Wharf Road Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wharf Road Observatory clear sky chart from 2005-11-06 to 2024-02-15.

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	19% 11% 4 8% 6% 3 4 4 4 6% 30%	78209
	Night	20% 13% 6% 10% 7% 3 4 4 4 6% 24%	80860
Transparency	Day	57% 4 11% 18% 9% 1	77913
	Night	62% 4 10% 16% 7% 1	80691
Seeing	Day	31% 19% 30% 15% 4 1	15622
	Night	31% 18% 28% 18% 5%	23577

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	17% 18% 8% 12% 12% 5% 4 3 3 3 15%	2207
	11th to 20th	Day	18% 15% 9% 21% 11% 4 4 3 3 3 10%	2627
	21st to end	Day	17% 16% 7% 18% 12% 4 3 3 3 4 13%	3124
February	1st to 10th	Day	19% 16% 9% 14% 12% 4 3 4 4 5% 10%	1710
	11th to 20th	Day	19% 13% 6% 13% 14% 5% 3 4 3 4 16%	1609
	21st to end	Day	11% 14% 8% 11% 10% 4 5% 4 4 5% 25%	1411
March	1st to 10th	Day	15% 17% 8% 12% 10% 4 3 3 3 4 22%	1933
	11th to 20th	Day	15% 11% 7% 9% 8% 4 4 3 5% 5% 29%	1980
	21st to end	Day	18% 12% 6% 8% 5% 2 3 4 3 4 34%	2178
April	1st to 10th	Day	22% 13% 4 6% 5% 2 4 4 5% 6% 29%	2088
	11th to 20th	Day	20% 9% 3 4 3 2 4 3 4 7% 39%	2289
	21st to end	Day	21% 11% 3 5% 5% 3 4 4 4 6% 33%	2340
May	1st to 10th	Day	22% 9% 4 6% 6% 4 4 5% 6% 5% 30%	2340
	11th to 20th	Day	20% 7% 3 6% 4 2 4 4 4 7% 39%	2432
	21st to end	Day	20% 7% 3 5% 5% 3 3 4 5% 9% 36%	2724
June	1st to 10th	Day	24% 8% 2 5% 5% 3 5% 5% 5% 7% 32%	2625
	11th to 20th	Day	20% 7% 2 5% 5% 3 4 4 6% 7% 37%	2700
	21st to end	Day	21% 8% 3 7% 6% 3 5% 4 5% 6% 32%	2700
July	1st to 10th	Day	15% 6% 2 5% 5% 3 5% 5% 7% 9% 38%	2700
	11th to 20th	Day	15% 7% 3 5% 6% 3 5% 5% 7% 9% 36%	2638
	21st to end	Day	18% 6% 3 5% 5% 4 5% 6% 6% 7% 36%	2549
August	1st to 10th	Day	15% 6% 2 5% 5% 3 5% 6% 6% 7% 41%	2327
	11th to 20th	Day	16% 7% 2 6% 5% 3 5% 5% 5% 6% 39%	2304
	21st to end	Day	14% 6% 2 4 5% 2 3 4 5% 6% 48%	2540
September	1st to 10th	Day	17% 5% 2 4 3 2 3 4 4 7% 48%	2160
	11th to 20th	Day	15% 7% 3 5% 4 3 3 4 5% 7% 46%	1993
	21st to end	Day	18% 6% 3 5% 3 2 3 4 5% 5% 47%	1980
October	1st to 10th	Day	18% 9% 2 5% 4 2 4 4 4 7% 41%	1805
	11th to 20th	Day	18% 10% 3 7% 4 3 4 4 5% 7% 35%	1800
	21st to end	Day	24% 11% 3 6% 5% 3 4 4 4 5% 31%	1936
November	1st to 10th	Day	20% 13% 4 7% 7% 3 5% 4 4 7% 29%	1595
	11th to 20th	Day	18% 17% 8% 8% 5% 3 4 3 4 7% 22%	1520
	21st to end	Day	20% 16% 8% 11% 6% 4 4 3 4 4 18%	1520
December	1st to 10th	Day	24% 21% 7% 13% 6% 2 3 3 3 4 13%	1520
	11th to 20th	Day	23% 17% 7% 15% 9% 4 4 3 3 3 11%	1874
	21st to end	Day	24% 17% 10% 13% 9% 3 3 3 2 4 12%	2431
January	1st to 10th	Night	18% 17% 9% 18% 10% 3 4 3 3 3 12%	4748
	11th to 20th	Night	17% 21% 8% 18% 7% 4 3 3 4 4 11%	4329
	21st to end	Night	19% 14% 7% 16% 12% 4 4 4 4 5% 10%	4532
February	1st to 10th	Night	20% 18% 8% 17% 10% 3 4 3 3 4 11%	2470
	11th to 20th	Night	19% 16% 7% 14% 10% 5% 5% 3 4 5% 13%	2332
	21st to end	Night	13% 15% 8% 13% 9% 4 5% 4 4 6% 21%	1844
March	1st to 10th	Night	16% 17% 7% 11% 8% 3 3 3 3 5% 23%	2013
	11th to 20th	Night	19% 12% 7% 10% 8% 3 5% 4 4 5% 24%	1979
	21st to end	Night	20% 12% 6% 7% 6% 2 4 3 4 5% 30%	2178
April	1st to 10th	Night	25% 14% 4 6% 5% 3 3 3 4 6% 27%	1872
	11th to 20th	Night	22% 12% 3 5% 4 2 5% 5% 5% 8% 29%	1617
	21st to end	Night	24% 10% 3 6% 5% 3 4 4 4 7% 30%	1620
May	1st to 10th	Night	21% 11% 4 6% 5% 3 4 4 5% 7% 31%	1620
	11th to 20th	Night	22% 10% 3 6% 5% 3 3 3 5% 7% 32%	1461
	21st to end	Night	18% 9% 4 6% 5% 3 5% 5% 5% 7% 32%	1550
June	1st to 10th	Night	26% 7% 3 6% 4 3 3 5% 7% 9% 26%	1349
	11th to 20th	Night	21% 6% 3 5% 4 3 5% 5% 7% 8% 33%	1260
	21st to end	Night	20% 8% 4 7% 7% 5% 6% 4 6% 8% 26%	1260
July	1st to 10th	Night	18% 8% 3 5% 5% 3 4 6% 6% 10% 32%	1260
	11th to 20th	Night	16% 9% 4 7% 6% 4 6% 6% 7% 8% 28%	1301
	21st to end	Night	17% 9% 3 7% 6% 3 5% 6% 6% 7% 31%	1765
August	1st to 10th	Night	15% 8% 2 6% 5% 3 5% 6% 6% 8% 38%	1612
	11th to 20th	Night	18% 9% 4 6% 6% 3 4 5% 6% 7% 33%	1596
	21st to end	Night	14% 7% 2 6% 5% 3 4 4 6% 8% 41%	1814
September	1st to 10th	Night	15% 5% 3 5% 4 3 5% 5% 5% 7% 43%	1800
	11th to 20th	Night	17% 8% 3 4 4 2 4 3 5% 7% 42%	1966
	21st to end	Night	16% 7% 2 5% 6% 3 4 4 6% 7% 39%	1980
October	1st to 10th	Night	19% 7% 3 5% 5% 3 4 4 5% 7% 39%	2155
	11th to 20th	Night	18% 9% 3 6% 5% 3 4 4 5% 7% 36%	2160
	21st to end	Night	26% 13% 3 6% 5% 3 3 4 4 5% 28%	2416
November	1st to 10th	Night	23% 11% 4 6% 6% 3 4 3 5% 6% 29%	2483
	11th to 20th	Night	20% 18% 7% 9% 6% 3 4 4 4 6% 20%	2660
	21st to end	Night	21% 18% 7% 9% 6% 3 4 4 4 5% 20%	2660
December	1st to 10th	Night	26% 20% 8% 12% 6% 2 3 3 4 5% 11%	2660
	11th to 20th	Night	22% 18% 8% 16% 9% 3 4 2 3 4 12%	3302
	21st to end	Night	25% 20% 7% 12% 6% 2 2 3 3 4 16%	5236

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	77% 3 14% 5% 2	2208
	11th to 20th	Day	82% 4 6% 6% 2	2627
	21st to end	Day	73% 8% 10% 7% 2	3124
February	1st to 10th	Day	79% 4 8% 6% 3	1710
	11th to 20th	Day	75% 4 8% 9% 3	1617
	21st to end	Day	62% 5% 11% 15% 6% 1	1411
March	1st to 10th	Day	69% 3 7% 14% 6% 1	1937
	11th to 20th	Day	60% 3 9% 15% 10% 1	1980
	21st to end	Day	58% 3 7% 20% 10% 2	2178
April	1st to 10th	Day	60% 3 8% 15% 12% 1	2088
	11th to 20th	Day	49% 3 9% 24% 13% 2	2289
	21st to end	Day	54% 2 10% 19% 11% 2	2340
May	1st to 10th	Day	56% 4 9% 19% 10% 2	2340
	11th to 20th	Day	49% 4 8% 24% 14% 1	2436
	21st to end	Day	49% 4 14% 21% 10% 1	2724
June	1st to 10th	Day	54% 4 10% 22% 10%	2625
	11th to 20th	Day	47% 4 13% 21% 13% 2	2700
	21st to end	Day	54% 5% 12% 18% 11% 1	2700
July	1st to 10th	Day	41% 4 17% 23% 13% 1	2625
	11th to 20th	Day	44% 5% 15% 26% 10% 1	2557
	21st to end	Day	47% 5% 15% 23% 9% 1	2406
August	1st to 10th	Day	44% 5% 14% 25% 13%	2314
	11th to 20th	Day	45% 4 16% 23% 11%	2304
	21st to end	Day	37% 3 15% 28% 15% 1	2540
September	1st to 10th	Day	39% 3 12% 28% 15% 2	2160
	11th to 20th	Day	40% 3 12% 26% 17% 2	1993
	21st to end	Day	43% 3 9% 27% 16% 2	1980
October	1st to 10th	Day	45% 4 11% 27% 13% 1	1805
	11th to 20th	Day	51% 5% 12% 24% 8%	1800
	21st to end	Day	58% 3 9% 18% 11% 1	1936
November	1st to 10th	Day	59% 4 10% 19% 8% 1	1595
	11th to 20th	Day	66% 4 10% 15% 5% 1	1520
	21st to end	Day	72% 4 10% 11% 2	1520
December	1st to 10th	Day	77% 4 8% 9% 2	1520
	11th to 20th	Day	80% 4 6% 7% 3	1873
	21st to end	Day	81% 2 11% 4 2	2431
January	1st to 10th	Night	77% 4 8% 9% 1	4748
	11th to 20th	Night	79% 4 8% 7% 3	4329
	21st to end	Night	75% 5% 9% 9% 2	4532
February	1st to 10th	Night	79% 4 6% 7% 4	2470
	11th to 20th	Night	77% 3 7% 9% 4	2335
	21st to end	Night	66% 5% 10% 13% 6% 1	1844
March	1st to 10th	Night	65% 5% 8% 15% 7% 1	2022
	11th to 20th	Night	64% 4 10% 12% 9% 1	1980
	21st to end	Night	59% 4 8% 18% 10% 2	2178
April	1st to 10th	Night	61% 3 9% 13% 11% 3	1872
	11th to 20th	Night	53% 4 9% 20% 12% 1	1617
	21st to end	Night	57% 4 10% 18% 11% 1	1620
May	1st to 10th	Night	54% 3 11% 21% 10% 1	1620
	11th to 20th	Night	51% 5% 7% 25% 11% 1	1462
	21st to end	Night	50% 6% 14% 20% 9% 1	1551
June	1st to 10th	Night	53% 5% 13% 21% 7% 1	1349
	11th to 20th	Night	47% 5% 13% 23% 10% 1	1260
	21st to end	Night	53% 8% 12% 15% 9% 3	1260
July	1st to 10th	Night	45% 7% 17% 21% 9%	1225
	11th to 20th	Night	50% 7% 15% 19% 9% 1	1259
	21st to end	Night	50% 6% 14% 21% 9% 1	1668
August	1st to 10th	Night	43% 4 14% 29% 10%	1600
	11th to 20th	Night	48% 5% 17% 22% 8%	1596
	21st to end	Night	41% 5% 15% 27% 12%	1814
September	1st to 10th	Night	39% 6% 12% 29% 13% 1	1800
	11th to 20th	Night	42% 3 11% 27% 16% 1	1966
	21st to end	Night	44% 4 9% 25% 16% 2	1980
October	1st to 10th	Night	46% 4 11% 25% 13% 1	2155
	11th to 20th	Night	48% 4 14% 25% 8%	2160
	21st to end	Night	61% 3 9% 17% 9% 1	2416
November	1st to 10th	Night	56% 6% 12% 18% 9%	2483
	11th to 20th	Night	66% 6% 9% 13% 6%	2660
	21st to end	Night	67% 5% 14% 11% 3	2660
December	1st to 10th	Night	77% 3 9% 9% 2	2660
	11th to 20th	Night	78% 4 6% 10% 2	3304
	21st to end	Night	75% 3 9% 11% 2	5236

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	45% 25% 22% 8%	180
	11th to 20th	Day	42% 26% 23% 7% 2	276
	21st to end	Day	28% 27% 33% 10% 1	407
February	1st to 10th	Day	35% 26% 27% 10% 1	370
	11th to 20th	Day	40% 28% 22% 8% 2	348
	21st to end	Day	32% 28% 27% 12% 1	316
March	1st to 10th	Day	35% 25% 31% 7% 2	420
	11th to 20th	Day	35% 28% 25% 9% 3	420
	21st to end	Day	35% 27% 24% 10% 3 1	462
April	1st to 10th	Day	45% 23% 22% 8% 2 1	420
	11th to 20th	Day	35% 25% 26% 12% 3	412
	21st to end	Day	36% 18% 28% 13% 5%	420
May	1st to 10th	Day	34% 22% 30% 10% 4	423
	11th to 20th	Day	28% 20% 29% 16% 6%	578
	21st to end	Day	31% 17% 30% 18% 3 1	680
June	1st to 10th	Day	36% 15% 25% 19% 5%	630
	11th to 20th	Day	25% 17% 33% 18% 6% 1	630
	21st to end	Day	30% 12% 34% 17% 5% 1	630
July	1st to 10th	Day	22% 12% 37% 20% 7% 1	620
	11th to 20th	Day	22% 8% 38% 22% 9% 1	618
	21st to end	Day	22% 10% 41% 23% 4	489
August	1st to 10th	Day	16% 12% 43% 24% 4 1	446
	11th to 20th	Day	22% 11% 34% 21% 9% 2	439
	21st to end	Day	18% 14% 30% 27% 8% 2	495
September	1st to 10th	Day	19% 12% 40% 21% 6% 1	450
	11th to 20th	Day	25% 17% 31% 19% 6% 3	450
	21st to end	Day	25% 18% 30% 18% 8% 2	450
October	1st to 10th	Day	29% 16% 24% 19% 9% 3	363
	11th to 20th	Day	30% 18% 28% 16% 5% 2	360
	21st to end	Day	36% 21% 25% 13% 4 1	396
November	1st to 10th	Day	33% 21% 29% 12% 4 1	365
	11th to 20th	Day	41% 22% 22% 12% 4	370
	21st to end	Day	39% 25% 25% 6% 3 1	370
December	1st to 10th	Day	40% 26% 23% 10% 1	370
	11th to 20th	Day	49% 26% 19% 5% 1	351
	21st to end	Day	42% 27% 24% 5% 1 1	198
January	1st to 10th	Night	38% 25% 23% 13% 1	850
	11th to 20th	Night	39% 24% 23% 11% 3	773
	21st to end	Night	31% 27% 28% 12% 3	836
February	1st to 10th	Night	36% 24% 27% 11% 2	760
	11th to 20th	Night	39% 23% 26% 10% 2	722
	21st to end	Night	27% 28% 27% 16% 3	592
March	1st to 10th	Night	32% 25% 28% 13% 1	720
	11th to 20th	Night	32% 21% 26% 18% 3	720
	21st to end	Night	31% 20% 27% 17% 4	792
April	1st to 10th	Night	40% 18% 26% 15% 2	612
	11th to 20th	Night	30% 21% 30% 16% 3	534
	21st to end	Night	34% 16% 26% 18% 6%	540
May	1st to 10th	Night	29% 15% 32% 19% 5% 1	540
	11th to 20th	Night	30% 14% 29% 23% 4	532
	21st to end	Night	22% 15% 38% 20% 5% 1	583
June	1st to 10th	Night	30% 12% 31% 22% 5%	449
	11th to 20th	Night	25% 12% 31% 26% 6% 1	360
	21st to end	Night	23% 8% 40% 19% 9% 1	360
July	1st to 10th	Night	18% 9% 40% 26% 7%	350
	11th to 20th	Night	23% 7% 32% 24% 12% 1	389
	21st to end	Night	20% 8% 34% 33% 5%	590
August	1st to 10th	Night	18% 8% 35% 30% 8% 1	538
	11th to 20th	Night	21% 9% 30% 30% 9% 1	532
	21st to end	Night	19% 8% 33% 29% 10% 1	594
September	1st to 10th	Night	18% 10% 35% 27% 10% 1	540
	11th to 20th	Night	23% 10% 27% 26% 12% 1	706
	21st to end	Night	23% 13% 31% 21% 10% 1	720
October	1st to 10th	Night	23% 10% 27% 28% 10% 1	720
	11th to 20th	Night	23% 20% 29% 19% 8% 1	720
	21st to end	Night	38% 20% 22% 16% 4	792
November	1st to 10th	Night	33% 17% 25% 18% 5% 1	776
	11th to 20th	Night	35% 22% 21% 16% 6%	850
	21st to end	Night	36% 21% 24% 15% 3	850
December	1st to 10th	Night	41% 22% 24% 11% 2	850
	11th to 20th	Night	39% 27% 23% 9% 2	850
	21st to end	Night	41% 24% 21% 11% 2	935

Page generated at 2024-02-12 07:35:36. Version ac07

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