Holgate
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Holgate clear sky chart from 2005-11-06 to 2024-12-24.

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% 7% 2 6% 4 4 4 4 6% 7% 41%	101658
	Night	16% 8% 3 6% 4 4 4 3 5% 7% 41%	98463
Transparency	Day	40% 6% 13% 24% 15% 2	105229
	Night	42% 5% 11% 23% 16% 3	102981
Seeing	Day	17% 6% 20% 31% 21% 4	15249
	Night	18% 8% 25% 30% 16% 3	24528

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% 9% 3 6% 3 3 3 3 4 6% 47%	2517
	11th to 20th	Day	15% 8% 2 7% 5% 4 4 3 5% 6% 42%	2520
	21st to end	Day	20% 11% 4 7% 5% 4 4 3 4 5% 34%	3124
February	1st to 10th	Day	15% 8% 3 7% 3 4 4 3 6% 8% 39%	1743
	11th to 20th	Day	17% 8% 3 6% 3 4 4 3 5% 5% 43%	1848
	21st to end	Day	17% 9% 3 6% 4 3 3 4 7% 6% 38%	1570
March	1st to 10th	Day	25% 8% 2 5% 3 3 3 3 4 5% 40%	3116
	11th to 20th	Day	10% 4 2 5% 4 4 4 4 5% 8% 50%	3370
	21st to end	Day	20% 7% 2 6% 3 3 3 3 5% 5% 42%	4122
April	1st to 10th	Day	16% 9% 2 6% 4 4 4 3 5% 7% 41%	2280
	11th to 20th	Day	14% 7% 2 6% 4 3 3 4 5% 6% 46%	2254
	21st to end	Day	16% 7% 3 6% 4 4 4 4 6% 6% 40%	2280
May	1st to 10th	Day	21% 13% 5% 9% 5% 4 4 3 5% 6% 26%	4064
	11th to 20th	Day	24% 9% 2 7% 4 5% 4 3 5% 6% 32%	4292
	21st to end	Day	11% 8% 3 7% 4 4 5% 4 6% 9% 39%	4837
June	1st to 10th	Day	12% 7% 2 5% 5% 4 4 5% 8% 8% 39%	2660
	11th to 20th	Day	11% 6% 2 5% 4 5% 5% 4 8% 10% 41%	2660
	21st to end	Day	8% 4 2 5% 4 4 5% 6% 8% 9% 45%	2660
July	1st to 10th	Day	7% 7% 2 7% 4 5% 5% 5% 8% 11% 39%	4440
	11th to 20th	Day	10% 5% 2 7% 4 5% 5% 5% 8% 11% 39%	4440
	21st to end	Day	10% 7% 2 7% 6% 5% 6% 5% 7% 9% 36%	4814
August	1st to 10th	Day	14% 5% 2 6% 4 4 5% 4 7% 11% 37%	3991
	11th to 20th	Day	12% 6% 2 6% 4 5% 4 4 6% 9% 43%	3730
	21st to end	Day	8% 5% 2 5% 4 3 4 4 7% 8% 51%	4180
September	1st to 10th	Day	14% 6% 2 4 4 3 3 3 5% 7% 48%	2280
	11th to 20th	Day	10% 5% 2 6% 3 4 5% 3 4 7% 50%	2203
	21st to end	Day	19% 8% 2 6% 5% 3 4 2 5% 6% 38%	2090
October	1st to 10th	Day	18% 6% 2 6% 3 4 2 3 5% 6% 45%	1983
	11th to 20th	Day	15% 5% 2 5% 3 2 3 3 4 6% 52%	1900
	21st to end	Day	16% 5% 2 5% 3 5% 4 3 5% 6% 45%	1976
November	1st to 10th	Day	14% 6% 2 5% 4 3 4 3 4 7% 49%	1761
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 6% 47%	1800
	21st to end	Day	15% 5% 2 5% 5% 4 3 2 5% 7% 46%	1771
December	1st to 10th	Day	17% 8% 2 5% 3 4 4 3 6% 7% 41%	1600
	11th to 20th	Day	17% 8% 2 6% 3 3 2 3 4 5% 46%	1986
	21st to end	Day	15% 7% 3 6% 4 4 4 4 6% 7% 40%	2796
January	1st to 10th	Night	16% 7% 2 5% 3 3 4 4 5% 6% 46%	4429
	11th to 20th	Night	20% 9% 2 6% 4 3 2 2 4 4 44%	4437
	21st to end	Night	20% 10% 3 7% 4 3 4 4 5% 5% 36%	4532
February	1st to 10th	Night	18% 7% 3 6% 4 3 3 3 5% 6% 42%	2434
	11th to 20th	Night	19% 8% 2 5% 4 3 4 4 5% 6% 41%	2218
	21st to end	Night	18% 7% 3 6% 3 3 4 3 4 6% 43%	1884
March	1st to 10th	Night	22% 11% 4 6% 3 3 3 2 4 6% 37%	3724
	11th to 20th	Night	13% 6% 3 6% 4 4 4 3 5% 5% 47%	3585
	21st to end	Night	20% 9% 3 6% 4 3 3 3 3 4 41%	3509
April	1st to 10th	Night	17% 8% 3 6% 4 3 4 4 4 6% 40%	1900
	11th to 20th	Night	14% 8% 3 6% 5% 4 4 3 4 6% 44%	1875
	21st to end	Night	18% 7% 3 5% 4 4 5% 4 6% 7% 40%	1900
May	1st to 10th	Night	19% 12% 5% 10% 4 4 5% 3 5% 7% 27%	2873
	11th to 20th	Night	25% 10% 3 7% 4 4 4 3 4 6% 30%	2629
	21st to end	Night	14% 10% 3 9% 4 4 4 3 5% 8% 36%	2738
June	1st to 10th	Night	15% 8% 2 7% 4 4 5% 4 5% 8% 38%	1520
	11th to 20th	Night	12% 6% 2 6% 5% 5% 4 4 6% 8% 42%	1520
	21st to end	Night	7% 6% 2 6% 5% 4 5% 5% 8% 11% 42%	1520
July	1st to 10th	Night	8% 9% 2 9% 6% 6% 5% 4 7% 8% 35%	2520
	11th to 20th	Night	9% 5% 3 7% 5% 5% 5% 4 7% 11% 39%	2520
	21st to end	Night	15% 9% 3 8% 6% 5% 5% 5% 5% 7% 33%	2739
August	1st to 10th	Night	18% 8% 3 8% 5% 4 5% 4 6% 9% 31%	2901
	11th to 20th	Night	9% 6% 2 6% 5% 4 4 4 6% 8% 45%	3097
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 8% 52%	3476
September	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	1900
	11th to 20th	Night	12% 6% 2 5% 2 3 4 4 6% 8% 49%	1976
	21st to end	Night	20% 8% 3 6% 4 4 4 3 6% 5% 38%	2090
October	1st to 10th	Night	20% 6% 2 6% 3 4 4 3 4 5% 42%	2194
	11th to 20th	Night	17% 5% 1 4 3 3 3 3 5% 6% 50%	2280
	21st to end	Night	17% 6% 2 5% 3 3 4 3 5% 5% 45%	2620
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 7% 51%	2537
	11th to 20th	Night	16% 7% 2 6% 4 3 3 3 4 5% 47%	2600
	21st to end	Night	13% 6% 2 4 4 4 4 3 6% 7% 47%	2625
December	1st to 10th	Night	17% 8% 2 6% 4 3 4 3 5% 7% 40%	2800
	11th to 20th	Night	17% 6% 2 6% 4 4 3 4 5% 7% 41%	3428
	21st to end	Night	14% 8% 3 6% 4 4 4 4 6% 7% 39%	4933

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	39% 4 10% 28% 16% 3	2518
	11th to 20th	Day	44% 5% 11% 24% 13% 4	2520
	21st to end	Day	54% 4 9% 22% 10% 2	3124
February	1st to 10th	Day	44% 4 14% 23% 12% 1	1743
	11th to 20th	Day	44% 4 8% 25% 15% 3	1857
	21st to end	Day	45% 5% 11% 22% 13% 4	1570
March	1st to 10th	Day	48% 3 8% 27% 11% 3	3119
	11th to 20th	Day	30% 6% 10% 32% 19% 3	3370
	21st to end	Day	44% 5% 8% 18% 20% 5%	4122
April	1st to 10th	Day	43% 5% 10% 20% 16% 6%	2280
	11th to 20th	Day	39% 5% 13% 23% 16% 4	2254
	21st to end	Day	42% 7% 10% 19% 18% 5%	2280
May	1st to 10th	Day	59% 5% 10% 16% 8% 2	4078
	11th to 20th	Day	52% 6% 14% 19% 8% 1	4296
	21st to end	Day	39% 8% 14% 21% 17% 1	4837
June	1st to 10th	Day	39% 9% 13% 23% 15% 2	2660
	11th to 20th	Day	36% 9% 14% 28% 11% 2	2660
	21st to end	Day	31% 9% 18% 25% 17% 1	2660
July	1st to 10th	Day	37% 11% 18% 20% 13% 1	4370
	11th to 20th	Day	37% 9% 18% 25% 9% 1	4365
	21st to end	Day	42% 9% 13% 21% 13% 1	4661
August	1st to 10th	Day	40% 8% 20% 23% 9%	3977
	11th to 20th	Day	38% 6% 14% 31% 11% 1	3766
	21st to end	Day	30% 6% 14% 31% 18% 2	4180
September	1st to 10th	Day	35% 7% 14% 22% 19% 2	2280
	11th to 20th	Day	34% 6% 11% 24% 22% 2	2203
	21st to end	Day	48% 5% 9% 19% 17% 2	2090
October	1st to 10th	Day	33% 5% 10% 23% 25% 4	3295
	11th to 20th	Day	25% 4 9% 26% 30% 6%	3140
	21st to end	Day	29% 3 14% 28% 21% 5%	3240
November	1st to 10th	Day	38% 3 11% 28% 17% 3	1761
	11th to 20th	Day	39% 3 11% 22% 21% 3	1800
	21st to end	Day	39% 4 12% 30% 14% 2	1771
December	1st to 10th	Day	43% 4 17% 22% 11% 2	1600
	11th to 20th	Day	42% 3 11% 26% 15% 2	1986
	21st to end	Day	41% 8% 14% 24% 13% 1	2796
January	1st to 10th	Night	38% 4 9% 31% 14% 3	4429
	11th to 20th	Night	45% 3 11% 25% 14% 2	4437
	21st to end	Night	50% 4 10% 22% 13% 1	4532
February	1st to 10th	Night	44% 4 15% 23% 13% 1	2434
	11th to 20th	Night	44% 4 8% 21% 18% 5%	2220
	21st to end	Night	43% 3 9% 22% 17% 5%	1884
March	1st to 10th	Night	51% 3 8% 23% 13% 2	3734
	11th to 20th	Night	38% 5% 11% 26% 16% 5%	3586
	21st to end	Night	49% 3 5% 17% 22% 4	3509
April	1st to 10th	Night	45% 5% 9% 19% 18% 5%	1900
	11th to 20th	Night	43% 4 9% 21% 19% 4	1875
	21st to end	Night	44% 5% 9% 18% 19% 5%	1900
May	1st to 10th	Night	57% 5% 8% 20% 9% 1	2879
	11th to 20th	Night	56% 5% 10% 17% 10% 1	2630
	21st to end	Night	45% 6% 13% 17% 16% 2	2739
June	1st to 10th	Night	45% 6% 9% 21% 17% 1	1520
	11th to 20th	Night	39% 7% 11% 27% 14% 2	1520
	21st to end	Night	34% 8% 16% 25% 15% 2	1520
July	1st to 10th	Night	45% 8% 14% 20% 10% 2	2480
	11th to 20th	Night	37% 8% 20% 26% 8% 1	2472
	21st to end	Night	49% 6% 14% 16% 14% 1	2651
August	1st to 10th	Night	50% 6% 18% 18% 8%	2891
	11th to 20th	Night	36% 7% 13% 33% 10% 1	3127
	21st to end	Night	30% 5% 11% 31% 21% 2	3476
September	1st to 10th	Night	41% 6% 12% 20% 18% 3	1900
	11th to 20th	Night	33% 5% 12% 25% 22% 3	1976
	21st to end	Night	48% 5% 8% 19% 18% 2	2090
October	1st to 10th	Night	38% 5% 9% 23% 23% 2	3662
	11th to 20th	Night	25% 3 12% 26% 28% 6%	3779
	21st to end	Night	27% 3 12% 31% 23% 5%	4306
November	1st to 10th	Night	35% 4 11% 25% 20% 4	2537
	11th to 20th	Night	40% 4 10% 21% 20% 4	2600
	21st to end	Night	37% 4 13% 27% 17% 2	2625
December	1st to 10th	Night	45% 4 13% 24% 12% 2	2800
	11th to 20th	Night	43% 4 13% 20% 18% 3	3428
	21st to end	Night	42% 6% 15% 24% 11% 1	4933

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	14% 12% 36% 29% 8% 1	180
	11th to 20th	Day	17% 17% 36% 26% 4 1	180
	21st to end	Day	23% 9% 33% 24% 10% 1	297
February	1st to 10th	Day	21% 10% 31% 31% 7%	303
	11th to 20th	Day	24% 12% 35% 25% 4	456
	21st to end	Day	23% 10% 33% 26% 7% 1	382
March	1st to 10th	Day	18% 11% 33% 28% 9% 1	460
	11th to 20th	Day	17% 9% 33% 32% 8% 2	460
	21st to end	Day	21% 7% 31% 32% 8% 1	506
April	1st to 10th	Day	22% 7% 32% 27% 11% 1	460
	11th to 20th	Day	17% 6% 26% 39% 11% 1	452
	21st to end	Day	21% 6% 24% 36% 12% 1	460
May	1st to 10th	Day	25% 5% 23% 34% 11% 2	463
	11th to 20th	Day	23% 3 17% 38% 17% 2	487
	21st to end	Day	18% 3 12% 29% 32% 7%	529
June	1st to 10th	Day	17% 2 13% 35% 28% 6%	490
	11th to 20th	Day	10% 3 12% 39% 30% 6%	490
	21st to end	Day	10% 2 11% 42% 32% 4	490
July	1st to 10th	Day	10% 3 7% 30% 39% 11%	485
	11th to 20th	Day	4 2 6% 34% 43% 11%	484
	21st to end	Day	11% 2 10% 38% 34% 5%	532
August	1st to 10th	Day	12% 3 8% 37% 34% 7%	486
	11th to 20th	Day	13% 2 8% 29% 39% 10%	479
	21st to end	Day	11% 4 9% 32% 32% 13%	539
September	1st to 10th	Day	16% 2 14% 26% 30% 12%	490
	11th to 20th	Day	13% 3 10% 32% 34% 9%	490
	21st to end	Day	24% 6% 15% 32% 20% 3	490
October	1st to 10th	Day	23% 4 14% 29% 24% 7%	490
	11th to 20th	Day	17% 6% 20% 29% 24% 4	490
	21st to end	Day	19% 7% 24% 28% 19% 4	479
November	1st to 10th	Day	16% 8% 25% 28% 20% 4	395
	11th to 20th	Day	15% 12% 31% 31% 12% 1	400
	21st to end	Day	16% 12% 29% 28% 14% 1	371
December	1st to 10th	Day	22% 10% 32% 24% 12% 1	200
	11th to 20th	Day	24% 11% 32% 25% 10% 1	200
	21st to end	Day	20% 9% 30% 25% 14% 1	204
January	1st to 10th	Night	20% 16% 36% 22% 6%	760
	11th to 20th	Night	23% 15% 31% 24% 6%	760
	21st to end	Night	20% 15% 38% 25% 3	836
February	1st to 10th	Night	22% 12% 36% 26% 4	760
	11th to 20th	Night	23% 13% 41% 21% 2	743
	21st to end	Night	23% 11% 35% 26% 5%	628
March	1st to 10th	Night	19% 12% 35% 26% 6% 1	760
	11th to 20th	Night	20% 9% 32% 29% 8% 2	760
	21st to end	Night	21% 7% 32% 31% 8% 1	836
April	1st to 10th	Night	21% 9% 31% 31% 8% 1	760
	11th to 20th	Night	18% 5% 25% 38% 14%	751
	21st to end	Night	21% 5% 26% 34% 13% 1	760
May	1st to 10th	Night	19% 5% 22% 38% 12% 3	596
	11th to 20th	Night	22% 3 20% 41% 12% 2	456
	21st to end	Night	18% 2 11% 28% 34% 6%	411
June	1st to 10th	Night	20% 2 13% 33% 29% 3	380
	11th to 20th	Night	13% 3 11% 41% 30% 3	380
	21st to end	Night	9% 1 12% 44% 30% 4	380
July	1st to 10th	Night	12% 2 8% 38% 35% 6%	370
	11th to 20th	Night	8% 2 7% 33% 44% 6%	368
	21st to end	Night	11% 2 11% 36% 37% 3	416
August	1st to 10th	Night	12% 2 8% 34% 39% 5%	604
	11th to 20th	Night	11% 1 11% 35% 33% 9%	750
	21st to end	Night	11% 2 8% 33% 37% 9%	836
September	1st to 10th	Night	17% 3 13% 28% 31% 8%	760
	11th to 20th	Night	16% 2 11% 30% 33% 8%	760
	21st to end	Night	23% 3 17% 31% 22% 4	760
October	1st to 10th	Night	23% 4 20% 24% 21% 8%	760
	11th to 20th	Night	19% 8% 23% 31% 18% 1	760
	21st to end	Night	20% 9% 27% 29% 12% 2	836
November	1st to 10th	Night	16% 9% 27% 31% 14% 3	780
	11th to 20th	Night	20% 16% 26% 29% 10% 1	800
	21st to end	Night	16% 14% 33% 27% 9% 1	800
December	1st to 10th	Night	22% 15% 32% 22% 7% 2	800
	11th to 20th	Night	20% 14% 37% 23% 6% 1	800
	21st to end	Night	20% 11% 35% 28% 6%	851

Page generated at 2024-12-21 04:13:49. Version ac07

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