Hopkinton City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hopkinton City clear sky chart from 2005-11-06 to 2024-11-30.

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 3 5% 7% 39%	101408
	Night	19% 8% 2 6% 4 4 4 3 5% 6% 39%	98192
Transparency	Day	25% 47% 6% 12% 9% 1	104972
	Night	25% 46% 6% 12% 9% 1	102717
Seeing	Day	23% 16% 33% 19% 7% 2	15196
	Night	22% 13% 31% 25% 8% 1	24166

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% 8% 3 7% 4 3 4 3 4 4 45%	2517
	11th to 20th	Day	19% 8% 2 6% 4 4 4 4 5% 4 39%	2520
	21st to end	Day	24% 12% 3 5% 3 3 3 2 4 5% 35%	2772
February	1st to 10th	Day	19% 8% 2 5% 4 3 4 3 6% 7% 38%	1830
	11th to 20th	Day	14% 7% 2 6% 5% 4 5% 3 5% 6% 42%	1848
	21st to end	Day	21% 9% 3 7% 3 4 3 3 4 7% 37%	1570
March	1st to 10th	Day	26% 12% 3 6% 3 3 3 2 4 4 34%	3116
	11th to 20th	Day	11% 6% 2 5% 3 4 5% 4 6% 8% 46%	3308
	21st to end	Day	22% 9% 3 6% 4 4 4 4 5% 5% 35%	4069
April	1st to 10th	Day	20% 8% 2 5% 4 4 4 4 5% 6% 38%	2280
	11th to 20th	Day	19% 7% 3 5% 3 3 3 3 4 7% 42%	2254
	21st to end	Day	22% 6% 2 5% 4 5% 4 3 6% 7% 37%	2441
May	1st to 10th	Day	28% 10% 3 6% 4 3 4 3 4 6% 29%	4106
	11th to 20th	Day	23% 9% 3 8% 5% 3 4 2 4 7% 32%	4129
	21st to end	Day	16% 6% 2 5% 3 4 4 3 5% 8% 44%	4837
June	1st to 10th	Day	19% 6% 2 5% 5% 5% 4 4 6% 9% 35%	2660
	11th to 20th	Day	16% 6% 2 6% 4 4 6% 5% 6% 7% 37%	2660
	21st to end	Day	15% 7% 2 5% 4 4 4 4 7% 9% 38%	2660
July	1st to 10th	Day	16% 7% 2 6% 5% 5% 5% 4 7% 9% 35%	4440
	11th to 20th	Day	17% 5% 2 5% 4 5% 4 4 6% 10% 38%	4440
	21st to end	Day	22% 7% 3 6% 5% 4 5% 4 6% 7% 30%	4814
August	1st to 10th	Day	20% 8% 2 7% 5% 5% 5% 4 6% 7% 31%	4141
	11th to 20th	Day	14% 5% 2 7% 5% 4 5% 4 6% 8% 39%	3888
	21st to end	Day	7% 4 2 6% 5% 5% 6% 5% 8% 9% 44%	4180
September	1st to 10th	Day	15% 7% 2 5% 4 4 3 3 4 6% 45%	2280
	11th to 20th	Day	14% 5% 2 5% 3 3 3 3 5% 7% 50%	2100
	21st to end	Day	20% 7% 2 5% 3 4 4 4 5% 5% 40%	2090
October	1st to 10th	Day	22% 7% 2 6% 3 2 3 3 4 5% 42%	2090
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 6% 7% 47%	1877
	21st to end	Day	19% 5% 2 7% 4 3 3 3 4 5% 45%	1881
November	1st to 10th	Day	15% 6% 2 6% 4 4 3 3 4 5% 48%	1761
	11th to 20th	Day	17% 6% 1 5% 3 4 3 3 5% 5% 49%	1800
	21st to end	Day	17% 6% 3 6% 4 3 3 3 4 5% 45%	1798
December	1st to 10th	Day	21% 7% 2 5% 5% 3 4 3 5% 7% 37%	1573
	11th to 20th	Day	22% 7% 2 4 3 2 3 2 3 5% 46%	1906
	21st to end	Day	21% 10% 3 7% 4 3 3 3 4 5% 37%	2772
January	1st to 10th	Night	17% 7% 2 4 3 3 3 3 4 6% 48%	4429
	11th to 20th	Night	17% 10% 3 7% 4 3 3 3 3 4 42%	4440
	21st to end	Night	23% 12% 3 7% 5% 4 3 3 4 5% 31%	4884
February	1st to 10th	Night	15% 10% 3 7% 5% 3 3 2 4 6% 42%	2343
	11th to 20th	Night	18% 8% 3 6% 4 3 4 3 5% 5% 42%	2218
	21st to end	Night	19% 10% 2 5% 4 4 4 3 4 5% 40%	1884
March	1st to 10th	Night	27% 12% 2 5% 3 3 3 2 4 5% 34%	3724
	11th to 20th	Night	11% 8% 3 6% 4 5% 5% 4 5% 7% 44%	3650
	21st to end	Night	24% 8% 2 6% 3 4 4 4 5% 5% 35%	3547
April	1st to 10th	Night	19% 9% 3 6% 4 4 4 3 5% 7% 38%	1900
	11th to 20th	Night	19% 7% 3 6% 4 4 4 3 6% 5% 40%	1875
	21st to end	Night	22% 8% 2 6% 4 4 4 2 4 5% 40%	1738
May	1st to 10th	Night	25% 10% 4 9% 5% 4 4 3 4 6% 28%	2834
	11th to 20th	Night	23% 11% 3 8% 4 5% 5% 3 5% 7% 25%	2793
	21st to end	Night	18% 8% 2 5% 4 4 4 4 7% 6% 37%	2738
June	1st to 10th	Night	18% 7% 3 6% 4 4 5% 3 5% 7% 38%	1520
	11th to 20th	Night	21% 8% 1 5% 4 3 4 4 5% 8% 38%	1520
	21st to end	Night	16% 9% 2 5% 4 3 4 3 6% 10% 39%	1520
July	1st to 10th	Night	20% 8% 3 8% 5% 4 4 4 6% 7% 31%	2520
	11th to 20th	Night	20% 6% 2 5% 4 4 4 4 6% 8% 36%	2520
	21st to end	Night	22% 9% 3 6% 4 5% 4 4 5% 7% 31%	2739
August	1st to 10th	Night	25% 7% 3 6% 4 5% 4 5% 7% 7% 27%	2757
	11th to 20th	Night	10% 7% 3 9% 4 5% 5% 5% 8% 9% 36%	2936
	21st to end	Night	8% 4 2 5% 3 3 4 3 6% 8% 54%	3476
September	1st to 10th	Night	16% 7% 2 6% 6% 3 5% 3 5% 6% 42%	1900
	11th to 20th	Night	14% 6% 2 5% 3 2 3 3 3 6% 51%	2080
	21st to end	Night	21% 7% 2 6% 4 6% 4 3 5% 4 39%	2090
October	1st to 10th	Night	20% 7% 3 6% 4 3 4 3 4 5% 41%	2090
	11th to 20th	Night	15% 5% 2 6% 3 3 3 3 5% 6% 48%	2300
	21st to end	Night	20% 7% 2 6% 3 4 3 3 5% 7% 41%	2717
November	1st to 10th	Night	13% 6% 3 6% 4 3 4 3 4 6% 48%	2537
	11th to 20th	Night	18% 7% 3 6% 3 3 3 3 4 5% 47%	2600
	21st to end	Night	16% 5% 2 5% 5% 3 3 3 4 6% 47%	2598
December	1st to 10th	Night	21% 8% 2 5% 4 3 5% 3 4 5% 40%	2603
	11th to 20th	Night	20% 7% 2 5% 4 4 3 3 4 5% 42%	3288
	21st to end	Night	20% 12% 3 7% 4 3 3 2 4 5% 38%	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	28% 37% 4 19% 10% 2	2518
	11th to 20th	Day	29% 38% 5% 19% 8% 1	2520
	21st to end	Day	39% 39% 3 11% 6% 1	2772
February	1st to 10th	Day	17% 65% 6% 8% 3 1	1830
	11th to 20th	Day	17% 64% 2 8% 8% 1	1857
	21st to end	Day	16% 65% 6% 7% 4 1	1570
March	1st to 10th	Day	39% 42% 5% 7% 6% 2	3119
	11th to 20th	Day	16% 42% 7% 24% 10% 1	3308
	21st to end	Day	34% 41% 2 11% 9% 3	4069
April	1st to 10th	Day	19% 65% 3 6% 5% 1	2280
	11th to 20th	Day	15% 66% 2 8% 8% 1	2254
	21st to end	Day	18% 65% 3 7% 5% 1	2441
May	1st to 10th	Day	38% 41% 10% 7% 4	4120
	11th to 20th	Day	37% 40% 9% 10% 4	4133
	21st to end	Day	24% 41% 5% 16% 13%	4837
June	1st to 10th	Day	16% 66% 3 8% 6% 1	2660
	11th to 20th	Day	15% 65% 4 10% 6% 1	2660
	21st to end	Day	14% 65% 4 10% 7%	2660
July	1st to 10th	Day	31% 39% 8% 12% 10% 1	4370
	11th to 20th	Day	28% 38% 11% 15% 8% 1	4365
	21st to end	Day	36% 38% 8% 10% 7% 1	4661
August	1st to 10th	Day	35% 38% 10% 12% 4	4127
	11th to 20th	Day	25% 40% 10% 20% 4	3927
	21st to end	Day	17% 41% 11% 19% 12% 1	4180
September	1st to 10th	Day	16% 60% 5% 11% 7% 1	2280
	11th to 20th	Day	15% 60% 4 9% 10% 1	2100
	21st to end	Day	21% 60% 4 8% 8%	2090
October	1st to 10th	Day	22% 39% 6% 15% 14% 5%	3480
	11th to 20th	Day	15% 37% 4 15% 26% 3	3093
	21st to end	Day	17% 37% 9% 20% 15% 2	3081
November	1st to 10th	Day	18% 56% 6% 9% 9% 1	1761
	11th to 20th	Day	14% 57% 3 9% 13% 3	1800
	21st to end	Day	16% 57% 4 14% 7% 2	1798
December	1st to 10th	Day	21% 59% 5% 5% 9%	1573
	11th to 20th	Day	22% 48% 5% 9% 11% 4	1906
	21st to end	Day	34% 37% 5% 16% 7%	2772
January	1st to 10th	Night	24% 36% 6% 24% 7% 4	4429
	11th to 20th	Night	28% 37% 7% 16% 9% 2	4440
	21st to end	Night	42% 39% 5% 8% 5% 1	4884
February	1st to 10th	Night	17% 65% 5% 8% 4 1	2343
	11th to 20th	Night	16% 64% 2 6% 10% 2	2220
	21st to end	Night	16% 65% 3 7% 7% 2	1884
March	1st to 10th	Night	39% 40% 4 10% 5% 1	3734
	11th to 20th	Night	21% 41% 10% 15% 11% 1	3651
	21st to end	Night	34% 41% 2 6% 14% 3	3547
April	1st to 10th	Night	19% 65% 3 7% 5% 1	1900
	11th to 20th	Night	15% 66% 5% 6% 7% 1	1875
	21st to end	Night	18% 64% 3 8% 6% 1	1738
May	1st to 10th	Night	38% 40% 9% 9% 3	2840
	11th to 20th	Night	41% 41% 9% 6% 2	2794
	21st to end	Night	28% 41% 8% 15% 7% 1	2739
June	1st to 10th	Night	15% 65% 2 9% 7% 1	1520
	11th to 20th	Night	14% 65% 5% 10% 6% 1	1520
	21st to end	Night	13% 64% 4 12% 6% 1	1520
July	1st to 10th	Night	36% 38% 6% 11% 8%	2480
	11th to 20th	Night	30% 38% 10% 15% 6%	2472
	21st to end	Night	37% 38% 9% 8% 8% 1	2651
August	1st to 10th	Night	39% 40% 7% 9% 4 1	2747
	11th to 20th	Night	27% 42% 9% 19% 4	2963
	21st to end	Night	12% 39% 12% 22% 15%	3476
September	1st to 10th	Night	17% 60% 4 12% 6% 1	1900
	11th to 20th	Night	15% 60% 5% 8% 11% 1	2080
	21st to end	Night	22% 60% 2 7% 8%	2090
October	1st to 10th	Night	24% 38% 7% 17% 12% 2	3480
	11th to 20th	Night	11% 37% 4 16% 28% 4	3823
	21st to end	Night	17% 37% 7% 20% 17% 1	4467
November	1st to 10th	Night	18% 56% 6% 9% 9% 2	2537
	11th to 20th	Night	17% 56% 4 8% 11% 4	2600
	21st to end	Night	16% 57% 6% 14% 6% 2	2598
December	1st to 10th	Night	21% 59% 4 8% 7%	2603
	11th to 20th	Night	22% 49% 5% 10% 12% 2	3288
	21st to end	Night	34% 37% 5% 15% 9%	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% 31% 17% 2	180
	11th to 20th	Day	25% 33% 30% 8% 4	180
	21st to end	Day	24% 27% 37% 8% 4 1	198
February	1st to 10th	Day	29% 24% 33% 13% 1	400
	11th to 20th	Day	29% 27% 34% 9% 2	456
	21st to end	Day	29% 21% 35% 12% 3 1	382
March	1st to 10th	Day	27% 23% 31% 17% 2	460
	11th to 20th	Day	26% 25% 33% 12% 3 1	460
	21st to end	Day	33% 19% 31% 12% 3 1	506
April	1st to 10th	Day	31% 24% 27% 12% 5%	460
	11th to 20th	Day	28% 24% 31% 13% 3	452
	21st to end	Day	31% 18% 33% 12% 4 2	460
May	1st to 10th	Day	33% 20% 30% 12% 3	463
	11th to 20th	Day	24% 13% 45% 14% 3 1	487
	21st to end	Day	21% 10% 34% 28% 6% 2	529
June	1st to 10th	Day	20% 15% 35% 22% 7% 1	490
	11th to 20th	Day	18% 14% 37% 22% 7% 1	490
	21st to end	Day	19% 11% 37% 24% 6% 2	490
July	1st to 10th	Day	20% 6% 33% 28% 12% 1	485
	11th to 20th	Day	17% 7% 33% 29% 12% 2	484
	21st to end	Day	16% 11% 37% 26% 9% 1	532
August	1st to 10th	Day	16% 9% 33% 28% 10% 3	486
	11th to 20th	Day	18% 8% 32% 26% 12% 4	479
	21st to end	Day	12% 8% 34% 27% 14% 5%	539
September	1st to 10th	Day	20% 10% 27% 25% 14% 3	490
	11th to 20th	Day	16% 10% 30% 25% 12% 7%	490
	21st to end	Day	23% 9% 36% 20% 8% 3	490
October	1st to 10th	Day	25% 12% 28% 21% 10% 4	490
	11th to 20th	Day	21% 16% 31% 20% 11% 2	453
	21st to end	Day	25% 14% 31% 20% 7% 2	429
November	1st to 10th	Day	18% 18% 33% 21% 8% 2	395
	11th to 20th	Day	24% 25% 29% 17% 6%	400
	21st to end	Day	25% 20% 30% 18% 7% 1	400
December	1st to 10th	Day	26% 25% 30% 15% 4	233
	11th to 20th	Day	32% 26% 32% 8% 3	180
	21st to end	Day	25% 23% 34% 12% 5% 2	198
January	1st to 10th	Night	22% 21% 34% 20% 3	760
	11th to 20th	Night	29% 18% 33% 17% 3	760
	21st to end	Night	22% 22% 32% 21% 3	836
February	1st to 10th	Night	22% 20% 34% 22% 2	760
	11th to 20th	Night	25% 21% 38% 13% 2	743
	21st to end	Night	26% 21% 33% 18% 2	628
March	1st to 10th	Night	25% 19% 35% 18% 3	760
	11th to 20th	Night	23% 17% 37% 20% 3	760
	21st to end	Night	26% 17% 34% 18% 3 1	836
April	1st to 10th	Night	27% 15% 33% 22% 3	760
	11th to 20th	Night	23% 14% 37% 21% 5%	751
	21st to end	Night	24% 13% 35% 22% 5% 1	598
May	1st to 10th	Night	28% 11% 31% 23% 7% 1	570
	11th to 20th	Night	23% 14% 37% 22% 4	555
	21st to end	Night	22% 5% 27% 36% 8% 1	411
June	1st to 10th	Night	20% 5% 27% 36% 11%	380
	11th to 20th	Night	23% 6% 27% 34% 10%	380
	21st to end	Night	22% 3 26% 39% 10%	380
July	1st to 10th	Night	20% 4 22% 37% 16% 1	370
	11th to 20th	Night	18% 3 20% 43% 14% 2	368
	21st to end	Night	17% 5% 22% 43% 13% 1	416
August	1st to 10th	Night	15% 4 28% 39% 13% 1	525
	11th to 20th	Night	15% 4 25% 35% 18% 2	651
	21st to end	Night	14% 4 21% 38% 19% 3	836
September	1st to 10th	Night	18% 4 29% 31% 16% 2	760
	11th to 20th	Night	18% 5% 25% 31% 18% 4	760
	21st to end	Night	23% 7% 28% 27% 14% 2	760
October	1st to 10th	Night	23% 9% 28% 25% 13% 2	760
	11th to 20th	Night	19% 12% 33% 25% 10% 2	760
	21st to end	Night	24% 12% 34% 22% 8%	836
November	1st to 10th	Night	16% 14% 33% 24% 12% 1	780
	11th to 20th	Night	22% 18% 33% 19% 7% 1	800
	21st to end	Night	22% 19% 31% 21% 6% 1	800
December	1st to 10th	Night	27% 17% 31% 21% 4 1	760
	11th to 20th	Night	24% 20% 32% 19% 4	760
	21st to end	Night	25% 18% 36% 18% 3	836

Page generated at 2024-11-27 17:30:55. Version ac07

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