Newbrook Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Newbrook Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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	9% 9% 3 9% 6% 6% 6% 5% 7% 8% 33%	135479
	Night	8% 9% 4 10% 6% 6% 6% 5% 7% 8% 32%	134055
Transparency	Day	46% 8% 17% 22% 7%	135176
	Night	47% 7% 16% 20% 9% 1	133940
Seeing	Day	13% 7% 26% 30% 18% 6%	17552
	Night	12% 5% 29% 36% 16% 2	26212

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	7% 15% 6% 12% 8% 6% 6% 5% 6% 7% 20%	4125
	11th to 20th	Day	2 7% 4 12% 7% 6% 6% 7% 9% 9% 30%	4119
	21st to end	Day	5% 11% 3 11% 8% 6% 6% 5% 7% 8% 28%	4707
February	1st to 10th	Day	7% 12% 3 11% 8% 6% 8% 6% 7% 9% 22%	1680
	11th to 20th	Day	6% 10% 5% 14% 7% 6% 7% 5% 8% 7% 27%	1739
	21st to end	Day	4 11% 5% 10% 8% 8% 8% 6% 8% 8% 24%	1502
March	1st to 10th	Day	4 9% 5% 12% 8% 7% 8% 6% 7% 10% 25%	4518
	11th to 20th	Day	5% 11% 5% 13% 7% 6% 4 4 6% 9% 30%	4989
	21st to end	Day	9% 14% 5% 16% 6% 5% 4 4 6% 8% 22%	5524
April	1st to 10th	Day	7% 13% 4 8% 6% 6% 6% 5% 6% 8% 31%	2527
	11th to 20th	Day	9% 11% 3 9% 7% 6% 5% 5% 7% 8% 31%	2570
	21st to end	Day	10% 11% 3 9% 6% 6% 6% 6% 7% 8% 29%	2607
May	1st to 10th	Day	12% 7% 3 8% 6% 6% 6% 4 6% 7% 36%	6731
	11th to 20th	Day	15% 13% 3 9% 6% 5% 5% 4 6% 7% 28%	6734
	21st to end	Day	9% 8% 3 8% 5% 5% 6% 4 6% 8% 38%	7405
June	1st to 10th	Day	15% 7% 3 8% 6% 5% 6% 5% 6% 7% 31%	3000
	11th to 20th	Day	20% 10% 4 9% 6% 5% 6% 4 7% 8% 22%	3169
	21st to end	Day	10% 7% 2 7% 6% 6% 6% 5% 7% 9% 35%	3200
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 10% 42%	7107
	11th to 20th	Day	9% 5% 2 6% 5% 4 6% 4 7% 9% 42%	6780
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 7% 9% 42%	7376
August	1st to 10th	Day	13% 7% 2 6% 4 4 4 4 6% 8% 43%	4757
	11th to 20th	Day	9% 6% 2 7% 4 5% 5% 5% 8% 9% 39%	4289
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 9% 42%	4664
September	1st to 10th	Day	10% 8% 3 8% 4 5% 4 4 5% 7% 42%	2567
	11th to 20th	Day	13% 7% 2 6% 4 5% 5% 4 6% 8% 41%	2200
	21st to end	Day	8% 6% 2 8% 5% 6% 5% 3 7% 8% 42%	2200
October	1st to 10th	Day	9% 9% 3 9% 5% 5% 5% 4 6% 9% 35%	3353
	11th to 20th	Day	11% 11% 3 8% 4 5% 5% 4 6% 8% 36%	2996
	21st to end	Day	8% 11% 5% 10% 6% 5% 5% 4 6% 7% 32%	3082
November	1st to 10th	Day	10% 13% 5% 9% 8% 6% 5% 4 5% 7% 27%	1648
	11th to 20th	Day	6% 11% 5% 12% 8% 5% 6% 4 6% 9% 27%	1497
	21st to end	Day	5% 12% 5% 13% 9% 6% 5% 4 7% 7% 27%	1470
December	1st to 10th	Day	8% 12% 5% 13% 8% 8% 7% 6% 8% 8% 19%	2360
	11th to 20th	Day	10% 13% 4 11% 7% 6% 6% 6% 7% 7% 23%	2712
	21st to end	Day	3 7% 3 11% 8% 8% 7% 5% 7% 8% 31%	3575
January	1st to 10th	Night	7% 12% 6% 16% 8% 7% 7% 6% 6% 7% 19%	8768
	11th to 20th	Night	2 8% 4 9% 6% 6% 6% 5% 6% 8% 39%	8779
	21st to end	Night	6% 11% 4 11% 9% 7% 6% 5% 7% 8% 27%	9530
February	1st to 10th	Night	6% 11% 4 11% 7% 7% 7% 5% 8% 8% 25%	2940
	11th to 20th	Night	5% 11% 4 11% 7% 8% 6% 4 7% 7% 30%	2657
	21st to end	Night	3 9% 4 9% 8% 7% 6% 7% 8% 8% 31%	2125
March	1st to 10th	Night	3 8% 4 10% 7% 6% 7% 6% 8% 10% 29%	5376
	11th to 20th	Night	5% 9% 4 11% 7% 6% 6% 5% 7% 9% 32%	5010
	21st to end	Night	10% 16% 6% 14% 7% 5% 5% 3 6% 6% 23%	5447
April	1st to 10th	Night	6% 10% 3 9% 7% 6% 7% 4 6% 7% 34%	1873
	11th to 20th	Night	8% 9% 3 9% 7% 6% 6% 6% 6% 7% 32%	1781
	21st to end	Night	10% 11% 3 7% 6% 5% 6% 4 7% 7% 35%	1792
May	1st to 10th	Night	14% 7% 3 7% 4 3 4 4 6% 7% 41%	3228
	11th to 20th	Night	15% 10% 4 9% 6% 6% 6% 4 6% 6% 28%	3159
	21st to end	Night	11% 7% 3 7% 5% 5% 5% 5% 7% 10% 35%	3470
June	1st to 10th	Night	16% 7% 3 8% 6% 6% 4 4 6% 7% 33%	1400
	11th to 20th	Night	18% 8% 3 6% 5% 5% 6% 5% 7% 9% 26%	1227
	21st to end	Night	9% 7% 3 7% 7% 4 5% 4 7% 7% 40%	1200
July	1st to 10th	Night	8% 4 2 6% 4 5% 5% 4 7% 9% 46%	2851
	11th to 20th	Night	8% 6% 3 8% 5% 5% 5% 4 6% 8% 42%	3180
	21st to end	Night	12% 5% 2 5% 4 3 5% 4 6% 8% 45%	3467
August	1st to 10th	Night	10% 5% 2 6% 6% 4 5% 4 6% 7% 44%	2378
	11th to 20th	Night	10% 7% 3 7% 4 5% 6% 4 6% 8% 40%	2765
	21st to end	Night	11% 6% 2 5% 4 4 5% 4 6% 8% 46%	3245
September	1st to 10th	Night	12% 6% 3 6% 3 3 4 4 5% 8% 46%	1831
	11th to 20th	Night	11% 7% 2 6% 3 4 4 3 6% 8% 47%	2200
	21st to end	Night	8% 8% 2 7% 4 5% 5% 4 6% 8% 45%	2200
October	1st to 10th	Night	7% 7% 3 8% 6% 6% 5% 4 7% 9% 38%	3839
	11th to 20th	Night	10% 7% 3 8% 5% 4 5% 5% 7% 9% 37%	4149
	21st to end	Night	8% 8% 4 9% 6% 5% 6% 5% 8% 9% 33%	4686
November	1st to 10th	Night	11% 15% 6% 10% 7% 5% 5% 3 5% 6% 27%	2870
	11th to 20th	Night	7% 12% 5% 12% 8% 7% 5% 4 6% 7% 26%	3119
	21st to end	Night	5% 12% 6% 13% 9% 6% 5% 5% 6% 8% 26%	3150
December	1st to 10th	Night	9% 15% 5% 13% 8% 7% 5% 5% 6% 6% 20%	5040
	11th to 20th	Night	8% 16% 5% 14% 8% 7% 6% 5% 7% 7% 18%	5700
	21st to end	Night	3 7% 4 11% 7% 7% 6% 5% 7% 9% 36%	7623

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	61% 6% 10% 13% 10%	4125
	11th to 20th	Day	45% 6% 17% 16% 16% 1	4140
	21st to end	Day	51% 8% 20% 15% 6%	4708
February	1st to 10th	Day	55% 7% 14% 15% 9%	1680
	11th to 20th	Day	52% 7% 15% 17% 9%	1748
	21st to end	Day	51% 9% 16% 17% 7%	1502
March	1st to 10th	Day	52% 7% 16% 19% 6%	4518
	11th to 20th	Day	50% 7% 16% 21% 6%	4990
	21st to end	Day	57% 7% 11% 20% 5%	5524
April	1st to 10th	Day	47% 9% 17% 19% 8% 1	2527
	11th to 20th	Day	47% 8% 14% 21% 10%	2570
	21st to end	Day	48% 10% 13% 21% 7% 1	2607
May	1st to 10th	Day	44% 6% 11% 24% 14% 1	6731
	11th to 20th	Day	53% 7% 11% 23% 6%	6738
	21st to end	Day	40% 9% 20% 20% 10% 1	7406
June	1st to 10th	Day	48% 8% 14% 21% 8%	3000
	11th to 20th	Day	58% 9% 13% 16% 4	3169
	21st to end	Day	41% 11% 20% 21% 6% 1	3200
July	1st to 10th	Day	34% 9% 23% 27% 7%	7030
	11th to 20th	Day	35% 8% 16% 31% 10%	6699
	21st to end	Day	37% 7% 23% 27% 5%	7169
August	1st to 10th	Day	38% 8% 21% 30% 2	4739
	11th to 20th	Day	37% 9% 24% 23% 7%	4331
	21st to end	Day	36% 8% 29% 24% 4	4663
September	1st to 10th	Day	40% 8% 18% 25% 7% 1	2567
	11th to 20th	Day	39% 7% 21% 26% 6%	2200
	21st to end	Day	38% 9% 18% 25% 9% 1	2200
October	1st to 10th	Day	44% 6% 23% 23% 4	3353
	11th to 20th	Day	46% 6% 14% 27% 7%	2996
	21st to end	Day	50% 6% 17% 24% 3	3082
November	1st to 10th	Day	55% 7% 14% 17% 7%	1648
	11th to 20th	Day	52% 6% 19% 17% 6%	1497
	21st to end	Day	53% 9% 14% 18% 5% 1	1470
December	1st to 10th	Day	60% 8% 17% 10% 4 1	2360
	11th to 20th	Day	57% 7% 16% 15% 4	2714
	21st to end	Day	49% 6% 10% 27% 8% 1	3575
January	1st to 10th	Night	61% 6% 10% 12% 10% 1	8769
	11th to 20th	Night	41% 5% 17% 19% 16% 2	8820
	21st to end	Night	52% 7% 20% 15% 6%	9530
February	1st to 10th	Night	53% 7% 13% 16% 9% 1	2940
	11th to 20th	Night	51% 7% 13% 18% 11% 1	2658
	21st to end	Night	46% 8% 13% 22% 10% 1	2125
March	1st to 10th	Night	46% 6% 19% 22% 7%	5376
	11th to 20th	Night	45% 8% 17% 22% 8%	5010
	21st to end	Night	58% 8% 9% 15% 10%	5447
April	1st to 10th	Night	46% 7% 14% 21% 12% 1	1873
	11th to 20th	Night	48% 7% 11% 20% 13% 2	1781
	21st to end	Night	44% 7% 13% 23% 12% 1	1792
May	1st to 10th	Night	40% 6% 11% 25% 16% 3	3228
	11th to 20th	Night	52% 7% 12% 21% 7% 1	3159
	21st to end	Night	40% 10% 18% 22% 9% 1	3470
June	1st to 10th	Night	48% 7% 12% 21% 10% 1	1400
	11th to 20th	Night	50% 10% 16% 18% 5%	1227
	21st to end	Night	41% 8% 20% 24% 6% 1	1200
July	1st to 10th	Night	33% 8% 23% 21% 14%	2819
	11th to 20th	Night	39% 6% 15% 32% 8%	3138
	21st to end	Night	35% 7% 23% 30% 5%	3369
August	1st to 10th	Night	38% 8% 20% 33% 2	2371
	11th to 20th	Night	40% 9% 19% 24% 8%	2789
	21st to end	Night	35% 7% 25% 27% 6%	3245
September	1st to 10th	Night	35% 8% 19% 29% 7% 2	1831
	11th to 20th	Night	35% 6% 17% 31% 11% 1	2200
	21st to end	Night	36% 8% 16% 26% 11% 2	2200
October	1st to 10th	Night	40% 7% 21% 25% 7%	3839
	11th to 20th	Night	41% 6% 15% 31% 6%	4149
	21st to end	Night	45% 6% 23% 21% 5%	4686
November	1st to 10th	Night	58% 5% 12% 20% 6%	2870
	11th to 20th	Night	56% 8% 13% 17% 6%	3119
	21st to end	Night	54% 8% 15% 17% 5% 1	3150
December	1st to 10th	Night	62% 7% 12% 13% 5% 1	5040
	11th to 20th	Night	62% 7% 16% 11% 4	5697
	21st to end	Night	43% 7% 15% 22% 12% 1	7623

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	10% 5% 29% 31% 21% 5%	220
	11th to 20th	Day	10% 10% 31% 30% 15% 5%	220
	21st to end	Day	9% 9% 36% 33% 10% 4	242
February	1st to 10th	Day	15% 4 32% 30% 14% 5%	220
	11th to 20th	Day	8% 5% 31% 33% 19% 4	283
	21st to end	Day	9% 7% 31% 32% 14% 7%	266
March	1st to 10th	Day	9% 7% 29% 36% 15% 3	500
	11th to 20th	Day	9% 5% 33% 35% 14% 5%	500
	21st to end	Day	16% 7% 26% 32% 16% 3	550
April	1st to 10th	Day	9% 10% 33% 32% 13% 3	500
	11th to 20th	Day	14% 8% 28% 30% 15% 5%	492
	21st to end	Day	14% 7% 32% 29% 14% 5%	507
May	1st to 10th	Day	14% 10% 26% 27% 20% 4	703
	11th to 20th	Day	13% 6% 24% 31% 20% 7%	725
	21st to end	Day	14% 6% 22% 30% 20% 8%	789
June	1st to 10th	Day	16% 9% 27% 31% 14% 3	730
	11th to 20th	Day	21% 5% 21% 25% 20% 7%	899
	21st to end	Day	11% 5% 19% 31% 25% 9%	930
July	1st to 10th	Day	12% 4 17% 33% 24% 8%	863
	11th to 20th	Day	13% 5% 21% 28% 25% 8%	718
	21st to end	Day	10% 3 20% 31% 26% 10%	794
August	1st to 10th	Day	14% 4 16% 30% 24% 12%	665
	11th to 20th	Day	8% 5% 30% 31% 20% 6%	517
	21st to end	Day	11% 6% 21% 30% 23% 9%	583
September	1st to 10th	Day	14% 9% 28% 24% 18% 7%	530
	11th to 20th	Day	17% 6% 22% 32% 19% 4	530
	21st to end	Day	11% 11% 35% 26% 13% 4	530
October	1st to 10th	Day	15% 10% 27% 29% 16% 3	387
	11th to 20th	Day	16% 8% 33% 31% 12% 2	330
	21st to end	Day	20% 9% 35% 23% 12% 2	363
November	1st to 10th	Day	17% 5% 35% 30% 11% 2	330
	11th to 20th	Day	9% 6% 39% 29% 13% 3	234
	21st to end	Day	5% 6% 35% 33% 14% 6%	220
December	1st to 10th	Day	11% 8% 36% 30% 11% 4	220
	11th to 20th	Day	11% 9% 33% 31% 14% 2	220
	21st to end	Day	7% 4 26% 37% 19% 6%	242
January	1st to 10th	Night	12% 6% 35% 34% 12% 2	1050
	11th to 20th	Night	9% 8% 34% 35% 12% 2	1050
	21st to end	Night	12% 10% 36% 30% 10% 2	1113
February	1st to 10th	Night	11% 5% 28% 37% 17% 3	840
	11th to 20th	Night	9% 4 32% 37% 17% 1	804
	21st to end	Night	5% 4 31% 38% 18% 5%	660
March	1st to 10th	Night	8% 5% 30% 40% 14% 3	800
	11th to 20th	Night	10% 5% 31% 37% 15% 2	800
	21st to end	Night	14% 5% 27% 35% 17% 3	880
April	1st to 10th	Night	9% 5% 26% 38% 18% 3	673
	11th to 20th	Night	13% 6% 28% 37% 15% 1	593
	21st to end	Night	15% 7% 24% 36% 17% 2	600
May	1st to 10th	Night	15% 6% 23% 34% 20% 2	422
	11th to 20th	Night	13% 4 24% 37% 20% 2	394
	21st to end	Night	19% 6% 19% 33% 22% 2	433
June	1st to 10th	Night	18% 8% 19% 38% 17% 1	400
	11th to 20th	Night	20% 5% 16% 36% 22% 2	400
	21st to end	Night	11% 3 19% 38% 25% 4	400
July	1st to 10th	Night	14% 2 19% 39% 25% 1	390
	11th to 20th	Night	11% 3 21% 38% 24% 3	388
	21st to end	Night	11% 2 14% 42% 27% 5%	438
August	1st to 10th	Night	8% 3 14% 37% 32% 6%	398
	11th to 20th	Night	9% 4 19% 39% 26% 2	506
	21st to end	Night	13% 4 20% 38% 23% 2	660
September	1st to 10th	Night	16% 3 21% 36% 21% 2	610
	11th to 20th	Night	13% 5% 19% 42% 19% 1	800
	21st to end	Night	12% 6% 30% 36% 16% 1	800
October	1st to 10th	Night	14% 5% 29% 37% 14% 1	800
	11th to 20th	Night	13% 5% 32% 36% 12% 3	800
	21st to end	Night	14% 6% 36% 32% 12% 1	930
November	1st to 10th	Night	15% 8% 32% 33% 10% 2	1025
	11th to 20th	Night	12% 7% 37% 31% 11% 3	1050
	21st to end	Night	9% 6% 38% 34% 13% 2	1050
December	1st to 10th	Night	12% 8% 35% 30% 13% 3	1050
	11th to 20th	Night	14% 6% 33% 34% 12% 1	1050
	21st to end	Night	10% 5% 27% 38% 17% 3	1155

Page generated at 2026-02-12 23:42:11. Version ac07

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