Halliday Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Halliday Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	16% 7% 2 6% 4 4 5% 4 6% 7% 40%	101470
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	98077
Transparency	Day	23% 48% 7% 13% 9% 1	105015
	Night	23% 47% 6% 13% 9% 1	102608
Seeing	Day	19% 11% 30% 24% 11% 4	15149
	Night	19% 8% 31% 29% 11% 1	24341

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% 3 5% 3 3 3 3 5% 4 47%	2517
	11th to 20th	Day	15% 10% 3 7% 4 4 5% 3 5% 5% 40%	2520
	21st to end	Day	23% 11% 3 8% 4 3 3 3 4 5% 32%	3064
February	1st to 10th	Day	16% 9% 3 7% 5% 4 4 2 4 6% 41%	1738
	11th to 20th	Day	17% 7% 3 6% 4 3 3 3 5% 5% 43%	1848
	21st to end	Day	17% 8% 3 7% 4 4 4 4 5% 5% 39%	1570
March	1st to 10th	Day	27% 7% 2 5% 3 3 4 3 4 5% 37%	3116
	11th to 20th	Day	9% 5% 2 5% 4 5% 5% 4 5% 7% 48%	3342
	21st to end	Day	20% 8% 2 5% 4 3 4 3 4 5% 43%	4130
April	1st to 10th	Day	18% 8% 2 5% 3 4 5% 3 5% 7% 40%	2280
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 6% 8% 42%	2254
	21st to end	Day	18% 6% 2 5% 5% 4 5% 4 6% 7% 40%	2280
May	1st to 10th	Day	24% 11% 3 7% 4 4 4 4 5% 7% 27%	4105
	11th to 20th	Day	27% 7% 2 6% 4 4 4 3 5% 6% 32%	4318
	21st to end	Day	14% 6% 2 5% 4 4 5% 4 6% 9% 42%	4837
June	1st to 10th	Day	14% 6% 2 5% 4 5% 6% 4 7% 10% 37%	2660
	11th to 20th	Day	13% 6% 2 6% 5% 4 6% 4 6% 9% 40%	2660
	21st to end	Day	10% 5% 2 5% 5% 6% 6% 5% 7% 10% 41%	2660
July	1st to 10th	Day	8% 5% 2 7% 5% 6% 6% 6% 8% 11% 36%	4440
	11th to 20th	Day	11% 7% 2 6% 5% 5% 6% 5% 8% 10% 36%	4440
	21st to end	Day	12% 7% 3 8% 5% 5% 7% 5% 7% 9% 31%	4814
August	1st to 10th	Day	18% 6% 2 7% 5% 4 5% 5% 7% 9% 32%	4065
	11th to 20th	Day	13% 6% 3 6% 4 5% 5% 4 6% 8% 41%	3730
	21st to end	Day	9% 4 2 5% 3 4 6% 5% 7% 10% 45%	4180
September	1st to 10th	Day	14% 6% 3 5% 4 3 3 3 5% 8% 46%	2280
	11th to 20th	Day	11% 5% 2 6% 3 3 4 4 5% 8% 48%	2196
	21st to end	Day	19% 7% 3 6% 4 3 4 4 4 6% 40%	2090
October	1st to 10th	Day	20% 5% 2 6% 3 3 4 3 5% 6% 44%	1990
	11th to 20th	Day	15% 5% 2 4 4 2 3 2 4 6% 52%	1900
	21st to end	Day	18% 6% 3 5% 3 3 3 2 4 6% 46%	1956
November	1st to 10th	Day	14% 5% 2 5% 3 3 4 3 5% 6% 51%	1761
	11th to 20th	Day	16% 6% 2 5% 4 3 4 3 5% 5% 48%	1800
	21st to end	Day	16% 5% 2 5% 4 3 5% 3 4 7% 45%	1731
December	1st to 10th	Day	17% 7% 3 7% 3 4 4 4 5% 6% 41%	1520
	11th to 20th	Day	19% 7% 2 4 3 3 4 3 5% 5% 45%	1906
	21st to end	Day	17% 6% 3 6% 4 4 5% 4 5% 7% 38%	2772
January	1st to 10th	Night	17% 6% 2 4 3 3 3 3 4 6% 48%	4429
	11th to 20th	Night	18% 9% 2 6% 3 3 3 3 3 4 44%	4440
	21st to end	Night	23% 9% 3 6% 4 3 4 2 5% 5% 35%	4587
February	1st to 10th	Night	17% 10% 2 6% 3 3 3 3 5% 6% 42%	2439
	11th to 20th	Night	18% 9% 2 5% 4 3 3 3 5% 5% 42%	2218
	21st to end	Night	19% 7% 2 5% 3 3 3 3 5% 6% 44%	1884
March	1st to 10th	Night	22% 11% 4 6% 3 3 2 2 4 5% 38%	3724
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 4 6% 47%	3612
	21st to end	Night	20% 9% 3 6% 4 3 3 2 4 4 42%	3501
April	1st to 10th	Night	17% 9% 3 5% 4 3 4 3 5% 6% 41%	1900
	11th to 20th	Night	16% 8% 3 7% 4 3 4 3 5% 6% 42%	1875
	21st to end	Night	18% 6% 2 5% 3 4 4 4 5% 7% 42%	1900
May	1st to 10th	Night	23% 11% 4 8% 4 4 4 3 5% 7% 27%	2834
	11th to 20th	Night	27% 10% 3 5% 4 4 4 3 4 6% 31%	2605
	21st to end	Night	16% 8% 2 6% 4 4 3 3 6% 9% 40%	2738
June	1st to 10th	Night	16% 7% 3 5% 4 4 4 4 5% 8% 41%	1520
	11th to 20th	Night	13% 6% 3 5% 5% 5% 5% 4 5% 9% 41%	1520
	21st to end	Night	8% 5% 2 7% 5% 6% 6% 4 8% 11% 40%	1520
July	1st to 10th	Night	8% 8% 3 8% 5% 5% 6% 5% 7% 9% 35%	2520
	11th to 20th	Night	11% 8% 2 6% 4 4 5% 4 7% 10% 38%	2520
	21st to end	Night	16% 8% 3 7% 5% 5% 4 4 7% 8% 34%	2739
August	1st to 10th	Night	22% 8% 2 7% 4 4 4 3 6% 8% 32%	2831
	11th to 20th	Night	12% 6% 2 7% 4 4 4 4 6% 8% 44%	3097
	21st to end	Night	8% 5% 2 5% 4 4 4 3 5% 7% 53%	3476
September	1st to 10th	Night	14% 6% 2 5% 4 4 4 4 4 7% 44%	1900
	11th to 20th	Night	13% 5% 2 5% 2 4 3 3 5% 6% 51%	1982
	21st to end	Night	20% 8% 2 6% 3 3 3 3 5% 6% 41%	2090
October	1st to 10th	Night	20% 6% 2 5% 4 4 3 2 5% 5% 43%	2186
	11th to 20th	Night	15% 5% 1 5% 3 3 3 3 5% 6% 51%	2280
	21st to end	Night	17% 7% 2 5% 4 3 3 2 5% 5% 47%	2641
November	1st to 10th	Night	12% 5% 2 5% 4 3 3 2 5% 6% 53%	2537
	11th to 20th	Night	17% 6% 2 5% 4 3 3 3 4 5% 48%	2600
	21st to end	Night	14% 6% 2 5% 4 4 4 4 5% 7% 48%	2600
December	1st to 10th	Night	20% 7% 2 6% 4 4 4 3 4 6% 41%	2660
	11th to 20th	Night	18% 5% 2 5% 4 4 3 3 6% 6% 44%	3288
	21st to end	Night	17% 9% 3 5% 4 4 4 3 5% 6% 39%	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	25% 37% 7% 17% 11% 2	2518
	11th to 20th	Day	28% 38% 7% 16% 9% 2	2520
	21st to end	Day	39% 42% 3 11% 4 1	3064
February	1st to 10th	Day	17% 66% 6% 7% 3 1	1738
	11th to 20th	Day	16% 64% 2 9% 8% 1	1857
	21st to end	Day	17% 65% 5% 7% 4 2	1570
March	1st to 10th	Day	33% 41% 6% 14% 4 2	3119
	11th to 20th	Day	16% 42% 8% 22% 10% 1	3342
	21st to end	Day	27% 41% 6% 9% 14% 4	4130
April	1st to 10th	Day	17% 65% 4 7% 5% 1	2280
	11th to 20th	Day	13% 66% 6% 8% 6%	2254
	21st to end	Day	15% 65% 5% 7% 7% 1	2280
May	1st to 10th	Day	39% 42% 6% 7% 4	4119
	11th to 20th	Day	35% 41% 9% 11% 3	4322
	21st to end	Day	22% 43% 7% 15% 12% 1	4837
June	1st to 10th	Day	16% 65% 3 7% 7%	2660
	11th to 20th	Day	13% 66% 4 11% 6%	2660
	21st to end	Day	11% 65% 6% 8% 9%	2660
July	1st to 10th	Day	30% 43% 7% 10% 10% 1	4370
	11th to 20th	Day	27% 41% 13% 11% 7%	4365
	21st to end	Day	31% 39% 8% 12% 9% 1	4661
August	1st to 10th	Day	32% 41% 11% 12% 4	4051
	11th to 20th	Day	24% 40% 9% 22% 5%	3766
	21st to end	Day	14% 39% 10% 23% 12% 1	4180
September	1st to 10th	Day	15% 61% 7% 8% 8% 1	2280
	11th to 20th	Day	14% 61% 4 10% 10% 1	2196
	21st to end	Day	22% 60% 4 8% 6%	2090
October	1st to 10th	Day	20% 38% 9% 14% 16% 4	3302
	11th to 20th	Day	10% 37% 7% 15% 26% 5%	3140
	21st to end	Day	13% 38% 11% 19% 18% 2	3194
November	1st to 10th	Day	16% 56% 6% 10% 9% 1	1761
	11th to 20th	Day	15% 56% 3 10% 14% 1	1800
	21st to end	Day	14% 58% 6% 15% 5% 1	1731
December	1st to 10th	Day	22% 60% 6% 6% 6% 1	1520
	11th to 20th	Day	22% 48% 4 14% 10% 1	1906
	21st to end	Day	28% 40% 7% 16% 8%	2772
January	1st to 10th	Night	24% 37% 7% 21% 8% 3	4429
	11th to 20th	Night	28% 37% 6% 17% 9% 2	4440
	21st to end	Night	36% 40% 5% 11% 7% 1	4587
February	1st to 10th	Night	16% 65% 6% 8% 3 1	2439
	11th to 20th	Night	16% 63% 2 7% 10% 1	2220
	21st to end	Night	17% 64% 4 6% 6% 2	1884
March	1st to 10th	Night	36% 41% 3 13% 6% 1	3734
	11th to 20th	Night	19% 42% 9% 18% 11% 2	3613
	21st to end	Night	31% 40% 3 8% 16% 2	3501
April	1st to 10th	Night	18% 65% 3 7% 6% 1	1900
	11th to 20th	Night	14% 66% 4 9% 7% 1	1875
	21st to end	Night	16% 65% 3 8% 7% 1	1900
May	1st to 10th	Night	37% 42% 7% 11% 3	2840
	11th to 20th	Night	38% 41% 9% 10% 2	2606
	21st to end	Night	24% 43% 9% 12% 11% 1	2739
June	1st to 10th	Night	15% 66% 2 7% 9%	1520
	11th to 20th	Night	13% 66% 4 11% 6%	1520
	21st to end	Night	13% 65% 5% 9% 7% 1	1520
July	1st to 10th	Night	31% 40% 9% 11% 8% 1	2480
	11th to 20th	Night	27% 39% 13% 16% 5%	2472
	21st to end	Night	35% 37% 10% 9% 9% 1	2651
August	1st to 10th	Night	37% 39% 12% 8% 4	2821
	11th to 20th	Night	24% 39% 9% 22% 6%	3127
	21st to end	Night	15% 38% 6% 25% 15% 1	3476
September	1st to 10th	Night	15% 61% 7% 9% 7% 1	1900
	11th to 20th	Night	14% 60% 4 9% 10% 2	1982
	21st to end	Night	22% 60% 3 8% 5%	2090
October	1st to 10th	Night	23% 38% 7% 15% 15% 2	3654
	11th to 20th	Night	10% 37% 6% 19% 25% 4	3779
	21st to end	Night	12% 37% 8% 22% 18% 4	4340
November	1st to 10th	Night	17% 56% 6% 11% 8% 2	2537
	11th to 20th	Night	16% 56% 4 9% 12% 3	2600
	21st to end	Night	15% 58% 6% 13% 7% 1	2600
December	1st to 10th	Night	21% 60% 5% 9% 5%	2660
	11th to 20th	Night	20% 49% 7% 9% 12% 3	3288
	21st to end	Night	29% 40% 8% 16% 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	22% 16% 42% 15% 4 1	180
	11th to 20th	Day	30% 27% 26% 14% 4	180
	21st to end	Day	24% 17% 37% 18% 3 1	281
February	1st to 10th	Day	24% 20% 38% 15% 2 1	298
	11th to 20th	Day	25% 18% 40% 15% 1	456
	21st to end	Day	28% 19% 32% 18% 3	382
March	1st to 10th	Day	24% 17% 36% 18% 5%	460
	11th to 20th	Day	19% 20% 39% 16% 5% 1	460
	21st to end	Day	27% 20% 31% 17% 4 1	506
April	1st to 10th	Day	23% 19% 34% 16% 6% 1	460
	11th to 20th	Day	21% 15% 35% 20% 8% 2	452
	21st to end	Day	25% 14% 35% 19% 5% 2	460
May	1st to 10th	Day	27% 12% 32% 19% 8% 2	463
	11th to 20th	Day	23% 8% 35% 24% 7% 2	487
	21st to end	Day	20% 5% 25% 28% 16% 5%	529
June	1st to 10th	Day	16% 7% 28% 30% 14% 4	490
	11th to 20th	Day	13% 7% 33% 30% 13% 4	490
	21st to end	Day	13% 4 31% 33% 16% 4	490
July	1st to 10th	Day	12% 3 24% 33% 20% 8%	485
	11th to 20th	Day	9% 4 22% 36% 22% 7%	484
	21st to end	Day	12% 5% 27% 34% 17% 5%	532
August	1st to 10th	Day	12% 3 23% 36% 19% 7%	486
	11th to 20th	Day	13% 5% 19% 33% 23% 8%	479
	21st to end	Day	12% 4 24% 31% 19% 10%	539
September	1st to 10th	Day	17% 6% 26% 25% 16% 9%	490
	11th to 20th	Day	13% 4 25% 32% 16% 11%	490
	21st to end	Day	25% 7% 26% 25% 13% 4	490
October	1st to 10th	Day	24% 8% 22% 24% 15% 7%	490
	11th to 20th	Day	16% 12% 30% 26% 13% 3	490
	21st to end	Day	20% 10% 34% 22% 11% 3	468
November	1st to 10th	Day	14% 12% 34% 25% 13% 2	395
	11th to 20th	Day	19% 16% 34% 22% 10%	400
	21st to end	Day	21% 10% 36% 23% 8% 1	349
December	1st to 10th	Day	24% 19% 36% 11% 8% 1	180
	11th to 20th	Day	29% 19% 31% 15% 6%	180
	21st to end	Day	26% 13% 32% 23% 5% 1	198
January	1st to 10th	Night	20% 12% 42% 21% 4	760
	11th to 20th	Night	26% 12% 34% 24% 4	760
	21st to end	Night	19% 14% 42% 22% 3	836
February	1st to 10th	Night	21% 11% 39% 25% 3	760
	11th to 20th	Night	24% 16% 42% 17% 1	743
	21st to end	Night	23% 16% 36% 21% 4	628
March	1st to 10th	Night	21% 12% 40% 23% 4	760
	11th to 20th	Night	22% 12% 40% 21% 4 1	760
	21st to end	Night	22% 9% 39% 24% 6%	836
April	1st to 10th	Night	22% 12% 37% 23% 6%	760
	11th to 20th	Night	20% 9% 34% 31% 6%	751
	21st to end	Night	21% 8% 34% 31% 6% 1	760
May	1st to 10th	Night	25% 8% 29% 29% 8% 1	570
	11th to 20th	Night	24% 7% 32% 30% 6%	445
	21st to end	Night	20% 2 19% 40% 18% 2	411
June	1st to 10th	Night	19% 4 21% 38% 17% 1	380
	11th to 20th	Night	14% 4 22% 41% 19%	380
	21st to end	Night	9% 2 22% 52% 15%	380
July	1st to 10th	Night	13% 4 15% 45% 20% 3	370
	11th to 20th	Night	12% 4 15% 43% 25% 2	368
	21st to end	Night	12% 3 20% 44% 21%	416
August	1st to 10th	Night	13% 2 14% 47% 22% 3	560
	11th to 20th	Night	13% 3 15% 41% 25% 3	750
	21st to end	Night	14% 3 15% 40% 24% 4	836
September	1st to 10th	Night	16% 3 22% 36% 20% 3	760
	11th to 20th	Night	16% 3 17% 35% 23% 6%	760
	21st to end	Night	23% 4 21% 31% 18% 2	760
October	1st to 10th	Night	23% 5% 25% 26% 17% 4	760
	11th to 20th	Night	17% 8% 28% 34% 12% 1	760
	21st to end	Night	22% 6% 36% 25% 11% 1	836
November	1st to 10th	Night	15% 8% 35% 29% 12% 1	780
	11th to 20th	Night	20% 12% 33% 26% 9% 1	800
	21st to end	Night	16% 12% 37% 26% 8% 1	789
December	1st to 10th	Night	25% 13% 35% 19% 8% 1	760
	11th to 20th	Night	21% 10% 39% 26% 4	760
	21st to end	Night	21% 10% 40% 26% 3	836

Page generated at 2024-11-25 00:22:21. Version ac07

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