Howell Woods
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Howell Woods clear sky chart from 2005-11-06 to 2024-04-03.

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	12% 6% 3 5% 5% 3 5% 5% 6% 7% 43%	78731
	Night	13% 6% 2 5% 5% 3 4 5% 5% 7% 44%	81376
Transparency	Day	39% 6% 11% 21% 18% 4	78452
	Night	38% 6% 11% 20% 20% 5%	81174
Seeing	Day	15% 8% 23% 25% 19% 9%	14543
	Night	15% 7% 25% 33% 18% 2	24991

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% 5% 2 5% 4 3 3 3 3 5% 51%	2836
	11th to 20th	Day	13% 6% 2 5% 4 2 4 4 4 4 52%	2840
	21st to end	Day	15% 9% 3 5% 4 3 4 4 4 4 44%	3124
February	1st to 10th	Day	15% 6% 3 5% 4 3 3 4 5% 7% 45%	1710
	11th to 20th	Day	20% 6% 3 4 4 3 2 3 4 5% 46%	1721
	21st to end	Day	17% 7% 3 5% 5% 4 5% 3 4 5% 42%	1676
March	1st to 10th	Day	15% 5% 2 4 3 3 3 4 4 6% 50%	2090
	11th to 20th	Day	14% 6% 3 5% 5% 3 4 5% 5% 7% 44%	2090
	21st to end	Day	14% 6% 4 6% 6% 3 5% 4 5% 7% 41%	2299
April	1st to 10th	Day	10% 4 2 3 3 3 4 4 4 8% 54%	2139
	11th to 20th	Day	9% 5% 3 5% 4 2 4 5% 6% 8% 50%	2134
	21st to end	Day	12% 5% 3 4 4 3 4 4 5% 6% 50%	2160
May	1st to 10th	Day	9% 6% 3 5% 5% 3 5% 5% 6% 9% 44%	2245
	11th to 20th	Day	12% 6% 3 6% 7% 4 5% 5% 5% 7% 40%	2301
	21st to end	Day	10% 6% 3 6% 6% 3 6% 7% 7% 9% 38%	2531
June	1st to 10th	Day	9% 6% 2 7% 7% 4 6% 6% 7% 9% 37%	2340
	11th to 20th	Day	9% 4 3 5% 6% 4 5% 6% 7% 10% 42%	2340
	21st to end	Day	9% 3 2 6% 6% 4 7% 7% 8% 10% 38%	2340
July	1st to 10th	Day	8% 4 2 7% 7% 4 7% 7% 8% 11% 34%	2340
	11th to 20th	Day	8% 6% 2 6% 7% 4 7% 7% 8% 11% 33%	2340
	21st to end	Day	6% 5% 3 6% 7% 5% 7% 6% 10% 11% 34%	2547
August	1st to 10th	Day	10% 7% 3 7% 7% 5% 6% 8% 7% 11% 30%	2327
	11th to 20th	Day	10% 7% 3 8% 7% 5% 7% 7% 8% 9% 31%	2188
	21st to end	Day	11% 5% 3 7% 6% 4 6% 5% 7% 12% 33%	2376
September	1st to 10th	Day	8% 4 2 5% 6% 4 6% 6% 7% 9% 42%	2160
	11th to 20th	Day	14% 6% 3 5% 5% 3 5% 4 5% 7% 42%	2090
	21st to end	Day	17% 7% 4 5% 6% 2 5% 5% 5% 6% 37%	1913
October	1st to 10th	Day	16% 6% 2 5% 3 3 3 3 5% 6% 48%	1800
	11th to 20th	Day	12% 5% 2 5% 4 2 3 4 4 6% 54%	1800
	21st to end	Day	12% 5% 2 5% 5% 3 3 3 3 6% 55%	1980
November	1st to 10th	Day	13% 6% 2 4 4 2 3 3 4 6% 53%	1857
	11th to 20th	Day	15% 4 2 4 5% 2 3 4 5% 6% 51%	1900
	21st to end	Day	14% 4 2 4 4 3 3 3 6% 6% 51%	1597
December	1st to 10th	Day	16% 6% 2 6% 4 4 5% 4 5% 7% 41%	1520
	11th to 20th	Day	16% 5% 2 3 4 2 2 2 3 5% 55%	1956
	21st to end	Day	15% 7% 4 5% 5% 3 3 4 4 7% 42%	3124
January	1st to 10th	Night	15% 6% 2 4 4 3 4 4 5% 6% 47%	4109
	11th to 20th	Night	14% 7% 3 6% 5% 3 4 4 5% 6% 43%	4120
	21st to end	Night	16% 7% 3 5% 5% 3 4 4 4 6% 44%	4532
February	1st to 10th	Night	17% 6% 2 5% 4 2 5% 4 5% 6% 45%	2470
	11th to 20th	Night	19% 6% 3 4 4 2 4 4 4 6% 42%	2342
	21st to end	Night	16% 6% 3 3 4 2 4 4 5% 7% 46%	1775
March	1st to 10th	Night	14% 6% 3 5% 4 2 3 4 3 5% 51%	2090
	11th to 20th	Night	16% 5% 2 6% 5% 3 5% 4 5% 7% 42%	2090
	21st to end	Night	14% 6% 2 4 5% 2 4 5% 6% 6% 45%	2299
April	1st to 10th	Night	13% 4 3 5% 5% 2 4 5% 5% 7% 48%	1864
	11th to 20th	Night	10% 5% 2 4 5% 3 5% 5% 5% 7% 49%	1775
	21st to end	Night	11% 4 2 4 5% 3 5% 4 5% 8% 50%	1800
May	1st to 10th	Night	9% 5% 2 5% 5% 3 6% 5% 5% 10% 45%	1728
	11th to 20th	Night	13% 6% 2 6% 5% 4 4 5% 5% 9% 40%	1592
	21st to end	Night	10% 6% 2 5% 5% 4 5% 5% 7% 10% 42%	1744
June	1st to 10th	Night	9% 5% 3 5% 5% 4 5% 6% 8% 11% 39%	1620
	11th to 20th	Night	10% 4 2 6% 6% 3 6% 5% 7% 11% 38%	1620
	21st to end	Night	7% 4 3 7% 6% 5% 5% 7% 8% 11% 37%	1620
July	1st to 10th	Night	7% 7% 3 6% 6% 5% 5% 7% 8% 12% 34%	1620
	11th to 20th	Night	7% 4 2 6% 5% 4 7% 7% 9% 12% 37%	1620
	21st to end	Night	7% 6% 2 7% 6% 4 6% 7% 9% 11% 36%	1771
August	1st to 10th	Night	8% 7% 3 8% 7% 3 5% 6% 7% 11% 34%	1611
	11th to 20th	Night	10% 6% 2 7% 8% 5% 6% 6% 9% 10% 31%	1694
	21st to end	Night	10% 6% 2 6% 6% 4 5% 7% 8% 11% 37%	1980
September	1st to 10th	Night	11% 5% 3 5% 5% 4 5% 6% 5% 9% 44%	1800
	11th to 20th	Night	13% 6% 3 5% 6% 2 4 4 7% 8% 42%	1865
	21st to end	Night	19% 6% 4 6% 5% 4 4 4 4 6% 37%	2046
October	1st to 10th	Night	13% 6% 2 4 4 2 3 4 5% 7% 50%	2160
	11th to 20th	Night	13% 5% 2 4 5% 2 3 4 4 5% 54%	2160
	21st to end	Night	11% 5% 2 4 4 2 3 3 5% 6% 56%	2376
November	1st to 10th	Night	13% 6% 2 5% 4 2 4 3 4 5% 53%	2221
	11th to 20th	Night	13% 5% 3 5% 3 2 4 4 5% 5% 50%	2280
	21st to end	Night	13% 4 3 4 4 2 3 4 5% 8% 50%	2571
December	1st to 10th	Night	16% 7% 4 6% 4 3 3 4 5% 6% 41%	2660
	11th to 20th	Night	17% 6% 2 4 3 2 3 3 4 5% 48%	3219
	21st to end	Night	15% 6% 2 5% 4 2 4 4 4 6% 47%	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	38% 3 7% 23% 24% 6%	2837
	11th to 20th	Day	36% 4 5% 17% 30% 7%	2840
	21st to end	Day	44% 4 6% 16% 20% 9%	3124
February	1st to 10th	Day	40% 4 10% 21% 20% 6%	1710
	11th to 20th	Day	42% 4 5% 18% 24% 7%	1730
	21st to end	Day	44% 4 9% 17% 19% 7%	1676
March	1st to 10th	Day	36% 4 9% 21% 22% 7%	2090
	11th to 20th	Day	39% 7% 9% 20% 18% 7%	2090
	21st to end	Day	43% 6% 11% 17% 19% 4	2299
April	1st to 10th	Day	30% 4 11% 23% 24% 7%	2139
	11th to 20th	Day	33% 5% 11% 23% 21% 7%	2134
	21st to end	Day	34% 7% 12% 23% 20% 5%	2160
May	1st to 10th	Day	35% 8% 14% 22% 17% 3	2245
	11th to 20th	Day	43% 7% 13% 23% 13% 2	2305
	21st to end	Day	39% 11% 14% 22% 14% 1	2531
June	1st to 10th	Day	41% 8% 14% 21% 15% 1	2340
	11th to 20th	Day	35% 8% 17% 24% 14% 2	2340
	21st to end	Day	38% 10% 17% 21% 13% 2	2340
July	1st to 10th	Day	40% 9% 17% 21% 11% 3	2275
	11th to 20th	Day	40% 10% 20% 20% 9% 2	2271
	21st to end	Day	39% 11% 19% 21% 9% 1	2405
August	1st to 10th	Day	45% 10% 17% 18% 9%	2314
	11th to 20th	Day	45% 11% 16% 17% 10% 1	2188
	21st to end	Day	42% 9% 17% 20% 9% 3	2376
September	1st to 10th	Day	37% 9% 15% 19% 16% 4	2160
	11th to 20th	Day	40% 6% 11% 19% 20% 4	2090
	21st to end	Day	48% 5% 10% 18% 15% 4	1913
October	1st to 10th	Day	38% 4 10% 22% 24% 3	1800
	11th to 20th	Day	33% 4 9% 26% 23% 6%	1800
	21st to end	Day	34% 4 6% 22% 27% 9%	1980
November	1st to 10th	Day	34% 3 7% 22% 26% 8%	1857
	11th to 20th	Day	35% 4 8% 20% 26% 8%	1900
	21st to end	Day	34% 3 8% 24% 24% 7%	1597
December	1st to 10th	Day	43% 5% 11% 19% 17% 4	1520
	11th to 20th	Day	35% 3 7% 24% 23% 8%	1952
	21st to end	Day	41% 4 9% 22% 22% 2	3124
January	1st to 10th	Night	38% 4 7% 20% 27% 5%	4109
	11th to 20th	Night	42% 4 8% 15% 25% 6%	4120
	21st to end	Night	42% 4 7% 17% 22% 8%	4532
February	1st to 10th	Night	41% 3 8% 21% 20% 7%	2470
	11th to 20th	Night	44% 4 9% 15% 21% 7%	2344
	21st to end	Night	39% 5% 9% 18% 21% 8%	1775
March	1st to 10th	Night	37% 4 8% 20% 22% 9%	2090
	11th to 20th	Night	41% 6% 10% 16% 20% 7%	2090
	21st to end	Night	38% 6% 12% 20% 19% 5%	2299
April	1st to 10th	Night	36% 5% 9% 18% 24% 8%	1864
	11th to 20th	Night	34% 6% 10% 22% 20% 7%	1775
	21st to end	Night	32% 7% 12% 26% 19% 5%	1800
May	1st to 10th	Night	35% 7% 14% 23% 18% 4	1728
	11th to 20th	Night	40% 8% 15% 22% 16% 1	1593
	21st to end	Night	36% 9% 16% 25% 13% 1	1745
June	1st to 10th	Night	36% 9% 19% 21% 12% 1	1620
	11th to 20th	Night	38% 10% 18% 20% 13% 1	1620
	21st to end	Night	39% 10% 17% 20% 11% 2	1620
July	1st to 10th	Night	39% 13% 16% 20% 10% 2	1575
	11th to 20th	Night	33% 13% 25% 20% 8% 2	1566
	21st to end	Night	36% 13% 21% 21% 9% 1	1672
August	1st to 10th	Night	41% 12% 21% 21% 6%	1600
	11th to 20th	Night	43% 12% 20% 17% 7% 1	1694
	21st to end	Night	37% 12% 18% 21% 9% 2	1980
September	1st to 10th	Night	37% 9% 15% 19% 15% 5%	1800
	11th to 20th	Night	39% 7% 12% 19% 19% 3	1865
	21st to end	Night	48% 5% 12% 16% 16% 3	2046
October	1st to 10th	Night	34% 5% 10% 22% 24% 4	2160
	11th to 20th	Night	33% 4 9% 22% 24% 8%	2160
	21st to end	Night	29% 4 9% 22% 26% 10%	2376
November	1st to 10th	Night	35% 4 6% 18% 28% 9%	2221
	11th to 20th	Night	36% 5% 9% 15% 25% 11%	2280
	21st to end	Night	33% 4 7% 22% 26% 8%	2571
December	1st to 10th	Night	44% 5% 10% 17% 18% 5%	2660
	11th to 20th	Night	39% 3 7% 19% 24% 7%	3222
	21st to end	Night	39% 3 7% 23% 25% 3	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	18% 18% 41% 18% 5%	270
	11th to 20th	Day	19% 23% 34% 17% 7%	270
	21st to end	Day	20% 19% 38% 17% 5%	297
February	1st to 10th	Day	20% 13% 40% 21% 4 1	270
	11th to 20th	Day	31% 14% 34% 18% 3	328
	21st to end	Day	23% 18% 31% 22% 5% 1	382
March	1st to 10th	Day	18% 17% 32% 25% 7% 1	460
	11th to 20th	Day	19% 17% 37% 20% 7% 1	460
	21st to end	Day	19% 12% 36% 22% 9% 1	506
April	1st to 10th	Day	16% 16% 30% 23% 14% 1	428
	11th to 20th	Day	11% 13% 30% 22% 18% 5%	412
	21st to end	Day	16% 10% 28% 24% 20% 2	420
May	1st to 10th	Day	12% 12% 31% 24% 14% 7%	423
	11th to 20th	Day	14% 7% 19% 27% 24% 10%	447
	21st to end	Day	17% 5% 13% 26% 23% 16%	485
June	1st to 10th	Day	12% 4 17% 31% 25% 12%	450
	11th to 20th	Day	12% 2 16% 24% 27% 19%	450
	21st to end	Day	10% 3 12% 29% 33% 13%	450
July	1st to 10th	Day	9% 3 9% 24% 33% 22%	445
	11th to 20th	Day	10% 3 8% 22% 36% 22%	444
	21st to end	Day	8% 2 8% 31% 36% 15%	488
August	1st to 10th	Day	12% 3 13% 22% 29% 21%	446
	11th to 20th	Day	13% 3 8% 22% 29% 24%	439
	21st to end	Day	12% 3 9% 27% 26% 24%	495
September	1st to 10th	Day	10% 3 14% 24% 26% 23%	450
	11th to 20th	Day	17% 2 13% 25% 28% 14%	450
	21st to end	Day	21% 4 19% 26% 23% 8%	450
October	1st to 10th	Day	19% 5% 19% 22% 24% 12%	450
	11th to 20th	Day	13% 6% 24% 28% 21% 7%	450
	21st to end	Day	12% 7% 25% 32% 19% 5%	495
November	1st to 10th	Day	16% 7% 27% 29% 15% 5%	455
	11th to 20th	Day	17% 12% 30% 29% 11% 2	460
	21st to end	Day	15% 10% 27% 28% 16% 3	246
December	1st to 10th	Day	21% 10% 39% 21% 9% 1	180
	11th to 20th	Day	21% 10% 34% 21% 12% 3	195
	21st to end	Day	22% 13% 32% 20% 12% 2	297
January	1st to 10th	Night	18% 14% 34% 28% 6%	760
	11th to 20th	Night	18% 12% 33% 30% 7%	760
	21st to end	Night	20% 10% 39% 27% 3	836
February	1st to 10th	Night	20% 10% 38% 28% 4	760
	11th to 20th	Night	22% 16% 39% 22% 2	743
	21st to end	Night	19% 14% 35% 27% 5%	628
March	1st to 10th	Night	16% 13% 35% 31% 5%	760
	11th to 20th	Night	19% 10% 39% 24% 6% 1	760
	21st to end	Night	16% 11% 38% 30% 5%	836
April	1st to 10th	Night	16% 14% 35% 28% 7%	729
	11th to 20th	Night	13% 11% 34% 30% 12% 1	711
	21st to end	Night	14% 6% 32% 37% 11% 1	720
May	1st to 10th	Night	12% 9% 32% 37% 10%	648
	11th to 20th	Night	15% 4 23% 40% 17% 1	531
	21st to end	Night	11% 2 13% 42% 29% 2	584
June	1st to 10th	Night	13% 2 16% 42% 25% 2	540
	11th to 20th	Night	11% 3 14% 38% 30% 4	540
	21st to end	Night	8% 2 14% 43% 30% 3	540
July	1st to 10th	Night	9% 3 7% 37% 38% 5%	525
	11th to 20th	Night	8% 2 5% 37% 43% 6%	522
	21st to end	Night	8% 2 9% 39% 40% 2	591
August	1st to 10th	Night	12% 2 9% 38% 35% 4	537
	11th to 20th	Night	14% 2 10% 31% 36% 6%	630
	21st to end	Night	12% 3 8% 32% 38% 7%	792
September	1st to 10th	Night	13% 3 9% 31% 37% 7%	720
	11th to 20th	Night	15% 3 15% 33% 32% 3	720
	21st to end	Night	22% 4 17% 30% 25% 2	720
October	1st to 10th	Night	14% 3 18% 33% 27% 4	720
	11th to 20th	Night	16% 6% 22% 33% 21% 2	720
	21st to end	Night	14% 6% 25% 33% 20% 2	792
November	1st to 10th	Night	16% 6% 23% 36% 16% 3	740
	11th to 20th	Night	16% 10% 27% 33% 13% 1	760
	21st to end	Night	15% 7% 30% 33% 15% 1	760
December	1st to 10th	Night	19% 11% 31% 33% 6%	760
	11th to 20th	Night	19% 8% 29% 34% 9% 1	760
	21st to end	Night	19% 11% 29% 31% 9%	836

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