Biggar
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Biggar clear sky chart from 2005-11-06 to 2026-07-01.

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	8% 8% 3 9% 6% 5% 5% 4 6% 8% 37%	141312
	Night	7% 8% 3 9% 6% 6% 6% 4 7% 8% 36%	139730
Transparency	Day	43% 7% 16% 24% 9% 1	141012
	Night	45% 7% 15% 22% 10% 1	139616
Seeing	Day	12% 9% 28% 29% 17% 5%	17916
	Night	11% 8% 31% 35% 14% 2	27146

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	6% 11% 5% 13% 9% 7% 6% 5% 7% 7% 24%	4125
	11th to 20th	Day	3 5% 2 11% 8% 8% 8% 5% 6% 9% 35%	4119
	21st to end	Day	6% 11% 4 11% 8% 6% 5% 4 7% 8% 30%	4650
February	1st to 10th	Day	7% 13% 5% 12% 8% 7% 6% 4 7% 8% 23%	1827
	11th to 20th	Day	6% 12% 5% 10% 7% 6% 5% 5% 7% 7% 29%	1845
	21st to end	Day	5% 10% 4 11% 8% 7% 9% 5% 7% 8% 25%	1557
March	1st to 10th	Day	4 10% 4 12% 8% 7% 6% 5% 7% 9% 29%	4647
	11th to 20th	Day	4 12% 6% 18% 7% 5% 4 3 5% 8% 28%	5109
	21st to end	Day	8% 12% 5% 16% 6% 5% 5% 4 5% 7% 27%	5781
April	1st to 10th	Day	8% 11% 4 9% 6% 5% 5% 4 6% 8% 34%	2520
	11th to 20th	Day	10% 13% 4 10% 5% 5% 5% 5% 6% 7% 28%	2659
	21st to end	Day	12% 11% 3 8% 5% 5% 5% 4 6% 7% 33%	2871
May	1st to 10th	Day	10% 8% 3 7% 5% 5% 5% 4 6% 7% 41%	8224
	11th to 20th	Day	13% 9% 4 9% 6% 6% 6% 5% 7% 8% 27%	8279
	21st to end	Day	9% 6% 3 7% 5% 5% 6% 4 7% 9% 39%	9649
June	1st to 10th	Day	13% 6% 3 8% 5% 5% 5% 4 6% 9% 36%	3282
	11th to 20th	Day	19% 7% 2 7% 5% 5% 6% 5% 7% 7% 29%	3360
	21st to end	Day	12% 6% 2 7% 5% 5% 6% 4 8% 9% 35%	3335
July	1st to 10th	Day	7% 5% 2 5% 4 4 5% 4 7% 9% 48%	6781
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 41%	6780
	21st to end	Day	6% 3 1 4 4 3 4 4 7% 10% 55%	7360
August	1st to 10th	Day	12% 6% 2 5% 5% 5% 5% 4 6% 7% 46%	4552
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 7% 11% 46%	4291
	21st to end	Day	10% 5% 1 4 3 4 4 4 6% 8% 51%	4635
September	1st to 10th	Day	10% 5% 2 6% 4 4 5% 3 7% 8% 47%	2400
	11th to 20th	Day	14% 7% 2 7% 4 4 4 4 5% 7% 42%	2400
	21st to end	Day	9% 4 2 5% 4 4 4 3 5% 8% 53%	2105
October	1st to 10th	Day	7% 7% 3 5% 3 5% 4 4 6% 8% 48%	3270
	11th to 20th	Day	6% 5% 2 6% 4 5% 5% 4 8% 13% 42%	3250
	21st to end	Day	5% 8% 4 9% 6% 5% 6% 4 7% 7% 39%	3020
November	1st to 10th	Day	12% 15% 4 10% 6% 4 5% 3 4 6% 31%	1648
	11th to 20th	Day	8% 12% 5% 14% 7% 6% 6% 4 5% 8% 25%	1680
	21st to end	Day	7% 12% 5% 13% 8% 6% 7% 5% 6% 7% 26%	1622
December	1st to 10th	Day	5% 12% 4 12% 8% 7% 8% 5% 7% 7% 25%	2020
	11th to 20th	Day	7% 13% 5% 13% 7% 9% 8% 6% 6% 7% 18%	2319
	21st to end	Day	3 6% 3 9% 7% 9% 6% 4 7% 8% 38%	3340
January	1st to 10th	Night	6% 11% 5% 13% 8% 7% 7% 5% 8% 8% 23%	8768
	11th to 20th	Night	2 7% 4 11% 8% 8% 8% 5% 7% 10% 30%	8779
	21st to end	Night	5% 9% 5% 12% 6% 6% 7% 5% 7% 8% 31%	9536
February	1st to 10th	Night	7% 11% 4 12% 8% 6% 6% 5% 8% 9% 24%	2813
	11th to 20th	Night	6% 10% 4 12% 7% 5% 6% 6% 7% 8% 30%	2662
	21st to end	Night	3 9% 4 9% 8% 6% 6% 6% 7% 9% 33%	2249
March	1st to 10th	Night	4 9% 3 13% 9% 6% 6% 5% 7% 9% 29%	5447
	11th to 20th	Night	5% 10% 4 13% 7% 6% 6% 5% 7% 8% 29%	5110
	21st to end	Night	9% 11% 5% 13% 7% 5% 5% 4 6% 7% 29%	5427
April	1st to 10th	Night	6% 10% 3 8% 6% 5% 3 4 7% 8% 41%	2100
	11th to 20th	Night	8% 13% 3 10% 5% 6% 5% 6% 7% 7% 30%	1908
	21st to end	Night	11% 11% 4 8% 6% 4 5% 4 4 7% 36%	1748
May	1st to 10th	Night	11% 8% 3 5% 3 3 4 3 5% 6% 48%	4724
	11th to 20th	Night	14% 10% 4 9% 6% 6% 5% 5% 7% 7% 28%	4606
	21st to end	Night	9% 6% 3 8% 5% 5% 5% 5% 7% 9% 39%	4522
June	1st to 10th	Night	9% 7% 3 6% 4 5% 5% 5% 9% 9% 38%	1334
	11th to 20th	Night	19% 6% 2 7% 4 5% 5% 4 7% 8% 32%	1260
	21st to end	Night	10% 5% 1 6% 5% 5% 5% 5% 6% 10% 42%	1279
July	1st to 10th	Night	7% 4 1 5% 4 4 5% 5% 7% 10% 48%	3180
	11th to 20th	Night	8% 4 2 6% 5% 5% 5% 4 7% 9% 46%	3180
	21st to end	Night	5% 4 1 4 3 3 4 4 6% 9% 58%	3484
August	1st to 10th	Night	7% 5% 2 5% 4 4 4 3 6% 9% 51%	2608
	11th to 20th	Night	6% 4 2 6% 4 4 6% 4 8% 9% 48%	2764
	21st to end	Night	8% 5% 2 5% 3 4 4 4 5% 8% 52%	3274
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 6% 8% 52%	2000
	11th to 20th	Night	12% 5% 2 7% 3 4 4 3 5% 7% 47%	2000
	21st to end	Night	7% 6% 2 5% 2 3 4 3 6% 9% 53%	2291
October	1st to 10th	Night	8% 8% 3 7% 3 5% 4 4 5% 7% 46%	3920
	11th to 20th	Night	6% 5% 2 6% 4 4 4 3 5% 8% 53%	3898
	21st to end	Night	8% 7% 3 7% 5% 5% 5% 4 7% 7% 42%	4747
November	1st to 10th	Night	15% 14% 4 8% 6% 4 4 4 6% 6% 29%	2870
	11th to 20th	Night	6% 10% 5% 12% 8% 7% 5% 5% 6% 8% 28%	2940
	21st to end	Night	7% 11% 4 12% 7% 6% 5% 4 7% 9% 28%	2989
December	1st to 10th	Night	8% 13% 5% 14% 9% 7% 7% 4 7% 7% 21%	5380
	11th to 20th	Night	5% 13% 5% 13% 8% 8% 8% 6% 8% 8% 18%	6093
	21st to end	Night	2 7% 3 9% 9% 8% 6% 4 5% 6% 42%	7840

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	58% 6% 10% 18% 8%	4125
	11th to 20th	Day	45% 6% 15% 21% 12% 1	4140
	21st to end	Day	51% 6% 18% 16% 9%	4650
February	1st to 10th	Day	57% 7% 12% 16% 7%	1827
	11th to 20th	Day	52% 7% 12% 19% 10% 1	1854
	21st to end	Day	55% 7% 11% 19% 8%	1557
March	1st to 10th	Day	48% 6% 19% 19% 7%	4647
	11th to 20th	Day	55% 7% 15% 16% 7%	5110
	21st to end	Day	53% 7% 11% 22% 7%	5781
April	1st to 10th	Day	47% 7% 15% 20% 11%	2520
	11th to 20th	Day	52% 7% 14% 18% 8% 1	2659
	21st to end	Day	46% 8% 13% 24% 8% 1	2871
May	1st to 10th	Day	40% 5% 11% 26% 15% 3	8224
	11th to 20th	Day	51% 7% 11% 22% 9%	8283
	21st to end	Day	37% 9% 14% 28% 12% 1	9650
June	1st to 10th	Day	44% 7% 16% 21% 11% 1	3282
	11th to 20th	Day	51% 9% 13% 20% 7% 1	3360
	21st to end	Day	42% 10% 20% 21% 7%	3335
July	1st to 10th	Day	31% 7% 23% 29% 9%	6707
	11th to 20th	Day	37% 7% 16% 34% 6%	6699
	21st to end	Day	24% 7% 24% 34% 10% 1	7153
August	1st to 10th	Day	36% 7% 19% 30% 7%	4536
	11th to 20th	Day	30% 8% 21% 35% 7%	4333
	21st to end	Day	30% 6% 21% 34% 9%	4634
September	1st to 10th	Day	33% 8% 16% 26% 13% 3	2400
	11th to 20th	Day	41% 7% 17% 27% 7% 1	2400
	21st to end	Day	31% 5% 17% 34% 12% 2	2105
October	1st to 10th	Day	34% 5% 24% 27% 10%	3270
	11th to 20th	Day	34% 5% 19% 34% 8%	3250
	21st to end	Day	42% 7% 17% 28% 6%	3020
November	1st to 10th	Day	55% 6% 12% 18% 9%	1648
	11th to 20th	Day	57% 8% 15% 16% 5%	1680
	21st to end	Day	55% 8% 15% 17% 5%	1622
December	1st to 10th	Day	56% 9% 15% 13% 6% 1	2020
	11th to 20th	Day	65% 8% 15% 8% 5%	2320
	21st to end	Day	43% 6% 11% 21% 15% 4	3340
January	1st to 10th	Night	55% 6% 13% 14% 11%	8769
	11th to 20th	Night	48% 6% 15% 16% 14% 1	8820
	21st to end	Night	49% 8% 17% 18% 8%	9536
February	1st to 10th	Night	53% 7% 12% 17% 9% 1	2813
	11th to 20th	Night	49% 8% 12% 19% 12% 1	2663
	21st to end	Night	44% 7% 14% 24% 11%	2249
March	1st to 10th	Night	48% 7% 19% 19% 7%	5447
	11th to 20th	Night	49% 8% 16% 18% 9%	5110
	21st to end	Night	53% 6% 10% 20% 11%	5427
April	1st to 10th	Night	39% 6% 16% 22% 15% 1	2100
	11th to 20th	Night	49% 6% 13% 20% 10% 2	1908
	21st to end	Night	46% 6% 12% 24% 11% 1	1748
May	1st to 10th	Night	36% 4 9% 29% 19% 2	4724
	11th to 20th	Night	51% 7% 10% 20% 11% 1	4606
	21st to end	Night	38% 8% 15% 26% 14% 1	4526
June	1st to 10th	Night	37% 10% 16% 24% 11% 1	1334
	11th to 20th	Night	46% 9% 16% 18% 10% 1	1260
	21st to end	Night	36% 8% 21% 27% 7% 1	1279
July	1st to 10th	Night	28% 8% 24% 30% 9%	3145
	11th to 20th	Night	34% 7% 17% 35% 7%	3138
	21st to end	Night	23% 6% 21% 36% 12% 1	3386
August	1st to 10th	Night	29% 7% 22% 30% 11% 1	2600
	11th to 20th	Night	29% 7% 21% 31% 10% 1	2788
	21st to end	Night	29% 6% 18% 34% 13%	3274
September	1st to 10th	Night	30% 7% 16% 28% 14% 5%	2000
	11th to 20th	Night	36% 6% 15% 30% 10% 2	2000
	21st to end	Night	28% 7% 15% 33% 16% 2	2291
October	1st to 10th	Night	37% 5% 19% 30% 9%	3920
	11th to 20th	Night	31% 4 14% 36% 14%	3898
	21st to end	Night	40% 6% 16% 33% 6% 1	4747
November	1st to 10th	Night	54% 7% 13% 18% 7% 1	2870
	11th to 20th	Night	53% 8% 16% 16% 6% 1	2940
	21st to end	Night	51% 9% 16% 18% 5%	2989
December	1st to 10th	Night	62% 7% 15% 11% 4 1	5380
	11th to 20th	Night	61% 8% 16% 12% 4	6091
	21st to end	Night	43% 6% 10% 23% 15% 3	7840

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	14% 8% 27% 27% 19% 5%	220
	11th to 20th	Day	11% 10% 34% 25% 16% 3	220
	21st to end	Day	13% 13% 32% 28% 10% 4	264
February	1st to 10th	Day	11% 10% 38% 28% 10% 2	330
	11th to 20th	Day	11% 7% 33% 29% 15% 5%	330
	21st to end	Day	5% 7% 36% 33% 15% 4	273
March	1st to 10th	Day	9% 11% 31% 34% 13% 2	368
	11th to 20th	Day	8% 11% 37% 29% 11% 4	540
	21st to end	Day	15% 8% 32% 31% 13% 2	594
April	1st to 10th	Day	11% 10% 36% 30% 10% 3	540
	11th to 20th	Day	14% 16% 29% 28% 11% 2	532
	21st to end	Day	14% 9% 30% 29% 15% 3	681
May	1st to 10th	Day	12% 9% 26% 33% 16% 4	753
	11th to 20th	Day	12% 11% 21% 33% 17% 5%	775
	21st to end	Day	13% 8% 23% 30% 20% 7%	844
June	1st to 10th	Day	12% 11% 29% 30% 14% 4	780
	11th to 20th	Day	19% 12% 27% 23% 16% 4	780
	21st to end	Day	14% 7% 22% 30% 20% 7%	780
July	1st to 10th	Day	8% 5% 23% 35% 24% 6%	722
	11th to 20th	Day	11% 5% 26% 28% 22% 8%	718
	21st to end	Day	7% 5% 24% 28% 27% 9%	794
August	1st to 10th	Day	13% 5% 20% 29% 25% 8%	726
	11th to 20th	Day	8% 9% 21% 32% 24% 6%	601
	21st to end	Day	12% 6% 24% 31% 21% 6%	583
September	1st to 10th	Day	13% 10% 27% 28% 19% 4	530
	11th to 20th	Day	18% 7% 24% 31% 17% 2	530
	21st to end	Day	12% 13% 30% 28% 14% 3	430
October	1st to 10th	Day	16% 6% 28% 31% 16% 2	330
	11th to 20th	Day	12% 9% 35% 27% 13% 4	330
	21st to end	Day	7% 11% 44% 23% 13% 2	363
November	1st to 10th	Day	16% 10% 35% 25% 11% 3	330
	11th to 20th	Day	13% 16% 36% 25% 10% 1	330
	21st to end	Day	8% 10% 37% 31% 10% 4	313
December	1st to 10th	Day	10% 7% 32% 33% 14% 4	220
	11th to 20th	Day	10% 12% 38% 29% 10% 1	220
	21st to end	Day	9% 5% 36% 28% 16% 6%	242
January	1st to 10th	Night	10% 9% 34% 36% 10% 1	1050
	11th to 20th	Night	10% 11% 37% 31% 9% 1	1050
	21st to end	Night	10% 11% 38% 32% 8% 1	1155
February	1st to 10th	Night	11% 8% 32% 34% 13% 2	923
	11th to 20th	Night	11% 7% 31% 37% 12% 2	824
	21st to end	Night	6% 6% 25% 37% 21% 4	692
March	1st to 10th	Night	9% 7% 33% 37% 13% 2	840
	11th to 20th	Night	9% 7% 35% 34% 13% 2	840
	21st to end	Night	13% 7% 27% 37% 13% 2	844
April	1st to 10th	Night	9% 7% 34% 36% 12% 2	630
	11th to 20th	Night	13% 9% 35% 32% 10% 2	623
	21st to end	Night	15% 8% 28% 35% 13% 1	630
May	1st to 10th	Night	13% 7% 27% 37% 15% 2	630
	11th to 20th	Night	12% 7% 27% 34% 19% 2	591
	21st to end	Night	14% 7% 22% 37% 18% 2	455
June	1st to 10th	Night	11% 8% 28% 36% 15% 3	420
	11th to 20th	Night	21% 6% 21% 35% 16% 1	420
	21st to end	Night	12% 6% 20% 41% 18% 2	420
July	1st to 10th	Night	8% 4 18% 47% 22% 1	390
	11th to 20th	Night	11% 3 27% 38% 21% 1	388
	21st to end	Night	4 5% 24% 39% 25% 3	443
August	1st to 10th	Night	5% 4 22% 39% 27% 4	597
	11th to 20th	Night	8% 3 21% 43% 23% 2	594
	21st to end	Night	8% 6% 25% 35% 24% 1	660
September	1st to 10th	Night	11% 5% 24% 40% 19% 2	600
	11th to 20th	Night	15% 5% 22% 40% 18% 1	600
	21st to end	Night	9% 7% 30% 38% 13% 2	792
October	1st to 10th	Night	15% 7% 30% 36% 11% 1	800
	11th to 20th	Night	11% 7% 33% 34% 13% 2	800
	21st to end	Night	14% 11% 34% 32% 9% 1	1065
November	1st to 10th	Night	21% 8% 32% 30% 8% 1	1025
	11th to 20th	Night	11% 11% 34% 31% 12% 2	1050
	21st to end	Night	10% 10% 37% 33% 9% 2	1050
December	1st to 10th	Night	12% 8% 36% 29% 13% 2	1050
	11th to 20th	Night	11% 11% 36% 31% 10% 1	1050
	21st to end	Night	9% 6% 32% 36% 15% 2	1155

Page generated at 2026-06-28 00:10:46. Version ac07

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