High Level Airport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the High Level Airport clear sky chart from 2005-11-06 to 2024-12-09.

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% 9% 3 9% 6% 5% 6% 5% 7% 8% 35%	106240
	Night	7% 10% 4 10% 7% 6% 6% 5% 6% 8% 32%	102076
Transparency	Day	45% 8% 17% 23% 7%	105952
	Night	48% 8% 15% 21% 7%	102010
Seeing	Day	13% 8% 26% 30% 18% 5%	17044
	Night	13% 7% 26% 34% 17% 2	24934

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% 14% 5% 13% 10% 7% 9% 8% 6% 6% 15%	1865
	11th to 20th	Day	5% 10% 4 12% 6% 6% 7% 6% 8% 6% 28%	1882
	21st to end	Day	7% 17% 7% 20% 10% 7% 6% 3 5% 4 16%	2127
February	1st to 10th	Day	7% 13% 3 11% 7% 7% 5% 5% 7% 7% 28%	1505
	11th to 20th	Day	6% 13% 3 9% 9% 6% 6% 6% 7% 8% 28%	1480
	21st to end	Day	3 14% 4 12% 8% 6% 7% 5% 7% 8% 26%	1412
March	1st to 10th	Day	3 9% 5% 15% 7% 7% 6% 7% 8% 9% 24%	3138
	11th to 20th	Day	5% 9% 4 12% 8% 6% 7% 4 5% 6% 33%	3263
	21st to end	Day	3 9% 3 11% 7% 6% 5% 4 6% 7% 40%	4134
April	1st to 10th	Day	5% 11% 3 10% 6% 5% 5% 5% 8% 8% 35%	2327
	11th to 20th	Day	5% 8% 3 8% 7% 6% 6% 5% 7% 7% 38%	2508
	21st to end	Day	10% 11% 4 10% 6% 6% 5% 4 5% 8% 31%	2665
May	1st to 10th	Day	7% 6% 2 5% 4 4 4 4 7% 8% 48%	4740
	11th to 20th	Day	10% 10% 3 8% 5% 5% 5% 4 6% 9% 33%	4933
	21st to end	Day	9% 7% 3 8% 6% 5% 5% 4 6% 8% 38%	5571
June	1st to 10th	Day	12% 10% 3 9% 5% 6% 5% 5% 6% 7% 33%	3230
	11th to 20th	Day	16% 9% 3 8% 5% 5% 5% 5% 7% 8% 28%	3230
	21st to end	Day	11% 7% 2 7% 5% 5% 6% 6% 7% 10% 34%	3230
July	1st to 10th	Day	7% 5% 2 5% 5% 6% 7% 6% 8% 11% 38%	5288
	11th to 20th	Day	8% 5% 2 6% 6% 6% 6% 5% 7% 9% 41%	5060
	21st to end	Day	11% 6% 2 6% 5% 6% 5% 5% 7% 10% 36%	5486
August	1st to 10th	Day	7% 5% 2 5% 4 5% 5% 5% 7% 7% 49%	4739
	11th to 20th	Day	7% 6% 2 7% 5% 5% 7% 6% 7% 8% 41%	4330
	21st to end	Day	13% 6% 2 7% 6% 5% 6% 5% 7% 8% 36%	4717
September	1st to 10th	Day	13% 7% 3 7% 5% 5% 5% 4 5% 7% 39%	2356
	11th to 20th	Day	8% 7% 3 7% 6% 4 4 4 7% 8% 42%	2215
	21st to end	Day	11% 7% 3 8% 5% 5% 5% 4 6% 8% 38%	2090
October	1st to 10th	Day	8% 10% 5% 10% 6% 4 5% 5% 6% 6% 36%	3129
	11th to 20th	Day	9% 14% 3 8% 4 4 5% 4 6% 8% 35%	2842
	21st to end	Day	9% 15% 7% 12% 5% 5% 5% 4 5% 6% 26%	2894
November	1st to 10th	Day	10% 15% 5% 12% 9% 7% 4 4 5% 6% 24%	1372
	11th to 20th	Day	10% 17% 5% 13% 9% 5% 6% 4 5% 7% 19%	1400
	21st to end	Day	6% 11% 6% 13% 9% 5% 6% 5% 7% 7% 25%	1155
December	1st to 10th	Day	6% 16% 6% 13% 8% 8% 5% 4 5% 7% 21%	990
	11th to 20th	Day	7% 17% 6% 17% 7% 5% 4 4 6% 7% 23%	1199
	21st to end	Day	5% 9% 5% 11% 7% 7% 6% 4 5% 6% 34%	1738
January	1st to 10th	Night	6% 13% 6% 17% 10% 8% 8% 5% 6% 6% 15%	5078
	11th to 20th	Night	5% 10% 3 10% 7% 7% 7% 8% 8% 8% 27%	5016
	21st to end	Night	6% 17% 7% 16% 10% 7% 5% 4 5% 5% 18%	5557
February	1st to 10th	Night	5% 11% 5% 11% 7% 6% 6% 4 6% 6% 33%	2675
	11th to 20th	Night	6% 13% 4 10% 6% 7% 5% 4 7% 7% 31%	2586
	21st to end	Night	5% 10% 4 10% 9% 7% 7% 5% 6% 7% 31%	2041
March	1st to 10th	Night	4 7% 5% 14% 8% 6% 5% 5% 6% 7% 33%	3736
	11th to 20th	Night	5% 11% 4 10% 7% 7% 7% 5% 8% 9% 27%	3716
	21st to end	Night	3 7% 4 10% 6% 5% 5% 4 6% 6% 44%	3505
April	1st to 10th	Night	6% 10% 4 8% 6% 6% 6% 4 7% 9% 33%	1852
	11th to 20th	Night	5% 9% 2 8% 7% 6% 6% 5% 6% 7% 36%	1621
	21st to end	Night	10% 11% 4 9% 5% 5% 5% 4 7% 9% 32%	1515
May	1st to 10th	Night	8% 7% 2 6% 4 5% 5% 5% 7% 7% 45%	2220
	11th to 20th	Night	9% 8% 3 8% 5% 6% 5% 5% 6% 8% 38%	1960
	21st to end	Night	9% 7% 2 6% 5% 5% 6% 5% 7% 9% 39%	2002
June	1st to 10th	Night	12% 7% 2 10% 6% 6% 4 5% 5% 7% 37%	950
	11th to 20th	Night	13% 8% 3 9% 5% 5% 6% 5% 5% 8% 34%	950
	21st to end	Night	10% 5% 3 8% 5% 5% 6% 6% 7% 9% 37%	950
July	1st to 10th	Night	6% 6% 1 5% 5% 5% 7% 7% 9% 13% 36%	1669
	11th to 20th	Night	10% 6% 2 6% 5% 5% 6% 5% 8% 8% 39%	1900
	21st to end	Night	10% 4 2 5% 5% 5% 5% 6% 7% 13% 39%	2066
August	1st to 10th	Night	6% 3 1 4 4 4 5% 4 6% 9% 56%	2189
	11th to 20th	Night	5% 7% 2 6% 4 5% 6% 5% 7% 9% 43%	2497
	21st to end	Night	9% 6% 2 6% 5% 4 5% 5% 7% 10% 40%	2944
September	1st to 10th	Night	12% 7% 3 7% 4 4 5% 4 6% 8% 40%	1821
	11th to 20th	Night	9% 7% 2 7% 5% 6% 5% 5% 7% 8% 39%	1964
	21st to end	Night	9% 7% 3 7% 6% 6% 5% 5% 7% 9% 36%	2090
October	1st to 10th	Night	8% 6% 3 7% 6% 5% 5% 5% 7% 10% 39%	3844
	11th to 20th	Night	9% 11% 4 8% 5% 5% 5% 4 6% 8% 37%	4086
	21st to end	Night	7% 13% 5% 13% 7% 6% 5% 4 6% 7% 27%	4628
November	1st to 10th	Night	12% 16% 5% 11% 6% 5% 4 4 5% 6% 26%	2925
	11th to 20th	Night	10% 17% 5% 14% 8% 6% 5% 4 5% 6% 20%	3000
	21st to end	Night	8% 13% 5% 13% 8% 5% 5% 4 6% 6% 25%	3239
December	1st to 10th	Night	8% 12% 4 11% 9% 7% 7% 5% 7% 8% 21%	3373
	11th to 20th	Night	8% 13% 6% 13% 8% 6% 6% 4 5% 7% 25%	3993
	21st to end	Night	4 9% 4 11% 7% 6% 7% 4 6% 8% 34%	5918

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	66% 8% 8% 14% 4	1865
	11th to 20th	Day	52% 8% 12% 14% 14% 1	1900
	21st to end	Day	72% 6% 9% 8% 4	2127
February	1st to 10th	Day	53% 7% 12% 18% 10%	1505
	11th to 20th	Day	52% 7% 18% 18% 5%	1488
	21st to end	Day	53% 9% 15% 17% 6%	1412
March	1st to 10th	Day	52% 9% 16% 21% 3	3138
	11th to 20th	Day	50% 7% 17% 21% 4	3263
	21st to end	Day	40% 8% 14% 24% 13%	4134
April	1st to 10th	Day	44% 8% 15% 24% 9%	2327
	11th to 20th	Day	40% 8% 15% 23% 13% 1	2508
	21st to end	Day	50% 8% 14% 19% 8% 1	2665
May	1st to 10th	Day	31% 7% 12% 31% 18% 1	4740
	11th to 20th	Day	44% 8% 10% 24% 12% 1	4937
	21st to end	Day	40% 9% 12% 24% 14% 1	5572
June	1st to 10th	Day	48% 7% 14% 21% 8% 1	3230
	11th to 20th	Day	50% 9% 14% 20% 5%	3230
	21st to end	Day	41% 11% 19% 22% 7% 1	3230
July	1st to 10th	Day	34% 10% 24% 29% 3	5206
	11th to 20th	Day	36% 10% 20% 27% 8%	4973
	21st to end	Day	39% 9% 20% 28% 3	5313
August	1st to 10th	Day	31% 10% 19% 33% 7%	4720
	11th to 20th	Day	36% 10% 19% 21% 12% 1	4372
	21st to end	Day	43% 9% 26% 20% 1	4716
September	1st to 10th	Day	42% 9% 24% 20% 5%	2356
	11th to 20th	Day	39% 8% 24% 27% 2	2215
	21st to end	Day	42% 10% 21% 21% 6%	2090
October	1st to 10th	Day	48% 6% 19% 24% 3	3129
	11th to 20th	Day	47% 6% 21% 23% 3	2842
	21st to end	Day	59% 7% 15% 17% 2	2894
November	1st to 10th	Day	59% 8% 14% 16% 3	1372
	11th to 20th	Day	66% 7% 14% 11% 2	1400
	21st to end	Day	56% 7% 16% 17% 4	1155
December	1st to 10th	Day	63% 6% 12% 14% 4	990
	11th to 20th	Day	61% 5% 11% 21% 2	1200
	21st to end	Day	47% 8% 13% 24% 8%	1738
January	1st to 10th	Night	67% 8% 9% 12% 4	5078
	11th to 20th	Night	49% 7% 11% 19% 13% 1	5060
	21st to end	Night	67% 7% 10% 11% 4	5557
February	1st to 10th	Night	50% 6% 14% 21% 10%	2675
	11th to 20th	Night	51% 7% 15% 21% 7%	2588
	21st to end	Night	49% 8% 14% 22% 7%	2041
March	1st to 10th	Night	47% 7% 14% 26% 6%	3736
	11th to 20th	Night	49% 8% 18% 21% 4	3717
	21st to end	Night	36% 7% 12% 30% 14% 1	3505
April	1st to 10th	Night	45% 7% 14% 23% 9% 2	1852
	11th to 20th	Night	43% 7% 10% 23% 15% 1	1621
	21st to end	Night	47% 7% 12% 22% 11% 1	1515
May	1st to 10th	Night	33% 8% 10% 29% 17% 3	2220
	11th to 20th	Night	43% 8% 8% 22% 17% 1	1960
	21st to end	Night	36% 10% 13% 24% 17% 1	2002
June	1st to 10th	Night	45% 8% 12% 23% 10% 1	950
	11th to 20th	Night	47% 9% 15% 21% 7%	950
	21st to end	Night	40% 9% 18% 22% 10% 1	950
July	1st to 10th	Night	34% 11% 23% 22% 10%	1642
	11th to 20th	Night	39% 8% 18% 27% 7% 1	1864
	21st to end	Night	33% 9% 20% 32% 6%	2000
August	1st to 10th	Night	24% 8% 20% 42% 7%	2183
	11th to 20th	Night	34% 10% 20% 25% 12%	2521
	21st to end	Night	37% 10% 24% 26% 3	2944
September	1st to 10th	Night	40% 10% 19% 23% 8%	1821
	11th to 20th	Night	40% 9% 18% 26% 6%	1964
	21st to end	Night	41% 10% 18% 22% 8%	2090
October	1st to 10th	Night	38% 9% 19% 28% 6% 1	3844
	11th to 20th	Night	45% 6% 19% 25% 5%	4086
	21st to end	Night	55% 8% 17% 18% 2	4628
November	1st to 10th	Night	58% 8% 14% 17% 3	2925
	11th to 20th	Night	63% 8% 12% 15% 2	3000
	21st to end	Night	58% 7% 15% 17% 3 1	3239
December	1st to 10th	Night	59% 10% 14% 13% 5%	3373
	11th to 20th	Night	58% 8% 13% 16% 5%	3991
	21st to end	Night	46% 8% 17% 20% 9%	5918

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	9% 8% 25% 36% 19% 3	180
	11th to 20th	Day	17% 9% 28% 31% 14% 1	180
	21st to end	Day	14% 11% 29% 32% 13% 1	198
February	1st to 10th	Day	17% 4 32% 29% 12% 6%	180
	11th to 20th	Day	12% 8% 32% 31% 14% 4	180
	21st to end	Day	7% 9% 35% 30% 16% 3	269
March	1st to 10th	Day	6% 10% 27% 32% 20% 4	460
	11th to 20th	Day	11% 12% 35% 28% 12% 3	460
	21st to end	Day	10% 10% 31% 35% 11% 2	506
April	1st to 10th	Day	8% 14% 36% 27% 14% 2	460
	11th to 20th	Day	8% 10% 30% 33% 16% 3	452
	21st to end	Day	14% 16% 26% 30% 13% 1	465
May	1st to 10th	Day	11% 13% 26% 29% 14% 5%	653
	11th to 20th	Day	13% 12% 23% 29% 20% 4	808
	21st to end	Day	12% 7% 20% 34% 21% 6%	940
June	1st to 10th	Day	14% 8% 28% 29% 16% 5%	870
	11th to 20th	Day	20% 7% 21% 29% 19% 4	870
	21st to end	Day	12% 5% 18% 33% 26% 7%	870
July	1st to 10th	Day	13% 5% 21% 28% 27% 6%	856
	11th to 20th	Day	14% 5% 19% 31% 23% 9%	852
	21st to end	Day	13% 4 18% 30% 26% 9%	947
August	1st to 10th	Day	11% 5% 18% 28% 28% 10%	696
	11th to 20th	Day	11% 10% 33% 30% 13% 3	477
	21st to end	Day	19% 6% 26% 31% 13% 5%	539
September	1st to 10th	Day	16% 10% 30% 25% 14% 4	490
	11th to 20th	Day	11% 9% 24% 30% 20% 6%	490
	21st to end	Day	11% 12% 32% 28% 12% 4	490
October	1st to 10th	Day	16% 12% 31% 27% 12% 3	442
	11th to 20th	Day	17% 9% 31% 29% 12% 2	300
	21st to end	Day	20% 10% 31% 23% 13% 3	290
November	1st to 10th	Day	14% 11% 34% 26% 13% 4	200
	11th to 20th	Day	16% 8% 33% 27% 14% 3	200
	21st to end	Day	15% 9% 30% 33% 12% 2	200
December	1st to 10th	Day	15% 7% 20% 37% 18% 2	196
	11th to 20th	Day	14% 9% 33% 32% 9% 3	180
	21st to end	Day	10% 3 24% 34% 20% 8%	198
January	1st to 10th	Night	14% 8% 24% 37% 16% 2	1040
	11th to 20th	Night	15% 8% 29% 34% 13% 2	1040
	21st to end	Night	15% 12% 30% 31% 10% 2	1135
February	1st to 10th	Night	9% 8% 30% 35% 15% 3	767
	11th to 20th	Night	12% 8% 29% 36% 14% 2	744
	21st to end	Night	9% 6% 34% 32% 17% 3	628
March	1st to 10th	Night	7% 8% 28% 33% 20% 4	760
	11th to 20th	Night	11% 9% 33% 32% 14% 1	760
	21st to end	Night	9% 7% 25% 42% 16% 2	836
April	1st to 10th	Night	11% 9% 28% 32% 17% 2	712
	11th to 20th	Night	8% 7% 31% 36% 16% 2	493
	21st to end	Night	12% 11% 28% 33% 13% 2	380
May	1st to 10th	Night	11% 7% 28% 33% 18% 3	380
	11th to 20th	Night	10% 10% 23% 34% 21% 2	374
	21st to end	Night	11% 4 20% 38% 25% 1	411
June	1st to 10th	Night	13% 3 24% 36% 21% 3	380
	11th to 20th	Night	17% 4 20% 31% 25% 3	380
	21st to end	Night	11% 3 19% 37% 27% 4	380
July	1st to 10th	Night	14% 3 19% 31% 31% 2	370
	11th to 20th	Night	14% 2 16% 36% 28% 4	368
	21st to end	Night	12% 2 14% 32% 35% 6%	416
August	1st to 10th	Night	10% 4 19% 31% 29% 8%	378
	11th to 20th	Night	8% 3 23% 42% 22% 2	376
	21st to end	Night	16% 3 20% 31% 28% 2	503
September	1st to 10th	Night	15% 5% 21% 34% 21% 4	681
	11th to 20th	Night	12% 6% 22% 36% 20% 3	760
	21st to end	Night	13% 9% 27% 31% 17% 3	760
October	1st to 10th	Night	15% 8% 27% 34% 15% 2	760
	11th to 20th	Night	13% 8% 29% 34% 14% 1	760
	21st to end	Night	18% 10% 29% 30% 11% 2	864
November	1st to 10th	Night	19% 8% 29% 29% 13% 2	975
	11th to 20th	Night	20% 8% 26% 34% 11% 2	1000
	21st to end	Night	15% 9% 30% 32% 12% 2	1088
December	1st to 10th	Night	15% 8% 25% 36% 15% 1	1091
	11th to 20th	Night	14% 9% 28% 34% 12% 3	1040
	21st to end	Night	11% 6% 24% 38% 18% 3	1144

Page generated at 2024-12-06 01:54:51. Version ac07

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