Poker Flat Research Range
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Poker Flat Research Range clear sky chart from 2005-11-06 to 2025-09-19.

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	13% 11% 4 10% 6% 6% 6% 4 6% 7% 27%	131671
	Night	8% 12% 5% 11% 6% 6% 5% 4 6% 6% 30%	126175
Transparency	Day	55% 7% 15% 16% 6% 1	131267
	Night	53% 6% 13% 16% 9% 2	126157
Seeing	Day	17% 5% 17% 27% 24% 10%	20015
	Night	13% 4 16% 31% 28% 8%	23951

By Month

Percentage Cloud Cover NW (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	4 11% 4 11% 4 5% 4 2 4 6% 44%	1140
	11th to 20th	Day	3 14% 6% 13% 7% 5% 4 4 6% 6% 32%	1808
	21st to end	Day	6% 10% 5% 11% 11% 8% 7% 5% 7% 6% 23%	2386
February	1st to 10th	Day	2 12% 5% 10% 5% 5% 5% 5% 6% 4 41%	1200
	11th to 20th	Day	3 11% 4 15% 9% 6% 7% 8% 5% 7% 24%	1457
	21st to end	Day	4 13% 7% 11% 9% 5% 7% 4 6% 5% 28%	1320
March	1st to 10th	Day	3 13% 8% 16% 8% 6% 5% 3 4 4 30%	4355
	11th to 20th	Day	2 8% 5% 12% 7% 6% 6% 4 6% 7% 35%	4612
	21st to end	Day	4 14% 5% 11% 6% 6% 5% 4 6% 7% 33%	5965
April	1st to 10th	Day	5% 16% 6% 11% 9% 6% 6% 4 6% 7% 25%	2567
	11th to 20th	Day	5% 11% 4 9% 5% 4 4 4 6% 7% 39%	2774
	21st to end	Day	5% 9% 3 8% 5% 6% 6% 5% 7% 7% 39%	3061
May	1st to 10th	Day	9% 15% 5% 12% 7% 7% 5% 4 5% 7% 24%	7431
	11th to 20th	Day	5% 8% 3 9% 7% 6% 6% 4 6% 7% 40%	7912
	21st to end	Day	12% 10% 4 11% 7% 7% 8% 6% 8% 7% 20%	9230
June	1st to 10th	Day	13% 8% 4 9% 7% 7% 7% 5% 7% 8% 25%	3967
	11th to 20th	Day	13% 8% 3 8% 6% 7% 6% 5% 7% 8% 28%	4000
	21st to end	Day	16% 7% 3 7% 5% 5% 7% 5% 7% 10% 29%	4000
July	1st to 10th	Day	27% 9% 2 6% 5% 5% 5% 3 5% 7% 28%	9060
	11th to 20th	Day	17% 9% 3 8% 5% 5% 7% 6% 8% 10% 23%	8466
	21st to end	Day	23% 9% 3 7% 5% 5% 6% 5% 6% 8% 23%	8861
August	1st to 10th	Day	27% 11% 4 7% 5% 5% 5% 4 5% 6% 20%	5253
	11th to 20th	Day	25% 15% 4 9% 6% 5% 5% 4 6% 6% 16%	5007
	21st to end	Day	26% 15% 4 9% 6% 5% 4 4 5% 6% 15%	5040
September	1st to 10th	Day	20% 12% 4 9% 5% 5% 5% 4 6% 7% 23%	2611
	11th to 20th	Day	22% 16% 4 10% 5% 4 5% 4 5% 5% 20%	2344
	21st to end	Day	18% 17% 4 10% 6% 5% 4 4 4 5% 23%	2062
October	1st to 10th	Day	9% 17% 6% 10% 6% 4 4 3 4 5% 32%	2984
	11th to 20th	Day	7% 17% 7% 16% 6% 6% 5% 3 5% 4 25%	2751
	21st to end	Day	11% 15% 7% 15% 7% 5% 5% 3 5% 5% 22%	2424
November	1st to 10th	Day	7% 14% 5% 13% 7% 6% 5% 4 6% 5% 26%	1189
	11th to 20th	Day	6% 13% 5% 14% 10% 8% 5% 3 4 5% 28%	1000
	21st to end	Day	9% 13% 5% 13% 8% 6% 4 5% 5% 6% 27%	703
December	1st to 10th	Day	7% 13% 5% 7% 5% 5% 5% 5% 6% 7% 34%	953
	11th to 20th	Day	2 13% 7% 11% 5% 8% 4 4 7% 7% 31%	766
	21st to end	Day	2 9% 5% 13% 6% 6% 7% 5% 8% 7% 33%	1012
January	1st to 10th	Night	3 11% 4 10% 6% 5% 5% 3 4 6% 44%	8868
	11th to 20th	Night	3 13% 5% 11% 6% 6% 6% 4 7% 7% 33%	8110
	21st to end	Night	6% 12% 4 12% 7% 6% 6% 5% 7% 6% 27%	8590
February	1st to 10th	Night	2 10% 6% 15% 6% 4 4 3 4 4 41%	3200
	11th to 20th	Night	4 10% 5% 11% 7% 7% 7% 5% 8% 8% 30%	2828
	21st to end	Night	4 12% 7% 15% 8% 6% 6% 5% 5% 6% 25%	2310
March	1st to 10th	Night	2 12% 7% 15% 7% 6% 5% 4 5% 6% 30%	5500
	11th to 20th	Night	3 8% 4 12% 7% 6% 7% 4 7% 8% 34%	5346
	21st to end	Night	5% 13% 4 10% 6% 5% 5% 4 6% 7% 34%	4963
April	1st to 10th	Night	5% 16% 5% 12% 6% 5% 6% 5% 7% 6% 27%	1830
	11th to 20th	Night	5% 8% 4 9% 6% 5% 7% 6% 6% 7% 37%	1575
	21st to end	Night	6% 8% 3 8% 7% 5% 5% 4 7% 6% 41%	1337
May	1st to 10th	Night	8% 11% 4 10% 6% 7% 6% 6% 7% 10% 26%	2541
	11th to 20th	Night	7% 6% 2 7% 5% 5% 6% 5% 7% 9% 40%	1994
	21st to end	Night	14% 10% 3 11% 7% 7% 6% 5% 5% 7% 25%	1667
June	1st to 10th	Night	10% 6% 2 10% 7% 7% 6% 7% 8% 9% 29%	430
	11th to 20th	Night	13% 5% 3 10% 7% 6% 5% 5% 8% 8% 31%	400
	21st to end	Night	17% 4 3 8% 5% 7% 6% 6% 9% 8% 29%	400
July	1st to 10th	Night	26% 9% 3 7% 4 4 3 3 5% 8% 29%	920
	11th to 20th	Night	16% 11% 3 9% 5% 5% 5% 4 6% 6% 29%	1512
	21st to end	Night	24% 9% 3 7% 5% 5% 4 4 5% 9% 27%	2002
August	1st to 10th	Night	22% 13% 3 9% 6% 4 6% 4 5% 7% 20%	1904
	11th to 20th	Night	31% 15% 4 9% 5% 4 3 3 5% 6% 16%	2051
	21st to end	Night	26% 16% 3 8% 6% 5% 5% 3 5% 4 19%	2866
September	1st to 10th	Night	18% 12% 3 9% 6% 5% 5% 4 6% 7% 26%	1787
	11th to 20th	Night	20% 15% 4 8% 6% 6% 5% 4 5% 6% 21%	2013
	21st to end	Night	18% 15% 4 9% 5% 5% 5% 4 6% 5% 25%	2117
October	1st to 10th	Night	9% 16% 5% 9% 5% 5% 6% 4 5% 7% 29%	3982
	11th to 20th	Night	9% 17% 6% 11% 6% 6% 5% 4 5% 6% 26%	4174
	21st to end	Night	9% 15% 7% 17% 8% 5% 4 3 4 4 23%	5135
November	1st to 10th	Night	7% 18% 6% 11% 7% 5% 4 3 5% 5% 29%	3107
	11th to 20th	Night	8% 14% 5% 14% 8% 5% 5% 4 5% 5% 27%	3400
	21st to end	Night	7% 14% 5% 13% 8% 6% 5% 4 6% 5% 27%	3677
December	1st to 10th	Night	5% 12% 5% 12% 6% 6% 6% 4 5% 6% 32%	6235
	11th to 20th	Night	4 14% 6% 13% 6% 6% 5% 4 5% 5% 32%	7438
	21st to end	Night	2 11% 5% 12% 7% 7% 6% 5% 6% 7% 31%	9966

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	44% 3 11% 19% 11% 11%	1140
	11th to 20th	Day	51% 5% 17% 14% 10% 3	1820
	21st to end	Day	58% 4 8% 14% 10% 6%	2386
February	1st to 10th	Day	45% 5% 6% 16% 20% 7%	1200
	11th to 20th	Day	55% 7% 11% 17% 10% 1	1463
	21st to end	Day	55% 6% 11% 16% 11% 2	1320
March	1st to 10th	Day	58% 3 7% 17% 14% 1	4355
	11th to 20th	Day	46% 5% 9% 19% 15% 5%	4612
	21st to end	Day	49% 7% 14% 15% 14% 2	5965
April	1st to 10th	Day	58% 6% 11% 17% 7% 1	2567
	11th to 20th	Day	43% 7% 16% 25% 9% 2	2774
	21st to end	Day	41% 7% 13% 30% 8%	3061
May	1st to 10th	Day	58% 7% 10% 20% 4	7431
	11th to 20th	Day	41% 8% 11% 23% 12% 5%	7915
	21st to end	Day	57% 10% 13% 17% 3	9231
June	1st to 10th	Day	53% 10% 14% 19% 3	3967
	11th to 20th	Day	50% 11% 16% 21% 2	4000
	21st to end	Day	49% 11% 20% 18% 2	4000
July	1st to 10th	Day	58% 7% 16% 14% 5%	8961
	11th to 20th	Day	53% 8% 24% 14% 1	8359
	21st to end	Day	58% 7% 22% 10% 3	8612
August	1st to 10th	Day	64% 7% 19% 10% 1	5233
	11th to 20th	Day	65% 9% 18% 8%	5055
	21st to end	Day	69% 8% 15% 7% 1	5039
September	1st to 10th	Day	59% 9% 20% 11% 1	2611
	11th to 20th	Day	65% 9% 15% 11%	2344
	21st to end	Day	62% 9% 11% 14% 3	2062
October	1st to 10th	Day	57% 5% 10% 23% 6%	2984
	11th to 20th	Day	63% 7% 11% 17% 2	2751
	21st to end	Day	66% 5% 12% 15% 3	2424
November	1st to 10th	Day	59% 7% 14% 15% 4 1	1189
	11th to 20th	Day	60% 6% 12% 16% 6%	1000
	21st to end	Day	57% 7% 10% 18% 7%	703
December	1st to 10th	Day	48% 6% 18% 19% 8% 1	953
	11th to 20th	Day	52% 4 17% 16% 6% 5%	768
	21st to end	Day	46% 5% 18% 14% 15% 2	1012
January	1st to 10th	Night	42% 5% 11% 20% 13% 9%	8868
	11th to 20th	Night	48% 5% 17% 17% 10% 3	8160
	21st to end	Night	54% 4 9% 14% 14% 5%	8590
February	1st to 10th	Night	47% 4 7% 15% 21% 7%	3200
	11th to 20th	Night	49% 7% 11% 20% 12% 2	2833
	21st to end	Night	58% 5% 11% 13% 10% 2	2310
March	1st to 10th	Night	56% 3 6% 22% 10% 2	5500
	11th to 20th	Night	47% 5% 9% 18% 17% 5%	5348
	21st to end	Night	46% 8% 14% 13% 16% 3	4963
April	1st to 10th	Night	54% 7% 13% 19% 7% 1	1830
	11th to 20th	Night	44% 10% 14% 23% 7% 2	1575
	21st to end	Night	42% 5% 16% 28% 10%	1337
May	1st to 10th	Night	49% 9% 14% 24% 3	2538
	11th to 20th	Night	37% 9% 12% 26% 13% 3	1994
	21st to end	Night	55% 8% 13% 18% 6%	1667
June	1st to 10th	Night	49% 10% 17% 21% 4	430
	11th to 20th	Night	50% 10% 15% 22% 4	400
	21st to end	Night	47% 12% 22% 18% 1	400
July	1st to 10th	Night	58% 7% 16% 14% 6%	910
	11th to 20th	Night	56% 6% 21% 16% 1	1496
	21st to end	Night	56% 7% 22% 11% 3	1946
August	1st to 10th	Night	64% 7% 20% 7% 2	1899
	11th to 20th	Night	69% 6% 17% 7%	2069
	21st to end	Night	68% 6% 16% 9% 1	2866
September	1st to 10th	Night	56% 10% 20% 14% 1	1787
	11th to 20th	Night	63% 8% 16% 12% 1	2013
	21st to end	Night	60% 9% 11% 16% 3	2117
October	1st to 10th	Night	55% 6% 11% 22% 5%	3982
	11th to 20th	Night	59% 7% 15% 17% 2	4174
	21st to end	Night	66% 5% 11% 16% 2	5135
November	1st to 10th	Night	58% 6% 13% 18% 3 2	3107
	11th to 20th	Night	59% 6% 14% 17% 4	3400
	21st to end	Night	57% 6% 11% 17% 8%	3677
December	1st to 10th	Night	52% 5% 14% 17% 9% 1	6235
	11th to 20th	Night	54% 4 16% 14% 8% 3	7435
	21st to end	Night	49% 6% 16% 11% 15% 3	9966

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	7% 5% 19% 39% 26% 4	100
	11th to 20th	Day	5% 4 20% 38% 27% 6%	100
	21st to end	Day	7% 8% 15% 33% 23% 12%	201
February	1st to 10th	Day	5% 5% 13% 32% 27% 18%	300
	11th to 20th	Day	7% 5% 20% 33% 26% 9%	362
	21st to end	Day	8% 7% 21% 34% 24% 6%	331
March	1st to 10th	Day	6% 5% 23% 31% 29% 7%	400
	11th to 20th	Day	8% 7% 25% 29% 21% 11%	400
	21st to end	Day	8% 9% 20% 32% 23% 9%	656
April	1st to 10th	Day	12% 8% 25% 30% 19% 5%	668
	11th to 20th	Day	12% 6% 23% 28% 26% 4	690
	21st to end	Day	9% 4 19% 32% 28% 10%	700
May	1st to 10th	Day	11% 5% 22% 28% 26% 8%	703
	11th to 20th	Day	9% 7% 22% 31% 24% 8%	831
	21st to end	Day	17% 7% 17% 29% 23% 8%	1143
June	1st to 10th	Day	14% 5% 16% 28% 25% 12%	1130
	11th to 20th	Day	13% 4 14% 24% 31% 13%	1130
	21st to end	Day	16% 2 12% 26% 30% 14%	1130
July	1st to 10th	Day	19% 3 14% 25% 29% 10%	1111
	11th to 20th	Day	22% 4 14% 24% 25% 11%	1004
	21st to end	Day	20% 3 15% 22% 24% 14%	1008
August	1st to 10th	Day	28% 4 17% 22% 21% 8%	726
	11th to 20th	Day	30% 6% 17% 24% 18% 5%	715
	21st to end	Day	34% 4 16% 21% 18% 6%	803
September	1st to 10th	Day	26% 7% 15% 21% 21% 10%	713
	11th to 20th	Day	30% 7% 16% 25% 17% 5%	580
	21st to end	Day	27% 7% 18% 18% 18% 12%	390
October	1st to 10th	Day	24% 8% 19% 20% 18% 11%	390
	11th to 20th	Day	14% 5% 19% 24% 23% 15%	390
	21st to end	Day	17% 6% 11% 23% 28% 14%	429
November	1st to 10th	Day	14% 6% 12% 29% 28% 11%	271
	11th to 20th	Day	7% 5% 11% 30% 30% 17%	100
	21st to end	Day	11% 2 11% 41% 31% 4	100
December	1st to 10th	Day	12% 4 20% 38% 19% 7%	100
	11th to 20th	Day	8% 7% 25% 31% 26% 3	100
	21st to end	Day	5% 10% 22% 25% 35% 5%	110
January	1st to 10th	Night	8% 3 18% 31% 29% 10%	1193
	11th to 20th	Night	10% 4 18% 39% 23% 7%	1000
	21st to end	Night	9% 4 21% 36% 23% 7%	1060
February	1st to 10th	Night	5% 6% 16% 34% 28% 10%	900
	11th to 20th	Night	7% 3 19% 38% 26% 6%	884
	21st to end	Night	8% 4 21% 38% 26% 3	743
March	1st to 10th	Night	7% 4 17% 38% 28% 5%	724
	11th to 20th	Night	8% 4 19% 39% 26% 5%	680
	21st to end	Night	9% 4 18% 34% 26% 8%	660
April	1st to 10th	Night	12% 4 20% 32% 28% 5%	600
	11th to 20th	Night	8% 3 17% 37% 28% 7%	593
	21st to end	Night	9% 2 12% 29% 39% 8%	537
May	1st to 10th	Night	13% 4 12% 26% 36% 9%	325
	11th to 20th	Night	10% 6% 14% 39% 29% 3	197
	21st to end	Night	15% 5% 8% 33% 32% 7%	217
June	1st to 10th	Night	10% 4 12% 29% 38% 9%	200
	11th to 20th	Night	13% 3 8% 28% 40% 9%	200
	21st to end	Night	18% 3 4 24% 43% 9%	200
July	1st to 10th	Night	14% 3 11% 25% 39% 8%	195
	11th to 20th	Night	21% 1 12% 24% 35% 8%	194
	21st to end	Night	24% 1 10% 22% 38% 5%	219
August	1st to 10th	Night	29% 3 6% 23% 34% 5%	361
	11th to 20th	Night	31% 4 8% 20% 31% 6%	465
	21st to end	Night	32% 3 10% 18% 27% 10%	660
September	1st to 10th	Night	24% 3 13% 23% 27% 11%	600
	11th to 20th	Night	27% 3 11% 26% 27% 5%	594
	21st to end	Night	24% 5% 15% 23% 28% 5%	585
October	1st to 10th	Night	22% 5% 17% 27% 25% 4	774
	11th to 20th	Night	16% 3 15% 28% 27% 11%	860
	21st to end	Night	14% 4 12% 33% 29% 9%	946
November	1st to 10th	Night	15% 5% 16% 32% 24% 8%	880
	11th to 20th	Night	14% 4 14% 27% 27% 14%	900
	21st to end	Night	12% 3 14% 33% 28% 9%	1085
December	1st to 10th	Night	12% 4 17% 38% 22% 7%	1200
	11th to 20th	Night	10% 4 19% 29% 29% 9%	1200
	21st to end	Night	8% 5% 15% 33% 29% 10%	1320

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