GifNet.US Observatory
Clear Sky Chart
History

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

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	12% 6% 2 6% 4 4 4 4 6% 7% 43%	100211
	Night	12% 6% 2 5% 4 4 4 3 5% 7% 47%	98894
Transparency	Day	36% 7% 11% 20% 19% 6%	103856
	Night	33% 6% 11% 20% 21% 9%	103390
Seeing	Day	13% 5% 18% 24% 25% 15%	15162
	Night	14% 5% 22% 33% 23% 4	24905

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	17% 12% 3 5% 3 3 3 2 5% 6% 42%	2847
	11th to 20th	Day	22% 8% 2 4 3 3 3 2 3 5% 45%	2850
	21st to end	Day	21% 8% 3 6% 4 3 3 2 3 5% 42%	3135
February	1st to 10th	Day	18% 9% 2 6% 4 4 3 3 4 6% 41%	1801
	11th to 20th	Day	21% 9% 3 6% 4 4 4 3 3 4 40%	1848
	21st to end	Day	20% 9% 3 8% 5% 3 3 3 3 5% 38%	1570
March	1st to 10th	Day	19% 10% 4 9% 6% 4 4 3 4 5% 31%	3425
	11th to 20th	Day	15% 8% 3 6% 5% 5% 5% 4 6% 8% 37%	3480
	21st to end	Day	13% 8% 4 8% 5% 4 4 3 4 6% 42%	3899
April	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 6% 6% 43%	2280
	11th to 20th	Day	16% 6% 2 5% 4 4 3 4 6% 7% 42%	2254
	21st to end	Day	10% 6% 3 6% 4 4 5% 4 6% 8% 46%	2280
May	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 5% 8% 42%	3765
	11th to 20th	Day	11% 5% 2 7% 4 5% 6% 4 6% 8% 43%	3764
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 9% 40%	4373
June	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 12% 40%	2474
	11th to 20th	Day	5% 4 2 5% 5% 6% 6% 5% 7% 10% 46%	2502
	21st to end	Day	5% 4 2 5% 4 5% 5% 5% 8% 9% 46%	2470
July	1st to 10th	Day	5% 5% 2 7% 6% 6% 7% 6% 9% 11% 34%	4120
	11th to 20th	Day	7% 6% 3 7% 5% 7% 6% 6% 8% 10% 34%	4120
	21st to end	Day	14% 8% 3 8% 5% 5% 5% 5% 7% 10% 29%	4465
August	1st to 10th	Day	3 2 1 3 3 3 3 3 5% 7% 65%	3858
	11th to 20th	Day	6% 4 2 5% 4 4 5% 5% 8% 11% 48%	3729
	21st to end	Day	9% 5% 2 6% 5% 5% 4 4 6% 8% 47%	4180
September	1st to 10th	Day	8% 4 2 6% 5% 6% 5% 4 7% 9% 42%	2280
	11th to 20th	Day	12% 6% 2 7% 4 5% 4 3 5% 6% 46%	2280
	21st to end	Day	11% 4 2 5% 3 4 4 3 5% 6% 54%	2045
October	1st to 10th	Day	6% 4 2 5% 3 3 4 3 4 6% 60%	1900
	11th to 20th	Day	11% 4 2 4 3 4 4 3 5% 5% 57%	1900
	21st to end	Day	16% 4 2 4 3 3 3 3 3 5% 55%	2090
November	1st to 10th	Day	12% 5% 1 5% 4 3 3 3 4 5% 54%	1958
	11th to 20th	Day	11% 5% 2 5% 4 3 3 4 4 6% 53%	1833
	21st to end	Day	16% 7% 2 6% 4 4 4 3 3 7% 44%	1710
December	1st to 10th	Day	18% 8% 3 6% 4 4 4 4 4 6% 39%	1691
	11th to 20th	Day	15% 8% 3 7% 4 5% 4 3 4 4 43%	1918
	21st to end	Day	14% 7% 2 6% 5% 4 4 3 4 6% 43%	3117
January	1st to 10th	Night	17% 8% 2 5% 4 3 3 3 4 5% 46%	4108
	11th to 20th	Night	17% 7% 2 7% 4 3 3 2 3 5% 46%	4120
	21st to end	Night	23% 8% 2 4 3 3 3 2 3 4 45%	4532
February	1st to 10th	Night	17% 8% 3 6% 4 3 4 3 5% 6% 42%	2375
	11th to 20th	Night	19% 7% 2 5% 5% 4 4 3 4 5% 43%	2218
	21st to end	Night	21% 8% 2 5% 4 3 4 2 4 5% 42%	1884
March	1st to 10th	Night	18% 8% 2 7% 4 4 4 3 5% 6% 37%	3457
	11th to 20th	Night	14% 7% 2 6% 4 4 4 4 5% 9% 42%	3480
	21st to end	Night	14% 7% 3 7% 4 4 4 4 4 6% 42%	3732
April	1st to 10th	Night	11% 5% 2 5% 5% 4 4 4 6% 8% 48%	1900
	11th to 20th	Night	13% 6% 2 5% 3 3 4 3 6% 7% 47%	1875
	21st to end	Night	9% 6% 2 4 4 5% 3 3 5% 6% 52%	1900
May	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 10% 43%	3130
	11th to 20th	Night	14% 6% 2 6% 4 4 4 3 7% 7% 43%	3129
	21st to end	Night	10% 5% 2 7% 5% 5% 5% 4 7% 8% 42%	3186
June	1st to 10th	Night	5% 5% 1 6% 4 4 4 5% 8% 11% 47%	1661
	11th to 20th	Night	4 3 1 4 3 2 4 5% 7% 11% 55%	1621
	21st to end	Night	5% 4 1 4 5% 4 4 4 7% 9% 51%	1710
July	1st to 10th	Night	5% 5% 2 7% 5% 5% 5% 5% 8% 11% 42%	2850
	11th to 20th	Night	7% 4 2 6% 5% 5% 6% 6% 9% 11% 39%	2850
	21st to end	Night	11% 8% 3 8% 5% 4 4 4 6% 9% 39%	3098
August	1st to 10th	Night	2 2 1 2 2 3 3 2 5% 9% 68%	3072
	11th to 20th	Night	4 3 2 4 4 4 4 5% 7% 14% 49%	3100
	21st to end	Night	6% 4 2 6% 4 4 5% 4 6% 8% 50%	3476
September	1st to 10th	Night	7% 4 2 5% 4 5% 5% 5% 7% 9% 48%	1900
	11th to 20th	Night	9% 5% 3 5% 5% 3 4 3 7% 7% 50%	1900
	21st to end	Night	9% 3 2 4 3 3 4 3 5% 7% 58%	2109
October	1st to 10th	Night	7% 3 1 4 2 3 2 2 4 6% 65%	2280
	11th to 20th	Night	10% 4 2 4 3 3 3 3 4 5% 58%	2280
	21st to end	Night	12% 5% 2 4 2 3 3 3 3 5% 58%	2508
November	1st to 10th	Night	12% 6% 2 5% 3 2 3 3 4 5% 57%	2340
	11th to 20th	Night	11% 5% 2 4 3 3 3 3 4 6% 56%	2349
	21st to end	Night	14% 5% 2 6% 4 4 4 3 5% 5% 48%	2470
December	1st to 10th	Night	17% 7% 2 5% 3 3 4 4 5% 6% 44%	2484
	11th to 20th	Night	16% 6% 2 6% 4 5% 4 3 4 4 47%	3278
	21st to end	Night	16% 8% 2 6% 4 3 4 3 4 6% 43%	4532

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	44% 4 5% 18% 26% 4	2848
	11th to 20th	Day	42% 4 11% 17% 22% 3	2850
	21st to end	Day	46% 4 5% 17% 22% 6%	3135
February	1st to 10th	Day	46% 4 7% 17% 16% 9%	1801
	11th to 20th	Day	48% 4 5% 17% 18% 7%	1858
	21st to end	Day	49% 5% 7% 13% 18% 8%	1570
March	1st to 10th	Day	54% 6% 8% 12% 15% 6%	3425
	11th to 20th	Day	43% 8% 8% 20% 16% 5%	3480
	21st to end	Day	43% 5% 8% 19% 20% 4	3899
April	1st to 10th	Day	39% 7% 9% 21% 17% 7%	2280
	11th to 20th	Day	40% 6% 10% 17% 20% 7%	2254
	21st to end	Day	35% 8% 11% 20% 24% 3	2280
May	1st to 10th	Day	38% 9% 13% 24% 13% 3	3800
	11th to 20th	Day	35% 9% 13% 21% 21% 2	3768
	21st to end	Day	35% 11% 16% 26% 11% 2	4385
June	1st to 10th	Day	35% 8% 16% 24% 15% 1	2474
	11th to 20th	Day	31% 8% 17% 23% 17% 3	2502
	21st to end	Day	30% 9% 17% 24% 16% 3	2470
July	1st to 10th	Day	37% 13% 22% 19% 7% 1	4056
	11th to 20th	Day	38% 11% 20% 23% 7% 1	4051
	21st to end	Day	48% 8% 15% 22% 6%	4325
August	1st to 10th	Day	17% 6% 13% 31% 29% 3	3844
	11th to 20th	Day	27% 10% 19% 30% 13% 1	3765
	21st to end	Day	34% 7% 13% 22% 21% 3	4179
September	1st to 10th	Day	35% 9% 14% 19% 17% 6%	2280
	11th to 20th	Day	38% 7% 10% 16% 22% 7%	2280
	21st to end	Day	31% 6% 10% 21% 22% 11%	2045
October	1st to 10th	Day	15% 3 6% 14% 25% 36%	3160
	11th to 20th	Day	18% 3 4 13% 35% 28%	3140
	21st to end	Day	24% 3 5% 17% 37% 14%	3428
November	1st to 10th	Day	33% 4 9% 17% 29% 9%	1958
	11th to 20th	Day	33% 5% 7% 18% 26% 12%	1833
	21st to end	Day	41% 4 6% 18% 23% 8%	1710
December	1st to 10th	Day	46% 6% 8% 16% 16% 8%	1691
	11th to 20th	Day	44% 5% 6% 15% 25% 5%	1915
	21st to end	Day	40% 6% 8% 17% 25% 4	3117
January	1st to 10th	Night	40% 4 6% 16% 27% 6%	4108
	11th to 20th	Night	41% 5% 6% 21% 20% 8%	4120
	21st to end	Night	43% 5% 8% 18% 21% 6%	4532
February	1st to 10th	Night	43% 5% 7% 17% 20% 8%	2375
	11th to 20th	Night	44% 5% 6% 16% 20% 9%	2219
	21st to end	Night	46% 5% 7% 13% 17% 13%	1884
March	1st to 10th	Night	45% 7% 10% 14% 16% 8%	3457
	11th to 20th	Night	38% 7% 12% 17% 18% 8%	3480
	21st to end	Night	40% 7% 9% 17% 23% 4	3732
April	1st to 10th	Night	33% 7% 11% 19% 19% 10%	1900
	11th to 20th	Night	35% 6% 10% 18% 22% 10%	1875
	21st to end	Night	32% 7% 8% 23% 26% 5%	1900
May	1st to 10th	Night	34% 9% 13% 23% 17% 4	3160
	11th to 20th	Night	36% 7% 12% 27% 17% 1	3130
	21st to end	Night	36% 10% 14% 24% 15% 2	3195
June	1st to 10th	Night	28% 10% 19% 25% 17% 2	1661
	11th to 20th	Night	22% 7% 18% 30% 18% 4	1621
	21st to end	Night	26% 9% 16% 27% 18% 4	1710
July	1st to 10th	Night	33% 11% 24% 21% 9% 2	2805
	11th to 20th	Night	32% 11% 24% 23% 9% 1	2796
	21st to end	Night	42% 8% 17% 25% 8% 1	2999
August	1st to 10th	Night	13% 6% 17% 31% 31% 3	3062
	11th to 20th	Night	23% 9% 19% 33% 13% 2	3130
	21st to end	Night	31% 8% 12% 20% 24% 5%	3476
September	1st to 10th	Night	30% 9% 14% 22% 16% 9%	1900
	11th to 20th	Night	32% 7% 13% 17% 22% 9%	1900
	21st to end	Night	25% 6% 9% 25% 22% 13%	2109
October	1st to 10th	Night	14% 3 7% 15% 23% 38%	3800
	11th to 20th	Night	18% 3 4 14% 29% 33%	3779
	21st to end	Night	19% 3 7% 14% 37% 20%	4120
November	1st to 10th	Night	32% 4 8% 17% 26% 13%	2340
	11th to 20th	Night	31% 4 8% 16% 28% 13%	2349
	21st to end	Night	37% 5% 7% 17% 23% 11%	2470
December	1st to 10th	Night	39% 6% 10% 18% 19% 7%	2484
	11th to 20th	Night	40% 5% 7% 14% 25% 9%	3280
	21st to end	Night	41% 5% 8% 19% 23% 5%	4532

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% 12% 39% 21% 7% 1	270
	11th to 20th	Day	26% 13% 31% 20% 8% 1	270
	21st to end	Day	20% 14% 35% 24% 6%	297
February	1st to 10th	Day	23% 8% 36% 24% 9% 1	270
	11th to 20th	Day	29% 16% 29% 20% 6%	270
	21st to end	Day	29% 17% 33% 16% 5%	225
March	1st to 10th	Day	20% 14% 32% 22% 10% 1	270
	11th to 20th	Day	18% 13% 37% 27% 4 1	270
	21st to end	Day	15% 14% 35% 24% 13% 1	344
April	1st to 10th	Day	15% 10% 37% 25% 12% 2	460
	11th to 20th	Day	21% 9% 27% 26% 14% 2	452
	21st to end	Day	12% 10% 26% 28% 20% 3	460
May	1st to 10th	Day	14% 6% 24% 35% 19% 3	463
	11th to 20th	Day	12% 2 18% 31% 25% 11%	487
	21st to end	Day	7% 3 17% 31% 26% 15%	669
June	1st to 10th	Day	10% 2 11% 29% 32% 17%	680
	11th to 20th	Day	6% 1 10% 29% 38% 15%	680
	21st to end	Day	6% 2 9% 25% 36% 22%	680
July	1st to 10th	Day	6% 2 7% 20% 41% 25%	671
	11th to 20th	Day	5% 2 5% 17% 40% 31%	668
	21st to end	Day	8% 1 4 19% 41% 27%	739
August	1st to 10th	Day	6% 5% 16% 40% 32%	534
	11th to 20th	Day	10% 4 14% 39% 32%	479
	21st to end	Day	13% 2 3 13% 31% 38%	539
September	1st to 10th	Day	8% 1 8% 21% 35% 27%	490
	11th to 20th	Day	13% 2 6% 18% 34% 28%	490
	21st to end	Day	13% 4 9% 21% 34% 19%	428
October	1st to 10th	Day	7% 2 14% 32% 28% 16%	300
	11th to 20th	Day	7% 4 24% 31% 25% 9%	300
	21st to end	Day	18% 6% 22% 27% 19% 8%	330
November	1st to 10th	Day	17% 7% 21% 26% 22% 8%	300
	11th to 20th	Day	10% 6% 33% 31% 15% 4	270
	21st to end	Day	19% 7% 29% 27% 13% 4	270
December	1st to 10th	Day	19% 7% 34% 25% 11% 3	270
	11th to 20th	Day	20% 11% 31% 21% 15% 2	270
	21st to end	Day	20% 12% 35% 23% 7% 3	297
January	1st to 10th	Night	20% 9% 33% 31% 7%	950
	11th to 20th	Night	23% 8% 33% 27% 9%	950
	21st to end	Night	22% 8% 34% 31% 4	1045
February	1st to 10th	Night	21% 10% 34% 30% 5%	855
	11th to 20th	Night	22% 10% 34% 29% 4	743
	21st to end	Night	25% 12% 34% 26% 3	628
March	1st to 10th	Night	19% 8% 32% 33% 8%	597
	11th to 20th	Night	15% 8% 36% 35% 5%	570
	21st to end	Night	16% 6% 34% 32% 12%	627
April	1st to 10th	Night	11% 8% 35% 36% 10%	570
	11th to 20th	Night	14% 9% 30% 35% 10% 1	563
	21st to end	Night	12% 6% 31% 36% 15% 1	570
May	1st to 10th	Night	11% 4 22% 47% 14% 2	570
	11th to 20th	Night	11% 3 20% 40% 24% 1	561
	21st to end	Night	6% 4 14% 37% 34% 6%	617
June	1st to 10th	Night	6% 3 8% 40% 39% 5%	570
	11th to 20th	Night	4 1 9% 30% 51% 5%	570
	21st to end	Night	5% 1 8% 30% 43% 13%	570
July	1st to 10th	Night	5% 2 5% 28% 51% 10%	555
	11th to 20th	Night	6% 1 4 26% 48% 15%	552
	21st to end	Night	5% 1 5% 28% 49% 13%	624
August	1st to 10th	Night	3 1 5% 23% 52% 16%	567
	11th to 20th	Night	8% 1 4 25% 50% 11%	564
	21st to end	Night	11% 1 3 23% 46% 16%	627
September	1st to 10th	Night	8% 1 6% 32% 44% 8%	570
	11th to 20th	Night	11% 2 8% 29% 42% 8%	570
	21st to end	Night	10% 2 9% 34% 39% 5%	722
October	1st to 10th	Night	8% 1 12% 35% 40% 4	760
	11th to 20th	Night	11% 3 21% 38% 23% 3	760
	21st to end	Night	14% 5% 19% 37% 22% 2	836
November	1st to 10th	Night	12% 5% 22% 36% 22% 3	780
	11th to 20th	Night	13% 5% 28% 38% 15% 1	763
	21st to end	Night	16% 6% 28% 32% 15% 2	760
December	1st to 10th	Night	19% 8% 29% 35% 10%	774
	11th to 20th	Night	21% 7% 28% 34% 9%	950
	21st to end	Night	22% 9% 29% 32% 7% 1	1045

Page generated at 2024-11-08 05:44:44. Version ac07

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