Brooks
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brooks clear sky chart from 2005-11-06 to 2024-02-05.

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	8% 8% 3 6% 6% 3 5% 5% 6% 8% 40%	77666
	Night	7% 8% 4 7% 6% 4 5% 6% 6% 8% 38%	81131
Transparency	Day	39% 8% 16% 24% 11% 1	77368
	Night	41% 8% 16% 22% 11% 2	81009
Seeing	Day	11% 7% 24% 31% 21% 6%	14362
	Night	12% 7% 29% 36% 16% 2	23756

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	4 11% 6% 10% 8% 4 5% 7% 9% 10% 25%	2219
	11th to 20th	Day	5% 8% 4 9% 9% 4 7% 11% 7% 7% 29%	2199
	21st to end	Day	4 10% 4 8% 8% 4 5% 5% 5% 7% 40%	2712
February	1st to 10th	Day	9% 11% 4 10% 9% 5% 6% 5% 6% 7% 27%	1563
	11th to 20th	Day	8% 12% 5% 10% 8% 6% 6% 6% 7% 8% 24%	1575
	21st to end	Day	4 11% 8% 13% 8% 4 6% 5% 4 8% 29%	1363
March	1st to 10th	Day	6% 11% 6% 11% 8% 4 6% 5% 5% 7% 30%	1845
	11th to 20th	Day	7% 9% 4 9% 7% 3 6% 5% 7% 8% 33%	1979
	21st to end	Day	9% 10% 5% 8% 7% 4 5% 5% 6% 8% 33%	2178
April	1st to 10th	Day	9% 9% 5% 9% 7% 4 6% 5% 6% 9% 30%	2204
	11th to 20th	Day	10% 11% 5% 7% 7% 4 6% 5% 5% 7% 34%	2310
	21st to end	Day	10% 9% 3 7% 6% 4 6% 6% 6% 9% 35%	2340
May	1st to 10th	Day	12% 8% 3 6% 6% 4 5% 5% 7% 8% 35%	2448
	11th to 20th	Day	9% 6% 2 5% 6% 3 5% 6% 5% 8% 44%	2618
	21st to end	Day	19% 6% 3 6% 5% 3 4 5% 6% 7% 34%	2917
June	1st to 10th	Day	14% 7% 3 5% 5% 4 6% 5% 6% 8% 38%	2700
	11th to 20th	Day	16% 7% 3 6% 6% 4 5% 6% 7% 10% 32%	2700
	21st to end	Day	7% 4 2 4 5% 3 5% 6% 7% 10% 48%	2700
July	1st to 10th	Day	5% 3 1 4 4 3 5% 5% 7% 9% 52%	2700
	11th to 20th	Day	6% 3 2 3 4 3 5% 5% 7% 9% 53%	2700
	21st to end	Day	4 3 2 2 3 2 4 4 6% 9% 62%	2938
August	1st to 10th	Day	5% 4 2 4 5% 2 4 4 5% 7% 56%	2453
	11th to 20th	Day	7% 3 1 3 4 2 5% 4 6% 9% 55%	2299
	21st to end	Day	8% 4 2 3 3 2 3 5% 6% 9% 56%	2574
September	1st to 10th	Day	11% 5% 2 4 3 2 4 4 5% 7% 53%	2252
	11th to 20th	Day	14% 5% 2 4 5% 3 3 4 4 8% 48%	1980
	21st to end	Day	8% 7% 2 5% 4 3 4 6% 5% 8% 49%	1980
October	1st to 10th	Day	10% 7% 4 8% 5% 3 5% 6% 4 7% 41%	1840
	11th to 20th	Day	9% 8% 3 5% 5% 3 5% 4 6% 8% 43%	1763
	21st to end	Day	9% 9% 3 6% 7% 3 5% 6% 6% 8% 38%	1777
November	1st to 10th	Day	11% 13% 6% 8% 8% 3 4 5% 5% 8% 29%	1488
	11th to 20th	Day	5% 11% 6% 8% 7% 4 6% 4 6% 8% 35%	1520
	21st to end	Day	6% 10% 6% 8% 7% 4 6% 4 6% 10% 33%	1378
December	1st to 10th	Day	9% 13% 5% 9% 7% 6% 6% 5% 6% 7% 27%	1330
	11th to 20th	Day	5% 11% 5% 9% 9% 5% 6% 5% 6% 7% 32%	1682
	21st to end	Day	4 9% 4 6% 5% 4 4 4 5% 8% 47%	2442
January	1st to 10th	Night	4 12% 6% 10% 8% 5% 6% 6% 7% 9% 28%	4726
	11th to 20th	Night	4 8% 5% 12% 8% 4 7% 6% 6% 8% 32%	4699
	21st to end	Night	4 9% 4 10% 7% 3 5% 4 6% 7% 41%	4962
February	1st to 10th	Night	7% 10% 4 10% 9% 4 6% 6% 6% 7% 32%	2490
	11th to 20th	Night	6% 12% 5% 9% 7% 4 7% 7% 6% 8% 28%	2272
	21st to end	Night	5% 8% 6% 9% 8% 4 6% 5% 7% 10% 31%	1890
March	1st to 10th	Night	5% 9% 5% 10% 8% 4 6% 6% 7% 9% 32%	2114
	11th to 20th	Night	7% 8% 5% 8% 8% 3 5% 7% 7% 8% 34%	1980
	21st to end	Night	7% 10% 4 8% 8% 5% 6% 6% 7% 9% 30%	2178
April	1st to 10th	Night	8% 10% 4 9% 7% 5% 5% 6% 6% 9% 31%	1752
	11th to 20th	Night	9% 10% 3 8% 8% 4 6% 6% 6% 8% 33%	1601
	21st to end	Night	10% 8% 3 7% 5% 4 5% 6% 6% 9% 37%	1620
May	1st to 10th	Night	12% 8% 4 7% 5% 3 5% 6% 4 8% 38%	1510
	11th to 20th	Night	10% 4 2 5% 5% 3 5% 7% 6% 8% 45%	1272
	21st to end	Night	18% 5% 3 5% 6% 3 6% 5% 7% 8% 34%	1358
June	1st to 10th	Night	14% 5% 4 6% 5% 3 7% 5% 7% 10% 35%	1260
	11th to 20th	Night	13% 6% 2 6% 5% 4 6% 6% 8% 10% 34%	1260
	21st to end	Night	7% 4 1 5% 6% 3 5% 5% 6% 9% 50%	1260
July	1st to 10th	Night	6% 4 2 5% 6% 2 6% 5% 7% 8% 49%	1260
	11th to 20th	Night	7% 4 2 4 5% 3 4 5% 7% 8% 51%	1260
	21st to end	Night	3 2 1 3 3 2 4 5% 5% 8% 62%	1379
August	1st to 10th	Night	6% 4 3 4 5% 3 5% 5% 6% 10% 50%	1483
	11th to 20th	Night	7% 2 1 4 4 3 4 4 6% 11% 52%	1602
	21st to end	Night	7% 3 1 5% 4 3 4 5% 6% 9% 53%	1782
September	1st to 10th	Night	11% 5% 2 4 4 3 4 5% 6% 8% 47%	1705
	11th to 20th	Night	13% 4 2 4 4 3 3 4 5% 6% 52%	1980
	21st to end	Night	7% 6% 2 5% 5% 3 4 6% 6% 9% 49%	1980
October	1st to 10th	Night	11% 7% 3 6% 5% 3 4 5% 5% 8% 45%	2119
	11th to 20th	Night	9% 7% 3 7% 6% 4 4 6% 6% 8% 42%	2196
	21st to end	Night	7% 8% 5% 8% 6% 3 5% 5% 6% 9% 38%	2574
November	1st to 10th	Night	11% 12% 4 6% 6% 4 5% 5% 6% 8% 34%	2576
	11th to 20th	Night	5% 9% 4 7% 7% 4 6% 5% 7% 10% 37%	2660
	21st to end	Night	7% 9% 5% 8% 7% 4 5% 5% 7% 8% 35%	2797
December	1st to 10th	Night	6% 11% 5% 9% 8% 4 6% 6% 6% 8% 31%	2850
	11th to 20th	Night	4 9% 4 9% 8% 4 6% 6% 7% 10% 33%	3510
	21st to end	Night	4 8% 4 7% 5% 4 5% 5% 6% 7% 45%	5214

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	48% 10% 16% 20% 6% 1	2219
	11th to 20th	Day	50% 9% 14% 13% 14% 1	2220
	21st to end	Day	39% 10% 21% 25% 5%	2712
February	1st to 10th	Day	53% 7% 17% 15% 7% 1	1563
	11th to 20th	Day	55% 10% 15% 15% 6% 1	1584
	21st to end	Day	54% 7% 11% 18% 10%	1363
March	1st to 10th	Day	51% 9% 15% 18% 7%	1845
	11th to 20th	Day	45% 8% 18% 21% 8% 1	1980
	21st to end	Day	48% 9% 18% 18% 7%	2178
April	1st to 10th	Day	47% 9% 15% 20% 8%	2204
	11th to 20th	Day	47% 7% 14% 23% 8% 1	2310
	21st to end	Day	44% 8% 15% 23% 9% 1	2340
May	1st to 10th	Day	43% 10% 15% 22% 10%	2448
	11th to 20th	Day	36% 8% 16% 26% 14% 1	2622
	21st to end	Day	46% 8% 15% 21% 9% 1	2918
June	1st to 10th	Day	42% 9% 16% 21% 11% 1	2700
	11th to 20th	Day	45% 10% 16% 20% 8% 1	2700
	21st to end	Day	29% 9% 20% 29% 10% 2	2700
July	1st to 10th	Day	25% 9% 20% 31% 12% 3	2626
	11th to 20th	Day	26% 8% 18% 30% 16% 2	2619
	21st to end	Day	18% 8% 17% 33% 20% 4	2775
August	1st to 10th	Day	25% 8% 17% 31% 15% 3	2435
	11th to 20th	Day	24% 8% 21% 32% 13% 2	2299
	21st to end	Day	24% 6% 19% 31% 17% 3	2574
September	1st to 10th	Day	30% 6% 16% 27% 15% 7%	2252
	11th to 20th	Day	35% 7% 15% 28% 13% 3	1980
	21st to end	Day	33% 6% 17% 29% 13% 3	1980
October	1st to 10th	Day	40% 8% 17% 25% 10% 1	1840
	11th to 20th	Day	38% 7% 17% 25% 11% 1	1763
	21st to end	Day	42% 9% 14% 24% 11%	1777
November	1st to 10th	Day	53% 8% 13% 18% 7% 1	1488
	11th to 20th	Day	46% 7% 17% 21% 8%	1520
	21st to end	Day	44% 7% 18% 21% 8% 1	1378
December	1st to 10th	Day	53% 11% 13% 16% 5% 2	1330
	11th to 20th	Day	48% 9% 16% 21% 5% 1	1684
	21st to end	Day	35% 6% 16% 25% 16% 2	2442
January	1st to 10th	Night	48% 11% 18% 19% 4 1	4726
	11th to 20th	Night	48% 7% 14% 16% 13% 2	4740
	21st to end	Night	41% 7% 17% 25% 8% 1	4962
February	1st to 10th	Night	50% 7% 13% 20% 9% 1	2490
	11th to 20th	Night	50% 10% 14% 17% 9%	2273
	21st to end	Night	45% 8% 16% 20% 10% 2	1890
March	1st to 10th	Night	46% 10% 16% 22% 6%	2114
	11th to 20th	Night	43% 8% 16% 21% 10% 1	1980
	21st to end	Night	47% 11% 17% 19% 7% 1	2178
April	1st to 10th	Night	46% 8% 14% 21% 10%	1752
	11th to 20th	Night	46% 8% 13% 21% 10% 1	1601
	21st to end	Night	41% 8% 15% 23% 11% 2	1620
May	1st to 10th	Night	44% 7% 12% 21% 14% 1	1510
	11th to 20th	Night	34% 8% 13% 27% 16% 2	1272
	21st to end	Night	47% 6% 15% 21% 9% 2	1358
June	1st to 10th	Night	41% 7% 18% 23% 10% 1	1260
	11th to 20th	Night	41% 11% 17% 21% 9% 1	1260
	21st to end	Night	29% 7% 20% 31% 12% 2	1260
July	1st to 10th	Night	29% 9% 19% 28% 14% 2	1225
	11th to 20th	Night	29% 9% 19% 24% 14% 5%	1218
	21st to end	Night	19% 6% 16% 32% 21% 6%	1302
August	1st to 10th	Night	28% 9% 18% 27% 15% 3	1476
	11th to 20th	Night	26% 7% 16% 28% 19% 4	1602
	21st to end	Night	26% 7% 13% 27% 22% 5%	1782
September	1st to 10th	Night	32% 7% 13% 24% 17% 6%	1705
	11th to 20th	Night	32% 7% 13% 28% 15% 5%	1980
	21st to end	Night	29% 8% 16% 29% 15% 3	1980
October	1st to 10th	Night	37% 7% 15% 25% 13% 2	2119
	11th to 20th	Night	38% 8% 14% 26% 12% 2	2196
	21st to end	Night	41% 8% 16% 26% 9% 1	2574
November	1st to 10th	Night	47% 8% 15% 21% 8% 1	2576
	11th to 20th	Night	41% 8% 20% 20% 10% 1	2660
	21st to end	Night	45% 9% 18% 18% 8% 1	2797
December	1st to 10th	Night	50% 8% 14% 19% 8% 1	2850
	11th to 20th	Night	44% 10% 25% 17% 4	3507
	21st to end	Night	36% 7% 14% 23% 16% 3	5214

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	6% 7% 27% 31% 19% 11%	180
	11th to 20th	Day	8% 8% 28% 36% 14% 6%	180
	21st to end	Day	7% 9% 29% 33% 17% 6%	198
February	1st to 10th	Day	16% 9% 34% 29% 9% 3	209
	11th to 20th	Day	11% 5% 32% 34% 15% 3	240
	21st to end	Day	7% 7% 25% 34% 21% 6%	229
March	1st to 10th	Day	10% 12% 31% 30% 13% 4	420
	11th to 20th	Day	9% 7% 31% 32% 14% 6%	420
	21st to end	Day	10% 10% 31% 25% 18% 6%	462
April	1st to 10th	Day	10% 13% 28% 31% 16% 3	420
	11th to 20th	Day	14% 8% 28% 32% 17% 2	412
	21st to end	Day	12% 8% 28% 32% 16% 5%	420
May	1st to 10th	Day	13% 8% 20% 29% 23% 7%	531
	11th to 20th	Day	15% 5% 17% 32% 24% 7%	625
	21st to end	Day	16% 6% 17% 28% 25% 9%	679
June	1st to 10th	Day	13% 7% 22% 30% 23% 4	630
	11th to 20th	Day	16% 8% 28% 30% 16% 3	630
	21st to end	Day	10% 2 21% 34% 23% 10%	630
July	1st to 10th	Day	6% 3 17% 35% 31% 9%	621
	11th to 20th	Day	9% 4 22% 34% 25% 7%	618
	21st to end	Day	5% 3 20% 32% 30% 10%	684
August	1st to 10th	Day	6% 5% 16% 35% 26% 13%	464
	11th to 20th	Day	8% 3 16% 29% 32% 12%	437
	21st to end	Day	8% 6% 19% 31% 24% 12%	495
September	1st to 10th	Day	13% 7% 23% 30% 22% 5%	450
	11th to 20th	Day	13% 6% 24% 28% 22% 6%	450
	21st to end	Day	14% 11% 26% 28% 16% 5%	450
October	1st to 10th	Day	17% 5% 20% 28% 23% 7%	310
	11th to 20th	Day	12% 9% 29% 29% 17% 5%	270
	21st to end	Day	15% 12% 28% 27% 14% 3	297
November	1st to 10th	Day	20% 11% 24% 29% 14% 1	270
	11th to 20th	Day	9% 9% 40% 27% 12% 3	270
	21st to end	Day	7% 9% 34% 29% 12% 8%	203
December	1st to 10th	Day	10% 9% 32% 26% 19% 3	180
	11th to 20th	Day	12% 13% 36% 27% 10% 3	180
	21st to end	Day	15% 5% 22% 29% 23% 7%	198
January	1st to 10th	Night	11% 9% 29% 35% 14% 2	950
	11th to 20th	Night	12% 9% 29% 34% 14% 2	950
	21st to end	Night	12% 7% 30% 34% 15% 1	897
February	1st to 10th	Night	12% 7% 25% 36% 17% 3	738
	11th to 20th	Night	11% 7% 31% 37% 13% 1	704
	21st to end	Night	8% 3 26% 37% 23% 3	592
March	1st to 10th	Night	8% 6% 33% 36% 14% 2	720
	11th to 20th	Night	10% 8% 31% 34% 15% 2	720
	21st to end	Night	12% 7% 28% 36% 16% 2	792
April	1st to 10th	Night	13% 7% 30% 34% 14% 3	608
	11th to 20th	Night	15% 5% 30% 36% 14% 1	533
	21st to end	Night	14% 6% 29% 38% 13% 1	540
May	1st to 10th	Night	15% 6% 23% 32% 22% 1	540
	11th to 20th	Night	10% 3 27% 38% 21% 2	387
	21st to end	Night	20% 4 24% 29% 22% 2	389
June	1st to 10th	Night	15% 7% 23% 35% 18% 2	360
	11th to 20th	Night	15% 7% 29% 34% 15% 1	360
	21st to end	Night	8% 4 27% 35% 23% 3	360
July	1st to 10th	Night	7% 5% 20% 47% 21% 1	350
	11th to 20th	Night	8% 5% 22% 47% 16% 1	348
	21st to end	Night	5% 4 23% 41% 24% 3	394
August	1st to 10th	Night	9% 3 22% 39% 26% 2	428
	11th to 20th	Night	8% 2 20% 42% 25% 2	534
	21st to end	Night	8% 4 23% 39% 24% 2	594
September	1st to 10th	Night	13% 3 22% 43% 16% 2	540
	11th to 20th	Night	15% 4 20% 39% 21% 1	720
	21st to end	Night	10% 7% 30% 33% 18% 3	720
October	1st to 10th	Night	14% 3 26% 39% 15% 2	720
	11th to 20th	Night	13% 5% 33% 33% 16% 2	720
	21st to end	Night	11% 9% 32% 36% 11%	792
November	1st to 10th	Night	17% 8% 33% 32% 9% 1	911
	11th to 20th	Night	11% 10% 39% 29% 10% 1	950
	21st to end	Night	12% 9% 33% 34% 12% 1	950
December	1st to 10th	Night	10% 8% 30% 33% 17% 2	950
	11th to 20th	Night	9% 9% 34% 34% 13% 1	950
	21st to end	Night	13% 5% 32% 35% 13% 2	1045

Page generated at 2024-02-02 03:20:32. Version ac07

Copyright 2024 Attilla Danko