Hearst
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hearst 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	17% 12% 5% 9% 7% 4 5% 5% 5% 6% 25%	77714
	Night	15% 14% 6% 10% 8% 4 6% 5% 5% 6% 23%	81185
Transparency	Day	59% 7% 11% 16% 7%	77403
	Night	61% 7% 11% 14% 6%	81031
Seeing	Day	23% 15% 32% 21% 8% 2	14436
	Night	22% 12% 31% 25% 9% 1	23830

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	11% 19% 7% 14% 9% 6% 8% 6% 6% 5% 10%	2208
	11th to 20th	Day	9% 11% 6% 18% 13% 5% 7% 6% 7% 5% 14%	2342
	21st to end	Day	12% 19% 10% 12% 8% 5% 6% 6% 6% 4 10%	2783
February	1st to 10th	Day	8% 12% 5% 8% 7% 6% 12% 7% 7% 6% 23%	1512
	11th to 20th	Day	9% 16% 6% 10% 9% 3 7% 8% 6% 6% 20%	1573
	21st to end	Day	7% 16% 6% 12% 8% 5% 8% 7% 6% 5% 19%	1470
March	1st to 10th	Day	10% 14% 5% 9% 6% 7% 6% 5% 5% 6% 27%	1798
	11th to 20th	Day	11% 16% 6% 11% 8% 4 5% 4 4 6% 25%	1970
	21st to end	Day	15% 12% 4 9% 5% 4 4 5% 4 6% 32%	2200
April	1st to 10th	Day	18% 14% 7% 10% 7% 3 5% 4 3 5% 24%	2203
	11th to 20th	Day	19% 13% 5% 8% 6% 3 4 4 4 5% 28%	2312
	21st to end	Day	15% 13% 5% 7% 5% 3 5% 4 5% 6% 32%	2340
May	1st to 10th	Day	19% 12% 5% 9% 6% 3 5% 5% 5% 5% 27%	2353
	11th to 20th	Day	22% 10% 3 7% 5% 3 4 5% 5% 7% 30%	2651
	21st to end	Day	21% 10% 3 6% 5% 3 5% 4 6% 7% 31%	2919
June	1st to 10th	Day	24% 8% 3 6% 5% 3 4 4 5% 7% 31%	2700
	11th to 20th	Day	18% 7% 3 6% 5% 3 5% 5% 5% 8% 36%	2700
	21st to end	Day	20% 7% 3 5% 6% 3 6% 5% 5% 7% 33%	2700
July	1st to 10th	Day	19% 6% 3 6% 6% 3 6% 5% 6% 7% 34%	2700
	11th to 20th	Day	15% 7% 3 6% 5% 4 5% 5% 7% 9% 35%	2700
	21st to end	Day	19% 7% 2 5% 6% 3 5% 6% 6% 9% 33%	2823
August	1st to 10th	Day	19% 7% 3 7% 6% 4 6% 6% 6% 9% 28%	2485
	11th to 20th	Day	17% 6% 2 4 6% 3 5% 4 6% 6% 39%	2303
	21st to end	Day	17% 9% 3 7% 7% 4 5% 5% 6% 7% 31%	2574
September	1st to 10th	Day	21% 8% 3 6% 6% 4 3 4 4 6% 35%	2192
	11th to 20th	Day	25% 11% 3 7% 6% 3 3 4 5% 6% 29%	1980
	21st to end	Day	24% 12% 4 6% 6% 3 4 3 4 5% 29%	1980
October	1st to 10th	Day	20% 17% 3 6% 4 3 3 4 4 6% 28%	1886
	11th to 20th	Day	26% 20% 6% 6% 6% 3 4 4 4 5% 18%	1702
	21st to end	Day	23% 24% 7% 8% 5% 3 4 3 4 4 16%	1782
November	1st to 10th	Day	20% 20% 8% 11% 6% 3 4 3 4 5% 16%	1586
	11th to 20th	Day	18% 22% 8% 14% 8% 3 4 3 4 4 13%	1520
	21st to end	Day	19% 19% 7% 16% 9% 4 5% 4 3 4 9%	1335
December	1st to 10th	Day	11% 18% 9% 15% 11% 5% 5% 6% 4 5% 12%	1330
	11th to 20th	Day	14% 16% 6% 11% 10% 8% 8% 7% 7% 5% 10%	1671
	21st to end	Day	15% 20% 7% 14% 12% 6% 6% 4 4 3 8%	2431
January	1st to 10th	Night	8% 17% 7% 12% 10% 8% 11% 7% 5% 5% 10%	4748
	11th to 20th	Night	8% 13% 7% 16% 12% 6% 7% 9% 7% 5% 10%	4627
	21st to end	Night	11% 18% 9% 12% 9% 5% 6% 6% 5% 4 14%	4884
February	1st to 10th	Night	7% 12% 5% 11% 9% 6% 10% 9% 5% 6% 20%	2543
	11th to 20th	Night	9% 16% 6% 10% 11% 4 7% 7% 6% 6% 19%	2273
	21st to end	Night	6% 16% 6% 10% 10% 5% 8% 6% 5% 6% 22%	1785
March	1st to 10th	Night	9% 10% 5% 11% 8% 6% 7% 8% 6% 6% 25%	2149
	11th to 20th	Night	13% 12% 6% 11% 8% 4 6% 4 3 5% 28%	1989
	21st to end	Night	13% 10% 4 9% 7% 5% 5% 3 4 6% 34%	2172
April	1st to 10th	Night	18% 14% 5% 8% 6% 5% 4 4 4 4 28%	1756
	11th to 20th	Night	17% 11% 4 8% 5% 3 5% 5% 5% 6% 31%	1597
	21st to end	Night	17% 12% 5% 7% 5% 2 4 3 3 5% 37%	1620
May	1st to 10th	Night	17% 10% 4 7% 6% 3 5% 5% 6% 7% 29%	1604
	11th to 20th	Night	21% 7% 3 7% 6% 3 4 5% 6% 5% 33%	1243
	21st to end	Night	20% 8% 3 6% 4 3 4 5% 5% 6% 36%	1357
June	1st to 10th	Night	19% 8% 2 5% 4 3 4 3 6% 8% 37%	1260
	11th to 20th	Night	17% 7% 3 4 4 3 5% 6% 5% 7% 38%	1260
	21st to end	Night	20% 5% 2 4 5% 3 5% 5% 6% 8% 37%	1260
July	1st to 10th	Night	16% 5% 2 4 5% 3 4 6% 6% 8% 41%	1260
	11th to 20th	Night	13% 5% 3 5% 6% 4 4 7% 6% 9% 38%	1260
	21st to end	Night	15% 6% 3 6% 5% 2 5% 5% 5% 9% 39%	1493
August	1st to 10th	Night	12% 7% 2 5% 6% 3 5% 6% 6% 9% 39%	1453
	11th to 20th	Night	14% 6% 2 5% 4 3 4 5% 5% 9% 43%	1598
	21st to end	Night	17% 6% 2 5% 7% 2 5% 5% 5% 8% 40%	1782
September	1st to 10th	Night	18% 6% 3 6% 5% 3 4 5% 5% 7% 38%	1746
	11th to 20th	Night	24% 9% 3 5% 4 3 4 5% 4 6% 35%	1980
	21st to end	Night	23% 10% 3 5% 5% 3 3 4 4 6% 34%	1980
October	1st to 10th	Night	21% 12% 4 5% 5% 3 4 3 4 6% 33%	2073
	11th to 20th	Night	26% 17% 5% 8% 5% 3 4 4 4 5% 19%	2256
	21st to end	Night	22% 21% 7% 9% 6% 3 3 4 5% 5% 15%	2574
November	1st to 10th	Night	21% 17% 7% 11% 7% 4 5% 4 4 5% 16%	2491
	11th to 20th	Night	20% 19% 7% 12% 9% 4 5% 4 3 3 13%	2660
	21st to end	Night	19% 19% 8% 14% 9% 4 4 3 3 4 12%	2840
December	1st to 10th	Night	11% 18% 9% 16% 10% 5% 6% 5% 3 4 13%	2850
	11th to 20th	Night	12% 18% 7% 11% 9% 7% 6% 5% 5% 5% 14%	3526
	21st to end	Night	16% 20% 7% 14% 11% 5% 5% 4 4 4 9%	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	75% 7% 9% 7% 3	2209
	11th to 20th	Day	69% 5% 10% 13% 3	2342
	21st to end	Day	74% 5% 7% 10% 4	2783
February	1st to 10th	Day	60% 5% 11% 18% 6%	1512
	11th to 20th	Day	63% 5% 12% 13% 7%	1582
	21st to end	Day	65% 4 10% 13% 7% 1	1470
March	1st to 10th	Day	58% 6% 10% 15% 11% 1	1800
	11th to 20th	Day	60% 6% 9% 16% 8%	1970
	21st to end	Day	54% 5% 9% 19% 11% 1	2200
April	1st to 10th	Day	63% 6% 7% 16% 8% 1	2203
	11th to 20th	Day	58% 4 9% 18% 10% 1	2312
	21st to end	Day	53% 6% 9% 16% 15% 2	2340
May	1st to 10th	Day	58% 7% 8% 15% 11% 1	2353
	11th to 20th	Day	52% 7% 11% 20% 10%	2655
	21st to end	Day	51% 8% 11% 20% 9% 1	2919
June	1st to 10th	Day	52% 8% 10% 17% 12% 1	2700
	11th to 20th	Day	45% 8% 12% 22% 13%	2700
	21st to end	Day	49% 8% 13% 20% 9% 1	2700
July	1st to 10th	Day	47% 9% 14% 24% 6%	2626
	11th to 20th	Day	42% 10% 17% 25% 5%	2619
	21st to end	Day	47% 10% 17% 21% 5%	2666
August	1st to 10th	Day	50% 10% 18% 18% 4	2470
	11th to 20th	Day	43% 9% 17% 22% 8%	2303
	21st to end	Day	51% 8% 14% 20% 6%	2574
September	1st to 10th	Day	50% 7% 14% 21% 7% 1	2192
	11th to 20th	Day	56% 8% 18% 16% 3	1980
	21st to end	Day	57% 7% 12% 18% 6%	1980
October	1st to 10th	Day	57% 7% 17% 15% 4	1886
	11th to 20th	Day	69% 6% 9% 14% 2	1702
	21st to end	Day	73% 5% 9% 8% 4	1782
November	1st to 10th	Day	70% 6% 11% 11% 3	1586
	11th to 20th	Day	77% 5% 8% 8% 2	1520
	21st to end	Day	81% 5% 6% 6% 2	1335
December	1st to 10th	Day	75% 5% 10% 8% 2	1330
	11th to 20th	Day	72% 8% 9% 8% 3	1671
	21st to end	Day	80% 5% 8% 6% 2	2431
January	1st to 10th	Night	74% 7% 11% 7% 1	4748
	11th to 20th	Night	71% 7% 11% 9% 2	4627
	21st to end	Night	70% 6% 10% 11% 2	4884
February	1st to 10th	Night	62% 8% 9% 15% 7%	2543
	11th to 20th	Night	63% 5% 11% 15% 6%	2275
	21st to end	Night	62% 6% 11% 15% 5% 1	1785
March	1st to 10th	Night	57% 7% 11% 16% 10% 1	2160
	11th to 20th	Night	59% 5% 9% 16% 10% 1	1990
	21st to end	Night	53% 5% 10% 18% 13% 2	2172
April	1st to 10th	Night	58% 6% 7% 17% 10% 1	1756
	11th to 20th	Night	53% 6% 9% 17% 13% 1	1597
	21st to end	Night	51% 5% 10% 15% 17% 3	1620
May	1st to 10th	Night	52% 8% 11% 17% 11% 1	1604
	11th to 20th	Night	50% 6% 9% 22% 11% 1	1244
	21st to end	Night	49% 6% 14% 20% 10% 2	1358
June	1st to 10th	Night	46% 6% 11% 22% 12% 2	1260
	11th to 20th	Night	44% 7% 11% 22% 15% 1	1260
	21st to end	Night	43% 9% 13% 23% 12%	1260
July	1st to 10th	Night	38% 10% 15% 25% 12%	1225
	11th to 20th	Night	39% 10% 17% 25% 8%	1218
	21st to end	Night	43% 8% 16% 28% 4	1410
August	1st to 10th	Night	41% 10% 21% 22% 5%	1444
	11th to 20th	Night	37% 9% 20% 25% 9%	1598
	21st to end	Night	41% 10% 15% 28% 6% 1	1782
September	1st to 10th	Night	46% 6% 15% 24% 8% 1	1746
	11th to 20th	Night	50% 8% 19% 18% 5%	1980
	21st to end	Night	51% 7% 15% 20% 6%	1980
October	1st to 10th	Night	53% 6% 15% 19% 6% 1	2073
	11th to 20th	Night	67% 8% 11% 12% 2	2256
	21st to end	Night	71% 7% 11% 9% 2	2574
November	1st to 10th	Night	71% 7% 9% 10% 2 1	2491
	11th to 20th	Night	77% 6% 8% 8% 1	2660
	21st to end	Night	78% 5% 8% 7% 2	2840
December	1st to 10th	Night	75% 6% 7% 8% 4	2850
	11th to 20th	Night	70% 7% 9% 11% 3	3525
	21st to end	Night	78% 6% 8% 6% 2	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	19% 15% 39% 19% 5% 2	180
	11th to 20th	Day	16% 13% 38% 25% 7% 1	218
	21st to end	Day	19% 16% 31% 25% 6% 2	297
February	1st to 10th	Day	14% 24% 36% 21% 4	252
	11th to 20th	Day	21% 19% 38% 17% 4 1	240
	21st to end	Day	19% 24% 43% 13% 1	198
March	1st to 10th	Day	16% 16% 43% 22% 3 1	240
	11th to 20th	Day	24% 15% 31% 23% 5% 2	410
	21st to end	Day	23% 14% 34% 22% 6% 2	462
April	1st to 10th	Day	21% 21% 32% 19% 6% 1	420
	11th to 20th	Day	28% 19% 25% 20% 7% 2	412
	21st to end	Day	21% 19% 29% 19% 9% 2	420
May	1st to 10th	Day	25% 14% 34% 17% 7% 2	436
	11th to 20th	Day	22% 17% 31% 21% 6% 3	625
	21st to end	Day	26% 13% 33% 22% 6% 1	679
June	1st to 10th	Day	27% 13% 31% 19% 7% 2	630
	11th to 20th	Day	22% 13% 34% 21% 9% 1	630
	21st to end	Day	23% 12% 30% 21% 12% 2	630
July	1st to 10th	Day	19% 12% 33% 24% 10% 3	621
	11th to 20th	Day	19% 12% 30% 26% 12% 2	618
	21st to end	Day	17% 10% 32% 27% 10% 4	684
August	1st to 10th	Day	19% 9% 31% 26% 11% 2	604
	11th to 20th	Day	18% 11% 27% 25% 15% 5%	439
	21st to end	Day	21% 13% 29% 22% 11% 4	495
September	1st to 10th	Day	22% 15% 30% 20% 9% 2	450
	11th to 20th	Day	31% 15% 30% 14% 7% 3	450
	21st to end	Day	30% 10% 30% 18% 10% 1	450
October	1st to 10th	Day	29% 16% 26% 22% 6% 1	450
	11th to 20th	Day	34% 18% 31% 14% 3	352
	21st to end	Day	36% 18% 26% 18% 2	297
November	1st to 10th	Day	31% 23% 29% 12% 3	229
	11th to 20th	Day	36% 23% 27% 11% 3	180
	21st to end	Day	30% 24% 34% 9% 3	180
December	1st to 10th	Day	24% 15% 31% 21% 7% 2	180
	11th to 20th	Day	22% 18% 41% 15% 3 2	180
	21st to end	Day	26% 16% 30% 20% 7% 2	198
January	1st to 10th	Night	21% 14% 36% 21% 8% 1	950
	11th to 20th	Night	20% 13% 33% 26% 6% 2	950
	21st to end	Night	17% 11% 33% 28% 10% 2	1045
February	1st to 10th	Night	14% 13% 33% 30% 10% 1	883
	11th to 20th	Night	16% 14% 33% 27% 9% 1	703
	21st to end	Night	16% 14% 35% 27% 7% 1	592
March	1st to 10th	Night	16% 13% 34% 28% 8% 2	720
	11th to 20th	Night	20% 15% 34% 23% 7% 1	720
	21st to end	Night	17% 13% 34% 25% 9% 1	786
April	1st to 10th	Night	24% 14% 31% 23% 7% 1	540
	11th to 20th	Night	23% 12% 28% 26% 9% 1	533
	21st to end	Night	22% 11% 30% 25% 10% 1	540
May	1st to 10th	Night	21% 10% 32% 30% 8%	540
	11th to 20th	Night	23% 10% 33% 27% 6% 1	358
	21st to end	Night	22% 12% 32% 28% 7%	389
June	1st to 10th	Night	24% 11% 28% 25% 11% 1	360
	11th to 20th	Night	20% 11% 26% 34% 9%	360
	21st to end	Night	19% 9% 29% 32% 11% 1	360
July	1st to 10th	Night	18% 8% 30% 32% 11% 1	350
	11th to 20th	Night	16% 7% 34% 33% 10% 1	348
	21st to end	Night	18% 6% 29% 31% 16%	509
August	1st to 10th	Night	15% 5% 31% 32% 14% 2	537
	11th to 20th	Night	17% 6% 26% 34% 15% 2	534
	21st to end	Night	19% 8% 28% 30% 14% 2	594
September	1st to 10th	Night	21% 10% 29% 26% 12% 2	572
	11th to 20th	Night	28% 11% 32% 21% 8%	720
	21st to end	Night	28% 9% 27% 26% 9% 1	720
October	1st to 10th	Night	27% 15% 27% 22% 9% 1	720
	11th to 20th	Night	37% 10% 29% 20% 5% 1	720
	21st to end	Night	33% 12% 25% 23% 6%	792
November	1st to 10th	Night	30% 17% 29% 18% 5% 1	740
	11th to 20th	Night	32% 14% 30% 18% 6%	760
	21st to end	Night	29% 16% 32% 16% 6%	940
December	1st to 10th	Night	21% 15% 33% 22% 8% 1	950
	11th to 20th	Night	20% 14% 35% 22% 7% 1	950
	21st to end	Night	24% 15% 29% 21% 9% 2	1045

Page generated at 2024-02-02 05:20:31. Version ac07

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