CF Phelps WMA
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CF Phelps WMA clear sky chart from 2005-11-06 to 2025-02-21.

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% 6% 2 6% 4 4 4 4 6% 8% 42%	108633
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	109955
Transparency	Day	39% 5% 12% 23% 17% 4	112276
	Night	38% 4 11% 23% 19% 4	114450
Seeing	Day	18% 11% 26% 25% 14% 5%	15305
	Night	18% 9% 28% 31% 13% 1	25048

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% 5% 2 5% 4 3 4 3 5% 5% 49%	3892
	11th to 20th	Day	14% 8% 2 6% 3 4 4 3 4 4 49%	4060
	21st to end	Day	15% 8% 2 7% 4 3 4 3 4 6% 44%	4466
February	1st to 10th	Day	13% 8% 3 7% 5% 4 4 4 5% 7% 40%	1800
	11th to 20th	Day	18% 8% 2 6% 4 3 3 3 5% 6% 42%	1785
	21st to end	Day	17% 9% 3 6% 4 4 3 3 5% 6% 37%	1579
March	1st to 10th	Day	21% 8% 2 5% 5% 5% 4 3 4 6% 36%	3435
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 6% 51%	3480
	21st to end	Day	20% 7% 2 6% 4 4 3 3 6% 6% 38%	3832
April	1st to 10th	Day	12% 6% 2 6% 4 3 5% 4 5% 6% 47%	2280
	11th to 20th	Day	13% 6% 2 6% 4 4 3 3 4 6% 48%	2254
	21st to end	Day	17% 6% 2 6% 4 5% 4 4 6% 6% 41%	2280
May	1st to 10th	Day	19% 8% 2 7% 5% 5% 5% 5% 6% 8% 30%	4050
	11th to 20th	Day	23% 7% 2 6% 4 4 4 3 6% 9% 32%	4159
	21st to end	Day	11% 4 2 6% 4 4 5% 4 7% 10% 44%	4823
June	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 5% 6% 9% 44%	2660
	11th to 20th	Day	10% 4 2 7% 5% 5% 5% 4 7% 10% 41%	2660
	21st to end	Day	8% 4 1 5% 5% 5% 5% 5% 8% 10% 44%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 5% 6% 6% 9% 12% 39%	4440
	11th to 20th	Day	9% 5% 2 5% 4 4 6% 6% 8% 13% 37%	4133
	21st to end	Day	11% 7% 2 8% 6% 5% 6% 5% 7% 8% 36%	4466
August	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 5% 8% 12% 32%	4104
	11th to 20th	Day	9% 5% 2 7% 6% 6% 6% 5% 7% 9% 39%	3898
	21st to end	Day	9% 5% 1 5% 4 4 5% 4 5% 8% 50%	4180
September	1st to 10th	Day	14% 5% 2 5% 4 5% 5% 4 6% 6% 45%	2280
	11th to 20th	Day	12% 5% 2 5% 3 3 4 4 6% 9% 47%	2271
	21st to end	Day	22% 6% 2 6% 4 4 4 4 5% 6% 38%	1986
October	1st to 10th	Day	16% 6% 2 5% 3 4 4 3 4 6% 47%	1900
	11th to 20th	Day	16% 4 2 4 4 3 4 3 4 5% 51%	1900
	21st to end	Day	13% 5% 2 5% 4 3 4 3 5% 6% 51%	2090
November	1st to 10th	Day	12% 5% 2 4 4 4 3 3 4 6% 53%	1920
	11th to 20th	Day	14% 7% 1 4 3 3 4 3 6% 6% 49%	1760
	21st to end	Day	15% 5% 2 5% 4 4 3 3 4 6% 49%	1600
December	1st to 10th	Day	12% 5% 2 6% 4 4 3 3 5% 7% 50%	2600
	11th to 20th	Day	18% 8% 3 4 3 3 2 3 4 6% 45%	2990
	21st to end	Day	17% 7% 3 6% 4 4 4 4 5% 7% 39%	3960
January	1st to 10th	Night	13% 6% 2 4 3 3 4 3 4 6% 52%	6050
	11th to 20th	Night	13% 7% 2 5% 2 3 3 3 4 5% 54%	5900
	21st to end	Night	14% 8% 3 6% 3 3 3 2 4 5% 48%	6490
February	1st to 10th	Night	15% 7% 2 6% 3 5% 4 4 6% 6% 41%	2600
	11th to 20th	Night	20% 7% 3 6% 4 3 3 3 4 6% 43%	2499
	21st to end	Night	16% 8% 2 6% 4 4 4 3 5% 6% 42%	1872
March	1st to 10th	Night	21% 7% 2 7% 4 4 3 4 5% 6% 38%	3418
	11th to 20th	Night	12% 4 2 5% 4 4 4 3 5% 8% 49%	3480
	21st to end	Night	13% 7% 3 6% 4 3 4 3 5% 6% 47%	3800
April	1st to 10th	Night	14% 8% 2 5% 4 4 4 3 5% 7% 43%	1900
	11th to 20th	Night	11% 6% 3 5% 4 4 4 3 5% 7% 49%	1875
	21st to end	Night	16% 5% 2 5% 5% 3 4 3 5% 7% 44%	1900
May	1st to 10th	Night	20% 10% 3 7% 5% 4 4 3 5% 7% 31%	2861
	11th to 20th	Night	23% 9% 2 6% 4 4 4 4 6% 7% 32%	2731
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 3 7% 10% 43%	2732
June	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 8% 9% 44%	1520
	11th to 20th	Night	10% 6% 2 5% 5% 5% 5% 4 6% 9% 42%	1520
	21st to end	Night	9% 4 2 4 4 4 5% 5% 8% 9% 44%	1520
July	1st to 10th	Night	6% 5% 2 7% 5% 6% 6% 5% 9% 9% 41%	2520
	11th to 20th	Night	8% 6% 2 8% 5% 5% 6% 5% 7% 10% 37%	2823
	21st to end	Night	9% 8% 3 7% 6% 6% 6% 5% 7% 8% 34%	3087
August	1st to 10th	Night	15% 5% 3 8% 5% 6% 6% 4 7% 9% 32%	2825
	11th to 20th	Night	10% 8% 3 9% 6% 6% 5% 4 6% 8% 35%	2898
	21st to end	Night	11% 6% 2 5% 3 3 4 4 5% 9% 48%	3476
September	1st to 10th	Night	13% 6% 2 5% 3 4 5% 4 5% 7% 44%	1900
	11th to 20th	Night	10% 6% 2 6% 4 4 4 3 5% 8% 49%	1905
	21st to end	Night	20% 8% 3 6% 4 3 3 3 5% 7% 38%	2193
October	1st to 10th	Night	18% 6% 2 6% 4 4 3 3 5% 5% 46%	2280
	11th to 20th	Night	15% 5% 2 5% 4 3 4 3 5% 5% 50%	2280
	21st to end	Night	14% 4 1 5% 3 3 4 3 5% 7% 50%	2508
November	1st to 10th	Night	12% 6% 2 6% 3 3 4 2 4 5% 54%	2376
	11th to 20th	Night	14% 7% 2 4 4 3 3 2 5% 7% 49%	2635
	21st to end	Night	13% 5% 1 4 4 3 4 4 5% 6% 51%	2800
December	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 4 7% 54%	4580
	11th to 20th	Night	21% 7% 2 5% 4 4 4 3 4 6% 41%	5205
	21st to end	Night	16% 6% 2 6% 4 5% 4 4 6% 7% 40%	6996

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	36% 4 6% 24% 22% 9%	3893
	11th to 20th	Day	39% 3 6% 21% 20% 11%	4060
	21st to end	Day	43% 2 8% 25% 18% 4	4466
February	1st to 10th	Day	44% 3 11% 25% 14% 2	1800
	11th to 20th	Day	43% 3 8% 22% 19% 4	1794
	21st to end	Day	48% 3 12% 15% 18% 4	1579
March	1st to 10th	Day	49% 4 8% 20% 14% 5%	3435
	11th to 20th	Day	33% 4 7% 26% 24% 6%	3480
	21st to end	Day	47% 3 11% 19% 16% 4	3832
April	1st to 10th	Day	37% 5% 11% 21% 19% 8%	2280
	11th to 20th	Day	37% 4 11% 21% 22% 6%	2254
	21st to end	Day	43% 4 10% 24% 14% 5%	2280
May	1st to 10th	Day	51% 5% 12% 20% 10% 1	4087
	11th to 20th	Day	49% 6% 11% 24% 10% 1	4163
	21st to end	Day	34% 5% 17% 22% 19% 2	4837
June	1st to 10th	Day	37% 6% 14% 27% 15% 1	2660
	11th to 20th	Day	37% 7% 14% 26% 15% 2	2660
	21st to end	Day	33% 6% 16% 25% 18% 1	2660
July	1st to 10th	Day	34% 9% 21% 19% 11% 6%	4370
	11th to 20th	Day	35% 8% 18% 28% 10% 1	4063
	21st to end	Day	44% 6% 11% 21% 17% 1	4324
August	1st to 10th	Day	43% 7% 17% 26% 7%	4091
	11th to 20th	Day	38% 7% 13% 25% 15% 1	3937
	21st to end	Day	33% 4 15% 28% 18% 2	4180
September	1st to 10th	Day	39% 5% 12% 18% 21% 5%	2280
	11th to 20th	Day	34% 6% 7% 28% 22% 3	2271
	21st to end	Day	47% 4 9% 20% 17% 3	1986
October	1st to 10th	Day	37% 4 6% 18% 30% 5%	3160
	11th to 20th	Day	26% 3 6% 25% 29% 11%	3140
	21st to end	Day	22% 2 10% 29% 25% 12%	3428
November	1st to 10th	Day	33% 4 9% 26% 23% 5%	1920
	11th to 20th	Day	35% 4 10% 23% 22% 7%	1760
	21st to end	Day	37% 3 10% 25% 22% 3	1600
December	1st to 10th	Day	34% 3 11% 26% 20% 6%	2600
	11th to 20th	Day	41% 2 13% 26% 13% 4	2986
	21st to end	Day	44% 5% 13% 22% 15% 1	3960
January	1st to 10th	Night	34% 3 7% 23% 27% 6%	6050
	11th to 20th	Night	34% 3 7% 24% 23% 9%	5900
	21st to end	Night	40% 2 7% 28% 19% 3	6490
February	1st to 10th	Night	43% 5% 10% 24% 16% 2	2600
	11th to 20th	Night	44% 2 7% 21% 19% 6%	2501
	21st to end	Night	43% 3 9% 21% 17% 6%	1872
March	1st to 10th	Night	46% 5% 8% 24% 15% 2	3418
	11th to 20th	Night	33% 5% 8% 24% 26% 5%	3480
	21st to end	Night	39% 3 9% 23% 20% 5%	3800
April	1st to 10th	Night	39% 5% 9% 19% 22% 5%	1900
	11th to 20th	Night	36% 4 11% 22% 21% 6%	1875
	21st to end	Night	39% 4 11% 27% 14% 6%	1900
May	1st to 10th	Night	53% 4 11% 19% 10% 2	2888
	11th to 20th	Night	50% 7% 12% 21% 9% 1	2732
	21st to end	Night	37% 6% 16% 26% 13% 3	2739
June	1st to 10th	Night	34% 6% 15% 28% 15% 2	1520
	11th to 20th	Night	38% 6% 16% 24% 15% 2	1520
	21st to end	Night	33% 7% 18% 21% 19% 3	1520
July	1st to 10th	Night	37% 8% 23% 18% 12% 3	2480
	11th to 20th	Night	40% 8% 20% 22% 9% 1	2770
	21st to end	Night	44% 8% 14% 19% 13%	2988
August	1st to 10th	Night	46% 7% 17% 22% 7% 1	2814
	11th to 20th	Night	44% 7% 12% 23% 14% 1	2925
	21st to end	Night	34% 5% 13% 30% 18% 1	3476
September	1st to 10th	Night	39% 6% 12% 20% 17% 6%	1900
	11th to 20th	Night	34% 5% 8% 27% 22% 3	1905
	21st to end	Night	46% 4 10% 20% 17% 3	2193
October	1st to 10th	Night	42% 4 8% 20% 20% 6%	3800
	11th to 20th	Night	25% 3 8% 22% 32% 9%	3779
	21st to end	Night	23% 2 8% 31% 26% 10%	4120
November	1st to 10th	Night	34% 3 9% 25% 24% 6%	2376
	11th to 20th	Night	37% 3 7% 24% 23% 7%	2635
	21st to end	Night	34% 3 10% 26% 22% 5%	2800
December	1st to 10th	Night	31% 3 11% 28% 23% 4	4580
	11th to 20th	Night	45% 3 11% 19% 17% 5%	5208
	21st to end	Night	42% 5% 13% 23% 16% 1	6996

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	25% 22% 30% 19% 3	264
	11th to 20th	Day	27% 27% 26% 17% 3	300
	21st to end	Day	22% 24% 37% 13% 4 1	330
February	1st to 10th	Day	24% 26% 34% 12% 4	300
	11th to 20th	Day	35% 26% 29% 9% 1	332
	21st to end	Day	29% 20% 29% 18% 4	382
March	1st to 10th	Day	23% 19% 34% 20% 4	460
	11th to 20th	Day	22% 22% 31% 19% 6%	460
	21st to end	Day	24% 18% 32% 19% 6% 1	506
April	1st to 10th	Day	23% 21% 28% 21% 5% 1	460
	11th to 20th	Day	16% 18% 30% 20% 12% 3	452
	21st to end	Day	22% 12% 33% 22% 9% 1	460
May	1st to 10th	Day	21% 14% 31% 17% 13% 3	463
	11th to 20th	Day	21% 10% 28% 24% 13% 3	487
	21st to end	Day	19% 4 24% 26% 20% 6%	529
June	1st to 10th	Day	12% 6% 25% 31% 18% 7%	490
	11th to 20th	Day	12% 6% 26% 31% 18% 7%	490
	21st to end	Day	9% 4 25% 37% 19% 6%	490
July	1st to 10th	Day	12% 3 17% 32% 26% 11%	485
	11th to 20th	Day	7% 1 14% 37% 29% 12%	484
	21st to end	Day	13% 3 18% 31% 23% 11%	532
August	1st to 10th	Day	11% 3 17% 29% 29% 10%	486
	11th to 20th	Day	12% 4 17% 30% 24% 13%	479
	21st to end	Day	10% 4 18% 29% 22% 17%	539
September	1st to 10th	Day	17% 5% 17% 28% 19% 15%	490
	11th to 20th	Day	15% 3 19% 28% 23% 13%	490
	21st to end	Day	27% 10% 21% 25% 13% 4	490
October	1st to 10th	Day	21% 5% 23% 27% 17% 7%	490
	11th to 20th	Day	16% 13% 25% 27% 17% 3	490
	21st to end	Day	16% 11% 33% 27% 10% 3	539
November	1st to 10th	Day	16% 11% 30% 25% 15% 3	476
	11th to 20th	Day	20% 11% 35% 23% 10% 2	360
	21st to end	Day	23% 16% 33% 19% 9% 1	200
December	1st to 10th	Day	23% 17% 39% 15% 6% 2	200
	11th to 20th	Day	20% 16% 34% 21% 9%	200
	21st to end	Day	27% 16% 28% 20% 8%	220
January	1st to 10th	Night	21% 16% 39% 20% 3	800
	11th to 20th	Night	20% 15% 34% 27% 4	800
	21st to end	Night	19% 15% 38% 26% 2	880
February	1st to 10th	Night	20% 13% 39% 25% 3	800
	11th to 20th	Night	27% 18% 36% 18% 1	783
	21st to end	Night	23% 16% 37% 21% 3	629
March	1st to 10th	Night	20% 15% 38% 24% 3	760
	11th to 20th	Night	22% 16% 35% 22% 5% 1	760
	21st to end	Night	18% 15% 37% 24% 5%	836
April	1st to 10th	Night	17% 16% 38% 23% 5%	760
	11th to 20th	Night	14% 13% 34% 30% 9%	751
	21st to end	Night	18% 9% 35% 31% 7%	760
May	1st to 10th	Night	21% 8% 31% 28% 12% 1	605
	11th to 20th	Night	21% 4 27% 33% 14%	519
	21st to end	Night	14% 3 19% 39% 23% 2	411
June	1st to 10th	Night	11% 3 21% 44% 20% 1	380
	11th to 20th	Night	12% 3 18% 45% 21% 1	380
	21st to end	Night	10% 2 19% 48% 19% 2	380
July	1st to 10th	Night	11% 4 17% 37% 29% 3	370
	11th to 20th	Night	7% 2 12% 42% 33% 4	536
	21st to end	Night	9% 3 14% 41% 30% 4	624
August	1st to 10th	Night	11% 2 11% 42% 31% 3	567
	11th to 20th	Night	12% 4 11% 41% 29% 3	625
	21st to end	Night	13% 3 11% 38% 31% 5%	836
September	1st to 10th	Night	17% 2 14% 33% 29% 5%	760
	11th to 20th	Night	12% 3 14% 36% 32% 3	760
	21st to end	Night	25% 4 19% 31% 21% 1	760
October	1st to 10th	Night	21% 4 20% 32% 20% 4	760
	11th to 20th	Night	19% 8% 26% 31% 17% 1	760
	21st to end	Night	17% 7% 33% 29% 13% 1	836
November	1st to 10th	Night	15% 8% 31% 32% 13% 1	780
	11th to 20th	Night	17% 10% 34% 29% 8% 1	800
	21st to end	Night	16% 12% 33% 30% 10% 1	800
December	1st to 10th	Night	21% 10% 36% 25% 8% 1	800
	11th to 20th	Night	20% 10% 36% 30% 5%	800
	21st to end	Night	21% 10% 33% 32% 5%	880

Page generated at 2025-02-18 03:26:30. Version ac07

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