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 2024-11-30.

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	10% 9% 3 9% 6% 5% 5% 5% 7% 8% 33%	106490
	Night	8% 9% 4 10% 6% 6% 5% 5% 7% 8% 33%	101655
Transparency	Day	46% 8% 17% 22% 7%	106231
	Night	46% 8% 16% 21% 8% 1	101560
Seeing	Day	13% 6% 26% 30% 18% 6%	16049
	Night	12% 5% 28% 36% 16% 2	24555

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 14% 7% 13% 10% 7% 6% 5% 7% 7% 19%	2219
	11th to 20th	Day	3 9% 5% 11% 6% 6% 7% 9% 11% 10% 23%	2199
	21st to end	Day	6% 11% 4 12% 6% 6% 5% 4 6% 9% 31%	2535
February	1st to 10th	Day	7% 13% 3 12% 9% 6% 8% 6% 7% 8% 21%	1520
	11th to 20th	Day	6% 10% 6% 14% 7% 6% 7% 5% 8% 7% 26%	1609
	21st to end	Day	4 11% 5% 10% 8% 8% 8% 6% 8% 8% 24%	1429
March	1st to 10th	Day	3 11% 6% 13% 8% 6% 8% 5% 6% 10% 24%	3138
	11th to 20th	Day	4 9% 4 11% 6% 6% 5% 5% 6% 9% 34%	3479
	21st to end	Day	9% 13% 5% 16% 7% 5% 5% 4 6% 8% 23%	3850
April	1st to 10th	Day	7% 13% 4 9% 6% 6% 6% 5% 6% 8% 30%	2400
	11th to 20th	Day	10% 11% 3 9% 7% 6% 5% 5% 7% 7% 30%	2440
	21st to end	Day	11% 11% 3 9% 6% 6% 7% 5% 7% 7% 28%	2476
May	1st to 10th	Day	16% 9% 3 8% 6% 6% 5% 4 6% 7% 29%	4704
	11th to 20th	Day	13% 12% 3 8% 6% 5% 5% 4 6% 7% 31%	4694
	21st to end	Day	10% 9% 3 10% 7% 6% 7% 4 7% 9% 27%	5161
June	1st to 10th	Day	16% 7% 3 8% 6% 5% 6% 5% 6% 7% 30%	2850
	11th to 20th	Day	20% 10% 4 9% 6% 5% 6% 4 7% 8% 22%	3010
	21st to end	Day	10% 7% 2 7% 6% 6% 7% 5% 7% 9% 35%	3040
July	1st to 10th	Day	8% 5% 2 7% 6% 5% 5% 5% 7% 9% 42%	4969
	11th to 20th	Day	9% 5% 2 5% 5% 4 5% 4 7% 9% 45%	4740
	21st to end	Day	14% 5% 2 6% 4 4 5% 4 6% 8% 42%	5138
August	1st to 10th	Day	13% 7% 2 6% 4 4 4 4 5% 8% 43%	4610
	11th to 20th	Day	9% 6% 2 7% 4 5% 5% 5% 8% 10% 40%	4155
	21st to end	Day	10% 5% 2 7% 4 4 5% 4 7% 9% 41%	4521
September	1st to 10th	Day	11% 8% 3 8% 5% 5% 4 4 5% 7% 41%	2439
	11th to 20th	Day	14% 7% 2 7% 4 5% 4 4 6% 8% 39%	2090
	21st to end	Day	8% 7% 2 8% 5% 6% 5% 4 7% 8% 42%	2090
October	1st to 10th	Day	9% 9% 3 9% 5% 5% 5% 4 6% 9% 35%	3250
	11th to 20th	Day	11% 11% 3 8% 4 5% 5% 4 6% 8% 36%	2904
	21st to end	Day	8% 11% 5% 10% 6% 5% 5% 4 6% 7% 32%	2987
November	1st to 10th	Day	10% 13% 5% 9% 8% 7% 5% 4 5% 7% 27%	1568
	11th to 20th	Day	6% 11% 5% 13% 8% 5% 5% 4 6% 9% 27%	1426
	21st to end	Day	4 12% 5% 13% 9% 6% 6% 4 6% 7% 27%	1396
December	1st to 10th	Day	5% 11% 4 11% 8% 8% 8% 7% 8% 8% 24%	1330
	11th to 20th	Day	9% 9% 3 12% 7% 7% 7% 6% 8% 7% 26%	1682
	21st to end	Day	3 6% 3 9% 6% 6% 6% 5% 7% 9% 38%	2442
January	1st to 10th	Night	4 12% 6% 18% 9% 7% 6% 5% 6% 6% 21%	4726
	11th to 20th	Night	3 9% 4 9% 8% 7% 7% 6% 6% 7% 34%	4699
	21st to end	Night	7% 11% 4 11% 9% 5% 5% 5% 6% 7% 29%	5150
February	1st to 10th	Night	6% 12% 4 11% 8% 7% 7% 5% 7% 8% 25%	2660
	11th to 20th	Night	5% 11% 4 11% 7% 7% 6% 4 7% 6% 30%	2457
	21st to end	Night	3 9% 4 9% 9% 7% 6% 7% 8% 9% 30%	2022
March	1st to 10th	Night	3 10% 6% 11% 7% 6% 6% 5% 8% 10% 27%	3736
	11th to 20th	Night	5% 8% 4 10% 6% 6% 5% 4 7% 9% 37%	3500
	21st to end	Night	7% 12% 6% 16% 8% 6% 6% 4 7% 7% 23%	3799
April	1st to 10th	Night	6% 10% 3 9% 7% 7% 7% 4 6% 7% 33%	1780
	11th to 20th	Night	9% 9% 3 9% 7% 6% 5% 5% 6% 7% 32%	1691
	21st to end	Night	10% 11% 3 7% 6% 4 6% 4 7% 7% 35%	1703
May	1st to 10th	Night	19% 9% 3 8% 5% 4 5% 4 6% 6% 32%	2254
	11th to 20th	Night	15% 10% 4 7% 5% 5% 4 4 7% 7% 32%	2199
	21st to end	Night	12% 8% 3 8% 5% 5% 6% 5% 8% 10% 29%	2414
June	1st to 10th	Night	16% 7% 3 8% 6% 6% 4 4 6% 6% 33%	1330
	11th to 20th	Night	17% 8% 3 6% 5% 6% 6% 5% 7% 8% 27%	1166
	21st to end	Night	9% 7% 3 7% 6% 4 5% 4 7% 7% 40%	1140
July	1st to 10th	Night	9% 4 2 7% 4 5% 5% 3 6% 8% 47%	1989
	11th to 20th	Night	7% 5% 2 6% 5% 5% 5% 5% 6% 10% 44%	2220
	21st to end	Night	14% 6% 2 5% 4 3 5% 4 6% 8% 45%	2414
August	1st to 10th	Night	10% 5% 2 6% 6% 4 5% 4 6% 7% 44%	2305
	11th to 20th	Night	10% 7% 3 7% 4 5% 6% 4 6% 8% 41%	2679
	21st to end	Night	11% 6% 2 5% 4 4 5% 4 6% 8% 45%	3146
September	1st to 10th	Night	12% 6% 3 7% 3 3 4 4 5% 7% 45%	1739
	11th to 20th	Night	12% 7% 2 7% 3 3 3 3 6% 8% 46%	2090
	21st to end	Night	8% 8% 2 7% 4 5% 5% 4 6% 8% 45%	2090
October	1st to 10th	Night	7% 7% 3 8% 6% 6% 5% 4 7% 9% 38%	3722
	11th to 20th	Night	10% 7% 3 8% 5% 5% 5% 5% 7% 9% 37%	4021
	21st to end	Night	8% 8% 4 9% 6% 5% 5% 5% 8% 8% 33%	4540
November	1st to 10th	Night	11% 14% 6% 10% 7% 5% 5% 3 5% 7% 27%	2730
	11th to 20th	Night	8% 12% 5% 13% 8% 7% 5% 4 6% 7% 25%	2970
	21st to end	Night	5% 11% 6% 13% 9% 6% 5% 5% 6% 8% 26%	3000
December	1st to 10th	Night	6% 12% 5% 10% 8% 6% 5% 5% 6% 8% 28%	2850
	11th to 20th	Night	7% 14% 5% 14% 8% 7% 5% 5% 7% 7% 22%	3510
	21st to end	Night	3 7% 3 8% 6% 6% 6% 5% 7% 9% 40%	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	60% 8% 12% 15% 4 1	2219
	11th to 20th	Day	48% 6% 14% 16% 14% 1	2220
	21st to end	Day	48% 8% 20% 17% 7%	2535
February	1st to 10th	Day	57% 8% 13% 15% 8%	1520
	11th to 20th	Day	54% 7% 15% 16% 8%	1618
	21st to end	Day	52% 9% 16% 17% 7%	1429
March	1st to 10th	Day	53% 8% 15% 19% 5%	3138
	11th to 20th	Day	44% 8% 20% 21% 7%	3480
	21st to end	Day	57% 8% 13% 19% 3	3850
April	1st to 10th	Day	48% 10% 17% 18% 8% 1	2400
	11th to 20th	Day	48% 8% 14% 21% 9%	2440
	21st to end	Day	49% 10% 13% 20% 7% 1	2476
May	1st to 10th	Day	50% 8% 12% 23% 7%	4704
	11th to 20th	Day	49% 8% 11% 24% 9% 1	4698
	21st to end	Day	47% 11% 18% 16% 8%	5162
June	1st to 10th	Day	50% 8% 14% 21% 7%	2850
	11th to 20th	Day	57% 9% 13% 16% 4	3010
	21st to end	Day	41% 11% 20% 21% 6% 1	3040
July	1st to 10th	Day	36% 9% 20% 27% 8%	4892
	11th to 20th	Day	33% 8% 19% 28% 12%	4659
	21st to end	Day	38% 7% 22% 26% 7%	4976
August	1st to 10th	Day	38% 8% 21% 30% 2	4592
	11th to 20th	Day	36% 9% 24% 24% 7%	4197
	21st to end	Day	36% 8% 30% 23% 3	4520
September	1st to 10th	Day	41% 9% 18% 24% 7% 1	2439
	11th to 20th	Day	41% 7% 20% 26% 6%	2090
	21st to end	Day	39% 9% 18% 24% 9% 2	2090
October	1st to 10th	Day	44% 6% 23% 22% 4	3250
	11th to 20th	Day	46% 6% 14% 27% 6%	2904
	21st to end	Day	50% 6% 17% 24% 3	2987
November	1st to 10th	Day	56% 7% 14% 17% 6%	1568
	11th to 20th	Day	53% 6% 19% 17% 4	1426
	21st to end	Day	54% 9% 15% 17% 5% 1	1396
December	1st to 10th	Day	54% 9% 13% 15% 8% 1	1330
	11th to 20th	Day	52% 9% 15% 18% 6%	1684
	21st to end	Day	40% 7% 11% 29% 12% 1	2442
January	1st to 10th	Night	60% 8% 10% 14% 6% 1	4726
	11th to 20th	Night	47% 7% 14% 19% 13% 1	4740
	21st to end	Night	51% 7% 21% 15% 6%	5150
February	1st to 10th	Night	54% 8% 13% 17% 7% 1	2660
	11th to 20th	Night	51% 7% 13% 17% 10% 1	2458
	21st to end	Night	46% 9% 13% 22% 9% 1	2022
March	1st to 10th	Night	47% 8% 17% 22% 6%	3736
	11th to 20th	Night	40% 8% 21% 21% 9% 1	3500
	21st to end	Night	55% 10% 12% 17% 6%	3799
April	1st to 10th	Night	46% 7% 14% 20% 11% 1	1780
	11th to 20th	Night	48% 7% 12% 19% 12% 2	1691
	21st to end	Night	44% 8% 13% 22% 12% 1	1703
May	1st to 10th	Night	50% 7% 10% 22% 11% 1	2254
	11th to 20th	Night	46% 8% 12% 23% 10% 1	2199
	21st to end	Night	43% 13% 17% 18% 8% 1	2414
June	1st to 10th	Night	49% 7% 13% 21% 9% 1	1330
	11th to 20th	Night	50% 10% 16% 18% 5%	1166
	21st to end	Night	41% 8% 20% 24% 6% 1	1140
July	1st to 10th	Night	34% 8% 19% 24% 14% 1	1957
	11th to 20th	Night	34% 7% 17% 33% 9%	2178
	21st to end	Night	35% 7% 22% 28% 7%	2337
August	1st to 10th	Night	37% 8% 20% 33% 2	2298
	11th to 20th	Night	40% 9% 18% 24% 8%	2703
	21st to end	Night	35% 7% 26% 27% 5%	3146
September	1st to 10th	Night	36% 8% 19% 27% 8% 2	1739
	11th to 20th	Night	36% 6% 18% 30% 10% 1	2090
	21st to end	Night	36% 8% 16% 26% 12% 2	2090
October	1st to 10th	Night	40% 7% 21% 25% 7%	3722
	11th to 20th	Night	41% 6% 15% 32% 6%	4021
	21st to end	Night	45% 6% 23% 20% 5%	4540
November	1st to 10th	Night	57% 5% 12% 20% 5%	2730
	11th to 20th	Night	57% 8% 13% 16% 5%	2970
	21st to end	Night	55% 8% 15% 17% 4 1	3000
December	1st to 10th	Night	53% 6% 12% 19% 9% 1	2850
	11th to 20th	Night	58% 9% 14% 13% 6%	3507
	21st to end	Night	38% 8% 16% 21% 15% 2	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	8% 5% 28% 32% 21% 6%	180
	11th to 20th	Day	10% 7% 31% 29% 17% 6%	180
	21st to end	Day	9% 7% 34% 35% 10% 5%	198
February	1st to 10th	Day	17% 4 33% 29% 11% 5%	180
	11th to 20th	Day	9% 5% 30% 31% 20% 5%	243
	21st to end	Day	9% 6% 31% 32% 15% 7%	241
March	1st to 10th	Day	10% 8% 29% 36% 15% 3	460
	11th to 20th	Day	9% 5% 34% 34% 13% 5%	460
	21st to end	Day	16% 7% 26% 33% 16% 3	506
April	1st to 10th	Day	9% 10% 33% 31% 12% 3	460
	11th to 20th	Day	15% 6% 26% 32% 15% 5%	452
	21st to end	Day	15% 7% 32% 28% 13% 5%	466
May	1st to 10th	Day	14% 9% 26% 27% 21% 4	653
	11th to 20th	Day	13% 6% 24% 31% 20% 6%	675
	21st to end	Day	15% 7% 21% 29% 20% 8%	734
June	1st to 10th	Day	17% 8% 27% 31% 14% 4	680
	11th to 20th	Day	21% 5% 21% 25% 20% 7%	840
	21st to end	Day	11% 5% 17% 31% 27% 9%	870
July	1st to 10th	Day	13% 4 17% 33% 25% 9%	806
	11th to 20th	Day	13% 4 21% 28% 26% 8%	668
	21st to end	Day	11% 3 20% 31% 25% 10%	739
August	1st to 10th	Day	14% 4 16% 31% 23% 12%	618
	11th to 20th	Day	8% 4 29% 32% 20% 7%	477
	21st to end	Day	12% 6% 22% 31% 22% 8%	539
September	1st to 10th	Day	15% 10% 29% 23% 17% 7%	490
	11th to 20th	Day	18% 7% 24% 32% 16% 3	490
	21st to end	Day	11% 11% 34% 26% 14% 4	490
October	1st to 10th	Day	16% 10% 28% 27% 17% 3	354
	11th to 20th	Day	16% 7% 33% 31% 12% 2	300
	21st to end	Day	19% 9% 35% 22% 12% 3	330
November	1st to 10th	Day	16% 5% 33% 33% 12% 2	300
	11th to 20th	Day	9% 7% 38% 30% 12% 3	213
	21st to end	Day	5% 7% 37% 32% 14% 5%	199
December	1st to 10th	Day	9% 6% 34% 32% 14% 5%	180
	11th to 20th	Day	11% 7% 31% 34% 14% 2	180
	21st to end	Day	5% 3 28% 37% 20% 7%	198
January	1st to 10th	Night	12% 6% 34% 35% 12% 2	950
	11th to 20th	Night	10% 6% 33% 37% 13% 2	950
	21st to end	Night	12% 9% 35% 30% 11% 2	1007
February	1st to 10th	Night	11% 6% 28% 36% 17% 3	760
	11th to 20th	Night	10% 4 32% 35% 18% 1	744
	21st to end	Night	5% 4 29% 38% 19% 5%	628
March	1st to 10th	Night	9% 5% 30% 38% 14% 3	760
	11th to 20th	Night	10% 5% 31% 36% 15% 2	760
	21st to end	Night	14% 5% 27% 35% 17% 3	836
April	1st to 10th	Night	10% 5% 27% 38% 18% 3	640
	11th to 20th	Night	14% 5% 27% 38% 15% 1	563
	21st to end	Night	15% 7% 24% 36% 16% 2	570
May	1st to 10th	Night	15% 6% 21% 34% 21% 2	401
	11th to 20th	Night	14% 4 24% 37% 20% 2	374
	21st to end	Night	19% 5% 20% 31% 23% 2	411
June	1st to 10th	Night	17% 7% 18% 39% 17% 1	380
	11th to 20th	Night	19% 4 17% 36% 22% 2	380
	21st to end	Night	11% 3 19% 38% 25% 4	380
July	1st to 10th	Night	14% 2 17% 40% 26% 1	370
	11th to 20th	Night	11% 3 21% 38% 24% 3	368
	21st to end	Night	12% 2 14% 41% 26% 5%	416
August	1st to 10th	Night	7% 3 14% 38% 31% 7%	378
	11th to 20th	Night	9% 4 19% 39% 27% 2	480
	21st to end	Night	14% 4 20% 38% 23% 2	627
September	1st to 10th	Night	17% 3 22% 36% 20% 2	579
	11th to 20th	Night	14% 5% 20% 41% 19% 1	760
	21st to end	Night	11% 6% 29% 36% 16% 1	760
October	1st to 10th	Night	15% 4 28% 37% 14% 1	760
	11th to 20th	Night	13% 4 31% 37% 12% 3	760
	21st to end	Night	14% 6% 35% 32% 12% 1	883
November	1st to 10th	Night	15% 7% 32% 33% 11% 2	975
	11th to 20th	Night	12% 7% 36% 31% 11% 3	1000
	21st to end	Night	9% 5% 38% 34% 12% 2	1000
December	1st to 10th	Night	12% 7% 33% 31% 15% 3	950
	11th to 20th	Night	13% 6% 32% 35% 12% 1	950
	21st to end	Night	10% 5% 28% 37% 17% 3	1045

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