Worcester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Worcester clear sky chart from 2005-11-06 to 2024-11-04.

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% 7% 2 6% 4 4 4 4 5% 7% 38%	101229
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 39%	97788
Transparency	Day	44% 4 11% 23% 15% 2	104767
	Night	44% 3 11% 23% 15% 2	102339
Seeing	Day	24% 14% 33% 19% 7% 2	15018
	Night	23% 15% 34% 22% 6% 1	23941

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	13% 8% 3 6% 4 4 4 3 5% 6% 44%	2517
	11th to 20th	Day	16% 7% 4 7% 5% 5% 4 4 5% 5% 38%	2520
	21st to end	Day	20% 11% 3 6% 4 4 5% 4 4 5% 34%	2772
February	1st to 10th	Day	17% 8% 3 6% 4 5% 5% 4 5% 7% 35%	1775
	11th to 20th	Day	12% 7% 2 6% 5% 5% 6% 4 6% 7% 39%	1848
	21st to end	Day	18% 11% 2 7% 5% 4 4 2 4 6% 37%	1570
March	1st to 10th	Day	22% 14% 4 7% 4 4 4 3 4 5% 31%	3116
	11th to 20th	Day	12% 6% 2 5% 4 5% 5% 5% 7% 9% 40%	3306
	21st to end	Day	20% 10% 3 5% 3 4 4 3 6% 7% 34%	4088
April	1st to 10th	Day	17% 10% 3 7% 5% 5% 4 4 4 7% 37%	2280
	11th to 20th	Day	17% 6% 2 6% 5% 4 4 4 5% 7% 39%	2254
	21st to end	Day	21% 7% 2 7% 4 4 4 4 5% 7% 35%	2456
May	1st to 10th	Day	24% 11% 3 8% 5% 4 4 4 5% 7% 27%	4106
	11th to 20th	Day	23% 9% 3 8% 4 4 3 3 4 7% 33%	4200
	21st to end	Day	15% 5% 2 6% 4 4 4 4 6% 8% 44%	4837
June	1st to 10th	Day	18% 6% 2 6% 5% 5% 5% 4 6% 8% 35%	2660
	11th to 20th	Day	16% 6% 3 6% 4 4 5% 4 6% 8% 37%	2660
	21st to end	Day	17% 6% 2 7% 4 5% 4 4 7% 8% 34%	2660
July	1st to 10th	Day	12% 7% 3 6% 5% 6% 6% 4 7% 8% 35%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 10% 39%	4440
	21st to end	Day	17% 8% 3 7% 5% 4 5% 4 6% 7% 34%	4814
August	1st to 10th	Day	15% 6% 3 7% 6% 5% 6% 5% 6% 9% 32%	4187
	11th to 20th	Day	13% 7% 2 7% 5% 5% 5% 4 6% 7% 38%	3926
	21st to end	Day	7% 4 2 6% 5% 5% 6% 4 7% 9% 46%	4180
September	1st to 10th	Day	13% 6% 2 5% 4 5% 5% 3 5% 7% 45%	2280
	11th to 20th	Day	16% 6% 2 4 2 3 3 3 4 6% 50%	2104
	21st to end	Day	18% 6% 2 6% 4 4 4 3 4 7% 43%	2090
October	1st to 10th	Day	22% 6% 3 5% 4 4 4 3 4 6% 40%	2090
	11th to 20th	Day	13% 7% 2 5% 4 3 3 3 5% 8% 46%	1851
	21st to end	Day	19% 7% 2 7% 4 3 4 3 5% 5% 41%	1881
November	1st to 10th	Day	14% 8% 2 6% 4 3 3 3 4 5% 48%	1698
	11th to 20th	Day	19% 7% 2 4 3 3 3 2 6% 6% 45%	1710
	21st to end	Day	15% 8% 2 5% 4 5% 4 5% 5% 5% 42%	1710
December	1st to 10th	Day	17% 9% 3 6% 4 5% 4 3 6% 6% 37%	1525
	11th to 20th	Day	22% 6% 2 4 3 3 3 3 4 6% 44%	1906
	21st to end	Day	20% 12% 3 6% 4 4 4 3 5% 6% 32%	2772
January	1st to 10th	Night	17% 7% 2 4 3 3 3 3 5% 6% 46%	4429
	11th to 20th	Night	14% 10% 3 8% 5% 3 3 3 5% 6% 40%	4440
	21st to end	Night	21% 13% 4 7% 4 4 4 3 5% 5% 31%	4884
February	1st to 10th	Night	15% 9% 4 6% 4 4 4 4 5% 5% 39%	2399
	11th to 20th	Night	13% 8% 3 7% 4 5% 4 3 5% 7% 41%	2218
	21st to end	Night	17% 10% 3 6% 4 4 3 2 4 7% 40%	1884
March	1st to 10th	Night	25% 12% 2 4 4 4 3 3 5% 5% 32%	3724
	11th to 20th	Night	11% 8% 3 6% 5% 5% 4 3 6% 7% 42%	3653
	21st to end	Night	21% 10% 3 5% 3 4 4 4 6% 6% 34%	3543
April	1st to 10th	Night	16% 9% 2 7% 5% 5% 4 4 5% 7% 35%	1900
	11th to 20th	Night	18% 7% 2 6% 4 5% 3 4 4 6% 40%	1875
	21st to end	Night	20% 7% 3 6% 4 3 4 3 4 6% 40%	1722
May	1st to 10th	Night	25% 9% 3 8% 4 4 4 4 5% 6% 28%	2834
	11th to 20th	Night	21% 9% 3 9% 6% 5% 5% 4 6% 6% 28%	2721
	21st to end	Night	16% 6% 3 6% 3 4 4 3 6% 8% 42%	2738
June	1st to 10th	Night	17% 7% 2 6% 6% 5% 4 3 5% 8% 37%	1520
	11th to 20th	Night	18% 7% 1 6% 5% 3 4 4 4 8% 37%	1520
	21st to end	Night	14% 7% 2 5% 4 4 5% 4 6% 7% 41%	1520
July	1st to 10th	Night	13% 6% 3 8% 5% 4 5% 5% 8% 9% 34%	2520
	11th to 20th	Night	13% 7% 3 7% 4 4 4 4 7% 8% 39%	2520
	21st to end	Night	16% 9% 3 7% 5% 5% 5% 4 4 5% 37%	2739
August	1st to 10th	Night	20% 6% 3 8% 5% 5% 6% 4 5% 7% 31%	2698
	11th to 20th	Night	12% 7% 3 8% 5% 6% 5% 4 6% 7% 36%	2898
	21st to end	Night	8% 4 2 5% 3 3 3 3 5% 7% 58%	3476
September	1st to 10th	Night	13% 6% 3 6% 5% 3 4 4 6% 6% 45%	1900
	11th to 20th	Night	13% 6% 2 4 3 3 4 2 5% 5% 52%	2074
	21st to end	Night	17% 7% 3 6% 4 3 4 3 5% 6% 43%	2090
October	1st to 10th	Night	20% 6% 2 5% 4 3 3 4 4 6% 42%	2090
	11th to 20th	Night	15% 5% 2 5% 3 4 4 3 5% 6% 47%	2327
	21st to end	Night	21% 8% 3 6% 4 4 4 3 4 6% 40%	2717
November	1st to 10th	Night	14% 6% 2 5% 4 4 4 3 5% 5% 49%	2453
	11th to 20th	Night	18% 7% 2 4 4 4 3 2 5% 6% 45%	2470
	21st to end	Night	15% 7% 2 5% 4 4 5% 3 5% 6% 44%	2470
December	1st to 10th	Night	18% 9% 3 6% 5% 4 4 3 5% 6% 39%	2650
	11th to 20th	Night	19% 6% 2 5% 4 4 4 3 6% 7% 40%	3288
	21st to end	Night	19% 11% 4 7% 4 4 4 3 5% 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	42% 2 7% 35% 12% 2	2518
	11th to 20th	Day	48% 3 9% 26% 13% 2	2520
	21st to end	Day	53% 3 9% 22% 11% 2	2772
February	1st to 10th	Day	48% 3 13% 21% 13% 2	1775
	11th to 20th	Day	44% 5% 10% 23% 16% 3	1857
	21st to end	Day	50% 2 9% 21% 15% 3	1570
March	1st to 10th	Day	57% 2 10% 16% 12% 3	3119
	11th to 20th	Day	39% 3 14% 29% 13% 3	3306
	21st to end	Day	50% 3 5% 18% 19% 6%	4088
April	1st to 10th	Day	49% 3 9% 20% 16% 3	2280
	11th to 20th	Day	44% 3 11% 21% 18% 3	2254
	21st to end	Day	49% 3 8% 19% 18% 3	2456
May	1st to 10th	Day	58% 3 12% 15% 11% 1	4120
	11th to 20th	Day	53% 2 14% 19% 10% 2	4204
	21st to end	Day	38% 4 11% 27% 19% 2	4837
June	1st to 10th	Day	46% 5% 12% 25% 12% 1	2660
	11th to 20th	Day	43% 5% 13% 22% 15% 2	2660
	21st to end	Day	46% 6% 11% 23% 13% 1	2660
July	1st to 10th	Day	44% 7% 11% 22% 15% 1	4370
	11th to 20th	Day	39% 5% 16% 26% 12% 2	4365
	21st to end	Day	47% 5% 12% 21% 13% 2	4661
August	1st to 10th	Day	47% 6% 15% 23% 8% 1	4173
	11th to 20th	Day	43% 5% 15% 27% 10% 1	3965
	21st to end	Day	33% 5% 12% 32% 18% 1	4180
September	1st to 10th	Day	38% 4 11% 25% 20% 2	2280
	11th to 20th	Day	35% 3 8% 28% 23% 3	2104
	21st to end	Day	41% 4 9% 22% 21% 2	2090
October	1st to 10th	Day	41% 4 9% 23% 20% 3	3480
	11th to 20th	Day	31% 3 7% 28% 27% 4	3041
	21st to end	Day	33% 3 12% 29% 19% 3	3081
November	1st to 10th	Day	40% 3 11% 26% 17% 3	1698
	11th to 20th	Day	40% 3 9% 24% 21% 2	1710
	21st to end	Day	42% 4 13% 26% 13% 2	1710
December	1st to 10th	Day	47% 3 13% 18% 16% 2	1525
	11th to 20th	Day	43% 2 13% 19% 19% 3	1906
	21st to end	Day	53% 3 10% 21% 11% 1	2772
January	1st to 10th	Night	39% 2 11% 31% 13% 3	4429
	11th to 20th	Night	47% 4 10% 24% 13% 3	4440
	21st to end	Night	57% 2 9% 18% 12% 2	4884
February	1st to 10th	Night	46% 4 13% 21% 14% 2	2399
	11th to 20th	Night	44% 4 10% 21% 18% 4	2220
	21st to end	Night	46% 2 8% 25% 15% 4	1884
March	1st to 10th	Night	55% 2 8% 21% 11% 2	3734
	11th to 20th	Night	43% 3 14% 21% 16% 3	3654
	21st to end	Night	51% 2 5% 14% 21% 7%	3543
April	1st to 10th	Night	49% 3 9% 20% 17% 3	1900
	11th to 20th	Night	45% 3 9% 22% 19% 2	1875
	21st to end	Night	47% 3 9% 22% 15% 5%	1722
May	1st to 10th	Night	58% 2 12% 17% 9% 2	2840
	11th to 20th	Night	57% 3 13% 16% 9% 2	2722
	21st to end	Night	42% 3 15% 24% 16% 1	2739
June	1st to 10th	Night	45% 5% 11% 25% 13% 1	1520
	11th to 20th	Night	46% 4 13% 23% 13% 1	1520
	21st to end	Night	40% 5% 15% 25% 14% 1	1520
July	1st to 10th	Night	43% 7% 14% 22% 14% 1	2480
	11th to 20th	Night	41% 5% 16% 24% 13%	2472
	21st to end	Night	48% 5% 12% 19% 15% 1	2651
August	1st to 10th	Night	51% 6% 13% 20% 9% 1	2688
	11th to 20th	Night	45% 6% 15% 25% 10%	2925
	21st to end	Night	27% 4 15% 32% 21% 1	3476
September	1st to 10th	Night	39% 3 12% 26% 19% 1	1900
	11th to 20th	Night	34% 3 10% 25% 26% 2	2074
	21st to end	Night	43% 3 7% 25% 19% 3	2090
October	1st to 10th	Night	39% 4 14% 24% 17% 2	3480
	11th to 20th	Night	27% 3 11% 27% 29% 4	3876
	21st to end	Night	35% 3 12% 32% 17% 2	4467
November	1st to 10th	Night	38% 4 11% 23% 21% 4	2453
	11th to 20th	Night	41% 3 10% 23% 20% 3	2470
	21st to end	Night	40% 3 14% 27% 14% 2	2470
December	1st to 10th	Night	47% 3 12% 24% 14% 1	2650
	11th to 20th	Night	43% 3 14% 20% 17% 2	3288
	21st to end	Night	51% 3 7% 26% 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	27% 24% 28% 17% 4	180
	11th to 20th	Day	33% 26% 30% 7% 3	180
	21st to end	Day	28% 19% 36% 13% 4	198
February	1st to 10th	Day	33% 17% 35% 13% 1	357
	11th to 20th	Day	28% 27% 35% 9% 1	456
	21st to end	Day	33% 15% 35% 12% 4 1	382
March	1st to 10th	Day	31% 19% 36% 12% 3	460
	11th to 20th	Day	28% 25% 30% 13% 3 1	460
	21st to end	Day	29% 19% 35% 10% 6% 1	506
April	1st to 10th	Day	33% 18% 31% 11% 6% 1	460
	11th to 20th	Day	30% 18% 36% 12% 4	452
	21st to end	Day	33% 15% 32% 16% 3 2	460
May	1st to 10th	Day	33% 18% 30% 14% 4 1	463
	11th to 20th	Day	24% 15% 39% 16% 5% 1	487
	21st to end	Day	20% 12% 36% 21% 10% 2	529
June	1st to 10th	Day	19% 10% 37% 23% 9% 2	490
	11th to 20th	Day	17% 12% 36% 24% 8% 2	490
	21st to end	Day	20% 11% 37% 21% 9% 3	490
July	1st to 10th	Day	18% 7% 31% 27% 14% 3	485
	11th to 20th	Day	13% 6% 33% 34% 12% 3	484
	21st to end	Day	13% 8% 37% 31% 9% 2	532
August	1st to 10th	Day	13% 8% 31% 35% 11% 2	486
	11th to 20th	Day	17% 7% 31% 30% 12% 3	479
	21st to end	Day	13% 9% 32% 28% 15% 3	539
September	1st to 10th	Day	20% 9% 28% 24% 14% 5%	490
	11th to 20th	Day	20% 7% 28% 21% 15% 9%	490
	21st to end	Day	22% 10% 35% 20% 8% 4	490
October	1st to 10th	Day	28% 11% 26% 21% 10% 3	490
	11th to 20th	Day	19% 19% 31% 21% 8% 2	447
	21st to end	Day	29% 13% 33% 16% 7% 1	429
November	1st to 10th	Day	23% 18% 32% 19% 7% 1	374
	11th to 20th	Day	30% 19% 28% 18% 3 1	370
	21st to end	Day	29% 19% 32% 15% 5%	370
December	1st to 10th	Day	24% 27% 30% 15% 4	185
	11th to 20th	Day	39% 18% 36% 5% 2	180
	21st to end	Day	33% 20% 32% 11% 3 1	198
January	1st to 10th	Night	24% 21% 39% 15% 1	760
	11th to 20th	Night	29% 20% 35% 15% 2	760
	21st to end	Night	22% 22% 34% 19% 3	836
February	1st to 10th	Night	25% 18% 39% 17% 2	760
	11th to 20th	Night	22% 26% 38% 12% 1	743
	21st to end	Night	29% 21% 32% 16% 2	628
March	1st to 10th	Night	25% 21% 34% 18% 3	760
	11th to 20th	Night	22% 24% 35% 16% 2	760
	21st to end	Night	26% 18% 33% 20% 3	836
April	1st to 10th	Night	24% 18% 36% 18% 3	760
	11th to 20th	Night	24% 19% 35% 18% 5%	751
	21st to end	Night	25% 18% 35% 19% 3	582
May	1st to 10th	Night	34% 13% 30% 19% 4 1	570
	11th to 20th	Night	22% 15% 38% 20% 5%	509
	21st to end	Night	21% 8% 37% 28% 5%	411
June	1st to 10th	Night	21% 6% 34% 30% 8%	380
	11th to 20th	Night	22% 8% 37% 27% 6% 1	380
	21st to end	Night	15% 6% 42% 31% 7%	380
July	1st to 10th	Night	16% 6% 33% 36% 9% 1	370
	11th to 20th	Night	17% 4 30% 36% 12%	368
	21st to end	Night	13% 4 35% 38% 9%	416
August	1st to 10th	Night	13% 3 38% 35% 11%	492
	11th to 20th	Night	14% 5% 32% 34% 14% 1	626
	21st to end	Night	16% 5% 26% 38% 15% 2	836
September	1st to 10th	Night	17% 4 34% 31% 13% 1	760
	11th to 20th	Night	17% 6% 27% 29% 19% 2	760
	21st to end	Night	21% 8% 30% 28% 11% 2	760
October	1st to 10th	Night	25% 10% 30% 23% 10% 2	760
	11th to 20th	Night	20% 14% 33% 21% 11% 1	760
	21st to end	Night	28% 15% 32% 19% 6%	836
November	1st to 10th	Night	19% 15% 36% 21% 7% 1	755
	11th to 20th	Night	25% 21% 31% 16% 6% 1	760
	21st to end	Night	24% 20% 35% 16% 5% 1	760
December	1st to 10th	Night	27% 18% 35% 15% 4	760
	11th to 20th	Night	27% 19% 34% 17% 2	760
	21st to end	Night	27% 20% 36% 16% 2	836

Page generated at 2024-11-01 22:47:31. Version ac07

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