St. F.X. Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St. F.X. Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	18% 13% 4 9% 6% 5% 5% 4 5% 6% 26%	101634
	Night	18% 12% 4 11% 6% 5% 4 4 5% 6% 25%	97528
Transparency	Day	57% 7% 12% 16% 7% 1	105161
	Night	57% 7% 12% 16% 7% 1	102096
Seeing	Day	25% 18% 30% 20% 6% 1	17565
	Night	25% 17% 31% 22% 5%	25077

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% 14% 9% 25% 7% 5% 4 2 3 3 14%	2526
	11th to 20th	Day	11% 15% 7% 15% 7% 7% 5% 4 4 5% 19%	2530
	21st to end	Day	15% 14% 7% 16% 9% 6% 5% 4 5% 4 16%	2979
February	1st to 10th	Day	17% 14% 5% 12% 8% 6% 5% 4 5% 5% 20%	1710
	11th to 20th	Day	14% 16% 5% 10% 8% 7% 4 3 4 5% 22%	1663
	21st to end	Day	10% 17% 6% 8% 7% 5% 6% 4 5% 6% 25%	1515
March	1st to 10th	Day	22% 15% 4 7% 5% 5% 4 3 4 4 27%	3228
	11th to 20th	Day	9% 22% 9% 11% 7% 6% 5% 3 4 5% 18%	3480
	21st to end	Day	24% 21% 7% 11% 5% 3 4 2 3 3 17%	3943
April	1st to 10th	Day	19% 15% 6% 9% 5% 4 4 3 5% 5% 25%	2280
	11th to 20th	Day	20% 14% 4 7% 5% 4 3 3 4 6% 30%	2254
	21st to end	Day	22% 16% 4 7% 4 4 3 4 5% 6% 26%	2440
May	1st to 10th	Day	24% 21% 4 7% 4 4 3 3 4 5% 20%	4423
	11th to 20th	Day	19% 11% 3 7% 5% 4 4 4 6% 6% 31%	4398
	21st to end	Day	17% 11% 3 8% 5% 5% 5% 4 7% 8% 26%	4836
June	1st to 10th	Day	28% 12% 3 7% 5% 4 4 3 5% 7% 22%	2660
	11th to 20th	Day	22% 9% 2 7% 5% 4 3 3 5% 6% 33%	2660
	21st to end	Day	23% 11% 4 9% 6% 4 4 4 5% 5% 25%	2660
July	1st to 10th	Day	18% 8% 3 8% 6% 5% 6% 5% 6% 7% 29%	4440
	11th to 20th	Day	12% 6% 3 7% 6% 6% 6% 5% 8% 10% 31%	4440
	21st to end	Day	13% 7% 3 8% 5% 5% 5% 4 7% 7% 35%	4815
August	1st to 10th	Day	17% 9% 3 9% 5% 6% 5% 5% 6% 7% 27%	4243
	11th to 20th	Day	16% 9% 3 8% 5% 5% 6% 4 7% 7% 31%	4045
	21st to end	Day	11% 6% 3 6% 4 5% 5% 4 6% 7% 42%	4225
September	1st to 10th	Day	17% 7% 3 7% 5% 4 4 4 5% 7% 36%	2280
	11th to 20th	Day	19% 9% 3 6% 4 4 4 3 6% 7% 35%	2280
	21st to end	Day	18% 8% 3 6% 4 5% 5% 4 6% 7% 34%	2001
October	1st to 10th	Day	19% 9% 3 9% 5% 5% 5% 5% 5% 7% 30%	1900
	11th to 20th	Day	20% 10% 3 10% 5% 5% 4 4 5% 8% 25%	1900
	21st to end	Day	20% 14% 4 10% 6% 5% 4 3 4 7% 22%	1989
November	1st to 10th	Day	20% 14% 5% 10% 6% 4 4 4 5% 6% 22%	1642
	11th to 20th	Day	18% 18% 6% 11% 7% 4 4 4 4 6% 18%	1520
	21st to end	Day	15% 19% 7% 13% 6% 6% 5% 4 6% 4 16%	1520
December	1st to 10th	Day	19% 19% 6% 15% 7% 6% 5% 4 4 4 10%	1520
	11th to 20th	Day	27% 18% 6% 15% 6% 6% 3 3 4 4 8%	1906
	21st to end	Day	20% 15% 11% 14% 6% 5% 3 2 4 4 16%	2783
January	1st to 10th	Night	12% 14% 7% 23% 7% 6% 5% 3 4 5% 15%	4429
	11th to 20th	Night	15% 13% 5% 15% 8% 6% 5% 4 5% 5% 19%	4440
	21st to end	Night	13% 12% 7% 21% 9% 5% 5% 3 4 5% 17%	4678
February	1st to 10th	Night	19% 12% 5% 13% 8% 6% 4 3 5% 4 22%	2470
	11th to 20th	Night	14% 15% 5% 11% 9% 7% 6% 5% 4 5% 19%	2403
	21st to end	Night	10% 15% 5% 12% 8% 5% 5% 3 5% 5% 27%	1937
March	1st to 10th	Night	19% 16% 5% 9% 5% 5% 4 3 4 6% 24%	3608
	11th to 20th	Night	18% 19% 8% 9% 6% 4 4 3 4 5% 20%	3479
	21st to end	Night	24% 15% 6% 12% 6% 5% 3 3 3 4 19%	3689
April	1st to 10th	Night	20% 15% 4 7% 6% 6% 5% 3 4 6% 24%	1900
	11th to 20th	Night	18% 13% 3 8% 5% 4 4 3 5% 5% 31%	1876
	21st to end	Night	22% 13% 4 7% 5% 4 5% 3 4 5% 27%	1739
May	1st to 10th	Night	23% 26% 3 6% 4 3 3 3 4 5% 20%	2525
	11th to 20th	Night	18% 13% 4 7% 4 4 5% 4 5% 6% 31%	2506
	21st to end	Night	15% 10% 4 8% 6% 6% 6% 4 7% 8% 26%	2749
June	1st to 10th	Night	26% 10% 3 8% 5% 4 5% 3 5% 6% 25%	1520
	11th to 20th	Night	22% 8% 2 6% 5% 4 4 3 5% 8% 35%	1520
	21st to end	Night	22% 9% 3 8% 6% 4 5% 4 5% 8% 28%	1520
July	1st to 10th	Night	16% 8% 4 9% 5% 5% 5% 4 8% 9% 27%	2530
	11th to 20th	Night	13% 7% 3 7% 5% 5% 5% 5% 7% 10% 34%	2530
	21st to end	Night	14% 8% 3 6% 5% 4 5% 4 7% 7% 38%	2750
August	1st to 10th	Night	13% 8% 4 10% 6% 6% 5% 4 6% 7% 31%	2688
	11th to 20th	Night	14% 7% 3 7% 5% 5% 5% 4 6% 9% 35%	2782
	21st to end	Night	11% 6% 2 6% 4 4 4 4 7% 9% 42%	3430
September	1st to 10th	Night	15% 7% 3 7% 5% 4 5% 4 6% 8% 37%	1900
	11th to 20th	Night	18% 8% 2 6% 4 3 4 3 6% 7% 39%	1900
	21st to end	Night	19% 8% 2 7% 4 4 4 4 5% 7% 37%	2174
October	1st to 10th	Night	19% 8% 2 7% 5% 4 4 4 6% 6% 35%	2280
	11th to 20th	Night	20% 8% 3 8% 5% 4 4 3 5% 8% 32%	2280
	21st to end	Night	24% 13% 3 8% 6% 4 5% 3 4 5% 25%	2608
November	1st to 10th	Night	18% 13% 4 10% 6% 4 5% 4 5% 6% 24%	2531
	11th to 20th	Night	18% 16% 5% 11% 6% 5% 5% 4 5% 6% 19%	2660
	21st to end	Night	20% 15% 5% 10% 7% 5% 5% 5% 5% 6% 18%	2660
December	1st to 10th	Night	21% 16% 6% 14% 7% 4 5% 3 4 4 13%	2660
	11th to 20th	Night	26% 17% 5% 14% 7% 6% 4 2 3 3 13%	3293
	21st to end	Night	27% 16% 5% 13% 6% 4 3 3 3 3 17%	4884

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	73% 5% 13% 7% 2	2527
	11th to 20th	Day	61% 9% 11% 12% 7%	2530
	21st to end	Day	64% 9% 10% 9% 7% 1	2979
February	1st to 10th	Day	66% 5% 11% 11% 6%	1710
	11th to 20th	Day	64% 7% 12% 11% 6%	1671
	21st to end	Day	58% 5% 11% 14% 9% 3	1515
March	1st to 10th	Day	61% 4 9% 15% 10%	3232
	11th to 20th	Day	66% 9% 10% 11% 5% 1	3480
	21st to end	Day	73% 4 8% 9% 5% 1	3943
April	1st to 10th	Day	62% 6% 8% 12% 10% 3	2280
	11th to 20th	Day	56% 4 10% 17% 12% 1	2254
	21st to end	Day	59% 7% 10% 14% 9% 1	2440
May	1st to 10th	Day	64% 7% 10% 13% 5% 1	4438
	11th to 20th	Day	52% 9% 12% 19% 8%	4402
	21st to end	Day	52% 11% 14% 16% 6%	4836
June	1st to 10th	Day	62% 7% 11% 16% 4 1	2660
	11th to 20th	Day	51% 8% 11% 19% 10% 1	2660
	21st to end	Day	60% 8% 8% 13% 9% 1	2660
July	1st to 10th	Day	52% 8% 14% 16% 10% 1	4370
	11th to 20th	Day	45% 9% 18% 21% 7% 1	4364
	21st to end	Day	46% 8% 16% 21% 8%	4662
August	1st to 10th	Day	55% 9% 12% 19% 6%	4229
	11th to 20th	Day	50% 8% 13% 23% 6%	4084
	21st to end	Day	39% 6% 13% 28% 13%	4225
September	1st to 10th	Day	45% 8% 13% 22% 11% 1	2280
	11th to 20th	Day	48% 7% 11% 22% 12% 1	2280
	21st to end	Day	47% 7% 11% 23% 11%	2001
October	1st to 10th	Day	52% 8% 13% 18% 8%	3160
	11th to 20th	Day	47% 7% 13% 21% 11%	3140
	21st to end	Day	52% 7% 16% 18% 7% 1	3259
November	1st to 10th	Day	61% 7% 12% 14% 5%	1642
	11th to 20th	Day	66% 6% 13% 9% 5%	1520
	21st to end	Day	65% 8% 15% 8% 4	1520
December	1st to 10th	Day	74% 8% 9% 7% 2	1520
	11th to 20th	Day	77% 6% 9% 5% 2 1	1905
	21st to end	Day	69% 7% 15% 6% 2 1	2783
January	1st to 10th	Night	69% 8% 14% 7% 2	4429
	11th to 20th	Night	61% 9% 14% 12% 4	4440
	21st to end	Night	65% 10% 10% 10% 5%	4678
February	1st to 10th	Night	64% 6% 10% 11% 7% 1	2470
	11th to 20th	Night	66% 6% 11% 11% 5% 1	2406
	21st to end	Night	59% 4 10% 17% 9% 1	1937
March	1st to 10th	Night	60% 5% 8% 15% 10% 1	3617
	11th to 20th	Night	67% 5% 9% 13% 5% 1	3480
	21st to end	Night	68% 4 9% 12% 6% 1	3689
April	1st to 10th	Night	60% 7% 10% 11% 10% 2	1900
	11th to 20th	Night	53% 6% 9% 19% 11% 2	1876
	21st to end	Night	58% 5% 10% 15% 11% 1	1739
May	1st to 10th	Night	67% 6% 7% 14% 6%	2530
	11th to 20th	Night	52% 7% 12% 21% 7%	2507
	21st to end	Night	51% 13% 14% 16% 5%	2750
June	1st to 10th	Night	60% 8% 9% 18% 6%	1520
	11th to 20th	Night	49% 7% 12% 19% 13% 1	1520
	21st to end	Night	55% 10% 10% 16% 8% 1	1520
July	1st to 10th	Night	52% 7% 15% 17% 8% 1	2491
	11th to 20th	Night	44% 9% 18% 20% 9%	2482
	21st to end	Night	45% 9% 15% 22% 9%	2663
August	1st to 10th	Night	50% 8% 16% 22% 4	2677
	11th to 20th	Night	45% 10% 16% 25% 5%	2809
	21st to end	Night	35% 9% 17% 28% 11%	3429
September	1st to 10th	Night	42% 8% 13% 26% 11%	1900
	11th to 20th	Night	41% 7% 14% 26% 11% 1	1900
	21st to end	Night	46% 7% 12% 24% 9% 1	2174
October	1st to 10th	Night	50% 7% 15% 19% 9%	3800
	11th to 20th	Night	43% 7% 14% 26% 10%	3779
	21st to end	Night	50% 6% 14% 20% 8% 1	4294
November	1st to 10th	Night	58% 8% 13% 14% 6%	2531
	11th to 20th	Night	62% 8% 14% 10% 5%	2660
	21st to end	Night	63% 9% 15% 10% 3	2660
December	1st to 10th	Night	72% 7% 11% 8% 3	2660
	11th to 20th	Night	75% 4 10% 7% 3 1	3295
	21st to end	Night	71% 5% 13% 9% 2	4884

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	27% 24% 33% 13% 2	370
	11th to 20th	Day	28% 25% 28% 14% 5%	370
	21st to end	Day	23% 23% 36% 16% 2	407
February	1st to 10th	Day	29% 24% 30% 15% 2 1	370
	11th to 20th	Day	26% 31% 26% 16% 2	366
	21st to end	Day	21% 22% 35% 17% 5%	307
March	1st to 10th	Day	24% 23% 35% 17% 2	400
	11th to 20th	Day	21% 27% 33% 14% 5% 1	460
	21st to end	Day	30% 24% 26% 16% 3	506
April	1st to 10th	Day	30% 27% 28% 12% 3	460
	11th to 20th	Day	29% 23% 32% 12% 4	452
	21st to end	Day	27% 20% 30% 18% 4 1	460
May	1st to 10th	Day	34% 17% 28% 16% 3 2	651
	11th to 20th	Day	22% 12% 33% 23% 9% 1	674
	21st to end	Day	24% 15% 35% 21% 5% 1	735
June	1st to 10th	Day	33% 13% 29% 18% 7% 1	680
	11th to 20th	Day	22% 14% 33% 24% 5% 1	680
	21st to end	Day	26% 12% 29% 24% 9% 1	680
July	1st to 10th	Day	19% 8% 34% 30% 8% 1	670
	11th to 20th	Day	16% 8% 34% 30% 10% 1	668
	21st to end	Day	20% 10% 28% 31% 10% 1	740
August	1st to 10th	Day	17% 7% 30% 33% 11% 3	572
	11th to 20th	Day	19% 10% 30% 26% 12% 3	479
	21st to end	Day	17% 12% 30% 26% 13% 2	539
September	1st to 10th	Day	17% 14% 33% 26% 7% 2	490
	11th to 20th	Day	24% 14% 27% 24% 8% 2	490
	21st to end	Day	22% 15% 30% 20% 9% 3	415
October	1st to 10th	Day	23% 13% 28% 27% 6% 3	390
	11th to 20th	Day	25% 21% 28% 16% 9% 2	390
	21st to end	Day	28% 20% 31% 16% 5%	429
November	1st to 10th	Day	26% 24% 28% 19% 3 1	378
	11th to 20th	Day	31% 26% 25% 14% 4 1	370
	21st to end	Day	31% 25% 27% 14% 3 1	370
December	1st to 10th	Day	31% 25% 27% 14% 2	370
	11th to 20th	Day	36% 25% 28% 11% 1	370
	21st to end	Day	23% 29% 31% 13% 2 1	407
January	1st to 10th	Night	27% 24% 33% 14% 2	850
	11th to 20th	Night	26% 24% 32% 15% 3	850
	21st to end	Night	23% 25% 32% 17% 4	875
February	1st to 10th	Night	29% 17% 32% 19% 3	760
	11th to 20th	Night	24% 29% 30% 14% 2	743
	21st to end	Night	20% 20% 34% 20% 5%	628
March	1st to 10th	Night	25% 19% 34% 20% 3	760
	11th to 20th	Night	23% 19% 30% 21% 6% 1	760
	21st to end	Night	27% 18% 30% 21% 4	760
April	1st to 10th	Night	28% 20% 30% 19% 3	570
	11th to 20th	Night	24% 19% 32% 20% 5% 1	564
	21st to end	Night	29% 15% 29% 22% 5%	570
May	1st to 10th	Night	33% 14% 27% 19% 7% 1	570
	11th to 20th	Night	26% 10% 31% 25% 7% 1	562
	21st to end	Night	22% 14% 39% 21% 4	616
June	1st to 10th	Night	30% 9% 32% 23% 6%	570
	11th to 20th	Night	26% 9% 32% 28% 4 1	570
	21st to end	Night	24% 12% 29% 28% 6%	570
July	1st to 10th	Night	18% 7% 33% 33% 7% 1	556
	11th to 20th	Night	16% 6% 34% 34% 9% 1	552
	21st to end	Night	18% 7% 29% 36% 10%	623
August	1st to 10th	Night	15% 6% 29% 37% 12%	568
	11th to 20th	Night	20% 6% 27% 33% 13% 1	562
	21st to end	Night	15% 9% 27% 39% 10%	627
September	1st to 10th	Night	17% 8% 33% 33% 9% 1	570
	11th to 20th	Night	22% 12% 26% 28% 12%	570
	21st to end	Night	23% 12% 31% 27% 6% 1	703
October	1st to 10th	Night	22% 12% 31% 25% 9% 1	760
	11th to 20th	Night	22% 17% 33% 22% 7%	760
	21st to end	Night	30% 22% 29% 16% 4	889
November	1st to 10th	Night	27% 22% 30% 17% 4 1	854
	11th to 20th	Night	26% 26% 27% 15% 5%	850
	21st to end	Night	30% 23% 29% 16% 3	850
December	1st to 10th	Night	31% 23% 30% 12% 4	850
	11th to 20th	Night	33% 25% 29% 10% 2	850
	21st to end	Night	29% 26% 29% 13% 3 1	935

Page generated at 2024-11-03 03:11:09. Version ac07

Copyright © 2024 Attilla Danko.