Bridgewater Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bridgewater Hill Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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	17% 9% 4 7% 6% 4 5% 5% 5% 7% 31%	74792
	Night	16% 9% 4 7% 6% 4 5% 5% 5% 6% 32%	74964
Transparency	Day	50% 8% 12% 18% 11% 1	74497
	Night	48% 9% 13% 18% 10% 1	74793
Seeing	Day	24% 20% 29% 17% 7% 2	13700
	Night	21% 18% 28% 24% 9% 1	22782

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% 6% 8% 9% 5% 6% 5% 6% 6% 23%	1517
	11th to 20th	Day	14% 12% 4 9% 9% 4 5% 6% 6% 7% 23%	1464
	21st to end	Day	10% 10% 6% 11% 9% 3 6% 6% 6% 6% 26%	1584
February	1st to 10th	Day	14% 12% 5% 8% 9% 5% 6% 5% 6% 5% 24%	1600
	11th to 20th	Day	10% 10% 7% 11% 11% 4 5% 5% 5% 6% 25%	1748
	21st to end	Day	16% 12% 6% 11% 7% 4 4 4 4 5% 27%	1480
March	1st to 10th	Day	12% 10% 7% 11% 8% 4 6% 5% 6% 5% 28%	1797
	11th to 20th	Day	16% 13% 5% 8% 6% 3 5% 5% 3 4 30%	1843
	21st to end	Day	17% 11% 6% 7% 7% 3 5% 4 4 5% 32%	2376
April	1st to 10th	Day	18% 12% 6% 7% 5% 2 4 5% 4 6% 31%	2160
	11th to 20th	Day	16% 9% 3 6% 6% 4 6% 4 6% 6% 34%	2134
	21st to end	Day	22% 11% 4 8% 5% 3 4 4 5% 6% 28%	2312
May	1st to 10th	Day	22% 10% 4 8% 6% 3 4 4 4 5% 30%	2346
	11th to 20th	Day	18% 9% 3 5% 5% 3 4 4 5% 7% 36%	2478
	21st to end	Day	15% 7% 3 7% 6% 4 5% 5% 6% 7% 36%	2725
June	1st to 10th	Day	20% 7% 3 7% 7% 4 6% 5% 7% 6% 27%	2520
	11th to 20th	Day	19% 7% 3 6% 5% 4 4 5% 6% 8% 32%	2520
	21st to end	Day	19% 8% 4 8% 6% 4 5% 5% 6% 6% 28%	2520
July	1st to 10th	Day	18% 6% 3 4 6% 3 6% 5% 5% 7% 37%	2520
	11th to 20th	Day	13% 6% 3 6% 6% 4 6% 6% 7% 10% 33%	2520
	21st to end	Day	16% 6% 3 5% 6% 4 6% 6% 7% 8% 34%	2744
August	1st to 10th	Day	13% 6% 3 6% 7% 4 7% 6% 8% 8% 32%	2471
	11th to 20th	Day	14% 8% 2 6% 6% 4 6% 6% 7% 9% 32%	2223
	21st to end	Day	14% 5% 2 6% 5% 4 5% 6% 6% 9% 37%	2376
September	1st to 10th	Day	14% 6% 2 5% 5% 4 5% 5% 6% 8% 40%	2160
	11th to 20th	Day	13% 7% 2 6% 4 3 4 4 5% 7% 46%	2038
	21st to end	Day	16% 6% 2 5% 5% 3 4 3 5% 8% 41%	1980
October	1st to 10th	Day	23% 9% 3 7% 6% 3 4 4 5% 5% 32%	1939
	11th to 20th	Day	15% 10% 3 6% 8% 3 5% 4 6% 7% 35%	1746
	21st to end	Day	25% 14% 3 7% 5% 4 4 4 4 5% 26%	1782
November	1st to 10th	Day	12% 10% 3 7% 6% 3 4 5% 5% 7% 36%	1671
	11th to 20th	Day	17% 12% 6% 6% 5% 3 5% 5% 4 5% 33%	1710
	21st to end	Day	17% 11% 5% 9% 6% 4 5% 5% 4 6% 28%	1590
December	1st to 10th	Day	19% 14% 6% 11% 7% 4 4 4 5% 6% 20%	1520
	11th to 20th	Day	20% 12% 7% 7% 5% 3 4 4 5% 5% 28%	1906
	21st to end	Day	19% 16% 6% 10% 7% 3 5% 4 5% 5% 21%	2772
January	1st to 10th	Night	13% 10% 5% 8% 8% 4 7% 7% 6% 6% 25%	2649
	11th to 20th	Night	14% 13% 5% 8% 8% 4 7% 6% 6% 7% 22%	2569
	21st to end	Night	10% 8% 5% 11% 7% 5% 7% 6% 7% 6% 29%	2772
February	1st to 10th	Night	14% 12% 6% 8% 9% 5% 6% 6% 6% 7% 22%	2357
	11th to 20th	Night	10% 10% 4 8% 10% 5% 8% 6% 6% 7% 26%	2098
	21st to end	Night	14% 11% 5% 8% 8% 4 5% 5% 6% 6% 28%	1776
March	1st to 10th	Night	13% 9% 5% 9% 8% 4 5% 5% 6% 6% 29%	2150
	11th to 20th	Night	14% 10% 5% 8% 7% 5% 6% 4 4 6% 30%	2113
	21st to end	Night	16% 12% 3 6% 5% 4 4 4 5% 5% 35%	1980
April	1st to 10th	Night	17% 9% 3 9% 6% 4 5% 5% 5% 6% 31%	1800
	11th to 20th	Night	17% 9% 4 6% 6% 3 5% 4 6% 7% 33%	1775
	21st to end	Night	19% 9% 5% 7% 5% 3 5% 5% 6% 6% 30%	1648
May	1st to 10th	Night	23% 10% 3 6% 5% 3 4 4 5% 5% 30%	1620
	11th to 20th	Night	18% 8% 5% 6% 5% 3 4 5% 5% 6% 36%	1425
	21st to end	Night	17% 7% 3 6% 4 4 4 5% 6% 7% 37%	1550
June	1st to 10th	Night	20% 6% 3 6% 6% 3 6% 4 6% 7% 33%	1440
	11th to 20th	Night	20% 6% 3 6% 4 3 5% 5% 4 5% 39%	1440
	21st to end	Night	16% 7% 3 5% 7% 4 5% 5% 6% 7% 36%	1440
July	1st to 10th	Night	15% 6% 3 5% 5% 4 5% 5% 6% 7% 38%	1440
	11th to 20th	Night	14% 5% 3 5% 3 3 4 6% 7% 10% 40%	1440
	21st to end	Night	13% 5% 3 5% 5% 3 4 5% 7% 8% 44%	1574
August	1st to 10th	Night	11% 6% 2 6% 5% 4 5% 5% 6% 8% 43%	1448
	11th to 20th	Night	13% 6% 2 7% 6% 3 4 4 5% 8% 40%	1674
	21st to end	Night	15% 6% 2 5% 4 3 4 4 6% 8% 43%	1980
September	1st to 10th	Night	13% 5% 3 6% 4 3 4 5% 5% 7% 46%	1800
	11th to 20th	Night	14% 7% 2 4 5% 3 3 3 4 5% 49%	1921
	21st to end	Night	16% 8% 2 4 5% 3 4 4 5% 5% 45%	1980
October	1st to 10th	Night	20% 8% 3 6% 5% 4 4 4 4 6% 35%	2020
	11th to 20th	Night	16% 9% 3 5% 6% 4 5% 6% 6% 7% 34%	2214
	21st to end	Night	22% 11% 3 7% 6% 3 5% 5% 5% 6% 27%	2574
November	1st to 10th	Night	15% 10% 4 7% 7% 3 5% 5% 5% 6% 35%	2407
	11th to 20th	Night	15% 9% 4 7% 6% 4 6% 5% 6% 5% 32%	2470
	21st to end	Night	14% 10% 5% 9% 6% 3 5% 4 6% 6% 31%	2588
December	1st to 10th	Night	17% 12% 7% 11% 8% 4 6% 5% 5% 5% 20%	2660
	11th to 20th	Night	19% 11% 5% 9% 6% 4 5% 5% 5% 6% 25%	3288
	21st to end	Night	19% 14% 6% 12% 6% 4 5% 5% 5% 5% 21%	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	54% 11% 13% 16% 7%	1518
	11th to 20th	Day	55% 11% 12% 13% 8% 2	1464
	21st to end	Day	53% 9% 12% 15% 10% 2	1584
February	1st to 10th	Day	58% 9% 12% 13% 7% 1	1600
	11th to 20th	Day	55% 9% 11% 14% 10% 2	1757
	21st to end	Day	56% 8% 11% 13% 11% 1	1480
March	1st to 10th	Day	54% 9% 12% 14% 10% 3	1800
	11th to 20th	Day	54% 5% 12% 11% 14% 2	1843
	21st to end	Day	52% 6% 9% 15% 14% 4	2376
April	1st to 10th	Day	52% 7% 9% 19% 11% 3	2160
	11th to 20th	Day	47% 8% 10% 19% 14% 1	2134
	21st to end	Day	56% 7% 9% 15% 11% 3	2312
May	1st to 10th	Day	55% 6% 8% 18% 12% 2	2346
	11th to 20th	Day	47% 7% 9% 21% 14% 2	2482
	21st to end	Day	45% 9% 13% 22% 10% 1	2725
June	1st to 10th	Day	53% 8% 15% 15% 8%	2520
	11th to 20th	Day	48% 8% 11% 19% 13% 1	2520
	21st to end	Day	54% 9% 10% 16% 9% 1	2520
July	1st to 10th	Day	43% 9% 11% 22% 14% 1	2450
	11th to 20th	Day	43% 11% 14% 24% 8%	2445
	21st to end	Day	43% 9% 15% 23% 9% 1	2591
August	1st to 10th	Day	43% 12% 15% 21% 9%	2457
	11th to 20th	Day	45% 10% 16% 20% 9%	2223
	21st to end	Day	39% 9% 14% 24% 12% 1	2376
September	1st to 10th	Day	38% 9% 13% 26% 13% 1	2160
	11th to 20th	Day	37% 6% 11% 27% 18% 1	2038
	21st to end	Day	39% 8% 13% 25% 13% 2	1980
October	1st to 10th	Day	51% 8% 9% 17% 12% 2	1939
	11th to 20th	Day	46% 8% 14% 24% 7% 1	1746
	21st to end	Day	58% 7% 11% 15% 8% 2	1782
November	1st to 10th	Day	43% 9% 15% 20% 13%	1671
	11th to 20th	Day	48% 8% 14% 15% 13% 2	1710
	21st to end	Day	54% 7% 17% 15% 6% 1	1590
December	1st to 10th	Day	61% 9% 13% 11% 6% 1	1520
	11th to 20th	Day	56% 7% 12% 15% 9% 1	1906
	21st to end	Day	63% 8% 9% 12% 8%	2772
January	1st to 10th	Night	49% 13% 14% 13% 10% 1	2649
	11th to 20th	Night	55% 13% 10% 13% 7% 1	2569
	21st to end	Night	48% 10% 13% 15% 12% 2	2772
February	1st to 10th	Night	55% 12% 11% 12% 8% 1	2357
	11th to 20th	Night	49% 11% 13% 15% 11% 1	2100
	21st to end	Night	50% 10% 13% 17% 8% 3	1776
March	1st to 10th	Night	51% 9% 13% 16% 9% 2	2160
	11th to 20th	Night	51% 8% 12% 16% 12% 2	2114
	21st to end	Night	47% 7% 12% 16% 16% 3	1980
April	1st to 10th	Night	49% 8% 12% 18% 11% 2	1800
	11th to 20th	Night	47% 7% 12% 21% 13% 1	1775
	21st to end	Night	50% 8% 10% 17% 11% 3	1648
May	1st to 10th	Night	53% 7% 8% 17% 14% 2	1620
	11th to 20th	Night	46% 8% 10% 20% 13% 2	1426
	21st to end	Night	43% 11% 13% 21% 11% 1	1551
June	1st to 10th	Night	47% 10% 14% 17% 12%	1440
	11th to 20th	Night	45% 9% 14% 18% 13% 1	1440
	21st to end	Night	45% 10% 12% 24% 10%	1440
July	1st to 10th	Night	39% 12% 14% 22% 12% 1	1400
	11th to 20th	Night	35% 12% 17% 27% 9%	1392
	21st to end	Night	35% 9% 15% 28% 11% 2	1486
August	1st to 10th	Night	35% 12% 13% 27% 12%	1438
	11th to 20th	Night	39% 10% 16% 24% 10%	1674
	21st to end	Night	36% 9% 14% 28% 13%	1980
September	1st to 10th	Night	36% 9% 16% 27% 13% 1	1800
	11th to 20th	Night	35% 7% 12% 28% 17% 1	1921
	21st to end	Night	39% 7% 12% 26% 14% 2	1980
October	1st to 10th	Night	49% 8% 11% 21% 10% 2	2020
	11th to 20th	Night	46% 9% 14% 22% 8%	2214
	21st to end	Night	54% 9% 11% 15% 8% 2	2574
November	1st to 10th	Night	46% 8% 14% 18% 12% 2	2407
	11th to 20th	Night	47% 8% 14% 17% 11% 2	2470
	21st to end	Night	49% 10% 16% 18% 7%	2588
December	1st to 10th	Night	59% 11% 13% 13% 4	2660
	11th to 20th	Night	55% 9% 13% 12% 11%	3288
	21st to end	Night	62% 9% 10% 14% 5%	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	28% 27% 24% 17% 3 1	180
	11th to 20th	Day	32% 26% 30% 10% 2 1	166
	21st to end	Day	20% 27% 35% 14% 5%	176
February	1st to 10th	Day	37% 34% 24% 5% 1	238
	11th to 20th	Day	30% 27% 29% 12% 2	416
	21st to end	Day	29% 27% 29% 14% 2	346
March	1st to 10th	Day	25% 25% 34% 13% 3	420
	11th to 20th	Day	30% 26% 27% 12% 4 1	420
	21st to end	Day	31% 24% 26% 12% 6% 3	462
April	1st to 10th	Day	36% 19% 26% 12% 6% 1	420
	11th to 20th	Day	32% 25% 22% 13% 6% 2	412
	21st to end	Day	34% 22% 26% 11% 4 2	420
May	1st to 10th	Day	30% 24% 26% 12% 6% 2	423
	11th to 20th	Day	20% 21% 35% 17% 3 3	447
	21st to end	Day	19% 18% 33% 22% 6% 1	485
June	1st to 10th	Day	24% 18% 36% 15% 6% 1	450
	11th to 20th	Day	21% 18% 32% 18% 9% 1	450
	21st to end	Day	21% 18% 33% 19% 6% 2	450
July	1st to 10th	Day	18% 14% 31% 22% 12% 3	445
	11th to 20th	Day	16% 9% 37% 25% 11% 2	444
	21st to end	Day	15% 11% 43% 20% 9% 2	488
August	1st to 10th	Day	13% 13% 34% 24% 14% 3	446
	11th to 20th	Day	17% 13% 30% 20% 13% 6%	439
	21st to end	Day	14% 16% 28% 25% 12% 5%	495
September	1st to 10th	Day	15% 15% 28% 22% 14% 6%	450
	11th to 20th	Day	15% 17% 26% 17% 16% 9%	450
	21st to end	Day	18% 14% 31% 20% 11% 6%	450
October	1st to 10th	Day	28% 15% 24% 18% 12% 3	450
	11th to 20th	Day	21% 21% 25% 24% 9% 1	423
	21st to end	Day	36% 19% 21% 17% 6% 1	396
November	1st to 10th	Day	22% 22% 24% 22% 9% 1	365
	11th to 20th	Day	30% 24% 24% 16% 6% 1	370
	21st to end	Day	30% 21% 30% 16% 2 1	250
December	1st to 10th	Day	28% 27% 29% 12% 3 1	180
	11th to 20th	Day	33% 28% 31% 7% 2	180
	21st to end	Day	36% 20% 29% 12% 3 1	198
January	1st to 10th	Night	22% 23% 33% 19% 3	760
	11th to 20th	Night	23% 23% 31% 20% 2 1	735
	21st to end	Night	16% 23% 36% 21% 4	792
February	1st to 10th	Night	20% 26% 35% 16% 2	720
	11th to 20th	Night	20% 25% 34% 18% 2	703
	21st to end	Night	24% 22% 31% 20% 2	592
March	1st to 10th	Night	23% 20% 34% 20% 3	720
	11th to 20th	Night	23% 25% 27% 20% 5%	720
	21st to end	Night	24% 22% 26% 19% 7% 1	792
April	1st to 10th	Night	23% 24% 27% 21% 5%	720
	11th to 20th	Night	20% 26% 26% 19% 8% 1	711
	21st to end	Night	28% 18% 28% 20% 6%	568
May	1st to 10th	Night	29% 17% 25% 21% 8%	540
	11th to 20th	Night	19% 17% 29% 29% 6% 1	364
	21st to end	Night	17% 12% 27% 32% 11% 1	389
June	1st to 10th	Night	18% 12% 29% 30% 11%	360
	11th to 20th	Night	20% 11% 23% 34% 11% 1	360
	21st to end	Night	16% 9% 26% 37% 12% 1	360
July	1st to 10th	Night	18% 6% 20% 41% 13% 2	350
	11th to 20th	Night	14% 4 25% 38% 17% 2	348
	21st to end	Night	12% 7% 25% 39% 17% 1	394
August	1st to 10th	Night	12% 6% 20% 40% 22% 1	374
	11th to 20th	Night	15% 6% 25% 32% 18% 4	610
	21st to end	Night	16% 8% 21% 33% 20% 2	792
September	1st to 10th	Night	15% 10% 24% 30% 19% 2	720
	11th to 20th	Night	16% 11% 23% 26% 20% 4	720
	21st to end	Night	18% 12% 23% 27% 17% 3	720
October	1st to 10th	Night	25% 15% 19% 25% 15% 2	720
	11th to 20th	Night	19% 16% 25% 27% 11% 1	720
	21st to end	Night	28% 20% 25% 22% 6%	792
November	1st to 10th	Night	20% 20% 28% 23% 8% 1	740
	11th to 20th	Night	21% 21% 29% 20% 8% 1	760
	21st to end	Night	21% 24% 30% 19% 5% 1	760
December	1st to 10th	Night	24% 24% 30% 17% 4	760
	11th to 20th	Night	26% 24% 27% 20% 3	760
	21st to end	Night	28% 23% 31% 16% 3	836

Page generated at 2024-01-11 04:22:39. Version ac07

Copyright 2024 Attilla Danko