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 2024-01-12.

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% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	74657
	Night	14% 6% 2 5% 5% 3 4 4 5% 7% 44%	75064
Transparency	Day	38% 6% 12% 24% 17% 3	74370
	Night	39% 6% 11% 23% 18% 4	74870
Seeing	Day	17% 10% 26% 25% 15% 6%	13887
	Night	17% 10% 29% 29% 13% 1	23570

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	14% 6% 3 5% 4 3 4 4 6% 6% 43%	1612
	11th to 20th	Day	17% 7% 2 5% 5% 3 4 5% 3 7% 42%	1635
	21st to end	Day	16% 6% 3 6% 5% 3 4 5% 4 7% 42%	1782
February	1st to 10th	Day	15% 7% 2 6% 6% 3 5% 5% 5% 7% 38%	1620
	11th to 20th	Day	18% 5% 3 5% 5% 3 4 3 5% 6% 43%	1619
	21st to end	Day	18% 8% 3 5% 5% 4 4 4 5% 7% 36%	1480
March	1st to 10th	Day	13% 6% 2 5% 4 2 4 4 4 7% 50%	1966
	11th to 20th	Day	17% 6% 2 4 5% 3 5% 4 5% 6% 41%	1980
	21st to end	Day	17% 6% 3 6% 6% 3 5% 4 5% 7% 38%	2196
April	1st to 10th	Day	12% 5% 2 5% 5% 3 4 4 6% 7% 47%	2160
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 4 4 6% 49%	2134
	21st to end	Day	18% 5% 3 4 5% 3 4 5% 6% 6% 41%	2160
May	1st to 10th	Day	15% 5% 3 5% 5% 3 5% 5% 6% 9% 40%	2296
	11th to 20th	Day	18% 5% 2 5% 5% 3 5% 5% 5% 9% 38%	2366
	21st to end	Day	14% 4 2 5% 4 3 5% 5% 7% 9% 42%	2725
June	1st to 10th	Day	11% 4 2 5% 5% 3 5% 5% 6% 10% 44%	2520
	11th to 20th	Day	10% 4 3 6% 5% 4 5% 6% 6% 10% 42%	2520
	21st to end	Day	8% 3 2 4 6% 4 6% 5% 7% 10% 45%	2520
July	1st to 10th	Day	9% 5% 2 5% 7% 2 5% 5% 7% 9% 42%	2520
	11th to 20th	Day	6% 3 1 3 6% 3 5% 7% 9% 12% 44%	2386
	21st to end	Day	9% 4 2 6% 5% 4 7% 7% 8% 9% 38%	2547
August	1st to 10th	Day	9% 5% 2 7% 7% 4 6% 6% 6% 10% 38%	2327
	11th to 20th	Day	10% 5% 2 5% 7% 4 6% 6% 7% 9% 38%	2210
	21st to end	Day	10% 5% 2 5% 5% 4 4 5% 7% 9% 43%	2376
September	1st to 10th	Day	14% 4 1 5% 5% 2 4 5% 6% 8% 45%	2160
	11th to 20th	Day	11% 5% 2 4 4 3 3 5% 5% 8% 50%	2160
	21st to end	Day	19% 6% 3 5% 4 3 4 5% 6% 6% 39%	1885
October	1st to 10th	Day	17% 5% 2 4 5% 3 3 4 4 7% 47%	1800
	11th to 20th	Day	18% 4 2 3 4 2 4 4 4 6% 50%	1800
	21st to end	Day	15% 6% 2 5% 4 2 3 4 4 7% 49%	1980
November	1st to 10th	Day	13% 4 1 3 4 3 5% 3 4 6% 53%	1797
	11th to 20th	Day	15% 6% 2 3 3 2 4 4 5% 6% 51%	1696
	21st to end	Day	17% 4 1 4 4 2 3 4 4 5% 50%	1520
December	1st to 10th	Day	16% 6% 3 5% 5% 2 4 5% 5% 8% 42%	1520
	11th to 20th	Day	16% 7% 2 4 4 2 4 3 3 6% 49%	1910
	21st to end	Day	18% 6% 3 5% 6% 2 4 5% 6% 7% 38%	2772
January	1st to 10th	Night	17% 6% 2 5% 3 3 4 3 4 6% 47%	2550
	11th to 20th	Night	17% 7% 3 6% 6% 3 4 4 5% 7% 40%	2365
	21st to end	Night	16% 7% 2 4 4 3 4 4 4 7% 46%	2574
February	1st to 10th	Night	16% 7% 3 5% 5% 2 4 4 5% 7% 41%	2340
	11th to 20th	Night	19% 7% 3 5% 5% 2 3 3 4 5% 44%	2225
	21st to end	Night	17% 8% 3 4 4 3 4 4 5% 6% 44%	1776
March	1st to 10th	Night	14% 4 2 5% 5% 2 4 3 5% 5% 50%	1990
	11th to 20th	Night	19% 6% 2 4 4 2 4 4 5% 8% 42%	1980
	21st to end	Night	15% 6% 3 6% 5% 3 5% 4 4 7% 42%	2158
April	1st to 10th	Night	14% 6% 3 5% 4 3 4 4 5% 7% 44%	1800
	11th to 20th	Night	12% 5% 3 5% 5% 2 4 4 4 6% 50%	1775
	21st to end	Night	18% 4 2 4 4 2 4 4 6% 8% 43%	1800
May	1st to 10th	Night	15% 7% 2 5% 6% 3 5% 4 6% 9% 39%	1678
	11th to 20th	Night	15% 7% 3 5% 5% 3 4 6% 6% 9% 38%	1526
	21st to end	Night	14% 6% 1 5% 5% 4 4 5% 6% 10% 41%	1550
June	1st to 10th	Night	10% 4 2 5% 5% 4 5% 5% 6% 11% 42%	1440
	11th to 20th	Night	11% 5% 3 6% 6% 3 6% 6% 6% 8% 41%	1440
	21st to end	Night	9% 4 2 5% 5% 4 5% 6% 7% 10% 44%	1440
July	1st to 10th	Night	8% 6% 3 5% 6% 4 4 7% 6% 10% 41%	1440
	11th to 20th	Night	6% 3 2 5% 6% 4 5% 6% 7% 11% 45%	1570
	21st to end	Night	7% 3 2 6% 6% 4 7% 6% 10% 11% 38%	1771
August	1st to 10th	Night	8% 4 3 7% 6% 4 6% 7% 7% 9% 39%	1611
	11th to 20th	Night	11% 5% 3 6% 7% 4 6% 7% 7% 9% 36%	1671
	21st to end	Night	11% 6% 3 5% 6% 3 4 4 6% 10% 41%	1980
September	1st to 10th	Night	16% 4 2 4 5% 2 5% 6% 5% 7% 45%	1800
	11th to 20th	Night	10% 5% 3 5% 5% 3 3 4 4 8% 50%	1800
	21st to end	Night	18% 7% 2 6% 5% 3 4 4 5% 7% 39%	2071
October	1st to 10th	Night	18% 6% 2 4 4 3 4 4 4 6% 46%	2160
	11th to 20th	Night	17% 5% 2 5% 4 2 3 4 4 7% 48%	2160
	21st to end	Night	14% 5% 2 4 4 3 4 5% 5% 6% 48%	2376
November	1st to 10th	Night	13% 5% 3 4 4 2 4 3 4 5% 54%	2278
	11th to 20th	Night	14% 5% 2 4 4 2 4 4 4 6% 50%	2480
	21st to end	Night	12% 4 2 4 4 3 4 5% 5% 7% 50%	2660
December	1st to 10th	Night	16% 7% 3 5% 5% 3 4 4 5% 6% 42%	2660
	11th to 20th	Night	18% 5% 2 5% 4 2 4 4 4 6% 45%	3285
	21st to end	Night	17% 6% 2 5% 5% 4 4 5% 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	40% 5% 11% 24% 16% 5%	1613
	11th to 20th	Day	43% 5% 10% 23% 16% 3	1635
	21st to end	Day	42% 4 9% 24% 16% 4	1782
February	1st to 10th	Day	46% 5% 10% 25% 12% 2	1620
	11th to 20th	Day	43% 4 8% 24% 18% 4	1628
	21st to end	Day	47% 4 13% 16% 17% 4	1480
March	1st to 10th	Day	35% 5% 10% 25% 21% 4	1966
	11th to 20th	Day	43% 4 10% 18% 18% 7%	1980
	21st to end	Day	45% 5% 10% 18% 17% 5%	2196
April	1st to 10th	Day	35% 6% 11% 21% 20% 7%	2160
	11th to 20th	Day	35% 5% 11% 20% 22% 7%	2134
	21st to end	Day	41% 7% 9% 23% 14% 5%	2160
May	1st to 10th	Day	39% 7% 14% 21% 17% 2	2296
	11th to 20th	Day	42% 7% 13% 23% 13% 2	2370
	21st to end	Day	37% 8% 15% 26% 12% 1	2725
June	1st to 10th	Day	34% 7% 15% 27% 15% 1	2520
	11th to 20th	Day	36% 9% 13% 24% 16% 2	2520
	21st to end	Day	32% 8% 16% 25% 18% 1	2520
July	1st to 10th	Day	36% 9% 14% 21% 16% 4	2450
	11th to 20th	Day	28% 9% 18% 28% 14% 2	2314
	21st to end	Day	37% 9% 14% 21% 18% 1	2405
August	1st to 10th	Day	39% 9% 15% 25% 11% 1	2314
	11th to 20th	Day	39% 9% 14% 22% 14% 1	2210
	21st to end	Day	35% 7% 15% 24% 15% 4	2376
September	1st to 10th	Day	35% 7% 14% 20% 19% 4	2160
	11th to 20th	Day	33% 6% 9% 28% 21% 4	2160
	21st to end	Day	44% 5% 10% 20% 19% 2	1885
October	1st to 10th	Day	38% 4 9% 27% 19% 3	1800
	11th to 20th	Day	36% 4 9% 26% 23% 3	1800
	21st to end	Day	36% 4 8% 25% 23% 5%	1980
November	1st to 10th	Day	33% 4 10% 27% 22% 5%	1797
	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	40% 3 10% 21% 20% 7%	2550
	11th to 20th	Night	44% 5% 11% 21% 16% 3	2365
	21st to end	Night	40% 4 8% 25% 21% 3	2574
February	1st to 10th	Night	42% 5% 10% 24% 17% 2	2340
	11th to 20th	Night	44% 3 7% 21% 19% 6%	2227
	21st to end	Night	42% 4 10% 21% 17% 6%	1776
March	1st to 10th	Night	36% 4 9% 26% 21% 3	1990
	11th to 20th	Night	41% 5% 10% 20% 19% 4	1980
	21st to end	Night	42% 6% 9% 21% 16% 6%	2158
April	1st to 10th	Night	40% 6% 8% 19% 23% 4	1800
	11th to 20th	Night	35% 5% 11% 21% 22% 6%	1775
	21st to end	Night	39% 6% 11% 25% 13% 6%	1800
May	1st to 10th	Night	42% 7% 11% 21% 14% 4	1678
	11th to 20th	Night	41% 9% 13% 18% 16% 2	1527
	21st to end	Night	38% 9% 15% 24% 12% 1	1551
June	1st to 10th	Night	34% 8% 13% 27% 16% 2	1440
	11th to 20th	Night	38% 9% 15% 21% 14% 2	1440
	21st to end	Night	34% 8% 17% 19% 19% 3	1440
July	1st to 10th	Night	39% 8% 16% 19% 14% 4	1400
	11th to 20th	Night	32% 9% 16% 26% 16% 2	1519
	21st to end	Night	34% 10% 17% 25% 14% 1	1672
August	1st to 10th	Night	38% 10% 17% 21% 14% 1	1600
	11th to 20th	Night	42% 10% 13% 21% 13% 2	1671
	21st to end	Night	38% 7% 15% 23% 14% 2	1980
September	1st to 10th	Night	37% 8% 12% 21% 17% 6%	1800
	11th to 20th	Night	33% 5% 10% 25% 23% 3	1800
	21st to end	Night	43% 6% 12% 18% 17% 4	2071
October	1st to 10th	Night	40% 5% 9% 24% 18% 4	2160
	11th to 20th	Night	37% 5% 7% 26% 22% 4	2160
	21st to end	Night	36% 5% 9% 23% 23% 5%	2376
November	1st to 10th	Night	34% 4 8% 25% 22% 6%	2278
	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	23% 24% 29% 21% 2	245
	21st to end	Day	23% 22% 36% 15% 5%	264
February	1st to 10th	Day	23% 20% 39% 12% 6%	240
	11th to 20th	Day	26% 26% 35% 12% 1	286
	21st to end	Day	27% 20% 30% 21% 2	346
March	1st to 10th	Day	20% 21% 34% 22% 4	420
	11th to 20th	Day	23% 19% 33% 19% 5% 1	420
	21st to end	Day	22% 15% 36% 19% 6% 2	462
April	1st to 10th	Day	20% 18% 33% 21% 7% 1	420
	11th to 20th	Day	15% 16% 29% 24% 12% 3	412
	21st to end	Day	22% 13% 30% 24% 8% 2	420
May	1st to 10th	Day	22% 13% 31% 20% 11% 3	423
	11th to 20th	Day	19% 9% 31% 24% 14% 4	447
	21st to end	Day	19% 4 21% 25% 24% 7%	485
June	1st to 10th	Day	12% 4 25% 28% 23% 7%	450
	11th to 20th	Day	12% 8% 22% 32% 19% 8%	450
	21st to end	Day	9% 4 22% 36% 20% 9%	450
July	1st to 10th	Day	12% 3 16% 28% 29% 12%	445
	11th to 20th	Day	5% 1 12% 35% 34% 14%	444
	21st to end	Day	11% 3 15% 34% 25% 12%	488
August	1st to 10th	Day	12% 3 15% 30% 30% 11%	446
	11th to 20th	Day	13% 4 13% 30% 28% 12%	439
	21st to end	Day	10% 3 17% 29% 24% 16%	495
September	1st to 10th	Day	18% 2 17% 24% 21% 18%	450
	11th to 20th	Day	13% 3 16% 32% 23% 13%	450
	21st to end	Day	23% 8% 24% 28% 11% 6%	450
October	1st to 10th	Day	22% 6% 18% 27% 19% 8%	450
	11th to 20th	Day	17% 11% 24% 27% 17% 4	450
	21st to end	Day	16% 12% 34% 26% 10% 3	495
November	1st to 10th	Day	16% 9% 31% 26% 15% 3	426
	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	21% 17% 38% 21% 3	760
	11th to 20th	Night	21% 13% 35% 27% 4	728
	21st to end	Night	19% 16% 41% 22% 2	792
February	1st to 10th	Night	21% 13% 39% 24% 3	720
	11th to 20th	Night	24% 19% 39% 17% 1	703
	21st to end	Night	22% 19% 35% 23% 2	592
March	1st to 10th	Night	19% 15% 39% 24% 3	720
	11th to 20th	Night	22% 15% 37% 20% 5% 1	720
	21st to end	Night	17% 15% 38% 23% 5%	792
April	1st to 10th	Night	17% 19% 39% 21% 5%	720
	11th to 20th	Night	15% 11% 34% 30% 9%	711
	21st to end	Night	20% 10% 31% 31% 8%	720
May	1st to 10th	Night	21% 9% 31% 28% 11% 1	598
	11th to 20th	Night	18% 4 30% 31% 16%	465
	21st to end	Night	17% 4 18% 38% 22% 1	389
June	1st to 10th	Night	10% 3 22% 42% 22% 1	360
	11th to 20th	Night	14% 3 21% 36% 24% 2	360
	21st to end	Night	9% 3 18% 49% 20% 1	360
July	1st to 10th	Night	10% 2 18% 36% 29% 5%	350
	11th to 20th	Night	7% 2 11% 38% 35% 6%	475
	21st to end	Night	8% 1 16% 41% 29% 4	591
August	1st to 10th	Night	11% 2 11% 41% 31% 4	537
	11th to 20th	Night	13% 2 13% 40% 28% 4	607
	21st to end	Night	13% 3 14% 35% 30% 6%	792
September	1st to 10th	Night	18% 2 15% 31% 28% 5%	720
	11th to 20th	Night	11% 3 17% 34% 31% 4	720
	21st to end	Night	22% 5% 19% 33% 20% 1	720
October	1st to 10th	Night	21% 5% 20% 29% 21% 5%	720
	11th to 20th	Night	17% 8% 28% 29% 16% 1	720
	21st to end	Night	17% 10% 32% 27% 13% 1	792
November	1st to 10th	Night	16% 9% 31% 30% 12% 2	740
	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 2024-01-09 16:24:28. Version ac07

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