Brewster
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brewster 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	7% 7% 2 6% 4 4 4 4 6% 7% 48%	105561
	Night	8% 9% 3 7% 4 4 4 4 6% 7% 44%	102681
Transparency	Day	34% 7% 12% 21% 17% 8%	105330
	Night	39% 8% 13% 21% 14% 5%	102558
Seeing	Day	10% 8% 24% 32% 19% 6%	14337
	Night	12% 4 20% 41% 21% 2	23351

By Month

Percentage Cloud Cover NW (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% 21% 5% 9% 5% 4 5% 4 5% 6% 19%	2539
	11th to 20th	Day	16% 16% 4 10% 6% 5% 4 3 5% 6% 25%	2516
	21st to end	Day	25% 23% 6% 9% 4 3 3 2 4 6% 14%	2794
February	1st to 10th	Day	8% 14% 4 9% 7% 6% 7% 4 7% 7% 29%	1621
	11th to 20th	Day	8% 15% 3 8% 4 4 4 4 6% 7% 36%	1669
	21st to end	Day	5% 12% 4 9% 6% 5% 6% 6% 5% 8% 33%	1570
March	1st to 10th	Day	7% 9% 3 7% 5% 5% 6% 4 6% 8% 39%	3138
	11th to 20th	Day	4 5% 2 4 3 4 5% 4 6% 7% 56%	3352
	21st to end	Day	10% 10% 3 8% 6% 5% 5% 5% 7% 8% 34%	4103
April	1st to 10th	Day	8% 7% 2 7% 7% 6% 6% 6% 7% 8% 36%	2280
	11th to 20th	Day	5% 8% 3 7% 5% 6% 5% 5% 7% 9% 40%	2252
	21st to end	Day	5% 7% 2 7% 5% 5% 6% 5% 6% 9% 41%	2534
May	1st to 10th	Day	7% 5% 2 5% 4 3 4 4 5% 8% 53%	4420
	11th to 20th	Day	5% 4 2 5% 4 4 5% 4 7% 9% 50%	4377
	21st to end	Day	10% 8% 3 9% 6% 5% 6% 5% 7% 7% 33%	4813
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 9% 40%	2660
	11th to 20th	Day	7% 5% 2 7% 5% 5% 5% 5% 6% 8% 45%	2660
	21st to end	Day	4 4 1 5% 4 4 5% 4 6% 7% 56%	2660
July	1st to 10th	Day	1 1 1 3 2 2 3 2 4 4 76%	4420
	11th to 20th	Day	1 2 1 2 2 2 3 2 3 4 78%	4420
	21st to end	Day	2 2 1 2 2 2 2 2 4 5% 77%	4790
August	1st to 10th	Day	2 2 2 2 3 3 3 5% 7% 71%	4401
	11th to 20th	Day	1 1 1 3 3 3 4 3 6% 8% 67%	4210
	21st to end	Day	3 4 2 5% 3 4 4 3 5% 6% 61%	4183
September	1st to 10th	Day	3 2 1 3 2 3 3 3 5% 7% 68%	2280
	11th to 20th	Day	4 3 2 5% 4 4 5% 5% 6% 8% 54%	2263
	21st to end	Day	7% 4 2 4 4 4 4 3 6% 6% 57%	2071
October	1st to 10th	Day	4 3 1 4 3 3 4 3 6% 9% 60%	3180
	11th to 20th	Day	5% 4 2 7% 5% 5% 5% 5% 6% 9% 47%	3114
	21st to end	Day	8% 6% 3 6% 4 5% 5% 5% 6% 8% 43%	3101
November	1st to 10th	Day	12% 9% 4 7% 6% 5% 6% 5% 6% 9% 32%	1723
	11th to 20th	Day	10% 14% 4 8% 5% 4 5% 4 6% 6% 33%	1600
	21st to end	Day	9% 14% 6% 11% 6% 5% 5% 4 6% 6% 28%	1600
December	1st to 10th	Day	13% 15% 4 9% 6% 5% 5% 3 6% 6% 28%	1528
	11th to 20th	Day	16% 20% 6% 11% 5% 4 4 3 5% 5% 20%	1925
	21st to end	Day	13% 21% 6% 12% 6% 5% 6% 3 5% 5% 18%	2794
January	1st to 10th	Night	14% 22% 5% 11% 5% 5% 5% 4 5% 6% 18%	4406
	11th to 20th	Night	17% 16% 3 11% 4 3 4 3 7% 8% 24%	4382
	21st to end	Night	23% 22% 8% 11% 5% 4 4 2 3 4 13%	4862
February	1st to 10th	Night	11% 13% 3 9% 6% 5% 5% 4 7% 8% 29%	2556
	11th to 20th	Night	9% 10% 3 8% 5% 5% 5% 5% 7% 9% 35%	2398
	21st to end	Night	7% 12% 4 8% 6% 5% 5% 4 7% 8% 33%	1884
March	1st to 10th	Night	7% 9% 3 7% 5% 5% 6% 5% 8% 9% 37%	3736
	11th to 20th	Night	5% 7% 1 4 4 4 4 3 4 7% 58%	3623
	21st to end	Night	9% 10% 3 9% 6% 6% 6% 5% 7% 9% 30%	3550
April	1st to 10th	Night	6% 7% 3 7% 6% 6% 6% 4 7% 9% 39%	1900
	11th to 20th	Night	5% 8% 3 6% 4 5% 4 4 6% 8% 47%	1879
	21st to end	Night	6% 7% 2 5% 4 4 4 4 7% 8% 48%	1641
May	1st to 10th	Night	5% 5% 2 5% 3 4 4 4 6% 7% 54%	2540
	11th to 20th	Night	6% 4 1 5% 3 3 4 4 6% 9% 56%	2516
	21st to end	Night	6% 5% 1 6% 5% 4 5% 5% 7% 9% 47%	2762
June	1st to 10th	Night	7% 5% 2 5% 5% 5% 4 5% 7% 7% 48%	1520
	11th to 20th	Night	5% 4 2 6% 4 4 5% 5% 6% 9% 50%	1520
	21st to end	Night	3 3 1 4 3 4 5% 3 5% 7% 62%	1520
July	1st to 10th	Night	1 1 2 2 2 2 2 3 5% 80%	2540
	11th to 20th	Night	1 1 1 2 2 2 2 3 4 83%	2540
	21st to end	Night	1 1 1 2 2 2 2 3 4 5% 79%	2762
August	1st to 10th	Night	2 2 1 4 3 3 4 3 5% 6% 68%	2529
	11th to 20th	Night	2 2 1 3 2 3 4 3 5% 9% 67%	2619
	21st to end	Night	4 3 1 4 4 4 3 3 5% 6% 64%	3494
September	1st to 10th	Night	2 2 1 4 2 2 4 3 5% 7% 67%	1900
	11th to 20th	Night	5% 3 2 4 3 3 4 3 5% 7% 61%	1916
	21st to end	Night	5% 4 1 3 2 3 4 3 6% 9% 58%	2106
October	1st to 10th	Night	4 3 1 3 3 3 4 5% 7% 7% 58%	3800
	11th to 20th	Night	4 5% 1 6% 5% 4 5% 5% 7% 9% 49%	3820
	21st to end	Night	9% 7% 2 7% 5% 5% 4 4 6% 8% 44%	4457
November	1st to 10th	Night	15% 9% 3 6% 4 4 4 4 7% 7% 36%	2575
	11th to 20th	Night	11% 11% 3 7% 5% 5% 6% 5% 7% 7% 33%	2800
	21st to end	Night	12% 18% 5% 9% 4 4 4 4 7% 6% 27%	2800
December	1st to 10th	Night	12% 15% 5% 8% 5% 5% 5% 4 8% 6% 28%	2686
	11th to 20th	Night	14% 19% 8% 13% 7% 6% 4 4 5% 5% 16%	3280
	21st to end	Night	17% 23% 5% 10% 5% 5% 5% 3 5% 4 19%	4862

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	65% 9% 9% 11% 6% 1	2539
	11th to 20th	Day	60% 10% 14% 13% 1 2	2540
	21st to end	Day	78% 6% 7% 7% 2	2794
February	1st to 10th	Day	57% 11% 14% 12% 5% 1	1621
	11th to 20th	Day	50% 8% 16% 17% 8% 1	1678
	21st to end	Day	49% 13% 15% 15% 8% 1	1570
March	1st to 10th	Day	39% 12% 15% 21% 13% 1	3138
	11th to 20th	Day	27% 7% 16% 40% 10%	3352
	21st to end	Day	40% 13% 19% 17% 9% 1	4103
April	1st to 10th	Day	41% 10% 18% 21% 9% 2	2280
	11th to 20th	Day	37% 9% 16% 21% 13% 3	2252
	21st to end	Day	37% 9% 14% 23% 13% 3	2534
May	1st to 10th	Day	25% 7% 13% 24% 28% 4	4420
	11th to 20th	Day	22% 8% 15% 33% 18% 4	4380
	21st to end	Day	39% 13% 15% 22% 9% 1	4814
June	1st to 10th	Day	37% 8% 12% 21% 16% 6%	2660
	11th to 20th	Day	33% 8% 13% 26% 16% 5%	2660
	21st to end	Day	24% 6% 13% 26% 23% 8%	2660
July	1st to 10th	Day	11% 3 7% 15% 28% 36%	4351
	11th to 20th	Day	12% 3 4 12% 24% 45%	4345
	21st to end	Day	12% 2 5% 22% 32% 28%	4639
August	1st to 10th	Day	13% 3 7% 22% 36% 19%	4384
	11th to 20th	Day	16% 5% 11% 35% 27% 6%	4252
	21st to end	Day	24% 5% 12% 27% 26% 6%	4182
September	1st to 10th	Day	16% 5% 12% 28% 30% 9%	2280
	11th to 20th	Day	26% 8% 13% 23% 24% 6%	2263
	21st to end	Day	27% 7% 17% 27% 17% 5%	2071
October	1st to 10th	Day	24% 4 15% 36% 19% 2	3180
	11th to 20th	Day	35% 8% 17% 22% 17% 1	3114
	21st to end	Day	40% 7% 14% 23% 14% 2	3101
November	1st to 10th	Day	50% 10% 15% 15% 9% 1	1723
	11th to 20th	Day	54% 10% 13% 14% 8% 1	1600
	21st to end	Day	62% 10% 12% 10% 5% 1	1600
December	1st to 10th	Day	57% 9% 13% 14% 6%	1528
	11th to 20th	Day	71% 10% 8% 6% 4	1928
	21st to end	Day	72% 8% 7% 9% 4	2794
January	1st to 10th	Night	65% 10% 11% 10% 3	4406
	11th to 20th	Night	57% 8% 15% 15% 4	4420
	21st to end	Night	80% 5% 7% 5% 2	4862
February	1st to 10th	Night	56% 10% 14% 14% 5% 1	2556
	11th to 20th	Night	47% 11% 17% 17% 8%	2400
	21st to end	Night	45% 12% 16% 17% 8% 1	1884
March	1st to 10th	Night	36% 11% 17% 22% 12% 2	3736
	11th to 20th	Night	27% 7% 17% 35% 13% 1	3624
	21st to end	Night	44% 14% 17% 20% 4 1	3550
April	1st to 10th	Night	40% 10% 16% 24% 9% 2	1900
	11th to 20th	Night	33% 10% 15% 23% 16% 3	1879
	21st to end	Night	33% 8% 14% 26% 16% 3	1641
May	1st to 10th	Night	24% 8% 12% 23% 30% 3	2540
	11th to 20th	Night	20% 7% 15% 33% 23% 2	2516
	21st to end	Night	25% 11% 20% 32% 11% 1	2762
June	1st to 10th	Night	32% 8% 13% 23% 19% 4	1520
	11th to 20th	Night	28% 8% 17% 26% 17% 4	1520
	21st to end	Night	21% 7% 13% 28% 26% 6%	1520
July	1st to 10th	Night	10% 2 6% 15% 32% 34%	2500
	11th to 20th	Night	7% 3 5% 13% 25% 47%	2492
	21st to end	Night	9% 2 5% 21% 32% 31%	2674
August	1st to 10th	Night	18% 3 7% 22% 28% 22%	2521
	11th to 20th	Night	15% 5% 12% 35% 27% 6%	2643
	21st to end	Night	20% 5% 10% 28% 28% 9%	3494
September	1st to 10th	Night	16% 5% 11% 26% 31% 11%	1900
	11th to 20th	Night	23% 6% 13% 24% 26% 8%	1916
	21st to end	Night	23% 8% 14% 32% 16% 6%	2106
October	1st to 10th	Night	24% 5% 12% 38% 19% 1	3800
	11th to 20th	Night	33% 8% 15% 26% 17% 1	3820
	21st to end	Night	40% 7% 13% 26% 12% 2	4457
November	1st to 10th	Night	47% 10% 18% 15% 9% 2	2575
	11th to 20th	Night	49% 13% 13% 16% 7% 2	2800
	21st to end	Night	59% 9% 13% 12% 6% 1	2800
December	1st to 10th	Night	58% 9% 14% 16% 3	2686
	11th to 20th	Night	73% 9% 9% 7% 3	3276
	21st to end	Night	69% 9% 7% 9% 6% 1	4862

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	26% 4 14% 38% 12% 6%	180
	11th to 20th	Day	26% 7% 15% 29% 18% 5%	180
	21st to end	Day	29% 1 15% 35% 16% 3	198
February	1st to 10th	Day	12% 5% 30% 39% 13% 2	281
	11th to 20th	Day	16% 5% 32% 31% 13% 4	367
	21st to end	Day	9% 6% 31% 36% 15% 2	382
March	1st to 10th	Day	13% 8% 31% 31% 13% 4	460
	11th to 20th	Day	13% 10% 25% 25% 20% 6%	460
	21st to end	Day	11% 13% 32% 28% 14% 2	506
April	1st to 10th	Day	15% 14% 29% 26% 13% 3	460
	11th to 20th	Day	9% 17% 31% 26% 13% 5%	452
	21st to end	Day	8% 15% 30% 28% 16% 3	460
May	1st to 10th	Day	8% 13% 30% 32% 16% 2	463
	11th to 20th	Day	14% 9% 23% 29% 19% 6%	488
	21st to end	Day	11% 7% 25% 29% 19% 8%	529
June	1st to 10th	Day	10% 11% 28% 32% 15% 3	490
	11th to 20th	Day	8% 13% 31% 29% 16% 4	490
	21st to end	Day	5% 7% 22% 36% 24% 6%	490
July	1st to 10th	Day	5% 6% 21% 43% 22% 4	486
	11th to 20th	Day	3 8% 23% 35% 24% 7%	484
	21st to end	Day	3 4 22% 36% 27% 8%	531
August	1st to 10th	Day	5% 3 19% 34% 30% 9%	487
	11th to 20th	Day	2 3 18% 34% 31% 12%	477
	21st to end	Day	3 8% 21% 36% 23% 8%	539
September	1st to 10th	Day	4 5% 22% 32% 24% 13%	490
	11th to 20th	Day	6% 7% 21% 33% 26% 8%	490
	21st to end	Day	9% 9% 23% 32% 22% 5%	490
October	1st to 10th	Day	9% 8% 23% 30% 23% 7%	490
	11th to 20th	Day	9% 7% 24% 29% 23% 8%	468
	21st to end	Day	16% 4 25% 37% 14% 4	330
November	1st to 10th	Day	18% 7% 23% 36% 16% 1	279
	11th to 20th	Day	21% 5% 28% 25% 17% 6%	200
	21st to end	Day	19% 3 20% 35% 18% 7%	200
December	1st to 10th	Day	24% 5% 12% 30% 17% 12%	182
	11th to 20th	Day	19% 3 20% 43% 13% 2	180
	21st to end	Day	18% 3 13% 42% 18% 6%	198
January	1st to 10th	Night	23% 5% 21% 34% 16% 1	760
	11th to 20th	Night	23% 3 17% 37% 18% 3	760
	21st to end	Night	20% 3 16% 39% 20% 3	836
February	1st to 10th	Night	17% 3 21% 42% 14% 2	760
	11th to 20th	Night	14% 2 23% 41% 17% 2	744
	21st to end	Night	11% 5% 23% 41% 18% 2	628
March	1st to 10th	Night	15% 4 20% 42% 18% 2	760
	11th to 20th	Night	10% 4 23% 43% 19% 1	760
	21st to end	Night	11% 6% 24% 41% 17% 1	836
April	1st to 10th	Night	10% 5% 21% 42% 21% 1	760
	11th to 20th	Night	8% 7% 25% 38% 19% 2	751
	21st to end	Night	7% 6% 27% 43% 15% 2	501
May	1st to 10th	Night	5% 4 30% 39% 22%	380
	11th to 20th	Night	11% 4 19% 39% 26% 2	374
	21st to end	Night	9% 4 16% 41% 26% 4	411
June	1st to 10th	Night	9% 3 26% 39% 21% 2	380
	11th to 20th	Night	6% 6% 24% 40% 22% 1	380
	21st to end	Night	3 4 20% 48% 23% 1	380
July	1st to 10th	Night	3 4 19% 44% 29% 2	370
	11th to 20th	Night	2 1 22% 47% 26% 1	368
	21st to end	Night	2 15% 48% 34% 1	416
August	1st to 10th	Night	2 2 14% 40% 38% 4	378
	11th to 20th	Night	2 2 11% 40% 41% 5%	446
	21st to end	Night	4 4 16% 42% 32% 3	832
September	1st to 10th	Night	3 3 15% 45% 29% 5%	760
	11th to 20th	Night	7% 3 15% 33% 37% 7%	760
	21st to end	Night	7% 3 16% 45% 26% 3	760
October	1st to 10th	Night	10% 4 15% 43% 26% 2	760
	11th to 20th	Night	9% 3 23% 41% 22% 3	760
	21st to end	Night	16% 4 20% 40% 17% 3	836
November	1st to 10th	Night	20% 4 19% 44% 14% 1	780
	11th to 20th	Night	18% 3 25% 38% 15% 3	800
	21st to end	Night	22% 3 19% 37% 15% 4	800
December	1st to 10th	Night	17% 2 18% 39% 21% 3	768
	11th to 20th	Night	22% 3 19% 40% 15% 1	760
	21st to end	Night	26% 2 19% 43% 9% 1	836

Page generated at 2024-11-29 07:43:05. Version ac07

Copyright © 2024 Attilla Danko.