St. Anthony
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St. Anthony clear sky chart from 2005-11-06 to 2025-12-18.

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	20% 13% 4 9% 5% 5% 5% 3 5% 6% 24%	127837
	Night	19% 14% 5% 10% 6% 5% 5% 4 5% 5% 23%	123458
Transparency	Day	59% 7% 12% 15% 6%	131222
	Night	61% 7% 12% 14% 6%	128185
Seeing	Day	28% 10% 27% 24% 9% 2	19724
	Night	28% 11% 28% 24% 8% 1	26542

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	18% 22% 7% 11% 5% 5% 4 3 5% 4 16%	3176
	11th to 20th	Day	16% 20% 8% 16% 8% 5% 4 3 4 4 12%	3351
	21st to end	Day	5% 9% 4 10% 8% 11% 10% 6% 8% 8% 21%	3982
February	1st to 10th	Day	13% 14% 5% 9% 5% 5% 6% 5% 5% 5% 27%	1600
	11th to 20th	Day	14% 17% 4 9% 6% 5% 4 3 5% 6% 26%	1704
	21st to end	Day	12% 16% 4 9% 6% 4 4 3 5% 6% 31%	1650
March	1st to 10th	Day	13% 13% 4 10% 6% 7% 5% 4 5% 6% 28%	4474
	11th to 20th	Day	16% 19% 6% 11% 7% 4 4 3 3 4 23%	4786
	21st to end	Day	26% 15% 5% 10% 5% 4 4 3 4 4 20%	5777
April	1st to 10th	Day	21% 17% 5% 11% 5% 4 4 3 5% 5% 20%	2400
	11th to 20th	Day	19% 14% 5% 9% 5% 5% 4 3 5% 6% 25%	2566
	21st to end	Day	23% 15% 6% 11% 5% 4 3 3 4 5% 22%	2604
May	1st to 10th	Day	25% 17% 6% 10% 6% 4 4 3 3 4 18%	6345
	11th to 20th	Day	19% 15% 6% 12% 6% 5% 5% 3 4 6% 20%	6701
	21st to end	Day	22% 13% 5% 10% 5% 4 4 3 4 5% 24%	7428
June	1st to 10th	Day	33% 16% 3 7% 4 4 4 3 4 5% 17%	3000
	11th to 20th	Day	28% 14% 4 8% 4 4 4 3 4 6% 21%	3000
	21st to end	Day	25% 13% 4 9% 5% 4 5% 4 4 7% 22%	3000
July	1st to 10th	Day	18% 9% 3 8% 5% 4 4 4 6% 6% 32%	6800
	11th to 20th	Day	21% 11% 3 7% 5% 4 4 3 5% 6% 32%	6800
	21st to end	Day	19% 9% 3 9% 6% 5% 5% 5% 6% 7% 27%	7085
August	1st to 10th	Day	24% 10% 3 8% 5% 4 4 3 5% 6% 27%	4564
	11th to 20th	Day	21% 11% 4 8% 5% 5% 5% 4 5% 6% 27%	4313
	21st to end	Day	19% 8% 3 7% 4 4 5% 4 5% 6% 35%	4675
September	1st to 10th	Day	25% 8% 3 6% 3 5% 4 3 4 7% 32%	2420
	11th to 20th	Day	26% 11% 4 8% 4 6% 4 3 5% 5% 25%	2227
	21st to end	Day	23% 11% 3 7% 4 5% 5% 3 5% 7% 28%	2200
October	1st to 10th	Day	24% 13% 3 7% 4 5% 4 3 5% 4 29%	2125
	11th to 20th	Day	25% 14% 4 7% 5% 4 4 3 5% 5% 24%	1800
	21st to end	Day	22% 16% 5% 9% 5% 4 4 2 4 5% 24%	1980
November	1st to 10th	Day	22% 14% 4 9% 5% 3 3 4 4 4 28%	1788
	11th to 20th	Day	22% 15% 4 7% 6% 5% 3 2 4 5% 28%	1511
	21st to end	Day	25% 16% 5% 7% 4 3 4 4 4 5% 23%	1470
December	1st to 10th	Day	13% 15% 4 10% 6% 5% 5% 5% 6% 7% 26%	2360
	11th to 20th	Day	18% 14% 5% 10% 7% 7% 6% 5% 5% 5% 18%	2677
	21st to end	Day	19% 13% 4 11% 6% 5% 5% 3 5% 6% 23%	3498
January	1st to 10th	Night	19% 21% 6% 11% 5% 4 4 3 5% 5% 18%	6789
	11th to 20th	Night	13% 20% 7% 16% 7% 5% 5% 3 4 4 16%	6550
	21st to end	Night	7% 10% 4 9% 7% 8% 8% 9% 8% 7% 24%	6996
February	1st to 10th	Night	14% 12% 4 9% 7% 6% 6% 4 5% 6% 28%	2800
	11th to 20th	Night	15% 16% 5% 10% 7% 5% 5% 4 4 5% 26%	2580
	21st to end	Night	12% 12% 5% 10% 7% 5% 4 3 5% 6% 31%	1980
March	1st to 10th	Night	14% 13% 4 9% 7% 6% 6% 5% 5% 5% 26%	5366
	11th to 20th	Night	16% 16% 6% 13% 6% 5% 4 3 4 4 25%	5173
	21st to end	Night	22% 14% 6% 11% 6% 5% 4 3 5% 5% 20%	5151
April	1st to 10th	Night	22% 15% 6% 11% 5% 5% 4 3 5% 4 19%	2000
	11th to 20th	Night	21% 15% 4 8% 5% 4 4 3 5% 6% 24%	1782
	21st to end	Night	24% 14% 6% 7% 4 4 4 3 4 5% 24%	1794
May	1st to 10th	Night	29% 17% 5% 12% 6% 4 4 3 4 4 12%	3615
	11th to 20th	Night	25% 17% 4 11% 4 4 3 3 3 3 23%	3211
	21st to end	Night	25% 16% 5% 10% 4 3 4 2 3 4 24%	3468
June	1st to 10th	Night	34% 15% 3 7% 4 5% 4 3 4 4 16%	1400
	11th to 20th	Night	30% 12% 3 7% 5% 6% 4 3 5% 6% 18%	1400
	21st to end	Night	25% 15% 5% 8% 5% 4 6% 4 5% 6% 18%	1400
July	1st to 10th	Night	19% 12% 5% 9% 5% 5% 4 4 6% 7% 24%	3179
	11th to 20th	Night	22% 10% 3 7% 5% 4 4 4 6% 7% 28%	3180
	21st to end	Night	20% 10% 3 8% 5% 4 4 4 6% 6% 29%	3787
August	1st to 10th	Night	20% 10% 3 7% 4 4 4 4 7% 8% 29%	2596
	11th to 20th	Night	23% 7% 4 7% 4 5% 5% 3 7% 6% 28%	2743
	21st to end	Night	18% 8% 3 6% 4 3 6% 4 6% 7% 34%	3234
September	1st to 10th	Night	23% 9% 2 7% 5% 4 4 3 5% 6% 33%	1976
	11th to 20th	Night	23% 11% 4 8% 5% 4 4 4 5% 5% 27%	2172
	21st to end	Night	22% 11% 3 7% 4 4 4 3 5% 6% 29%	2200
October	1st to 10th	Night	25% 11% 4 7% 4 4 3 4 4 6% 27%	2273
	11th to 20th	Night	21% 14% 3 9% 5% 4 4 3 5% 5% 27%	2600
	21st to end	Night	26% 13% 4 8% 4 5% 4 3 5% 6% 23%	2860
November	1st to 10th	Night	22% 12% 3 9% 5% 5% 4 4 4 6% 26%	2728
	11th to 20th	Night	25% 15% 3 7% 4 4 3 4 5% 5% 25%	3108
	21st to end	Night	22% 18% 5% 9% 6% 4 4 3 4 4 20%	3150
December	1st to 10th	Night	13% 13% 5% 12% 8% 7% 6% 5% 5% 5% 21%	5050
	11th to 20th	Night	20% 13% 5% 11% 6% 6% 6% 4 5% 6% 18%	5687
	21st to end	Night	19% 13% 4 12% 6% 5% 5% 3 5% 6% 22%	7480

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	71% 6% 8% 12% 3	3177
	11th to 20th	Day	74% 8% 10% 6% 2	3378
	21st to end	Day	57% 12% 9% 13% 8% 1	3982
February	1st to 10th	Day	56% 6% 11% 19% 7% 1	1600
	11th to 20th	Day	58% 6% 10% 16% 9% 1	1711
	21st to end	Day	53% 5% 9% 17% 16%	1650
March	1st to 10th	Day	54% 7% 8% 13% 16% 1	4478
	11th to 20th	Day	64% 5% 8% 10% 9% 3	4786
	21st to end	Day	65% 6% 7% 12% 10% 1	5777
April	1st to 10th	Day	63% 6% 8% 13% 9% 1	2400
	11th to 20th	Day	57% 8% 11% 14% 10%	2566
	21st to end	Day	63% 5% 9% 15% 7% 1	2604
May	1st to 10th	Day	68% 7% 9% 12% 4	6357
	11th to 20th	Day	62% 8% 11% 13% 5%	6705
	21st to end	Day	59% 7% 13% 17% 4	7428
June	1st to 10th	Day	69% 6% 10% 11% 4	3000
	11th to 20th	Day	64% 6% 13% 14% 2	3000
	21st to end	Day	62% 8% 11% 15% 4 1	3000
July	1st to 10th	Day	51% 6% 14% 24% 5%	6725
	11th to 20th	Day	53% 6% 14% 21% 6%	6718
	21st to end	Day	54% 6% 18% 19% 3	6884
August	1st to 10th	Day	59% 6% 14% 18% 3	4550
	11th to 20th	Day	55% 7% 17% 17% 3	4355
	21st to end	Day	47% 7% 17% 24% 5%	4675
September	1st to 10th	Day	51% 7% 16% 19% 7%	2420
	11th to 20th	Day	58% 8% 14% 14% 5%	2227
	21st to end	Day	53% 8% 15% 17% 6%	2200
October	1st to 10th	Day	57% 7% 14% 16% 5%	3453
	11th to 20th	Day	58% 7% 13% 15% 7%	2922
	21st to end	Day	62% 5% 10% 14% 8% 1	3191
November	1st to 10th	Day	60% 6% 11% 15% 7% 1	1788
	11th to 20th	Day	59% 6% 12% 16% 6% 1	1511
	21st to end	Day	64% 6% 9% 14% 7%	1470
December	1st to 10th	Day	53% 11% 11% 20% 6%	2360
	11th to 20th	Day	67% 8% 12% 10% 2	2676
	21st to end	Day	61% 7% 13% 14% 4	3498
January	1st to 10th	Night	69% 7% 8% 8% 6% 1	6789
	11th to 20th	Night	69% 8% 13% 7% 2	6598
	21st to end	Night	53% 12% 12% 14% 9%	6996
February	1st to 10th	Night	58% 6% 10% 17% 8% 1	2800
	11th to 20th	Night	59% 6% 12% 15% 8% 1	2584
	21st to end	Night	54% 7% 10% 17% 11% 1	1980
March	1st to 10th	Night	57% 6% 9% 16% 11% 1	5375
	11th to 20th	Night	63% 5% 6% 12% 12% 2	5174
	21st to end	Night	63% 6% 9% 15% 7% 1	5151
April	1st to 10th	Night	66% 7% 8% 11% 8% 1	2000
	11th to 20th	Night	58% 7% 9% 17% 7%	1782
	21st to end	Night	62% 4 10% 14% 9% 1	1794
May	1st to 10th	Night	74% 8% 9% 7% 2	3620
	11th to 20th	Night	64% 6% 7% 13% 9%	3212
	21st to end	Night	63% 7% 10% 18% 2	3469
June	1st to 10th	Night	71% 6% 7% 11% 4 1	1400
	11th to 20th	Night	65% 9% 14% 10% 3	1400
	21st to end	Night	65% 8% 10% 14% 4	1400
July	1st to 10th	Night	60% 5% 14% 18% 4	3146
	11th to 20th	Night	53% 6% 15% 21% 5%	3138
	21st to end	Night	53% 6% 17% 22% 2	3674
August	1st to 10th	Night	51% 8% 20% 20% 2	2585
	11th to 20th	Night	53% 10% 18% 16% 4	2767
	21st to end	Night	47% 7% 18% 22% 6%	3233
September	1st to 10th	Night	52% 6% 16% 20% 6%	1976
	11th to 20th	Night	57% 7% 13% 17% 5%	2172
	21st to end	Night	54% 6% 15% 17% 7% 1	2200
October	1st to 10th	Night	66% 6% 11% 13% 5%	3728
	11th to 20th	Night	56% 7% 12% 16% 9%	4227
	21st to end	Night	59% 6% 14% 13% 6% 1	4610
November	1st to 10th	Night	58% 7% 13% 15% 7% 1	2728
	11th to 20th	Night	62% 6% 13% 15% 4	3108
	21st to end	Night	68% 7% 10% 10% 5%	3150
December	1st to 10th	Night	58% 12% 9% 15% 5%	5050
	11th to 20th	Night	66% 8% 13% 10% 3	5689
	21st to end	Night	64% 7% 12% 13% 4	7480

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	26% 16% 28% 20% 8% 2	400
	11th to 20th	Day	24% 18% 32% 17% 9% 1	400
	21st to end	Day	19% 19% 34% 21% 6% 1	440
February	1st to 10th	Day	21% 13% 36% 22% 6% 3	400
	11th to 20th	Day	22% 16% 36% 19% 5% 1	396
	21st to end	Day	19% 16% 35% 20% 7% 2	331
March	1st to 10th	Day	20% 15% 34% 22% 8% 1	400
	11th to 20th	Day	24% 12% 27% 23% 13% 3	400
	21st to end	Day	28% 14% 27% 22% 5% 3	506
April	1st to 10th	Day	26% 16% 30% 19% 6% 2	500
	11th to 20th	Day	26% 10% 28% 24% 9% 3	684
	21st to end	Day	28% 11% 26% 24% 9% 3	700
May	1st to 10th	Day	35% 10% 23% 20% 9% 3	703
	11th to 20th	Day	28% 8% 27% 22% 12% 3	724
	21st to end	Day	33% 8% 26% 22% 9% 2	790
June	1st to 10th	Day	42% 9% 18% 23% 8% 2	730
	11th to 20th	Day	34% 6% 23% 25% 10% 2	730
	21st to end	Day	28% 6% 24% 27% 12% 3	730
July	1st to 10th	Day	30% 5% 23% 28% 12% 3	720
	11th to 20th	Day	25% 6% 23% 32% 12% 2	718
	21st to end	Day	27% 4 23% 33% 11% 2	795
August	1st to 10th	Day	29% 4 22% 28% 15% 2	725
	11th to 20th	Day	27% 4 21% 33% 12% 3	717
	21st to end	Day	27% 7% 23% 27% 13% 3	803
September	1st to 10th	Day	27% 9% 28% 25% 10% 1	550
	11th to 20th	Day	33% 9% 25% 24% 7% 1	434
	21st to end	Day	26% 11% 32% 23% 6% 2	420
October	1st to 10th	Day	26% 13% 32% 23% 5% 1	420
	11th to 20th	Day	31% 10% 24% 23% 13% 1	420
	21st to end	Day	27% 14% 27% 22% 9% 2	462
November	1st to 10th	Day	30% 16% 33% 17% 2	425
	11th to 20th	Day	30% 16% 25% 20% 7% 1	430
	21st to end	Day	34% 15% 29% 17% 4	430
December	1st to 10th	Day	27% 14% 31% 18% 9% 1	430
	11th to 20th	Day	25% 18% 35% 18% 4 1	421
	21st to end	Day	28% 13% 30% 20% 7% 2	440
January	1st to 10th	Night	29% 18% 29% 16% 7% 1	900
	11th to 20th	Night	22% 16% 33% 21% 7% 1	900
	21st to end	Night	22% 17% 34% 23% 3	990
February	1st to 10th	Night	20% 15% 33% 24% 6% 1	900
	11th to 20th	Night	23% 16% 35% 20% 5% 1	863
	21st to end	Night	19% 10% 34% 27% 9% 2	660
March	1st to 10th	Night	19% 17% 33% 22% 7% 1	800
	11th to 20th	Night	23% 11% 27% 31% 8% 1	690
	21st to end	Night	29% 13% 30% 20% 6% 1	660
April	1st to 10th	Night	28% 10% 31% 21% 8% 2	600
	11th to 20th	Night	27% 10% 29% 23% 9% 1	594
	21st to end	Night	31% 7% 27% 24% 9% 1	600
May	1st to 10th	Night	36% 7% 21% 24% 10% 3	600
	11th to 20th	Night	33% 6% 25% 20% 14% 1	592
	21st to end	Night	35% 8% 24% 22% 10%	649
June	1st to 10th	Night	42% 5% 19% 24% 9% 1	600
	11th to 20th	Night	37% 5% 20% 26% 11% 1	600
	21st to end	Night	30% 5% 22% 29% 14% 1	600
July	1st to 10th	Night	31% 4 23% 30% 11% 1	586
	11th to 20th	Night	25% 4 28% 31% 11% 1	582
	21st to end	Night	27% 5% 21% 32% 14% 1	656
August	1st to 10th	Night	28% 6% 18% 32% 15% 1	598
	11th to 20th	Night	26% 4 21% 35% 13% 1	592
	21st to end	Night	25% 5% 23% 32% 14% 1	660
September	1st to 10th	Night	27% 8% 28% 27% 10%	600
	11th to 20th	Night	28% 10% 32% 26% 4 1	600
	21st to end	Night	29% 9% 32% 23% 6% 2	600
October	1st to 10th	Night	32% 7% 30% 25% 5% 1	653
	11th to 20th	Night	30% 9% 23% 27% 10%	910
	21st to end	Night	32% 12% 25% 22% 7% 1	1001
November	1st to 10th	Night	29% 15% 32% 19% 5% 1	930
	11th to 20th	Night	32% 14% 27% 19% 7% 1	950
	21st to end	Night	30% 18% 30% 18% 4 1	950
December	1st to 10th	Night	26% 16% 32% 20% 6%	950
	11th to 20th	Night	28% 20% 30% 18% 4	936
	21st to end	Night	24% 14% 32% 22% 8% 1	990

Page generated at 2025-12-15 02:13:50. Version ac07

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