Elginfield Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elginfield 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	15% 11% 4 9% 5% 5% 5% 4 6% 7% 31%	101591
	Night	15% 12% 4 9% 5% 4 4 3 5% 6% 30%	97392
Transparency	Day	51% 6% 12% 19% 11% 1	105183
	Night	52% 6% 12% 18% 11% 1	101889
Seeing	Day	19% 11% 28% 24% 13% 5%	15079
	Night	20% 10% 29% 28% 11% 1	24291

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% 20% 9% 14% 6% 6% 4 2 3 4 15%	2404
	11th to 20th	Day	12% 21% 10% 19% 9% 6% 5% 3 3 4 8%	2820
	21st to end	Day	21% 23% 9% 14% 6% 5% 4 2 3 3 9%	3124
February	1st to 10th	Day	15% 18% 5% 15% 10% 7% 5% 3 4 4 15%	1710
	11th to 20th	Day	13% 15% 8% 14% 10% 6% 5% 2 4 5% 17%	1664
	21st to end	Day	16% 15% 7% 13% 6% 4 5% 3 4 6% 22%	1570
March	1st to 10th	Day	18% 14% 6% 11% 6% 4 3 3 4 6% 25%	3335
	11th to 20th	Day	12% 16% 6% 11% 6% 4 4 4 4 6% 27%	3480
	21st to end	Day	18% 11% 4 10% 5% 4 4 3 5% 5% 30%	3815
April	1st to 10th	Day	16% 15% 5% 8% 4 3 5% 4 6% 6% 28%	2156
	11th to 20th	Day	19% 11% 3 6% 3 3 4 3 5% 8% 34%	2437
	21st to end	Day	19% 11% 4 7% 5% 3 4 3 6% 6% 33%	2470
May	1st to 10th	Day	18% 8% 3 7% 4 4 5% 3 6% 9% 33%	4108
	11th to 20th	Day	17% 9% 3 7% 4 5% 5% 4 7% 8% 30%	4081
	21st to end	Day	13% 6% 2 5% 4 4 4 3 5% 7% 46%	4837
June	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 7% 8% 38%	2679
	11th to 20th	Day	11% 7% 2 6% 5% 5% 5% 5% 6% 8% 40%	2850
	21st to end	Day	13% 6% 2 6% 4 4 5% 4 6% 8% 40%	2850
July	1st to 10th	Day	11% 5% 2 7% 5% 5% 5% 5% 7% 9% 40%	4760
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 9% 44%	4270
	21st to end	Day	8% 6% 2 6% 5% 6% 5% 5% 7% 9% 41%	4466
August	1st to 10th	Day	14% 7% 2 6% 5% 5% 5% 4 7% 10% 36%	4104
	11th to 20th	Day	11% 7% 2 7% 4 4 6% 5% 8% 11% 34%	4044
	21st to end	Day	9% 6% 3 7% 5% 4 6% 4 7% 9% 40%	4482
September	1st to 10th	Day	11% 7% 2 7% 5% 5% 5% 4 6% 8% 40%	2220
	11th to 20th	Day	11% 6% 2 6% 4 3 4 4 6% 9% 45%	2090
	21st to end	Day	17% 7% 2 6% 4 5% 5% 4 7% 8% 34%	2090
October	1st to 10th	Day	17% 7% 3 7% 5% 4 5% 4 6% 7% 35%	1944
	11th to 20th	Day	20% 11% 3 10% 6% 5% 4 3 6% 6% 25%	1900
	21st to end	Day	25% 13% 4 9% 5% 5% 5% 4 5% 6% 20%	2042
November	1st to 10th	Day	16% 15% 4 8% 6% 4 4 3 6% 6% 29%	1699
	11th to 20th	Day	16% 16% 4 9% 6% 5% 6% 4 6% 7% 21%	1558
	21st to end	Day	20% 20% 7% 11% 7% 5% 4 4 4 5% 14%	1520
December	1st to 10th	Day	16% 21% 9% 14% 7% 5% 4 3 5% 3 13%	1520
	11th to 20th	Day	19% 18% 8% 16% 6% 5% 5% 4 5% 3 13%	1906
	21st to end	Day	28% 20% 8% 11% 5% 4 3 3 4 5% 8%	2586
January	1st to 10th	Night	16% 19% 9% 18% 7% 5% 4 3 4 4 11%	4550
	11th to 20th	Night	15% 17% 9% 18% 9% 6% 5% 3 4 5% 10%	4121
	21st to end	Night	20% 19% 8% 16% 6% 5% 4 3 3 4 11%	4532
February	1st to 10th	Night	16% 18% 5% 13% 9% 6% 6% 3 4 4 17%	2470
	11th to 20th	Night	14% 16% 5% 12% 8% 6% 5% 4 5% 6% 18%	2399
	21st to end	Night	16% 14% 6% 12% 8% 5% 5% 4 5% 5% 21%	1884
March	1st to 10th	Night	15% 12% 5% 9% 5% 4 4 3 5% 6% 32%	3504
	11th to 20th	Night	10% 11% 5% 10% 5% 5% 5% 4 6% 7% 32%	3479
	21st to end	Night	16% 11% 3 8% 5% 5% 4 3 5% 5% 36%	3817
April	1st to 10th	Night	19% 12% 3 6% 5% 4 4 4 6% 5% 32%	2024
	11th to 20th	Night	17% 10% 3 7% 5% 4 3 3 6% 7% 35%	1706
	21st to end	Night	16% 11% 3 8% 4 4 5% 4 5% 7% 33%	1710
May	1st to 10th	Night	18% 8% 2 6% 4 4 3 4 5% 7% 39%	2833
	11th to 20th	Night	11% 9% 3 8% 6% 5% 5% 4 7% 8% 35%	2797
	21st to end	Night	11% 5% 2 4 3 3 4 3 6% 8% 50%	2738
June	1st to 10th	Night	12% 7% 2 6% 5% 4 4 4 5% 7% 43%	1495
	11th to 20th	Night	8% 6% 2 7% 5% 5% 5% 4 7% 10% 41%	1330
	21st to end	Night	10% 5% 2 6% 4 5% 3 4 6% 7% 47%	1330
July	1st to 10th	Night	6% 5% 1 5% 3 4 5% 4 7% 10% 50%	2210
	11th to 20th	Night	10% 4 2 5% 3 3 3 3 5% 8% 52%	2686
	21st to end	Night	6% 6% 2 6% 5% 5% 5% 5% 7% 8% 46%	3087
August	1st to 10th	Night	12% 6% 2 7% 4 4 5% 4 6% 7% 44%	2825
	11th to 20th	Night	13% 8% 3 5% 4 3 4 3 6% 7% 45%	2785
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 5% 8% 47%	3142
September	1st to 10th	Night	11% 6% 2 7% 4 4 4 3 5% 7% 47%	1957
	11th to 20th	Night	10% 5% 2 5% 3 4 3 3 5% 7% 52%	2090
	21st to end	Night	16% 6% 3 8% 5% 5% 4 3 5% 6% 40%	2090
October	1st to 10th	Night	14% 8% 3 8% 5% 4 4 3 5% 6% 40%	2234
	11th to 20th	Night	21% 10% 3 7% 4 4 5% 3 5% 6% 31%	2280
	21st to end	Night	24% 11% 4 9% 5% 4 5% 3 5% 6% 25%	2555
November	1st to 10th	Night	15% 12% 3 7% 5% 4 4 4 5% 6% 34%	2452
	11th to 20th	Night	16% 18% 4 10% 6% 5% 6% 4 6% 6% 21%	2619
	21st to end	Night	20% 17% 6% 10% 7% 4 4 4 5% 5% 18%	2660
December	1st to 10th	Night	19% 23% 8% 11% 7% 5% 4 3 4 4 12%	2660
	11th to 20th	Night	14% 22% 7% 13% 5% 5% 5% 4 5% 4 15%	3288
	21st to end	Night	26% 22% 8% 12% 5% 5% 4 3 3 3 10%	5053

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	72% 6% 11% 9% 2	2405
	11th to 20th	Day	81% 6% 6% 4 2	2820
	21st to end	Day	80% 5% 6% 5% 3	3124
February	1st to 10th	Day	71% 6% 10% 10% 3	1710
	11th to 20th	Day	69% 5% 8% 12% 5%	1673
	21st to end	Day	64% 5% 12% 12% 6% 1	1570
March	1st to 10th	Day	61% 4 10% 20% 4	3338
	11th to 20th	Day	55% 6% 16% 15% 7% 1	3480
	21st to end	Day	55% 5% 11% 17% 10% 2	3815
April	1st to 10th	Day	54% 6% 12% 18% 9%	2156
	11th to 20th	Day	48% 5% 13% 19% 13% 1	2437
	21st to end	Day	51% 6% 11% 18% 12% 2	2470
May	1st to 10th	Day	45% 7% 12% 21% 12% 3	4120
	11th to 20th	Day	48% 9% 14% 20% 8% 1	4085
	21st to end	Day	36% 6% 12% 20% 20% 5%	4837
June	1st to 10th	Day	40% 8% 13% 24% 12% 2	2679
	11th to 20th	Day	40% 8% 11% 23% 17% 2	2850
	21st to end	Day	40% 7% 13% 24% 16% 1	2850
July	1st to 10th	Day	41% 5% 13% 24% 16% 2	4686
	11th to 20th	Day	36% 4 12% 33% 14% 1	4195
	21st to end	Day	38% 6% 14% 21% 20% 1	4324
August	1st to 10th	Day	42% 6% 13% 23% 14% 1	4091
	11th to 20th	Day	42% 7% 15% 26% 10%	4083
	21st to end	Day	40% 4 12% 30% 13% 1	4482
September	1st to 10th	Day	41% 7% 13% 25% 13% 1	2220
	11th to 20th	Day	35% 7% 14% 29% 16%	2090
	21st to end	Day	46% 7% 13% 24% 10% 1	2090
October	1st to 10th	Day	42% 5% 12% 24% 16% 1	3230
	11th to 20th	Day	44% 4 13% 21% 17%	3140
	21st to end	Day	54% 4 17% 19% 6%	3344
November	1st to 10th	Day	55% 5% 13% 18% 7% 1	1699
	11th to 20th	Day	59% 6% 16% 11% 6% 1	1558
	21st to end	Day	72% 5% 11% 11% 2	1520
December	1st to 10th	Day	72% 8% 10% 8% 2	1520
	11th to 20th	Day	74% 7% 10% 8% 2	1906
	21st to end	Day	79% 5% 11% 4	2586
January	1st to 10th	Night	74% 7% 10% 7% 2	4550
	11th to 20th	Night	76% 8% 9% 5% 2	4121
	21st to end	Night	76% 5% 10% 7% 2 1	4532
February	1st to 10th	Night	68% 6% 10% 12% 3	2470
	11th to 20th	Night	64% 5% 12% 13% 5%	2401
	21st to end	Night	62% 6% 12% 14% 6%	1884
March	1st to 10th	Night	52% 7% 13% 22% 6%	3514
	11th to 20th	Night	46% 7% 17% 19% 9% 1	3480
	21st to end	Night	48% 7% 10% 20% 13% 1	3817
April	1st to 10th	Night	52% 5% 10% 20% 13% 1	2024
	11th to 20th	Night	48% 5% 10% 20% 16% 2	1706
	21st to end	Night	48% 6% 11% 17% 14% 3	1710
May	1st to 10th	Night	44% 6% 11% 20% 16% 4	2840
	11th to 20th	Night	44% 8% 13% 23% 10% 3	2798
	21st to end	Night	31% 7% 13% 23% 22% 4	2739
June	1st to 10th	Night	38% 5% 13% 25% 17% 2	1495
	11th to 20th	Night	36% 6% 12% 25% 17% 3	1330
	21st to end	Night	35% 6% 13% 26% 18% 1	1330
July	1st to 10th	Night	30% 4 13% 28% 18% 7%	2175
	11th to 20th	Night	30% 5% 14% 32% 18% 2	2638
	21st to end	Night	33% 6% 16% 22% 20% 2	2988
August	1st to 10th	Night	38% 5% 14% 25% 17% 1	2814
	11th to 20th	Night	38% 5% 14% 28% 14% 1	2812
	21st to end	Night	35% 5% 12% 32% 16% 1	3142
September	1st to 10th	Night	36% 7% 13% 26% 16% 2	1957
	11th to 20th	Night	32% 5% 12% 31% 19% 1	2090
	21st to end	Night	45% 5% 13% 24% 13%	2090
October	1st to 10th	Night	35% 4 9% 27% 24% 1	3728
	11th to 20th	Night	45% 3 17% 19% 15% 1	3779
	21st to end	Night	48% 4 14% 24% 10%	4203
November	1st to 10th	Night	48% 5% 14% 22% 10% 1	2452
	11th to 20th	Night	58% 7% 14% 14% 6% 1	2619
	21st to end	Night	66% 7% 15% 9% 3	2660
December	1st to 10th	Night	72% 8% 10% 8% 2	2660
	11th to 20th	Night	70% 5% 14% 9% 2	3288
	21st to end	Night	80% 5% 10% 5% 1	5053

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	21% 24% 28% 21% 5% 2	236
	11th to 20th	Day	20% 17% 46% 13% 3 1	270
	21st to end	Day	29% 12% 36% 19% 4	297
February	1st to 10th	Day	23% 22% 38% 13% 3	270
	11th to 20th	Day	24% 23% 36% 16%	270
	21st to end	Day	28% 28% 32% 11% 2	225
March	1st to 10th	Day	25% 14% 39% 16% 7%	397
	11th to 20th	Day	22% 15% 32% 24% 5% 1	460
	21st to end	Day	29% 15% 30% 20% 6% 1	506
April	1st to 10th	Day	21% 18% 34% 20% 7% 1	460
	11th to 20th	Day	29% 12% 28% 18% 10% 3	452
	21st to end	Day	24% 13% 32% 20% 9% 2	460
May	1st to 10th	Day	23% 12% 25% 27% 10% 4	463
	11th to 20th	Day	18% 9% 27% 24% 15% 6%	487
	21st to end	Day	14% 7% 24% 29% 18% 8%	529
June	1st to 10th	Day	13% 6% 35% 28% 14% 5%	509
	11th to 20th	Day	13% 9% 27% 34% 13% 4	680
	21st to end	Day	15% 8% 28% 32% 14% 4	680
July	1st to 10th	Day	10% 6% 22% 29% 24% 8%	671
	11th to 20th	Day	15% 6% 26% 27% 19% 7%	565
	21st to end	Day	9% 4 22% 33% 23% 9%	532
August	1st to 10th	Day	13% 4 18% 28% 25% 13%	486
	11th to 20th	Day	13% 3 20% 27% 22% 14%	479
	21st to end	Day	13% 5% 21% 28% 22% 11%	539
September	1st to 10th	Day	13% 6% 22% 28% 20% 11%	490
	11th to 20th	Day	9% 5% 19% 25% 29% 13%	490
	21st to end	Day	18% 9% 25% 27% 12% 9%	490
October	1st to 10th	Day	18% 12% 26% 22% 17% 5%	490
	11th to 20th	Day	23% 14% 32% 21% 8% 2	490
	21st to end	Day	28% 17% 32% 18% 4	491
November	1st to 10th	Day	24% 18% 28% 18% 9% 2	279
	11th to 20th	Day	27% 17% 35% 14% 6% 2	198
	21st to end	Day	28% 18% 37% 14% 3	180
December	1st to 10th	Day	29% 19% 33% 14% 4 1	180
	11th to 20th	Day	26% 25% 30% 15% 4	180
	21st to end	Day	30% 24% 31% 13% 2	198
January	1st to 10th	Night	24% 16% 38% 16% 5% 1	950
	11th to 20th	Night	29% 15% 32% 21% 4	761
	21st to end	Night	22% 11% 36% 24% 7%	836
February	1st to 10th	Night	25% 14% 36% 22% 3	760
	11th to 20th	Night	23% 14% 32% 25% 5%	743
	21st to end	Night	25% 16% 35% 21% 3	628
March	1st to 10th	Night	19% 13% 36% 25% 7%	760
	11th to 20th	Night	18% 16% 35% 23% 7% 1	760
	21st to end	Night	25% 11% 29% 27% 8% 1	836
April	1st to 10th	Night	23% 14% 30% 28% 5%	760
	11th to 20th	Night	22% 11% 34% 23% 10% 1	582
	21st to end	Night	19% 10% 33% 30% 7% 1	570
May	1st to 10th	Night	22% 5% 31% 30% 12% 1	570
	11th to 20th	Night	16% 4 30% 35% 13% 2	559
	21st to end	Night	13% 3 28% 39% 17% 1	411
June	1st to 10th	Night	15% 4 29% 37% 14% 1	380
	11th to 20th	Night	12% 3 26% 46% 13% 1	380
	21st to end	Night	11% 5% 21% 46% 15% 1	380
July	1st to 10th	Night	4 2 21% 48% 24% 1	370
	11th to 20th	Night	10% 3 20% 41% 24% 2	537
	21st to end	Night	9% 4 15% 47% 24% 1	624
August	1st to 10th	Night	9% 2 13% 43% 31% 2	567
	11th to 20th	Night	10% 3 13% 39% 31% 4	564
	21st to end	Night	13% 3 17% 38% 27% 3	632
September	1st to 10th	Night	12% 5% 22% 34% 23% 5%	760
	11th to 20th	Night	12% 3 17% 36% 28% 4	760
	21st to end	Night	18% 7% 21% 32% 17% 5%	760
October	1st to 10th	Night	19% 7% 26% 29% 18% 2	760
	11th to 20th	Night	26% 12% 25% 26% 10% 1	760
	21st to end	Night	28% 12% 31% 25% 4	836
November	1st to 10th	Night	21% 12% 28% 30% 8% 1	755
	11th to 20th	Night	25% 14% 34% 20% 6% 1	760
	21st to end	Night	29% 12% 31% 24% 5%	760
December	1st to 10th	Night	29% 17% 31% 18% 4	760
	11th to 20th	Night	24% 19% 37% 16% 3	760
	21st to end	Night	30% 14% 36% 17% 2	940

Page generated at 2024-11-01 22:47:36. Version ac07

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