Westlock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Westlock clear sky chart from 2005-11-06 to 2024-02-05.

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% 8% 4 7% 7% 4 6% 6% 7% 8% 34%	77875
	Night	9% 9% 4 8% 7% 4 6% 6% 6% 8% 33%	80915
Transparency	Day	46% 9% 18% 20% 7% 1	77570
	Night	47% 8% 16% 20% 9% 1	80800
Seeing	Day	13% 6% 23% 31% 20% 7%	14900
	Night	13% 5% 26% 37% 17% 2	23602

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% 12% 7% 9% 12% 6% 7% 6% 7% 7% 20%	2151
	11th to 20th	Day	5% 9% 5% 8% 7% 4 6% 8% 8% 9% 31%	2199
	21st to end	Day	8% 11% 4 8% 7% 4 6% 5% 6% 7% 34%	2602
February	1st to 10th	Day	9% 11% 5% 9% 9% 5% 7% 7% 8% 8% 23%	1472
	11th to 20th	Day	6% 11% 8% 9% 7% 5% 7% 7% 8% 6% 25%	1500
	21st to end	Day	4 11% 6% 9% 9% 5% 7% 7% 6% 7% 29%	1381
March	1st to 10th	Day	7% 14% 7% 9% 9% 5% 7% 6% 6% 8% 22%	1800
	11th to 20th	Day	9% 10% 6% 9% 7% 4 5% 6% 6% 6% 32%	1945
	21st to end	Day	9% 15% 7% 10% 6% 4 6% 6% 6% 8% 24%	2225
April	1st to 10th	Day	8% 10% 5% 8% 7% 4 7% 7% 7% 7% 31%	2245
	11th to 20th	Day	9% 11% 4 7% 6% 5% 6% 6% 6% 8% 32%	2310
	21st to end	Day	11% 9% 4 7% 6% 4 6% 6% 7% 8% 33%	2347
May	1st to 10th	Day	13% 8% 4 6% 7% 4 7% 6% 8% 8% 29%	2668
	11th to 20th	Day	10% 5% 2 5% 6% 3 6% 6% 7% 10% 41%	2654
	21st to end	Day	16% 7% 3 6% 5% 4 5% 5% 6% 7% 36%	2917
June	1st to 10th	Day	16% 6% 3 7% 6% 4 6% 6% 6% 8% 31%	2726
	11th to 20th	Day	20% 7% 4 7% 7% 4 6% 6% 7% 8% 24%	2880
	21st to end	Day	9% 5% 3 5% 6% 3 6% 6% 8% 9% 39%	2880
July	1st to 10th	Day	13% 5% 3 5% 6% 4 5% 5% 7% 9% 39%	2880
	11th to 20th	Day	12% 5% 3 5% 6% 3 6% 6% 7% 10% 36%	2706
	21st to end	Day	10% 4 2 5% 5% 3 5% 6% 7% 9% 44%	2938
August	1st to 10th	Day	10% 5% 2 6% 5% 4 6% 5% 8% 10% 39%	2589
	11th to 20th	Day	7% 5% 3 6% 5% 4 5% 6% 7% 10% 43%	2402
	21st to end	Day	10% 5% 2 6% 7% 4 5% 5% 6% 9% 40%	2574
September	1st to 10th	Day	13% 5% 2 7% 6% 3 5% 5% 6% 7% 40%	2292
	11th to 20th	Day	15% 6% 2 5% 5% 3 5% 5% 6% 7% 40%	1985
	21st to end	Day	9% 6% 2 6% 6% 3 5% 6% 7% 9% 42%	1980
October	1st to 10th	Day	12% 8% 4 8% 6% 3 5% 4 5% 6% 39%	1879
	11th to 20th	Day	10% 7% 4 6% 6% 3 7% 5% 7% 8% 37%	1625
	21st to end	Day	10% 13% 4 8% 7% 4 6% 5% 6% 6% 31%	1756
November	1st to 10th	Day	10% 12% 6% 8% 8% 5% 7% 6% 6% 6% 26%	1486
	11th to 20th	Day	9% 10% 6% 10% 7% 5% 5% 4 6% 8% 30%	1330
	21st to end	Day	4 11% 6% 11% 8% 5% 5% 5% 7% 8% 30%	1330
December	1st to 10th	Day	6% 9% 5% 11% 9% 6% 7% 5% 6% 7% 28%	1330
	11th to 20th	Day	8% 10% 4 10% 7% 6% 7% 7% 6% 8% 26%	1682
	21st to end	Day	4 6% 3 7% 8% 4 6% 6% 8% 8% 41%	2209
January	1st to 10th	Night	4 11% 6% 14% 11% 5% 7% 6% 6% 7% 25%	4787
	11th to 20th	Night	4 9% 4 8% 8% 5% 8% 7% 7% 7% 34%	4699
	21st to end	Night	8% 13% 5% 9% 8% 4 5% 5% 6% 8% 29%	5084
February	1st to 10th	Night	7% 10% 6% 11% 11% 5% 7% 5% 5% 7% 26%	2582
	11th to 20th	Night	7% 11% 6% 9% 9% 6% 7% 6% 7% 7% 27%	2346
	21st to end	Night	5% 10% 5% 8% 8% 5% 6% 7% 7% 9% 31%	1871
March	1st to 10th	Night	6% 10% 5% 9% 9% 5% 7% 4 5% 8% 31%	2160
	11th to 20th	Night	9% 10% 4 8% 8% 4 6% 6% 7% 10% 29%	2014
	21st to end	Night	10% 13% 5% 9% 7% 4 5% 6% 6% 8% 28%	2129
April	1st to 10th	Night	9% 10% 3 8% 8% 5% 7% 7% 6% 7% 31%	1715
	11th to 20th	Night	11% 11% 4 7% 8% 4 5% 6% 7% 6% 30%	1601
	21st to end	Night	12% 9% 4 6% 6% 4 5% 5% 6% 8% 35%	1612
May	1st to 10th	Night	11% 8% 4 9% 8% 4 7% 6% 7% 8% 30%	1291
	11th to 20th	Night	12% 8% 3 5% 6% 4 5% 5% 6% 8% 38%	1239
	21st to end	Night	17% 9% 3 6% 7% 4 5% 5% 5% 8% 31%	1358
June	1st to 10th	Night	15% 8% 3 6% 6% 4 7% 6% 6% 8% 31%	1229
	11th to 20th	Night	16% 9% 4 9% 6% 4 8% 8% 7% 9% 21%	1080
	21st to end	Night	8% 6% 4 6% 7% 4 5% 6% 9% 8% 36%	1080
July	1st to 10th	Night	11% 6% 2 5% 6% 3 5% 7% 7% 9% 39%	1080
	11th to 20th	Night	10% 4 3 5% 6% 4 7% 7% 7% 10% 36%	1250
	21st to end	Night	10% 5% 3 4 6% 3 4 5% 6% 9% 44%	1379
August	1st to 10th	Night	8% 5% 2 5% 7% 4 6% 7% 7% 10% 41%	1349
	11th to 20th	Night	9% 5% 3 6% 5% 3 4 5% 6% 9% 44%	1497
	21st to end	Night	13% 5% 2 6% 6% 4 5% 5% 6% 9% 39%	1782
September	1st to 10th	Night	13% 6% 3 6% 4 4 4 4 5% 8% 44%	1664
	11th to 20th	Night	12% 8% 3 4 5% 2 5% 5% 5% 7% 45%	1975
	21st to end	Night	10% 7% 2 5% 6% 3 5% 4 6% 8% 45%	1980
October	1st to 10th	Night	12% 8% 3 7% 7% 4 4 5% 5% 7% 39%	2080
	11th to 20th	Night	11% 6% 4 6% 6% 4 4 6% 6% 10% 38%	2332
	21st to end	Night	9% 12% 4 9% 7% 4 5% 5% 5% 6% 33%	2582
November	1st to 10th	Night	13% 14% 6% 8% 8% 4 5% 5% 5% 7% 26%	2590
	11th to 20th	Night	8% 12% 6% 10% 7% 5% 6% 6% 6% 6% 27%	2850
	21st to end	Night	6% 11% 6% 11% 8% 4 6% 5% 6% 8% 28%	2850
December	1st to 10th	Night	8% 11% 5% 10% 7% 5% 5% 5% 6% 7% 30%	2850
	11th to 20th	Night	9% 12% 5% 10% 9% 5% 6% 6% 6% 7% 25%	3510
	21st to end	Night	4 6% 4 8% 6% 4 6% 5% 7% 9% 42%	5438

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	58% 8% 14% 16% 4 1	2151
	11th to 20th	Day	47% 6% 13% 15% 18% 2	2220
	21st to end	Day	47% 7% 21% 19% 6%	2602
February	1st to 10th	Day	55% 8% 15% 15% 7%	1472
	11th to 20th	Day	54% 9% 16% 16% 5%	1508
	21st to end	Day	51% 8% 15% 20% 6%	1381
March	1st to 10th	Day	58% 8% 15% 14% 5%	1800
	11th to 20th	Day	49% 9% 14% 19% 9% 1	1946
	21st to end	Day	57% 8% 15% 16% 4	2225
April	1st to 10th	Day	48% 10% 19% 17% 6%	2245
	11th to 20th	Day	48% 7% 16% 21% 7%	2310
	21st to end	Day	47% 7% 18% 20% 6% 2	2347
May	1st to 10th	Day	48% 9% 14% 19% 9%	2668
	11th to 20th	Day	37% 8% 14% 30% 11% 1	2658
	21st to end	Day	45% 8% 14% 21% 11% 1	2918
June	1st to 10th	Day	50% 8% 15% 20% 6%	2726
	11th to 20th	Day	55% 10% 17% 14% 4	2880
	21st to end	Day	38% 11% 24% 21% 5% 1	2880
July	1st to 10th	Day	40% 9% 20% 25% 5% 1	2801
	11th to 20th	Day	40% 12% 27% 20% 1	2624
	21st to end	Day	34% 11% 27% 26% 2	2775
August	1st to 10th	Day	37% 12% 29% 19% 3	2571
	11th to 20th	Day	34% 10% 26% 25% 5%	2402
	21st to end	Day	38% 9% 24% 23% 6%	2574
September	1st to 10th	Day	42% 8% 21% 21% 6% 1	2292
	11th to 20th	Day	41% 6% 22% 24% 7%	1985
	21st to end	Day	37% 11% 17% 26% 8% 2	1980
October	1st to 10th	Day	46% 6% 18% 21% 8% 1	1879
	11th to 20th	Day	41% 10% 18% 24% 6%	1625
	21st to end	Day	50% 9% 13% 23% 5%	1756
November	1st to 10th	Day	56% 7% 15% 15% 6% 1	1486
	11th to 20th	Day	52% 7% 18% 18% 5%	1330
	21st to end	Day	51% 9% 16% 18% 5% 1	1330
December	1st to 10th	Day	53% 8% 13% 17% 8% 1	1330
	11th to 20th	Day	51% 9% 17% 16% 6%	1684
	21st to end	Day	38% 7% 12% 26% 15% 2	2209
January	1st to 10th	Night	56% 8% 13% 15% 6% 1	4787
	11th to 20th	Night	46% 8% 13% 17% 16% 1	4740
	21st to end	Night	52% 6% 20% 15% 6%	5084
February	1st to 10th	Night	56% 7% 13% 15% 8% 1	2582
	11th to 20th	Night	53% 7% 17% 15% 8%	2348
	21st to end	Night	47% 8% 15% 20% 8% 1	1871
March	1st to 10th	Night	50% 7% 15% 21% 6% 1	2160
	11th to 20th	Night	48% 6% 14% 20% 10% 1	2014
	21st to end	Night	52% 8% 16% 17% 7% 1	2129
April	1st to 10th	Night	47% 10% 14% 18% 10% 1	1715
	11th to 20th	Night	51% 6% 12% 17% 12% 2	1601
	21st to end	Night	45% 8% 10% 23% 13% 1	1612
May	1st to 10th	Night	49% 7% 15% 19% 10% 1	1291
	11th to 20th	Night	42% 7% 11% 24% 15% 1	1239
	21st to end	Night	50% 6% 14% 18% 11% 1	1358
June	1st to 10th	Night	49% 8% 16% 18% 9% 1	1229
	11th to 20th	Night	55% 10% 15% 16% 4	1080
	21st to end	Night	39% 10% 23% 22% 5%	1080
July	1st to 10th	Night	39% 9% 21% 24% 6% 1	1050
	11th to 20th	Night	39% 13% 24% 21% 3	1209
	21st to end	Night	33% 9% 25% 29% 4	1302
August	1st to 10th	Night	35% 13% 25% 25% 2	1342
	11th to 20th	Night	34% 10% 23% 26% 6% 1	1497
	21st to end	Night	40% 9% 17% 25% 8% 1	1782
September	1st to 10th	Night	38% 8% 18% 27% 7% 2	1664
	11th to 20th	Night	37% 6% 19% 28% 9% 1	1975
	21st to end	Night	37% 7% 15% 27% 12% 2	1980
October	1st to 10th	Night	44% 7% 15% 24% 10%	2080
	11th to 20th	Night	42% 8% 16% 25% 9%	2332
	21st to end	Night	49% 8% 12% 23% 7% 1	2582
November	1st to 10th	Night	57% 6% 12% 19% 6%	2590
	11th to 20th	Night	55% 8% 13% 17% 6%	2850
	21st to end	Night	53% 9% 16% 17% 4 1	2850
December	1st to 10th	Night	52% 7% 13% 19% 9% 1	2850
	11th to 20th	Night	55% 7% 16% 15% 6%	3507
	21st to end	Night	37% 7% 17% 22% 14% 2	5438

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% 5% 21% 38% 21% 6%	180
	11th to 20th	Day	10% 7% 28% 32% 18% 6%	180
	21st to end	Day	12% 7% 26% 32% 18% 5%	198
February	1st to 10th	Day	12% 9% 24% 36% 13% 7%	168
	11th to 20th	Day	12% 6% 29% 32% 15% 7%	206
	21st to end	Day	5% 4 26% 36% 20% 9%	247
March	1st to 10th	Day	12% 6% 24% 35% 20% 3	420
	11th to 20th	Day	12% 3 24% 36% 18% 7%	420
	21st to end	Day	14% 6% 22% 32% 22% 4	462
April	1st to 10th	Day	9% 5% 28% 36% 18% 4	420
	11th to 20th	Day	15% 5% 20% 34% 19% 7%	412
	21st to end	Day	14% 8% 24% 33% 15% 6%	420
May	1st to 10th	Day	13% 8% 26% 29% 20% 5%	571
	11th to 20th	Day	11% 5% 24% 33% 21% 6%	625
	21st to end	Day	16% 4 19% 32% 20% 9%	679
June	1st to 10th	Day	18% 6% 23% 31% 18% 4	656
	11th to 20th	Day	20% 6% 18% 28% 20% 7%	810
	21st to end	Day	11% 4 17% 30% 28% 10%	810
July	1st to 10th	Day	13% 4 17% 32% 26% 9%	796
	11th to 20th	Day	13% 3 20% 30% 26% 8%	623
	21st to end	Day	11% 2 17% 31% 27% 12%	684
August	1st to 10th	Day	13% 5% 16% 29% 22% 16%	529
	11th to 20th	Day	7% 6% 24% 32% 23% 7%	437
	21st to end	Day	10% 6% 22% 29% 22% 10%	495
September	1st to 10th	Day	18% 8% 26% 26% 16% 6%	450
	11th to 20th	Day	19% 8% 22% 30% 19% 3	450
	21st to end	Day	11% 10% 31% 26% 19% 3	450
October	1st to 10th	Day	17% 6% 26% 27% 19% 5%	349
	11th to 20th	Day	13% 7% 29% 32% 16% 3	270
	21st to end	Day	14% 11% 36% 22% 14% 3	297
November	1st to 10th	Day	19% 4 24% 35% 15% 2	268
	11th to 20th	Day	13% 4 33% 32% 13% 5%	180
	21st to end	Day	7% 7% 34% 34% 10% 8%	180
December	1st to 10th	Day	7% 7% 26% 39% 16% 5%	180
	11th to 20th	Day	11% 6% 28% 38% 15% 3	180
	21st to end	Day	7% 3 21% 39% 22% 8%	198
January	1st to 10th	Night	11% 4 30% 37% 15% 2	966
	11th to 20th	Night	12% 6% 28% 38% 13% 2	950
	21st to end	Night	16% 8% 31% 31% 11% 2	967
February	1st to 10th	Night	9% 6% 27% 35% 20% 3	738
	11th to 20th	Night	10% 6% 29% 35% 18% 2	704
	21st to end	Night	8% 3 26% 37% 20% 6%	592
March	1st to 10th	Night	9% 5% 27% 38% 18% 4	720
	11th to 20th	Night	12% 4 29% 36% 17% 2	720
	21st to end	Night	15% 4 24% 36% 18% 2	792
April	1st to 10th	Night	12% 4 23% 40% 18% 3	635
	11th to 20th	Night	16% 3 27% 36% 16% 2	533
	21st to end	Night	15% 6% 24% 38% 16% 1	532
May	1st to 10th	Night	13% 5% 25% 37% 18% 2	360
	11th to 20th	Night	13% 4 23% 39% 18% 2	354
	21st to end	Night	20% 4 21% 33% 20% 2	389
June	1st to 10th	Night	19% 7% 19% 39% 14% 2	360
	11th to 20th	Night	20% 5% 17% 32% 23% 4	360
	21st to end	Night	10% 4 14% 40% 26% 5%	360
July	1st to 10th	Night	14% 2 17% 38% 28% 1	350
	11th to 20th	Night	13% 3 18% 41% 23% 3	348
	21st to end	Night	11% 3 12% 42% 26% 4	394
August	1st to 10th	Night	10% 4 14% 36% 31% 5%	358
	11th to 20th	Night	11% 2 19% 40% 25% 2	429
	21st to end	Night	13% 3 18% 42% 23% 1	594
September	1st to 10th	Night	16% 3 19% 39% 22% 2	584
	11th to 20th	Night	14% 5% 19% 41% 20% 1	720
	21st to end	Night	13% 5% 26% 39% 14% 2	720
October	1st to 10th	Night	17% 3 25% 40% 14% 2	720
	11th to 20th	Night	13% 4 28% 39% 14% 2	720
	21st to end	Night	15% 7% 31% 33% 14% 1	800
November	1st to 10th	Night	19% 6% 29% 34% 11% 2	925
	11th to 20th	Night	14% 6% 33% 33% 11% 3	950
	21st to end	Night	9% 6% 35% 37% 12% 1	950
December	1st to 10th	Night	13% 6% 30% 32% 15% 4	950
	11th to 20th	Night	12% 7% 30% 35% 14% 2	950
	21st to end	Night	11% 3 26% 40% 18% 3	1108

Page generated at 2024-02-02 03:20:30. Version ac07

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