Stafford
Clear Sky Chart
History

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

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%	101178
	Night	15% 6% 2 6% 4 4 4 3 5% 7% 43%	97841
Transparency	Day	38% 6% 12% 24% 17% 4	104819
	Night	39% 6% 11% 23% 18% 4	102340
Seeing	Day	17% 10% 26% 26% 15% 6%	15044
	Night	17% 10% 29% 29% 13% 1	24605

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	17% 6% 2 4 3 3 3 3 5% 7% 48%	2677
	11th to 20th	Day	15% 9% 3 8% 4 4 4 4 4 6% 40%	2840
	21st to end	Day	18% 9% 3 6% 4 4 4 3 4 6% 38%	3124
February	1st to 10th	Day	14% 8% 2 7% 5% 4 5% 4 5% 6% 39%	1710
	11th to 20th	Day	18% 7% 2 5% 4 4 4 2 5% 6% 43%	1711
	21st to end	Day	18% 8% 2 6% 5% 5% 4 3 5% 7% 37%	1570
March	1st to 10th	Day	22% 7% 2 6% 4 4 5% 3 4 7% 36%	3421
	11th to 20th	Day	11% 4 2 5% 4 4 5% 3 5% 6% 51%	3480
	21st to end	Day	21% 7% 2 6% 4 3 4 4 5% 7% 38%	3860
April	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 6% 7% 46%	2280
	11th to 20th	Day	12% 6% 2 5% 5% 3 4 3 5% 6% 48%	2254
	21st to end	Day	17% 6% 2 5% 5% 4 4 3 6% 6% 41%	2280
May	1st to 10th	Day	21% 7% 3 6% 4 5% 4 4 7% 8% 30%	4011
	11th to 20th	Day	22% 7% 2 6% 4 3 4 4 6% 9% 32%	4202
	21st to end	Day	11% 4 2 5% 4 4 5% 4 8% 9% 45%	4823
June	1st to 10th	Day	11% 4 2 5% 5% 5% 4 4 6% 10% 44%	2660
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 6% 9% 43%	2660
	21st to end	Day	8% 3 2 5% 5% 6% 5% 4 7% 10% 44%	2660
July	1st to 10th	Day	5% 4 2 6% 5% 4 5% 5% 8% 12% 43%	4440
	11th to 20th	Day	10% 5% 2 5% 5% 4 6% 5% 9% 13% 36%	4194
	21st to end	Day	11% 6% 2 8% 6% 6% 5% 5% 7% 8% 36%	4466
August	1st to 10th	Day	15% 5% 2 7% 5% 5% 5% 5% 7% 12% 32%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 9% 40%	3867
	21st to end	Day	9% 4 2 5% 3 4 4 4 7% 8% 50%	4180
September	1st to 10th	Day	14% 4 1 6% 4 4 4 4 6% 8% 46%	2280
	11th to 20th	Day	11% 6% 2 4 3 4 3 4 6% 8% 49%	2280
	21st to end	Day	21% 6% 2 6% 3 4 4 4 5% 6% 37%	1988
October	1st to 10th	Day	17% 5% 2 5% 4 4 4 3 4 6% 47%	1900
	11th to 20th	Day	17% 4 2 4 3 3 4 3 4 6% 52%	1900
	21st to end	Day	14% 5% 2 5% 3 3 3 3 4 7% 51%	2090
November	1st to 10th	Day	13% 4 1 4 4 4 4 3 5% 6% 53%	1848
	11th to 20th	Day	15% 6% 1 3 3 3 3 3 5% 6% 51%	1696
	21st to end	Day	17% 5% 1 4 4 3 3 3 4 5% 50%	1520
December	1st to 10th	Day	16% 6% 3 5% 4 4 4 4 5% 8% 42%	1520
	11th to 20th	Day	16% 7% 2 5% 4 3 4 2 4 6% 49%	1910
	21st to end	Day	18% 6% 2 6% 5% 4 4 4 6% 7% 38%	2772
January	1st to 10th	Night	15% 7% 2 5% 4 4 3 3 4 6% 48%	4265
	11th to 20th	Night	17% 7% 2 5% 3 3 3 2 5% 5% 47%	4120
	21st to end	Night	19% 8% 3 6% 4 3 3 2 4 5% 43%	4532
February	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 6% 6% 42%	2470
	11th to 20th	Night	19% 7% 2 6% 4 3 3 2 4 5% 44%	2353
	21st to end	Night	16% 8% 3 5% 4 3 4 3 5% 6% 44%	1884
March	1st to 10th	Night	21% 7% 3 6% 4 3 4 3 5% 5% 39%	3428
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 5% 8% 50%	3480
	21st to end	Night	15% 8% 2 6% 4 4 3 3 4 5% 47%	3770
April	1st to 10th	Night	15% 7% 2 5% 4 4 4 3 5% 7% 44%	1900
	11th to 20th	Night	11% 5% 2 6% 6% 3 4 3 5% 6% 50%	1875
	21st to end	Night	18% 4 1 5% 4 3 5% 4 6% 8% 43%	1900
May	1st to 10th	Night	21% 10% 2 7% 5% 4 4 3 5% 8% 32%	2911
	11th to 20th	Night	23% 9% 2 6% 4 4 4 4 5% 7% 33%	2690
	21st to end	Night	11% 4 2 6% 4 5% 5% 4 7% 10% 43%	2732
June	1st to 10th	Night	10% 5% 2 6% 4 5% 5% 4 7% 11% 42%	1520
	11th to 20th	Night	11% 5% 2 7% 5% 5% 5% 5% 7% 8% 42%	1520
	21st to end	Night	9% 5% 1 5% 5% 5% 5% 5% 7% 10% 44%	1520
July	1st to 10th	Night	7% 5% 2 6% 5% 6% 5% 5% 7% 10% 42%	2520
	11th to 20th	Night	8% 5% 2 7% 6% 5% 5% 5% 7% 10% 39%	2762
	21st to end	Night	9% 7% 3 8% 6% 6% 6% 4 8% 8% 35%	3087
August	1st to 10th	Night	16% 6% 3 8% 5% 5% 4 5% 7% 9% 32%	2825
	11th to 20th	Night	10% 6% 3 9% 6% 5% 6% 5% 6% 8% 36%	2928
	21st to end	Night	11% 5% 2 5% 4 3 4 3 5% 8% 50%	3476
September	1st to 10th	Night	15% 5% 2 5% 4 4 5% 4 5% 7% 45%	1900
	11th to 20th	Night	11% 5% 3 5% 5% 3 3 3 4 8% 48%	1900
	21st to end	Night	21% 7% 2 6% 4 3 4 3 5% 7% 37%	2187
October	1st to 10th	Night	18% 5% 2 5% 4 4 4 3 4 6% 46%	2280
	11th to 20th	Night	16% 5% 2 6% 3 2 3 3 5% 6% 50%	2280
	21st to end	Night	14% 5% 2 5% 3 4 4 3 5% 6% 50%	2508
November	1st to 10th	Night	12% 5% 2 4 4 3 3 2 4 5% 54%	2349
	11th to 20th	Night	14% 6% 2 4 4 3 3 3 4 6% 50%	2480
	21st to end	Night	12% 4 1 4 4 4 4 4 5% 7% 50%	2660
December	1st to 10th	Night	16% 7% 3 6% 4 4 4 3 5% 6% 42%	2660
	11th to 20th	Night	18% 6% 2 5% 4 3 4 3 4 6% 45%	3285
	21st to end	Night	17% 7% 2 6% 4 5% 4 4 6% 8% 38%	4884

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 9% 31% 17% 5%	2678
	11th to 20th	Day	45% 4 8% 21% 16% 6%	2840
	21st to end	Day	47% 5% 9% 22% 14% 3	3124
February	1st to 10th	Day	44% 5% 10% 25% 13% 2	1710
	11th to 20th	Day	42% 4 8% 24% 18% 4	1720
	21st to end	Day	46% 4 13% 15% 17% 4	1570
March	1st to 10th	Day	47% 5% 10% 20% 13% 5%	3421
	11th to 20th	Day	33% 4 8% 26% 24% 6%	3480
	21st to end	Day	45% 5% 11% 19% 15% 4	3860
April	1st to 10th	Day	36% 6% 11% 21% 19% 7%	2280
	11th to 20th	Day	35% 5% 11% 21% 21% 7%	2254
	21st to end	Day	41% 7% 10% 23% 15% 5%	2280
May	1st to 10th	Day	48% 8% 11% 20% 11% 1	4048
	11th to 20th	Day	46% 8% 12% 24% 9% 1	4206
	21st to end	Day	32% 9% 16% 24% 18% 2	4837
June	1st to 10th	Day	34% 7% 15% 27% 15% 1	2660
	11th to 20th	Day	34% 8% 13% 25% 17% 2	2660
	21st to end	Day	32% 8% 15% 25% 18% 2	2660
July	1st to 10th	Day	31% 11% 21% 19% 12% 6%	4370
	11th to 20th	Day	34% 9% 19% 28% 9% 1	4122
	21st to end	Day	42% 8% 12% 20% 18% 1	4324
August	1st to 10th	Day	43% 8% 16% 26% 7%	4091
	11th to 20th	Day	37% 8% 14% 27% 15% 1	3906
	21st to end	Day	29% 7% 16% 28% 18% 2	4180
September	1st to 10th	Day	35% 7% 13% 20% 20% 4	2280
	11th to 20th	Day	33% 5% 8% 28% 21% 4	2280
	21st to end	Day	46% 5% 9% 20% 18% 3	1988
October	1st to 10th	Day	36% 5% 7% 18% 30% 5%	3160
	11th to 20th	Day	25% 3 7% 26% 29% 10%	3140
	21st to end	Day	21% 3 9% 29% 26% 11%	3428
November	1st to 10th	Day	32% 4 10% 27% 22% 5%	1848
	11th to 20th	Day	34% 5% 9% 23% 21% 7%	1696
	21st to end	Day	36% 4 10% 26% 21% 3	1520
December	1st to 10th	Day	40% 6% 11% 26% 12% 4	1520
	11th to 20th	Day	39% 3 8% 30% 15% 5%	1906
	21st to end	Day	44% 6% 11% 26% 13% 1	2772
January	1st to 10th	Night	38% 3 10% 25% 20% 5%	4265
	11th to 20th	Night	40% 3 9% 23% 20% 4	4120
	21st to end	Night	45% 4 7% 26% 17% 2	4532
February	1st to 10th	Night	41% 5% 10% 25% 17% 2	2470
	11th to 20th	Night	44% 3 7% 21% 19% 6%	2355
	21st to end	Night	41% 4 11% 21% 17% 6%	1884
March	1st to 10th	Night	46% 5% 8% 24% 14% 2	3428
	11th to 20th	Night	31% 5% 10% 25% 25% 4	3480
	21st to end	Night	39% 5% 8% 22% 20% 5%	3770
April	1st to 10th	Night	40% 6% 8% 19% 23% 4	1900
	11th to 20th	Night	35% 6% 11% 21% 22% 6%	1875
	21st to end	Night	39% 6% 11% 25% 13% 6%	1900
May	1st to 10th	Night	51% 7% 10% 19% 10% 3	2940
	11th to 20th	Night	49% 9% 11% 20% 9% 1	2691
	21st to end	Night	34% 8% 16% 26% 13% 3	2739
June	1st to 10th	Night	35% 8% 13% 27% 15% 2	1520
	11th to 20th	Night	37% 9% 15% 22% 14% 2	1520
	21st to end	Night	34% 8% 17% 20% 19% 3	1520
July	1st to 10th	Night	36% 10% 21% 18% 12% 3	2480
	11th to 20th	Night	38% 8% 20% 23% 9% 1	2711
	21st to end	Night	43% 9% 14% 19% 15%	2988
August	1st to 10th	Night	46% 8% 16% 21% 8% 1	2814
	11th to 20th	Night	43% 9% 11% 22% 14% 1	2955
	21st to end	Night	33% 5% 11% 29% 20% 1	3476
September	1st to 10th	Night	37% 8% 12% 20% 17% 6%	1900
	11th to 20th	Night	34% 5% 10% 25% 23% 3	1900
	21st to end	Night	45% 6% 12% 18% 16% 3	2187
October	1st to 10th	Night	40% 5% 9% 20% 19% 7%	3800
	11th to 20th	Night	24% 4 9% 22% 32% 9%	3779
	21st to end	Night	22% 4 8% 31% 26% 9%	4120
November	1st to 10th	Night	34% 4 9% 25% 22% 6%	2349
	11th to 20th	Night	36% 4 8% 22% 23% 7%	2480
	21st to end	Night	33% 4 10% 26% 22% 4	2660
December	1st to 10th	Night	43% 5% 9% 24% 15% 4	2660
	11th to 20th	Night	40% 4 10% 22% 19% 4	3288
	21st to end	Night	42% 7% 15% 21% 12% 1	4884

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	22% 23% 31% 20% 5%	225
	11th to 20th	Day	26% 25% 27% 19% 2	270
	21st to end	Day	22% 21% 36% 16% 5%	297
February	1st to 10th	Day	21% 19% 39% 14% 6%	270
	11th to 20th	Day	26% 26% 33% 13% 2	318
	21st to end	Day	26% 19% 30% 21% 3 1	382
March	1st to 10th	Day	22% 19% 34% 20% 4	460
	11th to 20th	Day	22% 18% 35% 18% 5% 1	460
	21st to end	Day	23% 15% 36% 20% 6% 1	506
April	1st to 10th	Day	21% 19% 34% 20% 6% 1	460
	11th to 20th	Day	15% 16% 30% 25% 12% 3	452
	21st to end	Day	21% 14% 30% 24% 8% 2	460
May	1st to 10th	Day	22% 13% 31% 20% 11% 3	463
	11th to 20th	Day	19% 9% 31% 23% 14% 3	487
	21st to end	Day	18% 4 23% 25% 23% 7%	529
June	1st to 10th	Day	12% 5% 27% 27% 22% 7%	490
	11th to 20th	Day	11% 7% 22% 34% 19% 7%	490
	21st to end	Day	9% 4 22% 36% 20% 8%	490
July	1st to 10th	Day	11% 4 15% 30% 28% 12%	485
	11th to 20th	Day	5% 1 13% 35% 32% 13%	484
	21st to end	Day	11% 3 15% 35% 24% 11%	532
August	1st to 10th	Day	13% 3 16% 29% 28% 10%	486
	11th to 20th	Day	12% 4 16% 31% 25% 11%	479
	21st to end	Day	10% 3 17% 31% 23% 15%	539
September	1st to 10th	Day	17% 3 19% 25% 20% 17%	490
	11th to 20th	Day	14% 3 17% 30% 23% 12%	490
	21st to end	Day	27% 8% 24% 26% 10% 6%	490
October	1st to 10th	Day	22% 6% 19% 27% 18% 8%	490
	11th to 20th	Day	17% 12% 23% 28% 17% 4	490
	21st to end	Day	14% 12% 33% 27% 10% 4	539
November	1st to 10th	Day	16% 9% 31% 27% 15% 2	447
	11th to 20th	Day	19% 11% 36% 21% 12% 1	356
	21st to end	Day	20% 16% 29% 22% 12% 1	180
December	1st to 10th	Day	19% 16% 37% 20% 6% 2	180
	11th to 20th	Day	21% 14% 34% 23% 8%	180
	21st to end	Day	26% 12% 32% 21% 9% 1	198
January	1st to 10th	Night	20% 17% 38% 21% 3	760
	11th to 20th	Night	21% 15% 34% 25% 4	760
	21st to end	Night	19% 16% 40% 22% 2	836
February	1st to 10th	Night	20% 12% 39% 25% 3	760
	11th to 20th	Night	24% 19% 39% 17% 1	743
	21st to end	Night	22% 18% 35% 23% 2	628
March	1st to 10th	Night	20% 15% 38% 24% 3	760
	11th to 20th	Night	22% 16% 36% 20% 5% 1	760
	21st to end	Night	18% 15% 38% 24% 5%	836
April	1st to 10th	Night	17% 19% 39% 21% 4	760
	11th to 20th	Night	14% 11% 35% 30% 9%	751
	21st to end	Night	19% 11% 31% 30% 9%	760
May	1st to 10th	Night	21% 9% 30% 28% 11% 1	631
	11th to 20th	Night	18% 5% 30% 31% 16%	491
	21st to end	Night	16% 4 19% 37% 22% 1	411
June	1st to 10th	Night	10% 2 23% 42% 21% 1	380
	11th to 20th	Night	13% 4 21% 38% 23% 2	380
	21st to end	Night	10% 3 19% 48% 20% 1	380
July	1st to 10th	Night	9% 2 18% 38% 28% 4	370
	11th to 20th	Night	7% 2 13% 38% 34% 6%	503
	21st to end	Night	9% 1 16% 42% 28% 4	624
August	1st to 10th	Night	12% 2 12% 40% 31% 4	567
	11th to 20th	Night	12% 3 14% 41% 27% 4	642
	21st to end	Night	13% 3 13% 36% 29% 6%	836
September	1st to 10th	Night	18% 2 15% 33% 27% 5%	760
	11th to 20th	Night	12% 3 16% 35% 30% 4	760
	21st to end	Night	24% 5% 19% 32% 19% 1	760
October	1st to 10th	Night	20% 5% 20% 29% 21% 4	760
	11th to 20th	Night	16% 9% 28% 30% 16% 1	760
	21st to end	Night	16% 10% 32% 28% 13% 1	836
November	1st to 10th	Night	16% 9% 31% 30% 12% 2	764
	11th to 20th	Night	17% 13% 33% 28% 9%	760
	21st to end	Night	15% 13% 34% 27% 10% 1	760
December	1st to 10th	Night	20% 12% 35% 24% 9%	760
	11th to 20th	Night	19% 10% 40% 26% 5%	760
	21st to end	Night	19% 12% 33% 32% 4	836

Page generated at 2024-11-03 13:19:02. Version ac07

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