Monsey Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Monsey Observatory clear sky chart from 2005-11-06 to 2024-02-10.

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% 6% 3 5% 5% 3 5% 5% 5% 7% 39%	78191
	Night	18% 7% 3 5% 5% 3 4 4 5% 7% 42%	80762
Transparency	Day	30% 36% 8% 15% 10% 2	77896
	Night	30% 35% 8% 16% 10% 1	80591
Seeing	Day	21% 16% 30% 21% 10% 3	13910
	Night	21% 12% 30% 27% 9% 1	23204

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 4 4 2 4 4 4 5% 47%	2517
	11th to 20th	Day	15% 9% 4 5% 6% 5% 5% 5% 5% 5% 35%	2520
	21st to end	Day	22% 11% 4 7% 5% 3 4 4 4 5% 32%	2996
February	1st to 10th	Day	17% 7% 3 6% 6% 4 5% 5% 4 8% 36%	1701
	11th to 20th	Day	16% 6% 2 6% 6% 3 4 4 5% 6% 43%	1748
	21st to end	Day	20% 9% 3 4 6% 2 4 4 5% 6% 38%	1480
March	1st to 10th	Day	15% 6% 2 6% 5% 2 4 4 6% 7% 42%	1797
	11th to 20th	Day	15% 6% 2 6% 5% 3 5% 5% 5% 7% 39%	1894
	21st to end	Day	20% 8% 2 5% 5% 3 4 4 5% 5% 39%	2357
April	1st to 10th	Day	19% 7% 3 5% 5% 2 4 4 5% 7% 40%	2160
	11th to 20th	Day	17% 6% 3 5% 5% 3 4 4 5% 7% 42%	2134
	21st to end	Day	21% 6% 2 4 4 3 4 4 6% 6% 38%	2186
May	1st to 10th	Day	24% 7% 3 5% 5% 3 4 4 5% 7% 34%	2340
	11th to 20th	Day	20% 7% 2 5% 5% 3 4 4 6% 7% 36%	2470
	21st to end	Day	16% 6% 2 5% 5% 3 4 5% 4 9% 40%	2725
June	1st to 10th	Day	18% 6% 2 4 5% 3 5% 6% 7% 9% 36%	2520
	11th to 20th	Day	17% 6% 3 5% 5% 3 6% 6% 7% 8% 34%	2520
	21st to end	Day	13% 5% 2 6% 5% 3 5% 5% 7% 9% 38%	2520
July	1st to 10th	Day	13% 6% 3 6% 5% 4 6% 6% 6% 8% 39%	2520
	11th to 20th	Day	11% 5% 3 4 5% 4 6% 5% 7% 10% 39%	2520
	21st to end	Day	13% 6% 3 6% 7% 4 6% 6% 6% 9% 36%	2744
August	1st to 10th	Day	12% 5% 3 6% 6% 5% 6% 6% 7% 8% 36%	2388
	11th to 20th	Day	13% 7% 3 5% 5% 4 6% 5% 7% 9% 37%	2126
	21st to end	Day	14% 6% 2 6% 5% 3 5% 5% 7% 8% 40%	2376
September	1st to 10th	Day	15% 5% 3 6% 6% 3 5% 6% 5% 6% 41%	2160
	11th to 20th	Day	14% 5% 2 5% 4 2 4 4 4 7% 49%	2084
	21st to end	Day	17% 6% 3 6% 4 3 4 5% 5% 6% 41%	1980
October	1st to 10th	Day	23% 6% 2 5% 3 2 4 4 5% 6% 41%	1877
	11th to 20th	Day	16% 5% 2 4 4 3 5% 4 5% 7% 46%	1800
	21st to end	Day	23% 5% 2 4 5% 3 4 4 5% 7% 39%	1832
November	1st to 10th	Day	15% 6% 3 4 3 2 3 3 5% 6% 51%	1671
	11th to 20th	Day	19% 6% 2 4 4 2 3 4 4 6% 46%	1710
	21st to end	Day	16% 6% 2 3 4 3 4 5% 6% 7% 43%	1620
December	1st to 10th	Day	19% 8% 3 4 5% 3 4 4 6% 7% 37%	1520
	11th to 20th	Day	22% 6% 1 5% 3 1 3 4 4 6% 45%	1906
	21st to end	Day	18% 8% 4 7% 6% 4 6% 4 5% 7% 32%	2772
January	1st to 10th	Night	17% 6% 2 4 4 2 4 4 4 6% 47%	4429
	11th to 20th	Night	16% 7% 3 6% 5% 3 4 4 4 6% 41%	4440
	21st to end	Night	23% 11% 3 4 4 3 3 4 4 6% 34%	4656
February	1st to 10th	Night	17% 9% 3 5% 4 3 4 4 4 7% 42%	2462
	11th to 20th	Night	17% 7% 3 5% 5% 3 5% 5% 5% 5% 41%	2098
	21st to end	Night	18% 7% 3 6% 4 3 4 4 4 5% 41%	1776
March	1st to 10th	Night	17% 6% 2 4 4 3 4 4 4 8% 45%	2150
	11th to 20th	Night	18% 8% 2 5% 5% 3 4 5% 5% 6% 41%	2061
	21st to end	Night	17% 7% 3 5% 5% 2 4 4 5% 6% 41%	1998
April	1st to 10th	Night	18% 7% 3 5% 5% 2 5% 4 5% 7% 38%	1800
	11th to 20th	Night	19% 5% 3 5% 5% 2 3 4 5% 8% 41%	1775
	21st to end	Night	21% 7% 2 5% 4 2 3 3 5% 6% 42%	1772
May	1st to 10th	Night	23% 7% 3 5% 6% 3 4 4 4 5% 36%	1620
	11th to 20th	Night	19% 8% 3 6% 4 2 4 5% 5% 5% 39%	1437
	21st to end	Night	16% 6% 2 5% 5% 2 4 5% 5% 8% 41%	1550
June	1st to 10th	Night	18% 6% 2 4 4 3 5% 5% 5% 8% 41%	1440
	11th to 20th	Night	15% 5% 3 4 5% 3 5% 5% 6% 10% 40%	1440
	21st to end	Night	12% 4 2 5% 6% 2 4 4 7% 9% 45%	1440
July	1st to 10th	Night	13% 5% 2 6% 5% 3 5% 5% 7% 8% 41%	1440
	11th to 20th	Night	12% 5% 2 6% 5% 3 5% 6% 6% 10% 40%	1440
	21st to end	Night	11% 5% 2 5% 4 3 5% 6% 8% 10% 42%	1574
August	1st to 10th	Night	10% 5% 2 5% 6% 5% 4 6% 5% 9% 43%	1526
	11th to 20th	Night	13% 6% 2 6% 7% 3 6% 5% 6% 8% 36%	1774
	21st to end	Night	15% 5% 3 5% 6% 3 3 5% 4 8% 44%	1980
September	1st to 10th	Night	16% 6% 3 5% 5% 3 4 5% 5% 7% 44%	1800
	11th to 20th	Night	14% 6% 2 3 4 2 2 4 4 6% 53%	1876
	21st to end	Night	17% 6% 2 4 5% 2 4 4 5% 5% 47%	1980
October	1st to 10th	Night	22% 7% 3 5% 4 2 4 3 4 5% 42%	2078
	11th to 20th	Night	16% 5% 2 5% 3 3 4 4 5% 7% 47%	2160
	21st to end	Night	23% 6% 3 4 4 2 3 4 4 5% 43%	2523
November	1st to 10th	Night	14% 5% 3 4 4 2 4 4 5% 6% 50%	2407
	11th to 20th	Night	20% 6% 2 4 3 2 3 4 4 5% 47%	2470
	21st to end	Night	15% 5% 2 4 5% 3 4 4 4 7% 47%	2558
December	1st to 10th	Night	20% 6% 3 5% 4 3 3 5% 4 7% 40%	2660
	11th to 20th	Night	20% 8% 2 3 5% 2 4 4 5% 5% 42%	3288
	21st to end	Night	21% 9% 3 5% 5% 3 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	29% 25% 8% 29% 8% 1	2518
	11th to 20th	Day	40% 25% 9% 17% 9% 1	2520
	21st to end	Day	46% 24% 7% 16% 6% 1	2996
February	1st to 10th	Day	30% 35% 7% 16% 11% 1	1701
	11th to 20th	Day	29% 37% 8% 16% 9% 2	1757
	21st to end	Day	31% 36% 7% 13% 10% 2	1480
March	1st to 10th	Day	27% 36% 9% 17% 10% 2	1800
	11th to 20th	Day	31% 37% 8% 13% 10% 2	1894
	21st to end	Day	30% 37% 5% 14% 12% 3	2357
April	1st to 10th	Day	28% 37% 6% 14% 12% 3	2160
	11th to 20th	Day	30% 36% 8% 13% 11% 3	2134
	21st to end	Day	28% 37% 7% 12% 11% 4	2186
May	1st to 10th	Day	31% 37% 6% 12% 12% 2	2340
	11th to 20th	Day	30% 38% 5% 13% 10% 3	2474
	21st to end	Day	25% 39% 10% 14% 10% 2	2725
June	1st to 10th	Day	27% 39% 10% 13% 9% 1	2520
	11th to 20th	Day	31% 38% 9% 15% 5% 2	2520
	21st to end	Day	28% 39% 9% 15% 8% 1	2520
July	1st to 10th	Day	29% 40% 8% 14% 9% 1	2450
	11th to 20th	Day	24% 41% 9% 16% 9% 2	2445
	21st to end	Day	27% 41% 8% 12% 11% 2	2591
August	1st to 10th	Day	28% 39% 8% 15% 9%	2374
	11th to 20th	Day	28% 37% 9% 15% 10% 1	2126
	21st to end	Day	31% 38% 6% 12% 11% 2	2376
September	1st to 10th	Day	28% 38% 6% 14% 13% 2	2160
	11th to 20th	Day	21% 37% 8% 16% 17% 2	2084
	21st to end	Day	29% 36% 6% 13% 13% 2	1980
October	1st to 10th	Day	28% 37% 6% 16% 13%	1877
	11th to 20th	Day	27% 37% 8% 18% 9% 1	1800
	21st to end	Day	29% 38% 6% 14% 10% 2	1832
November	1st to 10th	Day	20% 40% 7% 17% 14% 2	1671
	11th to 20th	Day	25% 40% 7% 15% 10% 2	1710
	21st to end	Day	26% 40% 8% 17% 8% 1	1620
December	1st to 10th	Day	28% 41% 9% 14% 7% 1	1520
	11th to 20th	Day	31% 31% 11% 16% 9% 2	1906
	21st to end	Day	40% 27% 9% 18% 6%	2772
January	1st to 10th	Night	30% 25% 9% 26% 8% 1	4429
	11th to 20th	Night	35% 26% 8% 20% 9% 2	4440
	21st to end	Night	43% 23% 7% 19% 7% 1	4656
February	1st to 10th	Night	29% 35% 8% 16% 10% 1	2462
	11th to 20th	Night	30% 38% 7% 13% 9% 3	2100
	21st to end	Night	31% 36% 4 17% 11% 2	1776
March	1st to 10th	Night	25% 36% 10% 17% 10% 2	2160
	11th to 20th	Night	30% 38% 8% 14% 8% 2	2062
	21st to end	Night	27% 37% 6% 14% 13% 3	1998
April	1st to 10th	Night	29% 36% 8% 13% 12% 2	1800
	11th to 20th	Night	32% 36% 6% 12% 13% 1	1775
	21st to end	Night	28% 37% 7% 13% 13% 3	1772
May	1st to 10th	Night	34% 37% 5% 12% 11% 2	1620
	11th to 20th	Night	29% 37% 6% 12% 13% 3	1438
	21st to end	Night	24% 40% 11% 14% 9% 2	1551
June	1st to 10th	Night	27% 39% 8% 14% 11% 1	1440
	11th to 20th	Night	26% 40% 11% 17% 6% 1	1440
	21st to end	Night	25% 40% 10% 16% 9%	1440
July	1st to 10th	Night	28% 40% 9% 13% 8% 2	1400
	11th to 20th	Night	26% 40% 10% 15% 8% 1	1392
	21st to end	Night	21% 41% 12% 13% 12% 2	1486
August	1st to 10th	Night	25% 41% 9% 15% 10% 1	1516
	11th to 20th	Night	30% 38% 8% 15% 8%	1774
	21st to end	Night	30% 38% 7% 12% 11% 1	1980
September	1st to 10th	Night	28% 38% 7% 15% 12% 1	1800
	11th to 20th	Night	22% 36% 6% 18% 16% 1	1876
	21st to end	Night	26% 37% 5% 16% 16% 1	1980
October	1st to 10th	Night	29% 37% 6% 16% 11% 1	2078
	11th to 20th	Night	27% 37% 9% 17% 10% 1	2160
	21st to end	Night	30% 37% 7% 15% 10% 1	2523
November	1st to 10th	Night	20% 41% 7% 14% 15% 3	2407
	11th to 20th	Night	27% 39% 6% 16% 11% 2	2470
	21st to end	Night	25% 40% 8% 18% 9%	2558
December	1st to 10th	Night	26% 40% 9% 15% 9% 1	2660
	11th to 20th	Night	30% 32% 10% 13% 13% 3	3288
	21st to end	Night	38% 26% 12% 15% 9%	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% 3	267
	11th to 20th	Day	27% 23% 35% 15% 1	416
	21st to end	Day	29% 20% 33% 16% 2	346
March	1st to 10th	Day	22% 27% 28% 20% 3	420
	11th to 20th	Day	20% 25% 32% 17% 4 1	420
	21st to end	Day	28% 22% 29% 16% 4 1	462
April	1st to 10th	Day	26% 23% 27% 14% 8% 1	420
	11th to 20th	Day	23% 21% 31% 15% 8% 2	412
	21st to end	Day	27% 21% 33% 13% 5% 1	420
May	1st to 10th	Day	30% 18% 31% 12% 6% 2	423
	11th to 20th	Day	21% 16% 35% 21% 7% 1	447
	21st to end	Day	20% 11% 23% 31% 12% 3	485
June	1st to 10th	Day	18% 12% 32% 24% 12% 2	450
	11th to 20th	Day	18% 16% 29% 26% 10% 1	450
	21st to end	Day	13% 13% 30% 26% 16% 2	450
July	1st to 10th	Day	16% 7% 27% 29% 16% 6%	445
	11th to 20th	Day	13% 5% 27% 34% 18% 4	444
	21st to end	Day	14% 8% 29% 33% 15% 1	488
August	1st to 10th	Day	13% 6% 25% 35% 14% 7%	446
	11th to 20th	Day	15% 5% 25% 33% 17% 5%	439
	21st to end	Day	13% 10% 26% 26% 17% 7%	495
September	1st to 10th	Day	18% 10% 27% 21% 18% 6%	450
	11th to 20th	Day	15% 9% 31% 21% 13% 11%	450
	21st to end	Day	20% 11% 29% 23% 11% 6%	450
October	1st to 10th	Day	27% 8% 29% 18% 13% 4	450
	11th to 20th	Day	17% 18% 28% 24% 11% 1	450
	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% 25% 2	759
	11th to 20th	Night	23% 21% 34% 21% 1	703
	21st to end	Night	24% 18% 35% 20% 3	592
March	1st to 10th	Night	23% 18% 35% 19% 4	720
	11th to 20th	Night	24% 16% 34% 22% 4	720
	21st to end	Night	22% 19% 33% 21% 5%	792
April	1st to 10th	Night	21% 21% 33% 21% 4	720
	11th to 20th	Night	22% 15% 34% 23% 6%	711
	21st to end	Night	22% 17% 31% 25% 5%	692
May	1st to 10th	Night	26% 14% 30% 23% 7%	540
	11th to 20th	Night	24% 11% 32% 27% 6%	376
	21st to end	Night	19% 9% 20% 41% 9% 2	389
June	1st to 10th	Night	19% 5% 28% 36% 11% 1	360
	11th to 20th	Night	16% 6% 28% 37% 13%	360
	21st to end	Night	12% 3 26% 45% 14%	360
July	1st to 10th	Night	14% 6% 20% 40% 19% 1	350
	11th to 20th	Night	12% 2 23% 45% 17% 1	348
	21st to end	Night	13% 4 21% 42% 19% 1	394
August	1st to 10th	Night	12% 1 22% 43% 20% 2	452
	11th to 20th	Night	14% 5% 18% 37% 25% 2	710
	21st to end	Night	17% 4 19% 37% 22% 2	792
September	1st to 10th	Night	18% 5% 25% 35% 16% 3	720
	11th to 20th	Night	18% 5% 23% 32% 19% 4	720
	21st to end	Night	20% 4 25% 33% 15% 2	720
October	1st to 10th	Night	24% 9% 28% 22% 15% 2	720
	11th to 20th	Night	18% 12% 29% 30% 11% 1	720
	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 2024-02-07 06:11:59. Version ac07

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