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 2024-02-05.

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	10% 8% 4 7% 7% 4 6% 5% 6% 8% 36%	77471
	Night	7% 8% 4 8% 7% 4 6% 6% 6% 8% 36%	81317
Transparency	Day	44% 8% 16% 22% 8% 1	77174
	Night	44% 8% 15% 22% 10% 1	81195
Seeing	Day	12% 8% 28% 30% 17% 5%	14598
	Night	11% 7% 30% 35% 14% 2	24068

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% 13% 5% 11% 11% 5% 5% 5% 6% 7% 26%	2219
	11th to 20th	Day	4 7% 3 9% 11% 8% 9% 9% 8% 11% 23%	2199
	21st to end	Day	6% 10% 4 9% 8% 5% 5% 5% 7% 8% 32%	2505
February	1st to 10th	Day	7% 11% 5% 10% 10% 6% 7% 6% 7% 8% 23%	1599
	11th to 20th	Day	7% 13% 6% 9% 9% 4 7% 5% 7% 6% 27%	1575
	21st to end	Day	6% 10% 5% 9% 10% 6% 8% 7% 6% 8% 25%	1332
March	1st to 10th	Day	7% 11% 5% 11% 12% 6% 8% 6% 5% 7% 22%	1814
	11th to 20th	Day	7% 11% 5% 8% 7% 4 6% 5% 6% 9% 32%	1979
	21st to end	Day	9% 13% 5% 10% 7% 4 5% 5% 5% 7% 29%	2245
April	1st to 10th	Day	8% 9% 5% 8% 8% 5% 6% 6% 5% 7% 33%	2160
	11th to 20th	Day	11% 12% 4 9% 7% 4 6% 6% 7% 7% 28%	2275
	21st to end	Day	13% 11% 3 7% 7% 3 5% 5% 5% 7% 33%	2460
May	1st to 10th	Day	13% 7% 3 7% 7% 3 6% 6% 7% 7% 34%	2520
	11th to 20th	Day	9% 5% 3 6% 6% 4 6% 5% 6% 9% 40%	2501
	21st to end	Day	17% 7% 4 6% 6% 4 5% 6% 6% 7% 33%	2917
June	1st to 10th	Day	14% 6% 3 7% 6% 4 5% 5% 6% 9% 36%	2812
	11th to 20th	Day	22% 7% 3 7% 5% 4 5% 5% 6% 7% 30%	2880
	21st to end	Day	10% 6% 2 6% 6% 4 6% 6% 7% 9% 37%	2859
July	1st to 10th	Day	6% 5% 2 5% 5% 3 6% 6% 7% 11% 43%	2700
	11th to 20th	Day	10% 4 2 4 5% 4 6% 6% 7% 9% 44%	2700
	21st to end	Day	6% 4 2 3 5% 3 5% 5% 6% 9% 53%	2934
August	1st to 10th	Day	11% 5% 2 4 6% 4 5% 5% 6% 8% 44%	2507
	11th to 20th	Day	10% 5% 3 4 5% 3 5% 5% 7% 10% 43%	2375
	21st to end	Day	11% 5% 2 3 4 2 4 5% 6% 9% 47%	2559
September	1st to 10th	Day	11% 5% 2 6% 5% 3 5% 4 6% 8% 46%	2160
	11th to 20th	Day	14% 7% 2 7% 5% 3 3 4 5% 7% 43%	2160
	21st to end	Day	10% 4 2 4 5% 3 4 4 5% 8% 51%	1895
October	1st to 10th	Day	13% 10% 4 6% 5% 3 5% 4 6% 7% 38%	1800
	11th to 20th	Day	10% 6% 4 6% 6% 3 5% 4 6% 8% 42%	1800
	21st to end	Day	7% 11% 5% 9% 8% 4 5% 6% 7% 7% 32%	1692
November	1st to 10th	Day	13% 13% 5% 9% 7% 3 5% 4 4 6% 30%	1488
	11th to 20th	Day	8% 12% 6% 13% 9% 5% 6% 5% 5% 8% 25%	1520
	21st to end	Day	7% 10% 5% 12% 9% 5% 6% 6% 6% 6% 26%	1469
December	1st to 10th	Day	6% 11% 6% 10% 9% 7% 8% 5% 7% 6% 25%	1140
	11th to 20th	Day	7% 9% 5% 11% 8% 5% 6% 6% 7% 8% 27%	1439
	21st to end	Day	3 6% 4 7% 5% 4 7% 5% 7% 9% 43%	2282
January	1st to 10th	Night	4 10% 5% 12% 10% 5% 7% 7% 7% 8% 24%	4726
	11th to 20th	Night	4 5% 3 11% 12% 7% 10% 8% 7% 9% 23%	4699
	21st to end	Night	6% 10% 4 9% 8% 5% 7% 6% 7% 9% 30%	5152
February	1st to 10th	Night	7% 9% 5% 10% 10% 4 5% 7% 8% 9% 25%	2474
	11th to 20th	Night	7% 10% 5% 11% 9% 3 7% 7% 7% 8% 27%	2272
	21st to end	Night	4 8% 5% 8% 8% 4 7% 7% 7% 10% 33%	1924
March	1st to 10th	Night	7% 8% 4 12% 11% 6% 6% 6% 6% 7% 28%	2142
	11th to 20th	Night	6% 10% 4 6% 7% 4 6% 5% 7% 9% 36%	1980
	21st to end	Night	8% 10% 5% 10% 8% 4 6% 5% 7% 8% 29%	2110
April	1st to 10th	Night	7% 9% 3 6% 6% 3 4 5% 7% 8% 42%	1800
	11th to 20th	Night	8% 12% 3 9% 6% 4 6% 6% 7% 8% 30%	1633
	21st to end	Night	11% 10% 4 7% 6% 3 6% 5% 5% 7% 35%	1499
May	1st to 10th	Night	11% 7% 3 5% 5% 3 5% 5% 6% 9% 41%	1440
	11th to 20th	Night	7% 5% 2 5% 5% 4 4 5% 7% 8% 47%	1392
	21st to end	Night	14% 6% 2 6% 4 3 4 5% 6% 9% 39%	1358
June	1st to 10th	Night	10% 6% 4 6% 5% 4 5% 7% 9% 8% 36%	1144
	11th to 20th	Night	20% 6% 2 5% 5% 3 6% 6% 6% 8% 32%	1080
	21st to end	Night	7% 4 2 5% 5% 3 6% 7% 6% 11% 44%	1096
July	1st to 10th	Night	7% 4 2 4 4 4 5% 5% 7% 12% 47%	1260
	11th to 20th	Night	8% 3 2 4 5% 3 5% 5% 7% 9% 50%	1260
	21st to end	Night	4 2 1 3 3 2 4 5% 5% 8% 62%	1383
August	1st to 10th	Night	4 3 1 4 4 3 4 6% 6% 10% 54%	1432
	11th to 20th	Night	8% 4 2 4 4 3 5% 5% 7% 9% 49%	1522
	21st to end	Night	7% 5% 2 5% 4 3 4 5% 5% 8% 52%	1797
September	1st to 10th	Night	9% 5% 2 4 5% 3 4 4 6% 8% 49%	1800
	11th to 20th	Night	12% 5% 2 5% 4 3 4 4 5% 8% 48%	1800
	21st to end	Night	8% 6% 2 5% 3 2 4 4 5% 9% 52%	2061
October	1st to 10th	Night	12% 9% 3 6% 5% 3 4 5% 5% 7% 41%	2160
	11th to 20th	Night	8% 6% 3 6% 6% 3 4 3 5% 7% 50%	2160
	21st to end	Night	9% 9% 4 7% 8% 4 5% 5% 6% 6% 36%	2645
November	1st to 10th	Night	15% 14% 5% 7% 7% 3 4 5% 5% 6% 29%	2590
	11th to 20th	Night	6% 9% 6% 11% 10% 5% 6% 6% 6% 7% 28%	2660
	21st to end	Night	7% 10% 5% 10% 8% 5% 6% 4 6% 9% 30%	2703
December	1st to 10th	Night	7% 10% 5% 10% 9% 6% 7% 5% 6% 8% 27%	3040
	11th to 20th	Night	6% 12% 5% 11% 10% 5% 7% 7% 7% 8% 22%	3753
	21st to end	Night	3 6% 3 6% 6% 4 5% 4 5% 7% 51%	5370

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% 9% 11% 16% 7%	2219
	11th to 20th	Day	52% 10% 14% 18% 5% 1	2220
	21st to end	Day	47% 9% 17% 20% 8%	2505
February	1st to 10th	Day	56% 8% 13% 16% 6%	1599
	11th to 20th	Day	55% 7% 12% 16% 9% 1	1584
	21st to end	Day	55% 7% 11% 18% 8%	1332
March	1st to 10th	Day	59% 9% 13% 15% 4	1814
	11th to 20th	Day	48% 7% 16% 21% 8%	1980
	21st to end	Day	53% 9% 15% 18% 5%	2245
April	1st to 10th	Day	49% 7% 13% 19% 11%	2160
	11th to 20th	Day	52% 8% 14% 17% 7% 1	2275
	21st to end	Day	48% 8% 14% 23% 7% 1	2460
May	1st to 10th	Day	45% 7% 15% 24% 9% 1	2520
	11th to 20th	Day	39% 8% 14% 27% 11% 1	2505
	21st to end	Day	48% 8% 15% 19% 10% 1	2918
June	1st to 10th	Day	44% 7% 17% 21% 10% 1	2812
	11th to 20th	Day	52% 9% 13% 19% 7% 1	2880
	21st to end	Day	39% 11% 21% 21% 8%	2859
July	1st to 10th	Day	31% 12% 21% 28% 8%	2626
	11th to 20th	Day	34% 11% 21% 28% 6%	2619
	21st to end	Day	26% 10% 24% 32% 8% 1	2771
August	1st to 10th	Day	36% 9% 21% 24% 9%	2491
	11th to 20th	Day	34% 9% 24% 24% 8%	2375
	21st to end	Day	32% 8% 17% 35% 8% 1	2559
September	1st to 10th	Day	35% 9% 17% 24% 12% 3	2160
	11th to 20th	Day	41% 7% 17% 27% 7% 1	2160
	21st to end	Day	32% 5% 17% 33% 11% 1	1895
October	1st to 10th	Day	44% 7% 18% 22% 8% 1	1800
	11th to 20th	Day	40% 7% 16% 27% 9% 1	1800
	21st to end	Day	48% 10% 14% 22% 6%	1692
November	1st to 10th	Day	56% 6% 12% 17% 9%	1488
	11th to 20th	Day	58% 8% 15% 16% 4	1520
	21st to end	Day	56% 8% 15% 16% 5%	1469
December	1st to 10th	Day	57% 7% 13% 15% 6% 2	1140
	11th to 20th	Day	52% 10% 19% 11% 7%	1440
	21st to end	Day	36% 8% 13% 21% 15% 6%	2282
January	1st to 10th	Night	53% 9% 16% 17% 4	4726
	11th to 20th	Night	53% 8% 14% 17% 7% 1	4740
	21st to end	Night	48% 11% 14% 21% 6%	5152
February	1st to 10th	Night	52% 8% 13% 18% 9% 1	2474
	11th to 20th	Night	52% 8% 13% 17% 10% 1	2273
	21st to end	Night	45% 7% 14% 24% 11%	1924
March	1st to 10th	Night	52% 7% 16% 16% 8%	2142
	11th to 20th	Night	42% 7% 16% 23% 11% 1	1980
	21st to end	Night	51% 8% 14% 18% 9%	2110
April	1st to 10th	Night	38% 6% 15% 23% 17% 1	1800
	11th to 20th	Night	48% 7% 14% 19% 10% 2	1633
	21st to end	Night	47% 6% 12% 23% 11% 2	1499
May	1st to 10th	Night	38% 6% 12% 29% 15%	1440
	11th to 20th	Night	33% 7% 13% 29% 16% 2	1392
	21st to end	Night	40% 8% 16% 23% 13% 1	1358
June	1st to 10th	Night	38% 10% 17% 24% 9% 1	1144
	11th to 20th	Night	47% 10% 15% 16% 10% 1	1080
	21st to end	Night	33% 9% 22% 27% 8% 1	1096
July	1st to 10th	Night	27% 11% 21% 32% 8% 1	1225
	11th to 20th	Night	28% 11% 23% 29% 8%	1218
	21st to end	Night	20% 8% 23% 39% 10% 1	1306
August	1st to 10th	Night	24% 11% 23% 29% 12% 1	1424
	11th to 20th	Night	29% 9% 21% 29% 10% 1	1522
	21st to end	Night	29% 7% 13% 35% 16% 1	1797
September	1st to 10th	Night	31% 7% 17% 26% 13% 5%	1800
	11th to 20th	Night	35% 6% 14% 31% 11% 3	1800
	21st to end	Night	29% 7% 15% 31% 15% 2	2061
October	1st to 10th	Night	42% 7% 15% 27% 9% 1	2160
	11th to 20th	Night	35% 6% 16% 30% 13% 1	2160
	21st to end	Night	47% 7% 13% 24% 7% 1	2645
November	1st to 10th	Night	55% 7% 13% 17% 7% 1	2590
	11th to 20th	Night	54% 8% 16% 17% 5% 1	2660
	21st to end	Night	51% 9% 17% 17% 5%	2703
December	1st to 10th	Night	54% 8% 14% 16% 7% 1	3040
	11th to 20th	Night	57% 11% 13% 14% 5%	3751
	21st to end	Night	33% 7% 12% 26% 18% 5%	5370

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% 7% 24% 28% 22% 4	180
	11th to 20th	Day	12% 8% 26% 31% 20% 4	180
	21st to end	Day	13% 11% 29% 31% 11% 5%	216
February	1st to 10th	Day	10% 9% 38% 31% 10% 2	252
	11th to 20th	Day	13% 8% 35% 28% 14% 3	240
	21st to end	Day	7% 3 34% 35% 16% 6%	198
March	1st to 10th	Day	9% 8% 29% 39% 13% 2	272
	11th to 20th	Day	9% 9% 35% 30% 11% 5%	420
	21st to end	Day	14% 8% 29% 33% 13% 2	462
April	1st to 10th	Day	11% 11% 35% 30% 9% 4	420
	11th to 20th	Day	14% 14% 30% 29% 11% 3	412
	21st to end	Day	15% 9% 32% 29% 12% 2	540
May	1st to 10th	Day	12% 7% 28% 31% 17% 5%	603
	11th to 20th	Day	10% 9% 21% 35% 18% 6%	625
	21st to end	Day	15% 8% 23% 28% 18% 8%	679
June	1st to 10th	Day	11% 9% 29% 32% 16% 4	630
	11th to 20th	Day	21% 13% 24% 23% 16% 4	630
	21st to end	Day	10% 6% 23% 32% 21% 8%	630
July	1st to 10th	Day	7% 5% 24% 36% 22% 6%	621
	11th to 20th	Day	11% 6% 28% 28% 21% 8%	618
	21st to end	Day	7% 5% 26% 26% 27% 9%	684
August	1st to 10th	Day	12% 6% 19% 30% 25% 8%	626
	11th to 20th	Day	8% 8% 21% 32% 25% 6%	513
	21st to end	Day	13% 5% 24% 30% 22% 6%	495
September	1st to 10th	Day	14% 10% 29% 28% 16% 3	450
	11th to 20th	Day	20% 6% 24% 32% 16% 2	450
	21st to end	Day	13% 12% 29% 28% 15% 3	360
October	1st to 10th	Day	19% 5% 26% 31% 17% 3	270
	11th to 20th	Day	12% 9% 34% 30% 12% 4	270
	21st to end	Day	8% 10% 42% 26% 13% 2	297
November	1st to 10th	Day	19% 8% 31% 26% 13% 3	270
	11th to 20th	Day	13% 14% 38% 25% 10% 1	270
	21st to end	Day	7% 11% 35% 32% 11% 5%	257
December	1st to 10th	Day	9% 6% 30% 34% 16% 5%	180
	11th to 20th	Day	9% 13% 36% 29% 11% 1	180
	21st to end	Day	9% 5% 34% 28% 18% 7%	198
January	1st to 10th	Night	10% 9% 33% 36% 11% 1	950
	11th to 20th	Night	10% 9% 36% 33% 10% 1	950
	21st to end	Night	10% 9% 38% 34% 8% 1	1045
February	1st to 10th	Night	11% 7% 31% 36% 13% 2	814
	11th to 20th	Night	12% 7% 33% 36% 11% 3	704
	21st to end	Night	6% 5% 23% 37% 24% 5%	592
March	1st to 10th	Night	9% 5% 34% 37% 13% 2	720
	11th to 20th	Night	9% 7% 33% 34% 14% 3	720
	21st to end	Night	13% 7% 26% 38% 14% 2	724
April	1st to 10th	Night	10% 7% 35% 33% 13% 3	540
	11th to 20th	Night	13% 9% 34% 32% 11% 2	533
	21st to end	Night	15% 9% 28% 36% 12% 1	540
May	1st to 10th	Night	13% 6% 27% 36% 17% 2	540
	11th to 20th	Night	9% 7% 27% 34% 20% 2	506
	21st to end	Night	16% 6% 22% 35% 19% 2	389
June	1st to 10th	Night	12% 7% 27% 37% 15% 3	360
	11th to 20th	Night	23% 6% 21% 32% 17% 2	360
	21st to end	Night	9% 6% 21% 43% 19% 2	360
July	1st to 10th	Night	7% 4 19% 49% 19% 1	350
	11th to 20th	Night	11% 3 28% 38% 20% 1	348
	21st to end	Night	4 5% 26% 37% 25% 3	398
August	1st to 10th	Night	4 4 22% 39% 26% 4	537
	11th to 20th	Night	9% 3 20% 42% 24% 2	534
	21st to end	Night	8% 5% 25% 36% 24% 1	594
September	1st to 10th	Night	12% 5% 25% 40% 16% 1	540
	11th to 20th	Night	14% 5% 23% 40% 17% 1	540
	21st to end	Night	10% 7% 30% 38% 13% 3	712
October	1st to 10th	Night	16% 7% 29% 36% 12% 1	720
	11th to 20th	Night	12% 6% 33% 33% 14% 2	720
	21st to end	Night	14% 11% 34% 32% 9% 1	958
November	1st to 10th	Night	22% 7% 31% 30% 9% 1	925
	11th to 20th	Night	10% 10% 33% 32% 12% 2	950
	21st to end	Night	10% 11% 37% 32% 9% 2	950
December	1st to 10th	Night	11% 7% 35% 30% 15% 2	950
	11th to 20th	Night	11% 10% 37% 31% 11% 1	950
	21st to end	Night	9% 6% 31% 36% 16% 2	1045

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