Prospect
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prospect clear sky chart from 2005-11-06 to 2024-12-02.

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% 7% 2 6% 4 4 4 4 6% 7% 38%	101500
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	98134
Transparency	Day	42% 7% 13% 21% 15% 2	105047
	Night	42% 6% 12% 22% 15% 2	102676
Seeing	Day	20% 18% 32% 20% 8% 2	15088
	Night	21% 15% 32% 25% 7% 1	24150

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	15% 7% 2 7% 3 4 3 3 5% 5% 45%	2517
	11th to 20th	Day	18% 9% 3 7% 4 5% 5% 4 4 5% 36%	2520
	21st to end	Day	22% 13% 4 6% 4 3 3 3 4 4 32%	2850
February	1st to 10th	Day	18% 7% 2 7% 4 5% 5% 3 5% 5% 38%	1767
	11th to 20th	Day	14% 7% 3 5% 4 4 4 4 7% 7% 41%	1848
	21st to end	Day	22% 8% 2 6% 4 3 3 4 4 6% 38%	1570
March	1st to 10th	Day	27% 10% 3 6% 4 4 3 2 4 4 34%	3116
	11th to 20th	Day	11% 5% 2 5% 4 5% 5% 5% 8% 8% 42%	3264
	21st to end	Day	21% 7% 2 6% 4 4 4 4 5% 6% 38%	4166
April	1st to 10th	Day	19% 8% 3 6% 4 4 4 3 6% 7% 37%	2280
	11th to 20th	Day	20% 5% 2 5% 4 3 3 3 5% 7% 41%	2254
	21st to end	Day	22% 5% 3 5% 4 4 4 3 5% 5% 40%	2380
May	1st to 10th	Day	28% 9% 2 6% 4 3 3 3 5% 7% 30%	4106
	11th to 20th	Day	23% 8% 3 6% 4 4 5% 4 5% 6% 32%	4288
	21st to end	Day	16% 5% 2 4 4 4 4 3 5% 8% 45%	4837
June	1st to 10th	Day	18% 4 2 6% 5% 5% 4 5% 7% 9% 35%	2660
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 4 7% 9% 36%	2660
	21st to end	Day	14% 6% 2 7% 5% 4 5% 4 6% 9% 38%	2660
July	1st to 10th	Day	13% 6% 2 7% 5% 6% 6% 4 6% 9% 35%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 4 5% 5% 7% 10% 38%	4440
	21st to end	Day	17% 9% 3 7% 5% 5% 5% 4 6% 7% 32%	4814
August	1st to 10th	Day	20% 6% 3 7% 6% 5% 5% 4 6% 8% 30%	4271
	11th to 20th	Day	11% 6% 2 7% 4 4 4 4 6% 8% 41%	3738
	21st to end	Day	10% 5% 2 6% 4 5% 5% 4 7% 9% 44%	4180
September	1st to 10th	Day	13% 6% 2 7% 4 4 4 4 4 7% 44%	2280
	11th to 20th	Day	13% 6% 2 5% 3 4 3 4 5% 6% 50%	2152
	21st to end	Day	19% 6% 3 6% 4 4 4 3 5% 6% 41%	2090
October	1st to 10th	Day	21% 7% 2 6% 3 4 3 3 4 6% 41%	2053
	11th to 20th	Day	15% 6% 2 5% 4 3 3 4 6% 6% 47%	1889
	21st to end	Day	21% 7% 2 6% 3 4 4 3 5% 6% 40%	1881
November	1st to 10th	Day	14% 6% 2 5% 5% 4 4 2 4 7% 49%	1761
	11th to 20th	Day	18% 5% 2 4 3 3 3 2 6% 5% 48%	1800
	21st to end	Day	18% 7% 2 5% 4 4 4 3 6% 6% 42%	1762
December	1st to 10th	Day	20% 5% 2 7% 5% 5% 4 4 5% 6% 38%	1528
	11th to 20th	Day	23% 6% 2 4 3 3 3 2 4 5% 44%	1906
	21st to end	Day	19% 11% 4 7% 5% 4 4 3 5% 6% 33%	2772
January	1st to 10th	Night	17% 6% 2 5% 4 4 3 3 5% 5% 46%	4429
	11th to 20th	Night	17% 9% 3 7% 4 3 3 3 4 4 43%	4440
	21st to end	Night	24% 12% 3 6% 4 3 4 3 4 4 33%	4788
February	1st to 10th	Night	17% 10% 3 5% 4 4 4 3 4 5% 41%	2411
	11th to 20th	Night	16% 8% 3 6% 4 5% 4 3 5% 6% 41%	2218
	21st to end	Night	20% 8% 2 6% 4 4 3 2 5% 5% 40%	1884
March	1st to 10th	Night	25% 12% 3 5% 3 3 3 3 4 5% 35%	3724
	11th to 20th	Night	12% 7% 3 6% 4 4 5% 4 6% 7% 43%	3691
	21st to end	Night	21% 9% 2 5% 3 3 3 3 5% 5% 40%	3466
April	1st to 10th	Night	19% 8% 2 6% 4 4 4 4 6% 6% 37%	1900
	11th to 20th	Night	19% 6% 2 6% 4 3 4 3 6% 6% 40%	1875
	21st to end	Night	20% 8% 3 6% 4 3 3 3 4 5% 42%	1800
May	1st to 10th	Night	24% 10% 3 8% 4 4 4 3 4 7% 28%	2834
	11th to 20th	Night	21% 9% 4 8% 4 4 3 4 4 6% 31%	2633
	21st to end	Night	18% 7% 2 5% 4 3 3 4 6% 7% 42%	2738
June	1st to 10th	Night	18% 7% 2 6% 5% 4 4 3 5% 6% 40%	1520
	11th to 20th	Night	16% 7% 2 5% 4 4 4 4 6% 8% 41%	1520
	21st to end	Night	13% 6% 3 6% 4 4 5% 3 5% 9% 41%	1520
July	1st to 10th	Night	14% 6% 2 7% 5% 4 5% 6% 7% 8% 36%	2520
	11th to 20th	Night	16% 7% 3 7% 4 4 4 4 6% 8% 36%	2520
	21st to end	Night	19% 9% 3 7% 4 5% 4 4 6% 7% 33%	2739
August	1st to 10th	Night	22% 8% 3 7% 5% 4 5% 4 6% 6% 30%	2626
	11th to 20th	Night	15% 7% 2 8% 5% 4 4 4 4 7% 41%	3086
	21st to end	Night	11% 4 2 4 3 3 3 3 5% 9% 53%	3476
September	1st to 10th	Night	14% 6% 3 6% 4 3 5% 3 5% 6% 45%	1900
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 6% 52%	2027
	21st to end	Night	18% 6% 2 6% 3 4 5% 3 4 5% 44%	2090
October	1st to 10th	Night	20% 6% 3 6% 4 4 3 3 5% 5% 42%	2123
	11th to 20th	Night	15% 5% 2 6% 3 3 4 3 3 6% 49%	2289
	21st to end	Night	22% 7% 2 5% 3 3 4 3 4 5% 41%	2717
November	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 4 6% 50%	2537
	11th to 20th	Night	19% 7% 2 4 3 4 3 3 4 5% 47%	2600
	21st to end	Night	16% 6% 2 5% 4 4 3 3 5% 6% 46%	2635
December	1st to 10th	Night	20% 7% 3 6% 3 3 4 3 5% 5% 40%	2686
	11th to 20th	Night	21% 7% 2 4 4 4 4 4 4 5% 41%	3288
	21st to end	Night	22% 11% 3 7% 3 3 4 3 4 5% 35%	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	37% 7% 11% 31% 11% 2	2518
	11th to 20th	Day	47% 7% 11% 23% 10% 1	2520
	21st to end	Day	51% 9% 9% 20% 10% 2	2850
February	1st to 10th	Day	46% 7% 13% 20% 13% 2	1767
	11th to 20th	Day	40% 7% 12% 23% 16% 3	1857
	21st to end	Day	48% 6% 11% 20% 12% 3	1570
March	1st to 10th	Day	52% 7% 12% 17% 11% 2	3119
	11th to 20th	Day	30% 11% 17% 28% 12% 1	3264
	21st to end	Day	44% 6% 9% 17% 20% 5%	4166
April	1st to 10th	Day	45% 6% 11% 19% 15% 3	2280
	11th to 20th	Day	42% 7% 11% 20% 17% 3	2254
	21st to end	Day	44% 7% 11% 19% 16% 4	2380
May	1st to 10th	Day	51% 9% 14% 14% 11% 1	4120
	11th to 20th	Day	48% 9% 14% 18% 9% 1	4292
	21st to end	Day	34% 10% 14% 24% 17% 1	4837
June	1st to 10th	Day	43% 9% 12% 23% 12% 1	2660
	11th to 20th	Day	41% 10% 15% 21% 12% 1	2660
	21st to end	Day	41% 9% 14% 21% 14% 1	2660
July	1st to 10th	Day	45% 9% 11% 19% 15% 1	4370
	11th to 20th	Day	40% 8% 17% 22% 13% 1	4365
	21st to end	Day	49% 7% 12% 16% 15% 1	4661
August	1st to 10th	Day	49% 8% 15% 20% 8%	4257
	11th to 20th	Day	38% 7% 14% 29% 11% 1	3774
	21st to end	Day	34% 6% 15% 26% 17% 2	4180
September	1st to 10th	Day	39% 8% 11% 21% 19% 2	2280
	11th to 20th	Day	33% 7% 11% 23% 23% 2	2152
	21st to end	Day	43% 6% 10% 20% 18% 3	2090
October	1st to 10th	Day	38% 5% 11% 18% 23% 6%	3417
	11th to 20th	Day	27% 5% 9% 24% 31% 4	3117
	21st to end	Day	32% 4 14% 23% 23% 3	3081
November	1st to 10th	Day	37% 5% 12% 23% 21% 3	1761
	11th to 20th	Day	37% 5% 11% 22% 21% 4	1800
	21st to end	Day	41% 5% 13% 26% 12% 3	1762
December	1st to 10th	Day	45% 7% 14% 18% 14% 1	1528
	11th to 20th	Day	42% 4 16% 18% 17% 2	1906
	21st to end	Day	50% 8% 11% 21% 9% 1	2772
January	1st to 10th	Night	38% 5% 12% 29% 11% 4	4429
	11th to 20th	Night	44% 5% 12% 23% 13% 3	4440
	21st to end	Night	53% 5% 9% 20% 11% 2	4788
February	1st to 10th	Night	44% 6% 13% 23% 12% 2	2411
	11th to 20th	Night	44% 4 11% 19% 18% 4	2220
	21st to end	Night	45% 4 10% 22% 14% 5%	1884
March	1st to 10th	Night	51% 5% 11% 19% 12% 2	3734
	11th to 20th	Night	36% 10% 16% 22% 14% 2	3692
	21st to end	Night	44% 5% 8% 13% 24% 5%	3466
April	1st to 10th	Night	45% 7% 11% 20% 14% 3	1900
	11th to 20th	Night	43% 6% 11% 20% 19% 1	1875
	21st to end	Night	45% 5% 9% 22% 15% 4	1800
May	1st to 10th	Night	54% 9% 12% 14% 10% 1	2840
	11th to 20th	Night	51% 11% 13% 14% 9% 1	2634
	21st to end	Night	40% 7% 15% 24% 12% 1	2739
June	1st to 10th	Night	44% 8% 11% 19% 16% 2	1520
	11th to 20th	Night	39% 9% 15% 25% 11% 1	1520
	21st to end	Night	38% 9% 13% 24% 14% 1	1520
July	1st to 10th	Night	43% 10% 15% 18% 13% 1	2480
	11th to 20th	Night	43% 7% 17% 21% 10% 1	2472
	21st to end	Night	49% 7% 14% 14% 15% 2	2651
August	1st to 10th	Night	52% 9% 14% 15% 9% 1	2616
	11th to 20th	Night	43% 6% 13% 29% 8% 1	3116
	21st to end	Night	27% 6% 15% 33% 17% 1	3476
September	1st to 10th	Night	40% 6% 10% 25% 18% 1	1900
	11th to 20th	Night	34% 5% 10% 23% 25% 2	2027
	21st to end	Night	42% 7% 8% 21% 20% 2	2090
October	1st to 10th	Night	39% 5% 13% 22% 19% 2	3539
	11th to 20th	Night	25% 5% 9% 27% 30% 4	3800
	21st to end	Night	32% 4 13% 29% 19% 3	4467
November	1st to 10th	Night	35% 6% 12% 22% 21% 4	2537
	11th to 20th	Night	40% 4 10% 23% 19% 4	2600
	21st to end	Night	39% 4 14% 29% 12% 2	2635
December	1st to 10th	Night	45% 6% 12% 21% 14% 1	2686
	11th to 20th	Night	44% 6% 14% 17% 17% 2	3288
	21st to end	Night	48% 7% 12% 21% 11% 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	24% 27% 32% 15% 2	180
	11th to 20th	Day	23% 34% 29% 12% 1	180
	21st to end	Day	21% 32% 32% 9% 5% 1	222
February	1st to 10th	Day	26% 29% 33% 12% 1	327
	11th to 20th	Day	23% 29% 36% 11% 1	456
	21st to end	Day	30% 23% 32% 13% 3	382
March	1st to 10th	Day	23% 25% 35% 14% 3	460
	11th to 20th	Day	23% 28% 34% 12% 3 1	460
	21st to end	Day	28% 24% 34% 11% 3 1	506
April	1st to 10th	Day	24% 29% 30% 11% 6% 1	460
	11th to 20th	Day	27% 22% 32% 13% 5% 1	452
	21st to end	Day	27% 20% 34% 14% 5% 1	460
May	1st to 10th	Day	29% 22% 29% 14% 6% 1	463
	11th to 20th	Day	21% 17% 38% 18% 5% 1	487
	21st to end	Day	19% 12% 33% 26% 8% 2	529
June	1st to 10th	Day	18% 13% 32% 24% 10% 2	490
	11th to 20th	Day	16% 13% 35% 26% 9% 1	490
	21st to end	Day	13% 13% 35% 27% 10% 2	490
July	1st to 10th	Day	17% 6% 32% 27% 15% 3	485
	11th to 20th	Day	13% 6% 34% 31% 15% 2	484
	21st to end	Day	14% 9% 36% 30% 9% 1	532
August	1st to 10th	Day	14% 7% 28% 37% 10% 5%	486
	11th to 20th	Day	14% 7% 29% 30% 15% 5%	479
	21st to end	Day	10% 11% 33% 25% 15% 5%	539
September	1st to 10th	Day	17% 12% 28% 22% 18% 4	490
	11th to 20th	Day	15% 9% 30% 25% 13% 8%	490
	21st to end	Day	22% 13% 33% 20% 9% 3	490
October	1st to 10th	Day	26% 11% 28% 18% 14% 3	490
	11th to 20th	Day	16% 21% 31% 23% 8% 2	483
	21st to end	Day	24% 17% 30% 19% 8% 1	429
November	1st to 10th	Day	16% 19% 31% 22% 9% 2	395
	11th to 20th	Day	22% 27% 27% 19% 5%	400
	21st to end	Day	22% 24% 28% 21% 5%	362
December	1st to 10th	Day	24% 23% 34% 15% 4	182
	11th to 20th	Day	31% 28% 27% 12% 2	180
	21st to end	Day	24% 22% 33% 15% 4 1	198
January	1st to 10th	Night	21% 22% 36% 18% 3	760
	11th to 20th	Night	25% 21% 33% 18% 3	760
	21st to end	Night	20% 22% 37% 19% 2	836
February	1st to 10th	Night	22% 21% 36% 21% 2	760
	11th to 20th	Night	23% 23% 38% 15% 1	743
	21st to end	Night	24% 22% 35% 16% 3	628
March	1st to 10th	Night	24% 20% 35% 18% 3	760
	11th to 20th	Night	21% 20% 37% 20% 3 1	760
	21st to end	Night	22% 22% 36% 16% 4	836
April	1st to 10th	Night	23% 20% 35% 19% 3	760
	11th to 20th	Night	23% 17% 35% 22% 3	751
	21st to end	Night	21% 19% 36% 20% 4	660
May	1st to 10th	Night	25% 13% 34% 22% 5%	570
	11th to 20th	Night	21% 15% 38% 21% 5%	460
	21st to end	Night	21% 7% 26% 37% 9%	411
June	1st to 10th	Night	19% 8% 31% 33% 9% 1	380
	11th to 20th	Night	17% 7% 31% 33% 12%	380
	21st to end	Night	16% 7% 30% 39% 8%	380
July	1st to 10th	Night	14% 4 27% 39% 15% 1	370
	11th to 20th	Night	14% 2 22% 46% 14% 1	368
	21st to end	Night	14% 5% 28% 39% 13% 1	416
August	1st to 10th	Night	12% 4 29% 42% 12% 1	446
	11th to 20th	Night	16% 4 23% 38% 17% 2	739
	21st to end	Night	14% 5% 24% 36% 18% 2	836
September	1st to 10th	Night	17% 6% 29% 34% 14% 2	760
	11th to 20th	Night	17% 6% 26% 30% 18% 3	760
	21st to end	Night	20% 8% 28% 29% 15% 1	760
October	1st to 10th	Night	23% 10% 28% 26% 12% 2	760
	11th to 20th	Night	18% 14% 32% 26% 9% 1	760
	21st to end	Night	26% 12% 35% 20% 7%	836
November	1st to 10th	Night	16% 15% 35% 24% 9% 1	780
	11th to 20th	Night	22% 17% 35% 20% 6% 1	800
	21st to end	Night	21% 19% 32% 23% 5% 1	800
December	1st to 10th	Night	25% 17% 32% 20% 5% 1	768
	11th to 20th	Night	24% 20% 32% 20% 3	760
	21st to end	Night	26% 18% 36% 18% 2	836

Page generated at 2024-11-29 10:43:06. Version ac07

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