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 2024-02-20.

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% 10% 4 8% 7% 4 6% 6% 6% 7% 28%	75891
	Night	8% 12% 5% 10% 8% 4 6% 5% 6% 6% 30%	83281
Transparency	Day	53% 9% 16% 16% 5% 1	75493
	Night	53% 7% 13% 17% 9% 2	83260
Seeing	Day	16% 5% 17% 26% 25% 10%	17528
	Night	13% 4 15% 32% 29% 8%	22149

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 10% 7% 3 6% 2 3 6% 46%	780
	11th to 20th	Day	3 10% 6% 10% 8% 4 6% 6% 7% 6% 33%	1258
	21st to end	Day	4 8% 5% 10% 9% 6% 7% 7% 8% 8% 28%	1659
February	1st to 10th	Day	2 11% 5% 9% 6% 4 5% 6% 6% 5% 41%	1140
	11th to 20th	Day	4 10% 6% 14% 11% 5% 7% 9% 5% 7% 23%	1375
	21st to end	Day	5% 13% 8% 10% 9% 3 6% 5% 6% 5% 28%	1184
March	1st to 10th	Day	4 11% 7% 12% 9% 5% 7% 4 6% 6% 29%	1745
	11th to 20th	Day	3 7% 5% 7% 7% 4 7% 5% 6% 6% 42%	1836
	21st to end	Day	5% 9% 6% 9% 7% 4 6% 4 6% 7% 38%	2372
April	1st to 10th	Day	6% 13% 6% 9% 10% 4 6% 6% 6% 7% 26%	2309
	11th to 20th	Day	6% 9% 4 8% 6% 3 5% 6% 6% 7% 41%	2492
	21st to end	Day	5% 9% 3 7% 5% 5% 6% 6% 6% 8% 39%	2754
May	1st to 10th	Day	7% 10% 5% 8% 8% 5% 7% 6% 6% 7% 28%	2947
	11th to 20th	Day	7% 8% 4 8% 8% 5% 6% 5% 6% 7% 36%	3104
	21st to end	Day	11% 8% 4 7% 7% 5% 7% 7% 8% 8% 29%	3622
June	1st to 10th	Day	13% 7% 4 8% 7% 6% 7% 7% 7% 8% 26%	3569
	11th to 20th	Day	15% 8% 3 7% 8% 5% 7% 6% 7% 8% 28%	3600
	21st to end	Day	17% 7% 3 6% 6% 4 7% 6% 7% 10% 29%	3600
July	1st to 10th	Day	16% 7% 3 6% 7% 4 6% 6% 6% 10% 29%	3600
	11th to 20th	Day	24% 9% 4 7% 7% 5% 6% 6% 6% 7% 19%	3368
	21st to end	Day	20% 9% 3 8% 6% 4 7% 7% 6% 8% 22%	3525
August	1st to 10th	Day	26% 10% 4 7% 7% 4 5% 5% 5% 6% 19%	2897
	11th to 20th	Day	24% 9% 4 8% 7% 4 5% 5% 6% 7% 21%	2771
	21st to end	Day	25% 11% 4 8% 7% 4 4 5% 6% 7% 20%	2774
September	1st to 10th	Day	21% 11% 4 7% 6% 4 5% 5% 6% 7% 25%	2351
	11th to 20th	Day	22% 14% 5% 8% 6% 3 5% 5% 5% 6% 21%	2129
	21st to end	Day	18% 16% 5% 8% 7% 4 5% 5% 5% 5% 23%	1954
October	1st to 10th	Day	14% 18% 6% 9% 8% 4 5% 4 4 6% 21%	1702
	11th to 20th	Day	9% 17% 6% 12% 8% 4 5% 5% 5% 5% 25%	1577
	21st to end	Day	10% 13% 5% 11% 8% 4 5% 5% 7% 6% 25%	1403
November	1st to 10th	Day	8% 13% 5% 11% 9% 4 6% 5% 6% 5% 27%	1129
	11th to 20th	Day	6% 11% 5% 12% 13% 7% 6% 4 3 5% 29%	950
	21st to end	Day	10% 11% 5% 12% 8% 4 5% 6% 5% 6% 27%	669
December	1st to 10th	Day	10% 15% 7% 7% 8% 4 4 5% 4 6% 30%	556
	11th to 20th	Day	2 15% 8% 12% 8% 8% 6% 6% 6% 8% 23%	486
	21st to end	Day	3 9% 6% 9% 8% 6% 6% 6% 10% 9% 29%	704
January	1st to 10th	Night	3 9% 5% 9% 8% 4 5% 5% 4 6% 41%	6204
	11th to 20th	Night	4 13% 6% 11% 7% 5% 5% 6% 6% 6% 32%	5650
	21st to end	Night	3 8% 4 9% 7% 4 6% 7% 9% 7% 34%	6005
February	1st to 10th	Night	3 9% 6% 13% 8% 3 4 5% 4 4 42%	3040
	11th to 20th	Night	4 9% 6% 10% 8% 5% 7% 7% 8% 8% 29%	2674
	21st to end	Night	5% 13% 8% 13% 9% 5% 6% 5% 5% 6% 26%	2072
March	1st to 10th	Night	3 12% 7% 12% 10% 4 7% 5% 5% 5% 30%	2214
	11th to 20th	Night	3 9% 4 7% 7% 4 6% 5% 4 7% 43%	2122
	21st to end	Night	6% 11% 5% 8% 5% 3 5% 4 5% 8% 40%	1981
April	1st to 10th	Night	6% 13% 5% 10% 8% 3 7% 6% 7% 7% 29%	1648
	11th to 20th	Night	5% 6% 4 8% 7% 4 7% 7% 6% 7% 39%	1417
	21st to end	Night	7% 7% 4 6% 8% 3 5% 5% 7% 7% 41%	1204
May	1st to 10th	Night	8% 10% 4 8% 8% 5% 8% 6% 6% 8% 30%	1013
	11th to 20th	Night	7% 7% 2 7% 6% 4 6% 6% 7% 11% 38%	790
	21st to end	Night	11% 8% 3 8% 8% 4 5% 5% 6% 7% 36%	653
June	1st to 10th	Night	10% 5% 3 8% 7% 5% 6% 6% 10% 9% 31%	388
	11th to 20th	Night	14% 4 3 10% 6% 5% 7% 6% 7% 8% 30%	360
	21st to end	Night	18% 4 3 8% 6% 5% 5% 7% 9% 9% 28%	360
July	1st to 10th	Night	11% 6% 3 6% 6% 3 6% 4 9% 14% 31%	360
	11th to 20th	Night	22% 11% 3 7% 6% 4 5% 5% 6% 5% 25%	590
	21st to end	Night	17% 8% 3 7% 6% 5% 5% 6% 6% 8% 28%	792
August	1st to 10th	Night	23% 13% 4 9% 8% 4 6% 5% 4 5% 21%	1040
	11th to 20th	Night	24% 9% 5% 8% 9% 4 5% 5% 6% 7% 20%	1129
	21st to end	Night	27% 10% 3 6% 6% 3 5% 4 6% 5% 24%	1579
September	1st to 10th	Night	18% 11% 3 7% 7% 4 4 6% 6% 8% 27%	1607
	11th to 20th	Night	20% 14% 4 7% 7% 4 5% 5% 5% 6% 23%	1831
	21st to end	Night	18% 14% 4 7% 6% 3 5% 5% 6% 6% 25%	2005
October	1st to 10th	Night	14% 19% 5% 9% 7% 3 6% 6% 5% 6% 21%	2258
	11th to 20th	Night	10% 14% 5% 10% 7% 3 5% 5% 5% 6% 30%	2380
	21st to end	Night	9% 14% 6% 10% 10% 4 6% 5% 5% 6% 25%	2953
November	1st to 10th	Night	8% 16% 6% 9% 8% 4 5% 4 5% 5% 30%	2947
	11th to 20th	Night	9% 13% 5% 12% 9% 4 5% 5% 5% 6% 27%	3230
	21st to end	Night	8% 12% 5% 11% 9% 5% 6% 5% 6% 5% 27%	3492
December	1st to 10th	Night	8% 13% 6% 12% 8% 4 6% 5% 5% 6% 27%	3622
	11th to 20th	Night	4 16% 8% 14% 10% 5% 6% 6% 5% 5% 20%	4708
	21st to end	Night	3 10% 6% 10% 9% 6% 7% 7% 6% 7% 29%	6963

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	43% 4 11% 23% 10% 8%	780
	11th to 20th	Day	49% 7% 17% 13% 10% 5%	1270
	21st to end	Day	51% 5% 9% 13% 14% 8%	1659
February	1st to 10th	Day	44% 6% 7% 17% 20% 7%	1140
	11th to 20th	Day	56% 7% 11% 17% 9% 1	1381
	21st to end	Day	56% 5% 11% 16% 10% 2	1184
March	1st to 10th	Day	54% 5% 13% 16% 9% 3	1745
	11th to 20th	Day	41% 6% 10% 26% 15% 2	1836
	21st to end	Day	44% 7% 17% 13% 14% 4	2372
April	1st to 10th	Day	56% 6% 12% 17% 7% 1	2309
	11th to 20th	Day	42% 7% 16% 25% 9% 2	2492
	21st to end	Day	42% 7% 13% 29% 8%	2754
May	1st to 10th	Day	52% 9% 14% 20% 5%	2947
	11th to 20th	Day	45% 8% 13% 26% 8%	3107
	21st to end	Day	48% 11% 16% 20% 5%	3623
June	1st to 10th	Day	53% 10% 15% 18% 4	3569
	11th to 20th	Day	52% 11% 15% 19% 2	3600
	21st to end	Day	50% 12% 19% 17% 2	3600
July	1st to 10th	Day	49% 13% 21% 15% 3	3501
	11th to 20th	Day	60% 12% 17% 10% 1	3261
	21st to end	Day	57% 14% 21% 8%	3329
August	1st to 10th	Day	63% 11% 18% 7%	2877
	11th to 20th	Day	60% 12% 19% 9%	2771
	21st to end	Day	63% 11% 17% 8% 1	2774
September	1st to 10th	Day	58% 10% 20% 11% 1	2351
	11th to 20th	Day	63% 10% 15% 12%	2129
	21st to end	Day	62% 9% 12% 14% 3 1	1954
October	1st to 10th	Day	65% 8% 13% 10% 4	1702
	11th to 20th	Day	60% 9% 15% 12% 4	1577
	21st to end	Day	57% 7% 18% 16% 1	1403
November	1st to 10th	Day	58% 7% 15% 15% 4 1	1129
	11th to 20th	Day	60% 7% 12% 16% 6%	950
	21st to end	Day	57% 7% 10% 18% 7%	669
December	1st to 10th	Day	54% 8% 13% 15% 7% 2	556
	11th to 20th	Day	60% 7% 11% 16% 5% 1	488
	21st to end	Day	46% 6% 16% 19% 12% 1	704
January	1st to 10th	Night	43% 6% 13% 26% 9% 3	6204
	11th to 20th	Night	51% 6% 14% 16% 9% 4	5700
	21st to end	Night	44% 5% 9% 15% 20% 7%	6005
February	1st to 10th	Night	46% 4 7% 16% 21% 7%	3040
	11th to 20th	Night	49% 7% 11% 21% 11% 1	2679
	21st to end	Night	59% 5% 11% 13% 10% 2	2072
March	1st to 10th	Night	56% 5% 9% 18% 9% 4	2214
	11th to 20th	Night	43% 4 9% 25% 16% 3	2124
	21st to end	Night	42% 7% 15% 16% 16% 4	1981
April	1st to 10th	Night	52% 7% 13% 20% 7% 1	1648
	11th to 20th	Night	42% 10% 16% 24% 7% 1	1417
	21st to end	Night	41% 5% 17% 27% 10%	1204
May	1st to 10th	Night	49% 9% 12% 25% 4 1	1013
	11th to 20th	Night	39% 8% 19% 26% 7%	790
	21st to end	Night	46% 8% 14% 24% 8%	653
June	1st to 10th	Night	47% 10% 17% 21% 5%	388
	11th to 20th	Night	51% 10% 15% 20% 4	360
	21st to end	Night	48% 13% 21% 18% 1	360
July	1st to 10th	Night	44% 13% 25% 15% 4	350
	11th to 20th	Night	60% 11% 17% 11% 1	574
	21st to end	Night	52% 14% 23% 11%	748
August	1st to 10th	Night	65% 9% 17% 9%	1035
	11th to 20th	Night	62% 11% 15% 12%	1129
	21st to end	Night	61% 9% 20% 9% 1	1579
September	1st to 10th	Night	55% 10% 20% 14% 1	1607
	11th to 20th	Night	61% 8% 17% 14% 1	1831
	21st to end	Night	60% 9% 12% 16% 3	2005
October	1st to 10th	Night	63% 9% 14% 10% 3	2258
	11th to 20th	Night	54% 9% 18% 15% 4	2380
	21st to end	Night	59% 8% 16% 13% 3	2953
November	1st to 10th	Night	58% 6% 13% 18% 3 2	2947
	11th to 20th	Night	59% 7% 14% 17% 4	3230
	21st to end	Night	57% 6% 11% 17% 8%	3492
December	1st to 10th	Night	57% 7% 13% 14% 7% 2	3622
	11th to 20th	Night	65% 6% 10% 12% 6%	4705
	21st to end	Night	51% 7% 12% 13% 15% 2	6963

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% 4 18% 39% 28% 4	90
	11th to 20th	Day	2 4 19% 38% 30% 7%	90
	21st to end	Day	6% 6% 14% 35% 25% 14%	185
February	1st to 10th	Day	5% 5% 14% 30% 28% 19%	280
	11th to 20th	Day	6% 5% 19% 32% 27% 10%	333
	21st to end	Day	9% 7% 21% 35% 23% 6%	280
March	1st to 10th	Day	7% 5% 23% 29% 29% 8%	340
	11th to 20th	Day	8% 7% 24% 29% 22% 11%	340
	21st to end	Day	9% 9% 21% 32% 23% 8%	568
April	1st to 10th	Day	11% 9% 25% 31% 20% 5%	574
	11th to 20th	Day	11% 6% 21% 29% 29% 5%	590
	21st to end	Day	9% 4 20% 31% 26% 10%	600
May	1st to 10th	Day	10% 4 21% 27% 29% 9%	603
	11th to 20th	Day	9% 6% 21% 31% 24% 8%	719
	21st to end	Day	16% 7% 18% 28% 23% 8%	997
June	1st to 10th	Day	14% 4 15% 27% 26% 13%	990
	11th to 20th	Day	14% 4 15% 24% 30% 12%	990
	21st to end	Day	17% 3 12% 25% 30% 13%	990
July	1st to 10th	Day	16% 3 14% 25% 31% 11%	971
	11th to 20th	Day	22% 4 14% 23% 25% 12%	875
	21st to end	Day	19% 3 15% 22% 25% 15%	877
August	1st to 10th	Day	28% 5% 16% 21% 21% 9%	626
	11th to 20th	Day	27% 6% 17% 26% 20% 5%	615
	21st to end	Day	31% 4 15% 22% 21% 7%	693
September	1st to 10th	Day	25% 7% 14% 20% 22% 11%	617
	11th to 20th	Day	27% 7% 16% 25% 19% 6%	509
	21st to end	Day	28% 7% 18% 19% 18% 11%	360
October	1st to 10th	Day	26% 9% 19% 19% 16% 11%	360
	11th to 20th	Day	14% 4 19% 24% 24% 15%	360
	21st to end	Day	16% 5% 10% 24% 30% 14%	396
November	1st to 10th	Day	14% 6% 11% 29% 28% 12%	251
	11th to 20th	Day	6% 6% 10% 32% 30% 17%	90
	21st to end	Day	11% 2 11% 40% 31% 4	90
December	1st to 10th	Day	13% 4 16% 39% 20% 8%	90
	11th to 20th	Day	7% 6% 26% 31% 28% 3	90
	21st to end	Day	4 11% 21% 26% 33% 4	99
January	1st to 10th	Night	8% 3 16% 32% 31% 10%	1124
	11th to 20th	Night	9% 4 16% 40% 25% 7%	940
	21st to end	Night	8% 4 20% 37% 24% 8%	998
February	1st to 10th	Night	5% 7% 16% 33% 29% 10%	850
	11th to 20th	Night	7% 3 19% 37% 28% 6%	831
	21st to end	Night	9% 4 19% 39% 25% 3	658
March	1st to 10th	Night	8% 4 16% 38% 29% 5%	642
	11th to 20th	Night	8% 3 17% 39% 27% 6%	604
	21st to end	Night	10% 4 17% 33% 27% 9%	594
April	1st to 10th	Night	11% 4 19% 31% 30% 6%	540
	11th to 20th	Night	8% 3 15% 38% 30% 8%	533
	21st to end	Night	10% 3 11% 27% 41% 9%	484
May	1st to 10th	Night	13% 3 10% 26% 38% 10%	293
	11th to 20th	Night	10% 5% 13% 38% 32% 2	177
	21st to end	Night	13% 5% 9% 33% 32% 7%	195
June	1st to 10th	Night	11% 3 11% 27% 38% 10%	180
	11th to 20th	Night	13% 3 8% 30% 36% 9%	180
	21st to end	Night	18% 3 3 23% 43% 9%	180
July	1st to 10th	Night	11% 3 10% 24% 42% 9%	175
	11th to 20th	Night	21% 1 12% 24% 34% 8%	174
	21st to end	Night	23% 1 9% 23% 39% 6%	197
August	1st to 10th	Night	30% 3 6% 20% 35% 6%	324
	11th to 20th	Night	28% 4 9% 22% 30% 7%	417
	21st to end	Night	30% 3 9% 18% 28% 11%	594
September	1st to 10th	Night	24% 3 12% 22% 28% 12%	540
	11th to 20th	Night	26% 3 11% 27% 27% 6%	540
	21st to end	Night	24% 4 15% 24% 28% 5%	553
October	1st to 10th	Night	23% 5% 16% 27% 25% 4	728
	11th to 20th	Night	15% 3 15% 29% 27% 11%	810
	21st to end	Night	13% 3 12% 34% 29% 9%	891
November	1st to 10th	Night	15% 5% 15% 33% 25% 7%	830
	11th to 20th	Night	14% 4 14% 28% 26% 14%	850
	21st to end	Night	12% 3 14% 33% 28% 9%	1020
December	1st to 10th	Night	13% 4 15% 38% 23% 8%	1130
	11th to 20th	Night	10% 3 19% 29% 30% 9%	1130
	21st to end	Night	8% 5% 15% 32% 29% 11%	1243

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