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 2024-09-29.

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 8% 6% 5% 5% 4 7% 8% 35%	102213
	Night	9% 10% 4 10% 6% 6% 5% 4 6% 8% 33%	96070
Transparency	Day	44% 8% 18% 22% 7%	101950
	Night	47% 8% 16% 20% 9% 1	95979
Seeing	Day	13% 6% 23% 31% 20% 7%	15943
	Night	13% 5% 26% 37% 17% 2	24289

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	5% 14% 6% 11% 11% 7% 7% 5% 7% 7% 20%	2151
	11th to 20th	Day	5% 10% 4 9% 6% 6% 5% 7% 8% 9% 31%	2199
	21st to end	Day	8% 12% 4 9% 6% 5% 6% 4 6% 7% 34%	2602
February	1st to 10th	Day	9% 13% 4 11% 7% 7% 6% 4 8% 8% 22%	1520
	11th to 20th	Day	6% 12% 7% 11% 6% 6% 7% 5% 8% 5% 27%	1585
	21st to end	Day	3 13% 6% 9% 9% 7% 6% 5% 6% 7% 29%	1465
March	1st to 10th	Day	4 12% 6% 13% 9% 5% 5% 4 5% 9% 28%	3138
	11th to 20th	Day	5% 9% 5% 10% 6% 4 4 5% 7% 9% 37%	3442
	21st to end	Day	7% 14% 5% 16% 6% 6% 5% 4 6% 7% 23%	3910
April	1st to 10th	Day	7% 12% 4 9% 5% 6% 6% 6% 7% 7% 31%	2370
	11th to 20th	Day	9% 12% 3 8% 5% 7% 6% 5% 6% 8% 33%	2440
	21st to end	Day	11% 11% 3 8% 5% 6% 6% 5% 7% 8% 32%	2478
May	1st to 10th	Day	18% 9% 3 6% 5% 5% 5% 4 6% 7% 32%	4694
	11th to 20th	Day	13% 9% 3 8% 5% 5% 6% 5% 7% 8% 31%	4694
	21st to end	Day	11% 8% 3 9% 7% 6% 6% 5% 7% 9% 27%	5161
June	1st to 10th	Day	15% 7% 3 8% 6% 6% 6% 5% 6% 7% 31%	2878
	11th to 20th	Day	19% 8% 3 8% 6% 5% 6% 5% 7% 8% 25%	3040
	21st to end	Day	9% 6% 2 6% 5% 5% 6% 5% 8% 9% 39%	3040
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 4 4 6% 8% 45%	5060
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 6% 9% 46%	4746
	21st to end	Day	13% 5% 2 5% 4 4 4 4 6% 8% 44%	5138
August	1st to 10th	Day	13% 6% 2 6% 4 4 4 3 6% 8% 43%	4539
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 5% 7% 9% 44%	4192
	21st to end	Day	11% 5% 2 7% 5% 5% 4 4 6% 9% 42%	4521
September	1st to 10th	Day	12% 5% 2 8% 5% 5% 5% 4 6% 7% 42%	2419
	11th to 20th	Day	14% 7% 2 5% 5% 5% 4 4 6% 7% 40%	2095
	21st to end	Day	9% 6% 2 7% 5% 4 5% 4 7% 9% 42%	2069
October	1st to 10th	Day	12% 8% 4 9% 4 5% 5% 3 5% 6% 39%	1879
	11th to 20th	Day	10% 8% 3 7% 5% 5% 6% 4 7% 8% 37%	1625
	21st to end	Day	9% 13% 4 9% 6% 5% 6% 4 6% 6% 31%	1756
November	1st to 10th	Day	10% 14% 5% 9% 8% 6% 6% 4 6% 6% 26%	1486
	11th to 20th	Day	9% 11% 5% 11% 6% 7% 4 3 6% 8% 30%	1330
	21st to end	Day	4 12% 5% 12% 7% 6% 4 4 7% 8% 30%	1330
December	1st to 10th	Day	6% 11% 4 12% 8% 8% 6% 4 7% 7% 28%	1330
	11th to 20th	Day	7% 11% 4 11% 6% 7% 8% 6% 6% 8% 26%	1682
	21st to end	Day	4 6% 3 8% 7% 5% 6% 5% 8% 8% 41%	2209
January	1st to 10th	Night	4 11% 5% 16% 8% 7% 7% 4 6% 7% 24%	4787
	11th to 20th	Night	4 9% 3 9% 7% 7% 8% 5% 7% 6% 34%	4699
	21st to end	Night	8% 13% 5% 10% 7% 6% 5% 4 6% 8% 29%	5084
February	1st to 10th	Night	6% 12% 5% 12% 10% 7% 7% 4 5% 6% 26%	2660
	11th to 20th	Night	6% 12% 4 10% 7% 7% 6% 5% 7% 7% 28%	2481
	21st to end	Night	4 12% 5% 9% 7% 6% 6% 6% 7% 8% 30%	1985
March	1st to 10th	Night	3 9% 5% 13% 8% 6% 6% 4 6% 10% 29%	3736
	11th to 20th	Night	5% 9% 3 10% 6% 5% 5% 4 7% 10% 35%	3537
	21st to end	Night	8% 12% 6% 16% 7% 6% 5% 4 6% 6% 24%	3741
April	1st to 10th	Night	8% 10% 3 9% 7% 8% 6% 6% 6% 7% 30%	1810
	11th to 20th	Night	10% 12% 4 8% 7% 6% 5% 5% 7% 6% 30%	1691
	21st to end	Night	11% 10% 3 8% 5% 5% 5% 5% 6% 7% 35%	1701
May	1st to 10th	Night	21% 9% 3 8% 5% 4 5% 4 5% 5% 31%	2265
	11th to 20th	Night	12% 11% 3 9% 6% 6% 6% 5% 6% 8% 29%	2199
	21st to end	Night	12% 9% 3 8% 6% 7% 5% 5% 7% 9% 28%	2414
June	1st to 10th	Night	15% 9% 3 7% 5% 5% 7% 4 7% 7% 31%	1297
	11th to 20th	Night	16% 10% 3 9% 6% 5% 7% 6% 8% 9% 22%	1140
	21st to end	Night	9% 6% 3 7% 6% 6% 4 5% 9% 7% 36%	1140
July	1st to 10th	Night	9% 6% 2 6% 4 4 5% 5% 5% 8% 46%	1900
	11th to 20th	Night	8% 4 3 6% 4 5% 6% 6% 6% 11% 42%	2210
	21st to end	Night	14% 6% 2 5% 5% 4 4 4 6% 9% 42%	2414
August	1st to 10th	Night	11% 6% 2 6% 5% 5% 5% 4 6% 7% 43%	2390
	11th to 20th	Night	13% 7% 3 7% 5% 4 4 4 6% 8% 39%	2640
	21st to end	Night	14% 4 2 5% 4 4 4 4 6% 9% 44%	3146
September	1st to 10th	Night	12% 6% 3 6% 3 5% 4 3 5% 8% 45%	1757
	11th to 20th	Night	12% 8% 2 5% 5% 3 5% 4 5% 7% 44%	2085
	21st to end	Night	10% 7% 2 7% 5% 4 5% 3 6% 8% 44%	2079
October	1st to 10th	Night	12% 9% 3 8% 5% 5% 4 3 5% 8% 38%	2080
	11th to 20th	Night	11% 6% 4 8% 5% 4 5% 5% 6% 9% 38%	2332
	21st to end	Night	9% 12% 4 10% 6% 6% 5% 4 5% 6% 33%	2582
November	1st to 10th	Night	13% 15% 4 9% 7% 5% 5% 4 5% 7% 26%	2590
	11th to 20th	Night	8% 13% 5% 12% 6% 7% 6% 5% 6% 6% 27%	2850
	21st to end	Night	6% 13% 5% 12% 7% 5% 5% 4 6% 8% 28%	2850
December	1st to 10th	Night	7% 13% 4 11% 6% 6% 5% 4 6% 7% 30%	2850
	11th to 20th	Night	9% 13% 5% 12% 7% 6% 5% 5% 7% 7% 25%	3510
	21st to end	Night	4 7% 3 8% 5% 5% 5% 4 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%	1520
	11th to 20th	Day	52% 9% 15% 17% 7%	1593
	21st to end	Day	51% 8% 15% 20% 6%	1465
March	1st to 10th	Day	52% 6% 16% 20% 6%	3138
	11th to 20th	Day	40% 10% 20% 21% 9%	3443
	21st to end	Day	56% 8% 16% 17% 3	3910
April	1st to 10th	Day	47% 10% 19% 17% 7% 1	2370
	11th to 20th	Day	47% 7% 16% 22% 8%	2440
	21st to end	Day	48% 7% 17% 20% 6% 1	2478
May	1st to 10th	Day	49% 7% 11% 24% 9%	4694
	11th to 20th	Day	45% 9% 13% 25% 8% 1	4698
	21st to end	Day	47% 10% 19% 15% 8%	5162
June	1st to 10th	Day	49% 8% 15% 20% 7% 1	2878
	11th to 20th	Day	54% 10% 17% 15% 4	3040
	21st to end	Day	38% 11% 23% 21% 6%	3040
July	1st to 10th	Day	34% 8% 17% 28% 12% 1	4981
	11th to 20th	Day	32% 9% 18% 28% 12%	4664
	21st to end	Day	37% 8% 22% 24% 8%	4976
August	1st to 10th	Day	36% 10% 21% 31% 2	4521
	11th to 20th	Day	33% 9% 24% 24% 9%	4234
	21st to end	Day	37% 9% 28% 23% 4	4520
September	1st to 10th	Day	40% 8% 21% 23% 7% 1	2419
	11th to 20th	Day	41% 6% 22% 24% 7%	2095
	21st to end	Day	37% 10% 17% 26% 8% 2	2069
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	2660
	11th to 20th	Night	51% 7% 17% 15% 9% 1	2483
	21st to end	Night	48% 8% 15% 20% 8% 1	1985
March	1st to 10th	Night	48% 6% 18% 21% 7%	3736
	11th to 20th	Night	40% 8% 22% 19% 11% 1	3537
	21st to end	Night	55% 9% 13% 16% 6%	3741
April	1st to 10th	Night	47% 10% 14% 18% 10% 1	1810
	11th to 20th	Night	50% 6% 13% 17% 12% 2	1691
	21st to end	Night	45% 8% 10% 23% 13% 1	1701
May	1st to 10th	Night	52% 6% 10% 20% 11% 1	2265
	11th to 20th	Night	47% 10% 12% 20% 10% 1	2199
	21st to end	Night	47% 9% 19% 16% 9% 1	2414
June	1st to 10th	Night	48% 7% 15% 18% 10% 1	1297
	11th to 20th	Night	54% 10% 15% 17% 4	1140
	21st to end	Night	40% 10% 23% 21% 6%	1140
July	1st to 10th	Night	35% 8% 17% 25% 14% 1	1870
	11th to 20th	Night	33% 10% 18% 28% 10%	2169
	21st to end	Night	38% 7% 20% 27% 8%	2337
August	1st to 10th	Night	38% 10% 21% 30% 2	2383
	11th to 20th	Night	41% 9% 19% 21% 10%	2664
	21st to end	Night	35% 8% 25% 26% 5%	3146
September	1st to 10th	Night	37% 8% 17% 28% 8% 2	1757
	11th to 20th	Night	37% 6% 18% 28% 9% 1	2085
	21st to end	Night	38% 7% 15% 26% 11% 2	2079
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% 34% 14% 6%	180
	11th to 20th	Day	10% 5% 27% 32% 17% 9%	231
	21st to end	Day	5% 6% 27% 36% 18% 8%	277
March	1st to 10th	Day	11% 6% 26% 35% 20% 3	460
	11th to 20th	Day	11% 4 24% 37% 18% 7%	460
	21st to end	Day	14% 6% 24% 32% 21% 4	506
April	1st to 10th	Day	10% 6% 29% 35% 17% 4	460
	11th to 20th	Day	14% 6% 21% 34% 18% 7%	452
	21st to end	Day	14% 9% 24% 32% 15% 6%	460
May	1st to 10th	Day	14% 8% 25% 29% 19% 4	620
	11th to 20th	Day	11% 6% 24% 33% 20% 6%	675
	21st to end	Day	15% 5% 20% 31% 20% 9%	734
June	1st to 10th	Day	18% 7% 25% 29% 17% 4	708
	11th to 20th	Day	20% 7% 19% 27% 20% 7%	870
	21st to end	Day	12% 4 17% 29% 28% 10%	870
July	1st to 10th	Day	12% 4 17% 31% 27% 9%	856
	11th to 20th	Day	13% 3 20% 29% 27% 9%	673
	21st to end	Day	12% 3 17% 31% 26% 11%	739
August	1st to 10th	Day	13% 5% 16% 29% 22% 15%	573
	11th to 20th	Day	7% 6% 23% 34% 23% 8%	477
	21st to end	Day	10% 6% 23% 29% 23% 9%	539
September	1st to 10th	Day	17% 8% 25% 25% 17% 8%	490
	11th to 20th	Day	19% 8% 21% 29% 20% 3	490
	21st to end	Day	11% 10% 33% 26% 18% 3	483
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% 19% 3	760
	11th to 20th	Night	10% 5% 29% 36% 19% 2	744
	21st to end	Night	8% 4 26% 37% 20% 6%	628
March	1st to 10th	Night	8% 5% 27% 38% 17% 4	760
	11th to 20th	Night	12% 4 30% 36% 16% 2	760
	21st to end	Night	14% 5% 25% 36% 18% 2	836
April	1st to 10th	Night	11% 5% 25% 40% 17% 2	670
	11th to 20th	Night	16% 3 26% 36% 16% 2	563
	21st to end	Night	15% 6% 24% 38% 16% 1	561
May	1st to 10th	Night	14% 6% 25% 36% 18% 2	380
	11th to 20th	Night	13% 4 25% 39% 18% 2	374
	21st to end	Night	19% 5% 22% 33% 20% 1	411
June	1st to 10th	Night	19% 7% 21% 38% 14% 2	380
	11th to 20th	Night	19% 6% 18% 32% 22% 3	380
	21st to end	Night	11% 4 15% 41% 25% 5%	380
July	1st to 10th	Night	14% 2 16% 39% 28% 1	370
	11th to 20th	Night	12% 2 18% 40% 24% 3	368
	21st to end	Night	12% 3 13% 41% 27% 4	416
August	1st to 10th	Night	10% 4 14% 36% 30% 6%	378
	11th to 20th	Night	11% 3 19% 40% 25% 2	454
	21st to end	Night	13% 3 19% 42% 22% 1	627
September	1st to 10th	Night	15% 2 19% 39% 22% 2	617
	11th to 20th	Night	13% 5% 18% 42% 20% 1	760
	21st to end	Night	13% 6% 27% 38% 14% 2	756
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 2024-09-26 07:52:20. Version ac07

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