McBride
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McBride clear sky chart from 2005-11-06 to 2026-06-01.

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% 12% 4 11% 7% 6% 6% 5% 6% 7% 26%	135563
	Night	7% 13% 5% 11% 7% 7% 7% 5% 7% 7% 25%	136247
Transparency	Day	52% 10% 17% 14% 5% 1	135255
	Night	53% 11% 18% 13% 4	136134
Seeing	Day	19% 16% 30% 24% 10% 1	18282
	Night	19% 12% 32% 26% 11% 1	26471

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	2 13% 5% 15% 10% 9% 9% 6% 7% 7% 15%	3564
	11th to 20th	Day	4 9% 5% 11% 6% 6% 7% 5% 6% 7% 33%	4119
	21st to end	Day	4 11% 4 10% 8% 7% 7% 5% 7% 10% 26%	4905
February	1st to 10th	Day	6% 18% 7% 13% 7% 7% 5% 6% 5% 6% 20%	1680
	11th to 20th	Day	3 18% 8% 15% 8% 7% 7% 4 6% 5% 20%	1808
	21st to end	Day	1 13% 6% 18% 11% 7% 7% 5% 6% 6% 21%	1625
March	1st to 10th	Day	1 12% 5% 13% 9% 9% 9% 7% 7% 8% 21%	4618
	11th to 20th	Day	3 12% 6% 12% 7% 7% 6% 6% 7% 10% 25%	4902
	21st to end	Day	3 14% 6% 14% 8% 7% 8% 5% 6% 7% 22%	6006
April	1st to 10th	Day	4 18% 7% 17% 8% 8% 6% 4 7% 6% 14%	2520
	11th to 20th	Day	4 17% 6% 13% 8% 7% 7% 4 6% 7% 21%	2620
	21st to end	Day	6% 16% 6% 13% 7% 6% 6% 4 6% 7% 23%	2940
May	1st to 10th	Day	10% 13% 4 10% 6% 6% 5% 4 6% 8% 28%	6460
	11th to 20th	Day	12% 14% 5% 12% 8% 6% 6% 5% 7% 8% 18%	6510
	21st to end	Day	15% 14% 5% 10% 6% 6% 5% 5% 6% 7% 21%	7983
June	1st to 10th	Day	16% 11% 4 9% 7% 6% 6% 5% 6% 7% 23%	3201
	11th to 20th	Day	20% 14% 5% 11% 7% 7% 6% 4 6% 5% 15%	3200
	21st to end	Day	16% 12% 4 11% 7% 6% 6% 4 6% 7% 23%	3200
July	1st to 10th	Day	12% 5% 2 6% 5% 5% 6% 5% 8% 8% 38%	7240
	11th to 20th	Day	11% 6% 3 7% 5% 6% 5% 4 6% 7% 40%	7070
	21st to end	Day	12% 6% 2 7% 6% 5% 6% 5% 7% 9% 36%	7181
August	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 7% 44%	4541
	11th to 20th	Day	11% 7% 2 8% 5% 6% 7% 5% 7% 7% 34%	4470
	21st to end	Day	17% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	4604
September	1st to 10th	Day	13% 11% 4 10% 6% 5% 4 3 5% 6% 31%	2400
	11th to 20th	Day	12% 11% 4 10% 6% 6% 5% 3 5% 8% 32%	2400
	21st to end	Day	17% 13% 3 11% 6% 7% 5% 4 5% 6% 22%	2141
October	1st to 10th	Day	15% 12% 3 9% 6% 6% 6% 5% 6% 8% 24%	3280
	11th to 20th	Day	14% 13% 4 10% 6% 6% 5% 5% 6% 8% 22%	3107
	21st to end	Day	6% 14% 5% 10% 6% 7% 7% 6% 7% 6% 27%	3145
November	1st to 10th	Day	10% 19% 6% 13% 8% 7% 6% 4 7% 5% 15%	1648
	11th to 20th	Day	6% 15% 6% 15% 9% 8% 8% 6% 6% 6% 16%	1554
	21st to end	Day	4 19% 7% 14% 9% 8% 6% 6% 6% 6% 14%	1470
December	1st to 10th	Day	5% 12% 5% 13% 9% 9% 9% 7% 7% 8% 17%	2071
	11th to 20th	Day	2 16% 5% 12% 8% 8% 9% 6% 7% 7% 18%	2322
	21st to end	Day	2 14% 5% 13% 7% 8% 7% 5% 9% 8% 22%	3058
January	1st to 10th	Night	3 12% 6% 16% 10% 9% 10% 7% 7% 7% 13%	9366
	11th to 20th	Night	3 12% 5% 11% 7% 7% 7% 5% 7% 6% 30%	8800
	21st to end	Night	4 14% 6% 13% 8% 7% 7% 4 6% 6% 25%	9262
February	1st to 10th	Night	6% 19% 8% 13% 10% 6% 6% 4 6% 7% 16%	2940
	11th to 20th	Night	5% 17% 8% 14% 8% 6% 5% 5% 6% 7% 17%	2697
	21st to end	Night	2 15% 7% 16% 9% 6% 7% 5% 6% 7% 21%	2181
March	1st to 10th	Night	2 11% 5% 12% 10% 8% 8% 6% 9% 8% 21%	5496
	11th to 20th	Night	4 12% 5% 12% 7% 8% 8% 6% 8% 9% 20%	5304
	21st to end	Night	4 15% 5% 11% 6% 5% 6% 5% 8% 8% 28%	5210
April	1st to 10th	Night	4 15% 6% 12% 7% 7% 7% 6% 6% 8% 23%	2100
	11th to 20th	Night	3 13% 6% 9% 8% 6% 7% 6% 7% 9% 26%	1945
	21st to end	Night	7% 16% 4 10% 6% 6% 5% 5% 5% 6% 29%	1680
May	1st to 10th	Night	7% 12% 4 8% 5% 6% 6% 4 8% 9% 30%	3720
	11th to 20th	Night	11% 12% 4 10% 7% 5% 6% 4 7% 8% 26%	3603
	21st to end	Night	13% 13% 4 10% 5% 5% 5% 4 6% 7% 27%	3131
June	1st to 10th	Night	14% 10% 4 9% 6% 6% 7% 5% 6% 6% 29%	1200
	11th to 20th	Night	19% 12% 4 8% 6% 5% 6% 5% 6% 8% 21%	1200
	21st to end	Night	12% 7% 3 9% 5% 6% 6% 4 8% 9% 30%	1200
July	1st to 10th	Night	12% 6% 2 5% 5% 4 5% 4 6% 7% 45%	2720
	11th to 20th	Night	11% 5% 2 7% 5% 5% 5% 4 4 7% 47%	2874
	21st to end	Night	11% 5% 2 5% 4 6% 6% 5% 7% 7% 43%	3648
August	1st to 10th	Night	8% 5% 2 6% 5% 4 4 4 6% 8% 48%	2609
	11th to 20th	Night	11% 6% 3 7% 5% 5% 5% 4 6% 9% 40%	2577
	21st to end	Night	17% 7% 3 7% 5% 4 5% 4 6% 7% 34%	3305
September	1st to 10th	Night	16% 8% 4 9% 5% 4 5% 4 5% 7% 35%	2000
	11th to 20th	Night	12% 10% 3 8% 5% 4 4 3 5% 6% 38%	2000
	21st to end	Night	20% 12% 4 8% 5% 4 5% 4 5% 6% 28%	2255
October	1st to 10th	Night	12% 13% 3 9% 5% 6% 7% 5% 7% 8% 25%	3920
	11th to 20th	Night	12% 12% 3 8% 5% 5% 6% 5% 7% 11% 25%	4046
	21st to end	Night	7% 15% 5% 11% 7% 8% 6% 5% 6% 7% 24%	4652
November	1st to 10th	Night	11% 17% 5% 13% 9% 9% 7% 5% 6% 5% 13%	2870
	11th to 20th	Night	7% 17% 7% 14% 9% 8% 7% 6% 6% 6% 15%	3044
	21st to end	Night	5% 19% 7% 14% 8% 7% 7% 5% 7% 6% 13%	3150
December	1st to 10th	Night	6% 14% 5% 13% 8% 8% 7% 6% 7% 9% 18%	5312
	11th to 20th	Night	3 16% 7% 14% 10% 7% 7% 6% 7% 7% 16%	6090
	21st to end	Night	2 13% 6% 14% 8% 7% 7% 6% 8% 9% 21%	8140

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	61% 13% 16% 8% 3	3564
	11th to 20th	Day	48% 12% 19% 12% 6% 4	4140
	21st to end	Day	52% 15% 19% 11% 2	4906
February	1st to 10th	Day	62% 7% 10% 9% 10% 1	1680
	11th to 20th	Day	63% 7% 14% 11% 5% 1	1817
	21st to end	Day	61% 8% 12% 12% 5% 2	1625
March	1st to 10th	Day	55% 10% 16% 12% 7%	4618
	11th to 20th	Day	49% 10% 17% 18% 5%	4902
	21st to end	Day	56% 11% 12% 12% 8%	6006
April	1st to 10th	Day	67% 9% 14% 9% 2	2520
	11th to 20th	Day	59% 9% 16% 13% 3	2620
	21st to end	Day	57% 8% 17% 14% 3	2940
May	1st to 10th	Day	50% 8% 20% 19% 3	6460
	11th to 20th	Day	57% 11% 18% 11% 3	6513
	21st to end	Day	56% 11% 22% 10% 2	7984
June	1st to 10th	Day	57% 8% 15% 13% 7% 1	3201
	11th to 20th	Day	67% 8% 12% 11% 2	3200
	21st to end	Day	58% 9% 14% 15% 4 1	3200
July	1st to 10th	Day	39% 11% 14% 19% 15% 2	7161
	11th to 20th	Day	40% 9% 16% 26% 8% 1	6983
	21st to end	Day	40% 11% 21% 18% 10% 1	6978
August	1st to 10th	Day	35% 8% 17% 29% 11%	4524
	11th to 20th	Day	43% 12% 18% 21% 6%	4512
	21st to end	Day	48% 9% 22% 16% 4 1	4603
September	1st to 10th	Day	53% 6% 16% 17% 6% 1	2400
	11th to 20th	Day	50% 8% 18% 16% 7% 1	2400
	21st to end	Day	62% 8% 12% 12% 5% 1	2141
October	1st to 10th	Day	55% 14% 19% 10% 2	3280
	11th to 20th	Day	57% 9% 23% 10% 1	3107
	21st to end	Day	53% 11% 25% 9% 2	3145
November	1st to 10th	Day	66% 9% 13% 8% 2	1648
	11th to 20th	Day	64% 11% 13% 7% 4 1	1554
	21st to end	Day	65% 11% 11% 6% 5% 1	1470
December	1st to 10th	Day	63% 15% 14% 7% 2	2071
	11th to 20th	Day	60% 11% 17% 8% 3	2324
	21st to end	Day	54% 10% 24% 11% 2	3058
January	1st to 10th	Night	60% 14% 15% 8% 2	9367
	11th to 20th	Night	50% 9% 19% 12% 7% 3	8841
	21st to end	Night	58% 12% 16% 12% 2	9262
February	1st to 10th	Night	66% 6% 9% 10% 9%	2940
	11th to 20th	Night	63% 8% 13% 12% 5%	2699
	21st to end	Night	59% 8% 12% 14% 5% 1	2181
March	1st to 10th	Night	51% 12% 16% 13% 7%	5496
	11th to 20th	Night	52% 9% 18% 16% 4	5305
	21st to end	Night	47% 10% 19% 16% 8%	5210
April	1st to 10th	Night	56% 9% 19% 12% 4	2100
	11th to 20th	Night	50% 10% 18% 17% 4	1945
	21st to end	Night	52% 9% 15% 19% 5%	1680
May	1st to 10th	Night	46% 8% 22% 19% 4	3717
	11th to 20th	Night	48% 12% 21% 15% 5%	3603
	21st to end	Night	49% 10% 26% 13% 2	3131
June	1st to 10th	Night	52% 8% 16% 17% 7%	1200
	11th to 20th	Night	58% 8% 19% 13% 2	1200
	21st to end	Night	48% 10% 21% 16% 4	1200
July	1st to 10th	Night	36% 11% 19% 20% 13% 1	2690
	11th to 20th	Night	37% 8% 15% 32% 7% 1	2838
	21st to end	Night	34% 12% 24% 22% 7% 1	3546
August	1st to 10th	Night	31% 9% 21% 33% 6%	2601
	11th to 20th	Night	36% 12% 23% 25% 4	2601
	21st to end	Night	47% 10% 27% 10% 5% 1	3305
September	1st to 10th	Night	50% 7% 17% 20% 6% 2	2000
	11th to 20th	Night	45% 7% 16% 25% 7% 1	2000
	21st to end	Night	56% 9% 15% 13% 7%	2255
October	1st to 10th	Night	52% 15% 18% 12% 3	3920
	11th to 20th	Night	50% 12% 24% 13% 2	4046
	21st to end	Night	53% 14% 23% 7% 3	4652
November	1st to 10th	Night	69% 10% 11% 7% 2	2870
	11th to 20th	Night	66% 10% 12% 7% 4 1	3044
	21st to end	Night	67% 9% 11% 7% 4 1	3150
December	1st to 10th	Night	59% 17% 14% 7% 3	5312
	11th to 20th	Night	61% 12% 15% 8% 3	6087
	21st to end	Night	54% 11% 22% 10% 2	8140

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	11% 18% 39% 25% 5% 2	220
	11th to 20th	Day	20% 17% 33% 24% 4 2	220
	21st to end	Day	18% 19% 39% 18% 5% 2	242
February	1st to 10th	Day	21% 16% 35% 19% 8% 1	220
	11th to 20th	Day	16% 19% 37% 21% 7% 1	388
	21st to end	Day	13% 25% 37% 18% 7% 1	391
March	1st to 10th	Day	16% 21% 33% 21% 8% 1	540
	11th to 20th	Day	15% 23% 35% 19% 8% 1	540
	21st to end	Day	16% 25% 27% 19% 10% 2	594
April	1st to 10th	Day	19% 21% 33% 23% 5% 1	540
	11th to 20th	Day	16% 22% 32% 21% 8% 2	532
	21st to end	Day	18% 20% 31% 20% 10% 2	540
May	1st to 10th	Day	20% 17% 27% 24% 11% 1	543
	11th to 20th	Day	15% 12% 26% 29% 17% 2	609
	21st to end	Day	18% 13% 25% 26% 15% 3	1023
June	1st to 10th	Day	20% 15% 32% 26% 8%	931
	11th to 20th	Day	28% 11% 26% 23% 12% 1	930
	21st to end	Day	22% 13% 25% 26% 12% 2	930
July	1st to 10th	Day	20% 9% 29% 29% 13% 1	916
	11th to 20th	Day	20% 10% 28% 29% 12% 1	846
	21st to end	Day	17% 12% 26% 34% 10% 1	713
August	1st to 10th	Day	12% 12% 29% 32% 12% 3	527
	11th to 20th	Day	17% 14% 33% 25% 9% 1	517
	21st to end	Day	20% 13% 29% 22% 13% 3	583
September	1st to 10th	Day	22% 14% 25% 24% 13% 2	530
	11th to 20th	Day	20% 11% 30% 26% 12% 1	530
	21st to end	Day	34% 19% 27% 15% 6% 1	530
October	1st to 10th	Day	26% 17% 26% 22% 8% 1	530
	11th to 20th	Day	26% 18% 31% 18% 6% 1	440
	21st to end	Day	26% 16% 33% 20% 4 1	345
November	1st to 10th	Day	30% 20% 31% 15% 3 1	220
	11th to 20th	Day	19% 19% 40% 15% 6% 1	220
	21st to end	Day	17% 15% 36% 19% 7% 5%	220
December	1st to 10th	Day	15% 17% 36% 20% 10% 2	220
	11th to 20th	Day	18% 18% 33% 23% 5% 2	220
	21st to end	Day	10% 22% 40% 16% 12% 1	242
January	1st to 10th	Night	20% 16% 39% 21% 4 1	1160
	11th to 20th	Night	22% 15% 39% 20% 4 1	958
	21st to end	Night	20% 17% 38% 21% 4	975
February	1st to 10th	Night	23% 13% 34% 22% 8%	840
	11th to 20th	Night	17% 10% 39% 27% 8%	824
	21st to end	Night	11% 12% 39% 27% 11% 1	692
March	1st to 10th	Night	14% 14% 36% 25% 10%	840
	11th to 20th	Night	12% 14% 39% 25% 9% 1	840
	21st to end	Night	13% 10% 35% 28% 12% 1	924
April	1st to 10th	Night	14% 12% 29% 32% 12% 1	840
	11th to 20th	Night	10% 11% 33% 31% 14% 1	697
	21st to end	Night	18% 10% 28% 28% 15% 1	420
May	1st to 10th	Night	17% 6% 29% 30% 17%	420
	11th to 20th	Night	17% 7% 23% 32% 19% 1	414
	21st to end	Night	16% 7% 28% 27% 20% 2	455
June	1st to 10th	Night	20% 6% 24% 35% 14% 1	400
	11th to 20th	Night	27% 4 22% 29% 18% 1	400
	21st to end	Night	16% 7% 23% 32% 21% 2	400
July	1st to 10th	Night	19% 5% 21% 34% 21% 1	390
	11th to 20th	Night	20% 4 18% 34% 23% 1	388
	21st to end	Night	14% 4 13% 41% 26% 1	438
August	1st to 10th	Night	12% 4 16% 37% 29% 2	398
	11th to 20th	Night	15% 5% 18% 38% 22% 2	396
	21st to end	Night	24% 7% 19% 29% 20%	694
September	1st to 10th	Night	23% 5% 21% 35% 15% 1	800
	11th to 20th	Night	17% 9% 19% 34% 20% 2	800
	21st to end	Night	33% 11% 25% 21% 10% 1	800
October	1st to 10th	Night	25% 10% 26% 28% 10% 1	800
	11th to 20th	Night	22% 12% 34% 24% 9%	800
	21st to end	Night	25% 15% 34% 20% 6% 1	880
November	1st to 10th	Night	26% 17% 32% 19% 5%	820
	11th to 20th	Night	22% 19% 36% 18% 5%	944
	21st to end	Night	20% 16% 38% 20% 5% 1	1050
December	1st to 10th	Night	18% 13% 41% 22% 6% 1	1138
	11th to 20th	Night	19% 16% 39% 20% 6%	1160
	21st to end	Night	14% 17% 42% 21% 7%	1276

Page generated at 2026-05-28 22:53:32. Version ac07

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