Helmer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Helmer Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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% 4 4 5% 7% 32%	101358
	Night	14% 12% 4 10% 6% 5% 4 3 5% 6% 30%	97753
Transparency	Day	50% 6% 12% 21% 10% 1	104829
	Night	53% 6% 12% 19% 8% 1	102357
Seeing	Day	20% 16% 33% 21% 8% 3	15713
	Night	20% 12% 31% 26% 10% 1	25267

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	12% 16% 7% 21% 8% 6% 5% 3 4 5% 13%	2527
	11th to 20th	Day	12% 16% 5% 16% 9% 8% 6% 5% 6% 6% 10%	2530
	21st to end	Day	11% 19% 10% 16% 9% 7% 6% 4 4 4 10%	2783
February	1st to 10th	Day	8% 14% 5% 12% 11% 9% 6% 5% 8% 6% 18%	1562
	11th to 20th	Day	12% 15% 6% 15% 10% 7% 6% 4 5% 4 17%	1822
	21st to end	Day	11% 14% 8% 15% 9% 7% 5% 3 5% 5% 19%	1570
March	1st to 10th	Day	11% 14% 5% 9% 5% 4 5% 3 5% 6% 32%	3118
	11th to 20th	Day	9% 14% 6% 15% 7% 5% 5% 3 4 5% 26%	3368
	21st to end	Day	18% 13% 8% 14% 7% 4 4 3 4 5% 18%	3997
April	1st to 10th	Day	17% 16% 3 10% 5% 4 4 3 4 6% 28%	2280
	11th to 20th	Day	18% 13% 5% 8% 4 3 4 4 5% 5% 31%	2361
	21st to end	Day	16% 13% 3 7% 5% 4 4 4 5% 7% 33%	2470
May	1st to 10th	Day	15% 10% 3 7% 5% 4 4 3 4 6% 39%	4108
	11th to 20th	Day	13% 8% 2 6% 4 4 4 4 5% 7% 44%	4366
	21st to end	Day	15% 7% 2 6% 4 4 4 4 6% 9% 41%	4896
June	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 4 6% 8% 41%	2850
	11th to 20th	Day	14% 7% 2 7% 4 4 4 4 6% 8% 38%	2850
	21st to end	Day	15% 7% 2 6% 5% 4 4 4 6% 7% 39%	2850
July	1st to 10th	Day	15% 7% 3 6% 4 4 4 3 6% 8% 41%	4490
	11th to 20th	Day	7% 6% 2 6% 4 5% 5% 4 6% 9% 47%	4440
	21st to end	Day	10% 6% 2 5% 4 3 4 4 6% 9% 47%	4814
August	1st to 10th	Day	9% 6% 3 7% 5% 5% 5% 4 7% 8% 41%	4359
	11th to 20th	Day	14% 6% 2 6% 3 4 4 3 5% 7% 46%	4044
	21st to end	Day	15% 7% 3 6% 4 4 3 3 5% 8% 42%	4373
September	1st to 10th	Day	16% 7% 2 6% 4 4 5% 3 5% 8% 39%	2275
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 40%	2090
	21st to end	Day	16% 10% 3 7% 5% 4 4 4 6% 7% 35%	2090
October	1st to 10th	Day	19% 8% 3 9% 5% 4 5% 4 6% 6% 32%	2090
	11th to 20th	Day	22% 15% 4 10% 6% 4 4 4 6% 6% 20%	1754
	21st to end	Day	24% 17% 3 10% 6% 6% 4 4 5% 6% 15%	1881
November	1st to 10th	Day	18% 16% 5% 8% 6% 4 5% 4 5% 5% 25%	1699
	11th to 20th	Day	15% 19% 6% 13% 5% 5% 4 3 5% 6% 17%	1710
	21st to end	Day	18% 20% 7% 13% 8% 6% 5% 4 4 4 11%	1413
December	1st to 10th	Day	13% 18% 7% 17% 7% 5% 5% 3 5% 5% 16%	1330
	11th to 20th	Day	15% 21% 6% 15% 7% 6% 4 3 5% 5% 13%	1671
	21st to end	Day	24% 22% 8% 13% 6% 4 3 2 4 3 9%	2527
January	1st to 10th	Night	13% 17% 6% 21% 7% 5% 4 3 4 4 17%	4428
	11th to 20th	Night	9% 17% 5% 17% 11% 8% 6% 4 4 4 15%	4440
	21st to end	Night	13% 16% 9% 16% 10% 6% 6% 3 5% 5% 11%	4884
February	1st to 10th	Night	8% 16% 5% 12% 10% 7% 5% 5% 5% 5% 21%	2616
	11th to 20th	Night	10% 14% 6% 14% 10% 6% 5% 3 5% 5% 21%	2242
	21st to end	Night	12% 16% 6% 13% 7% 5% 5% 4 6% 6% 22%	1884
March	1st to 10th	Night	13% 11% 3 8% 4 3 3 3 6% 8% 37%	3722
	11th to 20th	Night	8% 14% 6% 9% 4 4 5% 3 5% 7% 33%	3590
	21st to end	Night	15% 11% 4 10% 6% 5% 5% 4 6% 6% 27%	3663
April	1st to 10th	Night	17% 14% 4 7% 5% 5% 4 4 7% 6% 27%	1900
	11th to 20th	Night	19% 9% 4 8% 4 3 4 4 5% 5% 35%	1768
	21st to end	Night	16% 10% 3 8% 5% 4 4 3 5% 5% 38%	1710
May	1st to 10th	Night	18% 9% 3 7% 4 3 4 3 5% 5% 40%	2833
	11th to 20th	Night	12% 8% 3 8% 5% 4 5% 4 5% 6% 40%	2523
	21st to end	Night	18% 8% 2 6% 4 3 4 5% 5% 8% 37%	2686
June	1st to 10th	Night	13% 6% 3 6% 4 4 4 5% 7% 8% 41%	1330
	11th to 20th	Night	14% 7% 2 6% 4 3 5% 3 8% 8% 41%	1330
	21st to end	Night	15% 8% 2 5% 3 3 3 3 5% 7% 45%	1330
July	1st to 10th	Night	13% 6% 2 7% 5% 5% 5% 5% 6% 8% 39%	2461
	11th to 20th	Night	8% 5% 2 5% 3 3 4 3 5% 7% 55%	2530
	21st to end	Night	8% 6% 2 6% 3 3 4 3 4 8% 52%	2750
August	1st to 10th	Night	11% 7% 3 7% 5% 5% 5% 3 6% 7% 44%	2578
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 52%	2785
	21st to end	Night	11% 6% 2 6% 4 3 4 3 5% 8% 48%	3279
September	1st to 10th	Night	12% 7% 2 6% 4 4 4 4 5% 6% 46%	1900
	11th to 20th	Night	14% 7% 2 6% 4 3 4 3 5% 8% 44%	2076
	21st to end	Night	16% 7% 2 6% 4 4 4 3 6% 7% 40%	2090
October	1st to 10th	Night	17% 9% 2 7% 4 4 4 4 5% 6% 37%	2090
	11th to 20th	Night	19% 13% 3 7% 5% 4 5% 4 6% 6% 27%	2421
	21st to end	Night	22% 14% 4 8% 5% 5% 5% 4 6% 6% 21%	2717
November	1st to 10th	Night	16% 16% 4 9% 6% 5% 5% 3 4 5% 28%	2452
	11th to 20th	Night	17% 15% 5% 12% 5% 5% 5% 4 7% 5% 20%	2470
	21st to end	Night	16% 17% 6% 11% 7% 5% 5% 3 5% 6% 18%	2762
December	1st to 10th	Night	13% 17% 7% 15% 6% 5% 5% 4 5% 6% 17%	2850
	11th to 20th	Night	15% 15% 5% 16% 7% 5% 5% 4 6% 5% 18%	3526
	21st to end	Night	22% 23% 11% 16% 5% 4 4 2 2 3 8%	5137

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	74% 7% 10% 7% 1	2528
	11th to 20th	Day	71% 9% 8% 11% 1	2530
	21st to end	Day	78% 7% 9% 5% 1	2783
February	1st to 10th	Day	64% 8% 11% 12% 5%	1562
	11th to 20th	Day	68% 7% 10% 10% 5%	1832
	21st to end	Day	67% 6% 8% 13% 5%	1570
March	1st to 10th	Day	51% 7% 14% 16% 11% 1	3120
	11th to 20th	Day	60% 5% 12% 16% 6% 1	3368
	21st to end	Day	67% 7% 8% 12% 6% 1	3997
April	1st to 10th	Day	58% 6% 9% 19% 9% 1	2280
	11th to 20th	Day	54% 5% 9% 20% 11% 1	2361
	21st to end	Day	51% 5% 9% 18% 13% 4	2470
May	1st to 10th	Day	44% 6% 9% 24% 14% 2	4120
	11th to 20th	Day	39% 6% 9% 30% 15% 1	4370
	21st to end	Day	39% 7% 13% 21% 17% 3	4896
June	1st to 10th	Day	40% 7% 12% 24% 15% 2	2850
	11th to 20th	Day	41% 7% 12% 23% 15% 1	2850
	21st to end	Day	43% 7% 14% 23% 11% 2	2850
July	1st to 10th	Day	40% 6% 15% 24% 14% 1	4421
	11th to 20th	Day	32% 8% 12% 34% 13% 1	4365
	21st to end	Day	33% 6% 11% 31% 18%	4662
August	1st to 10th	Day	38% 6% 13% 29% 12%	4344
	11th to 20th	Day	37% 6% 12% 33% 12%	4083
	21st to end	Day	41% 6% 15% 28% 10%	4372
September	1st to 10th	Day	43% 6% 12% 26% 12%	2275
	11th to 20th	Day	39% 8% 18% 28% 7%	2090
	21st to end	Day	46% 8% 16% 22% 9%	2090
October	1st to 10th	Day	39% 6% 14% 28% 12%	3480
	11th to 20th	Day	54% 5% 11% 22% 7%	2879
	21st to end	Day	63% 7% 14% 14% 3	3081
November	1st to 10th	Day	60% 6% 13% 16% 5%	1699
	11th to 20th	Day	66% 7% 13% 10% 4	1710
	21st to end	Day	74% 8% 10% 6% 1	1413
December	1st to 10th	Day	70% 6% 11% 9% 4	1330
	11th to 20th	Day	74% 7% 8% 9% 3	1671
	21st to end	Day	81% 5% 5% 5% 3	2527
January	1st to 10th	Night	72% 6% 8% 12% 2	4428
	11th to 20th	Night	70% 9% 9% 9% 3	4440
	21st to end	Night	74% 8% 10% 6% 2	4884
February	1st to 10th	Night	62% 7% 10% 13% 7% 1	2616
	11th to 20th	Night	64% 6% 11% 15% 5%	2243
	21st to end	Night	62% 7% 9% 15% 6%	1884
March	1st to 10th	Night	45% 5% 19% 23% 7%	3733
	11th to 20th	Night	49% 6% 12% 25% 8% 1	3591
	21st to end	Night	53% 7% 13% 17% 9% 1	3663
April	1st to 10th	Night	55% 7% 9% 17% 10% 2	1900
	11th to 20th	Night	50% 5% 9% 24% 10% 2	1768
	21st to end	Night	48% 5% 10% 19% 15% 3	1710
May	1st to 10th	Night	45% 5% 9% 24% 14% 2	2840
	11th to 20th	Night	44% 6% 9% 30% 11% 1	2524
	21st to end	Night	44% 8% 11% 19% 11% 7%	2687
June	1st to 10th	Night	38% 7% 14% 23% 16% 2	1330
	11th to 20th	Night	39% 6% 13% 23% 15% 3	1330
	21st to end	Night	38% 6% 11% 29% 14% 2	1330
July	1st to 10th	Night	41% 6% 14% 22% 14% 1	2421
	11th to 20th	Night	27% 5% 15% 38% 13% 2	2482
	21st to end	Night	32% 6% 10% 24% 24% 3	2662
August	1st to 10th	Night	39% 6% 11% 28% 14% 1	2569
	11th to 20th	Night	34% 5% 15% 33% 12% 1	2812
	21st to end	Night	34% 7% 13% 31% 14% 1	3279
September	1st to 10th	Night	37% 7% 14% 27% 13% 1	1900
	11th to 20th	Night	38% 8% 17% 27% 10% 1	2076
	21st to end	Night	42% 7% 17% 26% 8%	2090
October	1st to 10th	Night	41% 5% 12% 32% 9% 1	3480
	11th to 20th	Night	48% 6% 14% 24% 8%	4022
	21st to end	Night	58% 6% 15% 18% 3	4467
November	1st to 10th	Night	58% 6% 12% 17% 7%	2452
	11th to 20th	Night	64% 8% 10% 11% 6%	2470
	21st to end	Night	66% 8% 14% 9% 2	2762
December	1st to 10th	Night	67% 7% 12% 12% 2	2850
	11th to 20th	Night	67% 7% 12% 9% 4	3525
	21st to end	Night	83% 4 6% 5% 2	5137

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	20% 13% 43% 19% 3	270
	11th to 20th	Day	22% 16% 40% 18% 3 1	270
	21st to end	Day	21% 18% 37% 19% 5%	297
February	1st to 10th	Day	20% 23% 39% 12% 5% 1	270
	11th to 20th	Day	20% 24% 40% 11% 4 1	270
	21st to end	Day	24% 29% 35% 10% 2	225
March	1st to 10th	Day	20% 25% 38% 13% 4	270
	11th to 20th	Day	21% 19% 35% 16% 8% 1	387
	21st to end	Day	27% 19% 29% 17% 6% 2	506
April	1st to 10th	Day	26% 18% 32% 20% 3 1	460
	11th to 20th	Day	26% 22% 25% 18% 7% 1	452
	21st to end	Day	24% 15% 32% 18% 9% 2	460
May	1st to 10th	Day	25% 18% 30% 16% 7% 4	463
	11th to 20th	Day	18% 17% 38% 17% 8% 2	655
	21st to end	Day	17% 17% 34% 21% 9% 3	734
June	1st to 10th	Day	16% 17% 37% 20% 8% 1	680
	11th to 20th	Day	19% 16% 34% 23% 6% 3	680
	21st to end	Day	21% 13% 33% 24% 8% 3	680
July	1st to 10th	Day	10% 11% 38% 27% 11% 3	671
	11th to 20th	Day	11% 12% 34% 26% 11% 5%	668
	21st to end	Day	12% 9% 34% 26% 13% 6%	739
August	1st to 10th	Day	12% 11% 34% 26% 12% 5%	638
	11th to 20th	Day	16% 5% 22% 30% 20% 7%	479
	21st to end	Day	21% 10% 28% 24% 12% 5%	539
September	1st to 10th	Day	21% 12% 27% 22% 13% 5%	490
	11th to 20th	Day	13% 11% 32% 27% 12% 5%	490
	21st to end	Day	22% 13% 22% 30% 11% 2	490
October	1st to 10th	Day	23% 17% 29% 19% 9% 3	490
	11th to 20th	Day	29% 17% 35% 16% 2 1	334
	21st to end	Day	35% 22% 30% 11% 2	330
November	1st to 10th	Day	23% 22% 33% 19% 3	279
	11th to 20th	Day	24% 26% 31% 14% 5%	270
	21st to end	Day	28% 28% 32% 10% 1 1	192
December	1st to 10th	Day	24% 19% 31% 18% 7% 2	180
	11th to 20th	Day	23% 20% 40% 11% 2 3	180
	21st to end	Day	33% 20% 30% 12% 5%	225
January	1st to 10th	Night	18% 19% 35% 22% 7%	950
	11th to 20th	Night	21% 17% 34% 19% 8% 1	950
	21st to end	Night	20% 13% 37% 23% 6% 1	1045
February	1st to 10th	Night	16% 16% 38% 23% 7%	906
	11th to 20th	Night	21% 16% 34% 23% 6% 1	743
	21st to end	Night	19% 16% 38% 22% 5%	628
March	1st to 10th	Night	16% 15% 36% 24% 8% 1	760
	11th to 20th	Night	20% 18% 34% 23% 6% 1	760
	21st to end	Night	19% 11% 33% 27% 8% 1	746
April	1st to 10th	Night	25% 12% 30% 26% 6% 1	570
	11th to 20th	Night	25% 10% 30% 27% 8% 1	563
	21st to end	Night	21% 11% 32% 28% 8% 1	570
May	1st to 10th	Night	18% 11% 33% 30% 8% 1	570
	11th to 20th	Night	20% 7% 33% 31% 8% 1	561
	21st to end	Night	16% 9% 29% 32% 14%	579
June	1st to 10th	Night	15% 8% 33% 34% 9%	380
	11th to 20th	Night	18% 8% 28% 34% 11%	380
	21st to end	Night	17% 7% 31% 35% 9% 1	380
July	1st to 10th	Night	11% 4 30% 40% 13% 1	512
	11th to 20th	Night	13% 4 26% 34% 21% 1	552
	21st to end	Night	11% 4 23% 39% 20% 2	624
August	1st to 10th	Night	10% 3 24% 43% 20%	567
	11th to 20th	Night	12% 4 19% 36% 26% 2	564
	21st to end	Night	15% 5% 26% 35% 17% 2	627
September	1st to 10th	Night	16% 5% 24% 34% 19% 3	570
	11th to 20th	Night	17% 9% 25% 29% 17% 3	746
	21st to end	Night	20% 8% 25% 32% 14% 2	760
October	1st to 10th	Night	24% 9% 29% 25% 12% 1	760
	11th to 20th	Night	25% 13% 31% 23% 9%	760
	21st to end	Night	32% 12% 25% 24% 5% 1	836
November	1st to 10th	Night	25% 15% 32% 22% 6% 1	755
	11th to 20th	Night	26% 18% 30% 20% 7%	760
	21st to end	Night	26% 17% 32% 19% 5%	888
December	1st to 10th	Night	23% 20% 31% 20% 5% 1	950
	11th to 20th	Night	23% 19% 33% 17% 6% 2	950
	21st to end	Night	29% 15% 33% 20% 4	1045

Page generated at 2024-11-01 22:47:50. Version ac07

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