Lawshe Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lawshe Memorial Observatory 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	15% 11% 5% 8% 6% 3 4 4 5% 7% 32%	74559
	Night	16% 13% 5% 9% 7% 3 4 4 4 5% 28%	75146
Transparency	Day	52% 7% 11% 19% 10% 1	74265
	Night	59% 7% 10% 16% 8% 1	74975
Seeing	Day	21% 14% 29% 23% 11% 3	14451
	Night	22% 13% 28% 27% 10% 1	24188

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	13% 20% 10% 16% 9% 5% 6% 4 3 4 9%	1517
	11th to 20th	Day	16% 18% 10% 15% 9% 4 4 5% 4 4 10%	1448
	21st to end	Day	14% 17% 10% 14% 10% 5% 7% 4 4 3 12%	1584
February	1st to 10th	Day	9% 16% 9% 12% 16% 5% 5% 5% 4 5% 14%	1550
	11th to 20th	Day	13% 13% 8% 13% 9% 5% 5% 4 4 5% 22%	1708
	21st to end	Day	13% 15% 7% 12% 7% 4 4 4 5% 6% 23%	1480
March	1st to 10th	Day	13% 11% 5% 8% 9% 4 4 4 5% 6% 31%	1798
	11th to 20th	Day	11% 11% 5% 7% 7% 4 5% 4 4 6% 37%	1944
	21st to end	Day	17% 10% 4 6% 6% 3 5% 4 5% 8% 32%	2231
April	1st to 10th	Day	20% 14% 5% 7% 5% 3 5% 4 4 7% 27%	2160
	11th to 20th	Day	21% 11% 4 6% 4 3 3 4 5% 6% 34%	2253
	21st to end	Day	16% 11% 4 8% 5% 3 4 4 5% 7% 33%	2340
May	1st to 10th	Day	17% 8% 3 5% 5% 2 5% 4 5% 6% 40%	2340
	11th to 20th	Day	15% 7% 3 6% 5% 4 4 4 4 6% 41%	2371
	21st to end	Day	12% 6% 2 5% 5% 3 5% 4 6% 9% 44%	2755
June	1st to 10th	Day	14% 5% 2 4 5% 3 4 5% 6% 8% 43%	2700
	11th to 20th	Day	13% 4 2 5% 5% 3 6% 4 6% 8% 42%	2700
	21st to end	Day	16% 6% 3 4 5% 2 4 4 5% 8% 42%	2700
July	1st to 10th	Day	9% 4 2 4 4 2 4 5% 6% 9% 52%	2547
	11th to 20th	Day	13% 5% 2 4 4 2 4 5% 6% 8% 48%	2520
	21st to end	Day	11% 6% 2 5% 4 3 3 4 6% 9% 47%	2743
August	1st to 10th	Day	10% 5% 2 4 5% 4 6% 6% 6% 9% 43%	2402
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 5% 6% 7% 47%	2303
	21st to end	Day	15% 6% 2 4 5% 2 4 4 4 8% 45%	2513
September	1st to 10th	Day	17% 6% 3 5% 5% 2 4 4 5% 9% 42%	2120
	11th to 20th	Day	14% 6% 2 5% 5% 3 4 4 5% 8% 44%	1980
	21st to end	Day	18% 6% 2 6% 5% 3 4 5% 6% 9% 35%	1980
October	1st to 10th	Day	21% 10% 3 7% 5% 4 4 3 5% 7% 33%	1968
	11th to 20th	Day	26% 17% 5% 6% 6% 3 5% 3 4 5% 19%	1710
	21st to end	Day	25% 17% 4 8% 7% 4 5% 4 4 5% 16%	1782
November	1st to 10th	Day	20% 18% 5% 6% 5% 3 4 4 4 6% 24%	1672
	11th to 20th	Day	14% 23% 8% 12% 8% 5% 3 3 4 5% 15%	1710
	21st to end	Day	19% 23% 11% 12% 7% 2 4 3 3 4 11%	1498
December	1st to 10th	Day	14% 24% 14% 16% 7% 2 3 4 3 3 10%	1330
	11th to 20th	Day	16% 21% 10% 16% 10% 4 4 4 3 3 9%	1671
	21st to end	Day	21% 23% 9% 15% 8% 4 3 2 3 3 8%	2531
January	1st to 10th	Night	15% 17% 9% 19% 10% 5% 4 3 3 4 11%	2648
	11th to 20th	Night	15% 18% 9% 15% 12% 4 5% 4 3 4 13%	2535
	21st to end	Night	14% 16% 8% 15% 11% 6% 6% 4 4 4 12%	2772
February	1st to 10th	Night	10% 17% 9% 14% 12% 6% 6% 4 4 4 15%	2408
	11th to 20th	Night	12% 13% 7% 12% 10% 4 6% 4 4 5% 22%	2137
	21st to end	Night	16% 16% 5% 11% 7% 4 4 5% 5% 6% 21%	1776
March	1st to 10th	Night	12% 11% 5% 7% 6% 4 5% 4 4 5% 38%	2149
	11th to 20th	Night	12% 11% 5% 8% 7% 3 5% 4 4 5% 35%	2015
	21st to end	Night	16% 9% 4 7% 5% 3 5% 5% 5% 5% 36%	2142
April	1st to 10th	Night	21% 11% 4 6% 6% 4 4 4 6% 6% 28%	1800
	11th to 20th	Night	19% 10% 4 6% 5% 3 5% 4 5% 5% 35%	1655
	21st to end	Night	16% 10% 4 7% 5% 2 4 5% 5% 6% 36%	1620
May	1st to 10th	Night	15% 8% 3 6% 7% 5% 6% 5% 6% 5% 34%	1620
	11th to 20th	Night	14% 9% 3 8% 7% 3 4 5% 6% 6% 35%	1519
	21st to end	Night	12% 6% 2 5% 5% 4 4 4 6% 8% 45%	1519
June	1st to 10th	Night	15% 5% 3 5% 5% 4 5% 4 5% 7% 41%	1260
	11th to 20th	Night	11% 5% 3 5% 5% 3 5% 4 7% 10% 41%	1260
	21st to end	Night	13% 6% 2 5% 6% 3 4 5% 5% 6% 45%	1260
July	1st to 10th	Night	12% 3 2 4 4 1 4 5% 7% 10% 49%	1408
	11th to 20th	Night	9% 5% 2 6% 5% 4 5% 4 6% 7% 47%	1440
	21st to end	Night	9% 4 3 4 5% 3 4 5% 6% 8% 48%	1575
August	1st to 10th	Night	10% 5% 2 5% 4 3 5% 4 5% 8% 49%	1534
	11th to 20th	Night	11% 4 1 5% 4 2 4 5% 5% 8% 51%	1598
	21st to end	Night	15% 6% 2 5% 4 3 4 4 4 6% 47%	1840
September	1st to 10th	Night	13% 6% 3 5% 4 2 4 5% 5% 6% 47%	1822
	11th to 20th	Night	15% 6% 2 5% 6% 3 4 4 5% 7% 44%	1980
	21st to end	Night	19% 7% 3 5% 5% 4 4 4 5% 7% 38%	1980
October	1st to 10th	Night	18% 9% 4 6% 5% 2 3 4 4 6% 38%	1991
	11th to 20th	Night	24% 14% 4 8% 5% 3 4 5% 4 6% 23%	2248
	21st to end	Night	28% 15% 4 7% 6% 3 4 4 3 5% 21%	2574
November	1st to 10th	Night	18% 16% 5% 8% 6% 3 4 4 4 6% 26%	2406
	11th to 20th	Night	17% 21% 7% 11% 8% 4 5% 4 4 5% 16%	2470
	21st to end	Night	19% 22% 10% 13% 6% 2 4 4 4 4 13%	2678
December	1st to 10th	Night	14% 23% 13% 18% 8% 3 4 3 2 3 10%	2850
	11th to 20th	Night	15% 20% 9% 17% 10% 3 4 3 3 4 12%	3526
	21st to end	Night	22% 21% 9% 13% 8% 4 3 4 4 4 8%	5131

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	80% 6% 6% 6% 2	1518
	11th to 20th	Day	79% 6% 7% 6% 2 1	1448
	21st to end	Day	80% 5% 6% 6% 3	1584
February	1st to 10th	Day	73% 7% 9% 9% 2	1550
	11th to 20th	Day	67% 6% 9% 10% 7% 1	1718
	21st to end	Day	64% 6% 9% 16% 5%	1480
March	1st to 10th	Day	55% 7% 12% 16% 9% 1	1800
	11th to 20th	Day	49% 5% 13% 22% 8% 3	1944
	21st to end	Day	52% 7% 12% 18% 10% 1	2231
April	1st to 10th	Day	58% 6% 9% 17% 9% 1	2160
	11th to 20th	Day	51% 5% 10% 18% 14% 2	2253
	21st to end	Day	52% 6% 11% 14% 14% 3	2340
May	1st to 10th	Day	46% 6% 9% 23% 13% 3	2340
	11th to 20th	Day	45% 6% 9% 22% 15% 3	2375
	21st to end	Day	37% 9% 12% 25% 15% 2	2755
June	1st to 10th	Day	38% 7% 11% 28% 14% 2	2700
	11th to 20th	Day	38% 9% 12% 23% 17% 1	2700
	21st to end	Day	40% 7% 13% 24% 13% 2	2700
July	1st to 10th	Day	30% 7% 14% 29% 19% 2	2478
	11th to 20th	Day	33% 9% 10% 30% 16% 1	2445
	21st to end	Day	35% 7% 14% 26% 17% 1	2591
August	1st to 10th	Day	36% 9% 15% 28% 12% 1	2387
	11th to 20th	Day	36% 9% 13% 29% 12% 1	2303
	21st to end	Day	39% 6% 15% 26% 13% 1	2513
September	1st to 10th	Day	41% 7% 12% 25% 15% 1	2120
	11th to 20th	Day	39% 8% 14% 29% 9% 1	1980
	21st to end	Day	46% 7% 15% 24% 8%	1980
October	1st to 10th	Day	53% 6% 10% 23% 8% 1	1968
	11th to 20th	Day	68% 6% 9% 13% 3	1710
	21st to end	Day	71% 7% 10% 10% 3	1782
November	1st to 10th	Day	61% 6% 10% 17% 5%	1672
	11th to 20th	Day	73% 6% 9% 8% 4	1710
	21st to end	Day	78% 5% 9% 6% 1	1498
December	1st to 10th	Day	82% 5% 6% 5% 2	1330
	11th to 20th	Day	80% 8% 6% 5% 1	1671
	21st to end	Day	83% 6% 6% 2 3	2531
January	1st to 10th	Night	79% 5% 8% 6% 2	2648
	11th to 20th	Night	78% 6% 7% 7% 3	2535
	21st to end	Night	77% 5% 8% 6% 3	2772
February	1st to 10th	Night	74% 6% 7% 9% 3 1	2408
	11th to 20th	Night	66% 5% 10% 15% 4	2138
	21st to end	Night	65% 6% 10% 13% 6%	1776
March	1st to 10th	Night	50% 5% 12% 21% 11% 1	2160
	11th to 20th	Night	52% 5% 11% 19% 11% 2	2016
	21st to end	Night	49% 7% 9% 20% 13% 1	2142
April	1st to 10th	Night	55% 6% 10% 16% 12% 1	1800
	11th to 20th	Night	51% 4 9% 22% 12% 2	1655
	21st to end	Night	50% 6% 9% 19% 14% 3	1620
May	1st to 10th	Night	50% 7% 10% 18% 12% 4	1620
	11th to 20th	Night	50% 6% 9% 19% 15% 2	1520
	21st to end	Night	37% 8% 12% 24% 15% 4	1520
June	1st to 10th	Night	42% 5% 11% 25% 15% 1	1260
	11th to 20th	Night	38% 8% 13% 25% 14% 3	1260
	21st to end	Night	38% 8% 12% 25% 15% 2	1260
July	1st to 10th	Night	29% 6% 14% 30% 18% 3	1368
	11th to 20th	Night	35% 7% 12% 27% 19% 1	1392
	21st to end	Night	34% 8% 15% 25% 17% 1	1487
August	1st to 10th	Night	34% 7% 17% 30% 11% 1	1525
	11th to 20th	Night	31% 9% 16% 30% 14% 1	1598
	21st to end	Night	39% 7% 15% 23% 15% 1	1840
September	1st to 10th	Night	37% 7% 13% 24% 17% 2	1822
	11th to 20th	Night	39% 7% 16% 27% 9% 1	1980
	21st to end	Night	45% 8% 16% 23% 8%	1980
October	1st to 10th	Night	48% 7% 10% 23% 10% 1	1991
	11th to 20th	Night	62% 7% 11% 14% 5%	2248
	21st to end	Night	66% 7% 10% 12% 4	2574
November	1st to 10th	Night	60% 6% 11% 17% 6% 1	2406
	11th to 20th	Night	70% 5% 10% 9% 5%	2470
	21st to end	Night	75% 6% 11% 6% 1	2678
December	1st to 10th	Night	81% 5% 7% 6% 1	2850
	11th to 20th	Night	79% 6% 9% 4 2	3525
	21st to end	Night	80% 9% 6% 3 1	5131

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% 18% 37% 17% 4	270
	11th to 20th	Day	24% 17% 38% 16% 4 1	243
	21st to end	Day	29% 13% 33% 19% 6%	264
February	1st to 10th	Day	20% 34% 33% 9% 4	240
	11th to 20th	Day	19% 33% 32% 15% 3	240
	21st to end	Day	30% 25% 37% 6% 2	198
March	1st to 10th	Day	22% 27% 32% 15% 5%	240
	11th to 20th	Day	21% 16% 34% 22% 6% 1	384
	21st to end	Day	28% 15% 27% 22% 7% 1	462
April	1st to 10th	Day	27% 17% 30% 17% 6% 1	420
	11th to 20th	Day	31% 17% 24% 16% 10% 1	412
	21st to end	Day	22% 14% 33% 20% 9% 2	420
May	1st to 10th	Day	25% 18% 26% 17% 11% 2	423
	11th to 20th	Day	18% 14% 36% 22% 7% 4	517
	21st to end	Day	15% 10% 29% 29% 14% 3	679
June	1st to 10th	Day	15% 13% 30% 29% 10% 2	630
	11th to 20th	Day	16% 10% 32% 30% 10% 3	630
	21st to end	Day	17% 9% 29% 32% 12% 2	630
July	1st to 10th	Day	10% 8% 30% 32% 17% 4	621
	11th to 20th	Day	14% 9% 27% 31% 14% 5%	618
	21st to end	Day	13% 7% 30% 32% 15% 4	684
August	1st to 10th	Day	10% 8% 22% 34% 21% 5%	521
	11th to 20th	Day	13% 6% 22% 31% 19% 9%	439
	21st to end	Day	21% 8% 23% 25% 18% 5%	495
September	1st to 10th	Day	20% 9% 26% 22% 17% 6%	450
	11th to 20th	Day	14% 12% 22% 28% 18% 5%	450
	21st to end	Day	21% 11% 23% 27% 15% 4	450
October	1st to 10th	Day	26% 15% 25% 20% 13% 1	450
	11th to 20th	Day	34% 20% 25% 18% 3 1	360
	21st to end	Day	32% 20% 32% 11% 3 1	297
November	1st to 10th	Day	35% 16% 30% 13% 6%	270
	11th to 20th	Day	25% 24% 31% 16% 4	270
	21st to end	Day	28% 31% 28% 11% 2	187
December	1st to 10th	Day	32% 23% 29% 10% 5% 1	180
	11th to 20th	Day	25% 28% 34% 9% 2 1	180
	21st to end	Day	33% 28% 28% 7% 3 1	227
January	1st to 10th	Night	21% 20% 32% 21% 5% 1	950
	11th to 20th	Night	25% 17% 31% 21% 6%	906
	21st to end	Night	21% 15% 33% 26% 5% 1	990
February	1st to 10th	Night	19% 19% 34% 23% 4	788
	11th to 20th	Night	20% 19% 31% 24% 7%	703
	21st to end	Night	25% 16% 31% 23% 4	592
March	1st to 10th	Night	18% 14% 33% 26% 8% 1	720
	11th to 20th	Night	20% 14% 35% 23% 7% 1	720
	21st to end	Night	21% 10% 28% 31% 9% 1	756
April	1st to 10th	Night	26% 11% 31% 26% 5% 1	540
	11th to 20th	Night	25% 10% 29% 27% 9% 1	533
	21st to end	Night	20% 9% 30% 30% 9% 1	540
May	1st to 10th	Night	15% 9% 29% 36% 10% 1	540
	11th to 20th	Night	17% 7% 32% 33% 9% 1	531
	21st to end	Night	15% 6% 23% 38% 18% 1	552
June	1st to 10th	Night	18% 6% 25% 38% 13% 1	360
	11th to 20th	Night	11% 5% 24% 41% 18%	360
	21st to end	Night	14% 5% 26% 38% 17% 1	360
July	1st to 10th	Night	11% 3 20% 46% 18% 2	493
	11th to 20th	Night	10% 6% 21% 35% 25% 3	522
	21st to end	Night	9% 4 24% 39% 21% 2	591
August	1st to 10th	Night	12% 2 20% 39% 24% 1	537
	11th to 20th	Night	12% 5% 14% 38% 28% 4	534
	21st to end	Night	18% 5% 20% 36% 19% 2	594
September	1st to 10th	Night	16% 5% 22% 33% 20% 4	562
	11th to 20th	Night	19% 6% 23% 31% 19% 3	720
	21st to end	Night	23% 7% 22% 31% 14% 4	720
October	1st to 10th	Night	23% 11% 24% 28% 12% 1	720
	11th to 20th	Night	33% 13% 27% 20% 6% 1	720
	21st to end	Night	37% 13% 26% 19% 5% 1	792
November	1st to 10th	Night	28% 16% 29% 21% 6% 1	740
	11th to 20th	Night	29% 19% 30% 18% 5%	760
	21st to end	Night	31% 19% 32% 16% 3	797
December	1st to 10th	Night	26% 22% 32% 16% 4	950
	11th to 20th	Night	24% 24% 33% 15% 3 1	950
	21st to end	Night	31% 16% 32% 18% 3	1045

Page generated at 2024-01-08 22:31:26. Version ac07

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