Sprague
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sprague 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	12% 9% 4 8% 7% 4 5% 5% 6% 7% 33%	77745
	Night	11% 10% 4 9% 7% 4 5% 5% 6% 7% 32%	81151
Transparency	Day	49% 6% 14% 22% 8% 1	77429
	Night	51% 5% 14% 21% 8% 1	81000
Seeing	Day	16% 12% 33% 25% 11% 2	15087
	Night	16% 8% 33% 30% 11% 1	25194

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	6% 13% 6% 13% 9% 5% 7% 6% 6% 7% 22%	2218
	11th to 20th	Day	5% 9% 5% 14% 13% 8% 9% 7% 8% 8% 15%	2220
	21st to end	Day	8% 16% 11% 14% 8% 4 5% 5% 5% 6% 17%	2771
February	1st to 10th	Day	7% 11% 5% 10% 9% 4 8% 6% 6% 7% 25%	1656
	11th to 20th	Day	7% 11% 5% 7% 7% 6% 7% 8% 7% 8% 28%	1574
	21st to end	Day	6% 10% 5% 10% 11% 5% 6% 6% 5% 7% 28%	1350
March	1st to 10th	Day	12% 13% 5% 8% 7% 4 6% 4 5% 7% 28%	1897
	11th to 20th	Day	9% 10% 5% 9% 7% 3 5% 6% 5% 7% 33%	1980
	21st to end	Day	13% 11% 4 9% 7% 3 4 4 5% 7% 32%	2178
April	1st to 10th	Day	12% 10% 5% 6% 5% 3 5% 4 6% 8% 36%	2156
	11th to 20th	Day	13% 11% 4 7% 7% 3 5% 5% 6% 8% 31%	2312
	21st to end	Day	18% 9% 3 7% 6% 4 4 5% 5% 6% 31%	2340
May	1st to 10th	Day	19% 9% 3 5% 5% 3 4 4 5% 6% 37%	2452
	11th to 20th	Day	17% 7% 3 5% 5% 4 5% 5% 5% 7% 36%	2481
	21st to end	Day	18% 7% 3 6% 5% 3 5% 4 5% 7% 38%	2918
June	1st to 10th	Day	13% 6% 2 6% 6% 3 5% 6% 7% 8% 37%	2700
	11th to 20th	Day	16% 6% 3 6% 6% 4 5% 5% 6% 8% 36%	2700
	21st to end	Day	14% 7% 3 5% 6% 3 6% 6% 7% 9% 35%	2700
July	1st to 10th	Day	7% 3 2 4 4 4 6% 6% 7% 9% 47%	2700
	11th to 20th	Day	11% 4 2 5% 6% 4 5% 5% 6% 9% 42%	2700
	21st to end	Day	7% 4 2 5% 5% 3 5% 5% 6% 9% 49%	2932
August	1st to 10th	Day	9% 4 2 5% 6% 3 5% 7% 6% 9% 45%	2343
	11th to 20th	Day	11% 5% 2 5% 6% 3 4 6% 5% 9% 43%	2301
	21st to end	Day	11% 6% 3 5% 4 3 5% 5% 5% 9% 45%	2574
September	1st to 10th	Day	12% 5% 3 5% 5% 3 5% 4 5% 7% 47%	2196
	11th to 20th	Day	15% 6% 2 5% 5% 3 5% 5% 6% 9% 38%	2026
	21st to end	Day	19% 6% 3 5% 5% 4 4 4 5% 8% 37%	1967
October	1st to 10th	Day	18% 11% 4 7% 6% 4 5% 4 4 6% 32%	1800
	11th to 20th	Day	15% 12% 5% 7% 5% 4 5% 4 6% 6% 32%	1800
	21st to end	Day	16% 15% 5% 10% 7% 3 4 4 5% 6% 26%	1814
November	1st to 10th	Day	15% 14% 6% 7% 7% 3 5% 6% 6% 6% 27%	1487
	11th to 20th	Day	11% 13% 7% 14% 9% 3 5% 5% 4 5% 23%	1520
	21st to end	Day	12% 14% 5% 13% 9% 5% 5% 6% 4 6% 22%	1520
December	1st to 10th	Day	9% 12% 6% 14% 9% 5% 6% 7% 6% 7% 18%	1341
	11th to 20th	Day	11% 15% 8% 13% 8% 4 5% 5% 5% 6% 20%	1679
	21st to end	Day	14% 13% 6% 14% 9% 4 5% 4 5% 5% 20%	2442
January	1st to 10th	Night	5% 12% 6% 12% 11% 6% 8% 7% 7% 7% 19%	4737
	11th to 20th	Night	6% 12% 6% 13% 13% 7% 9% 7% 8% 6% 13%	4750
	21st to end	Night	10% 18% 8% 12% 8% 4 6% 6% 5% 6% 17%	4891
February	1st to 10th	Night	8% 9% 5% 9% 9% 4 7% 6% 7% 9% 28%	2399
	11th to 20th	Night	8% 10% 4 6% 5% 4 7% 6% 6% 8% 35%	2273
	21st to end	Night	6% 9% 5% 12% 9% 5% 6% 5% 6% 7% 30%	1923
March	1st to 10th	Night	11% 12% 4 9% 6% 3 5% 5% 6% 8% 30%	2050
	11th to 20th	Night	8% 9% 4 7% 6% 3 5% 5% 5% 8% 39%	1979
	21st to end	Night	14% 11% 5% 7% 6% 3 4 4 5% 6% 35%	2178
April	1st to 10th	Night	14% 8% 3 6% 6% 4 5% 4 6% 6% 38%	1801
	11th to 20th	Night	15% 10% 4 6% 5% 3 5% 5% 5% 6% 37%	1599
	21st to end	Night	15% 8% 4 6% 7% 4 5% 4 4 6% 36%	1620
May	1st to 10th	Night	16% 7% 4 6% 5% 2 4 4 4 6% 41%	1507
	11th to 20th	Night	17% 6% 3 5% 4 4 5% 5% 6% 7% 39%	1412
	21st to end	Night	15% 6% 3 6% 4 3 4 5% 4 7% 44%	1358
June	1st to 10th	Night	14% 5% 3 5% 5% 4 4 5% 6% 7% 43%	1260
	11th to 20th	Night	13% 4 2 6% 4 3 5% 5% 5% 9% 43%	1260
	21st to end	Night	9% 5% 3 6% 5% 2 5% 4 7% 8% 46%	1260
July	1st to 10th	Night	8% 3 1 3 3 2 3 4 5% 8% 59%	1260
	11th to 20th	Night	6% 3 2 4 5% 2 5% 5% 6% 11% 52%	1260
	21st to end	Night	7% 3 2 3 3 2 4 4 5% 8% 60%	1383
August	1st to 10th	Night	7% 3 2 4 4 2 4 5% 4 9% 57%	1593
	11th to 20th	Night	11% 3 2 3 3 3 4 4 6% 8% 53%	1600
	21st to end	Night	11% 4 1 5% 4 2 3 4 5% 8% 54%	1782
September	1st to 10th	Night	11% 6% 2 3 4 3 4 4 5% 6% 52%	1764
	11th to 20th	Night	13% 5% 2 4 4 2 4 4 5% 8% 48%	1930
	21st to end	Night	17% 7% 2 4 5% 2 4 4 5% 8% 42%	1980
October	1st to 10th	Night	16% 8% 3 6% 5% 3 4 5% 5% 8% 37%	2155
	11th to 20th	Night	17% 10% 3 6% 5% 3 4 4 6% 7% 34%	2160
	21st to end	Night	16% 12% 5% 8% 6% 4 5% 5% 6% 6% 28%	2538
November	1st to 10th	Night	14% 11% 6% 10% 6% 3 5% 4 5% 6% 28%	2591
	11th to 20th	Night	12% 12% 5% 13% 8% 4 6% 5% 5% 6% 24%	2660
	21st to end	Night	12% 12% 6% 10% 8% 4 5% 6% 6% 7% 24%	2660
December	1st to 10th	Night	7% 12% 6% 14% 11% 6% 7% 6% 6% 7% 18%	2835
	11th to 20th	Night	10% 14% 6% 14% 10% 4 6% 6% 6% 6% 18%	3518
	21st to end	Night	13% 13% 6% 11% 10% 4 5% 5% 5% 6% 20%	5225

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	60% 6% 11% 17% 5%	2219
	11th to 20th	Day	65% 4 14% 13% 3	2220
	21st to end	Day	67% 5% 10% 14% 5%	2771
February	1st to 10th	Day	56% 5% 12% 16% 10% 1	1656
	11th to 20th	Day	50% 7% 14% 19% 9% 1	1583
	21st to end	Day	55% 6% 12% 18% 9% 1	1350
March	1st to 10th	Day	56% 5% 14% 17% 8%	1899
	11th to 20th	Day	50% 7% 14% 21% 8% 1	1980
	21st to end	Day	53% 5% 13% 20% 9% 1	2178
April	1st to 10th	Day	47% 5% 11% 24% 12% 1	2156
	11th to 20th	Day	50% 6% 12% 20% 10% 1	2312
	21st to end	Day	53% 4 13% 19% 9% 1	2340
May	1st to 10th	Day	48% 5% 11% 21% 12% 2	2452
	11th to 20th	Day	47% 6% 9% 25% 11% 1	2485
	21st to end	Day	47% 4 13% 23% 12% 1	2918
June	1st to 10th	Day	43% 7% 18% 22% 9% 1	2700
	11th to 20th	Day	45% 6% 16% 24% 9%	2700
	21st to end	Day	44% 7% 20% 23% 6%	2700
July	1st to 10th	Day	31% 7% 19% 32% 10% 1	2626
	11th to 20th	Day	38% 7% 18% 28% 10%	2619
	21st to end	Day	33% 6% 17% 32% 11% 1	2769
August	1st to 10th	Day	34% 8% 19% 30% 8% 1	2328
	11th to 20th	Day	37% 7% 20% 30% 6% 1	2301
	21st to end	Day	37% 6% 16% 31% 10%	2574
September	1st to 10th	Day	36% 6% 16% 32% 10% 1	2196
	11th to 20th	Day	43% 6% 21% 24% 5%	2026
	21st to end	Day	46% 5% 14% 32% 4	1967
October	1st to 10th	Day	54% 5% 16% 18% 6%	1800
	11th to 20th	Day	53% 5% 11% 24% 6% 1	1800
	21st to end	Day	60% 5% 14% 17% 3	1814
November	1st to 10th	Day	58% 5% 15% 16% 5% 1	1487
	11th to 20th	Day	64% 4 14% 12% 5%	1520
	21st to end	Day	62% 6% 16% 13% 3	1520
December	1st to 10th	Day	62% 7% 13% 13% 4	1341
	11th to 20th	Day	65% 4 14% 14% 3	1680
	21st to end	Day	66% 4 7% 18% 5%	2442
January	1st to 10th	Night	64% 5% 14% 14% 4	4737
	11th to 20th	Night	68% 5% 9% 15% 3	4750
	21st to end	Night	68% 4 12% 12% 4	4891
February	1st to 10th	Night	51% 5% 15% 18% 10%	2399
	11th to 20th	Night	45% 6% 17% 20% 11% 1	2274
	21st to end	Night	53% 5% 12% 20% 10%	1923
March	1st to 10th	Night	52% 5% 13% 18% 10% 1	2061
	11th to 20th	Night	44% 5% 14% 24% 12% 1	1980
	21st to end	Night	50% 5% 13% 19% 12% 2	2178
April	1st to 10th	Night	46% 5% 10% 23% 14% 2	1801
	11th to 20th	Night	47% 5% 8% 22% 16% 2	1599
	21st to end	Night	48% 5% 9% 26% 9% 2	1620
May	1st to 10th	Night	46% 4 10% 23% 16% 1	1507
	11th to 20th	Night	44% 5% 11% 24% 15% 2	1413
	21st to end	Night	41% 5% 12% 23% 17% 2	1358
June	1st to 10th	Night	38% 6% 19% 24% 12% 1	1260
	11th to 20th	Night	38% 6% 15% 24% 15% 2	1260
	21st to end	Night	36% 7% 20% 28% 8% 1	1260
July	1st to 10th	Night	23% 4 18% 38% 14% 2	1225
	11th to 20th	Night	27% 6% 20% 29% 17% 1	1218
	21st to end	Night	23% 6% 16% 36% 17% 1	1306
August	1st to 10th	Night	25% 5% 19% 38% 11% 1	1584
	11th to 20th	Night	29% 7% 20% 35% 9% 1	1600
	21st to end	Night	30% 5% 15% 37% 13% 1	1782
September	1st to 10th	Night	33% 5% 15% 34% 14% 1	1764
	11th to 20th	Night	36% 6% 21% 27% 10%	1930
	21st to end	Night	41% 5% 15% 30% 8%	1980
October	1st to 10th	Night	45% 6% 17% 23% 9%	2155
	11th to 20th	Night	50% 4 13% 27% 6%	2160
	21st to end	Night	56% 5% 13% 20% 5%	2538
November	1st to 10th	Night	56% 5% 14% 18% 6% 1	2591
	11th to 20th	Night	60% 6% 14% 15% 5% 1	2660
	21st to end	Night	59% 6% 17% 13% 5%	2660
December	1st to 10th	Night	64% 6% 15% 12% 3	2835
	11th to 20th	Night	65% 5% 13% 13% 4	3516
	21st to end	Night	64% 6% 10% 15% 5%	5225

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	15% 13% 38% 24% 9% 1	270
	11th to 20th	Day	14% 11% 37% 30% 8%	270
	21st to end	Day	15% 9% 39% 25% 10% 1	297
February	1st to 10th	Day	14% 12% 41% 25% 6% 2	252
	11th to 20th	Day	11% 20% 40% 18% 8% 3	240
	21st to end	Day	14% 16% 40% 22% 8% 1	198
March	1st to 10th	Day	14% 11% 43% 24% 6% 2	240
	11th to 20th	Day	17% 14% 33% 22% 12% 2	240
	21st to end	Day	15% 14% 39% 22% 9% 1	264
April	1st to 10th	Day	14% 15% 38% 21% 11%	416
	11th to 20th	Day	21% 15% 31% 23% 8% 1	590
	21st to end	Day	22% 11% 32% 28% 8% 1	600
May	1st to 10th	Day	21% 15% 33% 23% 6% 2	603
	11th to 20th	Day	20% 12% 32% 24% 10% 2	625
	21st to end	Day	20% 12% 31% 26% 9% 1	679
June	1st to 10th	Day	16% 11% 32% 24% 14% 3	630
	11th to 20th	Day	18% 12% 34% 24% 10% 2	630
	21st to end	Day	17% 8% 29% 28% 13% 5%	630
July	1st to 10th	Day	10% 8% 31% 30% 15% 6%	621
	11th to 20th	Day	12% 11% 28% 30% 15% 3	618
	21st to end	Day	8% 7% 29% 34% 16% 6%	684
August	1st to 10th	Day	8% 10% 30% 30% 18% 4	626
	11th to 20th	Day	11% 7% 29% 30% 16% 6%	615
	21st to end	Day	14% 7% 33% 26% 17% 4	693
September	1st to 10th	Day	14% 11% 34% 26% 14% 1	486
	11th to 20th	Day	20% 13% 35% 23% 8% 1	316
	21st to end	Day	28% 14% 35% 19% 4 1	270
October	1st to 10th	Day	24% 13% 27% 24% 10% 1	270
	11th to 20th	Day	18% 14% 37% 26% 4	270
	21st to end	Day	28% 19% 31% 17% 5%	297
November	1st to 10th	Day	23% 13% 35% 23% 6%	270
	11th to 20th	Day	20% 21% 34% 20% 4	270
	21st to end	Day	21% 21% 34% 21% 2 1	270
December	1st to 10th	Day	16% 15% 36% 25% 7% 1	270
	11th to 20th	Day	18% 16% 44% 19% 3	270
	21st to end	Day	18% 10% 38% 23% 10% 2	297
January	1st to 10th	Night	11% 11% 35% 29% 12% 2	950
	11th to 20th	Night	15% 8% 36% 31% 9% 1	950
	21st to end	Night	15% 10% 38% 28% 8% 1	1045
February	1st to 10th	Night	12% 9% 34% 34% 10% 1	923
	11th to 20th	Night	13% 9% 36% 28% 11% 3	879
	21st to end	Night	10% 9% 40% 29% 11% 2	739
March	1st to 10th	Night	15% 10% 33% 29% 12% 1	621
	11th to 20th	Night	12% 9% 41% 28% 9% 1	540
	21st to end	Night	20% 10% 27% 28% 12% 3	594
April	1st to 10th	Night	18% 8% 31% 32% 10% 1	540
	11th to 20th	Night	19% 8% 33% 30% 10% 1	533
	21st to end	Night	17% 7% 32% 35% 9%	540
May	1st to 10th	Night	19% 9% 31% 31% 8% 1	540
	11th to 20th	Night	19% 9% 31% 30% 11% 1	531
	21st to end	Night	19% 6% 31% 33% 10%	584
June	1st to 10th	Night	16% 5% 28% 36% 14% 1	540
	11th to 20th	Night	15% 6% 32% 34% 13%	540
	21st to end	Night	9% 7% 25% 37% 20% 1	540
July	1st to 10th	Night	10% 2 26% 40% 21% 1	525
	11th to 20th	Night	7% 6% 27% 40% 17% 2	522
	21st to end	Night	8% 3 23% 45% 20% 2	591
August	1st to 10th	Night	8% 3 25% 42% 21% 1	537
	11th to 20th	Night	12% 5% 25% 35% 21% 3	534
	21st to end	Night	13% 5% 25% 36% 20% 1	594
September	1st to 10th	Night	13% 5% 31% 34% 15% 2	540
	11th to 20th	Night	15% 6% 34% 30% 14% 1	540
	21st to end	Night	21% 6% 33% 28% 12% 1	540
October	1st to 10th	Night	20% 10% 36% 27% 7%	715
	11th to 20th	Night	22% 9% 35% 26% 8% 1	720
	21st to end	Night	24% 12% 31% 26% 7% 1	937
November	1st to 10th	Night	20% 10% 37% 24% 9% 1	925
	11th to 20th	Night	18% 11% 35% 27% 7% 1	950
	21st to end	Night	19% 13% 39% 21% 6% 1	950
December	1st to 10th	Night	14% 8% 37% 29% 10% 1	950
	11th to 20th	Night	18% 11% 38% 25% 6% 1	950
	21st to end	Night	20% 10% 34% 27% 8% 1	1045

Page generated at 2024-02-02 04:20:27. Version ac07

Copyright 2024 Attilla Danko