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 2025-02-25.

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 8% 6% 5% 5% 4 6% 8% 37%	111468
	Night	7% 8% 3 9% 6% 6% 6% 5% 7% 8% 36%	115813
Transparency	Day	43% 8% 17% 24% 8% 1	111213
	Night	44% 7% 16% 23% 9% 1	115715
Seeing	Day	12% 9% 28% 30% 17% 5%	16008
	Night	11% 7% 31% 35% 14% 2	25467

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	5% 12% 5% 13% 8% 6% 5% 5% 7% 8% 25%	3179
	11th to 20th	Day	3 6% 3 11% 8% 8% 8% 5% 6% 9% 33%	3159
	21st to end	Day	7% 12% 4 11% 6% 5% 5% 4 6% 8% 32%	3589
February	1st to 10th	Day	7% 13% 5% 12% 8% 7% 6% 4 7% 8% 23%	1740
	11th to 20th	Day	6% 12% 5% 10% 8% 6% 6% 5% 6% 7% 28%	1755
	21st to end	Day	5% 11% 4 11% 8% 7% 9% 5% 6% 8% 25%	1449
March	1st to 10th	Day	5% 11% 3 11% 9% 9% 7% 5% 5% 6% 28%	3161
	11th to 20th	Day	4 11% 5% 11% 5% 5% 5% 4 6% 10% 33%	3489
	21st to end	Day	6% 9% 4 15% 7% 6% 6% 4 6% 7% 30%	3943
April	1st to 10th	Day	8% 11% 4 9% 7% 6% 6% 4 5% 7% 33%	2280
	11th to 20th	Day	11% 13% 4 10% 5% 5% 5% 4 6% 7% 28%	2403
	21st to end	Day	12% 11% 3 8% 5% 5% 5% 4 6% 7% 33%	2597
May	1st to 10th	Day	18% 11% 3 8% 5% 4 4 4 6% 6% 31%	4430
	11th to 20th	Day	8% 7% 3 9% 7% 6% 7% 5% 7% 8% 33%	4437
	21st to end	Day	12% 9% 4 10% 6% 6% 6% 5% 7% 8% 29%	5161
June	1st to 10th	Day	14% 6% 3 8% 5% 5% 5% 4 6% 8% 36%	2969
	11th to 20th	Day	21% 7% 3 7% 5% 5% 5% 4 6% 7% 29%	3040
	21st to end	Day	10% 6% 2 7% 6% 5% 6% 5% 8% 9% 37%	3017
July	1st to 10th	Day	6% 4 2 6% 5% 5% 6% 5% 8% 10% 45%	4740
	11th to 20th	Day	8% 4 2 5% 4 4 5% 5% 7% 9% 46%	4740
	21st to end	Day	4 3 1 4 4 3 4 4 7% 9% 57%	5122
August	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 6% 7% 46%	4412
	11th to 20th	Day	8% 4 2 4 4 4 5% 4 7% 11% 46%	4157
	21st to end	Day	10% 5% 1 4 3 4 4 4 6% 9% 51%	4493
September	1st to 10th	Day	10% 5% 2 6% 4 4 5% 3 6% 8% 47%	2280
	11th to 20th	Day	15% 8% 2 7% 4 4 4 4 5% 7% 42%	2280
	21st to end	Day	10% 5% 2 5% 4 4 4 3 5% 8% 51%	2000
October	1st to 10th	Day	8% 7% 3 5% 3 5% 5% 4 6% 8% 47%	3170
	11th to 20th	Day	6% 4 3 6% 4 5% 5% 4 8% 13% 41%	3150
	21st to end	Day	5% 8% 4 9% 6% 5% 6% 4 7% 7% 39%	2926
November	1st to 10th	Day	12% 15% 4 10% 6% 4 5% 4 4 6% 30%	1568
	11th to 20th	Day	8% 13% 6% 14% 7% 7% 5% 4 5% 8% 24%	1600
	21st to end	Day	7% 12% 5% 13% 8% 6% 7% 5% 6% 7% 26%	1545
December	1st to 10th	Day	5% 12% 4 12% 8% 7% 8% 5% 7% 6% 26%	1960
	11th to 20th	Day	7% 13% 5% 13% 7% 9% 8% 6% 6% 6% 18%	2259
	21st to end	Day	2 6% 3 9% 8% 9% 6% 4 7% 8% 38%	3268
January	1st to 10th	Night	3 10% 4 13% 8% 8% 8% 6% 9% 8% 23%	6766
	11th to 20th	Night	3 7% 4 12% 9% 9% 9% 5% 6% 9% 27%	6739
	21st to end	Night	5% 9% 4 10% 7% 6% 6% 5% 7% 9% 32%	7370
February	1st to 10th	Night	7% 11% 4 12% 9% 6% 6% 5% 8% 9% 24%	2679
	11th to 20th	Night	6% 10% 4 12% 7% 5% 6% 6% 7% 8% 29%	2532
	21st to end	Night	3 9% 4 8% 8% 6% 6% 6% 7% 9% 33%	2099
March	1st to 10th	Night	5% 9% 4 13% 9% 7% 7% 5% 7% 7% 27%	3701
	11th to 20th	Night	5% 9% 4 10% 6% 5% 6% 5% 8% 10% 33%	3490
	21st to end	Night	6% 8% 3 11% 7% 6% 6% 5% 7% 9% 32%	3705
April	1st to 10th	Night	7% 9% 3 7% 6% 5% 3 4 7% 8% 41%	1900
	11th to 20th	Night	8% 13% 3 10% 5% 6% 6% 5% 7% 8% 30%	1724
	21st to end	Night	11% 11% 4 8% 5% 4 5% 4 5% 7% 36%	1582
May	1st to 10th	Night	17% 12% 4 7% 4 4 4 3 5% 7% 33%	2540
	11th to 20th	Night	11% 7% 2 7% 5% 6% 5% 6% 7% 7% 38%	2464
	21st to end	Night	13% 8% 3 9% 4 5% 5% 5% 7% 8% 35%	2414
June	1st to 10th	Night	10% 7% 3 6% 4 5% 5% 5% 10% 8% 36%	1207
	11th to 20th	Night	20% 6% 2 6% 4 5% 5% 4 7% 8% 32%	1140
	21st to end	Night	8% 5% 1 6% 5% 5% 5% 5% 6% 10% 45%	1157
July	1st to 10th	Night	7% 4 1 5% 3 5% 5% 5% 8% 10% 45%	2220
	11th to 20th	Night	5% 3 2 5% 4 4 4 3 6% 9% 55%	2220
	21st to end	Night	3 2 1 3 3 3 4 4 5% 8% 66%	2431
August	1st to 10th	Night	6% 4 2 5% 4 4 4 3 6% 9% 52%	2528
	11th to 20th	Night	6% 4 2 6% 4 4 5% 4 8% 9% 49%	2678
	21st to end	Night	8% 5% 2 5% 3 4 4 4 5% 8% 52%	3174
September	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 6% 8% 51%	1900
	11th to 20th	Night	12% 5% 2 7% 3 4 4 3 5% 8% 46%	1900
	21st to end	Night	8% 6% 2 5% 2 3 4 3 6% 9% 52%	2176
October	1st to 10th	Night	9% 8% 3 7% 3 5% 4 4 5% 7% 46%	3800
	11th to 20th	Night	5% 5% 2 6% 4 4 4 3 5% 8% 53%	3778
	21st to end	Night	8% 7% 3 7% 5% 5% 5% 4 7% 7% 42%	4600
November	1st to 10th	Night	15% 15% 4 8% 6% 4 4 4 5% 6% 29%	2730
	11th to 20th	Night	6% 11% 5% 12% 8% 7% 5% 5% 6% 7% 27%	2800
	21st to end	Night	7% 11% 4 12% 7% 6% 5% 4 7% 9% 28%	2846
December	1st to 10th	Night	8% 13% 4 14% 9% 7% 6% 4 7% 7% 21%	5220
	11th to 20th	Night	5% 13% 5% 13% 8% 8% 8% 6% 8% 8% 18%	5933
	21st to end	Night	2 6% 3 8% 9% 8% 6% 4 5% 5% 43%	7670

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	56% 7% 11% 20% 6%	3179
	11th to 20th	Day	47% 7% 14% 19% 12% 1	3180
	21st to end	Day	49% 7% 22% 17% 5%	3589
February	1st to 10th	Day	57% 7% 12% 16% 7%	1740
	11th to 20th	Day	52% 7% 12% 18% 10% 2	1764
	21st to end	Day	54% 8% 12% 18% 8%	1449
March	1st to 10th	Day	53% 8% 16% 17% 7%	3161
	11th to 20th	Day	44% 10% 20% 17% 8%	3490
	21st to end	Day	48% 9% 15% 22% 7%	3943
April	1st to 10th	Day	48% 8% 14% 19% 11%	2280
	11th to 20th	Day	53% 7% 13% 18% 7% 1	2403
	21st to end	Day	47% 8% 14% 23% 7% 1	2597
May	1st to 10th	Day	50% 7% 15% 21% 7%	4430
	11th to 20th	Day	42% 10% 14% 22% 11% 1	4441
	21st to end	Day	47% 12% 16% 17% 8%	5162
June	1st to 10th	Day	44% 7% 17% 21% 10% 1	2969
	11th to 20th	Day	51% 9% 13% 20% 7% 1	3040
	21st to end	Day	40% 11% 21% 21% 8%	3017
July	1st to 10th	Day	31% 9% 21% 28% 10%	4666
	11th to 20th	Day	31% 9% 17% 36% 8%	4659
	21st to end	Day	23% 7% 19% 37% 13% 1	4960
August	1st to 10th	Day	36% 7% 19% 30% 8%	4396
	11th to 20th	Day	30% 7% 21% 35% 7%	4199
	21st to end	Day	30% 6% 21% 34% 8%	4492
September	1st to 10th	Day	33% 8% 16% 25% 14% 3	2280
	11th to 20th	Day	42% 7% 17% 26% 7% 1	2280
	21st to end	Day	32% 5% 17% 33% 12% 2	2000
October	1st to 10th	Day	35% 5% 24% 26% 10%	3170
	11th to 20th	Day	34% 5% 19% 34% 8%	3150
	21st to end	Day	42% 7% 17% 28% 6%	2926
November	1st to 10th	Day	55% 6% 13% 17% 8%	1568
	11th to 20th	Day	58% 8% 14% 15% 4	1600
	21st to end	Day	56% 8% 15% 16% 4	1545
December	1st to 10th	Day	56% 9% 15% 13% 6% 1	1960
	11th to 20th	Day	65% 8% 15% 8% 5%	2260
	21st to end	Day	43% 6% 10% 21% 15% 4	3268
January	1st to 10th	Night	54% 8% 15% 17% 7%	6766
	11th to 20th	Night	52% 7% 13% 14% 13% 1	6780
	21st to end	Night	47% 9% 20% 20% 4	7370
February	1st to 10th	Night	53% 8% 12% 17% 10% 1	2679
	11th to 20th	Night	49% 8% 13% 18% 12% 1	2533
	21st to end	Night	44% 7% 14% 24% 11%	2099
March	1st to 10th	Night	51% 8% 16% 19% 6%	3701
	11th to 20th	Night	41% 10% 20% 20% 9%	3490
	21st to end	Night	45% 8% 14% 22% 11%	3705
April	1st to 10th	Night	38% 7% 16% 22% 16% 1	1900
	11th to 20th	Night	49% 7% 13% 19% 10% 2	1724
	21st to end	Night	46% 6% 12% 23% 11% 1	1582
May	1st to 10th	Night	49% 7% 13% 23% 8%	2540
	11th to 20th	Night	39% 11% 12% 21% 16% 1	2464
	21st to end	Night	42% 11% 18% 22% 8%	2414
June	1st to 10th	Night	37% 10% 17% 24% 10% 1	1207
	11th to 20th	Night	47% 9% 14% 17% 11% 1	1140
	21st to end	Night	33% 9% 21% 28% 8% 1	1157
July	1st to 10th	Night	29% 10% 23% 27% 10%	2185
	11th to 20th	Night	25% 7% 17% 40% 10%	2178
	21st to end	Night	16% 6% 19% 41% 16% 2	2354
August	1st to 10th	Night	29% 8% 22% 30% 11% 1	2520
	11th to 20th	Night	29% 7% 21% 32% 10% 1	2702
	21st to end	Night	29% 6% 18% 34% 13%	3174
September	1st to 10th	Night	30% 7% 17% 27% 14% 5%	1900
	11th to 20th	Night	37% 6% 14% 30% 10% 3	1900
	21st to end	Night	29% 7% 15% 31% 15% 2	2176
October	1st to 10th	Night	38% 5% 19% 30% 8%	3800
	11th to 20th	Night	31% 4 15% 36% 14% 1	3778
	21st to end	Night	40% 6% 16% 33% 6% 1	4600
November	1st to 10th	Night	55% 7% 13% 18% 7% 1	2730
	11th to 20th	Night	54% 8% 16% 16% 5% 1	2800
	21st to end	Night	52% 9% 17% 17% 5%	2846
December	1st to 10th	Night	61% 7% 16% 11% 5% 1	5220
	11th to 20th	Night	61% 8% 16% 12% 3	5931
	21st to end	Night	43% 6% 10% 24% 15% 3	7670

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% 25% 28% 21% 6%	200
	11th to 20th	Day	11% 8% 32% 28% 18% 4	200
	21st to end	Day	13% 12% 32% 29% 10% 4	240
February	1st to 10th	Day	11% 9% 38% 29% 10% 2	300
	11th to 20th	Day	11% 6% 33% 29% 16% 6%	300
	21st to end	Day	6% 6% 32% 35% 16% 5%	237
March	1st to 10th	Day	9% 10% 28% 38% 13% 2	304
	11th to 20th	Day	8% 10% 35% 30% 11% 5%	460
	21st to end	Day	13% 8% 30% 33% 14% 2	506
April	1st to 10th	Day	12% 12% 34% 30% 9% 4	460
	11th to 20th	Day	14% 15% 29% 28% 11% 2	452
	21st to end	Day	14% 9% 32% 30% 13% 2	587
May	1st to 10th	Day	13% 8% 27% 31% 16% 5%	653
	11th to 20th	Day	9% 10% 21% 35% 19% 6%	675
	21st to end	Day	14% 8% 24% 28% 18% 8%	734
June	1st to 10th	Day	12% 11% 29% 31% 15% 3	680
	11th to 20th	Day	20% 13% 25% 22% 15% 4	680
	21st to end	Day	11% 7% 23% 31% 21% 7%	680
July	1st to 10th	Day	7% 5% 23% 35% 25% 6%	671
	11th to 20th	Day	10% 5% 26% 28% 22% 9%	668
	21st to end	Day	7% 5% 24% 27% 27% 9%	739
August	1st to 10th	Day	12% 5% 20% 30% 25% 8%	676
	11th to 20th	Day	8% 8% 21% 32% 25% 6%	557
	21st to end	Day	12% 6% 26% 30% 20% 6%	539
September	1st to 10th	Day	13% 10% 28% 28% 17% 4	490
	11th to 20th	Day	20% 7% 25% 30% 16% 2	490
	21st to end	Day	13% 13% 30% 27% 14% 3	395
October	1st to 10th	Day	18% 6% 27% 30% 16% 3	300
	11th to 20th	Day	11% 9% 34% 29% 13% 4	300
	21st to end	Day	7% 10% 44% 24% 14% 2	330
November	1st to 10th	Day	17% 8% 34% 26% 11% 3	300
	11th to 20th	Day	14% 15% 37% 23% 10% 1	300
	21st to end	Day	8% 11% 36% 31% 10% 4	285
December	1st to 10th	Day	9% 7% 32% 33% 15% 5%	200
	11th to 20th	Day	9% 13% 37% 30% 11% 1	200
	21st to end	Day	9% 4 34% 29% 17% 7%	220
January	1st to 10th	Night	9% 9% 35% 36% 11% 1	1000
	11th to 20th	Night	10% 10% 37% 32% 10% 1	1000
	21st to end	Night	10% 10% 39% 32% 8% 1	1100
February	1st to 10th	Night	11% 8% 32% 34% 13% 2	879
	11th to 20th	Night	10% 6% 32% 38% 12% 2	784
	21st to end	Night	6% 5% 24% 37% 23% 5%	646
March	1st to 10th	Night	9% 6% 33% 37% 13% 2	760
	11th to 20th	Night	9% 7% 34% 33% 14% 3	760
	21st to end	Night	12% 7% 27% 38% 14% 2	764
April	1st to 10th	Night	9% 7% 35% 34% 12% 2	570
	11th to 20th	Night	12% 9% 34% 32% 11% 2	563
	21st to end	Night	15% 8% 28% 36% 12% 1	570
May	1st to 10th	Night	14% 6% 27% 35% 16% 2	570
	11th to 20th	Night	9% 7% 27% 35% 20% 2	534
	21st to end	Night	15% 7% 21% 36% 19% 2	411
June	1st to 10th	Night	11% 7% 27% 37% 15% 3	380
	11th to 20th	Night	22% 6% 20% 33% 17% 2	380
	21st to end	Night	9% 7% 21% 43% 18% 2	380
July	1st to 10th	Night	8% 4 18% 48% 21% 1	370
	11th to 20th	Night	10% 2 27% 38% 21% 1	368
	21st to end	Night	4 5% 25% 38% 25% 3	421
August	1st to 10th	Night	5% 4 22% 39% 26% 4	567
	11th to 20th	Night	9% 3 20% 43% 24% 2	564
	21st to end	Night	8% 6% 26% 35% 24% 1	627
September	1st to 10th	Night	11% 5% 24% 40% 18% 2	570
	11th to 20th	Night	15% 5% 23% 39% 17% 1	570
	21st to end	Night	10% 7% 30% 38% 13% 2	752
October	1st to 10th	Night	16% 7% 29% 35% 12% 1	760
	11th to 20th	Night	11% 6% 33% 34% 14% 2	760
	21st to end	Night	14% 11% 34% 32% 9% 1	1012
November	1st to 10th	Night	21% 7% 31% 30% 8% 1	975
	11th to 20th	Night	10% 10% 34% 32% 12% 2	1000
	21st to end	Night	10% 10% 37% 32% 9% 2	1000
December	1st to 10th	Night	11% 7% 35% 30% 14% 2	1000
	11th to 20th	Night	11% 10% 36% 32% 10% 1	1000
	21st to end	Night	9% 5% 31% 37% 15% 3	1100

Page generated at 2025-02-22 05:51:39. Version ac07

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