Plano
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Plano clear sky chart from 2005-11-05 to 2008-11-27.

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% 5% 5% 7% 47%	12265
	Night	10% 7% 54%	12169
Transparency	Day	14% 26% 28% 9%	9331
	Night	12% 24% 29% 13%	9698
Seeing	Day	6% 17% 32% 33% 5%	695
	Night	7% 31% 35% 18%	3728

By Month

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	18% 8% 47%	833
	Night	15% 5% 5% 6% 52%	1207
February	Day	19% 52%	798
	Night	15% 5% 55%	983
March	Day	18% 5% 5% 40%	1022
	Night	16% 6% 5% 6% 43%	1021
April	Day	12% 7% 5% 8% 46%	1053
	Night	11% 10% 48%	922
May	Day	15% 5% 7% 8% 36%	1208
	Night	10% 5% 6% 6% 9% 42%	837
June	Day	10% 5% 5% 5% 8% 45%	1170
	Night	5% 6% 10% 54%	810
July	Day	8% 5% 5% 8% 6% 7% 12% 35%	1209
	Night	6% 5% 11% 52%	834
August	Day	8% 5% 6% 6% 7% 10% 42%	1156
	Night	5% 5% 5% 8% 13% 48%	875
September	Day	11% 5% 5% 5% 7% 46%	987
	Night	11% 6% 55%	990
October	Day	9% 5% 66%	941
	Night	7% 67%	1089
November	Day	9% 6% 61%	1051
	Night	6% 66%	1393
December	Day	14% 5% 55%	837
	Night	13% 5% 56%	1208

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	9% 29% 31% 9%	617
	Night	10% 23% 36% 13%	910
February	Day	8% 29% 27% 17%	579
	Night	7% 21% 34% 21%	748
March	Day	17% 22% 24% 11%	670
	Night	10% 16% 20% 24% 12%	733
April	Day	13% 23% 26% 17%	772
	Night	6% 14% 20% 23% 23%	700
May	Day	6% 18% 27% 26%	787
	Night	11% 18% 26% 25% 5%	584
June	Day	8% 15% 29% 33%	823
	Night	6% 23% 30% 27%	631
July	Day	8% 22% 31% 21%	701
	Night	6% 19% 35% 26%	528
August	Day	5% 19% 28% 17%	1059
	Night	6% 17% 32% 19%	801
September	Day	11% 20% 27% 10%	883
	Night	7% 19% 34% 12%	887
October	Day	8% 19% 35% 18%	869
	Night	5% 17% 32% 25%	995
November	Day	11% 35% 28% 9%	901
	Night	10% 29% 33% 12%	1218
December	Day	8% 22% 40% 9%	670
	Night	9% 24% 31% 15%	963

Seeing (when cloud cover <= 80%)
Color Meanings: Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month		Occurrence of each Forecast	Data Points
January	Night	13% 46% 29% 6%	406
February	Night	14% 48% 28%	296
March	Night	11% 44% 31%	257
April	Day	14% 40% 35%	64
	Night	9% 45% 35% 5%	253
May	Day	11% 29% 36% 15%	170
	Night	6% 29% 46% 11%	261
June	Day	17% 33% 36%	165
	Night	14% 47% 32%	248
July	Day	31% 52% 7%	157
	Night	39% 49%	239
August	Day	7% 28% 44% 10%	139
	Night	30% 47% 11%	265
September	Night	13% 34% 36% 5%	254
October	Night	6% 26% 33% 26%	335
November	Night	7% 32% 41% 13%	486
December	Night	10% 43% 32% 6%	428

Page generated at 2008-11-27 12:47:33. Version ab11