HG Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HG Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	14% 11% 4 9% 5% 5% 5% 4 5% 7% 33%	101849
	Night	13% 11% 4 10% 5% 5% 4 4 5% 6% 33%	97981
Transparency	Day	49% 6% 12% 22% 10% 1	105332
	Night	50% 6% 11% 22% 10% 1	102638
Seeing	Day	19% 13% 31% 23% 11% 3	16147
	Night	18% 10% 32% 29% 10% 1	26063

By Month

Percentage Cloud Cover SE (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	12% 16% 8% 21% 6% 5% 4 2 4 5% 17%	2527
	11th to 20th	Day	8% 16% 6% 16% 10% 8% 9% 3 5% 5% 14%	2530
	21st to end	Day	11% 19% 10% 16% 5% 5% 4 3 5% 5% 17%	2787
February	1st to 10th	Day	8% 14% 4 11% 5% 7% 7% 4 6% 6% 27%	1710
	11th to 20th	Day	9% 12% 5% 13% 7% 6% 5% 4 6% 6% 27%	1716
	21st to end	Day	12% 15% 6% 11% 7% 5% 4 4 5% 6% 24%	1570
March	1st to 10th	Day	12% 12% 4 9% 5% 4 3 3 3 6% 40%	3120
	11th to 20th	Day	8% 12% 5% 12% 7% 6% 5% 5% 5% 6% 29%	3374
	21st to end	Day	19% 14% 4 14% 5% 4 4 3 4 4 25%	4100
April	1st to 10th	Day	15% 14% 5% 10% 6% 5% 5% 4 4 5% 29%	2280
	11th to 20th	Day	20% 12% 5% 9% 5% 4 4 3 4 6% 29%	2254
	21st to end	Day	19% 11% 3 8% 5% 5% 5% 3 5% 6% 30%	2399
May	1st to 10th	Day	18% 8% 3 7% 4 4 4 4 5% 6% 37%	4399
	11th to 20th	Day	15% 8% 3 7% 4 4 4 4 5% 7% 39%	4399
	21st to end	Day	16% 9% 3 8% 5% 4 4 4 5% 6% 35%	4824
June	1st to 10th	Day	14% 7% 2 7% 4 4 4 4 6% 8% 40%	2660
	11th to 20th	Day	15% 7% 3 6% 5% 5% 5% 5% 6% 7% 37%	2660
	21st to end	Day	12% 7% 3 7% 5% 5% 5% 4 7% 9% 36%	2660
July	1st to 10th	Day	14% 4 2 6% 5% 4 5% 5% 7% 10% 37%	4440
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 5% 7% 10% 47%	4440
	21st to end	Day	8% 7% 2 6% 5% 5% 5% 4 7% 8% 44%	4813
August	1st to 10th	Day	13% 7% 3 8% 4 5% 5% 4 6% 7% 38%	4423
	11th to 20th	Day	14% 5% 2 5% 3 4 4 3 5% 7% 48%	4014
	21st to end	Day	14% 9% 3 7% 4 4 5% 3 5% 7% 38%	4180
September	1st to 10th	Day	14% 7% 2 6% 4 3 4 3 5% 8% 42%	2280
	11th to 20th	Day	14% 7% 2 6% 5% 5% 4 4 6% 8% 39%	2237
	21st to end	Day	17% 9% 3 6% 4 4 4 5% 5% 7% 36%	2090
October	1st to 10th	Day	18% 9% 3 6% 4 4 4 4 6% 7% 36%	1903
	11th to 20th	Day	20% 16% 3 7% 5% 4 4 4 5% 6% 25%	1897
	21st to end	Day	21% 15% 5% 9% 4 3 4 3 4 6% 27%	1881
November	1st to 10th	Day	16% 13% 3 8% 4 3 4 4 6% 6% 32%	1762
	11th to 20th	Day	16% 17% 5% 13% 6% 4 4 4 5% 5% 21%	1659
	21st to end	Day	14% 14% 5% 14% 7% 6% 4 4 5% 6% 20%	1600
December	1st to 10th	Day	11% 14% 6% 17% 8% 7% 5% 4 5% 5% 18%	1560
	11th to 20th	Day	13% 17% 6% 15% 8% 5% 6% 4 5% 4 16%	1918
	21st to end	Day	20% 24% 6% 13% 6% 4 4 3 3 3 13%	2783
January	1st to 10th	Night	12% 16% 7% 18% 6% 6% 5% 3 5% 5% 19%	4428
	11th to 20th	Night	8% 15% 6% 16% 8% 8% 7% 4 7% 5% 15%	4440
	21st to end	Night	10% 18% 9% 18% 6% 4 4 3 4 4 18%	4880
February	1st to 10th	Night	8% 11% 7% 12% 7% 6% 6% 4 5% 6% 29%	2470
	11th to 20th	Night	8% 11% 4 12% 7% 6% 5% 4 6% 6% 30%	2350
	21st to end	Night	12% 14% 5% 9% 7% 6% 5% 4 5% 5% 28%	1884
March	1st to 10th	Night	10% 7% 3 7% 4 4 4 4 6% 9% 40%	3733
	11th to 20th	Night	9% 10% 5% 13% 6% 4 4 4 5% 6% 35%	3617
	21st to end	Night	18% 14% 5% 10% 5% 4 4 3 4 5% 28%	3530
April	1st to 10th	Night	19% 12% 4 8% 4 3 4 4 5% 6% 30%	1900
	11th to 20th	Night	23% 10% 3 6% 3 3 3 3 5% 6% 35%	1875
	21st to end	Night	18% 11% 4 7% 4 4 4 3 6% 6% 34%	1777
May	1st to 10th	Night	18% 10% 2 6% 4 4 4 3 5% 7% 37%	2506
	11th to 20th	Night	12% 7% 3 7% 5% 4 4 4 4 6% 44%	2506
	21st to end	Night	15% 8% 3 8% 5% 5% 4 3 5% 7% 38%	2743
June	1st to 10th	Night	13% 6% 2 6% 3 4 4 4 6% 8% 43%	1520
	11th to 20th	Night	12% 6% 2 8% 6% 5% 4 4 6% 7% 39%	1520
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 9% 43%	1520
July	1st to 10th	Night	14% 6% 2 4 3 3 4 3 5% 8% 47%	2530
	11th to 20th	Night	6% 4 1 4 4 4 3 3 6% 10% 54%	2530
	21st to end	Night	8% 5% 2 6% 4 4 4 3 5% 7% 52%	2750
August	1st to 10th	Night	10% 7% 3 7% 5% 5% 5% 4 5% 9% 41%	2517
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 5% 6% 50%	2816
	21st to end	Night	15% 9% 3 6% 4 4 4 3 4 6% 44%	3476
September	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 5% 7% 49%	1900
	11th to 20th	Night	10% 7% 2 5% 4 4 4 4 5% 7% 48%	1924
	21st to end	Night	14% 9% 3 6% 4 4 4 3 5% 6% 41%	2090
October	1st to 10th	Night	15% 8% 2 6% 4 4 4 3 4 7% 42%	2275
	11th to 20th	Night	17% 13% 4 7% 4 4 4 4 4 8% 32%	2282
	21st to end	Night	19% 13% 3 8% 6% 4 5% 4 5% 6% 27%	2717
November	1st to 10th	Night	16% 13% 4 7% 4 4 4 3 4 7% 34%	2536
	11th to 20th	Night	14% 15% 7% 12% 5% 4 4 3 4 5% 26%	2739
	21st to end	Night	13% 16% 6% 13% 7% 5% 4 3 4 6% 23%	2800
December	1st to 10th	Night	11% 14% 6% 13% 7% 6% 5% 4 5% 6% 22%	2737
	11th to 20th	Night	11% 17% 7% 13% 8% 6% 5% 4 5% 5% 19%	3279
	21st to end	Night	22% 22% 6% 11% 5% 4 3 3 4 4 16%	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	69% 4 7% 17% 4	2528
	11th to 20th	Day	71% 5% 8% 10% 6%	2530
	21st to end	Day	68% 5% 11% 12% 4	2787
February	1st to 10th	Day	55% 5% 10% 17% 12%	1710
	11th to 20th	Day	54% 7% 10% 22% 7% 1	1725
	21st to end	Day	59% 5% 9% 17% 8% 1	1570
March	1st to 10th	Day	46% 4 13% 19% 17% 1	3120
	11th to 20th	Day	52% 6% 13% 18% 9% 1	3374
	21st to end	Day	62% 5% 8% 18% 7% 1	4100
April	1st to 10th	Day	56% 5% 10% 16% 11% 1	2280
	11th to 20th	Day	56% 5% 8% 20% 10% 1	2254
	21st to end	Day	55% 5% 9% 18% 12% 1	2399
May	1st to 10th	Day	46% 6% 10% 25% 13% 1	4440
	11th to 20th	Day	42% 7% 12% 26% 12% 1	4403
	21st to end	Day	48% 6% 10% 20% 15% 1	4837
June	1st to 10th	Day	41% 7% 14% 27% 11% 1	2660
	11th to 20th	Day	44% 8% 13% 21% 13% 1	2660
	21st to end	Day	41% 9% 16% 23% 10% 1	2660
July	1st to 10th	Day	40% 7% 16% 26% 10%	4371
	11th to 20th	Day	29% 7% 16% 33% 13% 2	4365
	21st to end	Day	36% 6% 12% 29% 15%	4662
August	1st to 10th	Day	42% 6% 15% 23% 12% 1	4408
	11th to 20th	Day	36% 6% 13% 33% 12%	4055
	21st to end	Day	45% 6% 14% 24% 11% 1	4179
September	1st to 10th	Day	39% 6% 14% 29% 12%	2280
	11th to 20th	Day	41% 8% 17% 26% 7%	2237
	21st to end	Day	46% 7% 12% 26% 9%	2090
October	1st to 10th	Day	34% 5% 13% 29% 18%	3163
	11th to 20th	Day	52% 4 11% 19% 14%	3125
	21st to end	Day	53% 4 17% 20% 6%	3081
November	1st to 10th	Day	51% 6% 11% 22% 9% 1	1762
	11th to 20th	Day	63% 5% 10% 14% 6%	1659
	21st to end	Day	62% 7% 14% 14% 3 1	1600
December	1st to 10th	Day	67% 5% 10% 14% 3	1560
	11th to 20th	Day	68% 7% 10% 11% 4	1915
	21st to end	Day	76% 4 6% 10% 5%	2783
January	1st to 10th	Night	65% 5% 9% 17% 3 1	4428
	11th to 20th	Night	68% 6% 9% 13% 4	4440
	21st to end	Night	68% 5% 7% 15% 4	4880
February	1st to 10th	Night	54% 5% 8% 20% 11% 2	2470
	11th to 20th	Night	51% 6% 11% 21% 9% 2	2351
	21st to end	Night	56% 5% 12% 17% 9% 1	1884
March	1st to 10th	Night	38% 6% 17% 25% 13% 1	3733
	11th to 20th	Night	48% 6% 11% 24% 10% 1	3617
	21st to end	Night	59% 4 8% 19% 8% 1	3530
April	1st to 10th	Night	53% 5% 9% 17% 15% 1	1900
	11th to 20th	Night	50% 4 9% 21% 13% 2	1875
	21st to end	Night	50% 6% 10% 20% 14% 1	1777
May	1st to 10th	Night	46% 6% 14% 20% 14% 1	2530
	11th to 20th	Night	39% 7% 11% 25% 15% 2	2507
	21st to end	Night	44% 9% 14% 17% 14% 1	2751
June	1st to 10th	Night	38% 6% 14% 29% 12% 1	1520
	11th to 20th	Night	42% 7% 13% 22% 14% 2	1520
	21st to end	Night	36% 9% 16% 29% 10% 1	1520
July	1st to 10th	Night	35% 6% 19% 25% 13% 2	2490
	11th to 20th	Night	24% 7% 16% 37% 14% 2	2482
	21st to end	Night	30% 6% 13% 30% 19% 2	2662
August	1st to 10th	Night	40% 7% 15% 21% 16% 1	2508
	11th to 20th	Night	34% 7% 14% 30% 13% 2	2841
	21st to end	Night	43% 5% 13% 24% 13% 2	3476
September	1st to 10th	Night	33% 6% 13% 33% 15% 1	1900
	11th to 20th	Night	35% 6% 15% 34% 9%	1924
	21st to end	Night	41% 7% 13% 27% 11% 1	2090
October	1st to 10th	Night	32% 4 9% 33% 21% 2	3795
	11th to 20th	Night	40% 5% 10% 31% 13% 1	3793
	21st to end	Night	55% 5% 10% 20% 9%	4467
November	1st to 10th	Night	49% 5% 12% 22% 11%	2536
	11th to 20th	Night	58% 5% 13% 15% 8%	2739
	21st to end	Night	61% 6% 12% 16% 4 1	2800
December	1st to 10th	Night	61% 6% 13% 17% 4	2737
	11th to 20th	Night	65% 5% 10% 15% 4	3281
	21st to end	Night	72% 4 6% 14% 4	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	17% 17% 31% 25% 9% 2	270
	11th to 20th	Day	21% 14% 36% 21% 7% 1	270
	21st to end	Day	19% 14% 38% 24% 5%	297
February	1st to 10th	Day	19% 14% 44% 16% 6% 2	270
	11th to 20th	Day	16% 23% 41% 14% 6%	270
	21st to end	Day	18% 20% 48% 12% 1	225
March	1st to 10th	Day	17% 18% 42% 16% 6%	270
	11th to 20th	Day	19% 19% 35% 17% 8% 2	270
	21st to end	Day	26% 14% 32% 19% 7% 2	467
April	1st to 10th	Day	24% 14% 33% 23% 6%	460
	11th to 20th	Day	29% 17% 25% 20% 8% 1	452
	21st to end	Day	24% 14% 28% 22% 10% 2	465
May	1st to 10th	Day	23% 16% 31% 20% 7% 2	653
	11th to 20th	Day	21% 14% 30% 23% 9% 3	675
	21st to end	Day	21% 13% 26% 25% 11% 3	734
June	1st to 10th	Day	13% 14% 31% 25% 13% 4	680
	11th to 20th	Day	18% 11% 34% 26% 9% 3	680
	21st to end	Day	14% 12% 30% 25% 14% 5%	680
July	1st to 10th	Day	8% 6% 27% 31% 20% 8%	671
	11th to 20th	Day	12% 8% 28% 27% 16% 7%	668
	21st to end	Day	7% 8% 28% 30% 18% 9%	739
August	1st to 10th	Day	12% 6% 27% 27% 23% 5%	676
	11th to 20th	Day	16% 5% 22% 27% 24% 6%	611
	21st to end	Day	17% 10% 25% 26% 17% 6%	539
September	1st to 10th	Day	19% 11% 21% 25% 19% 6%	490
	11th to 20th	Day	13% 8% 30% 30% 15% 3	490
	21st to end	Day	23% 12% 22% 26% 15% 3	490
October	1st to 10th	Day	21% 17% 27% 24% 8% 3	303
	11th to 20th	Day	24% 23% 34% 13% 6%	300
	21st to end	Day	34% 16% 36% 12% 2	330
November	1st to 10th	Day	24% 15% 36% 19% 5% 2	300
	11th to 20th	Day	25% 21% 39% 10% 4	300
	21st to end	Day	21% 21% 40% 14% 4	300
December	1st to 10th	Day	21% 12% 42% 20% 5%	285
	11th to 20th	Day	25% 16% 40% 15% 3	270
	21st to end	Day	27% 24% 33% 14% 3	297
January	1st to 10th	Night	16% 10% 41% 26% 6%	950
	11th to 20th	Night	19% 11% 37% 26% 6% 1	950
	21st to end	Night	18% 9% 37% 30% 6%	1045
February	1st to 10th	Night	14% 12% 39% 27% 8%	950
	11th to 20th	Night	14% 15% 40% 25% 6%	876
	21st to end	Night	20% 13% 39% 24% 4	628
March	1st to 10th	Night	16% 13% 36% 27% 8% 1	760
	11th to 20th	Night	16% 13% 36% 27% 6% 1	655
	21st to end	Night	21% 10% 29% 29% 10% 1	627
April	1st to 10th	Night	24% 10% 34% 26% 6% 1	570
	11th to 20th	Night	27% 9% 28% 29% 7%	563
	21st to end	Night	23% 9% 31% 29% 7% 1	570
May	1st to 10th	Night	22% 10% 33% 29% 6%	570
	11th to 20th	Night	18% 10% 31% 32% 8% 1	561
	21st to end	Night	16% 8% 26% 37% 13% 1	617
June	1st to 10th	Night	14% 8% 26% 41% 12%	570
	11th to 20th	Night	15% 7% 30% 37% 11%	570
	21st to end	Night	13% 5% 23% 43% 14% 1	570
July	1st to 10th	Night	10% 2 21% 41% 24% 2	555
	11th to 20th	Night	12% 4 28% 35% 21% 1	552
	21st to end	Night	7% 2 23% 44% 21% 3	624
August	1st to 10th	Night	11% 2 22% 41% 23% 1	567
	11th to 20th	Night	14% 4 19% 34% 27% 2	564
	21st to end	Night	15% 6% 21% 34% 22% 2	627
September	1st to 10th	Night	14% 6% 23% 36% 17% 3	570
	11th to 20th	Night	12% 5% 28% 35% 18% 2	594
	21st to end	Night	18% 9% 27% 32% 12% 1	760
October	1st to 10th	Night	19% 8% 31% 27% 14% 1	760
	11th to 20th	Night	22% 13% 32% 25% 8%	760
	21st to end	Night	25% 9% 32% 26% 8%	836
November	1st to 10th	Night	21% 11% 36% 26% 5% 1	780
	11th to 20th	Night	20% 15% 36% 22% 6%	939
	21st to end	Night	21% 15% 36% 23% 5%	1000
December	1st to 10th	Night	19% 13% 36% 25% 6% 1	978
	11th to 20th	Night	21% 12% 36% 23% 7% 1	950
	21st to end	Night	28% 13% 34% 21% 4	1045

Page generated at 2024-12-03 05:45:09. Version ac07

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