Ajax
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ajax clear sky chart from 2005-11-06 to 2024-03-01.

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% 8% 3 7% 6% 3 5% 5% 6% 8% 34%	78411
	Night	16% 9% 3 7% 6% 4 5% 5% 5% 7% 33%	80978
Transparency	Day	47% 8% 14% 20% 10% 1	78124
	Night	49% 8% 13% 19% 10% 1	80799
Seeing	Day	17% 9% 27% 28% 14% 4	13461
	Night	19% 9% 29% 29% 13% 2	23002

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	16% 11% 4 7% 6% 4 5% 5% 5% 6% 31%	2517
	11th to 20th	Day	12% 17% 7% 13% 10% 4 5% 4 4 6% 18%	2694
	21st to end	Day	21% 16% 6% 9% 7% 4 5% 5% 3 6% 18%	3124
February	1st to 10th	Day	16% 13% 5% 10% 8% 5% 6% 5% 5% 5% 22%	1710
	11th to 20th	Day	13% 12% 6% 10% 7% 4 5% 5% 5% 7% 28%	1663
	21st to end	Day	18% 12% 4 8% 7% 4 4 4 4 6% 28%	1460
March	1st to 10th	Day	14% 9% 3 8% 7% 4 6% 6% 5% 8% 30%	1977
	11th to 20th	Day	14% 10% 4 8% 6% 4 5% 4 5% 6% 33%	1980
	21st to end	Day	18% 9% 4 6% 5% 3 4 4 4 6% 36%	2178
April	1st to 10th	Day	17% 9% 4 7% 6% 3 5% 4 6% 7% 31%	2144
	11th to 20th	Day	19% 7% 3 6% 5% 3 5% 5% 5% 6% 37%	2177
	21st to end	Day	19% 7% 3 5% 6% 3 4 5% 6% 6% 35%	2340
May	1st to 10th	Day	15% 8% 3 6% 6% 3 6% 5% 6% 8% 35%	2353
	11th to 20th	Day	14% 6% 3 5% 6% 2 4 4 6% 7% 43%	2478
	21st to end	Day	11% 4 2 5% 5% 3 5% 5% 6% 9% 45%	2725
June	1st to 10th	Day	13% 6% 3 6% 6% 3 5% 6% 7% 9% 38%	2520
	11th to 20th	Day	11% 5% 2 6% 4 3 6% 4 6% 10% 42%	2520
	21st to end	Day	12% 5% 2 5% 4 3 4 5% 7% 10% 43%	2520
July	1st to 10th	Day	7% 4 2 4 4 3 6% 6% 7% 9% 48%	2520
	11th to 20th	Day	10% 4 2 4 5% 3 5% 7% 7% 9% 44%	2520
	21st to end	Day	9% 4 2 4 5% 5% 7% 7% 8% 11% 39%	2610
August	1st to 10th	Day	7% 4 3 4 7% 4 6% 6% 7% 9% 43%	2327
	11th to 20th	Day	8% 4 2 5% 5% 4 5% 6% 8% 9% 44%	2303
	21st to end	Day	9% 5% 2 5% 4 3 5% 5% 7% 9% 44%	2462
September	1st to 10th	Day	12% 5% 2 6% 4 3 6% 6% 5% 8% 44%	2160
	11th to 20th	Day	11% 5% 2 4 5% 3 3 5% 5% 8% 48%	2084
	21st to end	Day	12% 6% 3 5% 6% 4 5% 5% 6% 9% 41%	1926
October	1st to 10th	Day	16% 7% 3 6% 6% 3 5% 5% 5% 6% 37%	1800
	11th to 20th	Day	19% 8% 3 6% 6% 3 5% 5% 6% 7% 32%	1800
	21st to end	Day	23% 9% 4 7% 7% 3 5% 5% 6% 6% 25%	1980
November	1st to 10th	Day	14% 7% 3 7% 7% 4 5% 5% 5% 8% 34%	1601
	11th to 20th	Day	15% 10% 4 8% 7% 5% 6% 5% 7% 8% 26%	1520
	21st to end	Day	19% 11% 4 8% 6% 3 6% 4 5% 8% 25%	1520
December	1st to 10th	Day	18% 13% 5% 10% 7% 5% 6% 5% 6% 7% 19%	1520
	11th to 20th	Day	19% 12% 5% 7% 6% 3 5% 5% 6% 8% 25%	1906
	21st to end	Day	29% 14% 6% 10% 8% 4 4 4 3 5% 14%	2772
January	1st to 10th	Night	18% 14% 4 7% 7% 4 5% 5% 6% 6% 24%	4429
	11th to 20th	Night	16% 11% 5% 11% 10% 5% 6% 5% 6% 9% 17%	4249
	21st to end	Night	21% 13% 5% 8% 7% 4 5% 5% 5% 6% 21%	4532
February	1st to 10th	Night	14% 14% 5% 9% 7% 4 6% 6% 5% 6% 25%	2470
	11th to 20th	Night	15% 11% 5% 8% 8% 4 5% 5% 5% 6% 28%	2403
	21st to end	Night	15% 10% 4 8% 7% 4 5% 5% 6% 6% 30%	1991
March	1st to 10th	Night	13% 8% 4 7% 7% 4 6% 5% 5% 6% 36%	1977
	11th to 20th	Night	17% 11% 4 7% 7% 3 4 4 4 5% 34%	1979
	21st to end	Night	16% 7% 3 6% 5% 4 5% 5% 4 6% 40%	2178
April	1st to 10th	Night	19% 9% 4 5% 6% 3 4 4 5% 7% 34%	1815
	11th to 20th	Night	15% 6% 3 6% 6% 3 6% 5% 5% 6% 39%	1747
	21st to end	Night	17% 8% 2 6% 5% 3 5% 5% 6% 7% 35%	1620
May	1st to 10th	Night	17% 5% 3 5% 5% 4 4 5% 5% 8% 38%	1604
	11th to 20th	Night	13% 4 2 5% 4 3 5% 5% 5% 8% 45%	1415
	21st to end	Night	10% 3 2 5% 4 3 4 4 6% 7% 52%	1550
June	1st to 10th	Night	12% 5% 2 6% 4 4 5% 5% 6% 8% 43%	1440
	11th to 20th	Night	9% 4 2 5% 7% 3 5% 4 6% 9% 44%	1440
	21st to end	Night	13% 5% 2 4 5% 3 5% 4 6% 9% 43%	1440
July	1st to 10th	Night	5% 4 2 4 5% 3 4 4 5% 8% 56%	1440
	11th to 20th	Night	9% 4 2 5% 5% 3 4 4 5% 9% 49%	1440
	21st to end	Night	9% 3 2 4 4 3 4 6% 7% 9% 50%	1705
August	1st to 10th	Night	8% 4 2 5% 4 3 4 5% 6% 9% 49%	1611
	11th to 20th	Night	7% 5% 1 5% 5% 3 4 4 6% 9% 51%	1598
	21st to end	Night	10% 5% 2 5% 5% 4 4 4 5% 7% 48%	1876
September	1st to 10th	Night	10% 5% 3 5% 5% 4 5% 6% 5% 8% 46%	1800
	11th to 20th	Night	12% 4 2 4 4 2 3 4 6% 6% 54%	1873
	21st to end	Night	15% 6% 3 5% 5% 3 5% 5% 4 6% 44%	2034
October	1st to 10th	Night	16% 7% 3 5% 6% 3 4 5% 5% 7% 39%	2160
	11th to 20th	Night	20% 8% 3 7% 5% 3 4 5% 6% 6% 32%	2160
	21st to end	Night	23% 8% 3 6% 5% 3 5% 6% 5% 6% 30%	2376
November	1st to 10th	Night	17% 6% 3 6% 5% 3 5% 4 6% 7% 38%	2474
	11th to 20th	Night	17% 8% 3 7% 7% 4 5% 6% 6% 7% 31%	2660
	21st to end	Night	20% 9% 4 7% 6% 4 5% 5% 6% 8% 26%	2660
December	1st to 10th	Night	20% 13% 5% 8% 7% 4 6% 5% 4 5% 23%	2660
	11th to 20th	Night	17% 15% 4 8% 7% 4 6% 5% 6% 6% 23%	3288
	21st to end	Night	32% 12% 4 7% 6% 4 5% 5% 5% 6% 14%	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	52% 11% 19% 11% 7% 1	2518
	11th to 20th	Day	68% 8% 11% 9% 4	2694
	21st to end	Day	67% 9% 11% 9% 4 1	3124
February	1st to 10th	Day	62% 8% 11% 15% 4 1	1710
	11th to 20th	Day	56% 7% 13% 16% 7% 1	1672
	21st to end	Day	57% 7% 13% 17% 6%	1460
March	1st to 10th	Day	51% 8% 15% 16% 10% 1	1980
	11th to 20th	Day	51% 7% 11% 16% 12% 2	1980
	21st to end	Day	49% 5% 10% 18% 15% 3	2178
April	1st to 10th	Day	51% 7% 12% 17% 10% 2	2144
	11th to 20th	Day	46% 6% 11% 20% 14% 1	2177
	21st to end	Day	48% 7% 12% 18% 12% 3	2340
May	1st to 10th	Day	46% 7% 12% 19% 14% 2	2353
	11th to 20th	Day	41% 8% 11% 25% 14% 2	2482
	21st to end	Day	36% 8% 17% 24% 13% 2	2725
June	1st to 10th	Day	41% 9% 14% 21% 14% 1	2520
	11th to 20th	Day	37% 8% 13% 25% 15% 2	2520
	21st to end	Day	36% 8% 17% 23% 14% 1	2520
July	1st to 10th	Day	29% 9% 14% 26% 19% 3	2450
	11th to 20th	Day	34% 9% 16% 30% 10% 1	2445
	21st to end	Day	36% 11% 16% 23% 12% 1	2464
August	1st to 10th	Day	34% 11% 17% 24% 13% 1	2314
	11th to 20th	Day	33% 10% 18% 27% 12% 1	2303
	21st to end	Day	34% 9% 15% 28% 12% 1	2462
September	1st to 10th	Day	36% 10% 14% 28% 11% 1	2160
	11th to 20th	Day	32% 9% 15% 29% 14% 1	2084
	21st to end	Day	40% 9% 15% 27% 9% 1	1926
October	1st to 10th	Day	47% 8% 15% 18% 11% 1	1800
	11th to 20th	Day	51% 8% 14% 19% 7% 1	1800
	21st to end	Day	58% 7% 14% 15% 5% 1	1980
November	1st to 10th	Day	48% 8% 15% 19% 9% 1	1601
	11th to 20th	Day	53% 9% 15% 14% 8% 1	1520
	21st to end	Day	57% 8% 15% 16% 3	1520
December	1st to 10th	Day	64% 9% 13% 11% 3	1520
	11th to 20th	Day	57% 11% 14% 11% 6%	1906
	21st to end	Day	72% 9% 8% 10% 2	2772
January	1st to 10th	Night	58% 9% 17% 12% 4 1	4429
	11th to 20th	Night	63% 14% 11% 9% 3 1	4249
	21st to end	Night	62% 10% 13% 10% 4 1	4532
February	1st to 10th	Night	58% 9% 11% 18% 4 1	2470
	11th to 20th	Night	56% 6% 13% 16% 8% 1	2405
	21st to end	Night	53% 8% 12% 19% 8% 1	1991
March	1st to 10th	Night	49% 6% 15% 19% 10% 2	1987
	11th to 20th	Night	52% 5% 10% 20% 11% 2	1980
	21st to end	Night	46% 5% 9% 22% 15% 3	2178
April	1st to 10th	Night	50% 4 11% 20% 14% 1	1815
	11th to 20th	Night	46% 6% 10% 19% 16% 2	1747
	21st to end	Night	47% 8% 10% 19% 14% 2	1620
May	1st to 10th	Night	44% 7% 10% 20% 16% 3	1604
	11th to 20th	Night	38% 6% 11% 24% 18% 4	1416
	21st to end	Night	31% 6% 15% 24% 19% 4	1551
June	1st to 10th	Night	38% 8% 11% 24% 16% 2	1440
	11th to 20th	Night	37% 6% 12% 22% 22% 2	1440
	21st to end	Night	37% 8% 13% 24% 17% 1	1440
July	1st to 10th	Night	27% 6% 13% 26% 24% 4	1400
	11th to 20th	Night	32% 7% 12% 30% 18% 2	1392
	21st to end	Night	30% 8% 14% 29% 16% 2	1610
August	1st to 10th	Night	31% 7% 18% 28% 14% 2	1600
	11th to 20th	Night	30% 7% 16% 32% 14% 1	1598
	21st to end	Night	34% 7% 13% 29% 16% 1	1876
September	1st to 10th	Night	35% 8% 15% 26% 14% 2	1800
	11th to 20th	Night	30% 6% 13% 33% 18%	1873
	21st to end	Night	40% 7% 13% 27% 13%	2034
October	1st to 10th	Night	44% 7% 12% 22% 15% 1	2160
	11th to 20th	Night	51% 8% 13% 21% 7%	2160
	21st to end	Night	54% 7% 12% 16% 10%	2376
November	1st to 10th	Night	45% 7% 12% 22% 13% 1	2474
	11th to 20th	Night	51% 8% 15% 16% 10% 1	2660
	21st to end	Night	55% 9% 17% 15% 4	2660
December	1st to 10th	Night	61% 9% 11% 14% 4	2660
	11th to 20th	Night	61% 8% 13% 14% 4	3288
	21st to end	Night	69% 11% 11% 8% 2	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	23% 18% 31% 18% 9% 1	180
	11th to 20th	Day	23% 21% 33% 16% 6%	231
	21st to end	Day	24% 19% 33% 21% 3	297
February	1st to 10th	Day	21% 23% 35% 16% 5%	270
	11th to 20th	Day	21% 21% 39% 16% 3	270
	21st to end	Day	25% 24% 32% 17% 2	263
March	1st to 10th	Day	20% 14% 38% 22% 6%	420
	11th to 20th	Day	20% 16% 34% 23% 7%	420
	21st to end	Day	25% 11% 32% 23% 7% 1	462
April	1st to 10th	Day	18% 15% 32% 29% 6%	420
	11th to 20th	Day	24% 9% 29% 23% 12% 3	412
	21st to end	Day	22% 10% 34% 22% 10% 2	420
May	1st to 10th	Day	22% 7% 25% 29% 11% 6%	423
	11th to 20th	Day	16% 4 24% 34% 18% 4	447
	21st to end	Day	14% 3 21% 36% 21% 6%	485
June	1st to 10th	Day	13% 5% 27% 36% 16% 2	450
	11th to 20th	Day	13% 4 23% 35% 22% 2	450
	21st to end	Day	14% 3 21% 39% 18% 5%	450
July	1st to 10th	Day	8% 2 18% 35% 31% 7%	445
	11th to 20th	Day	13% 2 17% 36% 24% 8%	444
	21st to end	Day	8% 3 23% 40% 20% 6%	488
August	1st to 10th	Day	9% 2 17% 36% 25% 11%	446
	11th to 20th	Day	10% 3 16% 31% 30% 9%	439
	21st to end	Day	11% 3 20% 35% 22% 9%	495
September	1st to 10th	Day	12% 4 21% 32% 21% 10%	450
	11th to 20th	Day	10% 4 17% 34% 22% 14%	450
	21st to end	Day	13% 6% 29% 29% 15% 8%	450
October	1st to 10th	Day	20% 8% 25% 25% 16% 6%	450
	11th to 20th	Day	20% 14% 33% 24% 8% 1	450
	21st to end	Day	26% 14% 30% 22% 8%	495
November	1st to 10th	Day	20% 15% 28% 24% 12% 1	271
	11th to 20th	Day	18% 20% 32% 24% 6% 1	180
	21st to end	Day	25% 13% 39% 18% 5% 1	180
December	1st to 10th	Day	21% 16% 35% 21% 6% 2	180
	11th to 20th	Day	23% 24% 31% 17% 5%	180
	21st to end	Day	28% 19% 39% 13% 2	198
January	1st to 10th	Night	24% 14% 38% 18% 6%	760
	11th to 20th	Night	27% 14% 33% 23% 3 1	760
	21st to end	Night	19% 11% 37% 26% 6% 1	836
February	1st to 10th	Night	20% 16% 39% 22% 3	760
	11th to 20th	Night	22% 14% 36% 23% 5%	743
	21st to end	Night	21% 14% 40% 20% 4	628
March	1st to 10th	Night	18% 12% 37% 28% 5% 1	723
	11th to 20th	Night	21% 12% 35% 26% 6% 1	720
	21st to end	Night	20% 8% 31% 29% 12% 1	792
April	1st to 10th	Night	24% 10% 31% 29% 7%	720
	11th to 20th	Night	16% 10% 31% 30% 11% 1	683
	21st to end	Night	21% 6% 29% 32% 11%	540
May	1st to 10th	Night	19% 3 27% 31% 18% 2	524
	11th to 20th	Night	16% 1 29% 37% 17% 1	354
	21st to end	Night	10% 2 18% 44% 24% 2	389
June	1st to 10th	Night	13% 3 23% 41% 19% 1	360
	11th to 20th	Night	10% 3 24% 40% 21% 2	360
	21st to end	Night	12% 3 20% 41% 23% 1	360
July	1st to 10th	Night	6% 2 15% 45% 30% 2	350
	11th to 20th	Night	12% 3 16% 41% 26% 3	348
	21st to end	Night	9% 2 15% 47% 24% 3	525
August	1st to 10th	Night	10% 1 12% 40% 32% 4	537
	11th to 20th	Night	7% 2 14% 39% 32% 5%	534
	21st to end	Night	11% 2 21% 37% 26% 4	688
September	1st to 10th	Night	10% 5% 21% 34% 24% 6%	720
	11th to 20th	Night	13% 4 19% 29% 27% 7%	720
	21st to end	Night	17% 5% 20% 31% 22% 5%	720
October	1st to 10th	Night	18% 5% 28% 27% 20% 2	720
	11th to 20th	Night	23% 11% 28% 28% 9% 1	720
	21st to end	Night	26% 9% 29% 29% 6% 1	792
November	1st to 10th	Night	21% 9% 25% 32% 11% 1	740
	11th to 20th	Night	21% 14% 30% 27% 7% 2	760
	21st to end	Night	24% 10% 33% 25% 7%	760
December	1st to 10th	Night	29% 12% 33% 21% 4	760
	11th to 20th	Night	21% 13% 38% 23% 4 1	760
	21st to end	Night	31% 11% 36% 20% 2	836

Page generated at 2024-02-27 06:30:12. Version ac07

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