Morrow
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morrow clear sky chart from 2005-11-06 to 2026-01-02.

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	14% 9% 3 8% 5% 5% 5% 4 5% 7% 35%	127746
	Night	14% 10% 4 8% 5% 4 4 3 5% 7% 36%	123499
Transparency	Day	46% 6% 11% 23% 14% 1	131386
	Night	46% 5% 10% 22% 14% 2	127928
Seeing	Day	18% 10% 26% 23% 16% 7%	16828
	Night	18% 8% 26% 31% 15% 2	26361

By Month

Percentage Cloud Cover SE (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	15% 18% 9% 13% 4 3 3 3 4 4 23%	3794
	11th to 20th	Day	14% 16% 6% 14% 6% 6% 5% 3 3 4 25%	4060
	21st to end	Day	22% 13% 7% 9% 5% 5% 4 3 4 5% 22%	4466
February	1st to 10th	Day	19% 14% 5% 9% 6% 4 4 3 5% 4 28%	1880
	11th to 20th	Day	17% 11% 4 11% 7% 5% 3 3 5% 5% 28%	1948
	21st to end	Day	18% 14% 4 9% 5% 4 4 3 4 6% 30%	1650
March	1st to 10th	Day	17% 15% 6% 9% 5% 4 3 3 4 5% 30%	4561
	11th to 20th	Day	13% 8% 3 7% 5% 4 4 3 6% 7% 40%	4980
	21st to end	Day	17% 10% 3 8% 4 4 5% 3 6% 7% 34%	5465
April	1st to 10th	Day	16% 10% 4 7% 5% 5% 5% 4 5% 7% 34%	2335
	11th to 20th	Day	16% 9% 3 7% 5% 4 4 3 5% 5% 39%	2447
	21st to end	Day	18% 8% 3 7% 4 4 5% 3 5% 8% 35%	2600
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 5% 7% 29%	5862
	11th to 20th	Day	19% 8% 3 8% 4 4 5% 3 5% 8% 33%	5861
	21st to end	Day	14% 6% 2 7% 6% 5% 6% 5% 8% 9% 32%	6433
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 6% 8% 40%	2600
	11th to 20th	Day	10% 6% 2 6% 4 5% 4 5% 6% 9% 42%	2756
	21st to end	Day	8% 7% 2 6% 6% 5% 6% 5% 7% 9% 40%	2800
July	1st to 10th	Day	9% 6% 2 7% 4 5% 5% 4 6% 9% 41%	6360
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 10% 37%	6043
	21st to end	Day	10% 7% 3 8% 6% 6% 7% 5% 7% 10% 32%	6424
August	1st to 10th	Day	8% 5% 2 6% 4 5% 5% 5% 7% 10% 43%	4234
	11th to 20th	Day	8% 5% 2 6% 4 4 6% 5% 7% 10% 41%	4174
	21st to end	Day	6% 4 1 5% 3 4 4 3 5% 8% 55%	4390
September	1st to 10th	Day	12% 5% 2 5% 5% 4 4 3 5% 7% 50%	2260
	11th to 20th	Day	9% 5% 2 5% 5% 4 4 3 6% 9% 50%	2200
	21st to end	Day	16% 6% 3 6% 4 3 3 2 5% 6% 46%	2200
October	1st to 10th	Day	10% 4 2 5% 4 5% 5% 3 5% 6% 50%	2200
	11th to 20th	Day	14% 7% 2 5% 3 4 3 3 5% 6% 47%	2013
	21st to end	Day	20% 8% 3 6% 3 3 4 2 5% 6% 39%	2070
November	1st to 10th	Day	10% 7% 2 5% 4 4 4 3 4 6% 51%	1852
	11th to 20th	Day	14% 12% 4 8% 5% 4 4 3 5% 6% 35%	1890
	21st to end	Day	18% 12% 4 8% 5% 4 4 2 4 6% 34%	1890
December	1st to 10th	Day	18% 11% 4 8% 5% 4 3 3 4 5% 35%	3020
	11th to 20th	Day	18% 15% 5% 10% 5% 4 5% 3 5% 5% 24%	3463
	21st to end	Day	20% 20% 6% 10% 5% 5% 4 3 4 5% 18%	4565
January	1st to 10th	Night	15% 16% 7% 14% 8% 5% 4 3 4 4 19%	6015
	11th to 20th	Night	14% 16% 7% 13% 8% 5% 5% 4 4 5% 20%	5900
	21st to end	Night	21% 13% 5% 8% 5% 4 4 3 4 4 29%	6490
February	1st to 10th	Night	21% 13% 4 9% 4 5% 4 4 4 5% 28%	2516
	11th to 20th	Night	18% 11% 4 9% 5% 4 5% 3 5% 5% 30%	2338
	21st to end	Night	20% 14% 5% 7% 4 3 4 3 3 5% 31%	1980
March	1st to 10th	Night	18% 13% 3 6% 4 3 3 3 4 5% 37%	5291
	11th to 20th	Night	11% 7% 3 6% 4 4 5% 4 6% 7% 42%	4980
	21st to end	Night	18% 9% 4 8% 5% 5% 4 3 5% 6% 34%	5467
April	1st to 10th	Night	16% 9% 2 6% 4 4 5% 4 5% 5% 38%	2081
	11th to 20th	Night	14% 8% 3 6% 4 3 4 4 6% 8% 41%	1900
	21st to end	Night	16% 8% 3 6% 4 5% 3 4 7% 8% 37%	1800
May	1st to 10th	Night	21% 10% 4 8% 5% 5% 4 4 6% 7% 27%	4033
	11th to 20th	Night	16% 7% 2 7% 5% 4 5% 4 7% 9% 34%	4032
	21st to end	Night	13% 7% 2 6% 5% 5% 5% 4 7% 9% 38%	4421
June	1st to 10th	Night	9% 4 2 5% 5% 4 4 4 5% 9% 49%	1800
	11th to 20th	Night	9% 5% 2 5% 4 3 4 5% 8% 10% 46%	1637
	21st to end	Night	6% 4 1 5% 5% 5% 6% 5% 8% 9% 46%	1600
July	1st to 10th	Night	9% 6% 2 6% 4 4 4 3 5% 8% 48%	3618
	11th to 20th	Night	8% 6% 2 7% 5% 5% 5% 5% 6% 10% 42%	3915
	21st to end	Night	9% 6% 2 7% 5% 5% 5% 4 7% 9% 40%	4427
August	1st to 10th	Night	8% 6% 3 7% 4 5% 5% 4 7% 8% 43%	2915
	11th to 20th	Night	7% 8% 3 7% 5% 4 4 4 6% 8% 46%	2875
	21st to end	Night	4 3 1 4 3 4 5% 4 6% 9% 57%	3504
September	1st to 10th	Night	10% 5% 2 5% 3 4 4 3 5% 7% 52%	2118
	11th to 20th	Night	8% 4 2 5% 3 4 4 3 5% 7% 55%	2200
	21st to end	Night	15% 6% 2 6% 4 3 3 3 4 6% 49%	2200
October	1st to 10th	Night	9% 4 2 6% 3 4 3 4 4 7% 55%	2200
	11th to 20th	Night	13% 7% 2 7% 5% 3 4 4 5% 6% 45%	2386
	21st to end	Night	19% 7% 3 6% 4 3 4 3 5% 6% 40%	2769
November	1st to 10th	Night	13% 8% 2 6% 4 3 4 3 5% 6% 46%	2666
	11th to 20th	Night	16% 9% 3 7% 4 4 3 3 5% 6% 39%	2730
	21st to end	Night	19% 13% 4 7% 5% 4 4 3 5% 6% 30%	2730
December	1st to 10th	Night	16% 11% 4 9% 4 4 3 3 4 5% 36%	4380
	11th to 20th	Night	19% 14% 6% 10% 6% 4 4 3 4 6% 25%	4952
	21st to end	Night	21% 19% 7% 12% 5% 5% 4 3 4 5% 17%	6633

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	64% 4 8% 17% 7%	3795
	11th to 20th	Day	64% 4 9% 12% 10% 2	4060
	21st to end	Day	65% 3 10% 14% 6% 1	4466
February	1st to 10th	Day	59% 5% 9% 16% 9% 2	1880
	11th to 20th	Day	58% 4 9% 18% 10% 1	1958
	21st to end	Day	56% 4 9% 20% 8% 2	1650
March	1st to 10th	Day	57% 4 7% 19% 11% 2	4561
	11th to 20th	Day	42% 5% 10% 28% 15% 1	4980
	21st to end	Day	49% 5% 12% 21% 11% 2	5465
April	1st to 10th	Day	48% 6% 11% 22% 12% 1	2335
	11th to 20th	Day	46% 5% 10% 22% 13% 3	2447
	21st to end	Day	48% 5% 11% 22% 11% 2	2600
May	1st to 10th	Day	52% 7% 12% 18% 10% 1	5897
	11th to 20th	Day	49% 6% 12% 23% 9%	5865
	21st to end	Day	43% 8% 14% 21% 12% 1	6447
June	1st to 10th	Day	40% 7% 11% 23% 16% 2	2600
	11th to 20th	Day	36% 8% 14% 23% 17% 2	2756
	21st to end	Day	38% 8% 15% 21% 15% 3	2800
July	1st to 10th	Day	38% 6% 12% 26% 17% 1	6291
	11th to 20th	Day	39% 7% 14% 26% 13% 1	5970
	21st to end	Day	45% 8% 13% 19% 13% 2	6240
August	1st to 10th	Day	33% 8% 16% 32% 11% 1	4221
	11th to 20th	Day	34% 7% 12% 32% 15% 1	4213
	21st to end	Day	27% 5% 14% 31% 20% 3	4389
September	1st to 10th	Day	34% 5% 11% 25% 20% 5%	2260
	11th to 20th	Day	30% 6% 12% 26% 23% 3	2200
	21st to end	Day	40% 5% 9% 22% 22% 2	2200
October	1st to 10th	Day	23% 4 9% 31% 31% 2	3590
	11th to 20th	Day	30% 3 9% 30% 25% 2	3253
	21st to end	Day	36% 3 11% 24% 24% 2	3320
November	1st to 10th	Day	34% 5% 9% 29% 20% 3	1852
	11th to 20th	Day	49% 4 8% 21% 15% 3	1890
	21st to end	Day	53% 4 9% 23% 12% 1	1890
December	1st to 10th	Day	52% 4 10% 25% 9%	3020
	11th to 20th	Day	62% 5% 8% 18% 7%	3460
	21st to end	Day	68% 4 10% 11% 5% 1	4565
January	1st to 10th	Night	67% 5% 7% 13% 7%	6015
	11th to 20th	Night	67% 4 9% 12% 7% 2	5900
	21st to end	Night	58% 4 9% 19% 9% 1	6490
February	1st to 10th	Night	58% 4 10% 19% 8% 1	2516
	11th to 20th	Night	55% 4 9% 19% 11% 1	2339
	21st to end	Night	56% 4 10% 17% 10% 2	1980
March	1st to 10th	Night	50% 4 6% 27% 11% 2	5291
	11th to 20th	Night	39% 6% 11% 29% 15% 1	4980
	21st to end	Night	51% 5% 7% 24% 11% 2	5467
April	1st to 10th	Night	46% 6% 11% 23% 12% 2	2081
	11th to 20th	Night	41% 5% 12% 19% 19% 5%	1900
	21st to end	Night	44% 5% 11% 23% 14% 3	1800
May	1st to 10th	Night	55% 8% 9% 18% 7% 3	4060
	11th to 20th	Night	45% 8% 13% 23% 10% 1	4033
	21st to end	Night	39% 8% 16% 23% 10% 3	4429
June	1st to 10th	Night	31% 8% 11% 27% 21% 2	1800
	11th to 20th	Night	31% 9% 15% 22% 19% 4	1637
	21st to end	Night	31% 9% 16% 22% 17% 5%	1600
July	1st to 10th	Night	34% 6% 12% 24% 19% 4	3580
	11th to 20th	Night	35% 8% 15% 27% 14% 1	3868
	21st to end	Night	37% 7% 13% 25% 15% 3	4297
August	1st to 10th	Night	35% 8% 13% 31% 12% 1	2904
	11th to 20th	Night	35% 6% 12% 28% 18% 1	2902
	21st to end	Night	21% 6% 15% 32% 22% 3	3504
September	1st to 10th	Night	31% 5% 13% 25% 20% 6%	2118
	11th to 20th	Night	28% 5% 10% 25% 29% 3	2200
	21st to end	Night	37% 4 9% 22% 25% 3	2200
October	1st to 10th	Night	23% 3 7% 27% 37% 3	3590
	11th to 20th	Night	28% 4 10% 26% 31% 3	3885
	21st to end	Night	33% 3 8% 23% 27% 5%	4469
November	1st to 10th	Night	38% 4 11% 22% 21% 3	2666
	11th to 20th	Night	45% 4 9% 23% 17% 3	2730
	21st to end	Night	54% 4 11% 20% 10% 1	2730
December	1st to 10th	Night	51% 4 11% 24% 9%	4380
	11th to 20th	Night	61% 4 11% 18% 7%	4954
	21st to end	Night	70% 4 8% 14% 3	6633

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	23% 19% 37% 15% 5%	303
	11th to 20th	Day	27% 20% 37% 13% 3	300
	21st to end	Day	30% 18% 35% 15% 2	330
February	1st to 10th	Day	28% 19% 35% 15% 3	300
	11th to 20th	Day	29% 24% 33% 12% 2	300
	21st to end	Day	27% 18% 44% 10% 1	249
March	1st to 10th	Day	23% 24% 35% 15% 3	329
	11th to 20th	Day	25% 15% 36% 19% 5%	500
	21st to end	Day	30% 16% 30% 19% 5%	550
April	1st to 10th	Day	22% 16% 30% 22% 9% 1	500
	11th to 20th	Day	23% 16% 26% 21% 10% 3	492
	21st to end	Day	22% 12% 34% 20% 10% 2	500
May	1st to 10th	Day	24% 10% 31% 22% 8% 4	503
	11th to 20th	Day	21% 7% 27% 23% 15% 6%	527
	21st to end	Day	14% 6% 25% 27% 18% 10%	573
June	1st to 10th	Day	12% 5% 23% 29% 23% 8%	530
	11th to 20th	Day	13% 4 19% 31% 26% 7%	686
	21st to end	Day	9% 5% 22% 31% 22% 10%	730
July	1st to 10th	Day	13% 4 15% 26% 23% 19%	721
	11th to 20th	Day	9% 4 19% 29% 26% 14%	585
	21st to end	Day	11% 2 15% 29% 26% 16%	576
August	1st to 10th	Day	11% 3 12% 27% 29% 18%	526
	11th to 20th	Day	11% 4 17% 29% 25% 14%	519
	21st to end	Day	10% 3 12% 29% 30% 16%	583
September	1st to 10th	Day	11% 4 14% 27% 31% 13%	530
	11th to 20th	Day	10% 3 12% 25% 34% 16%	530
	21st to end	Day	18% 7% 20% 24% 22% 9%	530
October	1st to 10th	Day	10% 5% 21% 34% 22% 9%	530
	11th to 20th	Day	15% 12% 30% 25% 14% 5%	530
	21st to end	Day	24% 10% 35% 23% 7% 1	453
November	1st to 10th	Day	15% 12% 35% 24% 11% 3	330
	11th to 20th	Day	22% 18% 31% 20% 7% 2	330
	21st to end	Day	25% 14% 38% 20% 3	330
December	1st to 10th	Day	22% 18% 39% 15% 5% 1	330
	11th to 20th	Day	23% 18% 39% 15% 5%	330
	21st to end	Day	31% 15% 34% 17% 3	363
January	1st to 10th	Night	24% 16% 34% 22% 5%	866
	11th to 20th	Night	28% 15% 33% 22% 3	800
	21st to end	Night	22% 13% 38% 24% 3	880
February	1st to 10th	Night	27% 11% 35% 24% 2	800
	11th to 20th	Night	25% 13% 37% 23% 2	783
	21st to end	Night	28% 10% 37% 23% 2	660
March	1st to 10th	Night	22% 13% 34% 26% 5%	800
	11th to 20th	Night	22% 12% 35% 25% 6% 1	800
	21st to end	Night	22% 10% 35% 26% 7%	880
April	1st to 10th	Night	21% 11% 35% 26% 7%	681
	11th to 20th	Night	18% 10% 33% 28% 10% 1	593
	21st to end	Night	18% 6% 37% 29% 9% 1	600
May	1st to 10th	Night	22% 5% 31% 29% 12% 1	600
	11th to 20th	Night	18% 5% 22% 35% 18% 3	591
	21st to end	Night	10% 3 22% 38% 23% 5%	650
June	1st to 10th	Night	10% 2 18% 45% 24% 2	600
	11th to 20th	Night	10% 4 13% 45% 26% 3	600
	21st to end	Night	6% 2 18% 44% 28% 2	600
July	1st to 10th	Night	12% 2 10% 35% 32% 9%	585
	11th to 20th	Night	8% 2 11% 39% 35% 4	582
	21st to end	Night	11% 2 9% 41% 33% 4	657
August	1st to 10th	Night	9% 3 8% 40% 35% 5%	597
	11th to 20th	Night	9% 2 10% 43% 30% 5%	594
	21st to end	Night	7% 2 11% 38% 36% 7%	660
September	1st to 10th	Night	12% 2 13% 34% 34% 5%	718
	11th to 20th	Night	9% 3 14% 36% 34% 5%	800
	21st to end	Night	16% 5% 20% 32% 24% 2	800
October	1st to 10th	Night	11% 4 20% 37% 24% 4	800
	11th to 20th	Night	16% 8% 27% 34% 14% 1	800
	21st to end	Night	21% 8% 33% 27% 11%	880
November	1st to 10th	Night	17% 7% 31% 30% 14% 1	820
	11th to 20th	Night	20% 13% 32% 26% 9% 1	840
	21st to end	Night	25% 11% 26% 29% 7% 1	840
December	1st to 10th	Night	26% 9% 34% 25% 5%	840
	11th to 20th	Night	26% 9% 33% 26% 5% 1	840
	21st to end	Night	30% 11% 33% 24% 3	924

Page generated at 2025-12-30 01:14:04. Version ac07

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