Courthouse Hill
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Courthouse Hill clear sky chart from 2005-11-06 to 2024-12-02.

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	21% 13% 4 8% 5% 4 4 3 5% 6% 27%	102263
	Night	21% 13% 4 9% 5% 4 4 3 4 5% 27%	97434
Transparency	Day	57% 5% 11% 18% 8% 1	105848
	Night	58% 5% 11% 18% 8% 1	101939
Seeing	Day	30% 18% 30% 16% 5% 1	17485
	Night	28% 16% 30% 21% 5%	24885

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% 17% 7% 13% 6% 4 4 3 4 3 24%	2526
	11th to 20th	Day	14% 18% 6% 20% 6% 5% 4 3 4 5% 15%	2571
	21st to end	Day	18% 14% 8% 12% 8% 5% 3 2 4 5% 20%	3124
February	1st to 10th	Day	19% 16% 6% 10% 10% 6% 4 2 4 4 19%	1710
	11th to 20th	Day	17% 17% 5% 13% 7% 6% 3 3 4 5% 20%	1663
	21st to end	Day	12% 16% 6% 10% 6% 4 3 3 4 6% 29%	1446
March	1st to 10th	Day	24% 18% 3 8% 6% 6% 3 2 4 4 23%	3390
	11th to 20th	Day	13% 26% 8% 11% 5% 4 3 2 3 4 21%	3480
	21st to end	Day	29% 18% 5% 10% 4 3 4 2 2 3 20%	3833
April	1st to 10th	Day	24% 18% 4 8% 4 4 4 2 3 4 24%	2280
	11th to 20th	Day	21% 14% 3 6% 5% 4 4 3 5% 6% 31%	2311
	21st to end	Day	24% 15% 3 6% 4 4 3 4 5% 5% 27%	2470
May	1st to 10th	Day	28% 18% 3 7% 4 3 3 3 4 6% 21%	4252
	11th to 20th	Day	22% 11% 3 8% 5% 4 4 3 5% 6% 30%	4398
	21st to end	Day	19% 9% 3 7% 5% 5% 5% 4 6% 9% 28%	4836
June	1st to 10th	Day	28% 11% 3 7% 5% 4 4 3 4 6% 24%	2660
	11th to 20th	Day	24% 8% 3 6% 5% 4 4 3 4 7% 32%	2749
	21st to end	Day	30% 9% 2 6% 4 5% 4 3 5% 7% 25%	2850
July	1st to 10th	Day	22% 9% 3 6% 4 4 4 4 6% 8% 30%	4614
	11th to 20th	Day	18% 9% 3 7% 4 5% 5% 4 6% 8% 30%	4440
	21st to end	Day	16% 9% 4 6% 5% 4 4 5% 7% 8% 32%	4728
August	1st to 10th	Day	23% 10% 4 8% 5% 5% 4 4 5% 6% 26%	4105
	11th to 20th	Day	15% 8% 3 9% 5% 5% 4 4 7% 8% 32%	4045
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 9% 44%	4342
September	1st to 10th	Day	19% 5% 2 6% 4 3 5% 3 6% 7% 40%	2280
	11th to 20th	Day	21% 7% 2 6% 4 3 3 3 5% 6% 41%	2227
	21st to end	Day	20% 7% 3 5% 4 4 3 3 5% 7% 40%	2017
October	1st to 10th	Day	19% 7% 3 7% 4 3 5% 4 5% 7% 36%	1900
	11th to 20th	Day	20% 10% 2 6% 4 4 5% 4 5% 7% 32%	1900
	21st to end	Day	21% 13% 4 9% 4 3 3 3 5% 5% 29%	2085
November	1st to 10th	Day	23% 14% 4 7% 4 5% 4 4 4 4 28%	1613
	11th to 20th	Day	21% 21% 5% 8% 3 3 4 3 4 5% 24%	1600
	21st to end	Day	19% 18% 5% 10% 7% 5% 4 3 4 4 21%	1600
December	1st to 10th	Day	23% 20% 7% 9% 5% 4 3 2 4 5% 19%	1529
	11th to 20th	Day	30% 16% 7% 9% 7% 4 3 2 3 3 15%	1906
	21st to end	Day	22% 15% 11% 14% 5% 3 3 3 4 4 16%	2783
January	1st to 10th	Night	15% 13% 7% 14% 8% 4 4 3 4 6% 22%	4429
	11th to 20th	Night	18% 16% 6% 19% 6% 5% 4 3 4 4 16%	4394
	21st to end	Night	17% 14% 6% 14% 8% 5% 5% 3 4 5% 19%	4532
February	1st to 10th	Night	20% 15% 4 12% 10% 6% 5% 3 4 3 17%	2470
	11th to 20th	Night	18% 15% 5% 11% 8% 5% 4 4 5% 5% 19%	2403
	21st to end	Night	11% 14% 6% 10% 8% 7% 4 4 4 4 28%	2007
March	1st to 10th	Night	22% 16% 5% 11% 8% 5% 3 2 3 3 21%	3445
	11th to 20th	Night	19% 20% 7% 9% 4 4 4 3 4 5% 20%	3479
	21st to end	Night	29% 15% 6% 11% 4 3 3 2 3 3 23%	3799
April	1st to 10th	Night	24% 15% 4 7% 4 4 4 2 5% 5% 27%	1900
	11th to 20th	Night	23% 12% 3 7% 4 3 4 3 4 6% 31%	1816
	21st to end	Night	23% 14% 3 6% 4 4 4 3 4 6% 29%	1710
May	1st to 10th	Night	25% 20% 3 6% 4 3 4 3 4 6% 22%	2692
	11th to 20th	Night	21% 10% 3 6% 4 4 5% 4 6% 7% 31%	2506
	21st to end	Night	19% 10% 3 9% 5% 4 5% 4 5% 7% 28%	2749
June	1st to 10th	Night	28% 10% 3 6% 4 4 4 4 5% 6% 27%	1520
	11th to 20th	Night	23% 9% 2 5% 4 3 4 3 4 8% 34%	1441
	21st to end	Night	25% 9% 3 8% 6% 4 4 4 6% 7% 25%	1330
July	1st to 10th	Night	20% 11% 3 7% 6% 5% 5% 5% 7% 7% 25%	2306
	11th to 20th	Night	18% 8% 3 7% 4 4 4 4 7% 9% 32%	2530
	21st to end	Night	16% 8% 3 6% 5% 4 4 3 5% 7% 40%	2830
August	1st to 10th	Night	22% 9% 3 6% 4 4 5% 4 5% 7% 32%	2825
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 6% 7% 34%	2782
	21st to end	Night	14% 5% 2 5% 3 3 4 3 6% 7% 49%	3313
September	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 4 7% 44%	1900
	11th to 20th	Night	18% 8% 2 5% 4 3 2 3 4 6% 44%	1950
	21st to end	Night	20% 8% 3 6% 4 3 3 3 5% 7% 39%	2162
October	1st to 10th	Night	19% 7% 2 6% 4 5% 5% 3 5% 6% 38%	2280
	11th to 20th	Night	19% 9% 3 6% 5% 4 4 3 4 7% 37%	2280
	21st to end	Night	27% 10% 3 6% 4 4 3 3 4 6% 30%	2511
November	1st to 10th	Night	20% 14% 3 8% 4 4 4 2 5% 5% 31%	2681
	11th to 20th	Night	20% 17% 4 8% 5% 4 4 3 5% 5% 24%	2800
	21st to end	Night	23% 17% 5% 8% 5% 4 3 3 4 5% 22%	2800
December	1st to 10th	Night	24% 17% 4 10% 6% 4 4 3 4 4 19%	2685
	11th to 20th	Night	29% 17% 5% 10% 6% 4 3 2 2 3 19%	3293
	21st to end	Night	26% 16% 7% 11% 4 3 3 2 4 4 21%	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	66% 4 15% 11% 4 1	2527
	11th to 20th	Day	71% 8% 5% 12% 3	2571
	21st to end	Day	65% 6% 9% 10% 9%	3124
February	1st to 10th	Day	70% 4 8% 10% 7% 1	1710
	11th to 20th	Day	68% 5% 9% 12% 6% 1	1671
	21st to end	Day	57% 4 10% 17% 10% 2	1446
March	1st to 10th	Day	66% 4 8% 16% 6% 1	3394
	11th to 20th	Day	66% 5% 8% 13% 7% 1	3480
	21st to end	Day	72% 3 5% 12% 7% 1	3833
April	1st to 10th	Day	65% 3 6% 13% 10% 2	2280
	11th to 20th	Day	54% 5% 8% 20% 12% 1	2311
	21st to end	Day	59% 4 8% 17% 11% 2	2470
May	1st to 10th	Day	66% 4 9% 15% 6% 1	4266
	11th to 20th	Day	55% 4 14% 20% 6%	4402
	21st to end	Day	50% 7% 17% 17% 8%	4836
June	1st to 10th	Day	61% 5% 10% 19% 5% 1	2660
	11th to 20th	Day	52% 5% 12% 20% 10% 1	2749
	21st to end	Day	59% 5% 11% 16% 9%	2850
July	1st to 10th	Day	52% 6% 12% 18% 11% 1	4543
	11th to 20th	Day	50% 7% 15% 20% 7%	4364
	21st to end	Day	47% 8% 16% 21% 8%	4577
August	1st to 10th	Day	58% 5% 12% 18% 6%	4092
	11th to 20th	Day	47% 7% 14% 24% 8%	4084
	21st to end	Day	35% 6% 14% 27% 17%	4342
September	1st to 10th	Day	43% 5% 13% 25% 13% 1	2280
	11th to 20th	Day	44% 4 13% 24% 14% 1	2227
	21st to end	Day	44% 4 11% 26% 15%	2017
October	1st to 10th	Day	47% 8% 10% 24% 11%	3160
	11th to 20th	Day	46% 5% 10% 26% 12%	3140
	21st to end	Day	49% 5% 14% 21% 11%	3412
November	1st to 10th	Day	60% 5% 9% 19% 7%	1613
	11th to 20th	Day	62% 6% 11% 14% 6% 1	1600
	21st to end	Day	66% 7% 11% 12% 4	1600
December	1st to 10th	Day	69% 5% 9% 13% 4	1529
	11th to 20th	Day	75% 4 6% 11% 3 1	1905
	21st to end	Day	74% 4 10% 9% 3	2783
January	1st to 10th	Night	65% 5% 12% 16% 2	4429
	11th to 20th	Night	72% 6% 7% 10% 5%	4394
	21st to end	Night	66% 6% 8% 13% 5% 1	4532
February	1st to 10th	Night	71% 5% 7% 10% 6% 1	2470
	11th to 20th	Night	67% 5% 9% 12% 6% 1	2406
	21st to end	Night	61% 4 9% 17% 8% 1	2007
March	1st to 10th	Night	68% 4 6% 13% 7% 1	3454
	11th to 20th	Night	66% 6% 8% 13% 7% 1	3480
	21st to end	Night	69% 3 6% 14% 7% 1	3799
April	1st to 10th	Night	60% 4 8% 14% 10% 3	1900
	11th to 20th	Night	55% 4 7% 20% 14% 1	1816
	21st to end	Night	56% 4 10% 16% 11% 2	1710
May	1st to 10th	Night	64% 4 12% 13% 6%	2698
	11th to 20th	Night	52% 5% 14% 22% 7% 1	2507
	21st to end	Night	54% 7% 17% 17% 5% 1	2750
June	1st to 10th	Night	57% 6% 12% 19% 6%	1520
	11th to 20th	Night	49% 5% 13% 22% 10% 1	1441
	21st to end	Night	58% 7% 12% 16% 6% 1	1330
July	1st to 10th	Night	55% 8% 14% 14% 8% 1	2268
	11th to 20th	Night	48% 8% 18% 17% 9%	2482
	21st to end	Night	44% 5% 15% 23% 12% 1	2741
August	1st to 10th	Night	52% 7% 15% 23% 5%	2813
	11th to 20th	Night	46% 8% 15% 24% 7%	2809
	21st to end	Night	34% 6% 18% 27% 15% 1	3312
September	1st to 10th	Night	40% 6% 11% 28% 14% 1	1900
	11th to 20th	Night	41% 5% 12% 29% 13% 1	1950
	21st to end	Night	45% 5% 11% 26% 12% 1	2162
October	1st to 10th	Night	49% 5% 12% 23% 10%	3800
	11th to 20th	Night	42% 5% 12% 27% 14%	3779
	21st to end	Night	47% 4 15% 22% 13%	4135
November	1st to 10th	Night	56% 5% 11% 18% 9% 1	2681
	11th to 20th	Night	62% 6% 10% 15% 7%	2800
	21st to end	Night	64% 6% 13% 13% 4	2800
December	1st to 10th	Night	68% 5% 9% 13% 3	2685
	11th to 20th	Night	73% 4 6% 11% 5%	3295
	21st to end	Night	69% 4 10% 14% 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	35% 22% 29% 13% 1	370
	11th to 20th	Day	36% 23% 27% 10% 4	370
	21st to end	Day	26% 24% 33% 14% 2	407
February	1st to 10th	Day	34% 24% 28% 12% 3	370
	11th to 20th	Day	38% 27% 22% 11% 2	366
	21st to end	Day	28% 20% 36% 12% 3 1	307
March	1st to 10th	Day	32% 23% 34% 8% 2 1	447
	11th to 20th	Day	31% 29% 27% 8% 5% 1	460
	21st to end	Day	35% 27% 24% 10% 3 1	506
April	1st to 10th	Day	46% 22% 23% 8% 2	460
	11th to 20th	Day	35% 25% 25% 11% 2	452
	21st to end	Day	32% 22% 26% 14% 5%	460
May	1st to 10th	Day	40% 19% 25% 10% 4 1	544
	11th to 20th	Day	29% 17% 28% 19% 5% 1	674
	21st to end	Day	29% 19% 33% 16% 3 1	735
June	1st to 10th	Day	36% 15% 29% 16% 4	680
	11th to 20th	Day	28% 15% 32% 19% 5% 1	680
	21st to end	Day	35% 11% 29% 17% 7% 1	680
July	1st to 10th	Day	23% 10% 36% 23% 7% 1	670
	11th to 20th	Day	22% 9% 36% 23% 8% 1	668
	21st to end	Day	24% 9% 34% 25% 8% 1	689
August	1st to 10th	Day	19% 9% 37% 24% 9% 1	486
	11th to 20th	Day	21% 11% 33% 22% 11% 3	479
	21st to end	Day	18% 15% 32% 22% 10% 4	539
September	1st to 10th	Day	20% 14% 33% 25% 8% 1	490
	11th to 20th	Day	27% 13% 28% 20% 9% 2	490
	21st to end	Day	22% 17% 29% 20% 10% 2	451
October	1st to 10th	Day	24% 14% 31% 19% 9% 3	390
	11th to 20th	Day	27% 21% 27% 16% 7% 2	390
	21st to end	Day	30% 23% 28% 14% 5% 1	429
November	1st to 10th	Day	32% 18% 28% 14% 6% 1	395
	11th to 20th	Day	41% 20% 23% 12% 5% 1	400
	21st to end	Day	38% 22% 27% 10% 3 1	400
December	1st to 10th	Day	38% 20% 27% 13% 2 1	374
	11th to 20th	Day	43% 22% 25% 9% 1	370
	21st to end	Day	35% 23% 28% 11% 3	407
January	1st to 10th	Night	32% 21% 31% 14% 2	850
	11th to 20th	Night	33% 21% 27% 16% 3	835
	21st to end	Night	24% 24% 31% 18% 2	836
February	1st to 10th	Night	30% 21% 30% 17% 2	760
	11th to 20th	Night	33% 26% 26% 13% 1	743
	21st to end	Night	21% 23% 32% 21% 4	628
March	1st to 10th	Night	27% 24% 31% 16% 2	760
	11th to 20th	Night	26% 19% 30% 19% 5%	760
	21st to end	Night	29% 18% 30% 17% 5%	831
April	1st to 10th	Night	34% 19% 29% 16% 2	570
	11th to 20th	Night	30% 17% 34% 15% 3 1	564
	21st to end	Night	31% 17% 28% 19% 4 1	570
May	1st to 10th	Night	34% 14% 30% 18% 4	570
	11th to 20th	Night	29% 12% 31% 23% 5%	562
	21st to end	Night	21% 15% 43% 19% 3	616
June	1st to 10th	Night	32% 10% 33% 21% 3	570
	11th to 20th	Night	26% 10% 33% 26% 4	491
	21st to end	Night	28% 6% 28% 29% 9%	380
July	1st to 10th	Night	20% 6% 34% 34% 6%	424
	11th to 20th	Night	17% 7% 36% 31% 8%	552
	21st to end	Night	20% 6% 31% 36% 8%	623
August	1st to 10th	Night	18% 5% 31% 36% 8% 1	568
	11th to 20th	Night	19% 7% 26% 37% 10% 1	562
	21st to end	Night	16% 7% 29% 33% 13%	627
September	1st to 10th	Night	16% 9% 32% 32% 11%	570
	11th to 20th	Night	22% 10% 24% 33% 10%	620
	21st to end	Night	25% 12% 29% 25% 9% 1	760
October	1st to 10th	Night	23% 11% 29% 27% 9% 1	760
	11th to 20th	Night	24% 14% 35% 17% 8% 1	760
	21st to end	Night	34% 17% 27% 17% 4	839
November	1st to 10th	Night	32% 15% 28% 19% 5% 1	880
	11th to 20th	Night	31% 21% 26% 17% 5%	900
	21st to end	Night	35% 21% 25% 16% 2	900
December	1st to 10th	Night	35% 19% 29% 16% 2	859
	11th to 20th	Night	36% 23% 28% 12% 2	850
	21st to end	Night	33% 20% 27% 16% 3	935

Page generated at 2024-11-29 11:43:04. Version ac07

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