Porter West Preserve
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Porter West Preserve clear sky chart from 2005-11-06 to 2024-12-24.

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	14% 8% 3 7% 4 4 4 4 5% 7% 38%	101472
	Night	15% 10% 3 7% 4 4 4 3 5% 6% 39%	98672
Transparency	Day	43% 5% 11% 24% 15% 2	105123
	Night	44% 4 10% 22% 16% 2	103161
Seeing	Day	19% 14% 29% 22% 12% 4	15697
	Night	19% 13% 28% 25% 13% 2	25551

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	14% 16% 7% 9% 4 4 4 4 5% 4 29%	2527
	11th to 20th	Day	16% 12% 4 12% 7% 5% 4 3 5% 6% 25%	2530
	21st to end	Day	25% 18% 6% 8% 4 3 3 2 3 4 23%	2974
February	1st to 10th	Day	18% 12% 5% 8% 4 4 4 4 5% 6% 30%	1900
	11th to 20th	Day	16% 10% 5% 8% 4 4 4 4 5% 7% 33%	1848
	21st to end	Day	16% 15% 5% 8% 5% 3 4 3 4 5% 32%	1570
March	1st to 10th	Day	24% 15% 3 7% 3 3 3 2 3 4 33%	3120
	11th to 20th	Day	14% 8% 3 5% 5% 3 4 3 5% 7% 45%	3319
	21st to end	Day	14% 10% 4 9% 6% 5% 5% 3 6% 6% 32%	4037
April	1st to 10th	Day	15% 9% 3 7% 4 4 5% 3 5% 7% 37%	2280
	11th to 20th	Day	17% 9% 3 6% 4 4 4 3 5% 6% 39%	2254
	21st to end	Day	20% 7% 3 7% 5% 4 4 3 5% 6% 37%	2399
May	1st to 10th	Day	19% 9% 3 7% 5% 5% 5% 4 7% 9% 28%	4082
	11th to 20th	Day	21% 8% 3 6% 4 4 4 3 5% 5% 38%	4081
	21st to end	Day	12% 7% 2 7% 5% 5% 4 4 7% 8% 39%	4590
June	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 6% 8% 43%	2660
	11th to 20th	Day	9% 5% 2 5% 5% 5% 5% 5% 6% 8% 45%	2660
	21st to end	Day	11% 6% 2 5% 5% 5% 5% 5% 7% 8% 42%	2660
July	1st to 10th	Day	15% 5% 2 6% 4 4 5% 4 7% 11% 38%	4440
	11th to 20th	Day	7% 4 1 5% 4 4 5% 4 7% 11% 47%	4440
	21st to end	Day	10% 7% 3 8% 5% 5% 7% 6% 8% 10% 31%	4693
August	1st to 10th	Day	9% 4 2 5% 3 4 4 5% 6% 10% 49%	4104
	11th to 20th	Day	10% 4 2 6% 5% 5% 6% 5% 8% 10% 39%	3762
	21st to end	Day	5% 4 2 5% 3 4 5% 3 5% 10% 54%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 45%	2269
	11th to 20th	Day	9% 6% 2 6% 4 3 4 3 6% 7% 49%	2090
	21st to end	Day	13% 5% 2 5% 4 4 4 2 6% 6% 50%	2090
October	1st to 10th	Day	11% 4 2 6% 3 3 5% 3 4 7% 52%	2090
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 7% 45%	1952
	21st to end	Day	19% 9% 2 7% 4 4 4 3 4 5% 39%	1881
November	1st to 10th	Day	10% 5% 2 4 4 3 4 4 5% 6% 52%	1762
	11th to 20th	Day	16% 10% 4 7% 4 2 3 3 4 6% 40%	1800
	21st to end	Day	19% 11% 3 7% 4 3 3 3 3 6% 38%	1800
December	1st to 10th	Day	18% 14% 4 8% 4 4 3 3 4 5% 33%	1800
	11th to 20th	Day	16% 14% 6% 9% 3 4 4 3 4 6% 31%	2021
	21st to end	Day	21% 19% 8% 8% 5% 4 4 3 3 5% 20%	2807
January	1st to 10th	Night	17% 15% 7% 10% 5% 4 3 4 4 5% 26%	4428
	11th to 20th	Night	15% 18% 6% 13% 6% 5% 4 3 4 4 22%	4440
	21st to end	Night	26% 18% 6% 7% 3 3 3 2 3 4 24%	4685
February	1st to 10th	Night	20% 12% 5% 9% 5% 4 4 4 5% 5% 27%	2280
	11th to 20th	Night	15% 11% 5% 9% 6% 4 4 4 5% 6% 32%	2218
	21st to end	Night	20% 13% 4 8% 4 4 4 2 5% 6% 31%	1884
March	1st to 10th	Night	22% 17% 3 6% 4 2 3 3 3 4 32%	3733
	11th to 20th	Night	13% 6% 2 6% 4 4 3 3 5% 6% 48%	3640
	21st to end	Night	17% 8% 3 7% 5% 4 4 3 5% 6% 38%	3608
April	1st to 10th	Night	14% 10% 3 6% 5% 3 4 3 5% 6% 41%	1900
	11th to 20th	Night	17% 9% 3 6% 3 3 3 3 6% 6% 41%	1875
	21st to end	Night	17% 7% 2 7% 4 4 5% 3 6% 7% 37%	1780
May	1st to 10th	Night	18% 11% 3 8% 5% 5% 5% 3 6% 7% 29%	2813
	11th to 20th	Night	19% 7% 2 5% 3 4 3 3 5% 7% 41%	2812
	21st to end	Night	10% 5% 2 6% 5% 4 5% 4 6% 9% 43%	2965
June	1st to 10th	Night	9% 6% 2 5% 4 4 4 3 6% 10% 46%	1520
	11th to 20th	Night	9% 4 3 5% 4 4 4 4 6% 9% 49%	1520
	21st to end	Night	6% 3 2 4 3 5% 7% 5% 7% 10% 49%	1520
July	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 5% 8% 47%	2530
	11th to 20th	Night	6% 4 2 4 3 4 4 4 7% 9% 55%	2530
	21st to end	Night	9% 6% 3 8% 6% 5% 5% 5% 7% 8% 38%	2866
August	1st to 10th	Night	8% 5% 2 6% 4 4 4 3 5% 8% 51%	2825
	11th to 20th	Night	7% 5% 2 6% 4 4 5% 4 6% 9% 47%	3062
	21st to end	Night	4 3 1 4 4 4 5% 4 5% 8% 57%	3476
September	1st to 10th	Night	11% 6% 2 5% 4 3 4 4 4 6% 51%	1900
	11th to 20th	Night	8% 4 2 5% 3 4 3 3 5% 8% 56%	2080
	21st to end	Night	13% 5% 2 6% 3 4 3 3 5% 6% 50%	2090
October	1st to 10th	Night	8% 4 1 5% 4 3 3 3 5% 6% 57%	2090
	11th to 20th	Night	16% 7% 2 4 3 3 4 3 4 5% 49%	2224
	21st to end	Night	18% 9% 3 6% 4 3 3 3 5% 6% 42%	2717
November	1st to 10th	Night	12% 8% 2 5% 4 3 3 3 4 7% 49%	2536
	11th to 20th	Night	14% 9% 3 7% 5% 3 4 3 5% 7% 41%	2600
	21st to end	Night	19% 12% 3 7% 4 3 4 3 4 6% 35%	2600
December	1st to 10th	Night	18% 13% 4 8% 5% 3 4 3 5% 5% 32%	2600
	11th to 20th	Night	18% 13% 4 10% 4 4 3 3 5% 5% 31%	3392
	21st to end	Night	22% 20% 6% 9% 5% 4 4 3 4 4 19%	4933

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	57% 3 9% 21% 8% 1	2528
	11th to 20th	Day	61% 2 12% 17% 7%	2530
	21st to end	Day	67% 3 8% 18% 3 1	2974
February	1st to 10th	Day	55% 4 8% 21% 10% 2	1900
	11th to 20th	Day	52% 4 10% 23% 10% 2	1858
	21st to end	Day	54% 4 8% 22% 9% 3	1570
March	1st to 10th	Day	57% 3 6% 20% 11% 4	3120
	11th to 20th	Day	40% 4 10% 29% 15% 2	3319
	21st to end	Day	51% 5% 13% 21% 9% 1	4037
April	1st to 10th	Day	46% 5% 12% 21% 15% 1	2280
	11th to 20th	Day	45% 4 9% 25% 13% 3	2254
	21st to end	Day	49% 4 10% 22% 12% 3	2399
May	1st to 10th	Day	50% 7% 14% 21% 7%	4120
	11th to 20th	Day	47% 5% 11% 24% 12% 1	4085
	21st to end	Day	40% 7% 12% 19% 19% 3	4603
June	1st to 10th	Day	38% 6% 11% 25% 17% 3	2660
	11th to 20th	Day	35% 6% 13% 23% 20% 3	2660
	21st to end	Day	36% 9% 15% 19% 17% 4	2660
July	1st to 10th	Day	40% 6% 12% 24% 17% 2	4371
	11th to 20th	Day	29% 7% 13% 30% 19% 1	4365
	21st to end	Day	44% 8% 15% 18% 13% 2	4544
August	1st to 10th	Day	30% 7% 14% 32% 16% 1	4091
	11th to 20th	Day	36% 6% 12% 29% 16% 1	3799
	21st to end	Day	26% 5% 15% 33% 17% 4	4179
September	1st to 10th	Day	37% 6% 10% 24% 19% 4	2269
	11th to 20th	Day	33% 6% 10% 27% 21% 3	2090
	21st to end	Day	35% 4 9% 26% 24% 2	2090
October	1st to 10th	Day	22% 4 7% 30% 36% 2	3480
	11th to 20th	Day	30% 3 9% 27% 29% 2	3220
	21st to end	Day	39% 3 8% 24% 25% 2	3081
November	1st to 10th	Day	33% 4 11% 29% 18% 5%	1762
	11th to 20th	Day	45% 4 9% 22% 16% 4	1800
	21st to end	Day	50% 3 9% 22% 15% 1	1800
December	1st to 10th	Day	55% 4 10% 20% 11% 1	1800
	11th to 20th	Day	57% 3 8% 22% 9% 1	2018
	21st to end	Day	68% 3 10% 12% 7%	2807
January	1st to 10th	Night	60% 4 11% 17% 7%	4428
	11th to 20th	Night	67% 2 10% 13% 7%	4440
	21st to end	Night	66% 2 8% 15% 8% 1	4685
February	1st to 10th	Night	58% 5% 11% 18% 7% 1	2280
	11th to 20th	Night	53% 4 10% 19% 13% 1	2219
	21st to end	Night	55% 4 10% 18% 11% 2	1884
March	1st to 10th	Night	56% 3 7% 22% 11% 1	3733
	11th to 20th	Night	37% 5% 11% 23% 22% 1	3640
	21st to end	Night	47% 4 10% 28% 9% 1	3608
April	1st to 10th	Night	43% 4 10% 26% 14% 2	1900
	11th to 20th	Night	44% 4 9% 20% 18% 5%	1875
	21st to end	Night	45% 5% 11% 23% 13% 3	1780
May	1st to 10th	Night	52% 8% 13% 20% 7% 1	2840
	11th to 20th	Night	42% 7% 13% 27% 11% 1	2813
	21st to end	Night	36% 8% 13% 23% 16% 4	2973
June	1st to 10th	Night	34% 6% 11% 25% 21% 4	1520
	11th to 20th	Night	32% 4 12% 25% 21% 6%	1520
	21st to end	Night	27% 8% 15% 24% 20% 5%	1520
July	1st to 10th	Night	36% 6% 10% 26% 20% 3	2490
	11th to 20th	Night	25% 6% 13% 32% 22% 2	2482
	21st to end	Night	41% 7% 14% 23% 13% 3	2775
August	1st to 10th	Night	31% 5% 14% 36% 12% 2	2814
	11th to 20th	Night	32% 6% 15% 28% 18% 1	3091
	21st to end	Night	24% 7% 13% 31% 22% 4	3476
September	1st to 10th	Night	34% 5% 10% 25% 20% 7%	1900
	11th to 20th	Night	27% 4 10% 26% 28% 5%	2080
	21st to end	Night	35% 4 10% 22% 23% 5%	2090
October	1st to 10th	Night	19% 4 7% 21% 46% 3	3480
	11th to 20th	Night	26% 3 7% 26% 36% 3	3695
	21st to end	Night	35% 3 7% 24% 26% 5%	4467
November	1st to 10th	Night	36% 4 9% 25% 22% 4	2536
	11th to 20th	Night	44% 3 9% 22% 18% 4	2600
	21st to end	Night	51% 3 10% 22% 13% 1	2600
December	1st to 10th	Night	54% 3 11% 19% 12% 1	2600
	11th to 20th	Night	54% 4 9% 19% 13% 1	3394
	21st to end	Night	70% 3 8% 12% 7% 1	4933

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	28% 25% 27% 16% 3	270
	11th to 20th	Day	34% 24% 31% 9% 1	270
	21st to end	Day	28% 29% 31% 10% 1 1	297
February	1st to 10th	Day	30% 27% 30% 9% 2	270
	11th to 20th	Day	31% 28% 30% 9% 1 1	270
	21st to end	Day	33% 25% 36% 6%	225
March	1st to 10th	Day	30% 25% 35% 8% 1	270
	11th to 20th	Day	28% 23% 34% 10% 4 1	364
	21st to end	Day	30% 22% 30% 13% 4 1	506
April	1st to 10th	Day	25% 21% 32% 15% 6% 1	460
	11th to 20th	Day	27% 22% 23% 20% 8% 1	452
	21st to end	Day	28% 20% 32% 12% 7% 1	460
May	1st to 10th	Day	24% 16% 34% 18% 6% 2	463
	11th to 20th	Day	23% 11% 32% 21% 8% 5%	487
	21st to end	Day	13% 12% 31% 23% 15% 7%	591
June	1st to 10th	Day	13% 9% 33% 26% 16% 4	680
	11th to 20th	Day	12% 6% 29% 31% 17% 5%	680
	21st to end	Day	13% 9% 34% 23% 17% 5%	680
July	1st to 10th	Day	13% 4 22% 26% 23% 11%	671
	11th to 20th	Day	7% 5% 27% 32% 19% 8%	668
	21st to end	Day	11% 4 23% 34% 20% 7%	668
August	1st to 10th	Day	11% 5% 18% 34% 23% 9%	486
	11th to 20th	Day	14% 5% 26% 29% 20% 6%	479
	21st to end	Day	8% 4 18% 33% 25% 11%	539
September	1st to 10th	Day	11% 6% 20% 34% 23% 5%	490
	11th to 20th	Day	9% 3 19% 32% 27% 10%	490
	21st to end	Day	17% 11% 23% 23% 20% 6%	490
October	1st to 10th	Day	10% 10% 30% 30% 14% 6%	490
	11th to 20th	Day	17% 20% 35% 16% 8% 4	395
	21st to end	Day	31% 14% 39% 15% 1	330
November	1st to 10th	Day	12% 23% 35% 22% 6% 1	300
	11th to 20th	Day	26% 23% 32% 14% 4 1	300
	21st to end	Day	29% 13% 39% 14% 4	300
December	1st to 10th	Day	23% 27% 31% 15% 4 1	300
	11th to 20th	Day	28% 21% 36% 12% 3	300
	21st to end	Day	36% 20% 32% 9% 2 1	306
January	1st to 10th	Night	25% 23% 31% 18% 4	950
	11th to 20th	Night	28% 22% 34% 14% 2	950
	21st to end	Night	25% 20% 34% 18% 2	981
February	1st to 10th	Night	28% 19% 34% 18% 2	760
	11th to 20th	Night	23% 25% 34% 17% 2	743
	21st to end	Night	29% 21% 33% 16% 1	628
March	1st to 10th	Night	27% 19% 32% 20% 2	760
	11th to 20th	Night	24% 19% 32% 18% 6%	760
	21st to end	Night	26% 16% 30% 22% 5%	717
April	1st to 10th	Night	20% 16% 32% 26% 5% 1	570
	11th to 20th	Night	20% 17% 29% 24% 10%	563
	21st to end	Night	21% 12% 37% 22% 7% 1	570
May	1st to 10th	Night	21% 10% 34% 25% 10%	570
	11th to 20th	Night	17% 9% 28% 28% 16% 3	561
	21st to end	Night	11% 5% 26% 34% 21% 3	617
June	1st to 10th	Night	10% 6% 25% 36% 22% 1	570
	11th to 20th	Night	9% 5% 24% 42% 19% 1	570
	21st to end	Night	7% 3 27% 38% 24% 2	570
July	1st to 10th	Night	10% 2 16% 34% 30% 8%	555
	11th to 20th	Night	7% 4 18% 34% 32% 5%	552
	21st to end	Night	9% 2 15% 39% 29% 5%	624
August	1st to 10th	Night	8% 2 13% 39% 32% 7%	567
	11th to 20th	Night	7% 3 15% 39% 33% 4	564
	21st to end	Night	6% 1 18% 34% 36% 6%	627
September	1st to 10th	Night	13% 4 15% 35% 29% 4	570
	11th to 20th	Night	8% 4 20% 30% 34% 5%	750
	21st to end	Night	14% 9% 21% 30% 23% 4	760
October	1st to 10th	Night	10% 7% 25% 32% 22% 4	760
	11th to 20th	Night	19% 13% 29% 24% 14% 1	760
	21st to end	Night	23% 16% 32% 23% 7%	836
November	1st to 10th	Night	16% 12% 34% 25% 12% 1	780
	11th to 20th	Night	21% 19% 29% 23% 7% 1	800
	21st to end	Night	26% 19% 27% 23% 6%	800
December	1st to 10th	Night	26% 18% 33% 19% 4	800
	11th to 20th	Night	27% 16% 30% 21% 5% 1	973
	21st to end	Night	32% 19% 30% 16% 3	1063

Page generated at 2024-12-21 04:13:53. Version ac07

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