Johnsons Crossing
Clear Sky Chart
History

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

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	9% 13% 5% 12% 7% 7% 6% 5% 6% 7% 23%	106438
	Night	7% 14% 5% 13% 8% 7% 6% 5% 6% 7% 21%	101280
Transparency	Day	56% 11% 14% 14% 4	106134
	Night	58% 10% 13% 13% 5% 1	101231
Seeing	Day	15% 11% 24% 26% 18% 5%	17258
	Night	14% 7% 22% 32% 21% 4	23558

By Month

Percentage Cloud Cover NW (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	4 12% 6% 18% 15% 11% 8% 5% 5% 3 13%	1364
	11th to 20th	Day	4 15% 7% 18% 7% 7% 6% 4 5% 6% 19%	1882
	21st to end	Day	8% 22% 7% 15% 8% 7% 5% 4 6% 5% 13%	2090
February	1st to 10th	Day	4 14% 5% 14% 7% 6% 6% 6% 6% 11% 22%	1362
	11th to 20th	Day	4 18% 6% 12% 7% 8% 6% 5% 6% 9% 19%	1480
	21st to end	Day	2 13% 6% 13% 8% 7% 7% 5% 6% 9% 25%	1352
March	1st to 10th	Day	2 9% 5% 14% 10% 11% 9% 6% 7% 6% 22%	3126
	11th to 20th	Day	3 16% 7% 16% 7% 6% 6% 4 6% 8% 20%	3233
	21st to end	Day	1 10% 7% 17% 9% 8% 7% 5% 6% 7% 23%	4165
April	1st to 10th	Day	3 16% 7% 16% 8% 6% 5% 5% 7% 8% 20%	2326
	11th to 20th	Day	3 15% 6% 13% 9% 7% 5% 4 6% 7% 24%	2586
	21st to end	Day	4 15% 5% 11% 8% 6% 7% 4 6% 7% 25%	2697
May	1st to 10th	Day	12% 16% 5% 10% 6% 5% 5% 4 6% 7% 26%	4868
	11th to 20th	Day	7% 18% 6% 13% 8% 6% 6% 4 6% 6% 21%	5013
	21st to end	Day	9% 13% 4 11% 6% 6% 6% 5% 6% 7% 27%	5783
June	1st to 10th	Day	14% 12% 4 11% 8% 7% 5% 5% 6% 6% 22%	3375
	11th to 20th	Day	14% 12% 4 11% 7% 6% 6% 5% 6% 8% 21%	3420
	21st to end	Day	11% 9% 4 10% 8% 7% 7% 5% 7% 9% 23%	3420
July	1st to 10th	Day	9% 7% 3 8% 6% 7% 7% 5% 9% 8% 30%	5700
	11th to 20th	Day	15% 12% 5% 12% 8% 7% 7% 5% 6% 6% 17%	5308
	21st to end	Day	11% 9% 4 11% 8% 7% 6% 5% 7% 8% 24%	5486
August	1st to 10th	Day	8% 7% 3 8% 5% 5% 5% 4 6% 7% 45%	4992
	11th to 20th	Day	15% 8% 3 8% 5% 5% 5% 4 6% 8% 33%	4340
	21st to end	Day	18% 11% 4 9% 5% 6% 6% 5% 6% 8% 22%	4825
September	1st to 10th	Day	17% 13% 5% 12% 6% 6% 6% 4 6% 6% 20%	2349
	11th to 20th	Day	13% 10% 4 11% 6% 5% 6% 5% 6% 7% 27%	2252
	21st to end	Day	14% 15% 6% 12% 7% 5% 6% 4 5% 5% 19%	2065
October	1st to 10th	Day	11% 16% 5% 10% 8% 8% 7% 5% 6% 7% 16%	3095
	11th to 20th	Day	8% 14% 6% 14% 6% 5% 5% 4 6% 6% 24%	2843
	21st to end	Day	6% 18% 6% 15% 8% 8% 7% 5% 7% 6% 15%	2742
November	1st to 10th	Day	7% 16% 7% 16% 9% 8% 6% 6% 6% 7% 13%	1372
	11th to 20th	Day	7% 18% 6% 17% 11% 7% 6% 5% 5% 7% 11%	1223
	21st to end	Day	5% 14% 8% 17% 9% 9% 5% 5% 10% 6% 11%	969
December	1st to 10th	Day	7% 13% 5% 17% 10% 11% 7% 5% 7% 7% 11%	950
	11th to 20th	Day	4 15% 6% 12% 9% 6% 8% 5% 9% 9% 18%	999
	21st to end	Day	6% 17% 6% 15% 8% 8% 7% 6% 8% 6% 15%	1386
January	1st to 10th	Night	4 16% 6% 17% 13% 15% 9% 3 4 4 9%	5611
	11th to 20th	Night	5% 16% 6% 14% 7% 5% 6% 5% 6% 8% 21%	5016
	21st to end	Night	9% 22% 7% 16% 8% 6% 5% 4 5% 5% 12%	5566
February	1st to 10th	Night	5% 15% 6% 13% 8% 6% 7% 5% 7% 9% 18%	2816
	11th to 20th	Night	3 16% 6% 13% 9% 8% 7% 5% 7% 7% 19%	2587
	21st to end	Night	3 12% 5% 13% 9% 6% 6% 4 7% 7% 29%	2099
March	1st to 10th	Night	2 9% 5% 13% 8% 8% 6% 5% 7% 8% 28%	3738
	11th to 20th	Night	4 15% 7% 14% 9% 8% 6% 5% 6% 6% 21%	3721
	21st to end	Night	2 12% 7% 16% 8% 8% 8% 5% 7% 7% 20%	3477
April	1st to 10th	Night	3 11% 5% 15% 7% 7% 7% 5% 7% 7% 27%	1854
	11th to 20th	Night	3 11% 4 10% 7% 6% 6% 5% 8% 8% 32%	1541
	21st to end	Night	4 13% 4 9% 7% 8% 6% 4 7% 8% 29%	1483
May	1st to 10th	Night	7% 11% 5% 10% 6% 5% 5% 4 6% 8% 33%	2092
	11th to 20th	Night	5% 12% 6% 13% 8% 6% 7% 4 6% 7% 25%	1882
	21st to end	Night	6% 8% 3 9% 5% 5% 6% 5% 8% 9% 35%	1790
June	1st to 10th	Night	9% 7% 3 7% 8% 6% 7% 5% 8% 9% 31%	803
	11th to 20th	Night	11% 10% 4 7% 7% 5% 6% 5% 6% 10% 28%	760
	21st to end	Night	9% 8% 2 6% 8% 5% 8% 6% 8% 9% 31%	760
July	1st to 10th	Night	8% 6% 3 7% 5% 6% 5% 5% 9% 12% 33%	1260
	11th to 20th	Night	13% 11% 5% 10% 7% 7% 6% 5% 6% 9% 21%	1651
	21st to end	Night	13% 8% 3 8% 6% 6% 6% 5% 8% 9% 27%	2066
August	1st to 10th	Night	7% 5% 2 6% 4 3 4 5% 7% 8% 48%	1937
	11th to 20th	Night	11% 7% 3 7% 5% 4 5% 4 7% 10% 37%	2498
	21st to end	Night	15% 13% 5% 12% 7% 6% 6% 5% 5% 5% 23%	2842
September	1st to 10th	Night	14% 12% 3 9% 6% 6% 6% 4 6% 7% 27%	1829
	11th to 20th	Night	9% 8% 3 9% 7% 6% 5% 5% 6% 7% 35%	1928
	21st to end	Night	14% 15% 5% 11% 7% 7% 6% 4 6% 6% 21%	2114
October	1st to 10th	Night	11% 14% 4 10% 7% 6% 6% 5% 8% 9% 21%	3875
	11th to 20th	Night	10% 18% 6% 13% 7% 7% 6% 4 6% 6% 18%	4085
	21st to end	Night	8% 16% 4 13% 8% 6% 6% 5% 7% 8% 20%	4812
November	1st to 10th	Night	7% 15% 7% 14% 9% 8% 7% 6% 6% 7% 14%	2926
	11th to 20th	Night	6% 17% 7% 15% 9% 7% 8% 6% 7% 6% 12%	2977
	21st to end	Night	6% 18% 7% 18% 10% 7% 6% 5% 6% 6% 11%	3192
December	1st to 10th	Night	5% 18% 7% 16% 11% 8% 6% 6% 6% 7% 9%	3230
	11th to 20th	Night	4 17% 6% 17% 10% 8% 7% 4 7% 7% 14%	4192
	21st to end	Night	6% 17% 5% 12% 9% 8% 7% 6% 6% 6% 16%	6270

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	72% 8% 6% 5% 8% 2	1364
	11th to 20th	Day	64% 7% 6% 8% 13% 2	1900
	21st to end	Day	70% 9% 9% 8% 4 1	2090
February	1st to 10th	Day	55% 8% 11% 14% 9% 2	1362
	11th to 20th	Day	60% 8% 14% 11% 7% 1	1488
	21st to end	Day	53% 11% 15% 15% 6% 1	1352
March	1st to 10th	Day	56% 9% 10% 15% 9% 1	3126
	11th to 20th	Day	56% 12% 15% 13% 5%	3233
	21st to end	Day	53% 15% 15% 11% 4	4165
April	1st to 10th	Day	60% 10% 15% 11% 3	2326
	11th to 20th	Day	57% 9% 13% 15% 6%	2586
	21st to end	Day	53% 12% 16% 15% 4	2697
May	1st to 10th	Day	52% 10% 14% 20% 3	4868
	11th to 20th	Day	54% 13% 13% 16% 5%	5016
	21st to end	Day	49% 11% 14% 20% 6%	5784
June	1st to 10th	Day	60% 9% 12% 14% 4	3375
	11th to 20th	Day	58% 10% 14% 15% 3	3420
	21st to end	Day	55% 13% 16% 13% 3	3420
July	1st to 10th	Day	45% 12% 22% 19% 2	5611
	11th to 20th	Day	64% 11% 14% 11%	5212
	21st to end	Day	54% 12% 19% 14% 1	5313
August	1st to 10th	Day	38% 8% 17% 21% 13% 2	4973
	11th to 20th	Day	47% 10% 20% 18% 5%	4382
	21st to end	Day	59% 10% 15% 15% 1	4824
September	1st to 10th	Day	63% 11% 12% 10% 3	2349
	11th to 20th	Day	54% 10% 15% 17% 3	2252
	21st to end	Day	65% 9% 12% 11% 2	2065
October	1st to 10th	Day	65% 9% 11% 14% 1	3095
	11th to 20th	Day	59% 8% 16% 16% 1	2843
	21st to end	Day	65% 12% 15% 7% 1	2742
November	1st to 10th	Day	68% 10% 11% 9% 2	1372
	11th to 20th	Day	71% 7% 10% 10% 1	1223
	21st to end	Day	65% 11% 11% 8% 5%	969
December	1st to 10th	Day	67% 11% 11% 8% 2	950
	11th to 20th	Day	57% 8% 10% 17% 8%	1001
	21st to end	Day	62% 11% 8% 13% 5% 1	1386
January	1st to 10th	Night	77% 8% 6% 5% 4 1	5611
	11th to 20th	Night	57% 8% 7% 11% 14% 3	5060
	21st to end	Night	72% 8% 7% 8% 4	5566
February	1st to 10th	Night	60% 8% 9% 13% 9% 2	2816
	11th to 20th	Night	60% 9% 13% 11% 6% 1	2590
	21st to end	Night	50% 9% 17% 14% 8% 1	2099
March	1st to 10th	Night	49% 8% 11% 22% 9% 1	3738
	11th to 20th	Night	58% 11% 14% 12% 5% 1	3723
	21st to end	Night	55% 13% 17% 10% 5%	3477
April	1st to 10th	Night	52% 9% 16% 17% 5%	1854
	11th to 20th	Night	46% 11% 17% 19% 6% 1	1541
	21st to end	Night	49% 10% 17% 20% 4	1483
May	1st to 10th	Night	46% 10% 15% 26% 3	2092
	11th to 20th	Night	47% 15% 15% 17% 5% 1	1882
	21st to end	Night	37% 11% 16% 27% 8%	1790
June	1st to 10th	Night	46% 13% 17% 20% 3	803
	11th to 20th	Night	49% 10% 18% 18% 4	760
	21st to end	Night	44% 16% 20% 18% 2	760
July	1st to 10th	Night	40% 10% 28% 19% 3	1240
	11th to 20th	Night	56% 13% 17% 12% 3	1624
	21st to end	Night	49% 12% 22% 17% 1	2000
August	1st to 10th	Night	31% 11% 19% 24% 13% 1	1931
	11th to 20th	Night	40% 12% 20% 22% 6%	2522
	21st to end	Night	62% 9% 12% 15% 2	2842
September	1st to 10th	Night	55% 12% 18% 14% 1	1829
	11th to 20th	Night	47% 11% 19% 20% 3	1928
	21st to end	Night	63% 9% 11% 13% 4	2114
October	1st to 10th	Night	56% 11% 15% 16% 2	3875
	11th to 20th	Night	65% 9% 12% 13% 1	4085
	21st to end	Night	58% 12% 16% 13% 2	4812
November	1st to 10th	Night	65% 11% 12% 10% 2	2926
	11th to 20th	Night	68% 10% 10% 10% 2	2977
	21st to end	Night	70% 8% 10% 9% 2	3192
December	1st to 10th	Night	70% 10% 9% 8% 2	3230
	11th to 20th	Night	66% 7% 10% 10% 6%	4189
	21st to end	Night	61% 11% 8% 10% 8% 2	6270

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	3 11% 15% 39% 27% 6%	103
	11th to 20th	Day	13% 4 19% 29% 24% 10%	180
	21st to end	Day	15% 17% 20% 21% 22% 5%	198
February	1st to 10th	Day	12% 7% 24% 33% 20% 5%	335
	11th to 20th	Day	10% 11% 27% 28% 17% 7%	365
	21st to end	Day	8% 11% 28% 32% 16% 6%	307
March	1st to 10th	Day	6% 11% 28% 32% 15% 8%	370
	11th to 20th	Day	8% 12% 33% 27% 19% 2	379
	21st to end	Day	7% 11% 26% 29% 21% 6%	506
April	1st to 10th	Day	9% 15% 30% 25% 16% 3	460
	11th to 20th	Day	9% 11% 26% 30% 20% 5%	600
	21st to end	Day	11% 13% 26% 28% 17% 4	650
May	1st to 10th	Day	15% 15% 27% 26% 14% 3	653
	11th to 20th	Day	13% 13% 25% 25% 17% 6%	675
	21st to end	Day	12% 11% 25% 26% 22% 5%	892
June	1st to 10th	Day	16% 10% 24% 26% 21% 4	870
	11th to 20th	Day	17% 8% 23% 27% 21% 5%	870
	21st to end	Day	13% 7% 20% 29% 23% 7%	870
July	1st to 10th	Day	16% 7% 19% 28% 24% 6%	856
	11th to 20th	Day	21% 10% 19% 24% 21% 6%	749
	21st to end	Day	16% 11% 19% 24% 20% 9%	739
August	1st to 10th	Day	15% 8% 22% 26% 20% 9%	676
	11th to 20th	Day	25% 15% 24% 21% 11% 4	665
	21st to end	Day	23% 11% 22% 26% 14% 3	726
September	1st to 10th	Day	22% 15% 24% 20% 14% 5%	490
	11th to 20th	Day	17% 12% 25% 22% 18% 7%	490
	21st to end	Day	25% 16% 26% 20% 11% 3	476
October	1st to 10th	Day	24% 17% 26% 21% 9% 2	390
	11th to 20th	Day	23% 16% 29% 20% 10% 2	390
	21st to end	Day	12% 11% 23% 32% 18% 4	380
November	1st to 10th	Day	12% 12% 26% 30% 16% 5%	200
	11th to 20th	Day	10% 7% 24% 34% 14% 10%	182
	21st to end	Day	13% 10% 24% 29% 15% 9%	180
December	1st to 10th	Day	10% 6% 21% 36% 19% 7%	180
	11th to 20th	Day	7% 7% 23% 27% 27% 7%	107
	21st to end	Day	8% 12% 17% 29% 23% 10%	99
January	1st to 10th	Night	12% 4 25% 34% 21% 4	1020
	11th to 20th	Night	15% 8% 25% 33% 18% 2	850
	21st to end	Night	13% 10% 26% 34% 15% 3	935
February	1st to 10th	Night	12% 7% 23% 38% 18% 2	850
	11th to 20th	Night	9% 8% 27% 36% 18% 2	834
	21st to end	Night	7% 6% 27% 38% 18% 4	696
March	1st to 10th	Night	7% 7% 24% 33% 26% 3	760
	11th to 20th	Night	7% 7% 27% 31% 26% 2	740
	21st to end	Night	6% 6% 18% 33% 28% 9%	627
April	1st to 10th	Night	7% 6% 17% 33% 32% 5%	570
	11th to 20th	Night	6% 7% 20% 35% 28% 4	563
	21st to end	Night	9% 5% 21% 29% 31% 5%	533
May	1st to 10th	Night	12% 7% 21% 31% 26% 5%	380
	11th to 20th	Night	12% 5% 20% 30% 30% 3	374
	21st to end	Night	9% 4 20% 29% 34% 4	411
June	1st to 10th	Night	12% 3 18% 36% 30% 1	233
	11th to 20th	Night	17% 2 17% 33% 28% 3	190
	21st to end	Night	13% 4 15% 29% 37% 2	190
July	1st to 10th	Night	14% 2 16% 30% 36% 2	185
	11th to 20th	Night	15% 7% 19% 29% 26% 4	301
	21st to end	Night	13% 4 20% 29% 27% 6%	416
August	1st to 10th	Night	12% 4 20% 29% 31% 3	379
	11th to 20th	Night	19% 8% 19% 30% 19% 5%	564
	21st to end	Night	25% 4 18% 28% 22% 3	627
September	1st to 10th	Night	19% 7% 22% 29% 20% 3	570
	11th to 20th	Night	13% 6% 20% 29% 26% 5%	598
	21st to end	Night	25% 9% 23% 26% 14% 3	760
October	1st to 10th	Night	21% 10% 22% 30% 15% 2	760
	11th to 20th	Night	24% 10% 20% 30% 15% 2	760
	21st to end	Night	15% 9% 23% 33% 15% 4	921
November	1st to 10th	Night	14% 6% 25% 38% 15% 3	880
	11th to 20th	Night	13% 7% 21% 31% 23% 5%	855
	21st to end	Night	14% 8% 25% 33% 16% 4	1002
December	1st to 10th	Night	13% 8% 25% 33% 19% 2	1040
	11th to 20th	Night	13% 6% 21% 38% 18% 4	1040
	21st to end	Night	14% 8% 23% 31% 18% 5%	1144

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