Port Hilford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Hilford clear sky chart from 2005-11-06 to 2024-11-12.

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	23% 11% 3 7% 5% 4 4 4 5% 7% 27%	101692
	Night	24% 11% 4 7% 4 4 4 3 5% 6% 29%	97606
Transparency	Day	55% 8% 12% 17% 8% 1	105219
	Night	56% 8% 11% 17% 8% 1	102174
Seeing	Day	27% 11% 26% 26% 9% 1	17560
	Night	28% 11% 28% 24% 8% 1	25085

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	15% 11% 4 13% 5% 5% 5% 4 5% 7% 26%	2526
	11th to 20th	Day	16% 13% 4 11% 5% 4 5% 4 5% 5% 28%	2530
	21st to end	Day	17% 11% 3 7% 5% 5% 4 4 6% 7% 30%	3004
February	1st to 10th	Day	22% 11% 4 8% 5% 4 5% 4 5% 6% 25%	1710
	11th to 20th	Day	19% 12% 4 9% 6% 5% 5% 3 5% 5% 27%	1663
	21st to end	Day	14% 13% 4 7% 7% 4 4 3 6% 6% 32%	1531
March	1st to 10th	Day	25% 12% 3 7% 4 4 3 3 4 5% 30%	3224
	11th to 20th	Day	16% 13% 5% 9% 5% 4 5% 4 7% 6% 24%	3480
	21st to end	Day	32% 11% 3 9% 5% 4 4 3 4 4 21%	3960
April	1st to 10th	Day	26% 12% 3 8% 3 4 3 3 5% 6% 28%	2280
	11th to 20th	Day	26% 10% 3 6% 4 3 3 3 5% 7% 31%	2254
	21st to end	Day	26% 11% 3 6% 4 4 4 4 5% 5% 30%	2417
May	1st to 10th	Day	28% 11% 4 7% 5% 4 5% 3 4 6% 23%	4415
	11th to 20th	Day	26% 11% 4 6% 5% 4 4 3 4 5% 27%	4398
	21st to end	Day	22% 13% 3 7% 5% 5% 5% 4 7% 7% 22%	4836
June	1st to 10th	Day	31% 9% 3 7% 5% 4 4 4 5% 6% 22%	2660
	11th to 20th	Day	25% 10% 3 6% 5% 4 4 4 5% 6% 29%	2660
	21st to end	Day	35% 13% 4 6% 4 4 4 3 4 5% 19%	2660
July	1st to 10th	Day	26% 12% 3 8% 5% 5% 5% 4 5% 7% 21%	4440
	11th to 20th	Day	24% 15% 4 7% 5% 4 4 4 5% 7% 21%	4440
	21st to end	Day	22% 10% 3 7% 5% 5% 4 4 5% 8% 27%	4815
August	1st to 10th	Day	24% 11% 4 8% 4 4 5% 4 6% 8% 23%	4217
	11th to 20th	Day	20% 8% 3 7% 5% 5% 4 4 7% 9% 28%	4045
	21st to end	Day	12% 7% 2 6% 4 4 5% 3 5% 8% 44%	4194
September	1st to 10th	Day	20% 7% 2 6% 5% 4 3 3 6% 7% 37%	2280
	11th to 20th	Day	20% 8% 3 6% 3 3 4 3 6% 8% 35%	2280
	21st to end	Day	21% 6% 2 6% 5% 6% 4 4 4 6% 35%	2007
October	1st to 10th	Day	18% 9% 3 6% 4 5% 4 4 6% 7% 34%	1900
	11th to 20th	Day	21% 7% 2 6% 4 5% 4 4 6% 7% 33%	1900
	21st to end	Day	22% 8% 3 7% 5% 5% 5% 4 6% 6% 30%	1992
November	1st to 10th	Day	22% 9% 3 8% 5% 4 4 4 5% 7% 30%	1717
	11th to 20th	Day	23% 10% 3 7% 5% 4 4 4 5% 7% 28%	1528
	21st to end	Day	18% 10% 3 7% 5% 4 5% 4 7% 7% 30%	1520
December	1st to 10th	Day	23% 15% 4 8% 5% 4 4 4 5% 6% 23%	1520
	11th to 20th	Day	30% 12% 3 8% 4 4 5% 4 5% 4 21%	1906
	21st to end	Day	22% 11% 6% 9% 5% 4 4 3 5% 6% 26%	2783
January	1st to 10th	Night	16% 11% 4 9% 5% 4 4 4 6% 8% 30%	4429
	11th to 20th	Night	22% 11% 3 10% 5% 4 5% 4 5% 6% 25%	4440
	21st to end	Night	18% 10% 6% 8% 5% 4 4 3 6% 7% 30%	4654
February	1st to 10th	Night	22% 11% 5% 8% 5% 5% 4 4 5% 5% 26%	2470
	11th to 20th	Night	19% 12% 4 9% 6% 5% 4 4 5% 6% 27%	2403
	21st to end	Night	13% 13% 5% 8% 5% 5% 5% 4 5% 6% 31%	1922
March	1st to 10th	Night	22% 12% 3 9% 5% 4 5% 3 4 6% 27%	3612
	11th to 20th	Night	24% 13% 5% 6% 4 4 4 3 4 7% 27%	3479
	21st to end	Night	31% 11% 5% 8% 5% 4 3 2 3 4 24%	3671
April	1st to 10th	Night	27% 14% 3 6% 4 4 4 2 4 6% 27%	1900
	11th to 20th	Night	24% 9% 2 6% 4 3 4 3 6% 7% 31%	1876
	21st to end	Night	28% 9% 3 5% 4 4 4 3 5% 5% 30%	1762
May	1st to 10th	Night	28% 12% 4 9% 4 5% 4 3 4 6% 20%	2535
	11th to 20th	Night	29% 10% 3 6% 4 3 3 3 4 5% 29%	2506
	21st to end	Night	25% 16% 4 7% 3 4 4 3 4 7% 23%	2749
June	1st to 10th	Night	32% 12% 3 8% 4 3 4 2 4 6% 21%	1520
	11th to 20th	Night	27% 9% 3 6% 4 3 3 3 6% 6% 31%	1520
	21st to end	Night	37% 13% 3 6% 4 3 3 2 4 5% 20%	1520
July	1st to 10th	Night	30% 14% 5% 8% 4 3 4 3 5% 6% 20%	2530
	11th to 20th	Night	29% 18% 4 7% 4 3 3 3 4 5% 20%	2530
	21st to end	Night	26% 12% 3 5% 4 3 4 3 5% 6% 28%	2750
August	1st to 10th	Night	28% 13% 3 7% 4 3 3 3 4 5% 26%	2701
	11th to 20th	Night	20% 11% 3 7% 4 4 5% 4 5% 8% 29%	2782
	21st to end	Night	17% 6% 2 5% 3 3 4 3 5% 8% 47%	3461
September	1st to 10th	Night	20% 8% 2 5% 4 4 4 4 4 7% 38%	1900
	11th to 20th	Night	22% 8% 3 5% 3 3 3 3 5% 7% 40%	1900
	21st to end	Night	22% 9% 3 6% 4 4 3 3 5% 6% 36%	2170
October	1st to 10th	Night	20% 6% 2 5% 4 3 5% 3 5% 7% 39%	2280
	11th to 20th	Night	22% 6% 2 4 4 3 4 4 5% 7% 38%	2280
	21st to end	Night	25% 9% 2 6% 4 5% 4 3 5% 6% 32%	2604
November	1st to 10th	Night	22% 10% 2 7% 4 3 3 3 5% 8% 32%	2578
	11th to 20th	Night	23% 9% 3 6% 5% 4 4 3 5% 7% 30%	2675
	21st to end	Night	21% 11% 2 7% 4 5% 5% 4 5% 7% 30%	2660
December	1st to 10th	Night	26% 13% 4 6% 5% 4 4 3 4 6% 25%	2660
	11th to 20th	Night	32% 11% 4 6% 4 3 3 3 4 5% 25%	3293
	21st to end	Night	28% 11% 4 9% 3 3 4 3 5% 6% 24%	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	56% 14% 11% 15% 4 1	2527
	11th to 20th	Day	52% 10% 12% 19% 7%	2530
	21st to end	Day	53% 10% 10% 16% 11% 1	3004
February	1st to 10th	Day	59% 7% 12% 11% 10% 1	1710
	11th to 20th	Day	58% 7% 12% 15% 7% 1	1671
	21st to end	Day	50% 6% 11% 18% 11% 3	1531
March	1st to 10th	Day	56% 6% 10% 17% 11% 1	3228
	11th to 20th	Day	50% 13% 13% 17% 5% 1	3480
	21st to end	Day	64% 5% 9% 14% 6% 2	3960
April	1st to 10th	Day	53% 7% 11% 17% 10% 2	2280
	11th to 20th	Day	52% 6% 11% 19% 12% 1	2254
	21st to end	Day	54% 7% 11% 17% 10% 1	2417
May	1st to 10th	Day	62% 10% 11% 13% 4 1	4430
	11th to 20th	Day	56% 9% 12% 17% 6%	4402
	21st to end	Day	54% 15% 12% 14% 5%	4836
June	1st to 10th	Day	63% 9% 10% 14% 4	2660
	11th to 20th	Day	56% 6% 11% 18% 8% 1	2660
	21st to end	Day	70% 6% 7% 10% 7% 1	2660
July	1st to 10th	Day	65% 7% 9% 10% 9%	4370
	11th to 20th	Day	64% 9% 8% 12% 7%	4364
	21st to end	Day	55% 9% 12% 16% 8%	4662
August	1st to 10th	Day	61% 9% 11% 15% 5%	4203
	11th to 20th	Day	49% 10% 15% 21% 5%	4084
	21st to end	Day	38% 6% 14% 27% 14%	4194
September	1st to 10th	Day	45% 6% 14% 23% 11% 1	2280
	11th to 20th	Day	44% 7% 14% 24% 10% 1	2280
	21st to end	Day	48% 7% 11% 22% 12%	2007
October	1st to 10th	Day	48% 8% 14% 22% 9% 1	3160
	11th to 20th	Day	36% 6% 13% 29% 16%	3140
	21st to end	Day	46% 7% 15% 20% 10% 2	3262
November	1st to 10th	Day	53% 8% 13% 18% 7%	1717
	11th to 20th	Day	54% 9% 13% 16% 7% 1	1528
	21st to end	Day	53% 10% 15% 15% 7% 1	1520
December	1st to 10th	Day	62% 7% 11% 15% 4 1	1520
	11th to 20th	Day	65% 8% 11% 11% 5%	1905
	21st to end	Day	61% 7% 18% 9% 4 1	2783
January	1st to 10th	Night	54% 13% 17% 13% 3	4429
	11th to 20th	Night	57% 11% 12% 15% 5%	4440
	21st to end	Night	56% 10% 11% 15% 8%	4654
February	1st to 10th	Night	61% 8% 10% 12% 8% 1	2470
	11th to 20th	Night	59% 8% 11% 14% 7% 1	2406
	21st to end	Night	55% 6% 10% 18% 9% 1	1922
March	1st to 10th	Night	59% 6% 8% 16% 10% 1	3621
	11th to 20th	Night	58% 10% 11% 15% 6% 1	3480
	21st to end	Night	64% 5% 6% 18% 5% 1	3671
April	1st to 10th	Night	59% 5% 10% 14% 10% 2	1900
	11th to 20th	Night	50% 7% 10% 20% 11% 2	1876
	21st to end	Night	56% 5% 9% 17% 11% 1	1762
May	1st to 10th	Night	64% 8% 9% 14% 4 1	2540
	11th to 20th	Night	55% 8% 11% 20% 6%	2507
	21st to end	Night	60% 9% 11% 15% 4 1	2750
June	1st to 10th	Night	65% 6% 8% 16% 5%	1520
	11th to 20th	Night	55% 6% 8% 17% 12%	1520
	21st to end	Night	67% 7% 8% 13% 5%	1520
July	1st to 10th	Night	69% 5% 8% 11% 7% 1	2491
	11th to 20th	Night	68% 5% 8% 11% 7%	2482
	21st to end	Night	55% 8% 11% 18% 8%	2663
August	1st to 10th	Night	61% 7% 11% 17% 4	2690
	11th to 20th	Night	52% 9% 15% 20% 4	2809
	21st to end	Night	36% 7% 16% 28% 13%	3460
September	1st to 10th	Night	45% 7% 13% 23% 11% 1	1900
	11th to 20th	Night	44% 6% 12% 23% 14% 1	1900
	21st to end	Night	49% 6% 9% 24% 11% 1	2170
October	1st to 10th	Night	47% 7% 14% 22% 10%	3800
	11th to 20th	Night	35% 6% 14% 29% 17%	3779
	21st to end	Night	47% 7% 12% 23% 11%	4290
November	1st to 10th	Night	52% 8% 13% 18% 8%	2578
	11th to 20th	Night	54% 9% 14% 14% 9% 1	2675
	21st to end	Night	56% 9% 15% 14% 5%	2660
December	1st to 10th	Night	63% 7% 12% 14% 5%	2660
	11th to 20th	Night	65% 7% 9% 14% 5% 1	3295
	21st to end	Night	64% 8% 13% 12% 3	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	25% 19% 32% 18% 4	370
	11th to 20th	Day	27% 18% 32% 17% 5%	370
	21st to end	Day	23% 16% 35% 20% 5%	407
February	1st to 10th	Day	27% 18% 32% 19% 4	370
	11th to 20th	Day	25% 23% 29% 21% 3	366
	21st to end	Day	20% 16% 35% 23% 5% 1	307
March	1st to 10th	Day	24% 13% 37% 23% 4	398
	11th to 20th	Day	18% 17% 36% 24% 6%	460
	21st to end	Day	25% 17% 33% 18% 7%	506
April	1st to 10th	Day	30% 13% 31% 23% 3	460
	11th to 20th	Day	30% 10% 32% 21% 7% 1	452
	21st to end	Day	26% 10% 26% 28% 9% 1	460
May	1st to 10th	Day	33% 7% 29% 24% 5% 2	643
	11th to 20th	Day	26% 5% 24% 32% 11% 2	674
	21st to end	Day	30% 8% 22% 32% 7% 1	735
June	1st to 10th	Day	36% 5% 23% 27% 9%	680
	11th to 20th	Day	26% 5% 22% 35% 10% 1	680
	21st to end	Day	42% 6% 13% 28% 10% 1	680
July	1st to 10th	Day	32% 6% 15% 34% 13%	670
	11th to 20th	Day	32% 7% 15% 31% 13% 1	668
	21st to end	Day	32% 5% 17% 31% 14% 1	740
August	1st to 10th	Day	23% 4 19% 36% 14% 3	559
	11th to 20th	Day	23% 6% 21% 31% 15% 3	479
	21st to end	Day	19% 7% 21% 30% 20% 3	539
September	1st to 10th	Day	18% 8% 26% 30% 16% 2	490
	11th to 20th	Day	25% 7% 23% 31% 13% 2	490
	21st to end	Day	25% 6% 26% 27% 13% 4	413
October	1st to 10th	Day	19% 8% 26% 31% 13% 3	390
	11th to 20th	Day	22% 10% 27% 26% 14% 1	390
	21st to end	Day	25% 12% 35% 20% 7% 1	429
November	1st to 10th	Day	20% 14% 33% 25% 7% 2	395
	11th to 20th	Day	27% 20% 29% 18% 6% 1	373
	21st to end	Day	23% 18% 36% 18% 5% 1	370
December	1st to 10th	Day	33% 15% 28% 20% 4	370
	11th to 20th	Day	30% 27% 25% 16% 2	370
	21st to end	Day	24% 18% 35% 17% 6% 1	407
January	1st to 10th	Night	27% 19% 34% 17% 3	850
	11th to 20th	Night	28% 17% 34% 17% 4	850
	21st to end	Night	22% 17% 39% 16% 5%	868
February	1st to 10th	Night	28% 16% 34% 19% 3	760
	11th to 20th	Night	25% 19% 38% 16% 2	743
	21st to end	Night	19% 14% 41% 19% 7%	628
March	1st to 10th	Night	23% 15% 38% 20% 4	760
	11th to 20th	Night	24% 13% 29% 23% 10% 1	760
	21st to end	Night	26% 13% 30% 26% 6%	755
April	1st to 10th	Night	34% 10% 28% 22% 6%	570
	11th to 20th	Night	27% 8% 29% 27% 9% 1	564
	21st to end	Night	31% 5% 27% 27% 8% 1	570
May	1st to 10th	Night	36% 4 24% 26% 9% 2	570
	11th to 20th	Night	30% 6% 22% 27% 14% 1	562
	21st to end	Night	29% 6% 26% 30% 8% 1	616
June	1st to 10th	Night	40% 5% 19% 28% 8%	570
	11th to 20th	Night	31% 4 18% 36% 11% 1	570
	21st to end	Night	39% 6% 17% 27% 10% 1	570
July	1st to 10th	Night	32% 4 14% 35% 14% 1	556
	11th to 20th	Night	34% 4 15% 30% 16%	552
	21st to end	Night	36% 5% 14% 30% 14%	623
August	1st to 10th	Night	28% 5% 13% 36% 16% 2	568
	11th to 20th	Night	25% 4 16% 34% 18% 2	562
	21st to end	Night	22% 3 19% 31% 22% 2	627
September	1st to 10th	Night	23% 4 24% 31% 16% 2	570
	11th to 20th	Night	24% 5% 22% 32% 16% 1	570
	21st to end	Night	26% 6% 25% 30% 10% 2	693
October	1st to 10th	Night	23% 7% 27% 31% 11% 2	760
	11th to 20th	Night	24% 10% 30% 24% 11% 1	760
	21st to end	Night	29% 13% 31% 21% 5%	887
November	1st to 10th	Night	27% 12% 32% 24% 4 1	880
	11th to 20th	Night	27% 17% 29% 20% 6%	856
	21st to end	Night	26% 17% 33% 19% 4	850
December	1st to 10th	Night	33% 16% 31% 16% 4	850
	11th to 20th	Night	32% 20% 32% 12% 3	850
	21st to end	Night	29% 17% 33% 17% 3	935

Page generated at 2024-11-08 23:45:36. Version ac07

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