Little Bow Reservoir
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Little Bow Reservoir clear sky chart from 2005-11-06 to 2025-11-18.

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	8% 8% 3 7% 5% 5% 5% 4 6% 8% 42%	131085
	Night	6% 9% 3 9% 5% 5% 5% 4 6% 8% 39%	127995
Transparency	Day	38% 7% 14% 26% 13% 2	130784
	Night	41% 7% 15% 23% 12% 2	127873
Seeing	Day	11% 9% 25% 29% 19% 6%	16783
	Night	11% 9% 31% 33% 15% 2	25877

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% 15% 7% 13% 6% 5% 4 4 5% 8% 28%	3179
	11th to 20th	Day	3 8% 5% 11% 6% 6% 6% 6% 7% 7% 34%	3187
	21st to end	Day	3 6% 3 10% 6% 5% 4 4 5% 9% 44%	4004
February	1st to 10th	Day	7% 13% 4 11% 8% 6% 7% 5% 5% 8% 27%	1667
	11th to 20th	Day	6% 12% 5% 11% 8% 6% 6% 6% 6% 7% 29%	1755
	21st to end	Day	4 13% 6% 11% 8% 5% 4 4 6% 8% 31%	1570
March	1st to 10th	Day	4 11% 4 10% 6% 5% 5% 4 6% 10% 36%	4562
	11th to 20th	Day	5% 8% 3 9% 6% 6% 5% 4 6% 8% 39%	4999
	21st to end	Day	8% 17% 5% 12% 6% 5% 5% 5% 7% 8% 22%	5486
April	1st to 10th	Day	9% 12% 4 9% 6% 5% 5% 4 6% 7% 32%	2457
	11th to 20th	Day	10% 12% 3 8% 5% 5% 6% 5% 7% 7% 32%	2570
	21st to end	Day	10% 10% 3 8% 5% 5% 5% 5% 6% 8% 34%	2600
May	1st to 10th	Day	15% 9% 3 6% 3 3 4 4 5% 7% 41%	6035
	11th to 20th	Day	11% 8% 3 8% 6% 6% 7% 6% 8% 9% 30%	6730
	21st to end	Day	9% 7% 3 8% 5% 5% 6% 4 6% 8% 40%	7405
June	1st to 10th	Day	12% 7% 2 6% 5% 5% 6% 4 7% 9% 36%	3000
	11th to 20th	Day	15% 8% 2 8% 5% 4 5% 5% 8% 8% 32%	3000
	21st to end	Day	7% 5% 2 5% 5% 4 5% 4 7% 9% 47%	3000
July	1st to 10th	Day	7% 3 2 4 4 3 4 4 6% 8% 55%	6780
	11th to 20th	Day	8% 3 2 5% 3 4 4 3 6% 10% 51%	6780
	21st to end	Day	7% 4 1 4 3 3 3 3 5% 8% 59%	7248
August	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 7% 10% 47%	4458
	11th to 20th	Day	5% 4 2 5% 3 3 4 5% 7% 9% 51%	4158
	21st to end	Day	8% 3 1 4 3 3 3 4 5% 8% 58%	4664
September	1st to 10th	Day	9% 5% 2 4 4 3 3 3 5% 7% 56%	2477
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 6% 7% 48%	2200
	21st to end	Day	8% 7% 2 6% 3 4 4 4 5% 8% 50%	2200
October	1st to 10th	Day	8% 7% 2 7% 5% 4 5% 4 7% 8% 42%	3402
	11th to 20th	Day	5% 6% 2 6% 4 5% 5% 4 6% 8% 48%	3111
	21st to end	Day	7% 7% 3 6% 4 4 5% 4 6% 7% 47%	3200
November	1st to 10th	Day	10% 14% 3 8% 5% 5% 4 4 7% 7% 31%	1695
	11th to 20th	Day	6% 10% 3 8% 6% 5% 4 4 6% 10% 38%	1656
	21st to end	Day	4 11% 5% 10% 5% 5% 5% 4 7% 9% 34%	1420
December	1st to 10th	Day	5% 14% 5% 12% 5% 5% 5% 4 5% 7% 35%	2290
	11th to 20th	Day	4 10% 4 11% 8% 7% 6% 4 6% 8% 31%	2642
	21st to end	Day	3 9% 4 9% 6% 6% 5% 4 6% 7% 41%	3498
January	1st to 10th	Night	4 15% 7% 12% 6% 6% 6% 5% 6% 8% 26%	6766
	11th to 20th	Night	3 9% 4 12% 6% 6% 6% 5% 6% 8% 34%	6739
	21st to end	Night	3 8% 4 10% 6% 5% 5% 4 6% 7% 42%	6953
February	1st to 10th	Night	7% 11% 5% 11% 7% 7% 6% 4 5% 7% 30%	2732
	11th to 20th	Night	5% 13% 5% 11% 6% 7% 6% 5% 7% 8% 28%	2532
	21st to end	Night	4 13% 5% 10% 6% 6% 5% 4 6% 7% 33%	2056
March	1st to 10th	Night	2 8% 4 11% 6% 5% 5% 5% 7% 10% 37%	5332
	11th to 20th	Night	5% 8% 4 10% 5% 5% 6% 5% 6% 9% 37%	5000
	21st to end	Night	10% 17% 5% 12% 6% 4 5% 4 8% 8% 21%	5489
April	1st to 10th	Night	8% 12% 3 9% 6% 5% 5% 4 7% 9% 32%	1939
	11th to 20th	Night	9% 12% 5% 8% 5% 5% 5% 4 6% 9% 32%	1781
	21st to end	Night	10% 10% 3 7% 6% 6% 5% 5% 7% 7% 34%	1800
May	1st to 10th	Night	15% 11% 3 8% 5% 5% 5% 3 5% 6% 35%	3944
	11th to 20th	Night	9% 8% 3 8% 5% 7% 7% 5% 7% 10% 32%	3159
	21st to end	Night	9% 7% 2 9% 6% 5% 5% 5% 7% 8% 38%	3470
June	1st to 10th	Night	14% 7% 4 7% 4 5% 4 4 7% 7% 38%	1400
	11th to 20th	Night	16% 7% 2 5% 4 5% 6% 5% 8% 9% 32%	1400
	21st to end	Night	7% 4 2 6% 4 4 5% 4 7% 10% 48%	1400
July	1st to 10th	Night	6% 3 1 4 4 4 5% 4 7% 9% 52%	3180
	11th to 20th	Night	7% 5% 2 6% 3 4 5% 4 8% 10% 47%	3180
	21st to end	Night	6% 5% 2 5% 4 3 4 3 5% 8% 55%	3592
August	1st to 10th	Night	6% 4 2 6% 4 4 5% 5% 7% 8% 50%	2693
	11th to 20th	Night	5% 4 2 7% 4 5% 6% 5% 7% 10% 45%	2901
	21st to end	Night	6% 3 1 3 3 3 4 4 5% 8% 60%	3245
September	1st to 10th	Night	9% 5% 2 5% 3 4 4 4 6% 8% 50%	1920
	11th to 20th	Night	11% 5% 1 6% 4 3 3 3 5% 7% 52%	2200
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 6% 7% 49%	2200
October	1st to 10th	Night	7% 5% 2 5% 4 3 4 3 5% 8% 53%	3792
	11th to 20th	Night	7% 7% 3 7% 4 4 4 3 5% 8% 49%	4024
	21st to end	Night	6% 6% 2 7% 5% 5% 5% 4 6% 8% 47%	4600
November	1st to 10th	Night	9% 12% 3 9% 5% 5% 5% 4 6% 8% 35%	2801
	11th to 20th	Night	5% 10% 4 7% 5% 4 5% 5% 7% 8% 40%	2899
	21st to end	Night	5% 11% 3 9% 4 4 5% 4 7% 10% 37%	2978
December	1st to 10th	Night	4 11% 4 11% 7% 7% 7% 5% 6% 8% 32%	4890
	11th to 20th	Night	4 11% 5% 11% 6% 7% 6% 5% 7% 8% 30%	5550
	21st to end	Night	4 9% 4 8% 5% 5% 5% 4 6% 8% 42%	7458

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	53% 7% 12% 21% 6% 1	3179
	11th to 20th	Day	46% 6% 14% 17% 15% 2	3208
	21st to end	Day	37% 6% 12% 33% 11% 1	4004
February	1st to 10th	Day	55% 6% 13% 16% 8% 1	1667
	11th to 20th	Day	51% 9% 14% 18% 7% 2	1764
	21st to end	Day	50% 7% 12% 19% 11% 1	1570
March	1st to 10th	Day	41% 6% 13% 23% 16% 1	4562
	11th to 20th	Day	40% 6% 16% 23% 14% 1	5000
	21st to end	Day	55% 9% 15% 15% 5%	5486
April	1st to 10th	Day	48% 8% 14% 21% 8% 1	2457
	11th to 20th	Day	47% 7% 12% 22% 9% 2	2570
	21st to end	Day	44% 8% 14% 22% 10% 1	2600
May	1st to 10th	Day	42% 5% 9% 24% 15% 6%	6035
	11th to 20th	Day	43% 10% 14% 24% 8% 1	6734
	21st to end	Day	37% 8% 15% 27% 12%	7406
June	1st to 10th	Day	42% 8% 17% 21% 11% 2	3000
	11th to 20th	Day	44% 9% 15% 21% 10% 2	3000
	21st to end	Day	30% 8% 18% 29% 12% 3	3000
July	1st to 10th	Day	25% 6% 15% 26% 23% 5%	6706
	11th to 20th	Day	27% 6% 20% 29% 16% 3	6699
	21st to end	Day	23% 5% 14% 28% 19% 11%	7043
August	1st to 10th	Day	29% 6% 13% 36% 13% 2	4441
	11th to 20th	Day	27% 7% 18% 37% 9% 2	4197
	21st to end	Day	24% 4 13% 40% 17% 2	4663
September	1st to 10th	Day	29% 5% 14% 29% 16% 8%	2477
	11th to 20th	Day	34% 6% 13% 30% 14% 3	2200
	21st to end	Day	32% 7% 13% 31% 13% 3	2200
October	1st to 10th	Day	37% 6% 11% 33% 12% 1	3402
	11th to 20th	Day	33% 6% 17% 27% 15% 2	3111
	21st to end	Day	35% 5% 12% 33% 12% 3	3200
November	1st to 10th	Day	49% 8% 13% 20% 8% 2	1695
	11th to 20th	Day	41% 7% 18% 24% 9%	1656
	21st to end	Day	43% 8% 16% 21% 10% 2	1420
December	1st to 10th	Day	51% 6% 12% 24% 6% 2	2290
	11th to 20th	Day	50% 6% 17% 22% 4 1	2644
	21st to end	Day	39% 7% 13% 22% 19% 1	3498
January	1st to 10th	Night	54% 8% 12% 20% 5% 1	6766
	11th to 20th	Night	48% 6% 13% 16% 15% 2	6780
	21st to end	Night	39% 6% 14% 27% 13% 1	6953
February	1st to 10th	Night	51% 7% 12% 16% 12% 2	2732
	11th to 20th	Night	50% 9% 13% 17% 9% 1	2533
	21st to end	Night	46% 7% 16% 19% 9% 2	2056
March	1st to 10th	Night	39% 7% 18% 22% 12% 2	5332
	11th to 20th	Night	41% 7% 16% 25% 11% 1	5000
	21st to end	Night	57% 8% 15% 13% 6% 1	5489
April	1st to 10th	Night	46% 9% 13% 20% 12%	1939
	11th to 20th	Night	47% 7% 12% 22% 11% 2	1781
	21st to end	Night	45% 8% 12% 24% 9% 1	1800
May	1st to 10th	Night	48% 6% 9% 23% 11% 4	3941
	11th to 20th	Night	41% 10% 14% 27% 7% 1	3159
	21st to end	Night	40% 10% 15% 24% 9% 2	3470
June	1st to 10th	Night	42% 8% 13% 23% 12% 2	1400
	11th to 20th	Night	43% 8% 15% 22% 9% 3	1400
	21st to end	Night	30% 7% 19% 28% 15% 2	1400
July	1st to 10th	Night	25% 7% 18% 23% 23% 4	3145
	11th to 20th	Night	31% 6% 16% 29% 13% 4	3138
	21st to end	Night	28% 5% 15% 27% 17% 9%	3492
August	1st to 10th	Night	29% 7% 15% 30% 16% 2	2685
	11th to 20th	Night	32% 7% 19% 26% 13% 2	2928
	21st to end	Night	22% 5% 13% 37% 19% 4	3245
September	1st to 10th	Night	29% 8% 12% 26% 18% 7%	1920
	11th to 20th	Night	32% 6% 13% 28% 17% 5%	2200
	21st to end	Night	31% 6% 15% 29% 15% 4	2200
October	1st to 10th	Night	29% 5% 11% 33% 19% 3	3792
	11th to 20th	Night	33% 5% 15% 26% 18% 3	4024
	21st to end	Night	35% 6% 11% 31% 16% 1	4600
November	1st to 10th	Night	47% 6% 14% 21% 10% 1	2801
	11th to 20th	Night	39% 8% 18% 21% 14% 1	2899
	21st to end	Night	42% 7% 19% 19% 10% 3	2978
December	1st to 10th	Night	50% 8% 15% 19% 8% 1	4890
	11th to 20th	Night	50% 8% 21% 17% 4 1	5547
	21st to end	Night	39% 6% 12% 24% 16% 3	7458

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% 14% 28% 30% 14% 10%	200
	11th to 20th	Day	6% 10% 34% 31% 15% 5%	200
	21st to end	Day	8% 11% 35% 27% 15% 4	220
February	1st to 10th	Day	14% 9% 34% 31% 10% 3	235
	11th to 20th	Day	7% 10% 31% 33% 16% 3	300
	21st to end	Day	10% 13% 28% 31% 14% 4	334
March	1st to 10th	Day	10% 14% 33% 25% 13% 6%	500
	11th to 20th	Day	8% 11% 30% 28% 18% 5%	500
	21st to end	Day	12% 11% 31% 26% 15% 5%	550
April	1st to 10th	Day	13% 14% 30% 26% 14% 3	500
	11th to 20th	Day	13% 10% 29% 28% 15% 4	492
	21st to end	Day	14% 12% 27% 27% 16% 5%	500
May	1st to 10th	Day	14% 11% 21% 27% 20% 8%	567
	11th to 20th	Day	15% 6% 22% 28% 23% 6%	725
	21st to end	Day	15% 7% 19% 30% 20% 8%	789
June	1st to 10th	Day	13% 10% 24% 32% 17% 4	730
	11th to 20th	Day	16% 10% 25% 31% 16% 2	730
	21st to end	Day	8% 4 24% 32% 24% 8%	730
July	1st to 10th	Day	8% 4 17% 35% 27% 9%	721
	11th to 20th	Day	8% 4 20% 35% 24% 8%	718
	21st to end	Day	6% 4 20% 36% 25% 9%	741
August	1st to 10th	Day	8% 4 20% 34% 25% 9%	527
	11th to 20th	Day	8% 4 18% 33% 26% 11%	517
	21st to end	Day	9% 5% 20% 30% 26% 10%	583
September	1st to 10th	Day	11% 7% 23% 27% 22% 10%	530
	11th to 20th	Day	15% 7% 22% 25% 24% 7%	530
	21st to end	Day	12% 13% 27% 31% 12% 4	530
October	1st to 10th	Day	16% 10% 21% 26% 21% 7%	410
	11th to 20th	Day	11% 13% 30% 23% 18% 5%	330
	21st to end	Day	16% 17% 28% 24% 13% 2	363
November	1st to 10th	Day	21% 12% 28% 26% 12% 2	330
	11th to 20th	Day	12% 13% 38% 25% 10% 2	321
	21st to end	Day	7% 11% 37% 23% 15% 7%	210
December	1st to 10th	Day	9% 13% 32% 29% 15% 5%	200
	11th to 20th	Day	12% 16% 37% 22% 12% 2	200
	21st to end	Day	12% 8% 29% 26% 20% 5%	220
January	1st to 10th	Night	10% 14% 33% 27% 14% 1	1000
	11th to 20th	Night	9% 10% 36% 32% 11% 2	1000
	21st to end	Night	12% 11% 36% 28% 11% 2	881
February	1st to 10th	Night	10% 11% 29% 32% 14% 4	800
	11th to 20th	Night	10% 8% 32% 35% 13% 2	784
	21st to end	Night	11% 7% 28% 30% 20% 4	660
March	1st to 10th	Night	9% 7% 34% 33% 15% 2	800
	11th to 20th	Night	10% 10% 32% 34% 12% 2	800
	21st to end	Night	12% 10% 31% 30% 14% 3	880
April	1st to 10th	Night	13% 10% 33% 30% 13% 2	712
	11th to 20th	Night	16% 8% 31% 32% 12% 1	593
	21st to end	Night	15% 9% 29% 33% 14% 1	600
May	1st to 10th	Night	15% 9% 24% 33% 19% 1	600
	11th to 20th	Night	12% 7% 27% 31% 21% 2	394
	21st to end	Night	18% 7% 21% 31% 21% 2	433
June	1st to 10th	Night	18% 8% 28% 30% 15% 2	400
	11th to 20th	Night	18% 8% 29% 33% 12%	400
	21st to end	Night	8% 4 26% 41% 21% 1	400
July	1st to 10th	Night	7% 3 19% 46% 24% 1	390
	11th to 20th	Night	7% 4 24% 45% 19% 2	388
	21st to end	Night	5% 3 24% 44% 23% 2	438
August	1st to 10th	Night	8% 4 18% 42% 25% 2	443
	11th to 20th	Night	7% 3 22% 45% 21% 2	594
	21st to end	Night	8% 4 24% 40% 23% 1	660
September	1st to 10th	Night	11% 4 24% 38% 22% 2	655
	11th to 20th	Night	15% 4 19% 38% 23% 2	800
	21st to end	Night	9% 8% 32% 35% 14% 2	800
October	1st to 10th	Night	14% 8% 26% 33% 17% 2	800
	11th to 20th	Night	12% 8% 33% 31% 15% 2	800
	21st to end	Night	12% 10% 35% 31% 12% 1	880
November	1st to 10th	Night	17% 10% 39% 25% 9% 1	956
	11th to 20th	Night	10% 13% 40% 27% 8% 2	1036
	21st to end	Night	10% 14% 35% 30% 10% 1	1000
December	1st to 10th	Night	10% 11% 32% 32% 13% 2	1000
	11th to 20th	Night	8% 11% 37% 31% 11% 1	1000
	21st to end	Night	12% 11% 34% 29% 11% 2	1100

Page generated at 2025-11-14 22:55:58. Version ac07

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