Herridge Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Herridge Lake clear sky chart from 2005-11-06 to 2024-01-15.

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	18% 11% 4 8% 6% 3 5% 4 5% 7% 29%	74721
	Night	17% 13% 5% 8% 7% 3 4 4 5% 6% 28%	75066
Transparency	Day	55% 7% 11% 18% 8% 1	74416
	Night	57% 6% 11% 17% 8% 1	74906
Seeing	Day	23% 15% 31% 20% 8% 2	14011
	Night	24% 13% 31% 23% 8% 1	23208

By Month

Percentage Cloud Cover NE (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	15% 21% 8% 12% 7% 4 5% 4 5% 5% 13%	1328
	11th to 20th	Day	15% 18% 7% 12% 8% 2 5% 5% 4 6% 19%	1302
	21st to end	Day	14% 16% 6% 12% 9% 6% 6% 5% 4 5% 18%	1773
February	1st to 10th	Day	9% 17% 6% 12% 11% 5% 7% 5% 5% 6% 18%	1620
	11th to 20th	Day	11% 19% 6% 9% 7% 4 4 4 5% 5% 24%	1573
	21st to end	Day	15% 17% 6% 11% 8% 4 5% 5% 4 4 21%	1338
March	1st to 10th	Day	14% 12% 6% 10% 7% 4 4 5% 4 6% 27%	1945
	11th to 20th	Day	14% 14% 4 9% 8% 3 4 4 4 5% 30%	1980
	21st to end	Day	16% 13% 4 8% 6% 3 3 3 3 6% 35%	2178
April	1st to 10th	Day	19% 13% 6% 7% 6% 3 5% 4 5% 7% 25%	2134
	11th to 20th	Day	22% 9% 3 7% 5% 3 4 4 4 6% 33%	2287
	21st to end	Day	21% 12% 4 6% 4 2 4 4 4 5% 34%	2340
May	1st to 10th	Day	18% 9% 4 6% 6% 3 4 4 5% 6% 33%	2423
	11th to 20th	Day	20% 9% 4 7% 5% 3 5% 4 5% 6% 33%	2478
	21st to end	Day	18% 7% 3 5% 5% 3 4 4 5% 8% 38%	2743
June	1st to 10th	Day	20% 7% 4 6% 6% 3 5% 5% 6% 7% 32%	2700
	11th to 20th	Day	15% 5% 2 6% 6% 4 5% 6% 6% 8% 36%	2700
	21st to end	Day	19% 7% 3 6% 6% 4 6% 5% 5% 8% 31%	2700
July	1st to 10th	Day	14% 5% 3 5% 5% 3 5% 5% 7% 9% 39%	2700
	11th to 20th	Day	14% 7% 3 6% 5% 3 5% 5% 7% 9% 36%	2700
	21st to end	Day	13% 6% 2 6% 6% 4 6% 5% 7% 9% 35%	2753
August	1st to 10th	Day	14% 6% 3 6% 6% 4 6% 6% 8% 10% 31%	2327
	11th to 20th	Day	18% 7% 2 5% 4 3 5% 5% 5% 9% 36%	2303
	21st to end	Day	17% 7% 3 6% 6% 3 5% 5% 6% 7% 33%	2538
September	1st to 10th	Day	18% 8% 3 6% 6% 3 4 4 5% 8% 36%	2160
	11th to 20th	Day	19% 7% 3 6% 5% 3 5% 4 5% 7% 36%	2055
	21st to end	Day	22% 10% 4 6% 6% 3 4 4 5% 6% 31%	1946
October	1st to 10th	Day	21% 12% 3 6% 6% 2 4 4 4 7% 31%	1800
	11th to 20th	Day	27% 15% 5% 7% 6% 4 4 3 4 4 21%	1800
	21st to end	Day	29% 17% 4 8% 6% 3 3 4 4 5% 16%	1920
November	1st to 10th	Day	21% 16% 6% 7% 6% 2 3 3 4 6% 25%	1486
	11th to 20th	Day	19% 15% 7% 13% 7% 4 5% 4 3 6% 17%	1520
	21st to end	Day	27% 18% 6% 12% 7% 4 5% 3 3 4 13%	1520
December	1st to 10th	Day	17% 21% 7% 11% 8% 3 5% 4 4 4 14%	1520
	11th to 20th	Day	17% 19% 8% 10% 7% 3 4 3 4 4 21%	1700
	21st to end	Day	17% 23% 9% 14% 10% 2 3 2 3 3 13%	2431
January	1st to 10th	Night	16% 18% 8% 13% 8% 4 5% 4 3 5% 16%	2838
	11th to 20th	Night	17% 18% 8% 10% 8% 4 5% 5% 4 4 18%	2761
	21st to end	Night	14% 13% 6% 10% 10% 5% 7% 5% 6% 5% 21%	2581
February	1st to 10th	Night	11% 15% 6% 10% 11% 4 5% 5% 5% 5% 21%	2340
	11th to 20th	Night	13% 15% 8% 11% 8% 4 4 4 5% 5% 24%	2273
	21st to end	Night	12% 18% 6% 12% 8% 4 4 4 5% 5% 22%	1916
March	1st to 10th	Night	13% 13% 5% 10% 7% 5% 5% 4 5% 5% 28%	2002
	11th to 20th	Night	15% 13% 6% 9% 8% 4 4 4 5% 6% 28%	1979
	21st to end	Night	16% 10% 4 8% 5% 3 5% 4 4 6% 36%	2178
April	1st to 10th	Night	21% 14% 5% 8% 6% 3 4 3 4 4 28%	1825
	11th to 20th	Night	21% 10% 4 6% 5% 3 4 5% 3 7% 32%	1638
	21st to end	Night	20% 9% 4 6% 5% 3 4 4 5% 7% 32%	1620
May	1st to 10th	Night	17% 9% 4 7% 6% 4 4 4 4 6% 36%	1535
	11th to 20th	Night	17% 8% 3 6% 5% 3 5% 4 6% 6% 37%	1415
	21st to end	Night	15% 7% 3 6% 4 3 4 5% 5% 8% 41%	1528
June	1st to 10th	Night	15% 8% 3 6% 6% 4 5% 4 6% 6% 37%	1260
	11th to 20th	Night	18% 6% 2 4 5% 2 4 4 6% 9% 42%	1260
	21st to end	Night	15% 6% 3 6% 6% 3 4 6% 7% 8% 36%	1260
July	1st to 10th	Night	11% 5% 2 4 4 3 5% 7% 7% 8% 43%	1260
	11th to 20th	Night	11% 6% 3 5% 6% 3 4 4 6% 8% 45%	1260
	21st to end	Night	10% 4 2 6% 5% 3 6% 5% 7% 10% 42%	1560
August	1st to 10th	Night	13% 6% 2 5% 6% 4 5% 6% 6% 6% 40%	1611
	11th to 20th	Night	14% 6% 2 6% 5% 3 4 4 6% 8% 43%	1598
	21st to end	Night	18% 8% 3 5% 5% 2 5% 4 4 7% 39%	1800
September	1st to 10th	Night	17% 5% 2 4 3 3 4 4 6% 7% 44%	1800
	11th to 20th	Night	19% 7% 2 4 4 2 4 4 4 6% 44%	1902
	21st to end	Night	20% 8% 3 6% 4 2 4 3 5% 7% 38%	2013
October	1st to 10th	Night	20% 11% 3 6% 6% 3 4 4 3 5% 35%	2160
	11th to 20th	Night	28% 13% 3 5% 4 3 5% 4 5% 5% 24%	2160
	21st to end	Night	24% 17% 5% 8% 6% 2 4 3 3 4 23%	2434
November	1st to 10th	Night	19% 13% 4 7% 6% 3 4 4 4 6% 28%	2591
	11th to 20th	Night	19% 14% 6% 11% 8% 4 5% 5% 5% 5% 19%	2660
	21st to end	Night	22% 19% 6% 10% 7% 3 4 4 4 4 16%	2660
December	1st to 10th	Night	19% 20% 7% 11% 8% 4 4 4 3 5% 15%	2660
	11th to 20th	Night	18% 19% 6% 10% 9% 3 4 5% 5% 5% 16%	3492
	21st to end	Night	20% 20% 9% 12% 9% 3 3 2 3 3 14%	5236

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	73% 5% 8% 11% 3	1329
	11th to 20th	Day	68% 5% 8% 11% 8% 1	1302
	21st to end	Day	69% 5% 6% 13% 7% 1	1773
February	1st to 10th	Day	67% 5% 9% 11% 7% 1	1620
	11th to 20th	Day	62% 6% 9% 12% 10% 1	1582
	21st to end	Day	65% 5% 7% 14% 8%	1338
March	1st to 10th	Day	58% 5% 10% 16% 9% 1	1948
	11th to 20th	Day	58% 5% 8% 19% 9% 1	1980
	21st to end	Day	53% 4 9% 17% 15% 3	2178
April	1st to 10th	Day	59% 5% 11% 16% 8% 1	2134
	11th to 20th	Day	53% 5% 8% 22% 11% 1	2287
	21st to end	Day	54% 5% 7% 16% 14% 3	2340
May	1st to 10th	Day	50% 6% 12% 18% 12% 2	2423
	11th to 20th	Day	52% 5% 9% 19% 13% 1	2482
	21st to end	Day	45% 7% 13% 22% 13% 1	2743
June	1st to 10th	Day	50% 7% 12% 20% 10% 1	2700
	11th to 20th	Day	43% 9% 12% 23% 12% 1	2700
	21st to end	Day	50% 9% 11% 20% 9% 1	2700
July	1st to 10th	Day	39% 9% 15% 27% 9% 1	2626
	11th to 20th	Day	41% 8% 15% 27% 9%	2619
	21st to end	Day	44% 8% 17% 24% 6%	2599
August	1st to 10th	Day	45% 11% 17% 20% 7%	2314
	11th to 20th	Day	43% 9% 18% 21% 7% 1	2303
	21st to end	Day	47% 8% 15% 22% 8%	2538
September	1st to 10th	Day	47% 7% 13% 23% 9% 1	2160
	11th to 20th	Day	46% 8% 15% 24% 6%	2055
	21st to end	Day	53% 6% 15% 21% 5%	1946
October	1st to 10th	Day	54% 7% 12% 19% 8% 1	1800
	11th to 20th	Day	66% 7% 10% 12% 5%	1800
	21st to end	Day	70% 7% 9% 10% 4	1920
November	1st to 10th	Day	61% 6% 13% 14% 6%	1486
	11th to 20th	Day	68% 6% 9% 11% 4 1	1520
	21st to end	Day	77% 5% 7% 7% 3	1520
December	1st to 10th	Day	73% 5% 9% 10% 3	1520
	11th to 20th	Day	66% 6% 9% 15% 4	1700
	21st to end	Day	77% 5% 5% 11% 2	2431
January	1st to 10th	Night	72% 6% 9% 10% 4	2838
	11th to 20th	Night	70% 5% 8% 10% 7% 1	2761
	21st to end	Night	64% 6% 7% 13% 9% 1	2581
February	1st to 10th	Night	64% 6% 9% 14% 7% 1	2340
	11th to 20th	Night	63% 5% 11% 15% 6% 1	2275
	21st to end	Night	63% 5% 8% 15% 8% 1	1916
March	1st to 10th	Night	58% 6% 10% 14% 10% 3	2012
	11th to 20th	Night	57% 6% 11% 15% 10% 1	1980
	21st to end	Night	49% 7% 10% 16% 15% 4	2178
April	1st to 10th	Night	59% 5% 8% 15% 11% 2	1825
	11th to 20th	Night	53% 5% 7% 20% 13% 2	1638
	21st to end	Night	50% 6% 12% 13% 16% 3	1620
May	1st to 10th	Night	49% 7% 9% 19% 14% 2	1535
	11th to 20th	Night	47% 7% 9% 21% 14% 3	1416
	21st to end	Night	41% 8% 14% 20% 16% 2	1529
June	1st to 10th	Night	47% 7% 11% 22% 10% 3	1260
	11th to 20th	Night	40% 6% 12% 25% 16% 2	1260
	21st to end	Night	45% 8% 13% 19% 13% 1	1260
July	1st to 10th	Night	32% 11% 14% 28% 13% 1	1225
	11th to 20th	Night	36% 7% 16% 28% 13% 1	1218
	21st to end	Night	36% 10% 19% 28% 7%	1474
August	1st to 10th	Night	42% 9% 16% 24% 9% 1	1600
	11th to 20th	Night	37% 9% 18% 27% 8% 1	1598
	21st to end	Night	44% 8% 15% 23% 9% 1	1800
September	1st to 10th	Night	38% 8% 17% 25% 10% 2	1800
	11th to 20th	Night	39% 8% 15% 29% 8%	1902
	21st to end	Night	46% 6% 16% 26% 6%	2013
October	1st to 10th	Night	52% 6% 11% 20% 11%	2160
	11th to 20th	Night	61% 6% 13% 16% 4	2160
	21st to end	Night	66% 5% 11% 13% 6%	2434
November	1st to 10th	Night	55% 8% 16% 16% 5%	2591
	11th to 20th	Night	65% 7% 11% 12% 5% 1	2660
	21st to end	Night	71% 6% 11% 9% 3	2660
December	1st to 10th	Night	74% 6% 8% 10% 3	2660
	11th to 20th	Night	69% 7% 9% 11% 4	3491
	21st to end	Night	77% 4 5% 11% 3	5236

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	28% 21% 33% 13% 4 1	180
	11th to 20th	Day	23% 14% 40% 16% 7%	174
	21st to end	Day	24% 13% 33% 22% 7% 2	264
February	1st to 10th	Day	28% 28% 33% 8% 3	240
	11th to 20th	Day	28% 23% 36% 12% 1	240
	21st to end	Day	30% 29% 33% 8% 1	198
March	1st to 10th	Day	21% 21% 36% 20% 3	388
	11th to 20th	Day	22% 20% 37% 17% 3 1	420
	21st to end	Day	27% 21% 32% 16% 4 1	462
April	1st to 10th	Day	25% 19% 30% 18% 7% 1	420
	11th to 20th	Day	34% 16% 23% 17% 8% 2	412
	21st to end	Day	31% 19% 31% 12% 5% 2	420
May	1st to 10th	Day	26% 12% 29% 22% 9% 2	423
	11th to 20th	Day	23% 15% 33% 18% 9% 2	447
	21st to end	Day	22% 15% 34% 21% 8% 2	503
June	1st to 10th	Day	21% 14% 35% 22% 6% 1	630
	11th to 20th	Day	17% 17% 30% 27% 8% 2	630
	21st to end	Day	21% 12% 29% 28% 9% 1	630
July	1st to 10th	Day	12% 14% 33% 31% 9% 1	621
	11th to 20th	Day	17% 11% 31% 25% 13% 3	618
	21st to end	Day	13% 11% 29% 29% 13% 4	528
August	1st to 10th	Day	18% 8% 28% 29% 13% 3	446
	11th to 20th	Day	17% 6% 26% 27% 16% 8%	439
	21st to end	Day	19% 12% 29% 22% 13% 5%	495
September	1st to 10th	Day	23% 11% 29% 23% 11% 4	450
	11th to 20th	Day	20% 9% 30% 28% 8% 4	450
	21st to end	Day	26% 13% 26% 21% 12% 2	450
October	1st to 10th	Day	30% 13% 26% 19% 11% 1	450
	11th to 20th	Day	29% 22% 34% 10% 4 1	450
	21st to end	Day	35% 16% 32% 14% 2	435
November	1st to 10th	Day	37% 21% 31% 11% 2	180
	11th to 20th	Day	26% 25% 31% 15% 2 1	180
	21st to end	Day	38% 18% 31% 11% 3 1	180
December	1st to 10th	Day	28% 19% 32% 18% 3	180
	11th to 20th	Day	31% 18% 33% 13% 4 1	180
	21st to end	Day	29% 22% 36% 10% 3 1	198
January	1st to 10th	Night	26% 14% 36% 18% 5%	950
	11th to 20th	Night	27% 15% 31% 21% 5%	925
	21st to end	Night	22% 12% 31% 23% 11% 1	799
February	1st to 10th	Night	19% 18% 38% 20% 4 1	720
	11th to 20th	Night	23% 14% 39% 19% 4	703
	21st to end	Night	23% 20% 33% 20% 5%	592
March	1st to 10th	Night	20% 21% 33% 20% 5% 1	720
	11th to 20th	Night	24% 18% 33% 18% 6%	720
	21st to end	Night	21% 14% 35% 22% 5% 1	792
April	1st to 10th	Night	28% 15% 28% 24% 5%	720
	11th to 20th	Night	27% 17% 26% 21% 8% 1	574
	21st to end	Night	25% 13% 31% 23% 7% 1	540
May	1st to 10th	Night	22% 9% 31% 30% 9% 1	455
	11th to 20th	Night	21% 12% 31% 27% 8% 1	354
	21st to end	Night	19% 9% 37% 30% 5%	389
June	1st to 10th	Night	16% 11% 34% 31% 8% 1	360
	11th to 20th	Night	19% 10% 28% 31% 12%	360
	21st to end	Night	18% 8% 26% 33% 15% 1	360
July	1st to 10th	Night	12% 5% 36% 35% 11% 1	350
	11th to 20th	Night	14% 7% 26% 38% 15%	348
	21st to end	Night	10% 7% 29% 39% 15% 1	421
August	1st to 10th	Night	14% 6% 28% 35% 16% 2	537
	11th to 20th	Night	14% 6% 24% 34% 19% 3	534
	21st to end	Night	21% 8% 26% 28% 15% 2	612
September	1st to 10th	Night	21% 6% 28% 27% 17% 1	720
	11th to 20th	Night	21% 10% 26% 26% 16% 1	720
	21st to end	Night	24% 8% 25% 29% 13% 2	720
October	1st to 10th	Night	25% 12% 28% 25% 8% 1	720
	11th to 20th	Night	36% 12% 26% 18% 7% 1	720
	21st to end	Night	35% 13% 27% 21% 3 1	792
November	1st to 10th	Night	28% 13% 34% 20% 5%	740
	11th to 20th	Night	27% 17% 32% 18% 5%	760
	21st to end	Night	34% 14% 30% 17% 4	760
December	1st to 10th	Night	32% 17% 30% 15% 5% 1	760
	11th to 20th	Night	28% 15% 35% 17% 5% 1	916
	21st to end	Night	31% 16% 28% 20% 5%	1045

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