SAPM à Hemmingford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SAPM à Hemmingford clear sky chart from 2005-11-06 to 2026-06-16.

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	17% 10% 4 9% 5% 5% 5% 4 5% 7% 31%	137774
	Night	17% 12% 4 10% 6% 5% 5% 3 5% 6% 28%	134254
Transparency	Day	52% 6% 12% 20% 9% 1	141220
	Night	55% 6% 11% 18% 10% 1	138884
Seeing	Day	24% 16% 29% 20% 9% 2	16605
	Night	24% 14% 29% 24% 8% 1	25612

By Month

Percentage Cloud Cover NE (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% 19% 8% 14% 6% 6% 4 3 4 5% 17%	4661
	11th to 20th	Day	11% 17% 7% 17% 8% 6% 4 3 4 4 17%	4650
	21st to end	Day	11% 14% 5% 12% 8% 8% 6% 4 5% 6% 20%	5124
February	1st to 10th	Day	15% 16% 5% 13% 7% 4 5% 3 5% 5% 22%	1853
	11th to 20th	Day	12% 15% 5% 13% 7% 4 5% 4 4 5% 25%	1971
	21st to end	Day	16% 16% 5% 9% 7% 5% 5% 3 5% 6% 23%	1730
March	1st to 10th	Day	18% 12% 5% 12% 6% 5% 6% 3 4 5% 23%	4576
	11th to 20th	Day	14% 14% 5% 9% 6% 4 4 3 5% 6% 29%	4795
	21st to end	Day	19% 11% 4 9% 5% 4 4 3 4 5% 34%	6102
April	1st to 10th	Day	22% 12% 3 8% 5% 3 4 3 5% 5% 30%	2520
	11th to 20th	Day	21% 11% 3 7% 5% 4 4 3 4 5% 34%	2494
	21st to end	Day	22% 9% 3 7% 5% 4 3 4 4 6% 33%	2685
May	1st to 10th	Day	26% 10% 3 8% 4 4 5% 3 5% 6% 24%	8047
	11th to 20th	Day	20% 7% 3 7% 5% 5% 5% 4 6% 7% 32%	8221
	21st to end	Day	20% 9% 3 7% 4 4 5% 4 5% 7% 32%	9060
June	1st to 10th	Day	21% 7% 3 7% 5% 5% 4 4 6% 7% 31%	2940
	11th to 20th	Day	14% 7% 2 6% 5% 5% 5% 5% 6% 8% 37%	2870
	21st to end	Day	21% 7% 2 7% 5% 5% 5% 4 6% 7% 31%	2800
July	1st to 10th	Day	11% 7% 3 9% 5% 6% 7% 5% 6% 9% 33%	6360
	11th to 20th	Day	10% 5% 2 6% 4 5% 6% 5% 7% 9% 40%	6360
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 10% 43%	6926
August	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 5% 7% 8% 33%	4563
	11th to 20th	Day	14% 6% 2 6% 4 5% 5% 4 6% 8% 39%	4069
	21st to end	Day	15% 5% 2 6% 4 4 4 4 6% 9% 40%	4312
September	1st to 10th	Day	12% 6% 2 5% 5% 4 5% 4 5% 8% 45%	2400
	11th to 20th	Day	14% 6% 2 5% 4 3 4 3 4 7% 48%	2308
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 6% 8% 41%	2200
October	1st to 10th	Day	20% 6% 3 7% 4 5% 5% 4 5% 7% 35%	2078
	11th to 20th	Day	17% 7% 3 8% 6% 5% 6% 4 6% 6% 32%	1957
	21st to end	Day	24% 13% 4 7% 4 5% 3 3 4 6% 28%	1980
November	1st to 10th	Day	17% 13% 3 8% 5% 5% 4 3 6% 5% 31%	1851
	11th to 20th	Day	16% 15% 4 7% 5% 5% 4 5% 5% 6% 28%	1837
	21st to end	Day	20% 16% 5% 8% 6% 4 5% 4 5% 6% 21%	1680
December	1st to 10th	Day	16% 22% 6% 13% 7% 5% 4 3 4 5% 15%	2680
	11th to 20th	Day	18% 14% 6% 11% 5% 4 5% 3 6% 5% 24%	3066
	21st to end	Day	21% 14% 4 12% 6% 5% 5% 4 5% 4 21%	4048
January	1st to 10th	Night	13% 19% 7% 15% 7% 5% 4 2 4 4 19%	8234
	11th to 20th	Night	12% 17% 7% 16% 8% 6% 5% 3 5% 4 15%	8235
	21st to end	Night	12% 14% 4 12% 8% 7% 6% 4 5% 5% 22%	9057
February	1st to 10th	Night	14% 14% 6% 13% 7% 6% 6% 3 4 5% 21%	2764
	11th to 20th	Night	14% 11% 5% 11% 7% 7% 5% 4 6% 5% 26%	2535
	21st to end	Night	15% 14% 4 10% 5% 5% 5% 3 4 5% 30%	2076
March	1st to 10th	Night	20% 13% 4 8% 6% 5% 3 3 5% 5% 29%	5484
	11th to 20th	Night	14% 13% 4 9% 5% 5% 5% 4 5% 6% 29%	5368
	21st to end	Night	15% 12% 5% 11% 6% 5% 5% 3 4 5% 29%	5072
April	1st to 10th	Night	22% 11% 3 7% 5% 5% 4 3 5% 5% 29%	2100
	11th to 20th	Night	25% 10% 4 8% 4 4 4 3 4 5% 31%	2075
	21st to end	Night	19% 9% 3 8% 5% 5% 5% 3 4 5% 35%	1933
May	1st to 10th	Night	23% 11% 3 8% 5% 4 5% 4 5% 8% 24%	4905
	11th to 20th	Night	20% 8% 3 8% 4 4 5% 4 6% 7% 31%	4639
	21st to end	Night	19% 9% 3 8% 4 5% 4 3 5% 8% 32%	5114
June	1st to 10th	Night	22% 7% 3 5% 5% 5% 5% 3 7% 7% 31%	1680
	11th to 20th	Night	17% 6% 3 7% 4 4 5% 4 7% 8% 37%	1640
	21st to end	Night	18% 8% 2 7% 5% 4 4 4 6% 6% 35%	1600
July	1st to 10th	Night	13% 5% 3 7% 5% 5% 6% 5% 7% 9% 36%	3600
	11th to 20th	Night	12% 6% 3 6% 5% 5% 4 3 6% 8% 42%	3600
	21st to end	Night	10% 7% 3 7% 5% 5% 5% 3 6% 8% 41%	3926
August	1st to 10th	Night	16% 7% 3 8% 4 4 4 3 5% 7% 39%	2586
	11th to 20th	Night	14% 7% 2 8% 4 5% 5% 4 6% 6% 39%	2928
	21st to end	Night	16% 5% 2 6% 4 4 5% 4 5% 8% 42%	3586
September	1st to 10th	Night	12% 6% 3 6% 5% 4 4 3 6% 7% 45%	2000
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 4 6% 49%	2091
	21st to end	Night	17% 7% 2 5% 5% 4 4 3 5% 7% 42%	2200
October	1st to 10th	Night	18% 8% 3 6% 5% 4 4 4 5% 6% 39%	2319
	11th to 20th	Night	19% 9% 3 7% 5% 4 5% 4 6% 6% 34%	2441
	21st to end	Night	23% 10% 3 8% 5% 4 4 3 5% 6% 29%	2860
November	1st to 10th	Night	19% 11% 4 7% 5% 4 4 4 5% 6% 31%	2667
	11th to 20th	Night	18% 10% 4 9% 5% 4 4 3 4 5% 33%	2781
	21st to end	Night	19% 14% 4 10% 5% 4 5% 4 5% 6% 23%	2940
December	1st to 10th	Night	18% 20% 6% 12% 7% 5% 5% 3 4 5% 14%	4720
	11th to 20th	Night	21% 14% 5% 11% 6% 4 4 3 4 5% 23%	5348
	21st to end	Night	24% 14% 5% 11% 4 4 4 4 5% 6% 19%	7150

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	69% 5% 11% 12% 2	4662
	11th to 20th	Day	68% 7% 8% 9% 7% 1	4680
	21st to end	Day	62% 8% 9% 11% 10% 1	5124
February	1st to 10th	Day	64% 5% 8% 16% 5% 1	1853
	11th to 20th	Day	60% 7% 10% 16% 7% 1	1980
	21st to end	Day	61% 5% 11% 14% 8% 1	1730
March	1st to 10th	Day	61% 7% 8% 13% 8% 3	4579
	11th to 20th	Day	54% 6% 15% 14% 10% 1	4795
	21st to end	Day	54% 4 8% 16% 17% 2	6102
April	1st to 10th	Day	56% 5% 8% 19% 11% 2	2520
	11th to 20th	Day	53% 5% 7% 19% 15% 1	2494
	21st to end	Day	53% 6% 9% 18% 12% 3	2685
May	1st to 10th	Day	59% 6% 8% 17% 10%	8059
	11th to 20th	Day	49% 6% 13% 22% 8% 1	8225
	21st to end	Day	51% 6% 10% 23% 9% 1	9061
June	1st to 10th	Day	51% 8% 10% 19% 12% 1	2940
	11th to 20th	Day	43% 7% 11% 23% 14% 2	2870
	21st to end	Day	50% 7% 11% 21% 9% 1	2800
July	1st to 10th	Day	46% 5% 14% 23% 10%	6290
	11th to 20th	Day	38% 6% 13% 30% 12%	6285
	21st to end	Day	37% 6% 13% 36% 8%	6728
August	1st to 10th	Day	47% 7% 15% 22% 8%	4549
	11th to 20th	Day	40% 8% 17% 28% 7%	4110
	21st to end	Day	41% 6% 18% 22% 14%	4312
September	1st to 10th	Day	36% 8% 12% 30% 13%	2400
	11th to 20th	Day	36% 5% 12% 33% 13%	2308
	21st to end	Day	41% 7% 15% 26% 11% 1	2200
October	1st to 10th	Day	43% 5% 14% 29% 9%	3377
	11th to 20th	Day	43% 5% 18% 25% 8%	3160
	21st to end	Day	48% 4 17% 24% 7%	3180
November	1st to 10th	Day	54% 7% 12% 20% 7% 1	1851
	11th to 20th	Day	55% 8% 12% 15% 10% 1	1837
	21st to end	Day	62% 8% 11% 13% 4	1680
December	1st to 10th	Day	72% 5% 10% 12% 1	2680
	11th to 20th	Day	61% 6% 10% 16% 7%	3066
	21st to end	Day	66% 6% 10% 13% 6%	4048
January	1st to 10th	Night	69% 5% 10% 12% 4	8234
	11th to 20th	Night	70% 6% 8% 10% 6%	8280
	21st to end	Night	62% 4 8% 14% 11%	9057
February	1st to 10th	Night	64% 7% 8% 14% 6%	2764
	11th to 20th	Night	58% 7% 10% 17% 8%	2537
	21st to end	Night	56% 6% 10% 16% 12% 1	2076
March	1st to 10th	Night	58% 5% 7% 15% 13% 2	5494
	11th to 20th	Night	54% 6% 14% 15% 10% 1	5369
	21st to end	Night	56% 5% 6% 20% 11% 2	5072
April	1st to 10th	Night	56% 4 8% 18% 12% 1	2100
	11th to 20th	Night	57% 5% 8% 18% 12% 1	2075
	21st to end	Night	51% 6% 8% 17% 14% 4	1933
May	1st to 10th	Night	57% 6% 11% 18% 8% 1	4911
	11th to 20th	Night	51% 6% 10% 23% 9% 1	4640
	21st to end	Night	50% 6% 9% 20% 15% 1	5115
June	1st to 10th	Night	50% 7% 10% 20% 12% 1	1680
	11th to 20th	Night	44% 6% 14% 19% 15% 2	1640
	21st to end	Night	47% 9% 12% 20% 12% 1	1600
July	1st to 10th	Night	44% 6% 18% 22% 10%	3560
	11th to 20th	Night	39% 6% 14% 28% 12%	3552
	21st to end	Night	42% 6% 13% 28% 12%	3809
August	1st to 10th	Night	46% 6% 13% 26% 9%	2576
	11th to 20th	Night	44% 7% 18% 22% 9%	2953
	21st to end	Night	40% 6% 15% 23% 15% 1	3586
September	1st to 10th	Night	37% 8% 12% 29% 13% 1	2000
	11th to 20th	Night	35% 6% 13% 32% 12% 1	2091
	21st to end	Night	42% 7% 12% 24% 15% 1	2200
October	1st to 10th	Night	45% 6% 13% 26% 10%	3787
	11th to 20th	Night	45% 5% 11% 27% 11%	3977
	21st to end	Night	50% 5% 13% 21% 11% 1	4610
November	1st to 10th	Night	53% 6% 12% 19% 9% 1	2667
	11th to 20th	Night	54% 6% 11% 18% 10% 1	2781
	21st to end	Night	60% 8% 12% 15% 5%	2940
December	1st to 10th	Night	73% 5% 10% 10% 2	4720
	11th to 20th	Night	65% 5% 9% 12% 9%	5348
	21st to end	Night	65% 6% 8% 13% 8%	7150

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	28% 24% 23% 19% 5%	220
	11th to 20th	Day	32% 26% 28% 10% 3	220
	21st to end	Day	25% 21% 33% 14% 6%	242
February	1st to 10th	Day	32% 24% 35% 8% 1	311
	11th to 20th	Day	26% 24% 36% 12% 1	459
	21st to end	Day	29% 21% 32% 16% 2	446
March	1st to 10th	Day	29% 20% 30% 17% 4	540
	11th to 20th	Day	30% 22% 29% 13% 4 1	540
	21st to end	Day	33% 23% 24% 14% 6%	594
April	1st to 10th	Day	36% 17% 26% 14% 6%	540
	11th to 20th	Day	32% 21% 26% 13% 6% 2	532
	21st to end	Day	29% 18% 31% 14% 8% 1	540
May	1st to 10th	Day	30% 17% 30% 15% 7% 1	543
	11th to 20th	Day	21% 18% 30% 23% 8% 1	567
	21st to end	Day	19% 16% 32% 25% 7% 1	617
June	1st to 10th	Day	22% 15% 28% 26% 8% 1	570
	11th to 20th	Day	17% 15% 31% 26% 10% 2	550
	21st to end	Day	24% 13% 34% 20% 8% 2	530
July	1st to 10th	Day	15% 8% 30% 29% 16% 2	525
	11th to 20th	Day	13% 8% 35% 31% 11% 2	524
	21st to end	Day	13% 10% 30% 33% 13% 2	576
August	1st to 10th	Day	15% 8% 26% 32% 16% 4	526
	11th to 20th	Day	15% 7% 27% 29% 16% 6%	519
	21st to end	Day	17% 10% 29% 24% 14% 6%	583
September	1st to 10th	Day	14% 11% 29% 26% 14% 7%	530
	11th to 20th	Day	14% 10% 19% 26% 22% 9%	530
	21st to end	Day	16% 13% 29% 21% 15% 5%	530
October	1st to 10th	Day	21% 15% 25% 21% 14% 5%	530
	11th to 20th	Day	22% 20% 29% 20% 8% 2	505
	21st to end	Day	33% 17% 26% 21% 3	462
November	1st to 10th	Day	29% 20% 28% 18% 4	425
	11th to 20th	Day	29% 21% 29% 14% 7% 1	377
	21st to end	Day	35% 22% 24% 14% 5%	220
December	1st to 10th	Day	33% 16% 26% 18% 6%	220
	11th to 20th	Day	29% 24% 34% 11% 3	220
	21st to end	Day	28% 26% 29% 12% 4 2	242
January	1st to 10th	Night	27% 19% 34% 17% 4	840
	11th to 20th	Night	27% 19% 31% 18% 4	840
	21st to end	Night	21% 15% 35% 23% 5% 1	924
February	1st to 10th	Night	22% 18% 33% 23% 4	840
	11th to 20th	Night	24% 18% 36% 20% 2	823
	21st to end	Night	25% 16% 33% 23% 3	692
March	1st to 10th	Night	28% 17% 30% 21% 4	840
	11th to 20th	Night	28% 19% 29% 20% 4	840
	21st to end	Night	27% 18% 27% 22% 6%	924
April	1st to 10th	Night	29% 17% 28% 22% 4	840
	11th to 20th	Night	31% 16% 27% 21% 5%	831
	21st to end	Night	24% 19% 29% 20% 8%	673
May	1st to 10th	Night	29% 9% 29% 24% 9%	509
	11th to 20th	Night	21% 13% 33% 25% 8%	414
	21st to end	Night	18% 12% 32% 29% 9%	455
June	1st to 10th	Night	23% 10% 28% 29% 10%	420
	11th to 20th	Night	18% 10% 29% 31% 12% 1	410
	21st to end	Night	20% 7% 28% 32% 13% 1	400
July	1st to 10th	Night	12% 5% 33% 34% 17%	390
	11th to 20th	Night	10% 4 25% 45% 15% 1	388
	21st to end	Night	13% 5% 23% 43% 16% 1	438
August	1st to 10th	Night	16% 4 17% 45% 18% 1	398
	11th to 20th	Night	15% 4 23% 35% 21% 2	619
	21st to end	Night	17% 7% 22% 37% 16% 2	880
September	1st to 10th	Night	15% 7% 27% 35% 15% 1	800
	11th to 20th	Night	15% 7% 21% 32% 22% 4	800
	21st to end	Night	19% 8% 29% 25% 17% 2	800
October	1st to 10th	Night	21% 11% 27% 26% 14% 1	800
	11th to 20th	Night	24% 12% 31% 25% 7%	800
	21st to end	Night	28% 13% 33% 22% 5%	880
November	1st to 10th	Night	26% 19% 28% 20% 6% 1	820
	11th to 20th	Night	25% 18% 30% 18% 8% 1	840
	21st to end	Night	29% 18% 30% 16% 6%	840
December	1st to 10th	Night	30% 20% 29% 18% 4	840
	11th to 20th	Night	32% 18% 29% 15% 5% 1	840
	21st to end	Night	34% 17% 29% 16% 3	924

Page generated at 2026-06-13 02:31:39. Version ac07

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