Norway House
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norway House clear sky chart from 2005-11-06 to 2026-06-16.

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	11% 10% 4 9% 6% 5% 5% 4 6% 7% 33%	142576
	Night	9% 12% 5% 11% 7% 6% 6% 5% 6% 6% 27%	138284
Transparency	Day	48% 7% 14% 22% 8% 1	142271
	Night	55% 6% 12% 19% 8% 1	138171
Seeing	Day	16% 13% 34% 25% 9% 2	18650
	Night	17% 10% 32% 29% 11% 1	28299

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% 6% 15% 9% 8% 8% 10% 8% 4 10%	4125
	11th to 20th	Day	4 11% 6% 16% 10% 10% 9% 8% 10% 5% 10%	4119
	21st to end	Day	5% 16% 6% 14% 7% 6% 7% 7% 8% 6% 18%	4730
February	1st to 10th	Day	8% 12% 5% 10% 8% 7% 10% 6% 8% 7% 18%	1680
	11th to 20th	Day	6% 11% 4 11% 7% 6% 7% 7% 9% 7% 25%	1797
	21st to end	Day	4 10% 5% 11% 8% 8% 7% 5% 9% 8% 24%	1596
March	1st to 10th	Day	5% 12% 5% 11% 7% 7% 6% 4 6% 7% 29%	4600
	11th to 20th	Day	9% 13% 5% 13% 7% 9% 7% 4 4 5% 23%	5083
	21st to end	Day	4 10% 4 9% 6% 5% 6% 5% 7% 7% 37%	5617
April	1st to 10th	Day	7% 10% 5% 9% 6% 4 5% 4 5% 7% 38%	2652
	11th to 20th	Day	12% 10% 5% 9% 5% 5% 5% 4 4 6% 34%	2702
	21st to end	Day	8% 7% 4 9% 6% 5% 5% 4 6% 7% 40%	2730
May	1st to 10th	Day	11% 12% 6% 9% 4 4 4 3 5% 6% 37%	8703
	11th to 20th	Day	17% 10% 4 8% 5% 4 5% 4 6% 7% 32%	8786
	21st to end	Day	12% 8% 3 6% 3 3 3 3 5% 6% 49%	9683
June	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	3150
	11th to 20th	Day	18% 8% 3 6% 4 5% 5% 4 5% 7% 34%	3156
	21st to end	Day	14% 8% 2 7% 4 5% 5% 4 6% 8% 38%	3200
July	1st to 10th	Day	10% 4 1 5% 4 4 4 4 6% 9% 49%	6932
	11th to 20th	Day	8% 4 2 6% 4 5% 5% 5% 7% 10% 46%	6800
	21st to end	Day	10% 5% 2 5% 4 5% 5% 4 6% 9% 46%	7400
August	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 6% 7% 47%	4760
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 5% 6% 8% 45%	4276
	21st to end	Day	20% 7% 2 6% 4 4 4 4 5% 7% 37%	4675
September	1st to 10th	Day	15% 7% 2 7% 5% 5% 5% 4 6% 8% 35%	2561
	11th to 20th	Day	20% 10% 2 7% 4 4 4 4 6% 5% 34%	2200
	21st to end	Day	13% 11% 3 6% 5% 4 4 4 4 7% 37%	2200
October	1st to 10th	Day	14% 13% 3 8% 5% 5% 5% 4 6% 8% 28%	3308
	11th to 20th	Day	13% 16% 4 9% 6% 5% 6% 4 5% 5% 27%	2998
	21st to end	Day	17% 20% 7% 11% 6% 5% 4 4 4 4 20%	3077
November	1st to 10th	Day	14% 19% 6% 16% 9% 6% 5% 3 4 4 13%	1647
	11th to 20th	Day	13% 18% 6% 14% 9% 9% 5% 3 4 4 16%	1519
	21st to end	Day	9% 17% 7% 17% 9% 8% 7% 4 4 5% 13%	1470
December	1st to 10th	Day	8% 17% 6% 15% 11% 12% 8% 7% 5% 4 9%	2360
	11th to 20th	Day	11% 11% 4 15% 8% 7% 8% 7% 8% 8% 14%	2709
	21st to end	Day	5% 15% 6% 20% 9% 8% 6% 4 5% 5% 17%	3575
January	1st to 10th	Night	5% 15% 8% 17% 8% 8% 8% 7% 6% 4 14%	8799
	11th to 20th	Night	5% 12% 6% 19% 9% 7% 9% 10% 9% 4 9%	8809
	21st to end	Night	6% 15% 6% 15% 7% 8% 8% 6% 7% 5% 16%	9467
February	1st to 10th	Night	7% 13% 5% 9% 7% 8% 10% 7% 8% 7% 18%	2940
	11th to 20th	Night	5% 10% 5% 10% 9% 6% 8% 7% 8% 7% 26%	2710
	21st to end	Night	4 12% 6% 13% 10% 7% 6% 4 6% 5% 28%	2228
March	1st to 10th	Night	8% 14% 5% 11% 7% 6% 5% 3 5% 7% 29%	5494
	11th to 20th	Night	8% 12% 5% 11% 9% 7% 6% 5% 4 5% 28%	5094
	21st to end	Night	4 8% 4 10% 6% 8% 8% 5% 6% 7% 34%	5555
April	1st to 10th	Night	8% 11% 3 8% 6% 4 4 4 6% 6% 40%	1967
	11th to 20th	Night	12% 10% 5% 10% 6% 5% 5% 4 4 6% 32%	1869
	21st to end	Night	6% 8% 4 6% 6% 5% 6% 5% 6% 8% 41%	1890
May	1st to 10th	Night	11% 10% 3 8% 4 5% 5% 4 6% 7% 36%	4241
	11th to 20th	Night	19% 10% 3 8% 5% 4 4 4 5% 6% 32%	4107
	21st to end	Night	10% 7% 3 7% 4 4 5% 4 5% 6% 46%	4523
June	1st to 10th	Night	15% 7% 3 7% 5% 5% 4 4 5% 7% 38%	1470
	11th to 20th	Night	15% 7% 3 7% 5% 5% 6% 4 6% 6% 35%	1348
	21st to end	Night	13% 7% 2 7% 4 4 5% 4 6% 10% 38%	1200
July	1st to 10th	Night	9% 3 1 5% 4 4 4 4 6% 9% 51%	3037
	11th to 20th	Night	7% 5% 2 5% 4 5% 5% 4 6% 8% 48%	3180
	21st to end	Night	6% 4 2 5% 5% 4 5% 5% 7% 9% 48%	3466
August	1st to 10th	Night	11% 4 2 4 4 4 4 4 7% 8% 49%	2398
	11th to 20th	Night	11% 4 2 5% 3 3 4 3 6% 10% 48%	2783
	21st to end	Night	16% 7% 2 6% 4 4 4 3 5% 8% 40%	3234
September	1st to 10th	Night	13% 7% 3 6% 4 4 4 3 5% 7% 44%	1836
	11th to 20th	Night	18% 9% 2 7% 4 5% 4 3 5% 7% 35%	2200
	21st to end	Night	13% 8% 3 7% 6% 5% 5% 4 4 7% 39%	2200
October	1st to 10th	Night	14% 11% 3 8% 6% 5% 6% 5% 6% 7% 28%	3838
	11th to 20th	Night	13% 13% 4 7% 4 5% 4 4 6% 9% 31%	4146
	21st to end	Night	17% 19% 6% 11% 5% 4 4 3 4 4 23%	4723
November	1st to 10th	Night	14% 17% 7% 15% 9% 5% 4 3 4 4 16%	2871
	11th to 20th	Night	14% 17% 7% 14% 10% 7% 4 3 3 4 16%	3098
	21st to end	Night	8% 20% 7% 17% 11% 6% 5% 3 4 5% 14%	3150
December	1st to 10th	Night	8% 18% 7% 16% 10% 9% 8% 6% 5% 4 8%	5050
	11th to 20th	Night	8% 14% 5% 11% 6% 7% 9% 8% 7% 7% 16%	5718
	21st to end	Night	7% 16% 7% 18% 8% 6% 6% 3 5% 5% 18%	7645

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	69% 6% 7% 13% 5% 1	4125
	11th to 20th	Day	68% 5% 7% 15% 5%	4140
	21st to end	Day	61% 6% 11% 17% 5%	4730
February	1st to 10th	Day	58% 8% 12% 15% 6% 1	1680
	11th to 20th	Day	52% 6% 13% 21% 8%	1806
	21st to end	Day	53% 7% 11% 19% 9% 1	1596
March	1st to 10th	Day	50% 6% 11% 21% 12%	4600
	11th to 20th	Day	58% 8% 9% 15% 9% 1	5085
	21st to end	Day	41% 8% 9% 28% 13% 1	5617
April	1st to 10th	Day	43% 8% 12% 24% 13% 1	2652
	11th to 20th	Day	50% 6% 9% 20% 14%	2702
	21st to end	Day	41% 8% 12% 26% 13% 2	2730
May	1st to 10th	Day	47% 6% 12% 24% 10% 1	8700
	11th to 20th	Day	48% 7% 14% 21% 9% 1	8790
	21st to end	Day	36% 6% 9% 26% 19% 5%	9683
June	1st to 10th	Day	45% 10% 13% 21% 11%	3150
	11th to 20th	Day	47% 7% 13% 22% 10%	3156
	21st to end	Day	42% 9% 16% 23% 9%	3200
July	1st to 10th	Day	30% 7% 22% 33% 7%	6858
	11th to 20th	Day	30% 8% 18% 37% 7%	6719
	21st to end	Day	33% 8% 21% 30% 8%	7193
August	1st to 10th	Day	34% 8% 16% 34% 7%	4743
	11th to 20th	Day	35% 8% 23% 29% 6%	4317
	21st to end	Day	45% 7% 18% 24% 6%	4674
September	1st to 10th	Day	44% 9% 20% 21% 5% 1	2561
	11th to 20th	Day	50% 9% 18% 21% 3	2200
	21st to end	Day	46% 7% 19% 22% 5%	2200
October	1st to 10th	Day	52% 6% 18% 17% 6%	3308
	11th to 20th	Day	57% 6% 12% 17% 7%	2998
	21st to end	Day	68% 6% 12% 13% 1	3077
November	1st to 10th	Day	74% 8% 9% 8% 1	1647
	11th to 20th	Day	72% 6% 13% 8% 2	1519
	21st to end	Day	75% 7% 10% 8% 1	1470
December	1st to 10th	Day	76% 8% 7% 6% 2	2360
	11th to 20th	Day	62% 7% 11% 16% 4	2710
	21st to end	Day	67% 7% 7% 15% 4	3575
January	1st to 10th	Night	68% 6% 9% 9% 7%	8800
	11th to 20th	Night	70% 5% 6% 13% 5%	8850
	21st to end	Night	65% 5% 9% 13% 7%	9467
February	1st to 10th	Night	57% 7% 13% 16% 6%	2940
	11th to 20th	Night	51% 6% 12% 22% 8%	2711
	21st to end	Night	56% 4 10% 20% 9%	2228
March	1st to 10th	Night	53% 5% 9% 20% 9% 3	5494
	11th to 20th	Night	55% 7% 8% 16% 13% 1	5094
	21st to end	Night	43% 7% 10% 25% 14% 1	5555
April	1st to 10th	Night	43% 5% 10% 24% 17% 1	1967
	11th to 20th	Night	51% 6% 7% 19% 15% 2	1869
	21st to end	Night	38% 6% 11% 27% 15% 2	1890
May	1st to 10th	Night	45% 7% 10% 28% 10% 1	4241
	11th to 20th	Night	51% 6% 12% 21% 9% 1	4107
	21st to end	Night	37% 7% 8% 25% 16% 8%	4526
June	1st to 10th	Night	43% 8% 12% 22% 14% 1	1470
	11th to 20th	Night	44% 9% 11% 21% 13% 1	1348
	21st to end	Night	40% 8% 18% 26% 9%	1200
July	1st to 10th	Night	29% 7% 20% 33% 10%	3002
	11th to 20th	Night	31% 8% 17% 36% 7%	3138
	21st to end	Night	30% 8% 21% 29% 10%	3368
August	1st to 10th	Night	31% 7% 14% 41% 7%	2391
	11th to 20th	Night	32% 6% 22% 35% 5%	2808
	21st to end	Night	43% 7% 19% 23% 8%	3234
September	1st to 10th	Night	38% 9% 20% 25% 7%	1836
	11th to 20th	Night	48% 7% 16% 25% 3	2200
	21st to end	Night	45% 7% 17% 24% 7%	2200
October	1st to 10th	Night	53% 6% 17% 20% 5%	3838
	11th to 20th	Night	50% 7% 16% 20% 7%	4146
	21st to end	Night	63% 6% 14% 14% 2	4723
November	1st to 10th	Night	70% 8% 11% 7% 4	2871
	11th to 20th	Night	73% 6% 9% 9% 3	3098
	21st to end	Night	73% 7% 10% 8% 2	3150
December	1st to 10th	Night	78% 7% 8% 5% 2	5050
	11th to 20th	Night	61% 6% 14% 14% 5%	5716
	21st to end	Night	66% 5% 8% 13% 7%	7645

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	12% 10% 38% 31% 8% 1	330
	11th to 20th	Day	9% 12% 43% 27% 8% 1	330
	21st to end	Day	17% 13% 36% 26% 7% 1	363
February	1st to 10th	Day	12% 9% 39% 29% 8% 2	330
	11th to 20th	Day	9% 12% 41% 26% 12% 1	330
	21st to end	Day	8% 14% 42% 21% 12% 3	273
March	1st to 10th	Day	10% 18% 35% 21% 13% 2	330
	11th to 20th	Day	11% 18% 42% 19% 8% 2	330
	21st to end	Day	10% 15% 35% 29% 8% 3	370
April	1st to 10th	Day	10% 8% 40% 28% 11% 2	672
	11th to 20th	Day	20% 14% 30% 26% 9% 1	740
	21st to end	Day	11% 15% 35% 29% 9% 2	750
May	1st to 10th	Day	16% 15% 37% 24% 7%	753
	11th to 20th	Day	15% 17% 33% 25% 9% 2	775
	21st to end	Day	18% 13% 32% 27% 9% 1	844
June	1st to 10th	Day	20% 17% 30% 21% 11% 2	780
	11th to 20th	Day	21% 14% 33% 22% 8% 3	756
	21st to end	Day	18% 10% 29% 31% 9% 3	730
July	1st to 10th	Day	13% 9% 33% 31% 10% 4	721
	11th to 20th	Day	14% 9% 31% 29% 13% 4	718
	21st to end	Day	15% 10% 29% 28% 14% 4	794
August	1st to 10th	Day	15% 12% 31% 29% 11% 3	726
	11th to 20th	Day	15% 10% 30% 27% 15% 4	715
	21st to end	Day	22% 10% 27% 25% 13% 2	803
September	1st to 10th	Day	19% 14% 35% 23% 8% 1	691
	11th to 20th	Day	26% 15% 28% 21% 8% 1	330
	21st to end	Day	19% 18% 33% 23% 7%	330
October	1st to 10th	Day	24% 15% 40% 13% 5% 2	330
	11th to 20th	Day	28% 17% 35% 14% 5% 1	330
	21st to end	Day	31% 12% 26% 22% 7% 1	363
November	1st to 10th	Day	19% 18% 34% 22% 6% 1	330
	11th to 20th	Day	21% 15% 40% 17% 5% 1	330
	21st to end	Day	21% 16% 35% 22% 6% 1	330
December	1st to 10th	Day	12% 12% 38% 25% 11% 1	330
	11th to 20th	Day	15% 15% 41% 22% 6% 1	330
	21st to end	Day	13% 10% 33% 33% 11% 1	363
January	1st to 10th	Night	14% 11% 34% 31% 9% 1	1050
	11th to 20th	Night	12% 10% 36% 31% 10% 1	1050
	21st to end	Night	18% 9% 35% 27% 9%	1155
February	1st to 10th	Night	12% 8% 36% 32% 10% 1	1050
	11th to 20th	Night	10% 8% 30% 33% 14% 3	1029
	21st to end	Night	8% 10% 37% 30% 14% 1	844
March	1st to 10th	Night	12% 10% 30% 33% 13% 2	840
	11th to 20th	Night	15% 12% 35% 26% 11% 1	634
	21st to end	Night	14% 8% 35% 28% 14% 2	693
April	1st to 10th	Night	12% 7% 33% 32% 14% 2	630
	11th to 20th	Night	16% 9% 30% 34% 10% 1	623
	21st to end	Night	10% 8% 37% 32% 13% 1	630
May	1st to 10th	Night	19% 8% 35% 28% 8% 1	630
	11th to 20th	Night	19% 13% 29% 29% 9% 1	621
	21st to end	Night	17% 9% 33% 31% 9%	683
June	1st to 10th	Night	19% 9% 29% 30% 12% 1	630
	11th to 20th	Night	18% 8% 31% 29% 13% 1	528
	21st to end	Night	14% 7% 28% 35% 16% 1	400
July	1st to 10th	Night	13% 6% 29% 35% 17% 1	520
	11th to 20th	Night	14% 6% 24% 34% 18% 3	582
	21st to end	Night	11% 6% 23% 35% 21% 4	657
August	1st to 10th	Night	12% 6% 27% 36% 18% 2	597
	11th to 20th	Night	14% 7% 23% 34% 21% 2	594
	21st to end	Night	20% 8% 28% 31% 14%	660
September	1st to 10th	Night	18% 8% 30% 31% 13% 1	600
	11th to 20th	Night	25% 8% 26% 32% 9% 1	600
	21st to end	Night	19% 8% 33% 30% 10%	600
October	1st to 10th	Night	24% 9% 33% 26% 6% 1	744
	11th to 20th	Night	30% 12% 26% 23% 8% 1	945
	21st to end	Night	31% 12% 29% 22% 6% 1	1100
November	1st to 10th	Night	21% 16% 31% 24% 7% 1	1025
	11th to 20th	Night	23% 11% 33% 24% 8% 1	1050
	21st to end	Night	17% 15% 36% 26% 6% 1	1050
December	1st to 10th	Night	14% 10% 35% 30% 9% 2	1050
	11th to 20th	Night	17% 11% 36% 25% 9% 1	1050
	21st to end	Night	15% 8% 31% 31% 13% 2	1155

Page generated at 2026-06-13 01:31:40. Version ac07

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