Norman Wells
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norman Wells 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	9% 10% 4 10% 7% 6% 6% 5% 7% 8% 28%	107744
	Night	6% 12% 5% 14% 8% 7% 7% 5% 7% 8% 22%	100495
Transparency	Day	50% 10% 17% 17% 5% 1	107398
	Night	56% 9% 14% 15% 6% 1	100487
Seeing	Day	16% 6% 19% 29% 22% 8%	17747
	Night	13% 6% 19% 32% 24% 6%	23222

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	3 8% 5% 16% 10% 6% 9% 6% 10% 13% 15%	939
	11th to 20th	Day	4 10% 7% 11% 12% 11% 5% 5% 6% 6% 23%	1058
	21st to end	Day	4 12% 4 13% 10% 7% 7% 7% 9% 8% 18%	1710
February	1st to 10th	Day	3 9% 3 11% 9% 7% 9% 7% 8% 11% 22%	1170
	11th to 20th	Day	3 10% 4 14% 11% 11% 7% 6% 9% 10% 15%	1321
	21st to end	Day	2 7% 6% 16% 12% 10% 7% 5% 7% 8% 20%	1337
March	1st to 10th	Day	1 8% 5% 17% 11% 8% 9% 6% 7% 6% 21%	2877
	11th to 20th	Day	4 16% 8% 19% 12% 7% 6% 5% 6% 5% 11%	3425
	21st to end	Day	3 9% 5% 17% 8% 7% 7% 6% 7% 7% 23%	4027
April	1st to 10th	Day	6% 15% 6% 11% 8% 7% 6% 5% 6% 7% 23%	2470
	11th to 20th	Day	7% 12% 5% 10% 6% 6% 6% 5% 7% 7% 29%	2650
	21st to end	Day	7% 12% 4 10% 6% 5% 5% 4 7% 9% 31%	2855
May	1st to 10th	Day	8% 10% 4 10% 5% 6% 6% 5% 7% 9% 30%	5279
	11th to 20th	Day	7% 9% 3 9% 6% 6% 7% 5% 8% 9% 31%	5446
	21st to end	Day	13% 10% 3 8% 6% 5% 5% 5% 6% 7% 32%	6544
June	1st to 10th	Day	11% 9% 3 7% 5% 6% 6% 4 7% 9% 32%	3735
	11th to 20th	Day	12% 7% 3 8% 5% 6% 6% 6% 8% 10% 30%	3990
	21st to end	Day	11% 7% 2 6% 5% 4 5% 5% 7% 9% 38%	3990
July	1st to 10th	Day	12% 9% 4 11% 7% 7% 7% 5% 7% 9% 21%	6288
	11th to 20th	Day	8% 6% 3 7% 6% 6% 6% 6% 9% 10% 32%	6020
	21st to end	Day	11% 7% 3 7% 6% 6% 6% 5% 7% 8% 36%	6047
August	1st to 10th	Day	8% 5% 2 5% 5% 4 5% 4 5% 8% 48%	5325
	11th to 20th	Day	15% 8% 3 6% 5% 5% 5% 5% 7% 9% 32%	4657
	21st to end	Day	14% 12% 4 10% 7% 6% 6% 4 6% 8% 21%	4975
September	1st to 10th	Day	14% 9% 3 7% 6% 5% 5% 5% 7% 8% 30%	2470
	11th to 20th	Day	12% 10% 3 10% 6% 5% 5% 4 5% 8% 33%	2251
	21st to end	Day	16% 19% 5% 11% 6% 4 4 4 5% 6% 20%	2060
October	1st to 10th	Day	9% 13% 5% 10% 5% 4 4 3 6% 6% 35%	3034
	11th to 20th	Day	6% 13% 4 14% 7% 6% 6% 5% 6% 7% 26%	2664
	21st to end	Day	6% 15% 6% 17% 11% 8% 8% 5% 5% 5% 13%	2509
November	1st to 10th	Day	6% 15% 7% 17% 8% 7% 7% 3 5% 9% 17%	1176
	11th to 20th	Day	5% 17% 7% 16% 10% 8% 7% 4 8% 6% 12%	930
	21st to end	Day	5% 11% 6% 15% 12% 9% 6% 6% 9% 11% 11%	727
December	1st to 10th	Day	5% 16% 8% 15% 7% 11% 6% 5% 6% 8% 14%	568
	11th to 20th	Day	3 12% 5% 13% 13% 8% 8% 7% 9% 11% 12%	476
	21st to end	Day	2 7% 3 11% 12% 10% 8% 7% 8% 14% 18%	744
January	1st to 10th	Night	2 9% 6% 16% 8% 8% 9% 6% 10% 14% 11%	6006
	11th to 20th	Night	4 11% 6% 16% 11% 8% 6% 5% 7% 8% 20%	5837
	21st to end	Night	3 11% 4 12% 8% 9% 9% 8% 9% 8% 18%	5946
February	1st to 10th	Night	3 9% 5% 13% 9% 9% 9% 7% 8% 9% 19%	3026
	11th to 20th	Night	3 10% 5% 12% 10% 9% 7% 7% 7% 9% 21%	2743
	21st to end	Night	2 10% 5% 14% 11% 9% 7% 6% 6% 8% 22%	2117
March	1st to 10th	Night	1 8% 4 18% 9% 8% 7% 5% 7% 7% 24%	3985
	11th to 20th	Night	5% 14% 8% 17% 11% 10% 7% 4 4 5% 16%	3552
	21st to end	Night	1 7% 5% 16% 6% 5% 6% 3 5% 10% 35%	3619
April	1st to 10th	Night	6% 16% 7% 13% 6% 5% 5% 4 7% 5% 26%	1710
	11th to 20th	Night	6% 15% 4 8% 4 4 4 3 7% 9% 37%	1479
	21st to end	Night	6% 12% 4 9% 6% 5% 6% 5% 7% 8% 32%	1325
May	1st to 10th	Night	10% 10% 4 9% 5% 5% 5% 5% 8% 10% 30%	1681
	11th to 20th	Night	7% 5% 2 7% 6% 6% 6% 6% 9% 8% 37%	1449
	21st to end	Night	13% 10% 3 8% 5% 4 6% 5% 7% 9% 30%	1030
June	1st to 10th	Night	14% 13% 4 8% 5% 5% 5% 4 7% 8% 26%	443
	11th to 20th	Night	11% 8% 3 8% 9% 7% 5% 3 7% 9% 31%	190
	21st to end	Night	13% 6% 2 7% 4 4 6% 3 8% 8% 37%	190
July	1st to 10th	Night	14% 11% 6% 13% 6% 5% 5% 5% 6% 8% 21%	674
	11th to 20th	Night	7% 6% 3 7% 6% 7% 6% 7% 9% 9% 31%	940
	21st to end	Night	11% 7% 2 6% 5% 6% 5% 6% 8% 9% 35%	1502
August	1st to 10th	Night	10% 7% 2 5% 4 4 4 3 5% 6% 50%	1604
	11th to 20th	Night	15% 8% 3 7% 5% 6% 6% 5% 7% 9% 29%	2170
	21st to end	Night	15% 12% 5% 11% 7% 7% 7% 4 6% 6% 20%	2682
September	1st to 10th	Night	12% 9% 4 8% 6% 6% 5% 5% 7% 8% 30%	1710
	11th to 20th	Night	14% 11% 4 9% 5% 5% 5% 5% 6% 7% 30%	1928
	21st to end	Night	17% 17% 4 11% 6% 5% 5% 4 5% 6% 20%	2120
October	1st to 10th	Night	8% 14% 6% 11% 6% 6% 5% 4 6% 6% 29%	3940
	11th to 20th	Night	7% 14% 5% 13% 5% 5% 5% 4 6% 9% 28%	4259
	21st to end	Night	6% 19% 9% 19% 9% 7% 6% 3 4 5% 14%	5009
November	1st to 10th	Night	5% 17% 7% 17% 11% 7% 6% 4 5% 7% 15%	3118
	11th to 20th	Night	5% 17% 7% 17% 11% 7% 6% 5% 6% 6% 11%	3468
	21st to end	Night	4 11% 5% 15% 9% 7% 8% 6% 9% 10% 15%	3670
December	1st to 10th	Night	5% 15% 6% 17% 10% 7% 6% 4 7% 8% 15%	3793
	11th to 20th	Night	3 14% 5% 16% 10% 8% 6% 6% 8% 9% 15%	4716
	21st to end	Night	4 10% 4 12% 9% 9% 9% 6% 9% 10% 20%	6864

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	54% 7% 9% 16% 14%	939
	11th to 20th	Day	58% 5% 7% 15% 11% 4	1068
	21st to end	Day	55% 8% 11% 12% 13% 1	1710
February	1st to 10th	Day	48% 10% 12% 19% 9% 1	1170
	11th to 20th	Day	60% 10% 10% 14% 6% 1	1328
	21st to end	Day	58% 7% 13% 14% 7%	1337
March	1st to 10th	Day	57% 8% 10% 16% 8%	2877
	11th to 20th	Day	72% 8% 7% 10% 4	3425
	21st to end	Day	55% 11% 14% 16% 4	4027
April	1st to 10th	Day	58% 11% 13% 12% 5% 1	2470
	11th to 20th	Day	51% 10% 14% 19% 6%	2650
	21st to end	Day	49% 10% 18% 20% 3	2855
May	1st to 10th	Day	44% 12% 19% 20% 4	5279
	11th to 20th	Day	44% 13% 16% 22% 6%	5450
	21st to end	Day	47% 10% 13% 20% 8% 1	6545
June	1st to 10th	Day	45% 12% 13% 23% 6%	3735
	11th to 20th	Day	45% 11% 16% 21% 7%	3990
	21st to end	Day	40% 10% 16% 28% 6%	3990
July	1st to 10th	Day	57% 11% 18% 11% 2	6193
	11th to 20th	Day	42% 12% 25% 20% 2	5915
	21st to end	Day	42% 11% 20% 23% 4	5855
August	1st to 10th	Day	33% 10% 22% 16% 8% 11%	5305
	11th to 20th	Day	47% 11% 26% 15% 2	4702
	21st to end	Day	58% 11% 21% 9%	4974
September	1st to 10th	Day	48% 14% 24% 13% 1	2470
	11th to 20th	Day	48% 10% 23% 17% 2	2251
	21st to end	Day	65% 8% 13% 12% 2	2060
October	1st to 10th	Day	46% 9% 17% 24% 5%	3034
	11th to 20th	Day	54% 9% 14% 21% 3	2664
	21st to end	Day	67% 10% 12% 10% 1	2509
November	1st to 10th	Day	65% 8% 12% 13% 3	1176
	11th to 20th	Day	68% 8% 11% 10% 4	930
	21st to end	Day	60% 11% 10% 13% 5% 1	727
December	1st to 10th	Day	66% 7% 10% 14% 3	568
	11th to 20th	Day	59% 8% 15% 10% 7% 1	476
	21st to end	Day	49% 7% 16% 12% 15% 1	744
January	1st to 10th	Night	57% 6% 10% 17% 10%	6006
	11th to 20th	Night	60% 5% 10% 14% 8% 4	5889
	21st to end	Night	54% 8% 12% 12% 15%	5946
February	1st to 10th	Night	54% 9% 12% 14% 10% 1	3026
	11th to 20th	Night	55% 9% 13% 14% 8% 1	2746
	21st to end	Night	58% 9% 10% 16% 6% 1	2117
March	1st to 10th	Night	55% 6% 8% 24% 6%	3985
	11th to 20th	Night	70% 6% 9% 10% 5%	3553
	21st to end	Night	44% 9% 21% 21% 6%	3619
April	1st to 10th	Night	57% 7% 15% 14% 5% 2	1710
	11th to 20th	Night	43% 8% 19% 23% 7%	1479
	21st to end	Night	47% 12% 18% 18% 6%	1325
May	1st to 10th	Night	45% 12% 19% 21% 3	1681
	11th to 20th	Night	36% 15% 22% 21% 6%	1449
	21st to end	Night	44% 13% 13% 23% 7% 1	1030
June	1st to 10th	Night	53% 12% 11% 18% 5%	443
	11th to 20th	Night	49% 9% 15% 21% 6% 1	190
	21st to end	Night	41% 8% 18% 29% 4	190
July	1st to 10th	Night	59% 11% 16% 11% 2	660
	11th to 20th	Night	42% 14% 24% 19% 1	922
	21st to end	Night	42% 12% 19% 23% 4	1455
August	1st to 10th	Night	34% 7% 22% 21% 10% 7%	1599
	11th to 20th	Night	49% 12% 22% 16% 1	2191
	21st to end	Night	62% 10% 18% 10%	2682
September	1st to 10th	Night	49% 12% 24% 13% 2	1710
	11th to 20th	Night	50% 11% 21% 16% 1	1928
	21st to end	Night	63% 11% 13% 11% 2	2120
October	1st to 10th	Night	51% 10% 15% 20% 3	3940
	11th to 20th	Night	50% 8% 18% 19% 4	4259
	21st to end	Night	71% 7% 9% 12% 1	5009
November	1st to 10th	Night	66% 9% 11% 12% 2	3118
	11th to 20th	Night	69% 9% 8% 11% 3	3468
	21st to end	Night	57% 11% 12% 15% 4	3670
December	1st to 10th	Night	64% 7% 11% 15% 3	3793
	11th to 20th	Night	61% 8% 12% 12% 7% 1	4715
	21st to end	Night	52% 9% 14% 14% 11%	6864

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	6% 12% 18% 34% 20% 10%	90
	11th to 20th	Day	11% 7% 26% 39% 16% 2	90
	21st to end	Day	10% 6% 22% 34% 21% 7%	191
February	1st to 10th	Day	10% 10% 18% 32% 23% 7%	180
	11th to 20th	Day	7% 8% 22% 32% 22% 10%	206
	21st to end	Day	7% 9% 29% 33% 20% 2	307
March	1st to 10th	Day	4 4 24% 29% 27% 11%	370
	11th to 20th	Day	10% 3 22% 32% 25% 7%	442
	21st to end	Day	7% 7% 24% 31% 22% 8%	506
April	1st to 10th	Day	15% 8% 20% 23% 22% 11%	460
	11th to 20th	Day	12% 4 17% 29% 26% 10%	540
	21st to end	Day	11% 6% 24% 29% 23% 6%	655
May	1st to 10th	Day	14% 6% 22% 33% 20% 5%	843
	11th to 20th	Day	15% 7% 20% 32% 20% 6%	862
	21st to end	Day	16% 4 19% 34% 22% 4	940
June	1st to 10th	Day	18% 8% 18% 29% 21% 5%	901
	11th to 20th	Day	16% 5% 19% 34% 21% 5%	1060
	21st to end	Day	16% 5% 20% 30% 22% 7%	1060
July	1st to 10th	Day	18% 5% 13% 34% 24% 7%	952
	11th to 20th	Day	18% 6% 14% 25% 25% 13%	852
	21st to end	Day	15% 4 16% 28% 26% 12%	947
August	1st to 10th	Day	19% 4 13% 27% 26% 12%	847
	11th to 20th	Day	25% 8% 17% 24% 22% 5%	665
	21st to end	Day	24% 4 14% 28% 21% 9%	675
September	1st to 10th	Day	22% 5% 18% 24% 21% 10%	490
	11th to 20th	Day	17% 8% 22% 28% 19% 7%	490
	21st to end	Day	29% 10% 18% 24% 16% 3	490
October	1st to 10th	Day	23% 11% 19% 24% 16% 7%	447
	11th to 20th	Day	17% 10% 22% 25% 20% 8%	288
	21st to end	Day	21% 9% 19% 21% 21% 10%	220
November	1st to 10th	Day	9% 8% 24% 24% 25% 11%	200
	11th to 20th	Day	13% 6% 16% 33% 25% 9%	200
	21st to end	Day	18% 4 15% 26% 26% 12%	163
December	1st to 10th	Day	14% 4 19% 38% 18% 8%	85
	21st to end	Day	6% 21% 42% 21% 9%	33
January	1st to 10th	Night	8% 7% 21% 29% 26% 9%	1040
	11th to 20th	Night	12% 7% 22% 35% 19% 4	1040
	21st to end	Night	11% 5% 23% 33% 22% 5%	1144
February	1st to 10th	Night	6% 6% 19% 35% 27% 6%	885
	11th to 20th	Night	7% 4 22% 39% 21% 6%	834
	21st to end	Night	6% 7% 22% 36% 23% 6%	664
March	1st to 10th	Night	5% 6% 19% 38% 25% 7%	760
	11th to 20th	Night	5% 4 23% 35% 26% 8%	760
	21st to end	Night	6% 7% 20% 31% 27% 10%	765
April	1st to 10th	Night	12% 5% 17% 33% 27% 6%	570
	11th to 20th	Night	12% 4 13% 39% 27% 5%	439
	21st to end	Night	11% 5% 24% 35% 21% 4	380
May	1st to 10th	Night	17% 3 20% 34% 23% 3	380
	11th to 20th	Night	13% 6% 17% 35% 26% 3	374
	21st to end	Night	16% 3 21% 34% 25%	214
June	1st to 10th	Night	19% 5% 22% 32% 20% 2	96
	July	1st to 10th	Night	18% 4 20% 30% 22% 5%	116
11th to 20th		Night	16% 4 10% 33% 35% 2	184
21st to end		Night	14% 2 11% 35% 35% 3	325
August	1st to 10th	Night	20% 4 9% 30% 31% 5%	378
	11th to 20th	Night	27% 3 12% 33% 19% 5%	376
	21st to end	Night	21% 5% 11% 34% 23% 6%	481
September	1st to 10th	Night	19% 4 15% 29% 27% 6%	570
	11th to 20th	Night	23% 5% 19% 31% 19% 3	717
	21st to end	Night	31% 7% 15% 24% 19% 4	760
October	1st to 10th	Night	22% 8% 19% 28% 19% 4	760
	11th to 20th	Night	22% 6% 16% 26% 24% 6%	760
	21st to end	Night	17% 6% 16% 29% 24% 8%	903
November	1st to 10th	Night	13% 6% 20% 30% 23% 8%	1072
	11th to 20th	Night	14% 6% 17% 30% 23% 9%	1100
	21st to end	Night	11% 4 19% 31% 26% 10%	1100
December	1st to 10th	Night	14% 6% 23% 31% 20% 5%	1091
	11th to 20th	Night	10% 8% 24% 32% 20% 6%	1040
	21st to end	Night	8% 6% 15% 33% 31% 8%	1144

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