Current Conditions
Temp6.9 C
RH18 %
WindN 28 mph
RoadOpen (4x4 only)
Mauna Kea Observatories Forecast
830 AM HST (1830 UTC) Wednesday 07 October 2015
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 11 C for this afternoon and 5 C for the night. Winds will be from the NW at 10-20 mph for today, tapering and switching to a more southerly direction by the end of the night. Seeing will be near 0.45-0.5 arcseconds, while precipitable water is expected to be in the 1-1.5 mm range for the night.
The tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure a dry and stable summit-level air mass through at least late Friday morning. There is a possibility that an influx of low-level moisture and upper-level instability will start to erode the inversion thereafter, increasing the risk for periods of fog and/or high humidity at the summit over the weekend. There is also an outside chance for isolated convection in the area and light rain at the summit, mainly for the afternoon hours. Daytime clouds will be minimal and short-lived through tomorrow, but could pick up on Friday and turn extensive over the weekend.

Skies overhead will remain predominately clear through Friday night, but there is a chance that thicker clouds will move in from the SE or more likely develop in the area, perhaps contributing to periods of extensive cloud cover for Saturday and Sunday night.

Precipitable water is expected to linger in the 1-1.5 mm range for at least the next 2 nights, but may trend toward 4 mm through Friday night and likely exceed that value for Saturday and Sunday night.

Diminishing summit-level winds, coupled with light/calm flow aloft should allow seeing to settle in near 0.45-0.5 arcseconds for at least the next 2 nights. There is a possibility that an increase in upper-level turbulence will start to degrade seeing through Friday night, and could contribute to poor seeing for Saturday and Sunday night.

Very dry/stable and warm air in the wake of the departing trough and along the eastern fringe of a building ridge will help maintain a well-defined tradwind inversion near 6-8 thousand feet and allow for more normal summit-level conditions and PW near 1-1.5 mm for at least the next 48 hours. Winds are also slated to rapidly diminish through the day, which should help seeing to settle in near 0.45-0.5 arcseconds as relatively calm/light flow prevails aloft during that time. Models are still suggesting that a rather large trough will brew to the north, cooling off the mid-level air mass and destabilizing the air mass a bit over much of the weekend. In addition, a new ridge fillin in from the SE is expected to bring a wave of tropical moisture to the area around that time. This moisture and instability is slated to erode the inversion and thus, increase the risk for fog and high humidity at the summit, as well as isolated afternoon convection along the slopes for the weekend. However, it should be noted that each subsequent run has slowly downplayed the amount of moisture in the area, and it wouldn't surprise me if that trends continues....
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)
Wed Oct 07 - 2 PM0-20Clear0 / 011NW/10-20NaN1-2
8 PM0-5Clear0 / 05W/5-150.4-0.61-1.5
Thu Oct 08 - 2 AM0-5Clear0 / 05S/0-100.4-0.51-1.5
2 PM0-20Clear0 / 010S/5-15NaN1-1.5
8 PM0-5Clear0 / 05SSW/5-150.4-0.51-1.2
Fri Oct 09 - 2 AM0-5Clear0 / 05SW/0-100.4-0.51-1.2
2 PM20-404-4.540 / 109.5S/5-15NaN2-4
8 PM0-20Clear25 / 54SE/5-150.45-0.652-3
Sat Oct 10 - 2 AM0-20Clear40 / 103SSE/5-150.5-0.83-4
2 PM60-804-775 / 307SSW/5-15NaN4-8
Sun Oct 11 - 2 AM60-804-760 / 152.5SSW/5-150.6-1.24-8
2 PM70-904-980 / 406WSW/0-10NaN6-10
Mon Oct 12 - 2 AM60-804-860 / 152WSW/0-100.6-1.24-8
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
Wed Oct 07 - Thu Oct 08 18:14 19:18 5:01 6:06 2:42 N/A 17 9 47.7 9 49
Thu Oct 08 - Fri Oct 09 18:13 19:17 5:02 6:06 3:31 N/A 11 10 33.6 6 33
Fri Oct 09 - Sat Oct 10 18:12 19:16 5:02 6:06 4:19 N/A 6 11 18.5 3 03
Sat Oct 10 - Sun Oct 11 18:11 19:16 5:02 6:06 5:07 17:03 2 12 03.0 -0 34
Sun Oct 11 - Mon Oct 12 18:10 19:15 5:02 6:07 5:55 17:40 0 12 47.4 -4 11
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 07 October (0300 UTC Thursday 8 October) 2015.
Additional Information
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