Pittsburgh Space Weather Observation Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pittsburgh Space Weather Observation Area clear sky chart from 2005-11-06 to 2024-01-12.

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% 10% 4 7% 6% 3 5% 5% 5% 7% 30%	74600
	Night	17% 11% 4 7% 6% 3 4 4 5% 6% 32%	75116
Transparency	Day	53% 6% 12% 18% 10% 1	74318
	Night	52% 6% 11% 18% 10% 1	74917
Seeing	Day	23% 15% 28% 20% 10% 4	13524
	Night	22% 13% 28% 25% 11% 1	23296

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	18% 17% 9% 10% 8% 3 4 4 4 4 18%	1677
	11th to 20th	Day	19% 20% 8% 11% 8% 3 3 3 3 4 17%	1635
	21st to end	Day	17% 19% 9% 12% 9% 3 4 3 4 5% 15%	1782
February	1st to 10th	Day	20% 18% 7% 11% 9% 3 4 3 3 3 19%	1620
	11th to 20th	Day	17% 13% 8% 13% 8% 3 4 4 5% 6% 19%	1573
	21st to end	Day	21% 15% 4 10% 5% 3 3 4 4 6% 23%	1469
March	1st to 10th	Day	17% 12% 6% 8% 7% 2 4 4 5% 6% 29%	1980
	11th to 20th	Day	19% 13% 4 7% 6% 3 5% 3 4 7% 29%	1980
	21st to end	Day	21% 12% 5% 8% 6% 2 4 4 4 6% 27%	2178
April	1st to 10th	Day	17% 12% 5% 7% 5% 3 5% 5% 5% 7% 31%	2075
	11th to 20th	Day	20% 11% 3 6% 6% 3 4 5% 5% 6% 32%	2177
	21st to end	Day	23% 9% 4 6% 5% 3 4 4 5% 6% 33%	2340
May	1st to 10th	Day	19% 9% 4 7% 6% 4 5% 5% 5% 8% 28%	2340
	11th to 20th	Day	21% 8% 2 6% 6% 4 6% 6% 5% 6% 30%	2301
	21st to end	Day	13% 6% 2 6% 5% 4 6% 7% 7% 8% 37%	2695
June	1st to 10th	Day	16% 7% 3 6% 6% 3 5% 6% 6% 9% 33%	2520
	11th to 20th	Day	16% 6% 3 6% 6% 3 6% 5% 6% 9% 35%	2520
	21st to end	Day	15% 6% 3 5% 5% 4 5% 5% 6% 9% 37%	2520
July	1st to 10th	Day	12% 6% 3 5% 6% 4 5% 5% 6% 8% 40%	2479
	11th to 20th	Day	13% 6% 3 6% 5% 3 6% 5% 7% 8% 38%	2340
	21st to end	Day	12% 5% 3 6% 7% 3 7% 7% 7% 9% 35%	2547
August	1st to 10th	Day	10% 7% 3 6% 7% 4 6% 6% 7% 10% 34%	2327
	11th to 20th	Day	14% 6% 3 6% 7% 4 6% 6% 7% 9% 32%	2303
	21st to end	Day	12% 6% 2 7% 6% 4 6% 6% 7% 8% 37%	2465
September	1st to 10th	Day	17% 7% 3 5% 3 3 4 5% 5% 8% 41%	2160
	11th to 20th	Day	13% 5% 3 5% 5% 3 5% 5% 7% 8% 41%	1986
	21st to end	Day	19% 7% 3 6% 5% 3 4 4 5% 7% 37%	1980
October	1st to 10th	Day	17% 7% 3 5% 5% 4 4 5% 6% 8% 37%	1800
	11th to 20th	Day	22% 8% 3 6% 6% 4 4 5% 4 5% 32%	1800
	21st to end	Day	25% 10% 4 7% 5% 2 3 5% 4 6% 29%	1980
November	1st to 10th	Day	12% 9% 4 5% 6% 3 5% 4 4 7% 40%	1762
	11th to 20th	Day	19% 15% 4 6% 6% 3 4 4 4 6% 30%	1567
	21st to end	Day	19% 16% 7% 9% 6% 3 3 4 5% 5% 23%	1520
December	1st to 10th	Day	20% 20% 10% 11% 6% 3 4 3 4 3 16%	1520
	11th to 20th	Day	19% 18% 8% 12% 5% 3 4 3 5% 5% 18%	1910
	21st to end	Day	26% 25% 8% 8% 5% 2 3 3 3 4 12%	2772
January	1st to 10th	Night	19% 18% 8% 10% 7% 4 5% 4 3 4 18%	2483
	11th to 20th	Night	20% 16% 7% 11% 8% 4 5% 4 3 4 18%	2365
	21st to end	Night	17% 18% 8% 10% 8% 4 5% 4 3 5% 20%	2574
February	1st to 10th	Night	19% 15% 5% 10% 9% 4 4 4 4 4 21%	2340
	11th to 20th	Night	19% 13% 6% 12% 7% 3 5% 3 5% 5% 22%	2273
	21st to end	Night	21% 12% 5% 11% 6% 4 5% 4 4 4 25%	1781
March	1st to 10th	Night	16% 12% 5% 7% 6% 4 4 4 5% 6% 30%	1980
	11th to 20th	Night	20% 11% 4 6% 5% 2 5% 3 4 6% 34%	1980
	21st to end	Night	19% 11% 5% 8% 6% 3 4 3 4 4 32%	2178
April	1st to 10th	Night	18% 11% 4 6% 5% 3 4 5% 4 7% 33%	1883
	11th to 20th	Night	18% 9% 3 5% 4 3 5% 5% 5% 6% 35%	1746
	21st to end	Night	17% 10% 4 6% 5% 3 5% 4 5% 7% 34%	1620
May	1st to 10th	Night	18% 8% 3 7% 5% 3 5% 5% 6% 7% 33%	1620
	11th to 20th	Night	17% 8% 3 5% 6% 2 4 5% 5% 8% 37%	1592
	21st to end	Night	10% 5% 2 5% 5% 3 5% 5% 7% 10% 43%	1576
June	1st to 10th	Night	10% 5% 2 5% 6% 3 5% 5% 6% 9% 44%	1440
	11th to 20th	Night	12% 6% 2 5% 5% 3 5% 5% 6% 8% 43%	1440
	21st to end	Night	11% 5% 3 5% 5% 3 5% 5% 7% 10% 41%	1440
July	1st to 10th	Night	8% 6% 2 5% 6% 4 5% 5% 5% 7% 47%	1476
	11th to 20th	Night	9% 4 2 5% 5% 4 5% 5% 5% 10% 46%	1620
	21st to end	Night	10% 5% 3 5% 5% 4 6% 5% 7% 9% 41%	1771
August	1st to 10th	Night	9% 5% 2 5% 4 4 4 6% 5% 9% 47%	1611
	11th to 20th	Night	10% 6% 3 5% 5% 2 4 4 6% 8% 46%	1598
	21st to end	Night	11% 5% 2 4 5% 3 5% 5% 6% 9% 46%	1872
September	1st to 10th	Night	14% 5% 2 5% 4 3 4 4 7% 7% 47%	1800
	11th to 20th	Night	11% 4 2 4 4 3 3 4 6% 8% 52%	1970
	21st to end	Night	17% 7% 2 6% 4 3 4 4 5% 6% 41%	1980
October	1st to 10th	Night	16% 6% 3 5% 4 3 4 4 5% 8% 43%	2160
	11th to 20th	Night	18% 8% 3 6% 6% 3 4 4 5% 6% 37%	2160
	21st to end	Night	25% 9% 3 5% 5% 2 4 4 4 7% 31%	2376
November	1st to 10th	Night	14% 9% 3 5% 5% 3 4 4 4 8% 41%	2311
	11th to 20th	Night	18% 12% 4 7% 6% 4 5% 5% 5% 6% 29%	2611
	21st to end	Night	19% 16% 4 7% 6% 3 4 4 4 7% 27%	2660
December	1st to 10th	Night	23% 16% 7% 10% 7% 3 4 3 4 5% 18%	2660
	11th to 20th	Night	19% 18% 8% 10% 6% 3 4 4 4 5% 20%	3285
	21st to end	Night	26% 20% 8% 8% 7% 3 4 4 4 4 12%	4884

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	70% 5% 11% 10% 4	1678
	11th to 20th	Day	72% 4 11% 10% 2	1635
	21st to end	Day	73% 4 9% 10% 3 1	1782
February	1st to 10th	Day	71% 3 9% 12% 5%	1620
	11th to 20th	Day	67% 5% 9% 13% 6%	1582
	21st to end	Day	62% 6% 10% 14% 7% 1	1469
March	1st to 10th	Day	55% 5% 13% 20% 7%	1980
	11th to 20th	Day	57% 5% 9% 17% 10% 2	1980
	21st to end	Day	59% 5% 8% 17% 11% 1	2178
April	1st to 10th	Day	52% 6% 12% 16% 12% 2	2075
	11th to 20th	Day	52% 7% 10% 17% 13% 2	2177
	21st to end	Day	52% 5% 10% 21% 10% 2	2340
May	1st to 10th	Day	54% 6% 12% 17% 9% 2	2340
	11th to 20th	Day	53% 8% 11% 15% 11% 2	2305
	21st to end	Day	41% 9% 15% 22% 10% 2	2695
June	1st to 10th	Day	47% 8% 12% 22% 11% 1	2520
	11th to 20th	Day	45% 8% 14% 19% 12% 1	2520
	21st to end	Day	43% 8% 11% 26% 11% 1	2520
July	1st to 10th	Day	41% 8% 13% 22% 14% 3	2411
	11th to 20th	Day	41% 8% 14% 23% 14% 1	2271
	21st to end	Day	42% 9% 13% 21% 14% 1	2405
August	1st to 10th	Day	41% 9% 15% 26% 8% 1	2314
	11th to 20th	Day	45% 8% 15% 20% 10% 1	2303
	21st to end	Day	42% 9% 13% 21% 13% 3	2465
September	1st to 10th	Day	42% 8% 11% 21% 16% 3	2160
	11th to 20th	Day	39% 7% 14% 24% 15% 1	1986
	21st to end	Day	47% 6% 11% 22% 13%	1980
October	1st to 10th	Day	44% 7% 13% 20% 15% 1	1800
	11th to 20th	Day	54% 5% 12% 20% 9%	1800
	21st to end	Day	56% 6% 12% 15% 9% 1	1980
November	1st to 10th	Day	45% 4 12% 20% 16% 2	1762
	11th to 20th	Day	56% 5% 11% 17% 9% 2	1567
	21st to end	Day	63% 5% 11% 15% 5% 1	1520
December	1st to 10th	Day	73% 5% 9% 10% 3	1520
	11th to 20th	Day	69% 5% 9% 14% 3	1906
	21st to end	Day	78% 4 9% 8% 2	2772
January	1st to 10th	Night	70% 3 9% 13% 4	2483
	11th to 20th	Night	71% 4 11% 12% 3	2365
	21st to end	Night	69% 4 9% 12% 4 1	2574
February	1st to 10th	Night	67% 5% 9% 14% 4	2340
	11th to 20th	Night	65% 4 10% 14% 6%	2275
	21st to end	Night	63% 5% 8% 15% 8% 1	1781
March	1st to 10th	Night	54% 6% 10% 20% 9% 1	1980
	11th to 20th	Night	52% 5% 12% 20% 9% 2	1980
	21st to end	Night	54% 5% 8% 17% 14% 2	2178
April	1st to 10th	Night	52% 6% 10% 19% 13% 1	1883
	11th to 20th	Night	48% 6% 12% 16% 15% 3	1746
	21st to end	Night	48% 5% 12% 20% 12% 3	1620
May	1st to 10th	Night	50% 7% 9% 18% 12% 3	1620
	11th to 20th	Night	46% 7% 11% 19% 15% 3	1593
	21st to end	Night	34% 8% 14% 27% 15% 2	1577
June	1st to 10th	Night	37% 7% 14% 25% 15% 1	1440
	11th to 20th	Night	38% 9% 13% 23% 15% 2	1440
	21st to end	Night	38% 8% 13% 23% 16% 1	1440
July	1st to 10th	Night	36% 10% 10% 22% 19% 3	1434
	11th to 20th	Night	32% 8% 15% 24% 19% 2	1566
	21st to end	Night	37% 9% 16% 22% 14% 3	1672
August	1st to 10th	Night	33% 7% 15% 26% 18% 1	1600
	11th to 20th	Night	35% 8% 15% 26% 14% 2	1598
	21st to end	Night	33% 8% 14% 25% 15% 4	1872
September	1st to 10th	Night	35% 7% 13% 23% 18% 4	1800
	11th to 20th	Night	29% 6% 15% 27% 21% 1	1970
	21st to end	Night	44% 6% 12% 21% 17% 1	1980
October	1st to 10th	Night	40% 7% 14% 22% 15% 2	2160
	11th to 20th	Night	47% 6% 13% 23% 12% 1	2160
	21st to end	Night	53% 6% 11% 18% 10% 2	2376
November	1st to 10th	Night	42% 5% 12% 23% 15% 3	2311
	11th to 20th	Night	56% 5% 10% 18% 9% 3	2611
	21st to end	Night	58% 5% 12% 18% 5% 1	2660
December	1st to 10th	Night	69% 5% 11% 10% 4	2660
	11th to 20th	Night	67% 5% 10% 15% 3	3288
	21st to end	Night	75% 6% 9% 8% 1	4884

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	32% 28% 26% 11% 3 1	256
	11th to 20th	Day	31% 30% 28% 8% 2	245
	21st to end	Day	28% 34% 28% 8% 2	264
February	1st to 10th	Day	35% 28% 35% 3	240
	11th to 20th	Day	37% 31% 25% 7%	240
	21st to end	Day	38% 30% 25% 8%	218
March	1st to 10th	Day	32% 23% 31% 11% 3	420
	11th to 20th	Day	34% 17% 35% 8% 5% 1	420
	21st to end	Day	34% 21% 26% 14% 4 1	462
April	1st to 10th	Day	30% 22% 26% 15% 7% 1	420
	11th to 20th	Day	26% 19% 27% 17% 7% 4	412
	21st to end	Day	30% 19% 30% 15% 4 2	420
May	1st to 10th	Day	30% 18% 28% 17% 5% 2	423
	11th to 20th	Day	26% 13% 31% 19% 9% 3	447
	21st to end	Day	17% 9% 28% 26% 14% 7%	485
June	1st to 10th	Day	16% 12% 32% 26% 12% 3	450
	11th to 20th	Day	19% 13% 26% 27% 12% 3	450
	21st to end	Day	16% 11% 34% 25% 12% 2	450
July	1st to 10th	Day	14% 6% 21% 27% 22% 10%	445
	11th to 20th	Day	14% 5% 28% 28% 18% 7%	444
	21st to end	Day	14% 7% 26% 30% 16% 8%	488
August	1st to 10th	Day	13% 6% 23% 28% 21% 9%	446
	11th to 20th	Day	15% 6% 24% 29% 16% 10%	439
	21st to end	Day	13% 5% 25% 29% 18% 9%	495
September	1st to 10th	Day	18% 8% 22% 26% 18% 8%	450
	11th to 20th	Day	13% 4 21% 32% 19% 10%	450
	21st to end	Day	21% 12% 26% 23% 14% 4	450
October	1st to 10th	Day	16% 12% 28% 23% 17% 4	450
	11th to 20th	Day	27% 15% 30% 20% 7% 1	450
	21st to end	Day	32% 16% 28% 17% 5%	495
November	1st to 10th	Day	20% 21% 31% 16% 10% 2	360
	11th to 20th	Day	34% 21% 29% 11% 3 2	202
	21st to end	Day	24% 26% 39% 8% 2	180
December	1st to 10th	Day	34% 28% 26% 7% 3 2	180
	11th to 20th	Day	30% 25% 33% 10% 2	180
	21st to end	Day	36% 27% 28% 8% 2	198
January	1st to 10th	Night	29% 21% 35% 12% 2	760
	11th to 20th	Night	32% 19% 32% 15% 2	728
	21st to end	Night	26% 23% 31% 17% 2	792
February	1st to 10th	Night	30% 20% 29% 19% 2	720
	11th to 20th	Night	29% 21% 36% 13% 1	703
	21st to end	Night	31% 20% 30% 16% 2	592
March	1st to 10th	Night	27% 19% 32% 19% 3	720
	11th to 20th	Night	29% 17% 28% 20% 5%	720
	21st to end	Night	25% 15% 36% 19% 4 1	792
April	1st to 10th	Night	25% 17% 30% 22% 6%	720
	11th to 20th	Night	23% 15% 33% 20% 8% 1	682
	21st to end	Night	22% 11% 34% 26% 5%	540
May	1st to 10th	Night	21% 10% 26% 32% 9% 1	540
	11th to 20th	Night	20% 8% 28% 34% 9% 1	531
	21st to end	Night	12% 4 28% 32% 21% 3	416
June	1st to 10th	Night	9% 4 30% 39% 18%	360
	11th to 20th	Night	13% 6% 26% 38% 17%	360
	21st to end	Night	11% 5% 28% 37% 18% 1	360
July	1st to 10th	Night	8% 3 19% 41% 23% 6%	384
	11th to 20th	Night	9% 3 20% 38% 25% 5%	522
	21st to end	Night	13% 3 14% 41% 27% 2	591
August	1st to 10th	Night	12% 2 15% 42% 26% 3	537
	11th to 20th	Night	12% 4 15% 38% 27% 4	534
	21st to end	Night	12% 4 21% 32% 27% 5%	684
September	1st to 10th	Night	16% 3 23% 30% 24% 3	720
	11th to 20th	Night	13% 4 17% 34% 29% 3	720
	21st to end	Night	20% 8% 25% 27% 17% 4	720
October	1st to 10th	Night	18% 8% 24% 29% 19% 2	720
	11th to 20th	Night	22% 12% 32% 26% 8% 1	720
	21st to end	Night	28% 14% 28% 24% 5%	792
November	1st to 10th	Night	20% 13% 28% 28% 11%	740
	11th to 20th	Night	27% 18% 28% 20% 7% 1	760
	21st to end	Night	28% 18% 30% 18% 5%	760
December	1st to 10th	Night	32% 21% 27% 16% 4	760
	11th to 20th	Night	27% 24% 29% 18% 3	760
	21st to end	Night	32% 18% 30% 18% 2	836

Page generated at 2024-01-09 16:24:24. Version ac07

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