Milford
Clear Sky Chart
History

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

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	17% 7% 2 6% 4 4 4 3 5% 7% 39%	101191
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 39%	97798
Transparency	Day	45% 5% 11% 22% 14% 2	100949
	Night	46% 5% 11% 21% 14% 2	97660
Seeing	Day	25% 14% 32% 19% 7% 2	15056
	Night	23% 13% 33% 23% 7% 1	23958

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	14% 8% 3 7% 4 3 4 3 4 5% 45%	2517
	11th to 20th	Day	16% 8% 4 7% 4 4 4 4 5% 5% 40%	2520
	21st to end	Day	21% 12% 4 6% 4 4 3 3 6% 4 34%	2772
February	1st to 10th	Day	19% 8% 3 6% 4 4 4 5% 5% 6% 36%	1788
	11th to 20th	Day	13% 8% 3 7% 4 5% 4 4 5% 6% 41%	1848
	21st to end	Day	19% 11% 2 6% 5% 5% 3 2 4 5% 38%	1570
March	1st to 10th	Day	24% 14% 3 8% 3 3 3 2 4 4 31%	3116
	11th to 20th	Day	12% 6% 2 5% 5% 4 5% 4 5% 8% 43%	3318
	21st to end	Day	22% 10% 2 6% 4 3 4 4 5% 6% 35%	4053
April	1st to 10th	Day	19% 9% 2 7% 4 4 3 3 4 7% 37%	2280
	11th to 20th	Day	17% 6% 2 6% 4 4 4 4 5% 8% 39%	2254
	21st to end	Day	21% 6% 2 7% 5% 3 5% 4 4 6% 36%	2470
May	1st to 10th	Day	24% 12% 3 7% 4 4 4 3 4 7% 27%	4106
	11th to 20th	Day	24% 9% 3 7% 5% 3 3 3 5% 6% 33%	4158
	21st to end	Day	15% 5% 2 5% 3 4 4 3 6% 9% 44%	4837
June	1st to 10th	Day	19% 6% 2 5% 4 5% 5% 4 6% 7% 36%	2660
	11th to 20th	Day	17% 6% 2 6% 5% 4 5% 4 6% 8% 37%	2660
	21st to end	Day	17% 6% 2 7% 5% 5% 4 4 6% 8% 36%	2660
July	1st to 10th	Day	13% 6% 3 7% 6% 5% 6% 5% 6% 9% 34%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 4 5% 4 6% 9% 39%	4440
	21st to end	Day	18% 8% 2 7% 5% 4 4 4 6% 8% 34%	4814
August	1st to 10th	Day	16% 7% 3 8% 5% 6% 5% 4 6% 9% 32%	4151
	11th to 20th	Day	14% 7% 3 6% 4 5% 5% 4 6% 7% 39%	3956
	21st to end	Day	7% 4 2 5% 5% 5% 5% 5% 7% 10% 45%	4180
September	1st to 10th	Day	14% 5% 2 5% 4 3 4 3 5% 8% 46%	2280
	11th to 20th	Day	15% 6% 2 4 4 3 4 2 4 6% 51%	2091
	21st to end	Day	19% 6% 3 5% 3 4 4 3 5% 6% 43%	2090
October	1st to 10th	Day	23% 5% 3 5% 4 3 3 2 4 5% 42%	2090
	11th to 20th	Day	15% 6% 2 4 3 3 4 3 5% 6% 48%	1858
	21st to end	Day	20% 7% 2 5% 4 4 4 3 4 6% 41%	1881
November	1st to 10th	Day	16% 7% 2 6% 4 3 3 3 4 4 49%	1681
	11th to 20th	Day	19% 7% 2 4 3 3 4 3 5% 5% 46%	1710
	21st to end	Day	17% 7% 2 4 4 4 4 3 6% 5% 43%	1710
December	1st to 10th	Day	18% 9% 3 5% 4 4 5% 4 5% 6% 38%	1554
	11th to 20th	Day	21% 7% 2 4 4 3 4 2 3 5% 45%	1906
	21st to end	Day	21% 11% 3 7% 4 4 4 3 4 6% 33%	2772
January	1st to 10th	Night	17% 8% 2 4 3 3 3 3 3 6% 48%	4429
	11th to 20th	Night	16% 10% 3 8% 5% 3 4 3 4 5% 40%	4440
	21st to end	Night	22% 13% 4 6% 4 4 3 3 4 5% 30%	4884
February	1st to 10th	Night	17% 9% 3 6% 5% 3 4 4 5% 5% 39%	2389
	11th to 20th	Night	14% 9% 3 6% 4 4 4 4 5% 6% 40%	2218
	21st to end	Night	18% 10% 2 6% 3 3 4 3 4 5% 41%	1884
March	1st to 10th	Night	28% 11% 2 4 4 3 3 3 4 5% 33%	3724
	11th to 20th	Night	11% 9% 3 7% 5% 5% 4 4 5% 6% 41%	3639
	21st to end	Night	24% 9% 3 5% 3 3 5% 3 5% 5% 34%	3576
April	1st to 10th	Night	18% 8% 2 7% 5% 4 4 4 5% 6% 36%	1900
	11th to 20th	Night	19% 7% 3 6% 5% 5% 3 4 4 6% 39%	1875
	21st to end	Night	21% 8% 3 6% 5% 4 3 3 3 6% 40%	1710
May	1st to 10th	Night	26% 9% 3 8% 4 4 4 3 4 7% 29%	2834
	11th to 20th	Night	23% 9% 3 7% 6% 6% 4 4 6% 6% 26%	2763
	21st to end	Night	16% 6% 3 6% 4 4 4 3 5% 8% 41%	2738
June	1st to 10th	Night	17% 7% 2 6% 4 4 4 3 6% 8% 38%	1520
	11th to 20th	Night	19% 7% 2 5% 4 4 4 4 5% 8% 36%	1520
	21st to end	Night	14% 7% 2 6% 3 3 4 4 7% 9% 40%	1520
July	1st to 10th	Night	13% 6% 2 7% 4 5% 6% 4 7% 10% 35%	2520
	11th to 20th	Night	15% 7% 3 5% 4 4 4 4 6% 9% 39%	2520
	21st to end	Night	17% 9% 3 7% 4 4 5% 4 5% 6% 35%	2739
August	1st to 10th	Night	20% 7% 2 8% 5% 5% 5% 4 6% 8% 30%	2748
	11th to 20th	Night	12% 8% 3 8% 5% 6% 6% 4 6% 8% 34%	2868
	21st to end	Night	8% 4 2 5% 3 4 3 3 5% 7% 57%	3476
September	1st to 10th	Night	13% 6% 2 6% 5% 5% 4 3 5% 6% 45%	1900
	11th to 20th	Night	14% 5% 2 5% 3 3 3 2 4 7% 51%	2087
	21st to end	Night	18% 7% 2 6% 4 3 3 4 4 5% 43%	2090
October	1st to 10th	Night	22% 5% 2 5% 4 3 4 3 5% 6% 42%	2090
	11th to 20th	Night	16% 5% 2 5% 4 3 4 3 5% 6% 48%	2315
	21st to end	Night	21% 8% 3 6% 4 3 4 3 4 6% 39%	2717
November	1st to 10th	Night	15% 5% 2 6% 4 4 4 2 4 5% 48%	2431
	11th to 20th	Night	19% 7% 3 5% 3 4 3 3 5% 5% 46%	2470
	21st to end	Night	16% 6% 1 5% 4 4 3 3 5% 7% 45%	2470
December	1st to 10th	Night	19% 8% 2 6% 4 4 4 2 5% 5% 40%	2622
	11th to 20th	Night	19% 7% 2 5% 4 3 4 4 5% 6% 41%	3288
	21st to end	Night	20% 11% 3 7% 4 3 4 3 5% 6% 34%	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	42% 4 8% 32% 13% 2	2518
	11th to 20th	Day	47% 4 9% 25% 13% 2	2520
	21st to end	Day	53% 4 9% 22% 11% 2	2772
February	1st to 10th	Day	48% 5% 12% 19% 14% 3	1788
	11th to 20th	Day	44% 6% 9% 22% 16% 3	1857
	21st to end	Day	50% 3 10% 20% 14% 3	1570
March	1st to 10th	Day	58% 3 10% 16% 10% 3	3119
	11th to 20th	Day	37% 7% 12% 27% 13% 3	3318
	21st to end	Day	50% 4 7% 17% 16% 7%	4053
April	1st to 10th	Day	48% 3 10% 20% 16% 3	2280
	11th to 20th	Day	43% 5% 10% 21% 18% 3	2254
	21st to end	Day	48% 5% 8% 19% 17% 4	2470
May	1st to 10th	Day	57% 5% 12% 14% 11% 1	4120
	11th to 20th	Day	53% 5% 14% 16% 10% 2	4162
	21st to end	Day	36% 6% 11% 25% 19% 2	4837
June	1st to 10th	Day	46% 6% 12% 24% 11% 1	2660
	11th to 20th	Day	44% 6% 12% 21% 15% 2	2660
	21st to end	Day	45% 7% 12% 21% 14% 1	2660
July	1st to 10th	Day	46% 7% 10% 21% 14% 2	4370
	11th to 20th	Day	42% 5% 15% 24% 12% 2	4365
	21st to end	Day	49% 5% 11% 20% 13% 2	4661
August	1st to 10th	Day	49% 6% 16% 21% 8% 1	4137
	11th to 20th	Day	43% 5% 13% 27% 10% 1	3995
	21st to end	Day	33% 6% 12% 29% 18% 1	4180
September	1st to 10th	Day	38% 6% 11% 25% 20% 2	2280
	11th to 20th	Day	36% 4 8% 25% 24% 3	2091
	21st to end	Day	43% 3 9% 21% 22% 2	2090
October	1st to 10th	Day	47% 4 8% 22% 15% 4	2090
	11th to 20th	Day	37% 4 11% 28% 19% 2	1858
	21st to end	Day	44% 4 13% 20% 16% 3	1881
November	1st to 10th	Day	40% 3 12% 24% 18% 2	1681
	11th to 20th	Day	40% 4 10% 22% 21% 2	1710
	21st to end	Day	41% 5% 12% 27% 12% 3	1710
December	1st to 10th	Day	47% 5% 13% 16% 17% 2	1554
	11th to 20th	Day	44% 3 12% 18% 17% 5%	1906
	21st to end	Day	52% 5% 10% 21% 11% 1	2772
January	1st to 10th	Night	39% 3 11% 30% 13% 3	4429
	11th to 20th	Night	47% 4 11% 23% 12% 3	4440
	21st to end	Night	57% 4 9% 17% 11% 2	4884
February	1st to 10th	Night	46% 5% 13% 21% 14% 2	2389
	11th to 20th	Night	45% 4 10% 19% 18% 4	2220
	21st to end	Night	46% 4 7% 24% 16% 4	1884
March	1st to 10th	Night	55% 3 8% 20% 11% 3	3734
	11th to 20th	Night	41% 7% 14% 19% 16% 3	3640
	21st to end	Night	52% 3 6% 14% 18% 7%	3576
April	1st to 10th	Night	49% 4 9% 19% 16% 3	1900
	11th to 20th	Night	47% 4 9% 19% 18% 3	1875
	21st to end	Night	47% 4 9% 20% 16% 4	1710
May	1st to 10th	Night	56% 6% 13% 15% 8% 2	2840
	11th to 20th	Night	56% 8% 12% 14% 8% 2	2764
	21st to end	Night	41% 8% 14% 23% 13% 1	2739
June	1st to 10th	Night	45% 6% 14% 22% 12% 1	1520
	11th to 20th	Night	46% 6% 12% 22% 14% 1	1520
	21st to end	Night	39% 8% 15% 24% 13% 1	1520
July	1st to 10th	Night	44% 7% 14% 20% 14% 1	2480
	11th to 20th	Night	41% 6% 17% 23% 12% 1	2472
	21st to end	Night	50% 6% 11% 17% 14% 2	2651
August	1st to 10th	Night	52% 6% 14% 18% 9% 1	2738
	11th to 20th	Night	46% 7% 13% 24% 9%	2895
	21st to end	Night	27% 5% 14% 30% 22% 1	3476
September	1st to 10th	Night	40% 7% 10% 23% 19% 1	1900
	11th to 20th	Night	35% 5% 10% 23% 26% 2	2087
	21st to end	Night	44% 4 8% 22% 19% 2	2090
October	1st to 10th	Night	44% 4 12% 23% 13% 4	2090
	11th to 20th	Night	37% 5% 12% 29% 17% 1	2315
	21st to end	Night	47% 4 11% 21% 15% 2	2717
November	1st to 10th	Night	39% 5% 11% 22% 19% 3	2431
	11th to 20th	Night	42% 3 10% 22% 20% 3	2470
	21st to end	Night	40% 4 13% 27% 14% 2	2470
December	1st to 10th	Night	47% 4 12% 22% 14% 1	2622
	11th to 20th	Night	43% 5% 14% 18% 17% 2	3288
	21st to end	Night	51% 5% 8% 25% 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	31% 22% 27% 16% 4	180
	11th to 20th	Day	34% 21% 32% 9% 3	180
	21st to end	Day	29% 20% 35% 13% 3 1	198
February	1st to 10th	Day	37% 18% 30% 14% 2	378
	11th to 20th	Day	33% 25% 31% 9% 2	456
	21st to end	Day	35% 17% 30% 14% 3	382
March	1st to 10th	Day	34% 17% 33% 12% 4	460
	11th to 20th	Day	31% 23% 29% 12% 4 1	460
	21st to end	Day	32% 18% 33% 10% 5% 3	506
April	1st to 10th	Day	36% 20% 27% 12% 5% 1	460
	11th to 20th	Day	31% 19% 33% 12% 4 1	452
	21st to end	Day	32% 15% 33% 16% 3 2	460
May	1st to 10th	Day	36% 19% 27% 13% 4 1	463
	11th to 20th	Day	26% 14% 39% 16% 4 2	487
	21st to end	Day	21% 13% 36% 22% 7% 2	529
June	1st to 10th	Day	22% 11% 35% 23% 8% 2	490
	11th to 20th	Day	19% 12% 40% 21% 7% 2	490
	21st to end	Day	19% 11% 36% 24% 8% 2	490
July	1st to 10th	Day	19% 7% 32% 28% 12% 3	485
	11th to 20th	Day	18% 6% 30% 32% 11% 3	484
	21st to end	Day	14% 7% 40% 30% 8% 2	532
August	1st to 10th	Day	13% 7% 33% 34% 10% 2	486
	11th to 20th	Day	18% 7% 32% 27% 13% 4	479
	21st to end	Day	12% 8% 33% 28% 14% 6%	539
September	1st to 10th	Day	19% 11% 27% 23% 16% 4	490
	11th to 20th	Day	20% 8% 28% 21% 12% 10%	490
	21st to end	Day	24% 8% 33% 22% 9% 4	490
October	1st to 10th	Day	28% 10% 26% 20% 11% 4	490
	11th to 20th	Day	22% 14% 33% 19% 9% 3	440
	21st to end	Day	27% 13% 33% 18% 8% 2	429
November	1st to 10th	Day	25% 14% 30% 19% 9% 3	369
	11th to 20th	Day	31% 16% 30% 18% 5%	370
	21st to end	Day	29% 18% 30% 16% 7%	370
December	1st to 10th	Day	27% 26% 29% 13% 5%	214
	11th to 20th	Day	39% 19% 31% 8% 2	180
	21st to end	Day	32% 20% 31% 11% 3 3	198
January	1st to 10th	Night	25% 18% 37% 17% 3	760
	11th to 20th	Night	31% 17% 34% 16% 2	760
	21st to end	Night	24% 20% 33% 20% 3	836
February	1st to 10th	Night	26% 17% 36% 19% 3	760
	11th to 20th	Night	25% 23% 36% 15% 1	743
	21st to end	Night	32% 18% 31% 16% 3	628
March	1st to 10th	Night	27% 18% 33% 18% 4	760
	11th to 20th	Night	24% 23% 35% 16% 3	760
	21st to end	Night	29% 17% 32% 17% 4	836
April	1st to 10th	Night	26% 19% 33% 18% 3	760
	11th to 20th	Night	25% 18% 34% 19% 5%	751
	21st to end	Night	25% 19% 35% 19% 3	570
May	1st to 10th	Night	31% 12% 29% 22% 4 1	570
	11th to 20th	Night	22% 14% 38% 21% 4	538
	21st to end	Night	19% 6% 41% 28% 6%	411
June	1st to 10th	Night	21% 6% 34% 30% 9%	380
	11th to 20th	Night	21% 6% 38% 29% 6% 1	380
	21st to end	Night	15% 6% 38% 33% 8%	380
July	1st to 10th	Night	15% 5% 31% 36% 13%	370
	11th to 20th	Night	14% 2 30% 40% 14%	368
	21st to end	Night	16% 4 33% 38% 9%	416
August	1st to 10th	Night	12% 4 35% 38% 10%	516
	11th to 20th	Night	14% 4 29% 40% 13%	609
	21st to end	Night	16% 4 24% 38% 15% 3	836
September	1st to 10th	Night	16% 5% 33% 33% 12% 1	760
	11th to 20th	Night	18% 6% 28% 27% 19% 3	760
	21st to end	Night	22% 7% 27% 30% 11% 3	760
October	1st to 10th	Night	25% 8% 28% 26% 11% 1	760
	11th to 20th	Night	20% 11% 31% 23% 13% 1	760
	21st to end	Night	28% 13% 31% 21% 7%	836
November	1st to 10th	Night	19% 12% 34% 24% 9% 1	748
	11th to 20th	Night	26% 16% 33% 17% 7% 1	760
	21st to end	Night	25% 18% 32% 19% 5% 1	760
December	1st to 10th	Night	28% 16% 34% 17% 5%	760
	11th to 20th	Night	27% 18% 32% 20% 3	760
	21st to end	Night	28% 17% 35% 17% 3	836

Page generated at 2024-10-30 13:19:23. Version ac07

Copyright © 2024 Attilla Danko.