Lewisporte
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lewisporte clear sky chart from 2005-11-06 to 2024-03-30.

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	22% 13% 5% 8% 6% 3 5% 5% 5% 6% 23%	78304
	Night	21% 13% 5% 8% 6% 3 5% 4 5% 6% 23%	81766
Transparency	Day	61% 8% 12% 13% 5% 1	77995
	Night	61% 8% 12% 13% 5% 1	81610
Seeing	Day	29% 15% 29% 19% 7% 1	17165
	Night	29% 15% 31% 19% 5%	24138

By Month

Percentage Cloud Cover NE (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	13% 16% 8% 13% 11% 5% 5% 4 5% 5% 15%	2216
	11th to 20th	Day	18% 13% 7% 13% 8% 4 6% 5% 5% 5% 17%	2503
	21st to end	Day	11% 12% 6% 10% 10% 6% 7% 5% 6% 6% 21%	2783
February	1st to 10th	Day	17% 13% 6% 10% 10% 3 6% 5% 7% 6% 19%	1520
	11th to 20th	Day	19% 17% 6% 10% 7% 3 5% 5% 5% 4 17%	1712
	21st to end	Day	14% 12% 6% 10% 9% 5% 8% 5% 4 5% 23%	1570
March	1st to 10th	Day	18% 15% 6% 10% 7% 4 5% 5% 4 4 23%	1896
	11th to 20th	Day	18% 15% 7% 11% 8% 4 5% 5% 4 5% 18%	2029
	21st to end	Day	24% 19% 7% 10% 7% 3 3 3 3 4 18%	2362
April	1st to 10th	Day	20% 16% 6% 10% 7% 3 6% 5% 4 6% 18%	2160
	11th to 20th	Day	23% 17% 7% 6% 4 3 3 3 4 7% 23%	2298
	21st to end	Day	21% 19% 5% 7% 6% 3 5% 4 4 5% 21%	2340
May	1st to 10th	Day	27% 18% 5% 6% 5% 2 5% 3 4 5% 19%	2420
	11th to 20th	Day	24% 15% 4 6% 6% 4 5% 4 4 5% 24%	2556
	21st to end	Day	26% 14% 4 7% 5% 3 4 4 4 6% 22%	2918
June	1st to 10th	Day	32% 13% 4 7% 5% 3 5% 5% 5% 5% 17%	2700
	11th to 20th	Day	30% 11% 3 6% 5% 3 4 4 4 6% 24%	2700
	21st to end	Day	24% 9% 4 6% 6% 4 6% 5% 5% 7% 25%	2700
July	1st to 10th	Day	22% 9% 4 6% 5% 3 5% 5% 6% 7% 28%	2700
	11th to 20th	Day	18% 8% 3 7% 6% 3 5% 6% 6% 8% 31%	2674
	21st to end	Day	21% 10% 3 7% 7% 4 5% 6% 5% 7% 25%	2745
August	1st to 10th	Day	21% 10% 3 7% 6% 3 5% 6% 6% 9% 24%	2506
	11th to 20th	Day	21% 8% 4 7% 7% 4 5% 5% 6% 7% 27%	2310
	21st to end	Day	20% 9% 2 5% 5% 3 5% 6% 6% 7% 31%	2574
September	1st to 10th	Day	23% 7% 3 5% 5% 3 5% 4 5% 8% 33%	2162
	11th to 20th	Day	29% 8% 3 5% 5% 2 4 4 5% 6% 28%	1980
	21st to end	Day	20% 9% 3 6% 5% 3 4 4 6% 9% 32%	1980
October	1st to 10th	Day	23% 11% 3 6% 6% 3 4 3 5% 6% 32%	1940
	11th to 20th	Day	25% 12% 3 7% 6% 3 5% 5% 5% 6% 22%	1645
	21st to end	Day	26% 18% 4 6% 6% 3 5% 4 4 4 19%	1782
November	1st to 10th	Day	23% 17% 5% 8% 6% 4 4 5% 4 5% 19%	1670
	11th to 20th	Day	21% 17% 6% 8% 5% 2 4 5% 4 6% 23%	1483
	21st to end	Day	23% 16% 6% 9% 6% 3 4 3 4 6% 20%	1330
December	1st to 10th	Day	21% 17% 6% 10% 7% 3 4 5% 4 6% 17%	1330
	11th to 20th	Day	25% 14% 6% 11% 8% 3 5% 5% 3 6% 14%	1668
	21st to end	Day	22% 18% 6% 12% 9% 4 4 4 4 5% 13%	2442
January	1st to 10th	Night	13% 17% 7% 14% 8% 6% 7% 4 4 5% 16%	4739
	11th to 20th	Night	12% 12% 6% 12% 9% 4 6% 5% 6% 7% 22%	4463
	21st to end	Night	10% 11% 5% 11% 10% 5% 8% 5% 5% 6% 23%	4884
February	1st to 10th	Night	17% 11% 6% 11% 9% 4 6% 5% 5% 6% 20%	2660
	11th to 20th	Night	20% 16% 6% 9% 7% 3 6% 5% 4 5% 19%	2352
	21st to end	Night	15% 13% 5% 8% 8% 4 5% 5% 4 6% 26%	1884
March	1st to 10th	Night	19% 16% 5% 8% 6% 3 5% 5% 5% 5% 24%	2271
	11th to 20th	Night	16% 16% 6% 10% 7% 4 6% 6% 4 5% 20%	2149
	21st to end	Night	24% 15% 5% 10% 7% 2 3 4 4 5% 21%	2190
April	1st to 10th	Night	24% 16% 6% 6% 5% 3 4 4 5% 6% 22%	1800
	11th to 20th	Night	25% 16% 5% 6% 4 2 4 4 4 6% 25%	1611
	21st to end	Night	26% 17% 4 6% 5% 2 3 3 4 5% 24%	1620
May	1st to 10th	Night	28% 16% 4 7% 6% 3 3 4 5% 5% 19%	1535
	11th to 20th	Night	28% 15% 6% 5% 4 2 3 3 4 6% 24%	1335
	21st to end	Night	29% 13% 3 5% 5% 3 4 4 5% 5% 23%	1356
June	1st to 10th	Night	34% 11% 4 6% 5% 2 4 4 5% 7% 17%	1260
	11th to 20th	Night	33% 8% 3 4 4 2 4 5% 5% 7% 24%	1260
	21st to end	Night	24% 10% 4 7% 6% 4 5% 4 4 7% 25%	1260
July	1st to 10th	Night	23% 8% 3 5% 4 2 5% 4 6% 7% 32%	1260
	11th to 20th	Night	17% 8% 3 7% 6% 3 4 5% 6% 8% 34%	1283
	21st to end	Night	21% 9% 3 6% 6% 4 5% 5% 5% 7% 29%	1573
August	1st to 10th	Night	20% 9% 3 8% 6% 4 3 6% 6% 7% 28%	1433
	11th to 20th	Night	21% 9% 3 7% 5% 3 4 5% 6% 7% 31%	1588
	21st to end	Night	22% 7% 3 5% 6% 3 4 4 5% 7% 34%	1782
September	1st to 10th	Night	24% 7% 3 6% 4 2 3 4 4 6% 36%	1795
	11th to 20th	Night	25% 9% 3 5% 5% 3 4 4 5% 5% 32%	1980
	21st to end	Night	22% 10% 4 7% 4 2 5% 4 5% 7% 30%	1980
October	1st to 10th	Night	24% 11% 3 6% 5% 2 5% 4 5% 6% 30%	2020
	11th to 20th	Night	26% 12% 3 6% 5% 3 4 4 5% 6% 26%	2312
	21st to end	Night	30% 17% 3 6% 5% 2 4 4 3 5% 21%	2574
November	1st to 10th	Night	22% 15% 4 8% 7% 4 5% 5% 5% 7% 19%	2408
	11th to 20th	Night	23% 15% 5% 8% 6% 2 5% 5% 5% 6% 21%	2693
	21st to end	Night	19% 16% 7% 8% 7% 3 4 4 5% 6% 20%	2850
December	1st to 10th	Night	20% 17% 7% 11% 7% 4 4 5% 5% 5% 16%	2850
	11th to 20th	Night	28% 17% 6% 12% 7% 4 5% 3 4 4 12%	3531
	21st to end	Night	22% 14% 6% 10% 7% 4 5% 4 5% 6% 17%	5225

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	65% 13% 11% 8% 3 1	2217
	11th to 20th	Day	65% 10% 10% 9% 6%	2503
	21st to end	Day	60% 10% 10% 12% 6% 2	2783
February	1st to 10th	Day	64% 8% 12% 10% 6% 1	1520
	11th to 20th	Day	68% 7% 11% 11% 4	1719
	21st to end	Day	61% 7% 9% 13% 8% 1	1570
March	1st to 10th	Day	63% 6% 10% 13% 8% 1	1900
	11th to 20th	Day	69% 6% 9% 10% 6%	2029
	21st to end	Day	72% 4 6% 11% 6% 1	2362
April	1st to 10th	Day	68% 5% 9% 12% 5% 1	2160
	11th to 20th	Day	62% 5% 10% 14% 8% 1	2298
	21st to end	Day	66% 5% 8% 13% 8%	2340
May	1st to 10th	Day	68% 5% 10% 12% 6%	2420
	11th to 20th	Day	61% 8% 9% 13% 7% 1	2560
	21st to end	Day	62% 6% 12% 15% 5%	2918
June	1st to 10th	Day	69% 6% 9% 11% 4	2700
	11th to 20th	Day	61% 7% 12% 15% 5% 1	2700
	21st to end	Day	58% 9% 12% 13% 7% 1	2700
July	1st to 10th	Day	52% 8% 14% 19% 6%	2625
	11th to 20th	Day	50% 8% 16% 19% 6%	2592
	21st to end	Day	56% 11% 13% 15% 4 1	2592
August	1st to 10th	Day	54% 9% 17% 17% 3	2492
	11th to 20th	Day	54% 9% 16% 14% 6%	2310
	21st to end	Day	50% 9% 18% 18% 5%	2574
September	1st to 10th	Day	49% 7% 12% 22% 8% 2	2162
	11th to 20th	Day	58% 7% 12% 17% 6%	1980
	21st to end	Day	50% 6% 19% 18% 6%	1980
October	1st to 10th	Day	54% 7% 12% 19% 8% 1	1940
	11th to 20th	Day	61% 7% 13% 14% 4	1645
	21st to end	Day	68% 6% 9% 11% 5% 1	1782
November	1st to 10th	Day	67% 7% 12% 10% 3	1670
	11th to 20th	Day	63% 7% 11% 11% 6% 1	1483
	21st to end	Day	66% 8% 13% 8% 5% 1	1330
December	1st to 10th	Day	69% 7% 11% 9% 3	1330
	11th to 20th	Day	71% 8% 12% 7% 2	1667
	21st to end	Day	73% 8% 10% 8% 2	2442
January	1st to 10th	Night	63% 12% 12% 9% 3	4739
	11th to 20th	Night	59% 8% 13% 13% 6%	4463
	21st to end	Night	58% 10% 14% 10% 5% 2	4884
February	1st to 10th	Night	63% 7% 12% 11% 6%	2660
	11th to 20th	Night	67% 7% 10% 12% 4	2356
	21st to end	Night	56% 8% 10% 16% 8% 1	1884
March	1st to 10th	Night	62% 6% 10% 13% 8% 1	2280
	11th to 20th	Night	64% 7% 10% 12% 6% 1	2150
	21st to end	Night	65% 6% 9% 12% 7% 1	2190
April	1st to 10th	Night	63% 5% 9% 13% 9% 1	1800
	11th to 20th	Night	62% 4 10% 16% 7% 1	1611
	21st to end	Night	64% 6% 9% 13% 8%	1620
May	1st to 10th	Night	67% 5% 9% 13% 5% 1	1535
	11th to 20th	Night	63% 4 11% 15% 7%	1336
	21st to end	Night	62% 8% 11% 12% 7% 1	1357
June	1st to 10th	Night	67% 7% 12% 9% 4	1260
	11th to 20th	Night	59% 8% 14% 14% 5%	1260
	21st to end	Night	60% 8% 11% 14% 7% 1	1260
July	1st to 10th	Night	50% 8% 16% 19% 6%	1226
	11th to 20th	Night	47% 9% 16% 20% 8%	1241
	21st to end	Night	55% 9% 14% 18% 5%	1486
August	1st to 10th	Night	53% 10% 16% 18% 4	1422
	11th to 20th	Night	51% 9% 17% 17% 6%	1588
	21st to end	Night	49% 7% 17% 21% 6%	1782
September	1st to 10th	Night	49% 7% 13% 22% 9% 1	1795
	11th to 20th	Night	54% 6% 13% 18% 9% 1	1980
	21st to end	Night	53% 7% 14% 18% 7% 1	1980
October	1st to 10th	Night	54% 6% 14% 16% 8% 1	2020
	11th to 20th	Night	58% 7% 13% 16% 5%	2312
	21st to end	Night	67% 5% 9% 12% 6% 1	2574
November	1st to 10th	Night	65% 8% 11% 11% 4	2408
	11th to 20th	Night	64% 7% 13% 13% 3	2693
	21st to end	Night	64% 7% 12% 10% 5%	2850
December	1st to 10th	Night	70% 7% 10% 10% 3	2850
	11th to 20th	Night	77% 6% 9% 6% 2	3533
	21st to end	Night	67% 10% 13% 9% 2	5225

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	24% 22% 35% 14% 5%	370
	11th to 20th	Day	23% 24% 35% 16% 3	370
	21st to end	Day	28% 19% 31% 17% 4	407
February	1st to 10th	Day	26% 26% 28% 16% 4	370
	11th to 20th	Day	27% 24% 34% 11% 2 1	366
	21st to end	Day	20% 23% 37% 15% 3 1	307
March	1st to 10th	Day	24% 21% 39% 12% 4 1	370
	11th to 20th	Day	28% 16% 28% 17% 8% 2	370
	21st to end	Day	37% 20% 22% 15% 3 2	442
April	1st to 10th	Day	29% 22% 29% 17% 3	420
	11th to 20th	Day	33% 13% 28% 19% 5% 1	576
	21st to end	Day	32% 17% 30% 19% 3 1	600
May	1st to 10th	Day	38% 12% 24% 17% 6% 2	603
	11th to 20th	Day	30% 12% 29% 18% 9% 2	624
	21st to end	Day	33% 12% 31% 19% 4 1	680
June	1st to 10th	Day	39% 11% 24% 15% 8% 1	630
	11th to 20th	Day	35% 11% 25% 20% 9% 1	630
	21st to end	Day	27% 10% 27% 22% 11% 3	630
July	1st to 10th	Day	29% 10% 27% 21% 9% 3	620
	11th to 20th	Day	22% 11% 28% 28% 11% 1	618
	21st to end	Day	24% 11% 24% 31% 10% 1	685
August	1st to 10th	Day	25% 9% 27% 26% 10% 2	625
	11th to 20th	Day	23% 8% 28% 25% 14% 2	617
	21st to end	Day	24% 9% 28% 23% 13% 3	693
September	1st to 10th	Day	26% 11% 31% 22% 8% 1	454
	11th to 20th	Day	36% 13% 27% 19% 4 1	360
	21st to end	Day	22% 19% 36% 17% 5% 2	360
October	1st to 10th	Day	24% 20% 34% 16% 4 2	360
	11th to 20th	Day	36% 10% 25% 18% 8% 3	360
	21st to end	Day	34% 19% 25% 14% 6% 2	396
November	1st to 10th	Day	38% 17% 29% 13% 2	365
	11th to 20th	Day	33% 22% 24% 15% 5% 1	370
	21st to end	Day	36% 20% 31% 12% 1	370
December	1st to 10th	Day	27% 16% 33% 17% 6% 1	370
	11th to 20th	Day	30% 25% 29% 13% 3	370
	21st to end	Day	24% 21% 31% 18% 5% 1	407
January	1st to 10th	Night	26% 20% 31% 18% 5% 1	850
	11th to 20th	Night	23% 24% 34% 16% 3	850
	21st to end	Night	24% 20% 38% 15% 3	935
February	1st to 10th	Night	26% 20% 35% 16% 3	850
	11th to 20th	Night	29% 22% 34% 12% 2	804
	21st to end	Night	21% 15% 40% 16% 6% 1	628
March	1st to 10th	Night	28% 19% 34% 14% 5% 1	760
	11th to 20th	Night	24% 16% 29% 23% 7%	630
	21st to end	Night	32% 17% 29% 17% 4	622
April	1st to 10th	Night	32% 19% 28% 16% 4 1	540
	11th to 20th	Night	32% 10% 33% 19% 5% 1	534
	21st to end	Night	33% 11% 34% 20% 2	540
May	1st to 10th	Night	35% 9% 25% 23% 6% 1	540
	11th to 20th	Night	36% 10% 27% 18% 9%	532
	21st to end	Night	35% 10% 31% 18% 5%	583
June	1st to 10th	Night	40% 9% 22% 24% 4	540
	11th to 20th	Night	38% 7% 22% 25% 7% 1	540
	21st to end	Night	29% 8% 31% 23% 9%	540
July	1st to 10th	Night	25% 8% 33% 26% 7% 1	526
	11th to 20th	Night	21% 9% 31% 34% 5%	522
	21st to end	Night	24% 7% 30% 32% 7%	590
August	1st to 10th	Night	25% 6% 29% 31% 10%	538
	11th to 20th	Night	24% 5% 29% 31% 10%	532
	21st to end	Night	24% 8% 28% 31% 9% 1	594
September	1st to 10th	Night	27% 7% 34% 25% 7%	540
	11th to 20th	Night	29% 12% 32% 24% 3	540
	21st to end	Night	30% 12% 33% 21% 4	540
October	1st to 10th	Night	31% 11% 33% 21% 4 1	560
	11th to 20th	Night	34% 10% 29% 20% 7% 1	782
	21st to end	Night	39% 15% 23% 17% 5% 1	891
November	1st to 10th	Night	32% 20% 30% 14% 3	830
	11th to 20th	Night	33% 16% 31% 15% 5% 1	850
	21st to end	Night	32% 21% 32% 14% 2	850
December	1st to 10th	Night	29% 18% 34% 15% 5% 1	850
	11th to 20th	Night	33% 21% 32% 11% 2	850
	21st to end	Night	24% 20% 33% 17% 4 1	935

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