20th	Night	35% 5% 8% 21% 21% 10%	1775
	21st to end	Night	32% 6% 12% 26% 20% 3	1648
May	1st to 10th	Night	33% 8% 13% 22% 21% 3	1620
	11th to 20th	Night	38% 9% 18% 22% 12% 1	1593
	21st to end	Night	36% 9% 13% 26% 13% 3	1745
June	1st to 10th	Night	40% 11% 18% 20% 10% 2	1620
	11th to 20th	Night	29% 12% 24% 22% 12% 1	1620
	21st to end	Night	32% 13% 19% 21% 12% 4	1620
July	1st to 10th	Night	40% 12% 19% 17% 11% 1	1575
	11th to 20th	Night	36% 14% 24% 16% 8% 3	1566
	21st to end	Night	36% 14% 20% 20% 7% 2	1672
August	1st to 10th	Night	36% 14% 22% 21% 6% 1	1600
	11th to 20th	Night	40% 12% 17% 17% 13% 1	1720
	21st to end	Night	43% 11% 15% 17% 11% 2	1980
September	1st to 10th	Night	37% 10% 15% 17% 15% 5%	1948
	11th to 20th	Night	37% 10% 15% 17% 20% 2	1980
	21st to end	Night	32% 8% 12% 21% 19% 8%	1980
October	1st to 10th	Night	29% 6% 11% 18% 29% 7%	1980
	11th to 20th	Night	33% 5% 9% 21% 22% 10%	2082
	21st to end	Night	32% 4 6% 20% 27% 11%	2376
November	1st to 10th	Night	30% 5% 8% 19% 27% 11%	2404
	11th to 20th	Night	32% 5% 7% 18% 26% 12%	2470
	21st to end	Night	39% 6% 7% 18% 23% 7%	2470
December	1st to 10th	Night	46% 6% 9% 18% 17% 5%	2470
	11th to 20th	Night	39% 5% 9% 16% 25% 6%	3044
	21st to end	Night	47% 7% 9% 21% 13% 2	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	32% 23% 34% 10% 1	270
	11th to 20th	Day	33% 20% 28% 15% 4	249
	21st to end	Day	28% 28% 31% 10% 2 1	264
February	1st to 10th	Day	30% 24% 37% 9% 1	240
	11th to 20th	Day	45% 23% 27% 5%	240
	21st to end	Day	44% 20% 29% 6% 1	198
March	1st to 10th	Day	28% 19% 34% 15% 5%	285
	11th to 20th	Day	29% 20% 26% 19% 5% 1	420
	21st to end	Day	23% 19% 34% 18% 6%	462
April	1st to 10th	Day	24% 14% 28% 24% 9% 2	420
	11th to 20th	Day	17% 19% 31% 22% 11% 1	412
	21st to end	Day	20% 13% 28% 22% 15% 3	420
May	1st to 10th	Day	17% 13% 30% 22% 13% 5%	423
	11th to 20th	Day	14% 10% 23% 26% 18% 9%	447
	21st to end	Day	16% 7% 16% 30% 19% 12%	485
June	1st to 10th	Day	16% 4 20% 28% 20% 12%	450
	11th to 20th	Day	7% 6% 18% 27% 24% 20%	450
	21st to end	Day	10% 5% 21% 28% 22% 14%	450
July	1st to 10th	Day	12% 3 10% 27% 28% 20%	445
	11th to 20th	Day	9% 2 11% 25% 32% 20%	444
	21st to end	Day	7% 2 11% 26% 31% 23%	488
August	1st to 10th	Day	13% 4 17% 25% 22% 20%	446
	11th to 20th	Day	14% 3 12% 28% 29% 15%	439
	21st to end	Day	16% 4 13% 22% 32% 14%	495
September	1st to 10th	Day	10% 5% 16% 29% 27% 12%	450
	11th to 20th	Day	15% 5% 15% 26% 29% 9%	450
	21st to end	Day	13% 4 21% 27% 26% 8%	450
October	1st to 10th	Day	17% 6% 24% 29% 16% 9%	450
	11th to 20th	Day	17% 10% 25% 28% 17% 3	450
	21st to end	Day	20% 12% 26% 26% 13% 3	495
November	1st to 10th	Day	20% 14% 26% 27% 10% 3	270
	11th to 20th	Day	21% 21% 35% 19% 4 1	270
	21st to end	Day	17% 19% 37% 21% 4 1	270
December	1st to 10th	Day	35% 20% 26% 16% 2 1	270
	11th to 20th	Day	27% 19% 33% 18% 4	270
	21st to end	Day	35% 17% 30% 14% 2 1	297
January	1st to 10th	Night	28% 19% 27% 22% 4	760
	11th to 20th	Night	24% 18% 28% 22% 7%	736
	21st to end	Night	22% 18% 34% 23% 2	792
February	1st to 10th	Night	22% 15% 31% 27% 6%	720
	11th to 20th	Night	28% 17% 32% 20% 2	703
	21st to end	Night	26% 19% 34% 19% 3	592
March	1st to 10th	Night	19% 19% 31% 26% 4	720
	11th to 20th	Night	20% 15% 33% 24% 8% 1	720
	21st to end	Night	20% 15% 28% 28% 9%	792
April	1st to 10th	Night	17% 14% 28% 29% 11%	671
	11th to 20th	Night	16% 14% 26% 30% 13% 1	533
	21st to end	Night	14% 7% 25% 35% 18% 1	540
May	1st to 10th	Night	12% 10% 24% 31% 22% 1	540
	11th to 20th	Night	15% 6% 19% 32% 24% 5%	531
	21st to end	Night	14% 4 12% 30% 34% 6%	584
June	1st to 10th	Night	10% 2 14% 36% 33% 5%	540
	11th to 20th	Night	6% 3 13% 29% 36% 14%	540
	21st to end	Night	6% 2 10% 38% 37% 8%	540
July	1st to 10th	Night	9% 2 8% 27% 42% 12%	525
	11th to 20th	Night	8% 2 9% 23% 45% 13%	522
	21st to end	Night	8% 1 8% 27% 45% 12%	591
August	1st to 10th	Night	11% 2 8% 25% 43% 11%	537
	11th to 20th	Night	10% 3 12% 26% 41% 8%	534
	21st to end	Night	15% 3 11% 24% 37% 9%	594
September	1st to 10th	Night	11% 3 12% 27% 38% 9%	688
	11th to 20th	Night	13% 3 16% 29% 36% 3	720
	21st to end	Night	13% 5% 16% 35% 29% 2	720
October	1st to 10th	Night	15% 4 23% 29% 22% 6%	720
	11th to 20th	Night	13% 8% 26% 32% 18% 3	720
	21st to end	Night	16% 10% 22% 33% 16% 2	792
November	1st to 10th	Night	17% 8% 25% 29% 20% 2	740
	11th to 20th	Night	16% 14% 27% 29% 11% 2	760
	21st to end	Night	21% 14% 25% 28% 12% 1	760
December	1st to 10th	Night	25% 16% 25% 25% 7% 1	760
	11th to 20th	Night	22% 13% 29% 27% 7% 1	760
	21st to end	Night	30% 13% 27% 25% 5%	836

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