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 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	16% 10% 4 8% 5% 5% 5% 4 5% 7% 31%	108580
	Night	17% 12% 4 9% 5% 5% 4 3 5% 6% 29%	109992
Transparency	Day	51% 7% 12% 20% 9% 1	112072
	Night	55% 6% 11% 18% 10% 1	114651
Seeing	Day	23% 16% 29% 21% 9% 2	14881
	Night	24% 14% 29% 24% 9% 1	24006

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	16% 20% 7% 14% 6% 6% 3 3 3 4 19%	3597
	11th to 20th	Day	11% 17% 8% 17% 8% 6% 4 3 4 4 18%	3570
	21st to end	Day	13% 15% 6% 13% 6% 6% 5% 4 5% 6% 21%	3960
February	1st to 10th	Day	16% 16% 5% 13% 7% 4 5% 3 5% 5% 21%	1765
	11th to 20th	Day	12% 15% 4 13% 8% 4 5% 5% 4 5% 24%	1875
	21st to end	Day	17% 17% 4 8% 7% 5% 5% 3 5% 6% 24%	1570
March	1st to 10th	Day	21% 12% 4 10% 6% 5% 5% 3 4 5% 25%	3116
	11th to 20th	Day	15% 17% 6% 10% 7% 5% 4 3 4 5% 25%	3290
	21st to end	Day	16% 10% 3 8% 5% 3 4 3 4 6% 39%	4166
April	1st to 10th	Day	23% 12% 3 7% 4 4 4 3 5% 5% 30%	2280
	11th to 20th	Day	21% 10% 3 7% 5% 4 4 3 4 5% 35%	2254
	21st to end	Day	23% 9% 3 7% 5% 4 3 4 4 6% 32%	2429
May	1st to 10th	Day	23% 10% 3 7% 4 4 5% 3 6% 6% 29%	4320
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 6% 32%	4398
	21st to end	Day	14% 6% 3 7% 5% 5% 6% 4 7% 9% 35%	4837
June	1st to 10th	Day	22% 7% 3 7% 5% 5% 4 4 6% 7% 30%	2660
	11th to 20th	Day	14% 7% 2 6% 5% 5% 5% 5% 6% 8% 37%	2660
	21st to end	Day	22% 7% 2 7% 5% 5% 4 4 6% 7% 31%	2660
July	1st to 10th	Day	12% 6% 2 8% 5% 5% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 10% 37%	4440
	21st to end	Day	12% 6% 3 6% 4 4 5% 4 6% 8% 41%	4814
August	1st to 10th	Day	15% 7% 3 9% 5% 5% 6% 5% 7% 8% 32%	4423
	11th to 20th	Day	14% 6% 2 6% 4 5% 5% 4 6% 8% 38%	3942
	21st to end	Day	15% 5% 2 6% 4 4 4 4 6% 9% 41%	4180
September	1st to 10th	Day	12% 6% 2 5% 5% 4 5% 4 5% 8% 44%	2280
	11th to 20th	Day	15% 6% 2 5% 4 4 4 4 4 7% 47%	2193
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 6% 8% 41%	2090
October	1st to 10th	Day	21% 7% 3 7% 4 5% 5% 4 5% 7% 32%	1974
	11th to 20th	Day	17% 7% 3 7% 6% 5% 6% 4 6% 5% 31%	1859
	21st to end	Day	24% 13% 3 6% 4 5% 3 3 4 6% 28%	1881
November	1st to 10th	Day	17% 12% 3 8% 5% 5% 4 3 6% 5% 32%	1761
	11th to 20th	Day	16% 14% 4 7% 5% 5% 4 5% 5% 6% 29%	1750
	21st to end	Day	21% 15% 5% 8% 6% 4 5% 4 6% 6% 22%	1600
December	1st to 10th	Day	16% 22% 6% 13% 7% 5% 4 3 4 5% 15%	2600
	11th to 20th	Day	18% 14% 6% 10% 5% 4 5% 3 6% 5% 24%	2986
	21st to end	Day	21% 15% 4 12% 6% 5% 5% 4 5% 4 21%	3960
January	1st to 10th	Night	14% 20% 8% 15% 7% 5% 4 2 4 4 17%	6349
	11th to 20th	Night	10% 17% 7% 16% 8% 6% 5% 4 5% 5% 16%	6315
	21st to end	Night	15% 16% 5% 12% 7% 6% 5% 4 5% 5% 21%	6996
February	1st to 10th	Night	14% 15% 6% 13% 8% 6% 6% 3 5% 5% 20%	2633
	11th to 20th	Night	15% 11% 5% 11% 7% 6% 5% 4 6% 5% 26%	2411
	21st to end	Night	16% 13% 4 9% 6% 4 5% 3 4 5% 30%	1885
March	1st to 10th	Night	21% 11% 4 7% 5% 4 4 3 5% 5% 32%	3724
	11th to 20th	Night	17% 16% 5% 10% 5% 4 4 3 4 4 27%	3667
	21st to end	Night	14% 11% 4 9% 6% 5% 5% 3 5% 5% 35%	3466
April	1st to 10th	Night	22% 11% 3 7% 5% 5% 4 3 5% 5% 30%	1900
	11th to 20th	Night	25% 9% 3 7% 4 4 4 3 4 5% 32%	1875
	21st to end	Night	19% 9% 3 8% 5% 5% 5% 3 4 5% 35%	1749
May	1st to 10th	Night	23% 11% 3 7% 4 4 5% 3 5% 7% 28%	2647
	11th to 20th	Night	21% 9% 3 7% 4 4 3 3 5% 6% 35%	2495
	21st to end	Night	16% 6% 3 7% 4 5% 5% 3 5% 9% 37%	2738
June	1st to 10th	Night	22% 6% 3 5% 5% 6% 5% 3 7% 7% 30%	1520
	11th to 20th	Night	17% 5% 3 7% 4 4 5% 4 7% 8% 37%	1520
	21st to end	Night	18% 8% 2 7% 5% 4 4 4 6% 6% 35%	1520
July	1st to 10th	Night	14% 6% 3 8% 5% 5% 6% 4 6% 7% 36%	2520
	11th to 20th	Night	13% 5% 2 5% 4 4 5% 4 7% 8% 43%	2520
	21st to end	Night	11% 7% 3 7% 5% 5% 5% 3 6% 7% 41%	2739
August	1st to 10th	Night	16% 7% 4 8% 4 4 4 3 5% 7% 38%	2506
	11th to 20th	Night	14% 7% 2 8% 4 5% 5% 4 6% 6% 38%	2837
	21st to end	Night	16% 5% 2 6% 4 4 5% 4 5% 8% 42%	3476
September	1st to 10th	Night	12% 6% 2 6% 5% 4 4 3 6% 7% 45%	1900
	11th to 20th	Night	13% 6% 2 6% 4 4 3 3 4 6% 49%	1986
	21st to end	Night	17% 7% 2 4 5% 4 4 3 5% 7% 42%	2090
October	1st to 10th	Night	18% 8% 3 7% 5% 4 4 4 5% 5% 37%	2203
	11th to 20th	Night	19% 9% 2 7% 5% 4 5% 4 6% 6% 33%	2319
	21st to end	Night	23% 10% 3 8% 5% 4 4 3 5% 6% 29%	2717
November	1st to 10th	Night	18% 10% 4 7% 5% 4 4 4 5% 6% 31%	2537
	11th to 20th	Night	18% 10% 4 8% 5% 4 4 3 4 5% 33%	2648
	21st to end	Night	20% 14% 4 9% 5% 4 5% 4 5% 6% 24%	2800
December	1st to 10th	Night	18% 20% 6% 12% 7% 5% 5% 3 4 5% 14%	4580
	11th to 20th	Night	21% 14% 5% 11% 5% 4 4 3 4 5% 23%	5208
	21st to end	Night	24% 14% 5% 11% 4 4 4 4 6% 6% 19%	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	69% 6% 12% 12% 2	3598
	11th to 20th	Day	67% 7% 9% 10% 6% 1	3600
	21st to end	Day	61% 9% 9% 11% 9% 1	3960
February	1st to 10th	Day	65% 5% 8% 14% 5% 2	1765
	11th to 20th	Day	61% 7% 10% 15% 7% 1	1884
	21st to end	Day	61% 5% 11% 14% 8% 1	1570
March	1st to 10th	Day	59% 8% 9% 17% 6% 1	3119
	11th to 20th	Day	59% 8% 11% 12% 9% 1	3290
	21st to end	Day	47% 4 10% 19% 17% 2	4166
April	1st to 10th	Day	55% 5% 8% 19% 11% 2	2280
	11th to 20th	Day	51% 5% 8% 20% 15% 2	2254
	21st to end	Day	54% 6% 9% 17% 12% 3	2429
May	1st to 10th	Day	53% 8% 10% 18% 10% 1	4334
	11th to 20th	Day	48% 9% 14% 19% 8% 2	4402
	21st to end	Day	42% 9% 13% 23% 12% 1	4837
June	1st to 10th	Day	52% 8% 10% 18% 11% 1	2660
	11th to 20th	Day	43% 7% 11% 23% 14% 2	2660
	21st to end	Day	51% 8% 11% 21% 9% 1	2660
July	1st to 10th	Day	42% 6% 15% 26% 11%	4370
	11th to 20th	Day	41% 6% 15% 32% 6%	4365
	21st to end	Day	40% 7% 12% 32% 9%	4661
August	1st to 10th	Day	48% 7% 15% 21% 8%	4409
	11th to 20th	Day	40% 8% 18% 27% 6%	3983
	21st to end	Day	40% 6% 18% 22% 14%	4180
September	1st to 10th	Day	37% 8% 13% 28% 13%	2280
	11th to 20th	Day	37% 5% 12% 32% 13% 1	2193
	21st to end	Day	41% 7% 15% 26% 10% 1	2090
October	1st to 10th	Day	44% 6% 14% 28% 8%	3273
	11th to 20th	Day	44% 6% 18% 25% 7%	3062
	21st to end	Day	47% 4 17% 24% 7%	3081
November	1st to 10th	Day	53% 7% 12% 20% 7% 1	1761
	11th to 20th	Day	54% 8% 11% 15% 11% 1	1750
	21st to end	Day	62% 9% 12% 14% 4	1600
December	1st to 10th	Day	72% 5% 10% 12% 1	2600
	11th to 20th	Day	61% 6% 10% 16% 7% 1	2986
	21st to end	Day	65% 6% 10% 13% 6%	3960
January	1st to 10th	Night	71% 6% 10% 10% 3	6349
	11th to 20th	Night	68% 7% 9% 11% 4	6360
	21st to end	Night	64% 5% 9% 10% 11% 1	6996
February	1st to 10th	Night	65% 7% 8% 14% 6%	2633
	11th to 20th	Night	58% 7% 11% 16% 8%	2413
	21st to end	Night	56% 6% 10% 16% 12% 1	1885
March	1st to 10th	Night	54% 7% 9% 19% 10% 2	3734
	11th to 20th	Night	60% 6% 9% 14% 10% 1	3668
	21st to end	Night	49% 6% 7% 21% 14% 2	3466
April	1st to 10th	Night	56% 5% 9% 17% 12% 1	1900
	11th to 20th	Night	55% 5% 9% 18% 12% 1	1875
	21st to end	Night	52% 7% 8% 17% 13% 4	1749
May	1st to 10th	Night	54% 8% 9% 18% 9% 3	2653
	11th to 20th	Night	48% 8% 11% 21% 11% 2	2496
	21st to end	Night	42% 9% 10% 20% 17% 1	2739
June	1st to 10th	Night	50% 8% 11% 20% 10% 1	1520
	11th to 20th	Night	44% 6% 14% 19% 15% 2	1520
	21st to end	Night	47% 9% 12% 19% 12% 1	1520
July	1st to 10th	Night	46% 7% 12% 21% 13%	2480
	11th to 20th	Night	37% 7% 15% 31% 9%	2472
	21st to end	Night	43% 7% 14% 24% 13%	2651
August	1st to 10th	Night	47% 6% 12% 26% 9%	2496
	11th to 20th	Night	44% 7% 19% 21% 9%	2862
	21st to end	Night	40% 7% 15% 23% 15% 1	3476
September	1st to 10th	Night	37% 8% 12% 28% 14% 1	1900
	11th to 20th	Night	35% 7% 13% 32% 12% 1	1986
	21st to end	Night	41% 7% 12% 24% 14% 1	2090
October	1st to 10th	Night	46% 6% 13% 26% 9%	3671
	11th to 20th	Night	45% 5% 11% 27% 11%	3855
	21st to end	Night	50% 5% 13% 21% 11% 1	4467
November	1st to 10th	Night	53% 7% 12% 18% 9% 1	2537
	11th to 20th	Night	53% 6% 11% 18% 10% 1	2648
	21st to end	Night	60% 8% 12% 15% 5%	2800
December	1st to 10th	Night	73% 5% 10% 10% 2	4580
	11th to 20th	Night	64% 5% 9% 12% 9%	5208
	21st to end	Night	65% 6% 8% 13% 8%	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	29% 23% 23% 19% 6% 1	200
	11th to 20th	Day	30% 25% 30% 12% 3 1	200
	21st to end	Day	25% 21% 33% 15% 6%	220
February	1st to 10th	Day	35% 23% 35% 6% 1	283
	11th to 20th	Day	26% 25% 36% 11% 1	423
	21st to end	Day	30% 20% 30% 18% 2	382
March	1st to 10th	Day	30% 18% 30% 18% 5%	460
	11th to 20th	Day	26% 23% 30% 14% 5% 1	460
	21st to end	Day	32% 22% 24% 16% 6%	506
April	1st to 10th	Day	35% 17% 25% 16% 7%	460
	11th to 20th	Day	31% 20% 27% 13% 7% 3	452
	21st to end	Day	30% 17% 30% 14% 9% 1	460
May	1st to 10th	Day	27% 16% 32% 16% 8% 1	463
	11th to 20th	Day	20% 17% 30% 24% 9% 1	487
	21st to end	Day	17% 16% 31% 26% 8% 1	529
June	1st to 10th	Day	24% 16% 27% 25% 7% 1	490
	11th to 20th	Day	16% 14% 31% 26% 11% 2	490
	21st to end	Day	24% 13% 32% 20% 8% 2	490
July	1st to 10th	Day	15% 7% 30% 29% 16% 2	485
	11th to 20th	Day	14% 7% 35% 30% 12% 3	484
	21st to end	Day	13% 9% 29% 34% 13% 2	532
August	1st to 10th	Day	16% 8% 27% 30% 15% 4	486
	11th to 20th	Day	15% 7% 27% 29% 16% 6%	479
	21st to end	Day	17% 10% 28% 24% 15% 6%	539
September	1st to 10th	Day	15% 11% 28% 26% 14% 6%	490
	11th to 20th	Day	15% 11% 19% 25% 21% 9%	490
	21st to end	Day	16% 13% 29% 21% 16% 5%	490
October	1st to 10th	Day	22% 15% 24% 20% 14% 5%	490
	11th to 20th	Day	22% 20% 28% 20% 8% 2	467
	21st to end	Day	34% 17% 25% 21% 3	429
November	1st to 10th	Day	28% 19% 29% 19% 5% 1	395
	11th to 20th	Day	28% 23% 28% 15% 6% 1	350
	21st to end	Day	34% 21% 25% 15% 5% 1	200
December	1st to 10th	Day	34% 15% 26% 19% 7% 1	200
	11th to 20th	Day	29% 23% 34% 12% 3	200
	21st to end	Day	28% 25% 28% 13% 4 2	220
January	1st to 10th	Night	26% 20% 33% 17% 4	800
	11th to 20th	Night	25% 19% 32% 19% 5%	800
	21st to end	Night	21% 15% 36% 23% 5% 1	880
February	1st to 10th	Night	23% 19% 33% 22% 4	800
	11th to 20th	Night	23% 18% 37% 19% 2	783
	21st to end	Night	25% 17% 32% 23% 3	629
March	1st to 10th	Night	28% 16% 30% 23% 4	760
	11th to 20th	Night	28% 18% 29% 21% 4	760
	21st to end	Night	27% 17% 27% 23% 6%	836
April	1st to 10th	Night	28% 17% 27% 24% 4	760
	11th to 20th	Night	30% 16% 26% 21% 5%	751
	21st to end	Night	24% 19% 28% 21% 8%	609
May	1st to 10th	Night	28% 10% 29% 23% 10%	461
	11th to 20th	Night	21% 12% 33% 26% 8% 1	374
	21st to end	Night	17% 12% 32% 30% 9%	411
June	1st to 10th	Night	23% 10% 26% 30% 10% 1	380
	11th to 20th	Night	18% 9% 27% 32% 13% 1	380
	21st to end	Night	20% 7% 28% 32% 13% 1	380
July	1st to 10th	Night	12% 5% 32% 34% 18%	370
	11th to 20th	Night	9% 4 26% 44% 16% 1	368
	21st to end	Night	13% 4 22% 43% 17% 1	416
August	1st to 10th	Night	16% 4 18% 44% 17% 1	378
	11th to 20th	Night	16% 4 23% 35% 20% 2	588
	21st to end	Night	17% 6% 22% 36% 17% 2	836
September	1st to 10th	Night	15% 7% 27% 35% 14% 1	760
	11th to 20th	Night	15% 7% 21% 31% 21% 4	760
	21st to end	Night	19% 8% 28% 25% 17% 2	760
October	1st to 10th	Night	22% 11% 27% 25% 14% 1	760
	11th to 20th	Night	25% 13% 29% 25% 8%	760
	21st to end	Night	28% 13% 33% 21% 5%	836
November	1st to 10th	Night	25% 19% 29% 20% 7% 1	780
	11th to 20th	Night	24% 19% 30% 18% 8% 1	800
	21st to end	Night	29% 18% 30% 17% 7%	800
December	1st to 10th	Night	30% 19% 29% 18% 4	800
	11th to 20th	Night	32% 17% 29% 16% 5% 1	800
	21st to end	Night	34% 17% 30% 16% 3	880

Page generated at 2025-02-18 03:26:27. Version ac07

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