Wetzel Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wetzel Observatory clear sky chart from 2005-11-06 to 2024-02-15.

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	17% 7% 3 5% 5% 3 4 5% 5% 7% 39%	78109
	Night	18% 8% 3 5% 5% 3 4 4 5% 7% 38%	80885
Transparency	Day	44% 6% 11% 22% 14% 2	77814
	Night	45% 6% 11% 22% 14% 2	80714
Seeing	Day	23% 15% 30% 21% 9% 2	13905
	Night	22% 12% 31% 26% 8% 1	22885

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	15% 7% 3 5% 5% 3 4 5% 5% 7% 42%	2517
	11th to 20th	Day	16% 8% 3 6% 6% 4 4 4 5% 7% 38%	2520
	21st to end	Day	16% 11% 3 5% 5% 3 4 5% 5% 5% 38%	2772
February	1st to 10th	Day	16% 9% 3 6% 5% 3 4 5% 6% 7% 37%	1672
	11th to 20th	Day	12% 9% 3 6% 6% 4 5% 5% 5% 6% 38%	1788
	21st to end	Day	15% 10% 4 6% 6% 2 6% 5% 5% 5% 35%	1480
March	1st to 10th	Day	15% 8% 2 7% 6% 4 4 5% 5% 7% 36%	1797
	11th to 20th	Day	16% 7% 3 6% 5% 3 4 4 5% 6% 42%	1924
	21st to end	Day	17% 8% 3 5% 5% 3 4 3 4 5% 42%	2254
April	1st to 10th	Day	20% 9% 3 6% 5% 3 4 4 4 7% 36%	2160
	11th to 20th	Day	17% 6% 2 5% 6% 4 4 5% 5% 6% 39%	2208
	21st to end	Day	23% 8% 3 6% 6% 3 4 4 5% 5% 33%	2340
May	1st to 10th	Day	24% 7% 3 5% 5% 3 5% 4 5% 6% 33%	2340
	11th to 20th	Day	18% 6% 3 5% 6% 3 4 4 6% 7% 37%	2361
	21st to end	Day	16% 6% 3 6% 5% 3 4 5% 6% 8% 38%	2725
June	1st to 10th	Day	23% 8% 3 5% 6% 4 5% 4 5% 7% 30%	2520
	11th to 20th	Day	17% 6% 3 6% 4 3 5% 6% 5% 7% 40%	2520
	21st to end	Day	21% 7% 3 5% 5% 3 6% 5% 6% 7% 31%	2520
July	1st to 10th	Day	15% 5% 3 5% 6% 3 5% 6% 6% 8% 38%	2520
	11th to 20th	Day	13% 6% 3 6% 6% 4 6% 5% 7% 9% 35%	2520
	21st to end	Day	13% 5% 3 5% 5% 3 6% 6% 7% 9% 37%	2744
August	1st to 10th	Day	12% 6% 2 5% 6% 4 6% 5% 7% 9% 40%	2368
	11th to 20th	Day	13% 6% 2 5% 6% 3 6% 5% 6% 8% 39%	2304
	21st to end	Day	12% 4 2 4 5% 3 5% 4 7% 8% 47%	2445
September	1st to 10th	Day	13% 4 3 4 4 3 4 5% 6% 8% 48%	2134
	11th to 20th	Day	12% 5% 2 5% 4 2 3 3 4 6% 54%	1980
	21st to end	Day	16% 4 2 4 4 3 4 4 5% 7% 47%	1980
October	1st to 10th	Day	20% 8% 2 4 6% 3 3 4 4 6% 40%	1980
	11th to 20th	Day	18% 8% 2 4 4 2 5% 3 5% 7% 43%	1730
	21st to end	Day	24% 7% 3 5% 5% 3 4 4 4 5% 36%	1782
November	1st to 10th	Day	17% 5% 2 5% 3 2 4 4 5% 7% 46%	1671
	11th to 20th	Day	21% 4 1 4 5% 2 4 5% 6% 6% 42%	1710
	21st to end	Day	22% 8% 2 4 3 2 3 4 5% 7% 40%	1710
December	1st to 10th	Day	21% 9% 3 5% 5% 2 5% 4 4 6% 35%	1454
	11th to 20th	Day	22% 8% 3 4 4 2 4 4 4 5% 40%	1887
	21st to end	Day	25% 11% 3 5% 4 3 4 4 5% 6% 30%	2772
January	1st to 10th	Night	16% 9% 3 5% 4 3 4 4 5% 7% 40%	4429
	11th to 20th	Night	14% 8% 3 7% 6% 4 5% 5% 5% 7% 36%	4440
	21st to end	Night	19% 11% 4 7% 5% 3 5% 5% 4 6% 31%	4884
February	1st to 10th	Night	15% 10% 3 7% 5% 4 5% 5% 5% 7% 35%	2503
	11th to 20th	Night	13% 9% 3 6% 6% 4 5% 5% 5% 5% 40%	2153
	21st to end	Night	14% 8% 3 7% 6% 3 5% 4 5% 7% 39%	1776
March	1st to 10th	Night	14% 11% 3 5% 5% 3 6% 4 5% 5% 39%	2150
	11th to 20th	Night	17% 7% 3 6% 5% 4 4 5% 5% 6% 38%	2034
	21st to end	Night	17% 9% 3 5% 5% 2 4 5% 4 5% 42%	2099
April	1st to 10th	Night	21% 9% 3 5% 5% 3 4 4 4 6% 36%	1800
	11th to 20th	Night	18% 7% 3 6% 5% 3 4 4 5% 7% 37%	1701
	21st to end	Night	23% 7% 3 5% 4 3 4 5% 5% 6% 34%	1620
May	1st to 10th	Night	20% 8% 3 5% 5% 4 4 5% 5% 6% 33%	1620
	11th to 20th	Night	20% 7% 3 5% 5% 3 5% 5% 6% 8% 33%	1547
	21st to end	Night	18% 7% 4 7% 5% 3 5% 4 5% 7% 36%	1550
June	1st to 10th	Night	22% 8% 2 5% 6% 2 4 4 6% 6% 34%	1440
	11th to 20th	Night	18% 6% 3 4 5% 3 5% 5% 4 8% 40%	1440
	21st to end	Night	21% 5% 3 5% 5% 2 5% 5% 5% 9% 36%	1440
July	1st to 10th	Night	15% 5% 2 4 5% 3 5% 6% 6% 9% 39%	1440
	11th to 20th	Night	15% 6% 2 5% 5% 2 3 5% 8% 10% 39%	1440
	21st to end	Night	14% 3 2 4 4 5% 5% 5% 6% 10% 42%	1574
August	1st to 10th	Night	13% 5% 2 4 5% 3 5% 5% 7% 8% 42%	1553
	11th to 20th	Night	13% 7% 2 6% 5% 3 4 6% 5% 10% 39%	1596
	21st to end	Night	15% 5% 2 4 5% 3 4 4 5% 8% 46%	1908
September	1st to 10th	Night	13% 5% 2 3 4 2 4 5% 5% 8% 48%	1826
	11th to 20th	Night	15% 6% 2 3 3 2 3 4 4 6% 51%	1980
	21st to end	Night	15% 5% 2 4 4 3 3 4 5% 7% 47%	1980
October	1st to 10th	Night	19% 6% 2 5% 6% 3 4 5% 5% 6% 39%	1980
	11th to 20th	Night	17% 6% 2 5% 5% 3 4 5% 6% 7% 39%	2229
	21st to end	Night	26% 7% 3 5% 4 2 3 4 5% 6% 35%	2574
November	1st to 10th	Night	16% 6% 3 5% 4 3 4 4 4 7% 44%	2407
	11th to 20th	Night	18% 7% 2 4 4 3 4 5% 5% 6% 43%	2470
	21st to end	Night	17% 7% 2 6% 4 3 4 4 5% 6% 42%	2470
December	1st to 10th	Night	20% 9% 3 6% 6% 3 4 4 4 6% 34%	2660
	11th to 20th	Night	22% 8% 2 5% 4 3 4 4 5% 5% 38%	3288
	21st to end	Night	24% 10% 3 6% 4 3 4 3 4 5% 34%	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	42% 5% 11% 29% 12% 1	2518
	11th to 20th	Day	44% 7% 12% 24% 10% 2	2520
	21st to end	Day	47% 6% 11% 22% 12% 1	2772
February	1st to 10th	Day	47% 5% 12% 19% 14% 3	1672
	11th to 20th	Day	47% 5% 11% 19% 14% 4	1797
	21st to end	Day	50% 5% 9% 18% 14% 4	1480
March	1st to 10th	Day	46% 5% 12% 17% 15% 5%	1800
	11th to 20th	Day	43% 5% 9% 20% 17% 5%	1924
	21st to end	Day	45% 4 8% 17% 19% 6%	2254
April	1st to 10th	Day	48% 5% 8% 18% 16% 4	2160
	11th to 20th	Day	44% 6% 10% 21% 16% 3	2208
	21st to end	Day	52% 6% 9% 15% 14% 4	2340
May	1st to 10th	Day	51% 5% 8% 19% 15% 2	2340
	11th to 20th	Day	46% 5% 9% 20% 17% 3	2365
	21st to end	Day	43% 8% 13% 21% 12% 3	2725
June	1st to 10th	Day	52% 7% 11% 20% 11%	2520
	11th to 20th	Day	43% 6% 11% 20% 17% 3	2520
	21st to end	Day	51% 8% 11% 19% 10% 1	2520
July	1st to 10th	Day	41% 8% 11% 24% 15% 1	2450
	11th to 20th	Day	42% 8% 13% 25% 10% 1	2445
	21st to end	Day	40% 9% 14% 23% 13% 1	2591
August	1st to 10th	Day	39% 8% 16% 26% 11%	2354
	11th to 20th	Day	41% 7% 15% 26% 11% 1	2304
	21st to end	Day	34% 7% 13% 24% 19% 2	2445
September	1st to 10th	Day	33% 8% 13% 27% 18% 1	2134
	11th to 20th	Day	32% 4 9% 29% 23% 3	1980
	21st to end	Day	37% 5% 10% 28% 18% 2	1980
October	1st to 10th	Day	46% 5% 8% 23% 16% 2	1980
	11th to 20th	Day	42% 5% 11% 29% 12% 1	1730
	21st to end	Day	50% 5% 9% 20% 15% 2	1782
November	1st to 10th	Day	38% 4 13% 25% 16% 3	1671
	11th to 20th	Day	40% 5% 10% 21% 20% 3	1710
	21st to end	Day	44% 4 17% 21% 13% 1	1710
December	1st to 10th	Day	51% 4 10% 21% 12% 2	1454
	11th to 20th	Day	46% 4 10% 20% 16% 4	1887
	21st to end	Day	54% 6% 11% 18% 9% 2	2772
January	1st to 10th	Night	42% 6% 13% 26% 11% 2	4429
	11th to 20th	Night	46% 6% 13% 20% 13% 3	4440
	21st to end	Night	52% 6% 9% 20% 12% 2	4884
February	1st to 10th	Night	49% 5% 11% 18% 14% 3	2503
	11th to 20th	Night	46% 4 9% 22% 16% 3	2155
	21st to end	Night	44% 5% 10% 21% 15% 5%	1776
March	1st to 10th	Night	47% 5% 7% 22% 16% 3	2160
	11th to 20th	Night	46% 6% 10% 19% 14% 5%	2035
	21st to end	Night	45% 4 8% 18% 20% 5%	2099
April	1st to 10th	Night	49% 5% 7% 19% 16% 4	1800
	11th to 20th	Night	45% 5% 9% 22% 19% 1	1701
	21st to end	Night	50% 6% 10% 17% 13% 4	1620
May	1st to 10th	Night	51% 5% 9% 20% 13% 2	1620
	11th to 20th	Night	48% 7% 10% 19% 12% 4	1548
	21st to end	Night	49% 5% 13% 19% 12% 1	1551
June	1st to 10th	Night	51% 6% 10% 21% 11% 1	1440
	11th to 20th	Night	43% 6% 13% 20% 15% 2	1440
	21st to end	Night	46% 9% 13% 21% 9% 2	1440
July	1st to 10th	Night	39% 9% 15% 21% 14% 1	1400
	11th to 20th	Night	40% 8% 14% 26% 12%	1392
	21st to end	Night	37% 10% 14% 27% 11% 1	1486
August	1st to 10th	Night	38% 8% 14% 28% 11% 1	1543
	11th to 20th	Night	40% 7% 16% 23% 14%	1596
	21st to end	Night	37% 7% 11% 26% 18% 1	1908
September	1st to 10th	Night	34% 6% 13% 31% 15%	1826
	11th to 20th	Night	35% 5% 10% 29% 19% 2	1980
	21st to end	Night	36% 5% 11% 30% 16% 2	1980
October	1st to 10th	Night	45% 6% 11% 22% 15% 1	1980
	11th to 20th	Night	41% 7% 12% 26% 12% 1	2229
	21st to end	Night	50% 5% 9% 20% 13% 2	2574
November	1st to 10th	Night	41% 4 11% 26% 16% 2	2407
	11th to 20th	Night	41% 4 11% 24% 17% 3	2470
	21st to end	Night	42% 5% 14% 23% 15% 1	2470
December	1st to 10th	Night	51% 5% 10% 22% 11% 1	2660
	11th to 20th	Night	47% 5% 11% 18% 18% 1	3288
	21st to end	Night	54% 5% 10% 21% 11% 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	27% 20% 24% 23% 4 1	180
	11th to 20th	Day	25% 23% 29% 21% 1 2	180
	21st to end	Day	18% 21% 35% 21% 5%	198
February	1st to 10th	Day	28% 18% 35% 17% 2	320
	11th to 20th	Day	24% 23% 36% 15% 2	432
	21st to end	Day	26% 18% 35% 16% 4	346
March	1st to 10th	Day	26% 17% 39% 15% 4	420
	11th to 20th	Day	25% 23% 33% 15% 3 1	420
	21st to end	Day	26% 19% 33% 13% 6% 2	462
April	1st to 10th	Day	29% 22% 28% 14% 6% 1	420
	11th to 20th	Day	26% 22% 29% 16% 5% 2	412
	21st to end	Day	33% 18% 27% 14% 5% 2	420
May	1st to 10th	Day	32% 20% 24% 17% 5% 2	423
	11th to 20th	Day	21% 19% 35% 17% 7% 2	447
	21st to end	Day	22% 16% 31% 23% 8% 1	485
June	1st to 10th	Day	22% 13% 36% 19% 8% 2	450
	11th to 20th	Day	19% 16% 34% 20% 9% 2	450
	21st to end	Day	22% 14% 31% 23% 9% 1	450
July	1st to 10th	Day	18% 9% 30% 27% 11% 3	445
	11th to 20th	Day	16% 5% 35% 28% 12% 5%	444
	21st to end	Day	14% 7% 35% 29% 14% 3	488
August	1st to 10th	Day	12% 10% 29% 29% 17% 3	446
	11th to 20th	Day	16% 10% 25% 29% 14% 6%	439
	21st to end	Day	13% 10% 28% 28% 14% 6%	495
September	1st to 10th	Day	15% 9% 29% 24% 18% 5%	450
	11th to 20th	Day	18% 14% 27% 20% 13% 9%	450
	21st to end	Day	18% 11% 32% 24% 10% 6%	450
October	1st to 10th	Day	25% 13% 22% 24% 13% 4	450
	11th to 20th	Day	20% 16% 32% 20% 11% 2	374
	21st to end	Day	32% 15% 26% 19% 8%	396
November	1st to 10th	Day	22% 16% 30% 22% 8% 2	365
	11th to 20th	Day	29% 16% 29% 20% 5% 1	370
	21st to end	Day	30% 15% 27% 20% 7% 1	370
December	1st to 10th	Day	27% 24% 26% 17% 6%	180
	11th to 20th	Day	31% 17% 33% 15% 4	180
	21st to end	Day	32% 20% 25% 18% 4 1	198
January	1st to 10th	Night	21% 18% 36% 21% 4	760
	11th to 20th	Night	26% 16% 34% 21% 3	760
	21st to end	Night	20% 18% 38% 21% 4	836
February	1st to 10th	Night	24% 15% 35% 23% 3	760
	11th to 20th	Night	21% 17% 39% 21% 2	722
	21st to end	Night	22% 15% 33% 24% 5%	592
March	1st to 10th	Night	24% 16% 37% 21% 2	720
	11th to 20th	Night	24% 15% 35% 20% 6%	720
	21st to end	Night	25% 15% 33% 20% 6% 1	792
April	1st to 10th	Night	28% 14% 31% 23% 4	720
	11th to 20th	Night	22% 14% 36% 23% 5%	637
	21st to end	Night	27% 15% 32% 21% 5%	540
May	1st to 10th	Night	25% 11% 32% 26% 5% 1	540
	11th to 20th	Night	25% 11% 32% 26% 5%	486
	21st to end	Night	23% 8% 23% 36% 9% 1	389
June	1st to 10th	Night	24% 7% 30% 29% 10%	360
	11th to 20th	Night	21% 6% 25% 35% 14%	360
	21st to end	Night	23% 3 24% 39% 11%	360
July	1st to 10th	Night	16% 3 26% 39% 16%	350
	11th to 20th	Night	15% 4 23% 36% 22% 1	348
	21st to end	Night	15% 3 23% 41% 17% 1	394
August	1st to 10th	Night	14% 2 23% 43% 18%	479
	11th to 20th	Night	16% 3 27% 35% 17% 2	532
	21st to end	Night	15% 6% 24% 37% 17% 2	720
September	1st to 10th	Night	15% 3 30% 33% 17% 2	720
	11th to 20th	Night	18% 8% 26% 25% 18% 4	720
	21st to end	Night	19% 8% 29% 27% 16% 1	720
October	1st to 10th	Night	23% 10% 22% 29% 15% 1	720
	11th to 20th	Night	21% 9% 32% 25% 11% 1	720
	21st to end	Night	29% 13% 28% 24% 5%	792
November	1st to 10th	Night	22% 11% 32% 28% 6% 1	740
	11th to 20th	Night	23% 14% 31% 25% 6% 1	760
	21st to end	Night	22% 19% 31% 22% 5% 1	760
December	1st to 10th	Night	26% 11% 38% 19% 5%	760
	11th to 20th	Night	24% 18% 33% 22% 4	760
	21st to end	Night	28% 15% 32% 22% 3	836

Page generated at 2024-02-12 06:35:35. Version ac07

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