Deer Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deer Park clear sky chart from 2005-11-06 to 2026-03-18.

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	11% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	131068
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	130449
Transparency	Day	38% 6% 12% 18% 18% 8%	134902
	Night	37% 6% 12% 18% 19% 8%	134689
Seeing	Day	15% 8% 21% 25% 20% 11%	16056
	Night	14% 7% 22% 29% 22% 5%	26075

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	15% 7% 3 6% 3 3 4 3 5% 7% 44%	5717
	11th to 20th	Day	10% 6% 2 5% 3 3 4 3 5% 6% 54%	5880
	21st to end	Day	22% 8% 3 7% 4 4 4 3 4 5% 37%	6436
February	1st to 10th	Day	16% 8% 3 7% 4 5% 5% 4 4 5% 41%	2100
	11th to 20th	Day	18% 6% 2 5% 4 3 4 3 5% 7% 42%	2048
	21st to end	Day	16% 8% 2 8% 4 4 4 3 5% 7% 40%	1730
March	1st to 10th	Day	15% 9% 3 8% 4 4 5% 4 5% 6% 36%	4580
	11th to 20th	Day	11% 5% 2 6% 4 3 4 3 4 7% 50%	4805
	21st to end	Day	16% 5% 3 7% 5% 4 4 3 5% 6% 43%	5967
April	1st to 10th	Day	12% 6% 2 5% 6% 4 5% 4 6% 7% 43%	2400
	11th to 20th	Day	12% 6% 3 6% 4 5% 4 3 7% 7% 44%	2374
	21st to end	Day	7% 5% 2 6% 5% 4 4 4 5% 7% 50%	2400
May	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 4 6% 8% 37%	5405
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 5% 7% 10% 40%	5631
	21st to end	Day	7% 4 2 7% 5% 5% 6% 4 7% 10% 42%	6433
June	1st to 10th	Day	8% 7% 3 7% 6% 7% 7% 6% 7% 9% 33%	2600
	11th to 20th	Day	6% 5% 2 6% 8% 7% 7% 6% 8% 9% 36%	2600
	21st to end	Day	6% 6% 3 9% 7% 7% 7% 7% 9% 10% 30%	2600
July	1st to 10th	Day	6% 5% 3 8% 6% 8% 8% 6% 10% 12% 29%	5862
	11th to 20th	Day	5% 4 2 7% 7% 8% 8% 7% 10% 11% 31%	5440
	21st to end	Day	5% 5% 2 8% 7% 7% 8% 8% 11% 14% 24%	5922
August	1st to 10th	Day	3 3 1 5% 4 5% 6% 5% 8% 10% 49%	3905
	11th to 20th	Day	6% 4 2 6% 5% 6% 6% 5% 7% 10% 43%	3849
	21st to end	Day	7% 4 2 8% 6% 6% 6% 5% 8% 8% 38%	4312
September	1st to 10th	Day	8% 7% 3 8% 7% 5% 6% 4 6% 8% 39%	2400
	11th to 20th	Day	11% 6% 2 6% 5% 4 4 4 5% 7% 45%	2227
	21st to end	Day	8% 5% 2 6% 4 5% 4 3 5% 6% 52%	2200
October	1st to 10th	Day	9% 3 2 6% 4 4 3 3 5% 7% 54%	2200
	11th to 20th	Day	9% 4 2 5% 3 3 4 3 4 6% 56%	2120
	21st to end	Day	11% 4 2 5% 3 3 3 3 4 6% 56%	2200
November	1st to 10th	Day	10% 4 2 5% 4 3 3 3 4 5% 57%	1897
	11th to 20th	Day	13% 5% 2 3 3 2 3 2 4 5% 57%	1890
	21st to end	Day	12% 7% 2 6% 3 4 3 4 5% 7% 47%	1890
December	1st to 10th	Day	18% 6% 2 5% 3 3 3 3 5% 6% 46%	3020
	11th to 20th	Day	9% 7% 2 6% 4 4 4 3 5% 6% 50%	3463
	21st to end	Day	16% 8% 2 5% 3 4 3 3 4 6% 45%	4565
January	1st to 10th	Night	15% 7% 4 6% 4 3 4 3 5% 6% 44%	7158
	11th to 20th	Night	16% 9% 3 5% 3 2 2 2 4 6% 48%	7080
	21st to end	Night	21% 10% 3 8% 4 4 3 3 4 4 37%	7745
February	1st to 10th	Night	14% 8% 2 5% 4 3 4 4 5% 7% 43%	2520
	11th to 20th	Night	21% 8% 3 5% 3 3 3 3 4 4 42%	2458
	21st to end	Night	17% 8% 3 7% 4 4 4 3 4 5% 41%	2076
March	1st to 10th	Night	20% 10% 3 7% 4 3 4 3 4 6% 36%	5493
	11th to 20th	Night	14% 7% 2 6% 3 4 4 3 4 5% 48%	5348
	21st to end	Night	15% 6% 2 5% 4 4 4 3 4 6% 47%	4962
April	1st to 10th	Night	14% 6% 2 6% 4 4 4 4 6% 7% 44%	2000
	11th to 20th	Night	13% 4 3 6% 4 4 3 3 5% 7% 48%	1975
	21st to end	Night	7% 5% 2 5% 3 3 4 3 4 7% 57%	2000
May	1st to 10th	Night	13% 8% 3 7% 5% 4 4 4 6% 8% 38%	4490
	11th to 20th	Night	11% 6% 3 6% 5% 4 4 4 6% 9% 41%	4247
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 8% 13% 40%	4421
June	1st to 10th	Night	8% 6% 2 7% 5% 4 5% 4 8% 13% 37%	1800
	11th to 20th	Night	4 4 2 5% 5% 5% 5% 6% 8% 12% 44%	1800
	21st to end	Night	5% 7% 2 6% 6% 5% 6% 6% 9% 13% 37%	1800
July	1st to 10th	Night	5% 5% 2 8% 5% 6% 6% 6% 9% 12% 35%	4091
	11th to 20th	Night	3 4 2 6% 6% 6% 6% 6% 10% 13% 38%	4517
	21st to end	Night	4 5% 2 8% 6% 7% 8% 7% 10% 13% 29%	4929
August	1st to 10th	Night	2 3 1 4 4 5% 5% 5% 8% 14% 49%	3244
	11th to 20th	Night	4 3 2 6% 5% 5% 6% 5% 8% 12% 46%	3200
	21st to end	Night	6% 5% 2 7% 5% 7% 7% 5% 7% 11% 40%	3586
September	1st to 10th	Night	9% 6% 2 7% 5% 5% 6% 6% 7% 9% 37%	2000
	11th to 20th	Night	10% 6% 2 6% 5% 4 5% 4 6% 7% 45%	2150
	21st to end	Night	7% 5% 2 5% 4 5% 4 5% 7% 7% 50%	2200
October	1st to 10th	Night	8% 5% 2 6% 3 4 3 4 5% 7% 54%	2200
	11th to 20th	Night	9% 4 1 3 2 3 3 2 4 6% 63%	2275
	21st to end	Night	12% 5% 2 5% 3 2 3 2 4 6% 56%	2640
November	1st to 10th	Night	9% 4 2 5% 4 4 3 2 4 5% 57%	2619
	11th to 20th	Night	12% 6% 2 4 3 3 3 3 5% 6% 54%	2730
	21st to end	Night	12% 6% 2 5% 3 4 4 4 5% 7% 49%	2730
December	1st to 10th	Night	14% 6% 2 6% 3 3 4 3 5% 7% 46%	4380
	11th to 20th	Night	13% 6% 2 4 3 4 4 3 5% 5% 51%	4952
	21st to end	Night	18% 8% 2 5% 4 3 3 3 3 5% 47%	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	40% 4 8% 19% 24% 5%	5718
	11th to 20th	Day	32% 3 5% 18% 32% 11%	5880
	21st to end	Day	52% 3 5% 11% 16% 14%	6436
February	1st to 10th	Day	46% 3 7% 12% 22% 10%	2100
	11th to 20th	Day	42% 3 7% 17% 22% 9%	2058
	21st to end	Day	45% 4 8% 15% 17% 12%	1730
March	1st to 10th	Day	48% 4 8% 13% 19% 8%	4580
	11th to 20th	Day	35% 4 6% 17% 19% 18%	4805
	21st to end	Day	43% 4 9% 16% 19% 9%	5969
April	1st to 10th	Day	39% 6% 7% 19% 18% 11%	2400
	11th to 20th	Day	39% 5% 7% 18% 22% 10%	2374
	21st to end	Day	33% 5% 9% 21% 24% 7%	2400
May	1st to 10th	Day	43% 8% 10% 23% 14% 3	5440
	11th to 20th	Day	37% 7% 15% 24% 16% 1	5635
	21st to end	Day	34% 7% 13% 29% 14% 3	6447
June	1st to 10th	Day	43% 8% 14% 23% 11% 2	2600
	11th to 20th	Day	40% 9% 15% 21% 11% 3	2600
	21st to end	Day	45% 9% 19% 17% 9% 1	2600
July	1st to 10th	Day	41% 13% 24% 16% 5%	5797
	11th to 20th	Day	40% 14% 30% 13% 2	5377
	21st to end	Day	42% 15% 23% 18% 3	5752
August	1st to 10th	Day	26% 8% 16% 27% 21% 1	3893
	11th to 20th	Day	33% 8% 16% 25% 16% 1	3885
	21st to end	Day	39% 10% 18% 16% 15% 2	4311
September	1st to 10th	Day	43% 7% 15% 17% 14% 5%	2400
	11th to 20th	Day	39% 7% 11% 18% 19% 7%	2227
	21st to end	Day	33% 5% 11% 22% 20% 9%	2200
October	1st to 10th	Day	29% 2 7% 10% 22% 29%	3590
	11th to 20th	Day	19% 3 4 16% 25% 33%	3438
	21st to end	Day	23% 3 4 12% 40% 18%	3538
November	1st to 10th	Day	31% 3 6% 19% 25% 16%	1897
	11th to 20th	Day	31% 3 6% 17% 28% 15%	1890
	21st to end	Day	37% 4 7% 17% 23% 12%	1890
December	1st to 10th	Day	40% 3 8% 16% 24% 9%	3020
	11th to 20th	Day	37% 3 8% 20% 22% 10%	3460
	21st to end	Day	41% 3 5% 19% 27% 4	4565
January	1st to 10th	Night	42% 3 9% 15% 25% 5%	7159
	11th to 20th	Night	40% 2 4 16% 26% 11%	7080
	21st to end	Night	52% 2 5% 13% 20% 8%	7745
February	1st to 10th	Night	41% 3 8% 16% 22% 11%	2520
	11th to 20th	Night	46% 4 5% 13% 21% 11%	2459
	21st to end	Night	45% 5% 8% 15% 15% 13%	2076
March	1st to 10th	Night	49% 4 7% 13% 20% 8%	5493
	11th to 20th	Night	39% 4 8% 14% 20% 16%	5348
	21st to end	Night	39% 4 12% 18% 16% 11%	4962
April	1st to 10th	Night	40% 4 10% 13% 21% 11%	2000
	11th to 20th	Night	37% 4 9% 19% 22% 10%	1975
	21st to end	Night	28% 5% 11% 22% 27% 8%	2000
May	1st to 10th	Night	43% 7% 15% 18% 14% 4	4520
	11th to 20th	Night	38% 7% 18% 23% 13% 1	4248
	21st to end	Night	32% 8% 20% 27% 13% 2	4429
June	1st to 10th	Night	36% 9% 18% 22% 12% 2	1800
	11th to 20th	Night	29% 10% 21% 24% 13% 2	1800
	21st to end	Night	35% 11% 23% 20% 9% 2	1800
July	1st to 10th	Night	37% 13% 27% 18% 4	4048
	11th to 20th	Night	33% 16% 35% 14% 2	4460
	21st to end	Night	42% 17% 19% 20% 2	4785
August	1st to 10th	Night	22% 8% 24% 27% 17% 1	3232
	11th to 20th	Night	27% 10% 22% 25% 14% 1	3230
	21st to end	Night	37% 12% 17% 19% 12% 3	3586
September	1st to 10th	Night	40% 10% 17% 16% 12% 5%	2000
	11th to 20th	Night	38% 7% 13% 18% 17% 8%	2150
	21st to end	Night	30% 7% 12% 23% 19% 9%	2200
October	1st to 10th	Night	31% 4 8% 10% 24% 24%	3590
	11th to 20th	Night	16% 2 4 20% 24% 34%	3696
	21st to end	Night	20% 2 5% 12% 39% 22%	4252
November	1st to 10th	Night	30% 3 7% 17% 26% 17%	2619
	11th to 20th	Night	32% 3 6% 17% 28% 15%	2730
	21st to end	Night	35% 4 7% 20% 21% 13%	2730
December	1st to 10th	Night	38% 3 6% 20% 24% 9%	4380
	11th to 20th	Night	36% 3 9% 20% 25% 8%	4954
	21st to end	Night	42% 3 5% 18% 28% 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	25% 19% 35% 15% 4 1	330
	11th to 20th	Day	24% 15% 36% 18% 6% 1	330
	21st to end	Day	29% 18% 34% 16% 3	363
February	1st to 10th	Day	26% 19% 34% 16% 5% 1	330
	11th to 20th	Day	29% 19% 34% 13% 4	330
	21st to end	Day	26% 22% 36% 14% 3	273
March	1st to 10th	Day	21% 16% 41% 17% 5%	330
	11th to 20th	Day	24% 21% 33% 16% 5%	336
	21st to end	Day	18% 15% 31% 28% 8%	550
April	1st to 10th	Day	22% 13% 33% 22% 9% 2	500
	11th to 20th	Day	17% 12% 30% 26% 11% 3	492
	21st to end	Day	11% 12% 30% 28% 17% 3	500
May	1st to 10th	Day	11% 10% 29% 24% 22% 4	503
	11th to 20th	Day	9% 6% 24% 30% 19% 11%	527
	21st to end	Day	9% 3 19% 34% 23% 13%	573
June	1st to 10th	Day	10% 4 15% 31% 26% 14%	530
	11th to 20th	Day	7% 3 12% 29% 32% 17%	530
	21st to end	Day	10% 2 10% 26% 28% 23%	530
July	1st to 10th	Day	8% 2 6% 23% 36% 25%	525
	11th to 20th	Day	8% 2 3 15% 40% 33%	524
	21st to end	Day	6% 1 5% 22% 41% 25%	576
August	1st to 10th	Day	6% 1 6% 22% 32% 34%	526
	11th to 20th	Day	8% 2 4 19% 36% 31%	519
	21st to end	Day	12% 1 8% 25% 31% 23%	583
September	1st to 10th	Day	9% 2 8% 29% 34% 18%	530
	11th to 20th	Day	13% 4 11% 26% 32% 14%	530
	21st to end	Day	11% 3 12% 34% 26% 13%	530
October	1st to 10th	Day	11% 5% 22% 34% 22% 5%	530
	11th to 20th	Day	10% 6% 19% 33% 25% 6%	450
	21st to end	Day	19% 9% 21% 30% 17% 4	363
November	1st to 10th	Day	16% 9% 25% 34% 13% 3	330
	11th to 20th	Day	17% 13% 30% 28% 11% 2	330
	21st to end	Day	16% 14% 36% 21% 11% 2	330
December	1st to 10th	Day	25% 14% 34% 19% 7% 1	330
	11th to 20th	Day	22% 12% 41% 18% 7% 1	330
	21st to end	Day	27% 12% 30% 21% 9% 1	363
January	1st to 10th	Night	20% 14% 35% 26% 4	840
	11th to 20th	Night	20% 15% 27% 30% 7%	840
	21st to end	Night	25% 14% 31% 27% 3	924
February	1st to 10th	Night	21% 13% 32% 30% 5%	840
	11th to 20th	Night	26% 16% 31% 22% 6%	823
	21st to end	Night	22% 17% 38% 21% 2	692
March	1st to 10th	Night	18% 14% 33% 27% 7%	840
	11th to 20th	Night	19% 11% 35% 28% 6% 1	773
	21st to end	Night	16% 8% 35% 30% 10%	660
April	1st to 10th	Night	17% 13% 28% 29% 12% 1	600
	11th to 20th	Night	16% 7% 33% 29% 14% 1	593
	21st to end	Night	10% 6% 27% 39% 18% 1	600
May	1st to 10th	Night	12% 4 27% 37% 18% 3	600
	11th to 20th	Night	8% 2 21% 42% 21% 5%	591
	21st to end	Night	8% 2 14% 38% 31% 6%	650
June	1st to 10th	Night	9% 2 10% 35% 36% 8%	600
	11th to 20th	Night	5% 1 9% 33% 39% 14%	600
	21st to end	Night	7% 1 9% 28% 41% 15%	600
July	1st to 10th	Night	7% 1 3 23% 49% 16%	585
	11th to 20th	Night	6% 1 3 18% 45% 27%	582
	21st to end	Night	4 2 4 23% 50% 18%	657
August	1st to 10th	Night	4 1 3 19% 47% 27%	597
	11th to 20th	Night	8% 1 4 20% 47% 21%	594
	21st to end	Night	10% 2 5% 23% 43% 17%	660
September	1st to 10th	Night	10% 2 7% 28% 40% 14%	600
	11th to 20th	Night	11% 4 9% 28% 41% 8%	750
	21st to end	Night	10% 2 11% 32% 40% 5%	800
October	1st to 10th	Night	11% 3 23% 33% 27% 5%	800
	11th to 20th	Night	11% 4 22% 31% 28% 4	800
	21st to end	Night	14% 6% 21% 34% 23% 2	880
November	1st to 10th	Night	12% 6% 20% 41% 19% 2	820
	11th to 20th	Night	16% 8% 26% 34% 15% 1	840
	21st to end	Night	14% 11% 27% 33% 14% 1	840
December	1st to 10th	Night	19% 12% 28% 28% 12% 1	840
	11th to 20th	Night	21% 7% 31% 31% 10%	840
	21st to end	Night	23% 11% 29% 28% 8% 1	924

Page generated at 2026-03-15 01:23:53. Version ac07

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