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 2024-01-16.

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	10% 9% 4 8% 7% 4 6% 6% 6% 8% 33%	74398
	Night	8% 10% 4 9% 8% 4 6% 6% 6% 8% 31%	75405
Transparency	Day	47% 9% 17% 21% 6%	74050
	Night	50% 8% 15% 20% 7%	75271
Seeing	Day	13% 8% 25% 30% 18% 5%	15735
	Night	13% 7% 26% 34% 17% 3	23817

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	6% 11% 6% 10% 13% 6% 8% 7% 6% 6% 21%	1118
	11th to 20th	Day	10% 14% 6% 13% 7% 5% 7% 6% 8% 5% 20%	1112
	21st to end	Day	8% 12% 7% 12% 11% 6% 8% 6% 6% 5% 20%	1211
February	1st to 10th	Day	8% 11% 4 9% 9% 5% 6% 7% 7% 7% 28%	1426
	11th to 20th	Day	6% 13% 4 9% 9% 5% 6% 7% 7% 8% 27%	1400
	21st to end	Day	4 12% 6% 10% 10% 5% 6% 7% 7% 8% 26%	1331
March	1st to 10th	Day	4 10% 6% 12% 8% 5% 6% 7% 7% 8% 29%	1800
	11th to 20th	Day	9% 12% 5% 10% 8% 3 7% 5% 5% 6% 31%	1844
	21st to end	Day	5% 12% 5% 9% 7% 4 4 6% 6% 8% 35%	2358
April	1st to 10th	Day	5% 10% 3 9% 8% 4 5% 5% 7% 8% 34%	2204
	11th to 20th	Day	5% 8% 3 7% 9% 4 7% 6% 7% 8% 37%	2374
	21st to end	Day	10% 10% 4 9% 7% 5% 6% 6% 5% 8% 31%	2524
May	1st to 10th	Day	8% 7% 4 6% 6% 4 5% 6% 7% 8% 40%	2700
	11th to 20th	Day	10% 7% 4 5% 5% 3 5% 5% 6% 9% 42%	2781
	21st to end	Day	11% 5% 3 5% 6% 3 5% 5% 7% 9% 40%	3145
June	1st to 10th	Day	12% 8% 4 7% 6% 4 6% 6% 6% 8% 33%	3060
	11th to 20th	Day	16% 8% 3 7% 6% 4 5% 6% 7% 9% 29%	3060
	21st to end	Day	12% 6% 3 6% 6% 4 6% 7% 7% 11% 33%	3060
July	1st to 10th	Day	12% 6% 3 6% 6% 4 6% 6% 7% 9% 33%	3010
	11th to 20th	Day	12% 6% 3 6% 7% 4 7% 6% 7% 9% 33%	2880
	21st to end	Day	10% 5% 3 5% 6% 5% 6% 6% 7% 10% 37%	3135
August	1st to 10th	Day	10% 6% 3 5% 5% 4 6% 7% 7% 8% 38%	2706
	11th to 20th	Day	9% 6% 3 6% 6% 4 7% 7% 7% 8% 38%	2475
	21st to end	Day	15% 6% 3 6% 6% 4 5% 6% 6% 8% 35%	2692
September	1st to 10th	Day	14% 7% 3 6% 5% 3 6% 5% 5% 7% 39%	2232
	11th to 20th	Day	9% 7% 4 7% 6% 3 4 4 6% 8% 42%	2099
	21st to end	Day	11% 6% 3 7% 6% 4 5% 6% 6% 8% 38%	1980
October	1st to 10th	Day	12% 9% 4 7% 8% 4 5% 5% 6% 6% 34%	1778
	11th to 20th	Day	11% 13% 4 8% 6% 3 5% 5% 5% 9% 32%	1620
	21st to end	Day	12% 15% 5% 11% 7% 5% 5% 5% 5% 6% 23%	1666
November	1st to 10th	Day	11% 13% 6% 10% 10% 6% 5% 5% 5% 6% 25%	1302
	11th to 20th	Day	11% 16% 6% 10% 11% 3 6% 6% 5% 8% 20%	1330
	21st to end	Day	7% 11% 6% 12% 11% 3 5% 5% 6% 7% 26%	1098
December	1st to 10th	Day	7% 15% 7% 11% 10% 5% 7% 5% 5% 8% 21%	950
	11th to 20th	Day	7% 16% 6% 14% 9% 4 5% 5% 6% 7% 23%	1199
	21st to end	Day	5% 9% 5% 10% 8% 5% 6% 6% 5% 6% 34%	1738
January	1st to 10th	Night	8% 12% 6% 11% 10% 5% 7% 7% 6% 7% 19%	3045
	11th to 20th	Night	8% 14% 5% 11% 11% 6% 7% 7% 6% 6% 19%	2976
	21st to end	Night	7% 15% 6% 11% 11% 5% 6% 5% 5% 5% 23%	3159
February	1st to 10th	Night	5% 11% 5% 9% 8% 5% 6% 5% 6% 6% 34%	2534
	11th to 20th	Night	7% 12% 5% 9% 9% 4 7% 5% 6% 7% 29%	2446
	21st to end	Night	5% 9% 5% 9% 10% 4 8% 6% 5% 8% 31%	1924
March	1st to 10th	Night	5% 7% 5% 11% 7% 3 5% 5% 7% 7% 38%	2160
	11th to 20th	Night	7% 12% 6% 10% 7% 4 5% 5% 6% 5% 31%	2115
	21st to end	Night	5% 9% 5% 7% 7% 3 5% 6% 8% 8% 37%	1997
April	1st to 10th	Night	6% 9% 4 7% 7% 5% 6% 6% 6% 9% 33%	1755
	11th to 20th	Night	6% 7% 3 7% 9% 5% 7% 7% 6% 8% 36%	1535
	21st to end	Night	10% 9% 4 8% 7% 4 6% 5% 6% 9% 32%	1436
May	1st to 10th	Night	10% 7% 3 6% 7% 4 6% 7% 6% 7% 37%	1260
	11th to 20th	Night	7% 5% 4 5% 4 4 5% 6% 6% 8% 45%	1112
	21st to end	Night	11% 5% 3 5% 7% 3 5% 6% 5% 8% 43%	1128
June	1st to 10th	Night	11% 6% 2 9% 6% 4 6% 6% 4 9% 37%	900
	11th to 20th	Night	13% 8% 3 7% 6% 3 6% 6% 5% 8% 35%	900
	21st to end	Night	10% 5% 3 7% 7% 3 6% 7% 7% 9% 35%	900
July	1st to 10th	Night	11% 8% 2 5% 7% 3 6% 7% 7% 10% 35%	947
	11th to 20th	Night	11% 6% 3 5% 6% 4 6% 6% 8% 10% 36%	1080
	21st to end	Night	10% 5% 3 5% 5% 3 5% 7% 7% 12% 39%	1182
August	1st to 10th	Night	10% 4 2 4 4 3 6% 6% 7% 12% 43%	1231
	11th to 20th	Night	5% 5% 1 4 6% 4 6% 7% 8% 11% 42%	1424
	21st to end	Night	12% 6% 2 6% 6% 3 5% 6% 6% 9% 38%	1664
September	1st to 10th	Night	12% 7% 3 6% 6% 3 5% 5% 5% 8% 41%	1725
	11th to 20th	Night	10% 7% 2 6% 5% 4 5% 7% 7% 8% 40%	1860
	21st to end	Night	10% 6% 3 6% 7% 4 6% 7% 7% 9% 36%	1980
October	1st to 10th	Night	10% 8% 4 6% 7% 4 5% 5% 6% 9% 37%	2178
	11th to 20th	Night	8% 11% 4 7% 7% 4 5% 6% 6% 7% 35%	2340
	21st to end	Night	10% 14% 5% 10% 7% 4 5% 5% 7% 7% 27%	2670
November	1st to 10th	Night	12% 14% 5% 9% 8% 4 4 5% 5% 6% 27%	2775
	11th to 20th	Night	11% 15% 6% 11% 10% 5% 5% 6% 5% 6% 21%	2850
	21st to end	Night	9% 12% 6% 12% 9% 4 5% 5% 6% 7% 26%	3076
December	1st to 10th	Night	8% 11% 5% 10% 10% 6% 7% 6% 7% 8% 22%	3230
	11th to 20th	Night	8% 12% 6% 11% 9% 5% 6% 6% 5% 7% 25%	3993
	21st to end	Night	4 8% 5% 10% 8% 5% 7% 6% 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	61% 8% 11% 14% 6%	1118
	11th to 20th	Day	63% 8% 11% 13% 5% 1	1112
	21st to end	Day	64% 8% 10% 11% 7%	1211
February	1st to 10th	Day	53% 7% 12% 19% 10%	1426
	11th to 20th	Day	54% 7% 18% 17% 4	1408
	21st to end	Day	53% 9% 15% 17% 5%	1331
March	1st to 10th	Day	52% 8% 15% 21% 3 1	1800
	11th to 20th	Day	53% 6% 15% 20% 5%	1844
	21st to end	Day	45% 8% 16% 24% 6% 1	2358
April	1st to 10th	Day	45% 8% 15% 23% 9%	2204
	11th to 20th	Day	42% 8% 16% 23% 11% 1	2374
	21st to end	Day	50% 8% 14% 19% 8%	2524
May	1st to 10th	Day	40% 7% 16% 26% 11% 1	2700
	11th to 20th	Day	38% 6% 12% 25% 17% 1	2785
	21st to end	Day	39% 8% 12% 28% 13% 1	3146
June	1st to 10th	Day	47% 7% 15% 22% 8% 1	3060
	11th to 20th	Day	50% 9% 15% 20% 5%	3060
	21st to end	Day	42% 11% 20% 21% 5%	3060
July	1st to 10th	Day	43% 11% 20% 23% 3	2928
	11th to 20th	Day	45% 12% 24% 18% 1	2793
	21st to end	Day	39% 12% 23% 24% 1	2961
August	1st to 10th	Day	39% 13% 24% 21% 2	2687
	11th to 20th	Day	41% 11% 24% 21% 3	2475
	21st to end	Day	44% 10% 22% 21% 2	2692
September	1st to 10th	Day	42% 9% 24% 19% 5%	2232
	11th to 20th	Day	40% 9% 24% 26% 2	2099
	21st to end	Day	42% 10% 22% 22% 5%	1980
October	1st to 10th	Day	49% 6% 19% 21% 5%	1778
	11th to 20th	Day	49% 9% 18% 20% 4	1620
	21st to end	Day	61% 8% 14% 15% 3	1666
November	1st to 10th	Day	60% 8% 14% 16% 4	1302
	11th to 20th	Day	65% 7% 14% 11% 2	1330
	21st to end	Day	56% 7% 16% 17% 4	1098
December	1st to 10th	Day	63% 6% 12% 14% 4	950
	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	61% 8% 13% 12% 5%	3045
	11th to 20th	Night	63% 8% 13% 11% 4 1	2976
	21st to end	Night	62% 7% 12% 12% 8%	3159
February	1st to 10th	Night	50% 6% 14% 21% 10%	2534
	11th to 20th	Night	53% 7% 15% 20% 5%	2448
	21st to end	Night	49% 8% 14% 22% 7%	1924
March	1st to 10th	Night	43% 7% 16% 25% 9%	2160
	11th to 20th	Night	53% 6% 12% 23% 6%	2116
	21st to end	Night	41% 7% 15% 26% 9% 1	1997
April	1st to 10th	Night	46% 6% 14% 23% 9% 2	1755
	11th to 20th	Night	43% 7% 10% 24% 14% 1	1535
	21st to end	Night	47% 7% 13% 22% 11% 1	1436
May	1st to 10th	Night	42% 7% 11% 23% 14% 2	1260
	11th to 20th	Night	36% 7% 11% 24% 19% 2	1112
	21st to end	Night	37% 7% 11% 26% 18% 1	1128
June	1st to 10th	Night	44% 8% 12% 23% 11% 1	900
	11th to 20th	Night	47% 9% 15% 21% 8%	900
	21st to end	Night	41% 10% 19% 21% 9% 1	900
July	1st to 10th	Night	42% 12% 21% 21% 4	920
	11th to 20th	Night	43% 9% 22% 24% 2	1044
	21st to end	Night	35% 11% 23% 28% 3	1116
August	1st to 10th	Night	33% 12% 24% 25% 5%	1225
	11th to 20th	Night	31% 12% 26% 26% 4	1424
	21st to end	Night	40% 12% 19% 24% 5%	1664
September	1st to 10th	Night	40% 10% 19% 23% 8%	1725
	11th to 20th	Night	40% 9% 19% 26% 6%	1860
	21st to end	Night	41% 11% 18% 22% 8%	1980
October	1st to 10th	Night	42% 9% 18% 24% 7% 1	2178
	11th to 20th	Night	47% 7% 20% 21% 5%	2340
	21st to end	Night	57% 9% 15% 16% 3	2670
November	1st to 10th	Night	57% 8% 15% 17% 3	2775
	11th to 20th	Night	62% 8% 12% 15% 2	2850
	21st to end	Night	57% 7% 15% 17% 3 1	3076
December	1st to 10th	Night	58% 10% 14% 13% 5%	3230
	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	18% 9% 27% 32% 13% 1	171
	21st to end	Day	13% 11% 30% 31% 14% 1	176
February	1st to 10th	Day	18% 4 31% 29% 12% 6%	160
	11th to 20th	Day	13% 8% 33% 32% 12% 2	160
	21st to end	Day	7% 7% 35% 30% 17% 3	242
March	1st to 10th	Day	6% 11% 26% 33% 20% 4	420
	11th to 20th	Day	12% 11% 32% 29% 13% 3	420
	21st to end	Day	11% 11% 31% 34% 11% 2	462
April	1st to 10th	Day	8% 13% 35% 28% 14% 2	420
	11th to 20th	Day	8% 10% 30% 33% 16% 3	412
	21st to end	Day	13% 17% 28% 29% 13% 1	424
May	1st to 10th	Day	11% 13% 28% 30% 14% 4	603
	11th to 20th	Day	12% 11% 23% 29% 20% 4	750
	21st to end	Day	13% 7% 19% 33% 22% 6%	874
June	1st to 10th	Day	12% 8% 28% 30% 17% 5%	810
	11th to 20th	Day	20% 6% 21% 30% 20% 4	810
	21st to end	Day	12% 5% 18% 31% 25% 8%	810
July	1st to 10th	Day	14% 6% 21% 26% 27% 6%	796
	11th to 20th	Day	15% 5% 19% 31% 22% 9%	792
	21st to end	Day	12% 3 18% 30% 27% 9%	881
August	1st to 10th	Day	12% 5% 17% 27% 28% 11%	646
	11th to 20th	Day	11% 10% 33% 29% 13% 3	437
	21st to end	Day	20% 5% 25% 32% 14% 5%	495
September	1st to 10th	Day	17% 9% 30% 25% 15% 5%	450
	11th to 20th	Day	12% 10% 24% 28% 20% 5%	450
	21st to end	Day	11% 11% 33% 28% 13% 4	450
October	1st to 10th	Day	17% 11% 30% 27% 12% 2	405
	11th to 20th	Day	16% 8% 32% 30% 12% 3	270
	21st to end	Day	22% 11% 26% 24% 13% 3	261
November	1st to 10th	Day	14% 11% 34% 24% 13% 4	180
	11th to 20th	Day	17% 6% 34% 27% 13% 3	180
	21st to end	Day	17% 10% 32% 31% 11% 1	180
December	1st to 10th	Day	17% 6% 19% 38% 19% 2	180
	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% 9% 29% 33% 12% 2	1016
	21st to end	Night	15% 12% 31% 31% 9% 2	1069
February	1st to 10th	Night	9% 7% 30% 36% 15% 3	726
	11th to 20th	Night	13% 8% 30% 35% 13% 2	704
	21st to end	Night	9% 5% 34% 32% 16% 3	592
March	1st to 10th	Night	7% 8% 28% 33% 20% 4	720
	11th to 20th	Night	12% 8% 32% 32% 14% 2	720
	21st to end	Night	9% 7% 25% 41% 16% 2	792
April	1st to 10th	Night	11% 9% 27% 33% 18% 2	675
	11th to 20th	Night	8% 7% 32% 35% 16% 2	467
	21st to end	Night	12% 11% 28% 34% 12% 3	360
May	1st to 10th	Night	11% 7% 30% 32% 17% 3	360
	11th to 20th	Night	9% 9% 24% 34% 22% 2	354
	21st to end	Night	11% 4 20% 38% 25% 2	389
June	1st to 10th	Night	13% 3 23% 36% 22% 3	360
	11th to 20th	Night	17% 3 21% 31% 25% 4	360
	21st to end	Night	12% 3 19% 35% 28% 4	360
July	1st to 10th	Night	15% 3 19% 30% 32% 2	350
	11th to 20th	Night	14% 3 16% 36% 27% 4	348
	21st to end	Night	11% 2 14% 31% 35% 6%	394
August	1st to 10th	Night	11% 4 18% 30% 28% 8%	358
	11th to 20th	Night	8% 3 22% 42% 23% 2	356
	21st to end	Night	17% 3 18% 30% 29% 2	476
September	1st to 10th	Night	16% 5% 21% 33% 22% 4	645
	11th to 20th	Night	12% 6% 23% 37% 19% 3	720
	21st to end	Night	13% 8% 27% 31% 18% 3	720
October	1st to 10th	Night	15% 8% 27% 34% 15% 1	720
	11th to 20th	Night	13% 7% 29% 35% 15% 1	720
	21st to end	Night	19% 10% 28% 30% 12% 2	818
November	1st to 10th	Night	19% 8% 29% 29% 14% 2	925
	11th to 20th	Night	20% 8% 25% 34% 12% 2	950
	21st to end	Night	16% 9% 31% 31% 11% 2	1029
December	1st to 10th	Night	15% 8% 25% 36% 15% 2	1040
	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 2024-01-13 17:28:27. Version ac07

Copyright 2024 Attilla Danko