Porter
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Porter clear sky chart from 2005-11-06 to 2024-11-28.

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% 9% 3 7% 5% 4 4 4 6% 7% 36%	101426
	Night	16% 9% 3 7% 5% 4 4 3 5% 7% 37%	98069
Transparency	Day	45% 6% 11% 23% 14% 2	105155
	Night	45% 6% 10% 22% 15% 3	102479
Seeing	Day	20% 11% 26% 22% 15% 6%	15018
	Night	19% 9% 24% 30% 16% 2	25102

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	19% 17% 6% 9% 5% 4 4 3 5% 6% 22%	2836
	11th to 20th	Day	16% 18% 8% 13% 7% 3 3 2 3 3 23%	2840
	21st to end	Day	25% 19% 5% 8% 5% 4 4 3 4 4 19%	3124
February	1st to 10th	Day	22% 13% 5% 9% 5% 3 3 3 4 5% 29%	1710
	11th to 20th	Day	20% 14% 4 9% 4 4 4 3 5% 6% 27%	1814
	21st to end	Day	22% 14% 3 7% 4 3 4 2 4 5% 32%	1570
March	1st to 10th	Day	23% 14% 3 8% 5% 4 4 2 4 5% 27%	3334
	11th to 20th	Day	16% 7% 3 6% 5% 4 4 3 6% 7% 40%	3480
	21st to end	Day	20% 8% 3 6% 4 3 4 4 5% 7% 35%	3815
April	1st to 10th	Day	14% 11% 3 7% 5% 4 5% 3 6% 7% 36%	2090
	11th to 20th	Day	17% 8% 3 6% 4 3 4 3 5% 7% 40%	2389
	21st to end	Day	19% 8% 3 6% 5% 4 4 4 6% 6% 36%	2470
May	1st to 10th	Day	21% 9% 3 8% 5% 4 5% 4 6% 7% 28%	4082
	11th to 20th	Day	20% 7% 3 7% 5% 4 4 4 5% 7% 34%	4081
	21st to end	Day	12% 5% 2 7% 5% 5% 4 5% 7% 9% 38%	4476
June	1st to 10th	Day	12% 6% 3 6% 3 4 6% 5% 7% 9% 40%	2470
	11th to 20th	Day	8% 6% 2 7% 5% 5% 6% 5% 7% 9% 39%	2470
	21st to end	Day	11% 5% 2 5% 5% 5% 6% 5% 7% 10% 39%	2470
July	1st to 10th	Day	9% 6% 2 7% 4 5% 5% 4 7% 9% 42%	4120
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 5% 7% 10% 43%	4120
	21st to end	Day	14% 8% 3 8% 5% 5% 5% 4 7% 8% 32%	4466
August	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 5% 8% 10% 37%	4104
	11th to 20th	Day	9% 6% 2 7% 5% 6% 6% 4 7% 10% 39%	4044
	21st to end	Day	6% 3 2 5% 4 4 5% 4 6% 8% 54%	4441
September	1st to 10th	Day	14% 4 2 5% 4 4 4 4 6% 6% 47%	2090
	11th to 20th	Day	11% 4 2 6% 5% 4 4 4 5% 7% 48%	2090
	21st to end	Day	18% 7% 2 6% 5% 4 4 3 5% 5% 43%	2090
October	1st to 10th	Day	12% 5% 2 5% 3 4 3 4 6% 7% 48%	2014
	11th to 20th	Day	15% 6% 2 6% 4 4 4 3 4 6% 46%	1900
	21st to end	Day	20% 6% 2 6% 4 4 4 3 4 7% 40%	2090
November	1st to 10th	Day	12% 6% 3 5% 4 3 4 3 4 6% 51%	1776
	11th to 20th	Day	17% 12% 3 6% 5% 4 3 3 5% 6% 38%	1800
	21st to end	Day	17% 10% 3 7% 5% 3 5% 4 4 6% 36%	1773
December	1st to 10th	Day	24% 14% 4 8% 5% 5% 3 3 4 5% 25%	1710
	11th to 20th	Day	19% 15% 5% 9% 4 4 3 3 5% 6% 27%	2153
	21st to end	Day	20% 20% 4 10% 5% 5% 5% 3 5% 5% 18%	3124
January	1st to 10th	Night	17% 18% 5% 10% 5% 5% 4 4 5% 5% 21%	4109
	11th to 20th	Night	20% 14% 6% 12% 5% 4 3 3 4 4 24%	4120
	21st to end	Night	27% 15% 5% 7% 4 3 3 3 4 5% 23%	4532
February	1st to 10th	Night	22% 13% 4 8% 5% 4 4 3 4 5% 29%	2470
	11th to 20th	Night	22% 11% 3 8% 5% 4 4 3 5% 4 30%	2247
	21st to end	Night	22% 15% 4 7% 5% 3 3 3 4 5% 29%	1884
March	1st to 10th	Night	22% 12% 2 6% 4 4 3 3 5% 6% 33%	3519
	11th to 20th	Night	15% 9% 2 6% 5% 4 4 4 5% 7% 40%	3480
	21st to end	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	3817
April	1st to 10th	Night	15% 9% 3 7% 4 4 4 4 6% 7% 38%	2090
	11th to 20th	Night	14% 8% 2 6% 5% 3 4 3 6% 8% 41%	1754
	21st to end	Night	16% 7% 3 8% 4 4 5% 3 5% 7% 39%	1710
May	1st to 10th	Night	25% 8% 3 8% 4 4 5% 4 4 6% 29%	2813
	11th to 20th	Night	20% 7% 3 6% 4 3 4 3 4 8% 39%	2812
	21st to end	Night	12% 4 2 5% 4 5% 4 4 6% 9% 44%	3079
June	1st to 10th	Night	10% 5% 2 5% 5% 3 5% 5% 6% 9% 46%	1710
	11th to 20th	Night	8% 5% 2 6% 5% 4 5% 5% 7% 10% 44%	1710
	21st to end	Night	9% 5% 1 6% 3 3 5% 6% 7% 10% 45%	1710
July	1st to 10th	Night	9% 6% 2 6% 5% 5% 5% 4 7% 9% 44%	2840
	11th to 20th	Night	8% 7% 2 6% 4 4 5% 4 5% 8% 46%	2840
	21st to end	Night	11% 8% 3 7% 6% 5% 5% 4 6% 8% 38%	3087
August	1st to 10th	Night	9% 7% 3 9% 4 5% 6% 5% 6% 9% 38%	2825
	11th to 20th	Night	10% 6% 3 8% 5% 4 5% 4 6% 7% 44%	2785
	21st to end	Night	5% 3 1 5% 4 4 4 4 7% 9% 53%	3179
September	1st to 10th	Night	13% 4 2 5% 3 4 4 3 5% 6% 51%	2090
	11th to 20th	Night	10% 4 2 5% 3 4 4 3 4 6% 55%	2090
	21st to end	Night	16% 6% 2 5% 3 4 5% 4 5% 6% 45%	2090
October	1st to 10th	Night	11% 5% 2 6% 4 3 3 2 5% 6% 51%	2166
	11th to 20th	Night	14% 6% 2 5% 4 3 4 3 5% 7% 46%	2280
	21st to end	Night	21% 6% 2 5% 4 4 3 4 3 6% 43%	2508
November	1st to 10th	Night	12% 6% 2 6% 4 4 3 3 4 6% 50%	2517
	11th to 20th	Night	17% 8% 3 6% 5% 4 4 4 6% 6% 38%	2600
	21st to end	Night	18% 11% 3 6% 5% 4 4 2 4 6% 37%	2562
December	1st to 10th	Night	22% 13% 5% 7% 5% 4 4 4 4 5% 27%	2470
	11th to 20th	Night	17% 13% 6% 9% 5% 4 4 3 4 6% 30%	3042
	21st to end	Night	19% 16% 4 9% 6% 6% 5% 4 4 6% 21%	4532

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	62% 5% 11% 14% 7%	2837
	11th to 20th	Day	67% 4 7% 16% 6%	2840
	21st to end	Day	68% 5% 6% 15% 4 1	3124
February	1st to 10th	Day	59% 4 10% 17% 9% 1	1710
	11th to 20th	Day	58% 4 10% 17% 10% 1	1824
	21st to end	Day	56% 3 8% 21% 10% 2	1570
March	1st to 10th	Day	59% 4 8% 20% 7% 1	3334
	11th to 20th	Day	42% 6% 9% 26% 16% 1	3480
	21st to end	Day	47% 6% 9% 24% 13% 1	3815
April	1st to 10th	Day	47% 5% 11% 21% 12% 3	2090
	11th to 20th	Day	43% 6% 9% 21% 17% 4	2389
	21st to end	Day	47% 6% 12% 20% 12% 3	2470
May	1st to 10th	Day	53% 7% 10% 20% 9% 1	4120
	11th to 20th	Day	49% 7% 11% 20% 12% 1	4085
	21st to end	Day	37% 10% 15% 19% 16% 3	4489
June	1st to 10th	Day	38% 9% 13% 24% 15% 1	2470
	11th to 20th	Day	38% 10% 13% 21% 16% 2	2470
	21st to end	Day	37% 10% 15% 21% 15% 3	2470
July	1st to 10th	Day	38% 7% 13% 25% 15% 3	4055
	11th to 20th	Day	35% 6% 11% 32% 15% 1	4051
	21st to end	Day	49% 6% 11% 16% 15% 3	4324
August	1st to 10th	Day	39% 7% 14% 29% 11%	4091
	11th to 20th	Day	39% 5% 10% 29% 16% 1	4083
	21st to end	Day	28% 5% 15% 29% 21% 3	4441
September	1st to 10th	Day	36% 6% 9% 21% 21% 6%	2090
	11th to 20th	Day	34% 6% 11% 25% 21% 3	2090
	21st to end	Day	43% 6% 9% 22% 19% 1	2090
October	1st to 10th	Day	26% 4 7% 29% 32% 2	3352
	11th to 20th	Day	31% 3 11% 30% 21% 4	3140
	21st to end	Day	33% 2 11% 30% 22% 2	3428
November	1st to 10th	Day	35% 5% 9% 30% 19% 3	1776
	11th to 20th	Day	49% 4 7% 21% 17% 3	1800
	21st to end	Day	50% 5% 9% 21% 14% 1	1773
December	1st to 10th	Day	62% 4 9% 19% 5% 1	1710
	11th to 20th	Day	58% 6% 9% 18% 9%	2150
	21st to end	Day	67% 6% 11% 12% 4	3124
January	1st to 10th	Night	63% 6% 9% 14% 7% 1	4109
	11th to 20th	Night	63% 5% 10% 16% 5% 1	4120
	21st to end	Night	63% 5% 8% 18% 5% 1	4532
February	1st to 10th	Night	58% 4 9% 19% 9% 1	2470
	11th to 20th	Night	57% 4 8% 18% 13% 1	2248
	21st to end	Night	58% 5% 9% 16% 9% 3	1884
March	1st to 10th	Night	52% 5% 7% 22% 13% 1	3519
	11th to 20th	Night	42% 6% 10% 27% 15% 1	3480
	21st to end	Night	45% 6% 8% 26% 15% 1	3817
April	1st to 10th	Night	45% 6% 8% 21% 16% 3	2090
	11th to 20th	Night	41% 5% 10% 21% 16% 7%	1754
	21st to end	Night	45% 6% 10% 20% 17% 2	1710
May	1st to 10th	Night	55% 7% 10% 15% 10% 2	2840
	11th to 20th	Night	45% 8% 12% 22% 12% 2	2813
	21st to end	Night	33% 9% 14% 25% 14% 4	3087
June	1st to 10th	Night	33% 8% 11% 26% 18% 3	1710
	11th to 20th	Night	32% 10% 16% 19% 20% 3	1710
	21st to end	Night	32% 9% 16% 23% 18% 3	1710
July	1st to 10th	Night	36% 6% 12% 24% 18% 4	2795
	11th to 20th	Night	36% 5% 13% 28% 17% 2	2786
	21st to end	Night	44% 7% 10% 21% 12% 5%	2988
August	1st to 10th	Night	42% 6% 14% 27% 10% 1	2814
	11th to 20th	Night	39% 6% 9% 23% 22% 1	2812
	21st to end	Night	27% 4 13% 31% 22% 3	3179
September	1st to 10th	Night	33% 6% 12% 22% 20% 8%	2090
	11th to 20th	Night	30% 6% 11% 25% 24% 3	2090
	21st to end	Night	39% 6% 11% 20% 23% 1	2090
October	1st to 10th	Night	28% 3 7% 25% 32% 4	3608
	11th to 20th	Night	29% 3 9% 26% 25% 8%	3779
	21st to end	Night	32% 3 7% 27% 27% 5%	4120
November	1st to 10th	Night	37% 4 9% 23% 22% 4	2517
	11th to 20th	Night	46% 4 9% 21% 18% 4	2600
	21st to end	Night	49% 5% 9% 23% 13% 1	2562
December	1st to 10th	Night	59% 5% 9% 20% 7%	2470
	11th to 20th	Night	57% 5% 10% 20% 8% 1	3044
	21st to end	Night	64% 6% 10% 15% 6%	4532

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	29% 19% 35% 10% 6% 1	270
	11th to 20th	Day	32% 22% 34% 10% 2	270
	21st to end	Day	28% 25% 29% 14% 4	297
February	1st to 10th	Day	33% 21% 27% 14% 4	270
	11th to 20th	Day	41% 20% 31% 4 1 1	270
	21st to end	Day	32% 24% 36% 7% 1	225
March	1st to 10th	Day	28% 18% 32% 16% 5%	393
	11th to 20th	Day	25% 18% 34% 16% 6% 1	460
	21st to end	Day	30% 14% 31% 21% 4	506
April	1st to 10th	Day	23% 18% 28% 21% 9% 1	460
	11th to 20th	Day	23% 15% 30% 20% 9% 2	452
	21st to end	Day	25% 14% 33% 18% 8% 2	460
May	1st to 10th	Day	23% 15% 32% 17% 9% 4	463
	11th to 20th	Day	18% 11% 27% 23% 15% 6%	487
	21st to end	Day	12% 9% 24% 25% 22% 8%	529
June	1st to 10th	Day	14% 7% 23% 27% 21% 8%	490
	11th to 20th	Day	10% 7% 24% 31% 20% 9%	490
	21st to end	Day	13% 6% 28% 24% 20% 9%	490
July	1st to 10th	Day	14% 4 17% 24% 19% 22%	485
	11th to 20th	Day	8% 4 21% 30% 24% 12%	484
	21st to end	Day	16% 2 18% 26% 23% 14%	532
August	1st to 10th	Day	12% 3 17% 28% 27% 12%	486
	11th to 20th	Day	13% 5% 16% 30% 23% 13%	479
	21st to end	Day	9% 5% 15% 33% 24% 14%	539
September	1st to 10th	Day	14% 5% 15% 26% 26% 14%	490
	11th to 20th	Day	10% 3 14% 29% 31% 14%	490
	21st to end	Day	22% 8% 18% 24% 21% 6%	490
October	1st to 10th	Day	14% 8% 23% 27% 21% 7%	490
	11th to 20th	Day	16% 11% 29% 24% 14% 5%	490
	21st to end	Day	23% 12% 29% 24% 10% 1	539
November	1st to 10th	Day	18% 13% 33% 25% 8% 2	314
	11th to 20th	Day	27% 14% 28% 22% 7% 2	300
	21st to end	Day	21% 16% 40% 18% 4 1	291
December	1st to 10th	Day	29% 19% 31% 15% 6% 1	270
	11th to 20th	Day	25% 20% 33% 17% 4 1	270
	21st to end	Day	30% 18% 33% 13% 6%	297
January	1st to 10th	Night	26% 18% 31% 20% 5%	760
	11th to 20th	Night	32% 16% 29% 21% 3	760
	21st to end	Night	27% 14% 31% 24% 3	836
February	1st to 10th	Night	29% 11% 31% 28% 1	760
	11th to 20th	Night	30% 17% 31% 20% 2	743
	21st to end	Night	30% 14% 33% 21% 1	628
March	1st to 10th	Night	25% 14% 28% 27% 6%	760
	11th to 20th	Night	25% 15% 30% 22% 8% 1	760
	21st to end	Night	23% 14% 30% 26% 7%	836
April	1st to 10th	Night	21% 16% 30% 25% 8%	760
	11th to 20th	Night	18% 11% 33% 25% 12% 1	602
	21st to end	Night	19% 9% 32% 31% 8% 1	570
May	1st to 10th	Night	19% 8% 27% 33% 12% 1	570
	11th to 20th	Night	17% 7% 26% 30% 19% 1	561
	21st to end	Night	9% 5% 19% 33% 30% 4	617
June	1st to 10th	Night	9% 4 19% 41% 25% 2	570
	11th to 20th	Night	9% 3 18% 39% 28% 3	570
	21st to end	Night	11% 3 19% 35% 29% 3	570
July	1st to 10th	Night	11% 3 13% 33% 32% 8%	555
	11th to 20th	Night	8% 3 15% 34% 36% 5%	552
	21st to end	Night	11% 2 13% 33% 35% 5%	624
August	1st to 10th	Night	9% 4 8% 40% 37% 3	567
	11th to 20th	Night	10% 2 11% 37% 32% 8%	564
	21st to end	Night	10% 1 12% 34% 36% 7%	646
September	1st to 10th	Night	15% 2 11% 34% 33% 5%	760
	11th to 20th	Night	12% 3 12% 33% 35% 6%	760
	21st to end	Night	19% 4 19% 32% 23% 3	760
October	1st to 10th	Night	13% 5% 19% 34% 26% 3	760
	11th to 20th	Night	16% 8% 26% 32% 16% 2	760
	21st to end	Night	23% 9% 22% 31% 14% 1	836
November	1st to 10th	Night	15% 9% 25% 33% 17% 1	780
	11th to 20th	Night	21% 14% 26% 28% 9% 1	800
	21st to end	Night	24% 10% 26% 32% 8% 1	789
December	1st to 10th	Night	29% 14% 27% 23% 6%	760
	11th to 20th	Night	23% 13% 29% 28% 6%	760
	21st to end	Night	28% 14% 25% 29% 3	836

Page generated at 2024-11-25 00:22:16. Version ac07

Copyright © 2024 Attilla Danko.