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 2026-04-17.

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% 42%	131468
	Night	15% 8% 3 6% 4 4 4 3 5% 7% 43%	130688
Transparency	Day	40% 6% 12% 24% 16% 3	135021
	Night	41% 5% 11% 23% 17% 4	135222
Seeing	Day	17% 6% 21% 31% 21% 4	16931
	Night	18% 9% 25% 29% 16% 3	26265

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% 7% 2 5% 4 3 3 3 5% 6% 50%	4661
	11th to 20th	Day	15% 6% 2 6% 4 4 3 3 4 4 50%	4650
	21st to end	Day	15% 8% 3 6% 4 4 4 3 4 6% 44%	5780
February	1st to 10th	Day	14% 8% 3 7% 4 4 4 3 6% 8% 39%	1927
	11th to 20th	Day	17% 8% 3 6% 4 4 4 3 5% 5% 41%	2048
	21st to end	Day	17% 9% 3 5% 4 3 3 4 6% 6% 39%	1730
March	1st to 10th	Day	19% 7% 2 5% 3 3 3 3 4 5% 48%	4576
	11th to 20th	Day	12% 11% 2 4 4 3 4 3 5% 7% 46%	4934
	21st to end	Day	16% 7% 2 6% 4 3 4 3 5% 6% 45%	6042
April	1st to 10th	Day	17% 9% 2 6% 4 4 4 2 5% 7% 41%	2520
	11th to 20th	Day	14% 6% 2 6% 4 3 3 4 5% 6% 45%	2446
	21st to end	Day	16% 7% 3 6% 4 4 4 4 6% 7% 40%	2400
May	1st to 10th	Day	20% 11% 4 8% 5% 4 4 4 5% 6% 29%	5830
	11th to 20th	Day	23% 10% 2 6% 4 4 3 3 5% 6% 34%	6170
	21st to end	Day	17% 8% 3 7% 3 4 5% 4 6% 8% 34%	6949
June	1st to 10th	Day	13% 7% 3 5% 5% 4 4 4 7% 8% 39%	2800
	11th to 20th	Day	12% 6% 2 5% 4 5% 5% 4 7% 10% 40%	2800
	21st to end	Day	8% 4 2 5% 4 4 5% 5% 8% 9% 45%	2800
July	1st to 10th	Day	8% 7% 2 6% 4 4 4 4 7% 11% 43%	6360
	11th to 20th	Day	11% 7% 2 8% 5% 6% 6% 6% 8% 10% 31%	6360
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	6926
August	1st to 10th	Day	14% 6% 2 6% 4 4 5% 4 7% 11% 37%	4117
	11th to 20th	Day	13% 6% 2 6% 4 5% 4 4 6% 9% 42%	3850
	21st to end	Day	8% 5% 2 5% 4 3 4 4 6% 8% 51%	4312
September	1st to 10th	Day	14% 5% 2 4 3 3 3 3 5% 7% 49%	2400
	11th to 20th	Day	10% 6% 2 6% 3 4 4 3 4 7% 51%	2319
	21st to end	Day	19% 8% 2 7% 5% 4 4 3 5% 7% 37%	2200
October	1st to 10th	Day	17% 6% 2 5% 3 4 2 3 5% 6% 46%	2087
	11th to 20th	Day	16% 5% 2 5% 3 2 3 3 4 6% 52%	2000
	21st to end	Day	16% 5% 2 5% 4 4 4 3 5% 6% 45%	2080
November	1st to 10th	Day	14% 6% 2 5% 4 3 3 3 4 7% 50%	1851
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 6% 47%	1890
	21st to end	Day	15% 5% 2 5% 5% 4 3 2 5% 7% 46%	1859
December	1st to 10th	Day	13% 6% 2 4 3 4 4 3 6% 7% 49%	2680
	11th to 20th	Day	18% 8% 2 6% 3 3 2 3 3 5% 47%	3066
	21st to end	Day	13% 7% 3 6% 4 3 4 4 6% 7% 42%	4048
January	1st to 10th	Night	12% 7% 2 5% 4 3 4 3 5% 6% 49%	8234
	11th to 20th	Night	16% 7% 2 5% 3 3 3 2 4 5% 50%	8218
	21st to end	Night	15% 8% 2 6% 4 3 3 3 4 5% 46%	8401
February	1st to 10th	Night	18% 7% 3 6% 4 4 3 3 5% 6% 42%	2690
	11th to 20th	Night	20% 7% 2 5% 4 3 3 3 5% 6% 41%	2458
	21st to end	Night	17% 7% 3 6% 4 3 3 3 5% 6% 42%	2076
March	1st to 10th	Night	18% 9% 3 5% 3 3 3 2 3 5% 45%	5484
	11th to 20th	Night	12% 12% 3 6% 3 3 3 3 4 5% 46%	5241
	21st to end	Night	17% 7% 3 6% 5% 4 4 3 4 5% 42%	5131
April	1st to 10th	Night	17% 9% 3 6% 4 3 4 3 4 6% 40%	2100
	11th to 20th	Night	14% 8% 3 6% 5% 4 4 3 4 6% 44%	2036
	21st to end	Night	17% 7% 3 5% 4 4 5% 4 6% 7% 41%	2000
May	1st to 10th	Night	18% 11% 4 9% 4 4 5% 4 6% 8% 28%	4107
	11th to 20th	Night	22% 10% 4 7% 3 4 4 3 5% 7% 32%	3765
	21st to end	Night	21% 10% 3 7% 4 3 4 3 5% 7% 33%	3926
June	1st to 10th	Night	16% 8% 2 7% 4 4 5% 4 5% 8% 38%	1600
	11th to 20th	Night	13% 7% 2 6% 5% 5% 4 4 6% 8% 41%	1600
	21st to end	Night	8% 6% 2 6% 5% 4 5% 5% 8% 11% 41%	1600
July	1st to 10th	Night	9% 9% 3 9% 6% 6% 5% 4 7% 9% 34%	3600
	11th to 20th	Night	11% 6% 3 8% 6% 6% 6% 5% 7% 10% 31%	3600
	21st to end	Night	11% 7% 3 7% 5% 4 5% 4 6% 8% 39%	3926
August	1st to 10th	Night	17% 8% 3 8% 5% 5% 5% 4 5% 9% 32%	2993
	11th to 20th	Night	10% 6% 2 6% 5% 4 4 4 6% 8% 45%	3197
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 8% 52%	3586
September	1st to 10th	Night	15% 6% 2 7% 4 4 4 3 5% 6% 44%	2000
	11th to 20th	Night	13% 6% 2 5% 2 3 4 4 5% 8% 49%	2080
	21st to end	Night	20% 8% 3 6% 4 4 4 3 6% 6% 37%	2200
October	1st to 10th	Night	19% 5% 2 6% 3 4 5% 3 4 5% 43%	2310
	11th to 20th	Night	17% 5% 1 4 3 3 3 3 5% 6% 50%	2400
	21st to end	Night	17% 6% 2 5% 4 3 4 3 5% 5% 45%	2758
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 7% 51%	2667
	11th to 20th	Night	16% 7% 2 6% 4 3 3 3 4 5% 47%	2730
	21st to end	Night	13% 6% 2 5% 4 4 4 3 6% 6% 47%	2756
December	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 5% 7% 49%	4720
	11th to 20th	Night	21% 6% 2 5% 3 3 3 3 5% 7% 42%	5348
	21st to end	Night	14% 8% 3 6% 4 4 4 3 5% 7% 41%	7150

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	37% 3 7% 29% 22% 2	4662
	11th to 20th	Day	39% 3 7% 24% 20% 6%	4680
	21st to end	Day	43% 3 10% 30% 12% 2	5780
February	1st to 10th	Day	43% 4 14% 23% 13% 2	1927
	11th to 20th	Day	46% 4 8% 24% 15% 3	2057
	21st to end	Day	44% 5% 10% 24% 13% 4	1730
March	1st to 10th	Day	40% 3 8% 24% 17% 8%	4579
	11th to 20th	Day	38% 5% 8% 27% 17% 4	4934
	21st to end	Day	41% 5% 10% 17% 21% 6%	6042
April	1st to 10th	Day	43% 5% 10% 20% 17% 6%	2520
	11th to 20th	Day	39% 5% 13% 23% 16% 4	2446
	21st to end	Day	41% 6% 10% 19% 19% 4	2400
May	1st to 10th	Day	55% 6% 13% 17% 8% 1	5841
	11th to 20th	Day	50% 5% 10% 24% 10% 1	6174
	21st to end	Day	46% 6% 12% 21% 14% 1	6949
June	1st to 10th	Day	39% 8% 13% 23% 15% 2	2800
	11th to 20th	Day	37% 8% 14% 27% 11% 2	2800
	21st to end	Day	31% 9% 18% 25% 17% 1	2800
July	1st to 10th	Day	35% 10% 19% 22% 13% 1	6290
	11th to 20th	Day	44% 10% 18% 20% 7% 1	6285
	21st to end	Day	36% 8% 12% 24% 19% 1	6728
August	1st to 10th	Day	39% 7% 20% 23% 9%	4103
	11th to 20th	Day	38% 6% 13% 31% 10% 1	3886
	21st to end	Day	30% 6% 13% 31% 18% 2	4312
September	1st to 10th	Day	35% 7% 14% 23% 19% 2	2400
	11th to 20th	Day	34% 6% 11% 25% 22% 2	2319
	21st to end	Day	48% 5% 10% 18% 16% 2	2200
October	1st to 10th	Day	32% 5% 10% 24% 25% 4	3399
	11th to 20th	Day	26% 4 9% 26% 29% 6%	3240
	21st to end	Day	29% 3 14% 28% 21% 5%	3344
November	1st to 10th	Day	37% 3 11% 28% 17% 3	1851
	11th to 20th	Day	39% 3 11% 22% 21% 3	1890
	21st to end	Day	39% 4 12% 30% 14% 2	1859
December	1st to 10th	Day	35% 4 19% 26% 14% 2	2680
	11th to 20th	Day	43% 3 11% 27% 13% 3	3066
	21st to end	Day	40% 9% 12% 21% 16% 1	4048
January	1st to 10th	Night	37% 4 11% 26% 18% 5%	8234
	11th to 20th	Night	39% 2 9% 24% 19% 8%	8263
	21st to end	Night	41% 3 10% 25% 19% 3	8401
February	1st to 10th	Night	45% 4 14% 23% 13% 2	2690
	11th to 20th	Night	45% 4 8% 21% 18% 4	2460
	21st to end	Night	43% 4 9% 22% 17% 5%	2076
March	1st to 10th	Night	43% 3 8% 23% 13% 9%	5494
	11th to 20th	Night	42% 4 11% 23% 14% 6%	5242
	21st to end	Night	45% 4 7% 16% 23% 4	5131
April	1st to 10th	Night	45% 4 9% 19% 17% 5%	2100
	11th to 20th	Night	42% 4 9% 21% 19% 4	2036
	21st to end	Night	43% 5% 9% 18% 20% 5%	2000
May	1st to 10th	Night	53% 5% 12% 18% 9% 2	4113
	11th to 20th	Night	54% 4 9% 19% 13% 1	3766
	21st to end	Night	50% 5% 11% 19% 13% 1	3927
June	1st to 10th	Night	45% 6% 9% 21% 18% 1	1600
	11th to 20th	Night	40% 7% 12% 26% 13% 2	1600
	21st to end	Night	35% 8% 16% 25% 15% 2	1600
July	1st to 10th	Night	46% 8% 12% 21% 11% 1	3560
	11th to 20th	Night	47% 8% 18% 21% 6%	3552
	21st to end	Night	42% 7% 13% 20% 17% 1	3809
August	1st to 10th	Night	49% 6% 18% 18% 9%	2983
	11th to 20th	Night	37% 7% 13% 33% 10% 1	3227
	21st to end	Night	30% 5% 11% 31% 21% 2	3586
September	1st to 10th	Night	41% 5% 11% 22% 18% 3	2000
	11th to 20th	Night	33% 5% 12% 26% 22% 3	2080
	21st to end	Night	49% 5% 9% 19% 17% 2	2200
October	1st to 10th	Night	38% 5% 9% 23% 23% 2	3778
	11th to 20th	Night	26% 3 11% 26% 28% 6%	3899
	21st to end	Night	27% 3 12% 31% 23% 5%	4444
November	1st to 10th	Night	35% 4 11% 26% 20% 4	2667
	11th to 20th	Night	40% 4 10% 21% 20% 5%	2730
	21st to end	Night	37% 4 13% 27% 18% 2	2756
December	1st to 10th	Night	36% 4 14% 28% 16% 3	4720
	11th to 20th	Night	44% 3 11% 23% 15% 3	5348
	21st to end	Night	42% 7% 13% 20% 16% 2	7150

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% 13% 38% 28% 6% 1	220
	11th to 20th	Day	17% 16% 37% 25% 5%	220
	21st to end	Day	21% 8% 37% 25% 9% 1	363
February	1st to 10th	Day	19% 9% 34% 30% 8%	367
	11th to 20th	Day	23% 13% 34% 25% 4	536
	21st to end	Day	23% 9% 33% 28% 7%	446
March	1st to 10th	Day	19% 10% 34% 28% 9% 1	540
	11th to 20th	Day	17% 9% 32% 32% 8% 1	540
	21st to end	Day	20% 7% 33% 32% 7% 1	594
April	1st to 10th	Day	23% 7% 30% 27% 11% 1	540
	11th to 20th	Day	17% 5% 27% 38% 11% 1	516
	21st to end	Day	20% 5% 24% 36% 14% 1	500
May	1st to 10th	Day	24% 5% 23% 34% 11% 2	503
	11th to 20th	Day	23% 3 17% 39% 17% 2	527
	21st to end	Day	19% 3 12% 29% 30% 7%	573
June	1st to 10th	Day	18% 2 13% 34% 27% 5%	530
	11th to 20th	Day	12% 3 12% 39% 28% 6%	530
	21st to end	Day	10% 2 10% 40% 32% 6%	530
July	1st to 10th	Day	10% 3 6% 30% 39% 11%	525
	11th to 20th	Day	5% 2 6% 34% 43% 11%	524
	21st to end	Day	11% 2 9% 37% 35% 6%	576
August	1st to 10th	Day	12% 3 8% 37% 34% 7%	526
	11th to 20th	Day	15% 2 8% 27% 39% 10%	519
	21st to end	Day	10% 4 9% 33% 32% 12%	583
September	1st to 10th	Day	16% 2 15% 26% 30% 11%	530
	11th to 20th	Day	14% 3 10% 32% 34% 8%	530
	21st to end	Day	23% 6% 15% 32% 21% 3	530
October	1st to 10th	Day	21% 4 14% 28% 24% 9%	530
	11th to 20th	Day	18% 6% 20% 28% 23% 4	530
	21st to end	Day	18% 8% 25% 28% 18% 3	517
November	1st to 10th	Day	16% 8% 26% 28% 19% 3	425
	11th to 20th	Day	14% 13% 31% 30% 11%	430
	21st to end	Day	16% 13% 29% 28% 14% 1	399
December	1st to 10th	Day	22% 10% 32% 25% 10% 1	220
	11th to 20th	Day	22% 10% 35% 23% 9%	220
	21st to end	Day	19% 9% 30% 28% 13% 1	242
January	1st to 10th	Night	19% 17% 36% 22% 6%	840
	11th to 20th	Night	22% 17% 33% 23% 6%	840
	21st to end	Night	19% 16% 39% 24% 2	924
February	1st to 10th	Night	22% 12% 37% 25% 4	840
	11th to 20th	Night	24% 14% 39% 21% 2	823
	21st to end	Night	22% 11% 35% 27% 5%	692
March	1st to 10th	Night	20% 12% 35% 26% 7%	840
	11th to 20th	Night	20% 9% 31% 30% 8% 1	840
	21st to end	Night	21% 7% 33% 31% 7% 1	924
April	1st to 10th	Night	21% 10% 30% 30% 8% 1	840
	11th to 20th	Night	18% 5% 26% 37% 14%	816
	21st to end	Night	20% 5% 26% 35% 13% 1	800
May	1st to 10th	Night	19% 5% 22% 38% 13% 3	627
	11th to 20th	Night	22% 3 21% 41% 12% 2	480
	21st to end	Night	19% 2 12% 28% 33% 6%	433
June	1st to 10th	Night	20% 2 13% 34% 29% 3	400
	11th to 20th	Night	14% 3 11% 40% 29% 3	400
	21st to end	Night	9% 2 11% 43% 30% 5%	400
July	1st to 10th	Night	13% 2 7% 37% 35% 6%	390
	11th to 20th	Night	9% 2 7% 33% 43% 7%	388
	21st to end	Night	10% 2 10% 35% 39% 3	438
August	1st to 10th	Night	12% 2 8% 33% 39% 5%	636
	11th to 20th	Night	12% 2 10% 34% 33% 9%	790
	21st to end	Night	11% 2 8% 34% 36% 9%	880
September	1st to 10th	Night	17% 3 13% 28% 31% 8%	800
	11th to 20th	Night	17% 2 10% 30% 34% 8%	800
	21st to end	Night	23% 3 16% 31% 23% 4	800
October	1st to 10th	Night	22% 4 21% 24% 22% 9%	800
	11th to 20th	Night	19% 9% 22% 30% 18% 1	800
	21st to end	Night	20% 10% 28% 29% 12% 2	880
November	1st to 10th	Night	15% 10% 27% 31% 14% 3	820
	11th to 20th	Night	19% 17% 26% 28% 10% 1	840
	21st to end	Night	15% 15% 33% 27% 9% 1	840
December	1st to 10th	Night	21% 16% 33% 22% 7% 1	840
	11th to 20th	Night	19% 15% 37% 23% 6% 1	840
	21st to end	Night	19% 12% 35% 28% 6%	924

Page generated at 2026-04-14 02:44:25. Version ac07

Copyright © 2026 Attilla Danko.