Thomas Harriot Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thomas Harriot Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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	13% 5% 2 5% 5% 3 5% 5% 5% 8% 43%	74655
	Night	14% 6% 2 5% 5% 3 4 4 5% 7% 44%	75047
Transparency	Day	25% 37% 8% 16% 11% 2	74369
	Night	26% 37% 7% 15% 12% 2	74853
Seeing	Day	17% 9% 25% 27% 17% 6%	14056
	Night	17% 9% 28% 31% 14% 2	23748

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	15% 6% 2 5% 5% 2 4 4 4 6% 47%	1621
	11th to 20th	Day	16% 6% 2 5% 5% 3 4 4 5% 5% 44%	1629
	21st to end	Day	15% 7% 3 5% 4 3 4 4 4 6% 47%	1782
February	1st to 10th	Day	13% 8% 3 5% 4 3 5% 5% 6% 7% 39%	1620
	11th to 20th	Day	20% 5% 2 4 4 3 3 4 3 5% 46%	1684
	21st to end	Day	17% 8% 2 5% 5% 4 5% 6% 6% 6% 37%	1480
March	1st to 10th	Day	14% 5% 2 5% 4 1 3 4 5% 5% 52%	1930
	11th to 20th	Day	17% 6% 3 5% 4 3 3 4 6% 5% 44%	1980
	21st to end	Day	16% 6% 2 6% 6% 4 4 4 5% 6% 41%	2225
April	1st to 10th	Day	12% 5% 2 4 4 2 4 3 4 7% 52%	2160
	11th to 20th	Day	11% 5% 2 5% 5% 3 4 4 5% 7% 49%	2134
	21st to end	Day	14% 5% 3 4 5% 3 5% 5% 5% 7% 44%	2160
May	1st to 10th	Day	13% 6% 2 6% 5% 3 5% 5% 5% 8% 41%	2191
	11th to 20th	Day	17% 6% 3 5% 5% 3 6% 5% 5% 8% 39%	2367
	21st to end	Day	14% 5% 2 4 4 3 5% 5% 5% 9% 43%	2725
June	1st to 10th	Day	11% 3 3 4 4 3 6% 6% 6% 10% 43%	2520
	11th to 20th	Day	11% 5% 2 5% 6% 4 5% 6% 6% 9% 42%	2520
	21st to end	Day	8% 5% 2 5% 5% 4 6% 6% 7% 13% 39%	2520
July	1st to 10th	Day	7% 5% 2 6% 6% 4 6% 7% 8% 11% 38%	2520
	11th to 20th	Day	6% 4 2 5% 6% 4 7% 7% 9% 12% 40%	2376
	21st to end	Day	7% 4 2 5% 7% 5% 7% 7% 8% 12% 35%	2547
August	1st to 10th	Day	10% 6% 3 5% 6% 4 7% 8% 8% 9% 34%	2327
	11th to 20th	Day	12% 6% 2 6% 7% 4 6% 8% 5% 9% 35%	2139
	21st to end	Day	11% 5% 2 6% 5% 3 6% 5% 7% 10% 40%	2376
September	1st to 10th	Day	14% 5% 2 4 5% 3 5% 5% 6% 8% 42%	2160
	11th to 20th	Day	13% 5% 2 6% 5% 3 5% 5% 5% 8% 42%	2160
	21st to end	Day	19% 7% 3 6% 5% 4 4 4 5% 6% 37%	1913
October	1st to 10th	Day	16% 7% 2 4 4 3 4 3 5% 6% 45%	1800
	11th to 20th	Day	15% 5% 2 5% 4 2 3 4 4 5% 51%	1800
	21st to end	Day	13% 5% 2 5% 5% 3 4 3 4 5% 52%	1980
November	1st to 10th	Day	13% 6% 2 4 3 2 3 4 4 6% 53%	1786
	11th to 20th	Day	14% 7% 2 4 4 2 3 3 4 6% 52%	1710
	21st to end	Day	16% 3 1 5% 4 2 2 3 4 6% 52%	1611
December	1st to 10th	Day	18% 6% 2 5% 5% 2 4 5% 5% 8% 43%	1520
	11th to 20th	Day	16% 6% 2 5% 4 1 3 2 3 5% 53%	1910
	21st to end	Day	16% 7% 2 5% 4 3 4 4 4 6% 44%	2772
January	1st to 10th	Night	15% 6% 3 5% 4 2 4 3 5% 6% 47%	2541
	11th to 20th	Night	16% 7% 3 6% 5% 3 5% 5% 5% 6% 40%	2354
	21st to end	Night	16% 6% 3 4 4 2 3 3 5% 6% 48%	2574
February	1st to 10th	Night	17% 7% 3 4 4 3 4 4 5% 6% 42%	2340
	11th to 20th	Night	20% 7% 2 4 5% 2 4 4 4 6% 42%	2161
	21st to end	Night	18% 7% 2 5% 3 2 3 3 4 6% 47%	1776
March	1st to 10th	Night	14% 4 3 5% 5% 2 3 4 4 5% 50%	2026
	11th to 20th	Night	18% 6% 2 5% 5% 3 5% 5% 5% 7% 39%	1980
	21st to end	Night	16% 5% 4 6% 5% 3 5% 4 5% 6% 42%	2129
April	1st to 10th	Night	14% 6% 2 5% 5% 3 4 4 6% 7% 43%	1800
	11th to 20th	Night	12% 6% 2 4 4 3 3 3 5% 7% 49%	1775
	21st to end	Night	15% 6% 2 5% 4 2 3 5% 5% 8% 44%	1800
May	1st to 10th	Night	13% 7% 3 6% 6% 3 6% 5% 6% 8% 39%	1782
	11th to 20th	Night	14% 6% 3 5% 5% 3 4 5% 6% 8% 39%	1523
	21st to end	Night	14% 5% 2 5% 6% 3 4 4 5% 9% 43%	1550
June	1st to 10th	Night	12% 5% 2 4 6% 3 5% 5% 8% 9% 41%	1440
	11th to 20th	Night	10% 5% 2 6% 5% 3 7% 6% 6% 11% 40%	1440
	21st to end	Night	8% 5% 3 6% 5% 4 6% 5% 6% 10% 41%	1440
July	1st to 10th	Night	9% 4 2 4 7% 5% 6% 6% 6% 10% 42%	1440
	11th to 20th	Night	6% 4 2 4 4 3 6% 7% 8% 10% 45%	1580
	21st to end	Night	7% 5% 3 6% 5% 4 5% 6% 9% 10% 39%	1771
August	1st to 10th	Night	7% 6% 2 7% 7% 5% 5% 6% 7% 12% 37%	1611
	11th to 20th	Night	9% 6% 3 7% 6% 4 5% 6% 6% 10% 37%	1741
	21st to end	Night	9% 5% 2 6% 6% 3 6% 5% 8% 10% 40%	1980
September	1st to 10th	Night	12% 4 2 5% 5% 4 5% 5% 6% 8% 45%	1800
	11th to 20th	Night	11% 5% 2 6% 5% 3 4 4 5% 7% 46%	1800
	21st to end	Night	21% 7% 3 6% 4 3 4 5% 5% 5% 38%	2042
October	1st to 10th	Night	15% 5% 2 5% 5% 3 4 4 5% 6% 47%	2160
	11th to 20th	Night	15% 6% 2 4 5% 2 3 4 4 6% 49%	2160
	21st to end	Night	16% 4 2 3 4 3 4 3 4 5% 52%	2376
November	1st to 10th	Night	15% 6% 2 5% 4 2 4 3 4 5% 50%	2291
	11th to 20th	Night	15% 5% 2 5% 4 2 4 3 4 6% 49%	2470
	21st to end	Night	14% 4 2 4 4 3 4 4 6% 6% 50%	2565
December	1st to 10th	Night	17% 7% 3 6% 5% 3 4 4 4 5% 42%	2660
	11th to 20th	Night	17% 6% 2 4 5% 2 3 4 5% 6% 47%	3285
	21st to end	Night	15% 7% 2 5% 5% 3 4 4 5% 6% 45%	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	23% 39% 7% 19% 11% 1	1622
	11th to 20th	Day	26% 41% 6% 14% 11% 2	1629
	21st to end	Day	26% 36% 7% 16% 13% 2	1782
February	1st to 10th	Day	29% 36% 7% 16% 10% 2	1620
	11th to 20th	Day	26% 36% 5% 16% 14% 3	1693
	21st to end	Day	29% 36% 7% 13% 11% 3	1480
March	1st to 10th	Day	21% 35% 7% 19% 15% 3	1930
	11th to 20th	Day	26% 37% 7% 15% 11% 4	1980
	21st to end	Day	31% 37% 7% 13% 11% 1	2225
April	1st to 10th	Day	22% 36% 7% 15% 15% 6%	2160
	11th to 20th	Day	24% 36% 7% 15% 14% 4	2134
	21st to end	Day	26% 37% 6% 15% 12% 4	2160
May	1st to 10th	Day	28% 37% 10% 13% 10% 1	2191
	11th to 20th	Day	30% 38% 8% 15% 7% 2	2371
	21st to end	Day	24% 39% 9% 17% 10%	2725
June	1st to 10th	Day	23% 38% 11% 18% 9% 1	2520
	11th to 20th	Day	26% 38% 10% 15% 9% 1	2520
	21st to end	Day	25% 39% 11% 14% 10% 1	2520
July	1st to 10th	Day	24% 40% 11% 14% 9% 2	2450
	11th to 20th	Day	22% 41% 12% 16% 7% 2	2305
	21st to end	Day	24% 41% 14% 13% 7%	2405
August	1st to 10th	Day	26% 40% 9% 18% 7% 1	2314
	11th to 20th	Day	31% 37% 9% 14% 9%	2139
	21st to end	Day	28% 39% 10% 13% 8% 2	2376
September	1st to 10th	Day	25% 38% 8% 12% 14% 4	2160
	11th to 20th	Day	26% 37% 5% 17% 13% 2	2160
	21st to end	Day	30% 38% 4 12% 13% 3	1913
October	1st to 10th	Day	25% 36% 4 15% 17% 3	1800
	11th to 20th	Day	26% 36% 6% 15% 16% 3	1800
	21st to end	Day	24% 37% 4 16% 16% 3	1980
November	1st to 10th	Day	18% 40% 5% 18% 16% 2	1786
	11th to 20th	Day	21% 39% 8% 15% 14% 3	1710
	21st to end	Day	22% 39% 6% 16% 14% 3	1611
December	1st to 10th	Day	21% 40% 8% 17% 13% 1	1520
	11th to 20th	Day	26% 31% 5% 20% 13% 5%	1906
	21st to end	Day	30% 25% 8% 24% 12% 1	2772
January	1st to 10th	Night	24% 39% 6% 16% 13% 2	2541
	11th to 20th	Night	26% 42% 7% 14% 10% 1	2354
	21st to end	Night	26% 37% 5% 17% 13% 2	2574
February	1st to 10th	Night	29% 35% 5% 16% 12% 3	2340
	11th to 20th	Night	29% 36% 4 15% 13% 4	2163
	21st to end	Night	28% 36% 5% 13% 14% 4	1776
March	1st to 10th	Night	22% 36% 6% 18% 16% 2	2026
	11th to 20th	Night	30% 37% 6% 14% 10% 3	1980
	21st to end	Night	30% 37% 6% 15% 10% 3	2129
April	1st to 10th	Night	26% 36% 7% 12% 15% 4	1800
	11th to 20th	Night	23% 35% 8% 15% 15% 5%	1775
	21st to end	Night	23% 37% 8% 17% 12% 2	1800
May	1st to 10th	Night	28% 37% 9% 14% 10% 2	1782
	11th to 20th	Night	30% 39% 7% 13% 10% 1	1524
	21st to end	Night	25% 38% 9% 18% 8% 1	1551
June	1st to 10th	Night	23% 38% 12% 16% 10%	1440
	11th to 20th	Night	26% 39% 10% 15% 8% 1	1440
	21st to end	Night	28% 38% 8% 15% 8% 2	1440
July	1st to 10th	Night	25% 40% 10% 16% 7% 2	1400
	11th to 20th	Night	19% 42% 14% 16% 7% 2	1529
	21st to end	Night	25% 42% 11% 15% 6%	1672
August	1st to 10th	Night	24% 40% 13% 17% 6%	1600
	11th to 20th	Night	29% 38% 9% 13% 10%	1741
	21st to end	Night	27% 39% 13% 13% 6% 1	1980
September	1st to 10th	Night	23% 38% 9% 12% 14% 4	1800
	11th to 20th	Night	24% 37% 7% 15% 16% 2	1800
	21st to end	Night	30% 36% 6% 10% 14% 3	2042
October	1st to 10th	Night	25% 37% 5% 14% 17% 2	2160
	11th to 20th	Night	27% 36% 6% 15% 14% 3	2160
	21st to end	Night	24% 36% 4 16% 16% 4	2376
November	1st to 10th	Night	19% 40% 7% 16% 16% 3	2291
	11th to 20th	Night	24% 39% 6% 13% 14% 4	2470
	21st to end	Night	24% 39% 5% 16% 13% 3	2565
December	1st to 10th	Night	25% 39% 6% 14% 14% 2	2660
	11th to 20th	Night	28% 33% 6% 14% 15% 5%	3288
	21st to end	Night	29% 26% 9% 21% 14% 1	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	22% 17% 39% 15% 6%	229
	11th to 20th	Day	17% 24% 41% 16% 2	243
	21st to end	Day	19% 19% 37% 21% 3	264
February	1st to 10th	Day	17% 21% 43% 15% 5%	240
	11th to 20th	Day	28% 19% 35% 16% 3	352
	21st to end	Day	23% 18% 38% 16% 3 1	346
March	1st to 10th	Day	19% 19% 39% 19% 5%	420
	11th to 20th	Day	23% 17% 34% 19% 6% 1	420
	21st to end	Day	19% 16% 35% 23% 6% 1	462
April	1st to 10th	Day	17% 21% 33% 19% 9% 1	420
	11th to 20th	Day	12% 15% 34% 24% 11% 4	412
	21st to end	Day	17% 11% 35% 27% 8% 2	420
May	1st to 10th	Day	14% 13% 36% 26% 9% 2	423
	11th to 20th	Day	21% 5% 26% 28% 16% 4	447
	21st to end	Day	20% 3 19% 27% 22% 8%	485
June	1st to 10th	Day	14% 3 21% 31% 25% 6%	450
	11th to 20th	Day	13% 4 17% 33% 23% 10%	450
	21st to end	Day	10% 3 16% 38% 26% 7%	450
July	1st to 10th	Day	11% 1 11% 34% 33% 11%	445
	11th to 20th	Day	7% 1 11% 31% 36% 13%	444
	21st to end	Day	10% 2 14% 35% 29% 10%	488
August	1st to 10th	Day	13% 2 15% 31% 28% 11%	446
	11th to 20th	Day	14% 1 12% 31% 28% 14%	439
	21st to end	Day	8% 3 15% 29% 29% 16%	495
September	1st to 10th	Day	15% 1 16% 29% 23% 16%	450
	11th to 20th	Day	15% 3 13% 35% 21% 13%	450
	21st to end	Day	26% 5% 22% 28% 14% 5%	450
October	1st to 10th	Day	20% 4 21% 28% 20% 8%	450
	11th to 20th	Day	17% 8% 23% 29% 18% 5%	450
	21st to end	Day	15% 9% 30% 29% 13% 4	495
November	1st to 10th	Day	15% 9% 27% 28% 16% 5%	422
	11th to 20th	Day	18% 13% 31% 25% 11% 1	370
	21st to end	Day	19% 14% 31% 21% 14% 2	271
December	1st to 10th	Day	24% 11% 37% 19% 8% 2	180
	11th to 20th	Day	22% 10% 34% 23% 11%	180
	21st to end	Day	23% 11% 34% 18% 13% 1	198
January	1st to 10th	Night	18% 18% 36% 24% 3 1	760
	11th to 20th	Night	20% 15% 32% 26% 6%	725
	21st to end	Night	19% 12% 41% 26% 2	792
February	1st to 10th	Night	22% 12% 40% 23% 3	720
	11th to 20th	Night	24% 17% 39% 18% 2	703
	21st to end	Night	21% 16% 36% 24% 2	592
March	1st to 10th	Night	16% 15% 37% 27% 5%	720
	11th to 20th	Night	20% 14% 37% 23% 6% 1	720
	21st to end	Night	18% 12% 39% 26% 5%	792
April	1st to 10th	Night	17% 16% 39% 24% 4	720
	11th to 20th	Night	16% 8% 37% 27% 11% 1	711
	21st to end	Night	18% 8% 32% 34% 8%	720
May	1st to 10th	Night	17% 10% 35% 31% 7% 1	702
	11th to 20th	Night	15% 4 29% 38% 13% 1	462
	21st to end	Night	16% 2 18% 43% 20% 2	389
June	1st to 10th	Night	12% 2 19% 42% 23% 3	360
	11th to 20th	Night	11% 2 18% 47% 19% 3	360
	21st to end	Night	9% 3 19% 46% 21% 3	360
July	1st to 10th	Night	10% 2 12% 47% 27% 3	350
	11th to 20th	Night	7% 1 11% 41% 35% 5%	485
	21st to end	Night	9% 2 16% 43% 27% 3	591
August	1st to 10th	Night	9% 1 12% 43% 31% 4	537
	11th to 20th	Night	11% 2 13% 39% 29% 5%	677
	21st to end	Night	11% 2 12% 35% 33% 6%	792
September	1st to 10th	Night	13% 3 12% 38% 30% 5%	720
	11th to 20th	Night	14% 3 14% 35% 29% 5%	720
	21st to end	Night	24% 4 17% 35% 18% 2	720
October	1st to 10th	Night	18% 4 20% 28% 25% 5%	720
	11th to 20th	Night	19% 6% 24% 33% 15% 2	720
	21st to end	Night	17% 8% 27% 31% 15% 2	792
November	1st to 10th	Night	18% 7% 26% 32% 15% 3	740
	11th to 20th	Night	16% 11% 33% 30% 9% 1	760
	21st to end	Night	14% 12% 30% 30% 13% 1	760
December	1st to 10th	Night	21% 12% 32% 25% 9% 1	760
	11th to 20th	Night	19% 8% 38% 29% 6%	760
	21st to end	Night	19% 11% 30% 33% 6%	836

Page generated at 2024-01-08 22:31:23. Version ac07

Copyright 2024 Attilla Danko