Mambourg Farm Historical Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mambourg Farm Historical Park clear sky chart from 2005-11-06 to 2026-07-16.

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	15% 10% 4 8% 5% 5% 5% 4 5% 7% 32%	138036
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 34%	134659
Transparency	Day	49% 5% 10% 21% 12% 2	141697
	Night	49% 5% 10% 21% 13% 2	139058
Seeing	Day	21% 14% 27% 21% 12% 5%	17119
	Night	19% 11% 27% 28% 14% 2	27187

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% 20% 7% 13% 8% 4 3 3 4 5% 16%	5258
	11th to 20th	Day	13% 19% 6% 15% 8% 6% 4 2 3 4 20%	5280
	21st to end	Day	20% 14% 6% 10% 8% 6% 6% 4 5% 5% 16%	5780
February	1st to 10th	Day	21% 13% 5% 9% 6% 4 4 3 4 5% 25%	1890
	11th to 20th	Day	17% 13% 6% 12% 5% 5% 4 3 4 6% 26%	2003
	21st to end	Day	18% 14% 6% 9% 4 4 3 3 4 5% 31%	1730
March	1st to 10th	Day	18% 14% 5% 9% 5% 4 4 3 4 5% 29%	4852
	11th to 20th	Day	13% 8% 3 8% 4 5% 5% 4 5% 6% 39%	5090
	21st to end	Day	19% 9% 3 8% 5% 5% 5% 3 5% 6% 33%	5586
April	1st to 10th	Day	14% 13% 3 8% 5% 5% 4 3 5% 6% 33%	2320
	11th to 20th	Day	16% 9% 3 7% 4 4 4 4 6% 6% 37%	2671
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 6% 7% 34%	2730
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 7% 28%	7616
	11th to 20th	Day	18% 8% 3 7% 5% 4 4 3 6% 9% 33%	7626
	21st to end	Day	19% 8% 3 7% 4 4 5% 4 6% 8% 33%	8391
June	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 7% 9% 38%	2730
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 5% 6% 10% 37%	2730
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 5% 6% 10% 36%	2730
July	1st to 10th	Day	11% 6% 2 6% 5% 5% 4 3 6% 9% 42%	6030
	11th to 20th	Day	11% 6% 3 7% 5% 5% 6% 5% 8% 10% 34%	5965
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 5% 8% 8% 35%	6424
August	1st to 10th	Day	10% 5% 3 7% 5% 5% 5% 4 7% 10% 38%	4234
	11th to 20th	Day	9% 7% 2 6% 5% 5% 6% 5% 8% 9% 38%	4174
	21st to end	Day	5% 5% 2 6% 4 5% 5% 4 7% 9% 47%	4616
September	1st to 10th	Day	13% 6% 2 5% 4 3 4 3 6% 7% 47%	2200
	11th to 20th	Day	9% 4 2 6% 5% 5% 4 4 5% 8% 49%	2200
	21st to end	Day	18% 8% 3 7% 4 3 4 3 5% 6% 41%	2200
October	1st to 10th	Day	12% 7% 2 6% 4 3 4 3 6% 7% 45%	2125
	11th to 20th	Day	14% 7% 2 6% 4 4 5% 3 5% 7% 44%	2000
	21st to end	Day	21% 8% 3 8% 5% 3 4 3 4 5% 36%	2175
November	1st to 10th	Day	11% 8% 2 6% 4 3 3 3 5% 7% 48%	1852
	11th to 20th	Day	16% 14% 4 6% 4 4 4 3 5% 6% 34%	1890
	21st to end	Day	18% 14% 4 8% 4 4 4 3 4 7% 29%	1890
December	1st to 10th	Day	20% 13% 5% 14% 5% 5% 4 3 4 4 24%	3020
	11th to 20th	Day	23% 15% 6% 11% 5% 4 4 3 4 6% 21%	3463
	21st to end	Day	20% 21% 5% 11% 6% 4 5% 3 4 4 15%	4565
January	1st to 10th	Night	14% 16% 7% 16% 6% 5% 5% 3 4 4 18%	7635
	11th to 20th	Night	12% 16% 7% 15% 8% 7% 6% 3 4 4 18%	7680
	21st to end	Night	18% 13% 6% 9% 6% 5% 4 3 4 5% 27%	8401
February	1st to 10th	Night	19% 14% 4 9% 6% 4 4 3 5% 5% 29%	2730
	11th to 20th	Night	18% 13% 3 10% 6% 5% 5% 3 4 6% 26%	2500
	21st to end	Night	19% 13% 6% 10% 5% 4 3 3 4 4 28%	2076
March	1st to 10th	Night	20% 11% 4 7% 4 4 4 3 4 5% 34%	5219
	11th to 20th	Night	12% 8% 2 6% 4 4 5% 4 5% 7% 42%	5090
	21st to end	Night	17% 9% 3 7% 5% 4 5% 3 5% 6% 35%	5588
April	1st to 10th	Night	15% 11% 3 6% 4 4 4 4 5% 7% 37%	2310
	11th to 20th	Night	14% 8% 3 7% 4 5% 4 4 6% 9% 37%	1903
	21st to end	Night	15% 8% 3 7% 4 4 4 3 6% 7% 38%	1890
May	1st to 10th	Night	23% 9% 3 7% 5% 4 4 4 5% 7% 30%	5237
	11th to 20th	Night	15% 8% 3 7% 4 4 4 3 6% 10% 38%	5234
	21st to end	Night	17% 8% 3 7% 4 4 4 4 6% 8% 35%	5761
June	1st to 10th	Night	9% 6% 2 6% 5% 4 4 3 6% 8% 47%	1890
	11th to 20th	Night	10% 4 2 6% 4 4 4 4 8% 10% 43%	1890
	21st to end	Night	10% 6% 2 5% 3 5% 4 5% 7% 9% 44%	1890
July	1st to 10th	Night	10% 6% 3 6% 4 4 4 4 6% 7% 46%	4148
	11th to 20th	Night	10% 6% 2 7% 5% 5% 5% 4 7% 10% 38%	4102
	21st to end	Night	8% 5% 2 7% 6% 6% 5% 5% 8% 8% 39%	4427
August	1st to 10th	Night	7% 7% 3 8% 5% 5% 5% 4 8% 10% 39%	2915
	11th to 20th	Night	9% 6% 3 8% 5% 4 4 3 5% 7% 45%	2875
	21st to end	Night	5% 3 2 5% 4 4 5% 4 7% 10% 51%	3246
September	1st to 10th	Night	12% 4 2 4 3 4 4 3 5% 7% 52%	2196
	11th to 20th	Night	8% 3 2 4 3 4 4 3 5% 8% 55%	2200
	21st to end	Night	15% 8% 2 6% 3 3 3 3 4 6% 47%	2200
October	1st to 10th	Night	10% 5% 2 5% 4 3 4 3 6% 7% 50%	2275
	11th to 20th	Night	14% 7% 3 6% 4 3 4 3 5% 7% 45%	2400
	21st to end	Night	19% 8% 2 6% 4 3 4 3 5% 6% 39%	2660
November	1st to 10th	Night	14% 7% 2 5% 4 3 3 3 4 6% 49%	2666
	11th to 20th	Night	15% 10% 3 7% 5% 4 4 4 5% 6% 36%	2730
	21st to end	Night	19% 13% 4 8% 4 4 4 3 6% 5% 29%	2730
December	1st to 10th	Night	18% 13% 5% 10% 5% 4 4 3 5% 6% 27%	4380
	11th to 20th	Night	19% 17% 7% 10% 4 4 4 3 4 5% 23%	4952
	21st to end	Night	21% 19% 6% 10% 6% 5% 4 3 4 6% 16%	6633

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	71% 4 11% 11% 3	5259
	11th to 20th	Day	69% 4 8% 10% 9% 1	5280
	21st to end	Day	70% 4 10% 11% 6%	5780
February	1st to 10th	Day	61% 4 11% 15% 8%	1890
	11th to 20th	Day	61% 4 9% 16% 9%	2013
	21st to end	Day	57% 3 11% 19% 8% 1	1730
March	1st to 10th	Day	58% 4 7% 22% 8% 2	4852
	11th to 20th	Day	44% 5% 10% 29% 11% 1	5090
	21st to end	Day	52% 5% 9% 22% 11% 2	5586
April	1st to 10th	Day	52% 5% 10% 20% 11% 2	2320
	11th to 20th	Day	46% 5% 12% 19% 14% 3	2671
	21st to end	Day	49% 6% 9% 23% 11% 2	2730
May	1st to 10th	Day	54% 6% 9% 21% 9% 1	7651
	11th to 20th	Day	48% 5% 11% 23% 12%	7630
	21st to end	Day	47% 7% 10% 18% 14% 4	8405
June	1st to 10th	Day	41% 7% 11% 24% 15% 2	2730
	11th to 20th	Day	41% 8% 13% 22% 15% 1	2730
	21st to end	Day	41% 8% 15% 21% 14% 2	2730
July	1st to 10th	Day	39% 6% 11% 27% 15% 2	5965
	11th to 20th	Day	42% 8% 12% 25% 12% 1	5896
	21st to end	Day	43% 7% 11% 19% 17% 2	6240
August	1st to 10th	Day	39% 8% 14% 29% 10% 1	4221
	11th to 20th	Day	38% 7% 11% 30% 13% 1	4213
	21st to end	Day	32% 7% 14% 30% 15% 3	4616
September	1st to 10th	Day	36% 6% 10% 22% 23% 4	2200
	11th to 20th	Day	33% 5% 11% 27% 22% 2	2200
	21st to end	Day	44% 4 9% 22% 20% 1	2200
October	1st to 10th	Day	26% 4 8% 32% 28% 1	3463
	11th to 20th	Day	34% 3 11% 27% 22% 3	3240
	21st to end	Day	38% 3 11% 27% 19% 2	3489
November	1st to 10th	Day	37% 5% 9% 29% 17% 3	1852
	11th to 20th	Day	51% 5% 9% 21% 12% 3	1890
	21st to end	Day	56% 5% 10% 18% 10% 1	1890
December	1st to 10th	Day	65% 3 11% 17% 4	3020
	11th to 20th	Day	66% 3 10% 15% 5%	3460
	21st to end	Day	72% 5% 9% 11% 4	4565
January	1st to 10th	Night	70% 3 9% 14% 3	7636
	11th to 20th	Night	69% 4 8% 11% 7% 1	7680
	21st to end	Night	61% 2 12% 18% 6% 1	8401
February	1st to 10th	Night	57% 5% 10% 19% 8% 1	2730
	11th to 20th	Night	60% 4 9% 17% 9% 1	2501
	21st to end	Night	59% 4 10% 17% 8% 2	2076
March	1st to 10th	Night	52% 3 6% 26% 10% 2	5219
	11th to 20th	Night	40% 5% 9% 32% 12% 1	5090
	21st to end	Night	50% 4 7% 23% 14% 2	5588
April	1st to 10th	Night	47% 5% 11% 20% 15% 2	2310
	11th to 20th	Night	43% 6% 11% 18% 18% 4	1903
	21st to end	Night	45% 5% 10% 23% 15% 2	1890
May	1st to 10th	Night	53% 6% 11% 19% 8% 3	5264
	11th to 20th	Night	43% 7% 11% 26% 13% 1	5235
	21st to end	Night	46% 6% 11% 22% 12% 4	5771
June	1st to 10th	Night	35% 8% 10% 23% 21% 2	1890
	11th to 20th	Night	33% 8% 15% 24% 17% 2	1890
	21st to end	Night	34% 8% 14% 24% 17% 2	1890
July	1st to 10th	Night	37% 6% 11% 24% 18% 4	4105
	11th to 20th	Night	39% 8% 15% 26% 11% 1	4051
	21st to end	Night	39% 8% 12% 21% 16% 4	4297
August	1st to 10th	Night	38% 7% 15% 26% 12% 1	2904
	11th to 20th	Night	38% 6% 9% 25% 21%	2902
	21st to end	Night	27% 7% 14% 30% 19% 3	3246
September	1st to 10th	Night	32% 5% 11% 24% 23% 6%	2196
	11th to 20th	Night	27% 6% 11% 27% 26% 3	2200
	21st to end	Night	40% 5% 9% 20% 25% 1	2200
October	1st to 10th	Night	28% 4 6% 29% 30% 3	3717
	11th to 20th	Night	30% 3 10% 27% 23% 5%	3899
	21st to end	Night	33% 4 8% 26% 25% 4	4284
November	1st to 10th	Night	37% 4 11% 25% 19% 3	2666
	11th to 20th	Night	49% 5% 9% 21% 15% 2	2730
	21st to end	Night	56% 4 11% 19% 9% 1	2730
December	1st to 10th	Night	58% 4 12% 21% 5%	4380
	11th to 20th	Night	64% 4 11% 16% 5%	4954
	21st to end	Night	70% 4 9% 13% 4	6633

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% 25% 32% 10% 3	330
	11th to 20th	Day	32% 27% 33% 7% 1	330
	21st to end	Day	31% 27% 29% 10% 3	363
February	1st to 10th	Day	30% 25% 29% 13% 2 1	330
	11th to 20th	Day	36% 28% 26% 8% 2	330
	21st to end	Day	30% 27% 36% 6%	273
March	1st to 10th	Day	28% 24% 31% 14% 3	446
	11th to 20th	Day	29% 20% 32% 13% 6%	540
	21st to end	Day	31% 17% 33% 15% 4	594
April	1st to 10th	Day	24% 21% 31% 15% 7% 2	540
	11th to 20th	Day	26% 18% 30% 16% 7% 3	532
	21st to end	Day	23% 19% 31% 19% 7% 2	540
May	1st to 10th	Day	26% 21% 30% 15% 7% 2	543
	11th to 20th	Day	20% 14% 32% 22% 9% 4	567
	21st to end	Day	14% 12% 26% 26% 17% 6%	617
June	1st to 10th	Day	13% 9% 28% 30% 14% 6%	570
	11th to 20th	Day	14% 9% 26% 29% 16% 6%	570
	21st to end	Day	13% 7% 27% 29% 16% 7%	570
July	1st to 10th	Day	14% 4 16% 25% 24% 17%	565
	11th to 20th	Day	10% 5% 23% 27% 24% 10%	544
	21st to end	Day	14% 4 19% 27% 23% 12%	576
August	1st to 10th	Day	10% 5% 19% 31% 23% 12%	526
	11th to 20th	Day	13% 6% 21% 29% 20% 12%	519
	21st to end	Day	8% 5% 19% 31% 26% 11%	583
September	1st to 10th	Day	13% 7% 18% 26% 24% 12%	530
	11th to 20th	Day	10% 2 15% 27% 32% 14%	530
	21st to end	Day	24% 8% 19% 26% 19% 4	530
October	1st to 10th	Day	12% 7% 28% 28% 19% 6%	530
	11th to 20th	Day	17% 14% 31% 22% 13% 3	530
	21st to end	Day	26% 16% 31% 19% 8% 1	558
November	1st to 10th	Day	19% 18% 35% 19% 7% 2	330
	11th to 20th	Day	33% 16% 29% 15% 6% 1	330
	21st to end	Day	28% 23% 33% 14% 2	330
December	1st to 10th	Day	28% 22% 34% 12% 3 1	330
	11th to 20th	Day	27% 25% 35% 11% 2	330
	21st to end	Day	34% 21% 31% 12% 2	363
January	1st to 10th	Night	25% 21% 31% 18% 4	840
	11th to 20th	Night	27% 21% 31% 18% 2	840
	21st to end	Night	27% 17% 34% 20% 2	924
February	1st to 10th	Night	26% 16% 30% 26% 2	840
	11th to 20th	Night	28% 20% 32% 19% 1	823
	21st to end	Night	27% 16% 37% 18% 2	692
March	1st to 10th	Night	25% 15% 33% 23% 4	840
	11th to 20th	Night	22% 19% 32% 21% 7% 1	840
	21st to end	Night	24% 16% 31% 22% 6% 1	924
April	1st to 10th	Night	21% 16% 35% 22% 5%	840
	11th to 20th	Night	17% 13% 37% 22% 11% 1	630
	21st to end	Night	19% 9% 40% 26% 7% 1	630
May	1st to 10th	Night	21% 10% 31% 26% 12% 1	630
	11th to 20th	Night	20% 5% 28% 31% 15% 1	621
	21st to end	Night	10% 5% 23% 35% 24% 2	683
June	1st to 10th	Night	12% 4 25% 38% 20% 1	630
	11th to 20th	Night	11% 3 23% 41% 21% 1	630
	21st to end	Night	11% 3 22% 38% 23% 2	630
July	1st to 10th	Night	10% 3 16% 35% 30% 7%	615
	11th to 20th	Night	7% 2 16% 38% 31% 6%	597
	21st to end	Night	9% 3 13% 36% 36% 2	657
August	1st to 10th	Night	7% 2 13% 40% 34% 3	597
	11th to 20th	Night	8% 2 14% 39% 32% 5%	594
	21st to end	Night	9% 2 16% 32% 35% 6%	660
September	1st to 10th	Night	13% 4 16% 36% 27% 4	796
	11th to 20th	Night	10% 3 12% 36% 34% 5%	800
	21st to end	Night	18% 7% 22% 32% 20% 3	800
October	1st to 10th	Night	12% 5% 24% 33% 23% 3	800
	11th to 20th	Night	18% 11% 28% 30% 12% 2	800
	21st to end	Night	23% 12% 28% 28% 9%	880
November	1st to 10th	Night	17% 12% 27% 29% 14%	820
	11th to 20th	Night	22% 17% 28% 25% 8% 1	840
	21st to end	Night	26% 14% 28% 25% 6% 1	840
December	1st to 10th	Night	29% 17% 27% 23% 4	840
	11th to 20th	Night	25% 16% 31% 24% 4	840
	21st to end	Night	29% 17% 29% 23% 2	924

Page generated at 2026-07-13 03:14:52. Version ac07

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