Rosemere
Clear Sky Chart
History

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

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	16% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	101816
	Night	17% 10% 4 8% 5% 4 4 3 5% 6% 33%	97923
Transparency	Day	50% 3 12% 23% 10% 1	105279
	Night	53% 3 12% 21% 10% 1	102549
Seeing	Day	22% 8% 27% 26% 13% 4	14636
	Night	23% 6% 27% 31% 11% 1	23634

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	16% 14% 5% 13% 6% 5% 5% 3 4 4 24%	2517
	11th to 20th	Day	14% 12% 6% 10% 6% 4 3 4 5% 7% 28%	2520
	21st to end	Day	13% 16% 5% 10% 6% 6% 5% 4 5% 6% 24%	2772
February	1st to 10th	Day	14% 16% 4 10% 6% 4 5% 4 4 6% 28%	1667
	11th to 20th	Day	13% 12% 4 10% 6% 5% 6% 5% 5% 6% 28%	1757
	21st to end	Day	17% 16% 5% 9% 4 4 4 3 5% 5% 28%	1570
March	1st to 10th	Day	20% 12% 4 10% 6% 5% 4 3 5% 5% 26%	3116
	11th to 20th	Day	13% 17% 5% 10% 6% 4 5% 3 4 5% 28%	3283
	21st to end	Day	15% 8% 3 8% 5% 5% 4 3 5% 5% 39%	4161
April	1st to 10th	Day	21% 11% 3 7% 5% 4 4 3 4 5% 32%	2280
	11th to 20th	Day	21% 8% 2 6% 6% 4 4 3 4 5% 36%	2254
	21st to end	Day	21% 10% 4 7% 5% 3 4 4 4 5% 33%	2432
May	1st to 10th	Day	19% 8% 4 8% 5% 4 5% 4 6% 7% 30%	4382
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 3 6% 8% 31%	4398
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 7% 9% 36%	4837
June	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 4 5% 8% 30%	2660
	11th to 20th	Day	14% 6% 3 7% 5% 4 5% 5% 6% 8% 37%	2660
	21st to end	Day	19% 7% 3 8% 6% 5% 5% 4 7% 7% 29%	2660
July	1st to 10th	Day	11% 6% 2 7% 6% 6% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 9% 37%	4440
	21st to end	Day	11% 6% 2 5% 4 4 4 5% 7% 8% 45%	4814
August	1st to 10th	Day	14% 6% 2 8% 5% 5% 7% 4 7% 9% 33%	4423
	11th to 20th	Day	14% 6% 3 8% 5% 4 4 3 6% 8% 38%	4013
	21st to end	Day	15% 5% 2 6% 5% 4 4 4 6% 8% 40%	4180
September	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 9% 41%	2280
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 5% 6% 49%	2202
	21st to end	Day	16% 6% 3 6% 5% 4 4 3 5% 7% 41%	2090
October	1st to 10th	Day	20% 6% 2 7% 4 4 5% 3 6% 7% 36%	1957
	11th to 20th	Day	19% 7% 3 8% 7% 5% 5% 4 6% 7% 30%	1859
	21st to end	Day	23% 9% 3 7% 4 4 3 3 5% 6% 31%	1881
November	1st to 10th	Day	16% 10% 3 7% 4 5% 4 4 5% 8% 35%	1761
	11th to 20th	Day	17% 11% 4 7% 4 5% 5% 3 5% 7% 32%	1712
	21st to end	Day	22% 11% 3 7% 5% 5% 5% 4 6% 6% 26%	1600
December	1st to 10th	Day	23% 14% 5% 11% 5% 4 4 3 4 4 21%	1560
	11th to 20th	Day	22% 14% 4 8% 5% 3 4 3 5% 4 28%	1906
	21st to end	Day	27% 17% 3 10% 4 4 3 3 4 4 21%	2772
January	1st to 10th	Night	16% 15% 6% 11% 6% 5% 5% 3 4 5% 24%	4429
	11th to 20th	Night	11% 14% 5% 11% 7% 6% 6% 4 6% 6% 25%	4440
	21st to end	Night	15% 17% 5% 11% 6% 4 4 3 5% 5% 25%	4884
February	1st to 10th	Night	14% 15% 5% 12% 6% 5% 5% 3 5% 6% 24%	2509
	11th to 20th	Night	14% 11% 4 10% 6% 5% 5% 4 5% 6% 31%	2309
	21st to end	Night	15% 14% 4 9% 5% 4 4 3 5% 5% 31%	1884
March	1st to 10th	Night	20% 12% 3 7% 5% 4 4 3 4 5% 33%	3724
	11th to 20th	Night	17% 18% 5% 9% 4 4 4 2 5% 4 28%	3674
	21st to end	Night	12% 10% 4 9% 5% 5% 4 3 5% 5% 39%	3471
April	1st to 10th	Night	23% 11% 2 7% 4 4 4 4 4 6% 31%	1900
	11th to 20th	Night	22% 9% 3 6% 5% 4 4 3 4 5% 35%	1875
	21st to end	Night	21% 9% 3 6% 4 3 4 3 5% 5% 36%	1747
May	1st to 10th	Night	21% 9% 3 8% 5% 4 5% 3 5% 7% 31%	2588
	11th to 20th	Night	21% 8% 3 7% 4 3 4 4 5% 6% 35%	2495
	21st to end	Night	15% 8% 2 8% 5% 4 4 4 5% 8% 36%	2738
June	1st to 10th	Night	20% 8% 3 7% 4 4 5% 3 7% 8% 32%	1520
	11th to 20th	Night	16% 7% 3 6% 4 3 4 4 6% 7% 39%	1520
	21st to end	Night	19% 7% 3 7% 4 4 5% 4 6% 7% 34%	1520
July	1st to 10th	Night	14% 6% 3 8% 5% 5% 5% 4 7% 8% 34%	2520
	11th to 20th	Night	14% 6% 2 6% 4 4 4 4 6% 8% 42%	2520
	21st to end	Night	11% 6% 2 6% 5% 4 4 4 6% 8% 44%	2739
August	1st to 10th	Night	15% 8% 3 7% 5% 4 5% 3 5% 7% 38%	2506
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 4 5% 7% 39%	2781
	21st to end	Night	17% 5% 2 8% 5% 5% 4 4 5% 7% 39%	3476
September	1st to 10th	Night	11% 5% 2 7% 5% 4 4 4 6% 7% 45%	1900
	11th to 20th	Night	14% 5% 3 6% 3 3 3 3 4 7% 50%	1976
	21st to end	Night	16% 5% 2 7% 4 4 4 4 4 7% 44%	2090
October	1st to 10th	Night	18% 6% 2 7% 4 4 4 3 4 6% 40%	2220
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 4 6% 37%	2320
	21st to end	Night	21% 9% 3 8% 4 4 4 3 5% 6% 32%	2717
November	1st to 10th	Night	19% 9% 3 7% 5% 4 5% 4 5% 7% 33%	2537
	11th to 20th	Night	19% 10% 3 8% 4 4 4 4 5% 5% 34%	2685
	21st to end	Night	22% 13% 3 9% 6% 3 4 3 5% 5% 28%	2800
December	1st to 10th	Night	21% 15% 5% 10% 5% 5% 5% 4 4 6% 22%	2737
	11th to 20th	Night	23% 14% 5% 9% 4 4 3 3 4 5% 27%	3288
	21st to end	Night	28% 16% 5% 10% 4 3 3 2 4 4 22%	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	66% 2 12% 15% 5% 1	2518
	11th to 20th	Day	58% 2 14% 18% 8%	2520
	21st to end	Day	61% 3 15% 15% 6%	2772
February	1st to 10th	Day	59% 2 10% 21% 6% 2	1667
	11th to 20th	Day	57% 4 11% 17% 10% 1	1766
	21st to end	Day	60% 2 10% 16% 11% 2	1570
March	1st to 10th	Day	62% 2 8% 19% 8% 1	3119
	11th to 20th	Day	60% 2 10% 14% 12% 3	3283
	21st to end	Day	48% 2 7% 21% 19% 2	4161
April	1st to 10th	Day	56% 3 7% 19% 13% 2	2280
	11th to 20th	Day	51% 2 7% 23% 15% 2	2254
	21st to end	Day	55% 3 8% 19% 13% 3	2432
May	1st to 10th	Day	54% 2 7% 25% 10% 1	4396
	11th to 20th	Day	52% 3 14% 20% 9% 2	4402
	21st to end	Day	45% 3 11% 26% 14% 2	4837
June	1st to 10th	Day	52% 4 9% 21% 12% 2	2660
	11th to 20th	Day	44% 4 11% 24% 14% 3	2660
	21st to end	Day	52% 4 12% 20% 10% 1	2660
July	1st to 10th	Day	43% 6% 13% 28% 11% 1	4370
	11th to 20th	Day	40% 5% 15% 31% 8%	4365
	21st to end	Day	36% 5% 14% 35% 10%	4661
August	1st to 10th	Day	46% 5% 17% 23% 8%	4409
	11th to 20th	Day	43% 5% 18% 28% 7%	4055
	21st to end	Day	41% 5% 16% 22% 15% 1	4180
September	1st to 10th	Day	39% 4 13% 31% 13% 1	2280
	11th to 20th	Day	35% 3 12% 34% 15% 1	2202
	21st to end	Day	43% 4 13% 28% 11% 1	2090
October	1st to 10th	Day	45% 4 14% 28% 9%	3256
	11th to 20th	Day	45% 4 17% 28% 7%	3062
	21st to end	Day	43% 4 19% 24% 10% 1	3081
November	1st to 10th	Day	49% 3 13% 25% 9% 1	1761
	11th to 20th	Day	53% 3 11% 20% 12% 1	1712
	21st to end	Day	60% 4 14% 16% 6% 1	1600
December	1st to 10th	Day	68% 2 11% 14% 5%	1560
	11th to 20th	Day	60% 3 11% 19% 7%	1906
	21st to end	Day	70% 2 12% 10% 6%	2772
January	1st to 10th	Night	64% 2 15% 14% 5%	4429
	11th to 20th	Night	61% 3 12% 18% 5% 1	4440
	21st to end	Night	64% 3 12% 14% 7% 1	4884
February	1st to 10th	Night	62% 3 9% 19% 6% 1	2509
	11th to 20th	Night	55% 2 10% 22% 10% 1	2311
	21st to end	Night	56% 2 9% 18% 13% 1	1884
March	1st to 10th	Night	56% 1 9% 20% 10% 4	3734
	11th to 20th	Night	61% 2 8% 14% 13% 2	3675
	21st to end	Night	50% 2 5% 24% 16% 3	3471
April	1st to 10th	Night	55% 3 7% 20% 15% 2	1900
	11th to 20th	Night	53% 2 5% 23% 15% 2	1875
	21st to end	Night	51% 2 7% 20% 14% 4	1747
May	1st to 10th	Night	56% 1 10% 22% 9% 3	2594
	11th to 20th	Night	52% 2 11% 21% 12% 3	2496
	21st to end	Night	47% 3 9% 21% 18% 1	2739
June	1st to 10th	Night	51% 4 9% 22% 13% 1	1520
	11th to 20th	Night	43% 4 12% 24% 15% 3	1520
	21st to end	Night	49% 5% 12% 20% 14% 1	1520
July	1st to 10th	Night	46% 4 15% 21% 13%	2480
	11th to 20th	Night	40% 4 19% 28% 9%	2472
	21st to end	Night	38% 5% 19% 25% 13%	2651
August	1st to 10th	Night	47% 4 13% 26% 10%	2496
	11th to 20th	Night	45% 5% 18% 24% 8%	2805
	21st to end	Night	45% 5% 13% 22% 14% 1	3476
September	1st to 10th	Night	38% 3 13% 28% 16% 1	1900
	11th to 20th	Night	36% 3 14% 33% 13% 1	1976
	21st to end	Night	42% 4 11% 28% 15%	2090
October	1st to 10th	Night	44% 4 13% 27% 10% 1	3701
	11th to 20th	Night	44% 3 12% 32% 9%	3856
	21st to end	Night	47% 4 16% 19% 12% 2	4467
November	1st to 10th	Night	52% 3 11% 24% 9% 1	2537
	11th to 20th	Night	52% 3 12% 21% 11% 1	2685
	21st to end	Night	60% 2 11% 19% 7%	2800
December	1st to 10th	Night	65% 3 12% 16% 4	2737
	11th to 20th	Night	62% 2 9% 19% 8%	3288
	21st to end	Night	68% 2 10% 16% 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	26% 7% 27% 30% 11%	180
	11th to 20th	Day	29% 11% 31% 23% 5% 2	180
	21st to end	Day	20% 12% 30% 29% 8% 2	198
February	1st to 10th	Day	31% 15% 33% 18% 4	249
	11th to 20th	Day	22% 12% 37% 24% 4	364
	21st to end	Day	28% 10% 31% 26% 4	382
March	1st to 10th	Day	25% 11% 30% 25% 9%	460
	11th to 20th	Day	22% 10% 35% 25% 6% 1	460
	21st to end	Day	27% 10% 33% 20% 8% 3	506
April	1st to 10th	Day	29% 12% 26% 22% 9% 2	460
	11th to 20th	Day	29% 13% 26% 20% 10% 3	452
	21st to end	Day	28% 12% 29% 20% 9% 3	460
May	1st to 10th	Day	22% 9% 31% 26% 9% 3	463
	11th to 20th	Day	20% 6% 30% 26% 13% 5%	487
	21st to end	Day	19% 9% 31% 26% 13% 3	529
June	1st to 10th	Day	24% 8% 25% 27% 13% 3	490
	11th to 20th	Day	17% 9% 24% 32% 15% 4	490
	21st to end	Day	21% 8% 24% 27% 16% 4	490
July	1st to 10th	Day	14% 5% 22% 33% 20% 6%	485
	11th to 20th	Day	14% 5% 26% 32% 18% 4	484
	21st to end	Day	14% 3 23% 36% 19% 5%	532
August	1st to 10th	Day	15% 4 21% 32% 21% 7%	486
	11th to 20th	Day	13% 4 18% 32% 22% 11%	479
	21st to end	Day	15% 6% 24% 26% 20% 9%	539
September	1st to 10th	Day	13% 6% 25% 29% 19% 9%	490
	11th to 20th	Day	14% 5% 22% 25% 21% 13%	490
	21st to end	Day	19% 6% 26% 25% 19% 7%	490
October	1st to 10th	Day	20% 9% 27% 23% 14% 6%	490
	11th to 20th	Day	22% 9% 32% 22% 12% 3	467
	21st to end	Day	32% 10% 25% 25% 8% 1	429
November	1st to 10th	Day	29% 10% 25% 24% 11% 1	395
	11th to 20th	Day	24% 12% 35% 20% 8% 1	312
	21st to end	Day	34% 10% 27% 22% 7% 2	200
December	1st to 10th	Day	29% 9% 24% 27% 8% 3	190
	11th to 20th	Day	26% 12% 37% 19% 4 1	180
	21st to end	Day	32% 14% 29% 17% 8% 1	198
January	1st to 10th	Night	28% 8% 30% 28% 6%	760
	11th to 20th	Night	25% 9% 32% 28% 6%	760
	21st to end	Night	20% 7% 34% 30% 8% 1	836
February	1st to 10th	Night	22% 6% 36% 29% 6% 1	760
	11th to 20th	Night	22% 8% 35% 29% 5% 1	743
	21st to end	Night	24% 7% 32% 33% 5%	628
March	1st to 10th	Night	25% 8% 29% 31% 6%	760
	11th to 20th	Night	27% 8% 30% 26% 8%	760
	21st to end	Night	23% 7% 30% 32% 8%	836
April	1st to 10th	Night	27% 9% 27% 31% 6%	760
	11th to 20th	Night	27% 8% 29% 28% 7% 1	751
	21st to end	Night	28% 7% 30% 27% 8%	607
May	1st to 10th	Night	25% 4 31% 30% 8% 1	428
	11th to 20th	Night	23% 4 28% 35% 9% 1	374
	21st to end	Night	18% 4 34% 34% 9%	411
June	1st to 10th	Night	26% 3 22% 34% 13%	380
	11th to 20th	Night	18% 5% 25% 37% 14% 1	380
	21st to end	Night	22% 4 22% 37% 15% 1	380
July	1st to 10th	Night	12% 3 25% 42% 16% 1	370
	11th to 20th	Night	12% 2 21% 46% 17% 1	368
	21st to end	Night	12% 3 17% 46% 20% 1	416
August	1st to 10th	Night	16% 3 12% 44% 24% 1	378
	11th to 20th	Night	15% 2 18% 36% 25% 3	557
	21st to end	Night	16% 2 21% 37% 22% 2	836
September	1st to 10th	Night	15% 2 21% 42% 18% 1	760
	11th to 20th	Night	18% 3 15% 38% 24% 2	760
	21st to end	Night	18% 3 25% 33% 18% 2	760
October	1st to 10th	Night	21% 5% 27% 33% 14% 1	760
	11th to 20th	Night	25% 5% 26% 32% 11% 1	760
	21st to end	Night	27% 8% 28% 30% 7%	836
November	1st to 10th	Night	25% 10% 26% 29% 9%	780
	11th to 20th	Night	24% 8% 32% 26% 10% 1	800
	21st to end	Night	30% 10% 27% 24% 9% 1	800
December	1st to 10th	Night	30% 7% 29% 26% 7%	783
	11th to 20th	Night	28% 9% 32% 23% 6% 1	760
	21st to end	Night	34% 10% 28% 22% 6%	836

Page generated at 2024-12-03 06:45:09. Version ac07

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