Catoctin Mountain Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Catoctin Mountain Park clear sky chart from 2005-11-06 to 2024-11-04.

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% 6% 2 6% 4 4 5% 4 6% 8% 39%	101260
	Night	15% 7% 2 6% 4 4 4 4 5% 7% 41%	97691
Transparency	Day	40% 7% 12% 23% 14% 2	104899
	Night	40% 7% 12% 23% 15% 3	102191
Seeing	Day	19% 13% 25% 23% 15% 5%	14909
	Night	18% 10% 29% 30% 12% 1	24381

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	16% 6% 2 8% 4 5% 5% 3 4 6% 41%	2559
	11th to 20th	Day	14% 11% 4 9% 5% 5% 5% 4 5% 6% 33%	2840
	21st to end	Day	17% 12% 3 7% 4 4 5% 3 5% 6% 32%	3124
February	1st to 10th	Day	14% 9% 3 8% 6% 4 5% 5% 5% 6% 36%	1710
	11th to 20th	Day	14% 8% 3 7% 5% 5% 4 3 5% 6% 39%	1686
	21st to end	Day	18% 8% 3 6% 5% 4 4 3 6% 4 38%	1570
March	1st to 10th	Day	21% 8% 2 5% 5% 4 5% 4 5% 7% 35%	3395
	11th to 20th	Day	10% 6% 2 5% 5% 5% 5% 4 6% 7% 45%	3480
	21st to end	Day	18% 9% 2 6% 4 3 4 3 4 6% 41%	3865
April	1st to 10th	Day	13% 7% 2 7% 6% 5% 5% 4 6% 7% 37%	2280
	11th to 20th	Day	14% 7% 2 6% 4 5% 4 3 5% 7% 43%	2254
	21st to end	Day	19% 6% 2 6% 4 4 4 3 6% 6% 39%	2284
May	1st to 10th	Day	26% 7% 2 6% 4 4 4 4 6% 8% 29%	4082
	11th to 20th	Day	24% 7% 2 6% 4 4 5% 4 6% 7% 29%	4297
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 9% 44%	4823
June	1st to 10th	Day	13% 5% 2 5% 4 4 5% 5% 8% 10% 40%	2660
	11th to 20th	Day	12% 5% 2 5% 5% 5% 5% 4 8% 9% 39%	2660
	21st to end	Day	11% 4 1 5% 4 4 5% 4 7% 11% 44%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 5% 6% 5% 8% 10% 43%	4440
	11th to 20th	Day	8% 5% 2 5% 4 5% 5% 5% 7% 11% 42%	4326
	21st to end	Day	10% 7% 3 7% 6% 6% 5% 5% 6% 8% 37%	4466
August	1st to 10th	Day	17% 6% 2 6% 5% 6% 5% 5% 6% 9% 34%	4104
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 9% 40%	3925
	21st to end	Day	13% 5% 2 5% 4 4 4 4 6% 8% 46%	4180
September	1st to 10th	Day	16% 6% 1 5% 3 4 4 3 5% 6% 46%	2280
	11th to 20th	Day	13% 5% 2 5% 4 3 4 4 5% 8% 47%	2280
	21st to end	Day	23% 6% 2 5% 4 4 3 3 5% 6% 38%	1986
October	1st to 10th	Day	17% 6% 2 5% 4 4 4 3 5% 6% 45%	1900
	11th to 20th	Day	16% 5% 1 5% 3 3 3 3 6% 6% 47%	1900
	21st to end	Day	13% 6% 2 7% 3 3 4 4 5% 6% 46%	2090
November	1st to 10th	Day	11% 6% 2 4 3 4 3 3 6% 7% 50%	1788
	11th to 20th	Day	15% 6% 2 4 4 4 4 4 5% 6% 45%	1644
	21st to end	Day	15% 6% 2 7% 5% 3 4 4 6% 7% 41%	1520
December	1st to 10th	Day	17% 9% 3 6% 5% 4 4 5% 7% 8% 34%	1520
	11th to 20th	Day	16% 7% 2 7% 5% 4 5% 4 6% 7% 38%	1910
	21st to end	Day	18% 6% 3 8% 4 4 6% 4 6% 9% 32%	2772
January	1st to 10th	Night	13% 8% 2 7% 4 4 5% 4 6% 8% 39%	4383
	11th to 20th	Night	18% 8% 2 6% 4 4 5% 4 4 5% 41%	4120
	21st to end	Night	20% 10% 3 7% 5% 4 4 3 5% 6% 34%	4532
February	1st to 10th	Night	14% 7% 3 7% 5% 4 5% 4 6% 7% 39%	2470
	11th to 20th	Night	16% 8% 3 6% 4 4 5% 4 4 7% 40%	2380
	21st to end	Night	17% 9% 2 7% 5% 5% 4 4 5% 6% 36%	1884
March	1st to 10th	Night	20% 8% 2 5% 4 4 4 4 5% 6% 38%	3453
	11th to 20th	Night	12% 6% 2 5% 4 3 4 4 5% 6% 49%	3480
	21st to end	Night	13% 9% 3 6% 4 4 3 3 4 5% 47%	3766
April	1st to 10th	Night	15% 8% 2 7% 5% 5% 5% 5% 6% 6% 37%	1900
	11th to 20th	Night	13% 6% 2 6% 4 3 4 3 6% 8% 44%	1875
	21st to end	Night	18% 6% 2 5% 4 4 4 4 6% 7% 42%	1900
May	1st to 10th	Night	26% 8% 2 6% 4 4 3 3 5% 7% 30%	2825
	11th to 20th	Night	25% 10% 3 7% 4 3 4 3 5% 6% 31%	2594
	21st to end	Night	12% 5% 2 6% 5% 4 5% 4 8% 9% 40%	2732
June	1st to 10th	Night	12% 4 2 5% 4 3 5% 3 6% 8% 47%	1520
	11th to 20th	Night	11% 5% 2 7% 4 5% 5% 5% 7% 9% 40%	1520
	21st to end	Night	9% 4 2 6% 5% 4 5% 3 7% 10% 44%	1520
July	1st to 10th	Night	7% 4 2 6% 6% 5% 6% 5% 7% 11% 42%	2520
	11th to 20th	Night	7% 5% 2 7% 5% 5% 5% 6% 6% 10% 41%	2616
	21st to end	Night	12% 7% 2 6% 4 5% 5% 4 6% 9% 39%	3087
August	1st to 10th	Night	17% 5% 3 7% 4 4 5% 4 6% 8% 35%	2825
	11th to 20th	Night	10% 6% 2 8% 6% 4 5% 4 6% 7% 41%	2871
	21st to end	Night	14% 4 1 5% 4 4 4 4 5% 8% 48%	3476
September	1st to 10th	Night	14% 5% 2 5% 4 4 4 4 5% 6% 47%	1900
	11th to 20th	Night	13% 5% 2 6% 3 3 3 3 4 7% 53%	1900
	21st to end	Night	23% 5% 2 4 3 4 4 3 4 6% 42%	2189
October	1st to 10th	Night	20% 5% 3 5% 3 4 4 3 3 6% 44%	2280
	11th to 20th	Night	14% 6% 2 5% 3 3 4 3 4 6% 51%	2280
	21st to end	Night	15% 6% 1 5% 3 3 3 3 6% 7% 48%	2508
November	1st to 10th	Night	10% 7% 2 5% 3 4 3 3 5% 6% 53%	2363
	11th to 20th	Night	13% 8% 2 4 4 4 4 4 5% 6% 46%	2533
	21st to end	Night	13% 5% 2 5% 5% 4 4 4 6% 7% 44%	2660
December	1st to 10th	Night	16% 9% 3 6% 5% 4 5% 4 5% 6% 37%	2660
	11th to 20th	Night	17% 6% 2 5% 5% 4 5% 4 6% 6% 40%	3285
	21st to end	Night	16% 7% 2 6% 5% 5% 6% 5% 7% 8% 33%	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	43% 6% 13% 26% 9% 3	2560
	11th to 20th	Day	50% 6% 12% 17% 12% 2	2840
	21st to end	Day	51% 7% 11% 22% 8% 2	3124
February	1st to 10th	Day	47% 7% 13% 22% 10% 2	1710
	11th to 20th	Day	45% 6% 11% 22% 14% 2	1695
	21st to end	Day	49% 5% 11% 20% 12% 4	1570
March	1st to 10th	Day	48% 6% 11% 22% 11% 2	3395
	11th to 20th	Day	36% 6% 12% 27% 16% 3	3480
	21st to end	Day	45% 5% 11% 20% 16% 3	3865
April	1st to 10th	Day	44% 7% 12% 18% 16% 3	2280
	11th to 20th	Day	40% 6% 12% 21% 18% 4	2254
	21st to end	Day	44% 6% 10% 21% 17% 3	2284
May	1st to 10th	Day	51% 7% 10% 20% 10% 1	4120
	11th to 20th	Day	50% 10% 12% 19% 8% 2	4301
	21st to end	Day	34% 9% 14% 25% 16% 2	4837
June	1st to 10th	Day	36% 9% 15% 24% 16% 1	2660
	11th to 20th	Day	38% 11% 13% 23% 14% 2	2660
	21st to end	Day	33% 9% 14% 28% 15% 1	2660
July	1st to 10th	Day	33% 10% 17% 23% 11% 5%	4370
	11th to 20th	Day	33% 9% 16% 28% 12% 1	4251
	21st to end	Day	43% 7% 11% 20% 17% 1	4324
August	1st to 10th	Day	44% 9% 14% 24% 8%	4091
	11th to 20th	Day	37% 8% 12% 28% 14% 1	3964
	21st to end	Day	35% 6% 13% 27% 17% 2	4180
September	1st to 10th	Day	39% 6% 12% 19% 21% 4	2280
	11th to 20th	Day	34% 6% 11% 25% 21% 3	2280
	21st to end	Day	47% 5% 9% 18% 19% 2	1986
October	1st to 10th	Day	36% 5% 8% 20% 26% 5%	3160
	11th to 20th	Day	27% 4 12% 27% 21% 9%	3140
	21st to end	Day	25% 4 12% 30% 26% 3	3428
November	1st to 10th	Day	33% 5% 14% 24% 19% 4	1788
	11th to 20th	Day	37% 5% 14% 22% 18% 3	1644
	21st to end	Day	41% 6% 12% 28% 12% 1	1520
December	1st to 10th	Day	47% 8% 14% 22% 9% 1	1520
	11th to 20th	Day	44% 7% 13% 27% 7% 2	1906
	21st to end	Day	47% 9% 17% 17% 10%	2772
January	1st to 10th	Night	42% 8% 13% 23% 12% 2	4383
	11th to 20th	Night	43% 6% 14% 24% 11% 2	4120
	21st to end	Night	48% 6% 12% 24% 8% 1	4532
February	1st to 10th	Night	43% 7% 13% 23% 12% 1	2470
	11th to 20th	Night	44% 6% 10% 20% 17% 2	2382
	21st to end	Night	47% 6% 12% 19% 12% 5%	1884
March	1st to 10th	Night	46% 6% 9% 27% 10% 1	3453
	11th to 20th	Night	35% 6% 10% 32% 15% 2	3480
	21st to end	Night	40% 4 9% 22% 20% 4	3766
April	1st to 10th	Night	45% 8% 12% 17% 15% 3	1900
	11th to 20th	Night	38% 6% 12% 21% 18% 5%	1875
	21st to end	Night	40% 6% 12% 24% 15% 4	1900
May	1st to 10th	Night	53% 6% 9% 17% 13% 2	2852
	11th to 20th	Night	52% 9% 11% 17% 10% 1	2595
	21st to end	Night	36% 11% 16% 25% 10% 2	2739
June	1st to 10th	Night	34% 8% 11% 27% 17% 3	1520
	11th to 20th	Night	38% 9% 12% 24% 14% 2	1520
	21st to end	Night	34% 8% 13% 25% 17% 2	1520
July	1st to 10th	Night	36% 10% 18% 18% 13% 5%	2480
	11th to 20th	Night	36% 10% 15% 23% 15% 1	2568
	21st to end	Night	39% 9% 14% 19% 18% 1	2988
August	1st to 10th	Night	45% 8% 17% 22% 8% 1	2814
	11th to 20th	Night	39% 7% 12% 27% 14% 1	2898
	21st to end	Night	35% 5% 13% 29% 16% 2	3476
September	1st to 10th	Night	37% 7% 12% 19% 21% 4	1900
	11th to 20th	Night	33% 5% 9% 27% 23% 3	1900
	21st to end	Night	44% 6% 10% 20% 18% 2	2189
October	1st to 10th	Night	39% 5% 10% 22% 22% 2	3800
	11th to 20th	Night	24% 5% 11% 25% 28% 7%	3779
	21st to end	Night	25% 4 12% 31% 24% 5%	4120
November	1st to 10th	Night	32% 6% 11% 26% 20% 5%	2363
	11th to 20th	Night	38% 6% 10% 23% 20% 4	2533
	21st to end	Night	38% 7% 12% 24% 16% 2	2660
December	1st to 10th	Night	47% 7% 12% 23% 11% 1	2660
	11th to 20th	Night	43% 7% 12% 22% 14% 2	3288
	21st to end	Night	44% 11% 17% 18% 10%	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% 29% 27% 15% 5%	194
	11th to 20th	Day	28% 30% 28% 11% 3	270
	21st to end	Day	21% 29% 33% 13% 3 1	297
February	1st to 10th	Day	22% 25% 37% 13% 3	270
	11th to 20th	Day	31% 27% 34% 7% 1	293
	21st to end	Day	29% 20% 30% 17% 3	382
March	1st to 10th	Day	23% 23% 27% 23% 5%	460
	11th to 20th	Day	24% 22% 30% 17% 5% 1	460
	21st to end	Day	25% 19% 30% 19% 6% 1	506
April	1st to 10th	Day	20% 20% 30% 22% 6% 2	460
	11th to 20th	Day	17% 18% 29% 18% 14% 4	452
	21st to end	Day	25% 15% 28% 21% 8% 3	460
May	1st to 10th	Day	26% 14% 28% 19% 10% 3	463
	11th to 20th	Day	21% 14% 27% 22% 13% 3	487
	21st to end	Day	17% 7% 21% 25% 22% 7%	529
June	1st to 10th	Day	16% 8% 27% 24% 19% 6%	490
	11th to 20th	Day	16% 6% 26% 29% 18% 6%	490
	21st to end	Day	12% 6% 25% 30% 21% 5%	490
July	1st to 10th	Day	11% 4 19% 31% 23% 13%	485
	11th to 20th	Day	7% 5% 19% 29% 30% 11%	484
	21st to end	Day	11% 5% 19% 32% 25% 9%	532
August	1st to 10th	Day	12% 3 19% 26% 29% 12%	486
	11th to 20th	Day	12% 3 20% 30% 22% 13%	479
	21st to end	Day	12% 4 16% 29% 24% 14%	539
September	1st to 10th	Day	17% 7% 17% 24% 23% 12%	490
	11th to 20th	Day	15% 3 17% 28% 26% 12%	490
	21st to end	Day	28% 8% 22% 22% 16% 5%	490
October	1st to 10th	Day	20% 8% 22% 25% 19% 6%	490
	11th to 20th	Day	17% 14% 26% 27% 14% 2	490
	21st to end	Day	15% 12% 34% 27% 9% 2	539
November	1st to 10th	Day	17% 12% 27% 28% 13% 3	420
	11th to 20th	Day	20% 17% 29% 23% 10% 1	304
	21st to end	Day	19% 23% 32% 18% 7% 1	180
December	1st to 10th	Day	24% 24% 29% 17% 3 2	180
	11th to 20th	Day	22% 23% 28% 21% 7%	180
	21st to end	Day	23% 18% 29% 23% 6%	198
January	1st to 10th	Night	17% 17% 43% 20% 2	760
	11th to 20th	Night	23% 16% 33% 26% 3	760
	21st to end	Night	18% 16% 39% 25% 1	836
February	1st to 10th	Night	18% 17% 34% 29% 3	760
	11th to 20th	Night	24% 21% 36% 17% 1	743
	21st to end	Night	24% 18% 36% 19% 2	628
March	1st to 10th	Night	19% 16% 38% 23% 4	760
	11th to 20th	Night	23% 17% 33% 22% 5%	760
	21st to end	Night	19% 15% 38% 23% 5% 1	836
April	1st to 10th	Night	19% 18% 34% 25% 4	760
	11th to 20th	Night	15% 13% 34% 30% 9%	751
	21st to end	Night	21% 11% 32% 28% 8%	760
May	1st to 10th	Night	24% 8% 24% 32% 12%	582
	11th to 20th	Night	22% 6% 25% 34% 13% 1	434
	21st to end	Night	15% 4 22% 37% 21% 1	411
June	1st to 10th	Night	13% 2 27% 33% 24% 1	380
	11th to 20th	Night	12% 5% 19% 45% 17% 2	380
	21st to end	Night	8% 4 20% 49% 19%	380
July	1st to 10th	Night	12% 3 16% 41% 26% 3	370
	11th to 20th	Night	7% 1 17% 39% 33% 3	425
	21st to end	Night	10% 2 14% 42% 29% 3	624
August	1st to 10th	Night	12% 1 9% 44% 32% 2	567
	11th to 20th	Night	12% 3 14% 41% 28% 3	611
	21st to end	Night	14% 2 12% 40% 28% 4	836
September	1st to 10th	Night	16% 2 19% 34% 27% 3	760
	11th to 20th	Night	14% 3 17% 34% 29% 4	760
	21st to end	Night	26% 3 18% 33% 19% 1	760
October	1st to 10th	Night	21% 4 21% 29% 21% 3	760
	11th to 20th	Night	16% 9% 29% 33% 12% 1	760
	21st to end	Night	19% 8% 31% 30% 10% 1	836
November	1st to 10th	Night	13% 8% 33% 35% 9% 2	755
	11th to 20th	Night	19% 15% 31% 28% 8%	760
	21st to end	Night	15% 14% 35% 29% 7%	760
December	1st to 10th	Night	21% 14% 36% 22% 6%	760
	11th to 20th	Night	18% 10% 41% 26% 5%	760
	21st to end	Night	19% 12% 35% 31% 3	836

Page generated at 2024-11-01 22:47:53. Version ac07

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