Leominster
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leominster clear sky chart from 2005-11-06 to 2024-04-25.

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% 3 5% 5% 3 5% 5% 5% 7% 39%	83126
	Night	17% 7% 3 5% 5% 3 4 4 5% 7% 40%	85963
Transparency	Day	44% 6% 12% 22% 14% 2	82831
	Night	44% 6% 12% 22% 14% 2	85792
Seeing	Day	24% 17% 32% 19% 7% 2	14244
	Night	22% 15% 34% 23% 6%	23331

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% 7% 3 6% 6% 3 4 4 5% 6% 44%	2517
	11th to 20th	Day	16% 7% 3 7% 6% 3 6% 4 5% 5% 39%	2520
	21st to end	Day	20% 11% 3 5% 5% 3 4 4 4 6% 34%	2772
February	1st to 10th	Day	17% 7% 3 5% 5% 3 5% 5% 5% 7% 36%	1759
	11th to 20th	Day	12% 7% 3 6% 5% 3 7% 5% 6% 8% 39%	1848
	21st to end	Day	19% 10% 2 5% 6% 3 4 4 6% 5% 37%	1570
March	1st to 10th	Day	22% 14% 3 6% 5% 3 4 4 4 5% 31%	3116
	11th to 20th	Day	12% 7% 2 4 5% 3 5% 6% 6% 9% 41%	3306
	21st to end	Day	20% 8% 3 5% 5% 3 4 4 6% 7% 35%	4070
April	1st to 10th	Day	17% 9% 3 5% 7% 3 5% 5% 4 7% 37%	2280
	11th to 20th	Day	17% 6% 2 5% 5% 3 6% 5% 5% 7% 39%	2254
	21st to end	Day	21% 6% 2 6% 6% 3 4 5% 5% 6% 36%	2390
May	1st to 10th	Day	23% 8% 3 6% 4 3 4 4 5% 6% 32%	2340
	11th to 20th	Day	18% 7% 3 6% 5% 4 4 4 4 6% 40%	2372
	21st to end	Day	15% 5% 2 5% 5% 3 4 5% 5% 8% 42%	2725
June	1st to 10th	Day	19% 5% 2 5% 5% 3 5% 6% 6% 9% 34%	2520
	11th to 20th	Day	17% 5% 3 5% 5% 3 5% 6% 6% 9% 37%	2520
	21st to end	Day	17% 6% 3 6% 5% 4 5% 5% 6% 8% 34%	2520
July	1st to 10th	Day	14% 5% 2 5% 5% 3 5% 5% 6% 8% 40%	2520
	11th to 20th	Day	13% 5% 2 5% 6% 3 6% 6% 7% 9% 39%	2520
	21st to end	Day	12% 4 3 6% 5% 4 6% 6% 6% 9% 40%	2744
August	1st to 10th	Day	10% 6% 3 4 6% 4 6% 7% 7% 8% 39%	2386
	11th to 20th	Day	13% 5% 2 6% 6% 4 6% 5% 6% 9% 39%	2251
	21st to end	Day	12% 5% 2 5% 5% 3 4 6% 5% 9% 44%	2376
September	1st to 10th	Day	14% 5% 2 5% 4 3 5% 4 6% 8% 44%	2160
	11th to 20th	Day	16% 5% 2 4 3 3 3 3 5% 6% 50%	1994
	21st to end	Day	16% 5% 2 6% 4 3 4 4 5% 7% 45%	1980
October	1st to 10th	Day	24% 6% 2 4 5% 3 4 4 4 5% 39%	1980
	11th to 20th	Day	14% 6% 3 4 5% 3 4 4 6% 8% 45%	1749
	21st to end	Day	22% 6% 3 5% 5% 2 4 4 4 6% 39%	1782
November	1st to 10th	Day	14% 6% 3 5% 5% 3 3 4 4 4 49%	1671
	11th to 20th	Day	19% 7% 2 3 4 3 3 3 4 5% 47%	1710
	21st to end	Day	17% 6% 3 4 5% 3 4 4 4 6% 43%	1706
December	1st to 10th	Day	17% 7% 3 6% 5% 3 5% 5% 6% 5% 38%	1520
	11th to 20th	Day	22% 6% 2 3 4 2 3 3 4 6% 45%	1906
	21st to end	Day	20% 11% 3 6% 5% 3 4 4 5% 7% 33%	2772
January	1st to 10th	Night	17% 6% 2 4 4 2 3 3 5% 6% 46%	4429
	11th to 20th	Night	13% 8% 4 7% 6% 3 4 4 4 6% 40%	4440
	21st to end	Night	21% 12% 4 7% 6% 3 4 4 4 5% 31%	4884
February	1st to 10th	Night	15% 9% 3 5% 5% 3 4 5% 6% 7% 40%	2417
	11th to 20th	Night	12% 7% 4 6% 4 3 5% 5% 5% 7% 41%	2218
	21st to end	Night	16% 9% 3 5% 5% 2 4 4 5% 6% 41%	1884
March	1st to 10th	Night	25% 11% 2 4 4 3 4 4 4 6% 33%	3724
	11th to 20th	Night	11% 9% 3 5% 6% 4 6% 5% 6% 7% 39%	3652
	21st to end	Night	22% 8% 2 5% 4 3 4 4 6% 6% 35%	3544
April	1st to 10th	Night	17% 8% 3 5% 6% 4 4 4 5% 7% 37%	1900
	11th to 20th	Night	20% 5% 2 6% 5% 2 5% 4 5% 7% 39%	1875
	21st to end	Night	21% 7% 2 5% 5% 3 4 3 4 6% 40%	1670
May	1st to 10th	Night	24% 7% 3 6% 5% 3 4 4 5% 7% 32%	1620
	11th to 20th	Night	18% 6% 3 5% 4 3 5% 5% 5% 6% 39%	1536
	21st to end	Night	17% 6% 2 6% 5% 4 5% 4 5% 7% 40%	1550
June	1st to 10th	Night	19% 6% 3 6% 5% 3 3 4 5% 7% 38%	1440
	11th to 20th	Night	20% 6% 3 5% 6% 2 4 4 5% 7% 38%	1440
	21st to end	Night	15% 5% 2 4 5% 3 4 4 6% 9% 43%	1440
July	1st to 10th	Night	14% 4 2 5% 5% 3 6% 5% 6% 8% 42%	1440
	11th to 20th	Night	13% 6% 2 5% 5% 4 4 5% 6% 10% 40%	1440
	21st to end	Night	12% 4 2 4 4 4 6% 6% 5% 8% 46%	1574
August	1st to 10th	Night	10% 5% 2 5% 5% 2 5% 5% 7% 10% 44%	1534
	11th to 20th	Night	13% 4 2 5% 6% 4 7% 6% 7% 9% 37%	1645
	21st to end	Night	16% 4 1 4 4 2 3 4 5% 7% 49%	1980
September	1st to 10th	Night	14% 5% 1 3 5% 3 4 3 6% 7% 48%	1800
	11th to 20th	Night	13% 6% 2 4 3 3 4 3 5% 6% 53%	1966
	21st to end	Night	16% 5% 2 4 4 3 4 4 5% 6% 47%	1980
October	1st to 10th	Night	22% 6% 3 4 3 2 4 4 4 4 43%	1980
	11th to 20th	Night	15% 5% 1 5% 5% 3 4 4 5% 7% 46%	2208
	21st to end	Night	23% 7% 2 5% 4 3 4 4 5% 7% 38%	2574
November	1st to 10th	Night	15% 6% 1 5% 4 3 4 4 4 5% 49%	2407
	11th to 20th	Night	17% 7% 2 4 4 2 4 3 4 6% 46%	2470
	21st to end	Night	15% 6% 2 4 4 3 4 4 5% 7% 45%	2470
December	1st to 10th	Night	17% 8% 3 5% 5% 3 4 4 5% 7% 39%	2660
	11th to 20th	Night	19% 6% 2 5% 4 3 4 4 6% 7% 41%	3288
	21st to end	Night	20% 9% 3 5% 5% 3 4 4 5% 6% 36%	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	40% 6% 9% 33% 10% 2	2518
	11th to 20th	Day	46% 6% 9% 25% 12% 2	2520
	21st to end	Day	51% 6% 10% 21% 10% 2	2772
February	1st to 10th	Day	46% 7% 13% 20% 12% 2	1759
	11th to 20th	Day	44% 6% 11% 21% 15% 3	1857
	21st to end	Day	49% 5% 9% 20% 14% 3	1570
March	1st to 10th	Day	56% 4 12% 13% 12% 2	3119
	11th to 20th	Day	36% 8% 16% 24% 13% 3	3306
	21st to end	Day	48% 4 6% 18% 17% 6%	4070
April	1st to 10th	Day	48% 5% 9% 19% 15% 3	2280
	11th to 20th	Day	42% 7% 11% 20% 17% 3	2254
	21st to end	Day	49% 5% 9% 17% 17% 3	2390
May	1st to 10th	Day	52% 6% 9% 19% 12% 2	2340
	11th to 20th	Day	44% 5% 11% 20% 18% 3	2376
	21st to end	Day	40% 7% 14% 23% 14% 2	2725
June	1st to 10th	Day	45% 8% 14% 22% 10% 1	2520
	11th to 20th	Day	43% 9% 12% 20% 15% 2	2520
	21st to end	Day	46% 8% 12% 22% 11% 1	2520
July	1st to 10th	Day	41% 8% 11% 23% 15% 2	2450
	11th to 20th	Day	39% 9% 14% 25% 12% 1	2445
	21st to end	Day	38% 7% 15% 22% 14% 3	2591
August	1st to 10th	Day	39% 9% 15% 23% 13% 1	2372
	11th to 20th	Day	41% 8% 14% 24% 12% 1	2251
	21st to end	Day	36% 7% 12% 26% 17% 2	2376
September	1st to 10th	Day	38% 7% 12% 24% 18% 2	2160
	11th to 20th	Day	36% 5% 9% 25% 23% 3	1994
	21st to end	Day	39% 4 10% 23% 21% 2	1980
October	1st to 10th	Day	47% 6% 9% 21% 13% 4	1980
	11th to 20th	Day	36% 6% 13% 29% 14% 2	1749
	21st to end	Day	46% 5% 12% 20% 13% 3	1782
November	1st to 10th	Day	39% 5% 13% 25% 16% 2	1671
	11th to 20th	Day	39% 5% 10% 22% 20% 2	1710
	21st to end	Day	42% 6% 15% 23% 12% 2	1706
December	1st to 10th	Day	46% 7% 14% 17% 16% 1	1520
	11th to 20th	Day	43% 4 14% 18% 18% 3	1906
	21st to end	Day	51% 6% 12% 20% 11% 1	2772
January	1st to 10th	Night	39% 4 13% 29% 12% 3	4429
	11th to 20th	Night	46% 5% 12% 22% 12% 3	4440
	21st to end	Night	56% 5% 9% 17% 11% 2	4884
February	1st to 10th	Night	45% 6% 15% 20% 13% 2	2417
	11th to 20th	Night	43% 6% 11% 20% 17% 3	2220
	21st to end	Night	45% 5% 9% 24% 14% 4	1884
March	1st to 10th	Night	53% 5% 10% 20% 10% 2	3734
	11th to 20th	Night	41% 8% 15% 19% 15% 2	3653
	21st to end	Night	49% 5% 7% 14% 20% 7%	3544
April	1st to 10th	Night	47% 6% 10% 19% 15% 3	1900
	11th to 20th	Night	44% 6% 10% 20% 19% 2	1875
	21st to end	Night	45% 6% 10% 19% 15% 5%	1670
May	1st to 10th	Night	51% 6% 9% 18% 12% 3	1620
	11th to 20th	Night	43% 9% 12% 18% 15% 3	1537
	21st to end	Night	45% 7% 13% 21% 13% 1	1551
June	1st to 10th	Night	47% 7% 12% 22% 12% 1	1440
	11th to 20th	Night	46% 7% 12% 20% 13% 2	1440
	21st to end	Night	36% 11% 15% 24% 14%	1440
July	1st to 10th	Night	39% 8% 13% 22% 16% 1	1400
	11th to 20th	Night	39% 9% 16% 26% 10% 1	1392
	21st to end	Night	35% 8% 15% 28% 11% 2	1486
August	1st to 10th	Night	34% 10% 15% 25% 15% 1	1524
	11th to 20th	Night	40% 10% 17% 22% 12%	1645
	21st to end	Night	34% 7% 12% 27% 19% 1	1980
September	1st to 10th	Night	37% 6% 13% 25% 18% 1	1800
	11th to 20th	Night	33% 6% 10% 24% 26% 2	1966
	21st to end	Night	38% 6% 9% 26% 19% 3	1980
October	1st to 10th	Night	43% 5% 13% 23% 12% 4	1980
	11th to 20th	Night	38% 6% 13% 27% 14% 1	2208
	21st to end	Night	48% 5% 12% 20% 13% 2	2574
November	1st to 10th	Night	38% 6% 11% 21% 20% 4	2407
	11th to 20th	Night	41% 4 12% 21% 19% 3	2470
	21st to end	Night	40% 6% 14% 26% 14% 1	2470
December	1st to 10th	Night	46% 5% 13% 23% 13% 1	2660
	11th to 20th	Night	42% 6% 15% 18% 17% 2	3288
	21st to end	Night	49% 6% 11% 23% 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	28% 25% 28% 16% 3	180
	11th to 20th	Day	33% 24% 31% 9% 3	180
	21st to end	Day	26% 24% 34% 12% 4	198
February	1st to 10th	Day	32% 24% 31% 12% 1	347
	11th to 20th	Day	28% 30% 31% 10% 1	456
	21st to end	Day	33% 18% 34% 11% 3 1	382
March	1st to 10th	Day	30% 21% 35% 11% 3	460
	11th to 20th	Day	29% 26% 29% 12% 3 1	460
	21st to end	Day	30% 20% 33% 10% 5% 1	506
April	1st to 10th	Day	32% 22% 29% 12% 5% 1	460
	11th to 20th	Day	29% 22% 32% 10% 6%	452
	21st to end	Day	30% 19% 32% 15% 3 2	437
May	1st to 10th	Day	32% 22% 27% 14% 4 1	423
	11th to 20th	Day	22% 17% 42% 15% 4 1	447
	21st to end	Day	18% 14% 36% 22% 9% 1	485
June	1st to 10th	Day	18% 13% 37% 20% 8% 2	450
	11th to 20th	Day	18% 14% 37% 22% 6% 2	450
	21st to end	Day	19% 12% 37% 22% 7% 3	450
July	1st to 10th	Day	18% 10% 27% 29% 13% 3	445
	11th to 20th	Day	15% 7% 31% 31% 13% 3	444
	21st to end	Day	12% 8% 37% 31% 10% 2	488
August	1st to 10th	Day	10% 10% 33% 31% 14% 2	446
	11th to 20th	Day	18% 8% 29% 28% 14% 3	439
	21st to end	Day	12% 10% 32% 27% 14% 4	495
September	1st to 10th	Day	18% 11% 28% 24% 14% 6%	450
	11th to 20th	Day	19% 10% 30% 21% 13% 7%	450
	21st to end	Day	18% 14% 31% 23% 9% 6%	450
October	1st to 10th	Day	28% 14% 23% 21% 11% 3	450
	11th to 20th	Day	18% 18% 30% 24% 8% 2	409
	21st to end	Day	30% 15% 31% 18% 7% 1	396
November	1st to 10th	Day	22% 18% 30% 20% 10% 1	365
	11th to 20th	Day	30% 21% 26% 18% 4 1	370
	21st to end	Day	29% 19% 31% 15% 6%	366
December	1st to 10th	Day	23% 30% 28% 14% 4	180
	11th to 20th	Day	36% 24% 31% 6% 2	180
	21st to end	Day	31% 22% 34% 9% 4 1	198
January	1st to 10th	Night	23% 19% 40% 16% 1	760
	11th to 20th	Night	27% 20% 35% 16% 2	760
	21st to end	Night	21% 21% 38% 18% 3	836
February	1st to 10th	Night	23% 20% 38% 17% 1	760
	11th to 20th	Night	22% 23% 40% 14% 1	743
	21st to end	Night	27% 22% 33% 15% 2	628
March	1st to 10th	Night	26% 20% 35% 17% 2	760
	11th to 20th	Night	22% 23% 36% 16% 3	760
	21st to end	Night	25% 20% 33% 18% 4	836
April	1st to 10th	Night	25% 20% 33% 19% 3	760
	11th to 20th	Night	23% 21% 33% 18% 5%	751
	21st to end	Night	25% 21% 32% 19% 3	560
May	1st to 10th	Night	29% 14% 34% 20% 2	540
	11th to 20th	Night	20% 19% 38% 20% 4	475
	21st to end	Night	20% 9% 37% 29% 6%	389
June	1st to 10th	Night	21% 7% 37% 27% 8%	360
	11th to 20th	Night	21% 9% 34% 31% 5% 1	360
	21st to end	Night	14% 3 42% 36% 5%	360
July	1st to 10th	Night	15% 5% 32% 37% 10% 1	350
	11th to 20th	Night	12% 4 31% 41% 11% 1	348
	21st to end	Night	12% 4 33% 41% 9%	394
August	1st to 10th	Night	10% 4 33% 40% 12%	460
	11th to 20th	Night	14% 4 30% 37% 13% 1	581
	21st to end	Night	17% 4 25% 38% 15% 1	792
September	1st to 10th	Night	17% 6% 32% 33% 12% 1	720
	11th to 20th	Night	16% 8% 28% 28% 18% 2	720
	21st to end	Night	19% 9% 30% 28% 12% 2	720
October	1st to 10th	Night	25% 12% 27% 24% 10% 2	720
	11th to 20th	Night	19% 14% 33% 23% 11% 1	720
	21st to end	Night	28% 15% 32% 19% 5%	792
November	1st to 10th	Night	19% 15% 34% 24% 8% 1	740
	11th to 20th	Night	24% 19% 32% 18% 6% 1	760
	21st to end	Night	23% 20% 36% 17% 4 1	760
December	1st to 10th	Night	26% 20% 34% 16% 4	760
	11th to 20th	Night	25% 20% 34% 18% 2	760
	21st to end	Night	27% 18% 36% 16% 2	836

Page generated at 2024-04-22 09:25:40. Version ac07

Copyright © 2024 Attilla Danko.