Narrows Lock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Narrows Lock clear sky chart from 2005-11-06 to 2026-03-18.

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	16% 10% 3 8% 5% 5% 4 3 5% 7% 32%	131515
	Night	17% 11% 4 9% 5% 4 4 3 5% 6% 31%	129969
Transparency	Day	50% 6% 12% 21% 11% 1	135006
	Night	52% 6% 11% 19% 10% 1	134565
Seeing	Day	24% 16% 31% 19% 8% 2	16126
	Night	23% 14% 30% 23% 9% 1	25408

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% 6% 12% 7% 5% 5% 3 5% 5% 23%	4661
	11th to 20th	Day	12% 19% 8% 16% 6% 5% 4 3 4 4 19%	4650
	21st to end	Day	11% 16% 6% 15% 7% 8% 5% 3 4 5% 19%	5518
February	1st to 10th	Day	15% 15% 4 11% 7% 5% 4 4 5% 6% 24%	1890
	11th to 20th	Day	12% 14% 6% 11% 6% 5% 5% 3 5% 5% 27%	1843
	21st to end	Day	20% 15% 5% 10% 7% 5% 5% 3 4 4 23%	1724
March	1st to 10th	Day	19% 13% 4 10% 5% 4 4 3 4 5% 28%	4662
	11th to 20th	Day	11% 13% 4 8% 6% 5% 5% 4 6% 7% 32%	5057
	21st to end	Day	18% 11% 4 8% 4 4 3 3 4 4 38%	5726
April	1st to 10th	Day	20% 13% 3 7% 4 4 4 2 4 6% 33%	2400
	11th to 20th	Day	21% 10% 2 7% 4 3 3 3 4 5% 37%	2374
	21st to end	Day	21% 10% 3 8% 4 4 4 3 5% 5% 32%	2505
May	1st to 10th	Day	24% 10% 4 8% 5% 4 5% 3 4 6% 27%	6346
	11th to 20th	Day	16% 9% 3 8% 5% 5% 4 4 5% 7% 34%	6318
	21st to end	Day	19% 8% 2 7% 4 4 5% 4 6% 7% 34%	6949
June	1st to 10th	Day	20% 9% 3 7% 5% 5% 5% 4 6% 7% 31%	2800
	11th to 20th	Day	15% 6% 2 6% 5% 4 5% 4 6% 9% 38%	2800
	21st to end	Day	16% 8% 3 7% 6% 5% 5% 4 6% 7% 34%	2800
July	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 5% 7% 9% 36%	6360
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 4 7% 8% 43%	6360
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 9% 45%	6926
August	1st to 10th	Day	16% 8% 3 7% 4 4 4 4 5% 7% 38%	4382
	11th to 20th	Day	17% 7% 2 5% 4 4 4 4 6% 9% 37%	4141
	21st to end	Day	15% 6% 2 6% 4 4 4 4 6% 9% 39%	4312
September	1st to 10th	Day	13% 5% 2 6% 5% 4 6% 3 6% 8% 42%	2400
	11th to 20th	Day	12% 5% 2 5% 3 5% 4 3 5% 7% 48%	2400
	21st to end	Day	18% 6% 2 6% 4 5% 4 3 5% 7% 40%	2124
October	1st to 10th	Day	20% 8% 3 6% 4 4 4 2 4 7% 38%	2000
	11th to 20th	Day	19% 9% 4 8% 5% 4 4 3 6% 7% 30%	2000
	21st to end	Day	26% 9% 2 8% 5% 4 5% 4 5% 6% 27%	2077
November	1st to 10th	Day	15% 10% 3 7% 5% 5% 6% 3 6% 7% 33%	1851
	11th to 20th	Day	16% 13% 3 10% 5% 5% 4 3 4 6% 30%	1685
	21st to end	Day	20% 16% 4 9% 6% 5% 6% 3 5% 4 23%	1680
December	1st to 10th	Day	21% 18% 5% 12% 5% 5% 4 4 5% 5% 17%	2680
	11th to 20th	Day	18% 19% 4 11% 6% 4 4 3 4 4 23%	3066
	21st to end	Day	21% 17% 5% 13% 6% 4 3 2 3 4 22%	4048
January	1st to 10th	Night	14% 16% 7% 13% 7% 5% 5% 3 4 5% 21%	8234
	11th to 20th	Night	12% 18% 7% 15% 8% 6% 5% 4 4 5% 17%	8235
	21st to end	Night	14% 15% 6% 12% 7% 6% 5% 4 5% 5% 23%	8659
February	1st to 10th	Night	15% 15% 5% 10% 6% 5% 5% 4 6% 5% 24%	2730
	11th to 20th	Night	13% 16% 5% 10% 6% 5% 4 3 4 6% 29%	2663
	21st to end	Night	15% 15% 4 10% 6% 5% 4 3 5% 5% 28%	2081
March	1st to 10th	Night	21% 13% 3 9% 5% 5% 4 2 3 4 30%	5395
	11th to 20th	Night	15% 12% 3 7% 4 5% 5% 4 7% 8% 30%	5057
	21st to end	Night	19% 10% 3 9% 4 4 4 3 4 5% 35%	5204
April	1st to 10th	Night	22% 10% 3 8% 5% 4 4 3 4 6% 34%	2000
	11th to 20th	Night	21% 9% 3 6% 4 4 4 3 4 5% 37%	1975
	21st to end	Night	21% 10% 3 7% 4 3 4 4 4 6% 33%	1911
May	1st to 10th	Night	25% 10% 3 8% 4 5% 4 4 5% 6% 25%	3594
	11th to 20th	Night	15% 8% 3 7% 4 4 4 3 6% 7% 40%	3575
	21st to end	Night	18% 8% 2 7% 4 4 5% 4 6% 7% 35%	3926
June	1st to 10th	Night	16% 7% 2 7% 6% 5% 5% 6% 6% 8% 33%	1600
	11th to 20th	Night	14% 6% 3 5% 4 5% 4 4 6% 8% 41%	1600
	21st to end	Night	18% 7% 2 7% 5% 5% 4 4 6% 9% 35%	1600
July	1st to 10th	Night	12% 5% 2 7% 5% 5% 5% 5% 7% 9% 37%	3600
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 5% 7% 46%	3600
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 5% 7% 50%	3926
August	1st to 10th	Night	12% 7% 2 6% 5% 4 5% 4 6% 7% 43%	2750
	11th to 20th	Night	12% 7% 2 6% 5% 4 4 4 5% 7% 43%	2875
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	3586
September	1st to 10th	Night	12% 5% 2 6% 5% 4 4 3 5% 7% 47%	2000
	11th to 20th	Night	12% 4 2 5% 3 3 4 3 6% 7% 51%	2000
	21st to end	Night	17% 7% 2 5% 4 4 4 3 6% 6% 42%	2273
October	1st to 10th	Night	17% 7% 3 6% 5% 4 4 3 5% 6% 39%	2400
	11th to 20th	Night	21% 9% 2 7% 5% 4 4 4 5% 6% 32%	2400
	21st to end	Night	22% 10% 3 7% 4 5% 4 3 5% 5% 31%	2761
November	1st to 10th	Night	18% 11% 3 6% 4 4 4 4 6% 6% 34%	2667
	11th to 20th	Night	17% 10% 4 8% 5% 4 4 4 4 6% 33%	2934
	21st to end	Night	21% 14% 4 9% 5% 5% 5% 4 5% 6% 24%	2940
December	1st to 10th	Night	19% 17% 5% 12% 6% 5% 4 3 5% 6% 18%	4720
	11th to 20th	Night	22% 14% 4 9% 5% 4 4 3 4 5% 26%	5348
	21st to end	Night	27% 16% 4 11% 5% 3 3 3 4 4 20%	7150

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	62% 6% 12% 15% 5% 1	4662
	11th to 20th	Day	70% 4 9% 9% 8% 1	4680
	21st to end	Day	67% 5% 8% 10% 9% 1	5518
February	1st to 10th	Day	61% 5% 9% 17% 7% 1	1890
	11th to 20th	Day	59% 4 11% 17% 9% 1	1852
	21st to end	Day	65% 5% 8% 12% 9% 1	1724
March	1st to 10th	Day	58% 4 9% 14% 12% 3	4665
	11th to 20th	Day	51% 5% 18% 14% 11% 2	5057
	21st to end	Day	50% 3 6% 20% 18% 3	5726
April	1st to 10th	Day	55% 4 7% 18% 13% 3	2400
	11th to 20th	Day	50% 4 7% 20% 17% 2	2374
	21st to end	Day	54% 5% 8% 16% 14% 3	2505
May	1st to 10th	Day	57% 6% 8% 17% 10% 2	6357
	11th to 20th	Day	49% 7% 11% 19% 13% 1	6322
	21st to end	Day	48% 6% 12% 22% 10% 1	6949
June	1st to 10th	Day	50% 7% 10% 19% 12% 1	2800
	11th to 20th	Day	42% 6% 11% 26% 13% 2	2800
	21st to end	Day	47% 8% 13% 20% 11% 1	2800
July	1st to 10th	Day	41% 7% 14% 26% 11% 1	6290
	11th to 20th	Day	36% 7% 15% 28% 15%	6285
	21st to end	Day	34% 7% 14% 35% 10%	6728
August	1st to 10th	Day	44% 5% 15% 24% 11% 1	4368
	11th to 20th	Day	42% 7% 13% 27% 10% 1	4180
	21st to end	Day	39% 6% 15% 29% 11%	4312
September	1st to 10th	Day	38% 7% 14% 28% 12% 1	2400
	11th to 20th	Day	35% 6% 13% 30% 16% 1	2400
	21st to end	Day	44% 6% 12% 25% 12%	2124
October	1st to 10th	Day	42% 5% 13% 31% 9%	3260
	11th to 20th	Day	44% 5% 15% 26% 9% 1	3240
	21st to end	Day	48% 6% 15% 24% 7%	3328
November	1st to 10th	Day	49% 7% 13% 22% 9% 1	1851
	11th to 20th	Day	55% 6% 10% 17% 10% 1	1685
	21st to end	Day	63% 7% 11% 11% 8%	1680
December	1st to 10th	Day	68% 6% 14% 9% 3	2680
	11th to 20th	Day	65% 5% 10% 14% 6%	3066
	21st to end	Day	66% 4 8% 15% 6%	4048
January	1st to 10th	Night	65% 6% 12% 13% 5%	8234
	11th to 20th	Night	69% 6% 8% 10% 6%	8280
	21st to end	Night	61% 6% 8% 13% 11% 1	8659
February	1st to 10th	Night	61% 6% 10% 16% 7% 1	2730
	11th to 20th	Night	58% 4 11% 19% 8% 1	2665
	21st to end	Night	58% 5% 9% 17% 10% 1	2081
March	1st to 10th	Night	59% 4 6% 17% 10% 4	5405
	11th to 20th	Night	49% 6% 19% 15% 8% 3	5058
	21st to end	Night	51% 4 8% 21% 14% 2	5204
April	1st to 10th	Night	53% 4 7% 20% 14% 3	2000
	11th to 20th	Night	49% 6% 7% 20% 17% 1	1975
	21st to end	Night	52% 4 9% 16% 15% 4	1911
May	1st to 10th	Night	58% 6% 8% 16% 8% 3	3600
	11th to 20th	Night	43% 7% 14% 21% 14% 1	3576
	21st to end	Night	47% 7% 13% 18% 14% 1	3927
June	1st to 10th	Night	46% 8% 11% 21% 12% 1	1600
	11th to 20th	Night	40% 6% 13% 22% 18% 2	1600
	21st to end	Night	45% 9% 12% 20% 12% 1	1600
July	1st to 10th	Night	41% 7% 16% 19% 16% 1	3560
	11th to 20th	Night	35% 7% 13% 31% 12%	3552
	21st to end	Night	33% 7% 13% 32% 14% 1	3809
August	1st to 10th	Night	39% 7% 14% 27% 13% 1	2740
	11th to 20th	Night	39% 6% 13% 30% 10% 1	2902
	21st to end	Night	35% 9% 16% 28% 11% 1	3586
September	1st to 10th	Night	36% 7% 13% 30% 14% 1	2000
	11th to 20th	Night	31% 7% 13% 34% 14% 1	2000
	21st to end	Night	42% 6% 10% 29% 13% 1	2273
October	1st to 10th	Night	39% 6% 12% 28% 15%	3920
	11th to 20th	Night	43% 6% 15% 26% 10%	3899
	21st to end	Night	48% 6% 14% 25% 8%	4460
November	1st to 10th	Night	49% 6% 13% 21% 10% 1	2667
	11th to 20th	Night	52% 5% 12% 20% 11% 2	2934
	21st to end	Night	61% 7% 11% 16% 5%	2940
December	1st to 10th	Night	67% 6% 12% 12% 3	4720
	11th to 20th	Night	61% 6% 9% 15% 9% 1	5348
	21st to end	Night	67% 5% 7% 11% 9%	7150

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	27% 19% 37% 14% 3	220
	11th to 20th	Day	35% 17% 32% 14% 2	220
	21st to end	Day	24% 24% 31% 18% 4	314
February	1st to 10th	Day	32% 21% 33% 11% 2	330
	11th to 20th	Day	30% 24% 37% 9% 1	330
	21st to end	Day	34% 20% 34% 11% 1	440
March	1st to 10th	Day	28% 21% 32% 15% 4	540
	11th to 20th	Day	33% 20% 29% 14% 4	528
	21st to end	Day	33% 21% 28% 12% 6% 1	550
April	1st to 10th	Day	31% 22% 29% 13% 5%	500
	11th to 20th	Day	34% 18% 24% 13% 8% 2	492
	21st to end	Day	29% 19% 34% 11% 5% 2	500
May	1st to 10th	Day	25% 18% 30% 19% 6% 2	503
	11th to 20th	Day	19% 14% 37% 20% 9% 2	527
	21st to end	Day	21% 13% 31% 24% 9% 2	573
June	1st to 10th	Day	21% 15% 33% 23% 6% 2	530
	11th to 20th	Day	17% 15% 35% 19% 12% 2	530
	21st to end	Day	20% 16% 30% 23% 9% 3	530
July	1st to 10th	Day	12% 10% 32% 30% 14% 3	525
	11th to 20th	Day	15% 10% 31% 26% 14% 3	524
	21st to end	Day	13% 10% 33% 29% 11% 4	576
August	1st to 10th	Day	15% 7% 28% 32% 13% 4	526
	11th to 20th	Day	16% 5% 27% 30% 16% 6%	519
	21st to end	Day	16% 11% 31% 23% 13% 6%	583
September	1st to 10th	Day	14% 13% 30% 24% 12% 7%	530
	11th to 20th	Day	10% 9% 24% 27% 17% 12%	530
	21st to end	Day	20% 10% 28% 25% 13% 4	530
October	1st to 10th	Day	25% 16% 25% 18% 12% 4	530
	11th to 20th	Day	26% 19% 32% 15% 6% 2	530
	21st to end	Day	30% 19% 28% 19% 4	514
November	1st to 10th	Day	27% 19% 29% 18% 7%	425
	11th to 20th	Day	28% 16% 36% 11% 7% 2	225
	21st to end	Day	31% 21% 35% 11% 3	220
December	1st to 10th	Day	35% 17% 32% 12% 4	220
	11th to 20th	Day	35% 21% 35% 4 5%	220
	21st to end	Day	34% 19% 31% 12% 4	242
January	1st to 10th	Night	28% 18% 32% 19% 3	840
	11th to 20th	Night	30% 17% 29% 19% 5%	840
	21st to end	Night	20% 17% 35% 22% 6%	924
February	1st to 10th	Night	25% 19% 35% 19% 3	840
	11th to 20th	Night	24% 19% 38% 15% 3	823
	21st to end	Night	26% 18% 34% 18% 3	692
March	1st to 10th	Night	27% 17% 32% 21% 3	840
	11th to 20th	Night	28% 20% 27% 21% 3	829
	21st to end	Night	24% 17% 32% 20% 7%	880
April	1st to 10th	Night	28% 16% 32% 22% 3	800
	11th to 20th	Night	26% 20% 28% 18% 7% 1	791
	21st to end	Night	26% 13% 29% 23% 7% 1	711
May	1st to 10th	Night	26% 11% 25% 27% 11% 1	400
	11th to 20th	Night	15% 12% 34% 30% 8%	394
	21st to end	Night	13% 9% 39% 27% 11%	433
June	1st to 10th	Night	17% 7% 32% 34% 10% 1	400
	11th to 20th	Night	15% 11% 30% 31% 13% 1	400
	21st to end	Night	19% 7% 27% 35% 13% 1	400
July	1st to 10th	Night	11% 7% 31% 37% 14% 1	390
	11th to 20th	Night	14% 5% 27% 38% 15% 1	388
	21st to end	Night	9% 6% 29% 42% 13% 1	438
August	1st to 10th	Night	14% 4 26% 34% 21% 1	497
	11th to 20th	Night	13% 5% 23% 34% 23% 3	594
	21st to end	Night	12% 7% 30% 33% 16% 2	880
September	1st to 10th	Night	13% 7% 31% 31% 17% 1	800
	11th to 20th	Night	15% 7% 21% 28% 24% 6%	800
	21st to end	Night	20% 9% 25% 26% 18% 2	800
October	1st to 10th	Night	21% 12% 28% 21% 16% 2	800
	11th to 20th	Night	26% 13% 31% 22% 7% 1	800
	21st to end	Night	29% 13% 28% 24% 6%	880
November	1st to 10th	Night	28% 15% 30% 20% 7%	820
	11th to 20th	Night	25% 17% 33% 17% 8%	840
	21st to end	Night	31% 18% 28% 17% 5%	840
December	1st to 10th	Night	30% 19% 30% 18% 4	840
	11th to 20th	Night	27% 20% 32% 17% 2 1	840
	21st to end	Night	34% 17% 29% 18% 2	924

Page generated at 2026-03-15 02:23:56. Version ac07

Copyright © 2026 Attilla Danko.