Monsey Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Monsey Observatory clear sky chart from 2005-11-05 to 2024-10-14.

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	17% 7% 2 6% 4 4 4 4 6% 7% 39%	101126
	Night	18% 7% 2 6% 4 4 4 3 5% 6% 41%	97436
Transparency	Day	24% 48% 6% 13% 8% 1	100882
	Night	23% 49% 6% 13% 8% 1	97305
Seeing	Day	21% 16% 30% 22% 10% 3	14897
	Night	20% 12% 30% 27% 9% 1	24003

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% 8% 2 5% 4 3 4 3 5% 6% 46%	2517
	11th to 20th	Day	15% 9% 3 6% 6% 6% 5% 4 5% 5% 35%	2520
	21st to end	Day	22% 11% 4 8% 4 4 4 3 5% 4 32%	2996
February	1st to 10th	Day	17% 7% 3 7% 5% 5% 4 4 5% 8% 36%	1710
	11th to 20th	Day	15% 7% 2 6% 5% 4 4 3 5% 5% 43%	1848
	21st to end	Day	19% 9% 2 5% 5% 3 4 4 5% 6% 38%	1570
March	1st to 10th	Day	27% 8% 2 6% 4 3 4 3 4 5% 35%	3116
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 4 7% 8% 43%	3338
	21st to end	Day	20% 7% 2 6% 3 4 3 3 4 5% 42%	4133
April	1st to 10th	Day	19% 8% 2 5% 4 4 4 4 5% 7% 38%	2280
	11th to 20th	Day	17% 7% 2 6% 4 4 4 3 5% 7% 41%	2254
	21st to end	Day	20% 6% 2 5% 4 4 4 4 6% 6% 39%	2308
May	1st to 10th	Day	28% 8% 3 5% 3 3 3 3 5% 8% 30%	4106
	11th to 20th	Day	23% 8% 3 8% 5% 4 4 4 5% 7% 30%	4390
	21st to end	Day	14% 5% 2 5% 4 4 4 4 5% 10% 43%	4837
June	1st to 10th	Day	17% 7% 2 5% 5% 4 5% 4 7% 9% 36%	2660
	11th to 20th	Day	16% 7% 2 6% 4 4 6% 4 7% 8% 35%	2660
	21st to end	Day	13% 6% 2 7% 4 5% 5% 4 7% 9% 38%	2660
July	1st to 10th	Day	11% 6% 2 8% 5% 6% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	11% 7% 2 6% 4 5% 6% 4 7% 10% 37%	4440
	21st to end	Day	15% 8% 3 9% 6% 5% 5% 5% 6% 7% 32%	4814
August	1st to 10th	Day	21% 6% 2 7% 5% 5% 5% 4 6% 7% 31%	4208
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 6% 9% 40%	3730
	21st to end	Day	12% 6% 2 6% 4 4 4 3 6% 9% 46%	4180
September	1st to 10th	Day	15% 5% 2 7% 5% 5% 5% 4 5% 6% 42%	2280
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 5% 7% 49%	2199
	21st to end	Day	18% 6% 3 7% 4 4 4 4 6% 6% 40%	2090
October	1st to 10th	Day	22% 6% 2 5% 3 4 4 3 5% 6% 41%	1981
	11th to 20th	Day	16% 5% 2 5% 3 4 4 3 5% 7% 46%	1830
	21st to end	Day	23% 5% 2 4 4 4 4 3 5% 7% 39%	1832
November	1st to 10th	Day	15% 6% 3 4 3 3 3 3 5% 6% 51%	1671
	11th to 20th	Day	19% 6% 1 4 3 3 3 4 5% 6% 46%	1710
	21st to end	Day	16% 7% 2 4 4 4 4 4 6% 7% 43%	1620
December	1st to 10th	Day	19% 8% 3 5% 4 4 3 3 6% 6% 37%	1520
	11th to 20th	Day	22% 6% 1 5% 3 2 3 3 4 6% 45%	1906
	21st to end	Day	18% 8% 3 8% 5% 6% 5% 4 5% 7% 31%	2772
January	1st to 10th	Night	17% 6% 2 5% 3 3 3 3 4 6% 47%	4429
	11th to 20th	Night	16% 7% 3 7% 4 4 4 3 5% 6% 41%	4440
	21st to end	Night	23% 12% 3 5% 3 3 3 3 4 6% 34%	4656
February	1st to 10th	Night	17% 9% 2 6% 4 4 4 3 5% 6% 42%	2468
	11th to 20th	Night	16% 8% 2 6% 4 3 5% 4 5% 5% 42%	2218
	21st to end	Night	18% 8% 3 6% 4 4 4 3 4 5% 41%	1884
March	1st to 10th	Night	24% 9% 2 5% 4 3 4 3 4 6% 35%	3724
	11th to 20th	Night	12% 7% 2 6% 4 4 4 4 5% 7% 46%	3617
	21st to end	Night	18% 10% 3 6% 3 3 3 3 4 5% 42%	3498
April	1st to 10th	Night	18% 8% 3 6% 4 4 5% 4 5% 7% 38%	1900
	11th to 20th	Night	19% 6% 2 6% 4 3 4 3 5% 8% 40%	1875
	21st to end	Night	20% 7% 2 6% 3 3 3 2 5% 6% 42%	1870
May	1st to 10th	Night	27% 8% 3 7% 4 3 4 3 5% 6% 30%	2834
	11th to 20th	Night	24% 9% 3 7% 4 3 3 3 5% 5% 34%	2531
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 8% 42%	2738
June	1st to 10th	Night	17% 6% 2 5% 3 3 6% 4 6% 8% 41%	1520
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 6% 10% 40%	1520
	21st to end	Night	12% 5% 1 6% 5% 4 4 4 7% 9% 44%	1520
July	1st to 10th	Night	11% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	2520
	11th to 20th	Night	14% 6% 2 6% 4 4 4 5% 6% 10% 38%	2520
	21st to end	Night	18% 8% 3 6% 3 3 5% 4 7% 8% 37%	2739
August	1st to 10th	Night	22% 6% 3 7% 5% 5% 5% 4 4 8% 32%	2684
	11th to 20th	Night	15% 7% 2 7% 5% 4 5% 3 6% 6% 39%	3097
	21st to end	Night	11% 4 2 5% 4 3 4 3 5% 7% 52%	3476
September	1st to 10th	Night	15% 6% 3 5% 4 3 4 3 5% 6% 45%	1900
	11th to 20th	Night	14% 6% 2 3 4 3 3 3 5% 6% 53%	1981
	21st to end	Night	18% 6% 2 5% 4 3 4 3 5% 5% 45%	2090
October	1st to 10th	Night	21% 7% 2 6% 4 3 3 3 4 5% 42%	2194
	11th to 20th	Night	16% 5% 2 6% 3 3 3 3 5% 6% 47%	2203
	21st to end	Night	23% 6% 3 5% 3 3 3 3 4 5% 42%	2523
November	1st to 10th	Night	13% 5% 3 5% 3 3 3 3 5% 6% 50%	2407
	11th to 20th	Night	20% 7% 2 4 3 3 3 3 4 5% 47%	2470
	21st to end	Night	15% 5% 2 5% 4 4 4 3 4 7% 47%	2558
December	1st to 10th	Night	20% 7% 2 5% 4 4 3 4 5% 7% 39%	2660
	11th to 20th	Night	20% 8% 2 4 4 3 4 3 5% 5% 41%	3288
	21st to end	Night	21% 9% 3 5% 4 4 4 3 5% 6% 36%	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	24% 37% 5% 23% 8% 3	2518
	11th to 20th	Day	32% 37% 6% 16% 8% 1	2520
	21st to end	Day	39% 40% 5% 10% 5% 1	2996
February	1st to 10th	Day	17% 65% 6% 8% 3 1	1710
	11th to 20th	Day	15% 63% 2 10% 9% 1	1857
	21st to end	Day	17% 64% 4 9% 4 2	1570
March	1st to 10th	Day	36% 40% 7% 12% 5% 1	3119
	11th to 20th	Day	18% 42% 8% 22% 9% 1	3338
	21st to end	Day	28% 39% 4 8% 17% 4	4133
April	1st to 10th	Day	18% 64% 4 7% 5% 1	2280
	11th to 20th	Day	14% 65% 4 7% 9% 1	2254
	21st to end	Day	17% 65% 3 9% 6% 1	2308
May	1st to 10th	Day	34% 41% 9% 9% 6% 1	4120
	11th to 20th	Day	35% 42% 8% 12% 3	4394
	21st to end	Day	21% 41% 6% 19% 12% 1	4837
June	1st to 10th	Day	15% 65% 3 9% 7%	2660
	11th to 20th	Day	14% 65% 4 10% 7%	2660
	21st to end	Day	14% 64% 4 9% 9%	2660
July	1st to 10th	Day	28% 40% 7% 14% 11% 1	4370
	11th to 20th	Day	27% 39% 11% 14% 9% 1	4365
	21st to end	Day	34% 37% 6% 12% 10% 2	4661
August	1st to 10th	Day	35% 39% 8% 13% 5%	4194
	11th to 20th	Day	24% 39% 9% 22% 6%	3766
	21st to end	Day	19% 38% 7% 22% 13% 1	4180
September	1st to 10th	Day	16% 60% 5% 12% 8%	2280
	11th to 20th	Day	16% 60% 3 9% 11% 1	2199
	21st to end	Day	20% 59% 5% 9% 6% 1	2090
October	1st to 10th	Day	18% 60% 4 8% 8% 3	1981
	11th to 20th	Day	13% 61% 5% 11% 10%	1831
	21st to end	Day	17% 62% 3 9% 7% 1	1832
November	1st to 10th	Day	17% 58% 6% 10% 8% 1	1671
	11th to 20th	Day	14% 59% 3 11% 12% 2	1710
	21st to end	Day	14% 60% 6% 14% 5% 2	1620
December	1st to 10th	Day	21% 59% 6% 6% 8%	1520
	11th to 20th	Day	22% 47% 7% 14% 8% 2	1906
	21st to end	Day	36% 39% 5% 15% 5%	2772
January	1st to 10th	Night	25% 37% 6% 22% 7% 3	4429
	11th to 20th	Night	27% 37% 7% 17% 9% 2	4440
	21st to end	Night	37% 40% 5% 12% 5% 1	4656
February	1st to 10th	Night	15% 64% 5% 10% 4 1	2468
	11th to 20th	Night	15% 64% 2 8% 9% 2	2220
	21st to end	Night	16% 64% 3 8% 7% 2	1884
March	1st to 10th	Night	36% 42% 4 11% 6% 2	3734
	11th to 20th	Night	18% 41% 11% 17% 12% 1	3618
	21st to end	Night	29% 40% 4 7% 15% 4	3498
April	1st to 10th	Night	17% 65% 3 8% 5% 1	1900
	11th to 20th	Night	13% 66% 4 9% 8%	1875
	21st to end	Night	17% 64% 2 8% 7% 1	1870
May	1st to 10th	Night	36% 43% 6% 11% 4	2840
	11th to 20th	Night	36% 41% 10% 9% 4	2532
	21st to end	Night	25% 41% 9% 17% 7% 2	2739
June	1st to 10th	Night	15% 64% 2 10% 9% 1	1520
	11th to 20th	Night	13% 65% 5% 11% 5%	1520
	21st to end	Night	13% 63% 4 11% 8% 1	1520
July	1st to 10th	Night	25% 41% 9% 13% 10% 1	2480
	11th to 20th	Night	27% 38% 10% 16% 8%	2472
	21st to end	Night	33% 36% 9% 9% 13% 1	2651
August	1st to 10th	Night	38% 40% 9% 9% 4 1	2674
	11th to 20th	Night	27% 39% 8% 20% 6%	3127
	21st to end	Night	15% 39% 7% 26% 12%	3476
September	1st to 10th	Night	14% 60% 4 13% 8% 1	1900
	11th to 20th	Night	13% 60% 4 10% 10% 2	1981
	21st to end	Night	20% 59% 4 8% 8% 1	2090
October	1st to 10th	Night	18% 60% 5% 9% 6% 2	2194
	11th to 20th	Night	12% 61% 5% 13% 8% 1	2207
	21st to end	Night	17% 62% 3 10% 7% 1	2523
November	1st to 10th	Night	17% 59% 5% 10% 9% 1	2407
	11th to 20th	Night	15% 59% 3 10% 10% 3	2470
	21st to end	Night	14% 59% 6% 13% 6% 1	2558
December	1st to 10th	Night	20% 59% 5% 10% 6%	2660
	11th to 20th	Night	23% 48% 6% 9% 11% 3	3288
	21st to end	Night	33% 37% 10% 13% 7%	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	26% 27% 29% 15% 3	180
	11th to 20th	Day	32% 23% 32% 11% 2 1	180
	21st to end	Day	19% 27% 37% 11% 5% 2	261
February	1st to 10th	Day	29% 24% 33% 11% 2	270
	11th to 20th	Day	26% 23% 35% 15% 1	456
	21st to end	Day	29% 19% 33% 16% 3	382
March	1st to 10th	Day	24% 25% 28% 19% 3	460
	11th to 20th	Day	21% 25% 32% 17% 4 1	460
	21st to end	Day	29% 22% 29% 16% 3 1	506
April	1st to 10th	Day	27% 25% 26% 14% 7% 1	460
	11th to 20th	Day	24% 22% 30% 15% 7% 2	452
	21st to end	Day	25% 21% 34% 15% 4 2	460
May	1st to 10th	Day	30% 18% 30% 13% 6% 2	463
	11th to 20th	Day	21% 15% 34% 21% 8% 1	487
	21st to end	Day	19% 12% 25% 30% 12% 3	529
June	1st to 10th	Day	18% 12% 32% 24% 12% 2	490
	11th to 20th	Day	17% 15% 29% 27% 11% 1	490
	21st to end	Day	13% 13% 30% 26% 15% 2	490
July	1st to 10th	Day	15% 7% 27% 29% 16% 5%	485
	11th to 20th	Day	12% 5% 27% 35% 17% 4	484
	21st to end	Day	14% 8% 29% 33% 15% 1	532
August	1st to 10th	Day	15% 6% 26% 33% 14% 7%	486
	11th to 20th	Day	14% 6% 25% 33% 17% 5%	479
	21st to end	Day	13% 11% 26% 26% 18% 7%	539
September	1st to 10th	Day	17% 11% 27% 21% 18% 6%	490
	11th to 20th	Day	14% 8% 29% 23% 14% 12%	490
	21st to end	Day	22% 10% 28% 24% 10% 6%	490
October	1st to 10th	Day	26% 8% 29% 19% 13% 5%	490
	11th to 20th	Day	17% 18% 29% 24% 11% 1	462
	21st to end	Day	28% 15% 30% 17% 10% 1	421
November	1st to 10th	Day	17% 17% 30% 24% 10% 2	365
	11th to 20th	Day	26% 18% 31% 19% 5% 1	370
	21st to end	Day	20% 21% 31% 23% 4 2	280
December	1st to 10th	Day	26% 24% 31% 14% 5%	180
	11th to 20th	Day	31% 22% 34% 10% 2	180
	21st to end	Day	27% 18% 36% 14% 5% 1	198
January	1st to 10th	Night	19% 17% 40% 20% 4	760
	11th to 20th	Night	24% 17% 31% 24% 3	760
	21st to end	Night	20% 18% 36% 24% 3	836
February	1st to 10th	Night	22% 16% 35% 26% 2	760
	11th to 20th	Night	22% 21% 35% 20% 1	743
	21st to end	Night	25% 18% 35% 19% 4	628
March	1st to 10th	Night	23% 18% 35% 19% 4	760
	11th to 20th	Night	23% 17% 34% 21% 4	760
	21st to end	Night	22% 19% 32% 21% 5%	836
April	1st to 10th	Night	21% 21% 34% 21% 4	760
	11th to 20th	Night	22% 15% 34% 23% 6%	751
	21st to end	Night	22% 17% 31% 25% 5%	730
May	1st to 10th	Night	26% 15% 30% 22% 6%	570
	11th to 20th	Night	24% 11% 31% 28% 6%	397
	21st to end	Night	19% 9% 20% 41% 9% 2	411
June	1st to 10th	Night	19% 5% 28% 37% 11% 1	380
	11th to 20th	Night	15% 6% 27% 38% 14% 1	380
	21st to end	Night	13% 3 27% 43% 13%	380
July	1st to 10th	Night	14% 6% 20% 42% 18% 1	370
	11th to 20th	Night	12% 3 24% 43% 17% 1	368
	21st to end	Night	13% 4 20% 42% 19% 1	416
August	1st to 10th	Night	14% 1 22% 42% 20% 2	478
	11th to 20th	Night	14% 5% 19% 36% 24% 2	750
	21st to end	Night	16% 4 19% 37% 22% 2	836
September	1st to 10th	Night	17% 5% 25% 34% 16% 2	760
	11th to 20th	Night	17% 5% 22% 32% 21% 4	760
	21st to end	Night	21% 4 25% 33% 15% 2	760
October	1st to 10th	Night	24% 9% 28% 22% 15% 2	760
	11th to 20th	Night	18% 12% 29% 30% 10% 1	735
	21st to end	Night	27% 11% 32% 22% 8%	792
November	1st to 10th	Night	15% 12% 33% 28% 11% 1	740
	11th to 20th	Night	23% 13% 32% 23% 8% 1	760
	21st to end	Night	19% 16% 31% 26% 7%	760
December	1st to 10th	Night	25% 15% 32% 21% 5% 1	760
	11th to 20th	Night	23% 16% 34% 23% 4	760
	21st to end	Night	24% 15% 35% 23% 2	836

Page generated at 2024-10-11 10:49:58. Version ac07

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