Strawberry Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Strawberry Hill Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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	15% 11% 5% 8% 6% 3 5% 4 5% 6% 31%	74574
	Night	15% 12% 5% 9% 7% 3 4 4 5% 6% 29%	75243
Transparency	Day	54% 6% 11% 19% 10% 1	74274
	Night	57% 6% 11% 17% 9% 1	75064
Seeing	Day	21% 16% 30% 21% 9% 3	14523
	Night	20% 13% 30% 26% 9% 1	24474

By Month

Percentage Cloud Cover SE (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	13% 17% 11% 14% 9% 6% 6% 4 4 3 13%	1517
	11th to 20th	Day	15% 17% 10% 17% 11% 5% 5% 3 3 4 9%	1488
	21st to end	Day	12% 19% 11% 16% 10% 5% 6% 4 3 4 11%	1584
February	1st to 10th	Day	11% 16% 9% 13% 15% 5% 5% 4 4 5% 13%	1565
	11th to 20th	Day	11% 15% 9% 16% 12% 5% 6% 4 4 4 15%	1739
	21st to end	Day	13% 19% 9% 12% 9% 4 4 4 4 4 19%	1480
March	1st to 10th	Day	14% 11% 7% 11% 10% 4 4 4 5% 5% 27%	1800
	11th to 20th	Day	12% 12% 6% 9% 7% 4 4 5% 5% 5% 31%	1936
	21st to end	Day	17% 15% 5% 7% 6% 3 5% 4 4 5% 29%	2237
April	1st to 10th	Day	18% 14% 6% 9% 6% 3 4 3 4 6% 27%	2160
	11th to 20th	Day	21% 13% 4 6% 4 3 3 4 4 5% 34%	2231
	21st to end	Day	16% 12% 4 8% 5% 3 4 5% 5% 7% 30%	2340
May	1st to 10th	Day	16% 10% 4 7% 5% 3 5% 4 5% 6% 36%	2340
	11th to 20th	Day	16% 9% 3 6% 6% 3 4 4 5% 6% 38%	2349
	21st to end	Day	11% 6% 3 5% 6% 3 4 6% 6% 8% 41%	2725
June	1st to 10th	Day	14% 6% 2 5% 5% 3 5% 5% 6% 8% 42%	2574
	11th to 20th	Day	13% 6% 3 5% 5% 3 5% 5% 5% 9% 40%	2700
	21st to end	Day	14% 5% 3 6% 5% 3 5% 6% 6% 8% 38%	2557
July	1st to 10th	Day	9% 4 2 4 5% 3 4 5% 6% 10% 48%	2520
	11th to 20th	Day	12% 5% 3 6% 5% 3 5% 5% 6% 8% 41%	2520
	21st to end	Day	10% 5% 2 5% 4 3 6% 6% 7% 9% 43%	2743
August	1st to 10th	Day	10% 5% 2 6% 6% 4 6% 6% 6% 9% 38%	2386
	11th to 20th	Day	12% 6% 3 5% 6% 3 5% 5% 7% 8% 42%	2303
	21st to end	Day	14% 7% 3 5% 5% 3 4 5% 5% 7% 42%	2480
September	1st to 10th	Day	16% 5% 2 6% 5% 3 5% 5% 6% 8% 39%	2124
	11th to 20th	Day	15% 6% 2 5% 5% 3 4 4 5% 6% 46%	1980
	21st to end	Day	17% 7% 3 6% 5% 4 5% 5% 6% 8% 34%	1980
October	1st to 10th	Day	19% 9% 3 6% 5% 3 4 4 4 6% 36%	1980
	11th to 20th	Day	24% 15% 4 8% 6% 4 4 4 4 6% 20%	1715
	21st to end	Day	24% 18% 4 7% 7% 3 4 5% 5% 6% 18%	1782
November	1st to 10th	Day	16% 16% 5% 6% 5% 4 4 4 5% 7% 28%	1672
	11th to 20th	Day	13% 22% 8% 11% 7% 3 5% 3 4 7% 18%	1710
	21st to end	Day	18% 22% 10% 10% 6% 3 3 3 3 5% 16%	1629
December	1st to 10th	Day	14% 21% 12% 15% 9% 4 4 3 4 3 12%	1330
	11th to 20th	Day	15% 20% 9% 13% 8% 6% 5% 4 4 3 13%	1675
	21st to end	Day	20% 23% 11% 16% 7% 3 4 2 2 3 9%	2723
January	1st to 10th	Night	14% 15% 9% 18% 10% 5% 5% 4 3 5% 13%	2648
	11th to 20th	Night	15% 18% 8% 13% 11% 5% 5% 4 4 4 14%	2617
	21st to end	Night	12% 16% 9% 15% 11% 6% 7% 4 4 5% 12%	2772
February	1st to 10th	Night	11% 14% 9% 13% 13% 6% 7% 5% 3 4 14%	2394
	11th to 20th	Night	13% 13% 8% 15% 10% 4 5% 4 5% 5% 18%	2104
	21st to end	Night	15% 16% 6% 13% 9% 3 4 4 4 5% 21%	1776
March	1st to 10th	Night	12% 11% 5% 9% 6% 4 4 4 5% 5% 35%	2160
	11th to 20th	Night	13% 12% 6% 8% 6% 2 5% 4 4 5% 35%	2022
	21st to end	Night	16% 9% 5% 7% 5% 3 5% 5% 4 6% 34%	2134
April	1st to 10th	Night	17% 13% 6% 7% 5% 3 4 3 5% 7% 30%	1800
	11th to 20th	Night	20% 11% 4 5% 5% 2 4 5% 5% 5% 35%	1676
	21st to end	Night	15% 11% 4 5% 6% 3 3 4 5% 7% 38%	1620
May	1st to 10th	Night	15% 9% 3 6% 7% 3 5% 6% 6% 7% 34%	1620
	11th to 20th	Night	14% 10% 4 7% 7% 3 4 4 5% 6% 37%	1542
	21st to end	Night	12% 6% 3 4 3 3 4 4 6% 9% 45%	1551
June	1st to 10th	Night	13% 4 3 5% 6% 3 4 4 5% 8% 44%	1378
	11th to 20th	Night	10% 4 3 5% 5% 2 4 5% 7% 10% 44%	1260
	21st to end	Night	10% 6% 3 5% 5% 3 3 4 6% 7% 47%	1393
July	1st to 10th	Night	9% 3 2 4 4 2 5% 4 6% 10% 53%	1440
	11th to 20th	Night	7% 3 2 5% 6% 3 4 5% 7% 7% 50%	1440
	21st to end	Night	9% 6% 2 5% 6% 3 5% 4 5% 7% 49%	1575
August	1st to 10th	Night	8% 5% 2 5% 4 3 5% 5% 7% 9% 47%	1552
	11th to 20th	Night	10% 5% 1 4 4 3 4 5% 5% 8% 51%	1598
	21st to end	Night	13% 6% 2 5% 4 3 5% 5% 5% 7% 45%	1872
September	1st to 10th	Night	13% 5% 2 5% 4 2 4 4 5% 6% 50%	1818
	11th to 20th	Night	14% 6% 2 4 4 2 4 4 4 6% 48%	1980
	21st to end	Night	18% 6% 3 6% 5% 3 4 4 6% 8% 38%	1980
October	1st to 10th	Night	17% 10% 3 5% 5% 3 3 3 4 5% 41%	1980
	11th to 20th	Night	22% 11% 4 7% 5% 4 5% 5% 4 6% 28%	2240
	21st to end	Night	26% 15% 4 6% 5% 3 4 4 4 5% 25%	2574
November	1st to 10th	Night	13% 14% 4 7% 7% 4 5% 5% 5% 7% 30%	2406
	11th to 20th	Night	15% 18% 7% 10% 7% 4 5% 4 4 6% 20%	2470
	21st to end	Night	16% 20% 10% 10% 5% 3 4 4 4 5% 17%	2543
December	1st to 10th	Night	13% 19% 11% 14% 8% 4 5% 4 4 4 13%	2850
	11th to 20th	Night	14% 19% 8% 18% 9% 4 5% 4 5% 4 12%	3522
	21st to end	Night	23% 25% 9% 12% 5% 3 4 3 3 3 11%	4936

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	78% 5% 7% 7% 3	1518
	11th to 20th	Day	80% 6% 6% 6% 2	1488
	21st to end	Day	78% 6% 6% 7% 2	1584
February	1st to 10th	Day	76% 5% 9% 9% 2	1565
	11th to 20th	Day	72% 6% 8% 9% 4	1749
	21st to end	Day	71% 4 8% 14% 3	1480
March	1st to 10th	Day	60% 6% 10% 17% 7% 1	1800
	11th to 20th	Day	55% 5% 11% 18% 9% 2	1936
	21st to end	Day	57% 5% 10% 19% 8% 1	2237
April	1st to 10th	Day	59% 5% 11% 17% 9%	2160
	11th to 20th	Day	53% 4 9% 19% 14% 1	2231
	21st to end	Day	52% 6% 11% 14% 14% 3	2340
May	1st to 10th	Day	48% 6% 8% 23% 12% 2	2340
	11th to 20th	Day	47% 5% 9% 21% 15% 2	2353
	21st to end	Day	40% 7% 13% 26% 14% 2	2725
June	1st to 10th	Day	40% 6% 12% 26% 15% 2	2574
	11th to 20th	Day	40% 6% 13% 23% 17% 1	2700
	21st to end	Day	42% 6% 13% 24% 14% 1	2557
July	1st to 10th	Day	31% 7% 13% 29% 19% 2	2451
	11th to 20th	Day	39% 7% 11% 26% 15% 1	2445
	21st to end	Day	35% 9% 11% 26% 17% 2	2591
August	1st to 10th	Day	38% 8% 14% 27% 11% 1	2371
	11th to 20th	Day	39% 7% 13% 27% 14% 1	2303
	21st to end	Day	41% 7% 12% 23% 15% 2	2480
September	1st to 10th	Day	41% 6% 12% 24% 15% 1	2124
	11th to 20th	Day	38% 5% 15% 30% 11% 1	1980
	21st to end	Day	46% 7% 14% 24% 8%	1980
October	1st to 10th	Day	49% 6% 10% 23% 11% 1	1980
	11th to 20th	Day	66% 5% 10% 16% 3	1715
	21st to end	Day	68% 6% 11% 11% 4	1782
November	1st to 10th	Day	57% 5% 10% 19% 8%	1672
	11th to 20th	Day	68% 5% 12% 10% 4	1710
	21st to end	Day	73% 5% 11% 9% 2	1629
December	1st to 10th	Day	79% 5% 7% 8% 1	1330
	11th to 20th	Day	77% 4 10% 7% 1	1671
	21st to end	Day	84% 4 6% 5% 2	2723
January	1st to 10th	Night	76% 6% 8% 7% 3	2648
	11th to 20th	Night	75% 6% 9% 7% 3	2617
	21st to end	Night	75% 7% 8% 8% 2	2772
February	1st to 10th	Night	75% 4 7% 11% 3	2394
	11th to 20th	Night	69% 5% 8% 13% 4	2105
	21st to end	Night	66% 5% 11% 13% 5%	1776
March	1st to 10th	Night	51% 6% 12% 21% 9%	2160
	11th to 20th	Night	52% 5% 10% 19% 12% 2	2022
	21st to end	Night	52% 5% 10% 21% 11% 1	2134
April	1st to 10th	Night	55% 5% 9% 19% 11% 1	1800
	11th to 20th	Night	51% 5% 8% 20% 14% 2	1676
	21st to end	Night	47% 4 13% 19% 14% 2	1620
May	1st to 10th	Night	48% 6% 11% 20% 11% 3	1620
	11th to 20th	Night	49% 5% 9% 22% 14% 2	1543
	21st to end	Night	37% 6% 14% 25% 15% 2	1552
June	1st to 10th	Night	39% 6% 10% 26% 17% 1	1378
	11th to 20th	Night	35% 5% 15% 27% 16% 2	1260
	21st to end	Night	36% 6% 14% 26% 17% 2	1393
July	1st to 10th	Night	26% 6% 15% 31% 19% 3	1400
	11th to 20th	Night	31% 7% 15% 27% 20% 1	1392
	21st to end	Night	35% 6% 13% 28% 16% 1	1487
August	1st to 10th	Night	33% 6% 18% 31% 11% 1	1543
	11th to 20th	Night	31% 7% 16% 29% 16% 1	1598
	21st to end	Night	39% 6% 13% 25% 16% 1	1872
September	1st to 10th	Night	34% 7% 13% 27% 18% 2	1818
	11th to 20th	Night	38% 5% 14% 31% 12% 1	1980
	21st to end	Night	45% 6% 15% 25% 8%	1980
October	1st to 10th	Night	46% 5% 11% 24% 13% 1	1980
	11th to 20th	Night	57% 7% 12% 19% 5% 1	2240
	21st to end	Night	63% 5% 11% 14% 6%	2574
November	1st to 10th	Night	53% 7% 13% 18% 8% 1	2406
	11th to 20th	Night	66% 6% 11% 11% 5% 1	2470
	21st to end	Night	70% 6% 13% 10% 1	2543
December	1st to 10th	Night	78% 5% 7% 8% 2	2850
	11th to 20th	Night	76% 6% 10% 6% 2	3525
	21st to end	Night	81% 5% 8% 4 2	4936

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	23% 21% 39% 13% 4	270
	11th to 20th	Day	29% 17% 40% 11% 2	258
	21st to end	Day	26% 19% 34% 17% 3	264
February	1st to 10th	Day	23% 31% 35% 7% 4	240
	11th to 20th	Day	23% 32% 33% 11% 2	240
	21st to end	Day	31% 32% 32% 4 1	198
March	1st to 10th	Day	27% 33% 30% 9% 1	240
	11th to 20th	Day	24% 19% 34% 16% 5% 1	376
	21st to end	Day	30% 16% 26% 19% 8% 1	462
April	1st to 10th	Day	27% 20% 32% 16% 5% 1	420
	11th to 20th	Day	31% 19% 28% 14% 8% 2	412
	21st to end	Day	27% 17% 28% 19% 8% 2	420
May	1st to 10th	Day	26% 21% 27% 16% 6% 3	423
	11th to 20th	Day	19% 17% 31% 23% 6% 4	495
	21st to end	Day	14% 15% 30% 27% 11% 3	679
June	1st to 10th	Day	15% 17% 31% 24% 10% 3	630
	11th to 20th	Day	15% 13% 33% 25% 10% 3	630
	21st to end	Day	15% 12% 31% 30% 9% 3	630
July	1st to 10th	Day	11% 9% 27% 30% 15% 7%	621
	11th to 20th	Day	13% 11% 28% 29% 14% 5%	618
	21st to end	Day	12% 8% 35% 26% 16% 5%	684
August	1st to 10th	Day	11% 8% 29% 25% 18% 10%	505
	11th to 20th	Day	14% 7% 21% 30% 19% 10%	439
	21st to end	Day	18% 8% 25% 28% 16% 5%	495
September	1st to 10th	Day	18% 7% 28% 24% 16% 7%	450
	11th to 20th	Day	12% 11% 24% 30% 16% 7%	450
	21st to end	Day	23% 12% 20% 25% 13% 6%	450
October	1st to 10th	Day	25% 14% 26% 20% 12% 2	450
	11th to 20th	Day	33% 16% 33% 17% 2	360
	21st to end	Day	31% 25% 31% 9% 4 1	297
November	1st to 10th	Day	28% 19% 30% 19% 3	270
	11th to 20th	Day	23% 28% 37% 11% 2	270
	21st to end	Day	28% 32% 27% 11% 2	236
December	1st to 10th	Day	32% 22% 29% 11% 6% 1	180
	11th to 20th	Day	27% 29% 32% 10% 1 1	180
	21st to end	Day	25% 32% 34% 6% 2	281
January	1st to 10th	Night	21% 18% 35% 20% 5% 1	950
	11th to 20th	Night	25% 18% 34% 18% 5%	935
	21st to end	Night	19% 12% 39% 24% 5%	990
February	1st to 10th	Night	18% 18% 37% 21% 5%	774
	11th to 20th	Night	22% 20% 31% 23% 4	703
	21st to end	Night	26% 19% 31% 21% 3	592
March	1st to 10th	Night	18% 15% 35% 23% 9% 1	720
	11th to 20th	Night	20% 19% 33% 23% 5% 1	720
	21st to end	Night	21% 15% 31% 25% 7% 1	748
April	1st to 10th	Night	25% 13% 32% 24% 5% 1	540
	11th to 20th	Night	24% 15% 32% 22% 7% 1	533
	21st to end	Night	21% 11% 30% 30% 7% 1	540
May	1st to 10th	Night	18% 11% 34% 29% 7% 1	540
	11th to 20th	Night	19% 10% 33% 29% 9%	531
	21st to end	Night	14% 7% 27% 39% 12% 1	584
June	1st to 10th	Night	15% 8% 30% 36% 10% 1	478
	11th to 20th	Night	10% 9% 29% 41% 11% 1	360
	21st to end	Night	12% 6% 27% 37% 16% 1	493
July	1st to 10th	Night	9% 2 22% 42% 22% 2	525
	11th to 20th	Night	9% 5% 25% 35% 23% 2	522
	21st to end	Night	12% 5% 24% 37% 21% 1	591
August	1st to 10th	Night	10% 2 24% 42% 21% 2	537
	11th to 20th	Night	10% 5% 18% 37% 26% 4	534
	21st to end	Night	15% 6% 19% 40% 18% 1	594
September	1st to 10th	Night	15% 3 25% 32% 20% 4	558
	11th to 20th	Night	17% 6% 22% 34% 18% 3	720
	21st to end	Night	21% 9% 25% 28% 15% 3	720
October	1st to 10th	Night	21% 11% 27% 29% 11% 1	720
	11th to 20th	Night	29% 15% 26% 23% 6% 1	720
	21st to end	Night	32% 15% 27% 20% 5% 1	792
November	1st to 10th	Night	23% 14% 33% 22% 7% 1	740
	11th to 20th	Night	24% 19% 34% 19% 3	760
	21st to end	Night	26% 16% 35% 20% 3	765
December	1st to 10th	Night	22% 20% 36% 18% 4	950
	11th to 20th	Night	23% 20% 36% 16% 4 1	950
	21st to end	Night	28% 19% 33% 18% 2	1045

Page generated at 2024-01-14 09:55:01. Version ac07

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