Lookum Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookum Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	14% 12% 5% 9% 5% 4 4 3 5% 6% 32%	101407
	Night	14% 13% 5% 11% 5% 4 4 3 5% 6% 29%	97869
Transparency	Day	51% 7% 13% 20% 9% 1	104878
	Night	55% 7% 13% 18% 7% 1	102486
Seeing	Day	20% 16% 33% 21% 8% 2	15835
	Night	20% 13% 32% 25% 9% 1	25549

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	11% 19% 12% 18% 7% 5% 4 3 5% 6% 12%	2527
	11th to 20th	Day	9% 15% 7% 21% 13% 6% 5% 3 5% 5% 10%	2530
	21st to end	Day	9% 19% 11% 16% 8% 6% 6% 3 5% 5% 12%	2783
February	1st to 10th	Day	10% 14% 5% 16% 11% 8% 6% 3 6% 4 17%	1539
	11th to 20th	Day	10% 16% 7% 17% 9% 8% 5% 3 4 4 18%	1839
	21st to end	Day	11% 17% 6% 16% 9% 6% 5% 3 4 6% 18%	1570
March	1st to 10th	Day	11% 13% 7% 12% 6% 4 4 3 5% 6% 30%	3118
	11th to 20th	Day	8% 16% 5% 18% 7% 4 4 3 4 6% 26%	3305
	21st to end	Day	17% 16% 9% 16% 6% 4 4 2 4 4 18%	4091
April	1st to 10th	Day	17% 17% 4 9% 4 4 4 3 5% 5% 28%	2280
	11th to 20th	Day	20% 14% 5% 7% 3 3 3 3 5% 5% 30%	2323
	21st to end	Day	15% 13% 4 8% 4 4 4 4 4 6% 33%	2470
May	1st to 10th	Day	14% 10% 3 7% 4 3 4 3 4 6% 41%	4190
	11th to 20th	Day	13% 9% 3 7% 3 4 4 3 5% 7% 42%	4399
	21st to end	Day	13% 7% 2 7% 5% 5% 4 3 6% 7% 40%	4837
June	1st to 10th	Day	14% 6% 3 6% 4 4 5% 5% 6% 8% 39%	2764
	11th to 20th	Day	15% 8% 2 6% 4 4 5% 4 6% 8% 39%	2850
	21st to end	Day	16% 6% 2 5% 4 4 5% 4 7% 7% 38%	2765
July	1st to 10th	Day	14% 7% 2 6% 4 4 4 3 6% 7% 42%	4440
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 5% 8% 50%	4440
	21st to end	Day	12% 5% 1 4 3 3 4 4 6% 8% 51%	4814
August	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 7% 42%	4423
	11th to 20th	Day	17% 5% 2 5% 3 3 3 3 5% 6% 48%	4056
	21st to end	Day	18% 6% 2 5% 3 3 3 3 5% 7% 45%	4280
September	1st to 10th	Day	19% 6% 1 5% 4 4 4 3 6% 7% 40%	2280
	11th to 20th	Day	14% 7% 2 5% 4 4 5% 4 6% 9% 39%	2123
	21st to end	Day	19% 8% 3 6% 5% 4 4 4 7% 7% 33%	2090
October	1st to 10th	Day	20% 9% 3 8% 4 5% 4 4 5% 6% 32%	2071
	11th to 20th	Day	25% 16% 3 8% 5% 4 3 4 5% 6% 20%	1758
	21st to end	Day	23% 24% 3 9% 4 4 5% 3 5% 4 16%	1881
November	1st to 10th	Day	19% 19% 5% 7% 4 3 4 3 5% 6% 25%	1753
	11th to 20th	Day	16% 21% 9% 10% 6% 4 5% 3 5% 5% 15%	1710
	21st to end	Day	16% 23% 9% 14% 4 4 3 3 4 6% 15%	1443
December	1st to 10th	Day	12% 18% 10% 16% 7% 4 4 3 5% 5% 15%	1330
	11th to 20th	Day	14% 21% 8% 17% 6% 5% 4 3 4 5% 13%	1671
	21st to end	Day	18% 27% 13% 15% 5% 3 3 2 4 3 7%	2664
January	1st to 10th	Night	13% 18% 8% 22% 5% 4 3 2 3 4 17%	4428
	11th to 20th	Night	9% 17% 6% 22% 11% 6% 4 3 4 5% 14%	4440
	21st to end	Night	12% 15% 11% 16% 8% 5% 6% 4 5% 6% 13%	4884
February	1st to 10th	Night	8% 15% 6% 15% 10% 8% 5% 4 5% 5% 20%	2639
	11th to 20th	Night	10% 14% 5% 16% 9% 6% 4 4 5% 6% 22%	2226
	21st to end	Night	12% 17% 8% 14% 7% 6% 4 4 4 6% 19%	1884
March	1st to 10th	Night	11% 11% 5% 9% 6% 4 4 3 5% 8% 35%	3722
	11th to 20th	Night	7% 16% 7% 12% 6% 4 4 3 4 6% 30%	3653
	21st to end	Night	16% 11% 6% 14% 6% 5% 5% 3 5% 5% 22%	3570
April	1st to 10th	Night	17% 15% 4 9% 6% 5% 5% 4 5% 6% 25%	1900
	11th to 20th	Night	22% 9% 4 6% 3 5% 4 3 4 5% 34%	1806
	21st to end	Night	15% 12% 5% 7% 5% 4 4 3 5% 7% 33%	1710
May	1st to 10th	Night	19% 9% 3 5% 3 3 4 2 4 6% 42%	2752
	11th to 20th	Night	14% 8% 2 7% 5% 4 5% 4 5% 6% 40%	2506
	21st to end	Night	18% 8% 3 6% 4 4 5% 4 5% 7% 36%	2750
June	1st to 10th	Night	13% 7% 2 7% 5% 4 5% 4 6% 6% 41%	1411
	11th to 20th	Night	14% 6% 2 5% 5% 5% 5% 5% 6% 8% 38%	1330
	21st to end	Night	16% 7% 2 5% 5% 3 4 3 6% 8% 41%	1408
July	1st to 10th	Night	14% 7% 3 9% 5% 4 5% 3 5% 7% 39%	2530
	11th to 20th	Night	10% 6% 2 4 3 4 3 3 5% 8% 53%	2530
	21st to end	Night	8% 6% 2 5% 4 3 3 3 6% 7% 51%	2750
August	1st to 10th	Night	11% 7% 2 6% 5% 4 4 3 5% 8% 44%	2517
	11th to 20th	Night	17% 5% 2 4 3 3 4 2 5% 7% 48%	2772
	21st to end	Night	13% 6% 2 6% 3 4 3 3 5% 6% 48%	3373
September	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 4 7% 45%	1900
	11th to 20th	Night	16% 7% 2 7% 4 4 4 3 6% 7% 42%	2038
	21st to end	Night	18% 8% 2 7% 4 4 5% 4 6% 7% 37%	2090
October	1st to 10th	Night	20% 9% 2 6% 4 4 5% 3 6% 8% 34%	2107
	11th to 20th	Night	20% 14% 4 7% 4 5% 4 3 4 6% 29%	2422
	21st to end	Night	24% 19% 4 9% 5% 4 4 3 4 5% 20%	2717
November	1st to 10th	Night	16% 20% 4 7% 4 4 4 3 5% 6% 27%	2530
	11th to 20th	Night	16% 22% 6% 11% 6% 5% 3 3 3 4 20%	2470
	21st to end	Night	16% 19% 10% 12% 5% 4 4 4 4 5% 17%	2730
December	1st to 10th	Night	12% 20% 8% 14% 6% 5% 5% 3 5% 5% 17%	2850
	11th to 20th	Night	13% 15% 8% 19% 6% 6% 4 3 5% 5% 16%	3526
	21st to end	Night	20% 25% 12% 16% 5% 3 3 2 3 3 8%	4998

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	71% 9% 12% 7% 1	2528
	11th to 20th	Day	74% 8% 12% 6%	2530
	21st to end	Day	73% 7% 13% 5% 2	2783
February	1st to 10th	Day	66% 9% 12% 10% 4	1539
	11th to 20th	Day	68% 8% 11% 9% 4	1849
	21st to end	Day	66% 8% 9% 11% 5% 1	1570
March	1st to 10th	Day	54% 7% 13% 17% 8%	3120
	11th to 20th	Day	58% 7% 14% 14% 5% 1	3305
	21st to end	Day	67% 8% 11% 11% 4	4091
April	1st to 10th	Day	57% 7% 10% 18% 7%	2280
	11th to 20th	Day	55% 5% 9% 19% 10% 1	2323
	21st to end	Day	50% 8% 9% 18% 12% 2	2470
May	1st to 10th	Day	42% 7% 11% 23% 16% 1	4202
	11th to 20th	Day	39% 8% 13% 28% 11% 1	4403
	21st to end	Day	40% 10% 13% 19% 16% 2	4837
June	1st to 10th	Day	40% 9% 15% 21% 13% 2	2764
	11th to 20th	Day	42% 8% 13% 23% 14% 1	2850
	21st to end	Day	41% 8% 17% 22% 10% 1	2765
July	1st to 10th	Day	40% 5% 17% 25% 12% 1	4371
	11th to 20th	Day	32% 6% 15% 31% 14% 2	4365
	21st to end	Day	31% 6% 13% 33% 17%	4662
August	1st to 10th	Day	40% 6% 16% 28% 10% 1	4408
	11th to 20th	Day	38% 5% 14% 32% 11%	4095
	21st to end	Day	40% 5% 15% 29% 11% 1	4279
September	1st to 10th	Day	43% 8% 13% 26% 10%	2280
	11th to 20th	Day	40% 9% 20% 25% 6%	2123
	21st to end	Day	47% 8% 17% 20% 7%	2090
October	1st to 10th	Day	42% 6% 13% 28% 11%	3448
	11th to 20th	Day	58% 4 12% 16% 10%	2896
	21st to end	Day	66% 5% 14% 12% 2	3081
November	1st to 10th	Day	59% 6% 13% 16% 5%	1753
	11th to 20th	Day	69% 8% 12% 7% 4	1710
	21st to end	Day	71% 8% 13% 6% 2	1443
December	1st to 10th	Day	71% 8% 13% 6% 2	1330
	11th to 20th	Day	72% 7% 10% 9% 1	1671
	21st to end	Day	83% 5% 6% 5% 1	2664
January	1st to 10th	Night	73% 5% 9% 12% 1	4428
	11th to 20th	Night	72% 9% 14% 5% 1	4440
	21st to end	Night	70% 9% 15% 6% 1	4884
February	1st to 10th	Night	64% 6% 12% 13% 5%	2639
	11th to 20th	Night	61% 7% 14% 15% 3	2227
	21st to end	Night	64% 6% 11% 13% 6%	1884
March	1st to 10th	Night	46% 6% 21% 20% 6% 1	3733
	11th to 20th	Night	53% 7% 12% 22% 7%	3654
	21st to end	Night	60% 9% 11% 14% 5%	3570
April	1st to 10th	Night	58% 7% 11% 14% 9% 1	1900
	11th to 20th	Night	52% 6% 9% 21% 10% 2	1806
	21st to end	Night	50% 6% 12% 18% 12% 2	1710
May	1st to 10th	Night	42% 6% 11% 26% 13% 2	2759
	11th to 20th	Night	41% 9% 11% 28% 10% 1	2507
	21st to end	Night	46% 7% 13% 16% 13% 6%	2751
June	1st to 10th	Night	40% 7% 13% 26% 12% 2	1411
	11th to 20th	Night	41% 10% 12% 21% 15% 2	1330
	21st to end	Night	40% 6% 14% 23% 14% 2	1408
July	1st to 10th	Night	44% 6% 14% 22% 13% 2	2490
	11th to 20th	Night	29% 5% 15% 38% 11% 2	2482
	21st to end	Night	33% 5% 10% 25% 23% 3	2662
August	1st to 10th	Night	39% 6% 13% 28% 13% 1	2508
	11th to 20th	Night	36% 5% 15% 33% 10% 1	2799
	21st to end	Night	37% 5% 12% 29% 15% 2	3373
September	1st to 10th	Night	39% 6% 14% 27% 13% 1	1900
	11th to 20th	Night	42% 7% 18% 25% 9%	2038
	21st to end	Night	45% 9% 17% 22% 7% 1	2090
October	1st to 10th	Night	42% 6% 13% 30% 9% 1	3510
	11th to 20th	Night	50% 5% 13% 19% 13%	4023
	21st to end	Night	61% 5% 13% 18% 3	4467
November	1st to 10th	Night	56% 9% 13% 15% 6%	2530
	11th to 20th	Night	68% 7% 11% 9% 6%	2470
	21st to end	Night	70% 7% 13% 8% 1	2730
December	1st to 10th	Night	68% 9% 13% 8% 2	2850
	11th to 20th	Night	69% 8% 13% 7% 2	3525
	21st to end	Night	82% 5% 8% 4 1	4998

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	19% 20% 41% 18% 1	270
	11th to 20th	Day	23% 17% 44% 13% 3	270
	21st to end	Day	19% 19% 43% 16% 2	297
February	1st to 10th	Day	21% 24% 36% 13% 5% 1	270
	11th to 20th	Day	21% 30% 34% 11% 3	270
	21st to end	Day	24% 30% 37% 8% 1	225
March	1st to 10th	Day	21% 26% 37% 13% 3	270
	11th to 20th	Day	22% 20% 37% 17% 3 1	350
	21st to end	Day	28% 22% 25% 19% 5% 1	506
April	1st to 10th	Day	26% 20% 31% 19% 3 1	460
	11th to 20th	Day	28% 19% 27% 18% 7% 1	452
	21st to end	Day	22% 21% 29% 20% 5% 2	460
May	1st to 10th	Day	22% 21% 31% 15% 8% 2	506
	11th to 20th	Day	19% 18% 37% 18% 7% 2	675
	21st to end	Day	17% 14% 33% 24% 10% 2	734
June	1st to 10th	Day	16% 15% 35% 25% 8% 1	680
	11th to 20th	Day	18% 15% 34% 24% 8% 2	680
	21st to end	Day	19% 11% 33% 26% 9% 2	680
July	1st to 10th	Day	10% 8% 35% 30% 13% 3	671
	11th to 20th	Day	12% 10% 33% 30% 12% 3	668
	21st to end	Day	11% 7% 37% 28% 14% 5%	739
August	1st to 10th	Day	11% 9% 31% 32% 12% 4	676
	11th to 20th	Day	16% 7% 23% 28% 20% 7%	491
	21st to end	Day	21% 12% 25% 25% 12% 4	539
September	1st to 10th	Day	21% 12% 30% 21% 11% 5%	490
	11th to 20th	Day	14% 9% 34% 27% 11% 4	490
	21st to end	Day	22% 13% 24% 29% 9% 2	490
October	1st to 10th	Day	26% 15% 29% 20% 8% 2	471
	11th to 20th	Day	35% 20% 30% 13% 1	300
	21st to end	Day	38% 23% 29% 8% 2	330
November	1st to 10th	Day	25% 22% 34% 16% 3	297
	11th to 20th	Day	23% 31% 34% 10% 3	270
	21st to end	Day	29% 24% 31% 12% 3	233
December	1st to 10th	Day	23% 24% 31% 16% 6% 1	180
	11th to 20th	Day	27% 23% 35% 9% 5% 1	180
	21st to end	Day	25% 27% 35% 11% 3	265
January	1st to 10th	Night	19% 21% 38% 19% 3	950
	11th to 20th	Night	21% 19% 36% 18% 5% 1	950
	21st to end	Night	19% 14% 39% 22% 5% 1	1045
February	1st to 10th	Night	15% 19% 36% 23% 7% 1	950
	11th to 20th	Night	18% 19% 35% 23% 5%	751
	21st to end	Night	20% 17% 39% 20% 4	628
March	1st to 10th	Night	15% 15% 39% 23% 7%	760
	11th to 20th	Night	18% 19% 37% 20% 6% 1	760
	21st to end	Night	19% 14% 31% 27% 8% 1	692
April	1st to 10th	Night	23% 15% 30% 25% 6% 1	570
	11th to 20th	Night	26% 13% 26% 26% 8%	563
	21st to end	Night	21% 12% 31% 26% 8% 1	570
May	1st to 10th	Night	21% 11% 27% 32% 9% 1	570
	11th to 20th	Night	22% 11% 29% 28% 9% 2	561
	21st to end	Night	16% 8% 29% 31% 15%	617
June	1st to 10th	Night	14% 8% 29% 38% 11% 1	461
	11th to 20th	Night	16% 9% 28% 35% 12%	380
	21st to end	Night	18% 6% 27% 34% 13% 2	458
July	1st to 10th	Night	12% 3 26% 41% 17% 2	555
	11th to 20th	Night	13% 5% 26% 37% 17% 2	552
	21st to end	Night	11% 5% 24% 39% 19% 3	624
August	1st to 10th	Night	11% 3 26% 38% 21% 1	567
	11th to 20th	Night	12% 3 20% 37% 25% 3	564
	21st to end	Night	15% 5% 26% 36% 16% 2	627
September	1st to 10th	Night	17% 5% 26% 31% 18% 3	570
	11th to 20th	Night	18% 8% 29% 31% 13% 1	708
	21st to end	Night	19% 9% 27% 31% 13% 1	760
October	1st to 10th	Night	24% 12% 28% 24% 11% 1	760
	11th to 20th	Night	25% 15% 32% 22% 6%	760
	21st to end	Night	36% 14% 27% 18% 4	836
November	1st to 10th	Night	30% 13% 35% 17% 5%	779
	11th to 20th	Night	27% 19% 31% 18% 4	760
	21st to end	Night	26% 20% 32% 18% 4	946
December	1st to 10th	Night	22% 20% 38% 15% 4 1	950
	11th to 20th	Night	20% 20% 36% 17% 5% 1	950
	21st to end	Night	28% 20% 33% 17% 2	1045

Page generated at 2024-11-07 06:55:47. Version ac07

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