Current Conditions
Temp2.9 C
RH61 %
WindSE 0 mph
RoadOpen (4x4 only)
Mauna Kea Observatories Forecast
5 PM HST Friday 04 September (0300 UTC Saturday 5 September) 2015
High humidity
Chance for fog
Cloud Cover and Fog/Precipitation Forecast
There is a possibility for periods of fog and high humidity throughout the night; precipitation is unlikely. There is also a chance for patchy mid/upper-level clouds mainly along the western skies, particularly for the first half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 3 C, with light and variable winds and seeing around 0.45-0.5 arcseconds. Precipitable water is expected to exceed 8 mm through the night.
Although the tradewind inversion is expected to remain fairly well-established near 6-7 thousand feet throughout the forecast period, mid-level moisture will persist in the area, likely allowing summit-level humidity to linger in the 60-80% range during this time. Conequently, there is a moderate/high risk for periods of fog as well as a slight chance for light precipitation at the summit over the next 5 nights (particularly Saturday and Sunday night). Extensive daytime clouds are likely throughout the forecast period.

Skies overhead will remain predominately clear of organized clouds through at least Sunday night. However, there is a possibility for patches of mid/upper-level clouds in the area, particularly along the western and southern skies for Saturday and Sunday night. There is a chance that the latter set will begin to shift further northward on Monday, while thicker clouds to the northeast start to fill into the area on Tuesday. This could lead to periods of extensive cloud cover for the middle part of next week.

Precipitable water is expected to exceed 4 mm through the next 5 nights.

Relatively calm skies will prevail in the free atmosphere, which should allow for better than average seeing through at least Monday evening. However, there is a possibility that building mid/low-level turbulence will begin to disrupt seeing perhaps as early as Tuesday morning and especially for later that night.

Very little change since the morning forecast...The mid/low-level ridge to the NE will continue to gradually regain control of the air mass and maintain a fairly well-defined inversion near 6-7 thousand feet likely throughout the forecast period. Unfortunately, persistent mid-level moisture to the west, coupled with a fresh influx of tropical moisture drawn toward an upper-level low developing to the west and Jimena to the east will likely allow summit-level humidity to linger in the 60-80% range during most of this time. Consequently, there is a moderate/high risk for short periods of fog and patchy clouds in the area over the next 5 nights and especially when the extra moisture drifts in between early tomorrow afternoon and early Monday morning. While this moisture will likely keep PW near 10 mm through the next 5 nights, relatively calm flow will prevail in the free atmosphere, which should allow for better than average seeing likely through Monday evening. Beyond that seeing and eventually conditions/skies may take a turn for the worse...The GFS has been consistently suggesting that Hurricane Jimena will slowly meander to the NW over the next 3-4 days, then drift back toward the SW and the state around the early/middle part of next week (gradually weakening during the second leg to the SW). While this is certainly a plausible solution, the models hasn't had a very good track record with the past 3+ storms and Jimena hardly looks like it wants to go anywhere. Regardless, if this solution pans out, there is a possibility that deeper moisture, instability, clouds and turbulence will return to the area, resulting in another round of inoperable conditions for the middle to latter part of next week.

Please Note:Barring significant changes in the outlook over the weekend, there will be no forecasts on Monday, September 7, in observance of Labor Day; the normal forecast schedule will resume on Tuesday.
WRF Astronomical Observing Quality Guidance
Cloud Cover and Precipitable Water Analyses
MK CN² Profiles
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Fri Sep 04 - 8 PM20-405-860 / 153NNE/0-100.45-0.558-12
Sat Sep 05 - 2 AM0-205-650 / 103NE/0-100.4-0.58-12
2 PM60-804-880 / 407.5S/0-10NaN8-12
8 PM30-505-860 / 152.5NE/0-100.35-0.558-12
Sun Sep 06 - 2 AM40-605-875 / 202NE/0-100.4-0.68-12
2 PM70-904-990 / 507WSW/5-15NaN8-12
8 PM40-605-875 / 253W/0-100.4-0.68-12
Mon Sep 07 - 2 AM30-505-860 / 153WSW/0-100.4-0.58-12
2 PM60-804-980 / 408W/5-15NaN8-12
Tue Sep 08 - 2 AM40-604.5-950 / 104W/5-150.5-0.86-10
2 PM70-904-985 / 407WNW/10-20NaN6-10
Wed Sep 09 - 2 AM50-704.5-960 / 203WNW/15-300.6-1.26-10
2 PM70-904-990 / 507WNW/15-30NaN8-12
Rise and Set times for the Sun and Moon
Night (HST) Sun Set Twilight End Twilight Beg Sun Rise Moon Rise Moon Set Illumination (%) RA DEC
Fri Sep 04 - Sat Sep 05 18:43 19:49 4:53 5:58 23:37 N/A 49 4 51.0 17 01
Sat Sep 05 - Sun Sep 06 18:42 19:48 4:53 5:59 0:29 N/A 39 5 46.2 17 45
Sun Sep 06 - Mon Sep 07 18:42 19:47 4:53 5:59 1:21 N/A 29 6 39.9 17 30
Mon Sep 07 - Tue Sep 08 18:41 19:46 4:54 5:59 2:13 N/A 20 7 32.0 16 23
Tue Sep 08 - Wed Sep 09 18:40 19:45 4:54 5:59 3:05 N/A 13 8 22.3 14 31
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 8 September 2015.
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