Current Conditions
Temp-3.0 C
RH7 %
WindWSW 53 mph
RoadClosed
Mauna Kea Observatories Forecast
5 PM HST Friday 17 November (0300 UTC Saturday 18 November) 2017
Warning(s)
Strong (increasing) winds
Cloud Cover and Fog/Precipitation Forecast
There is a small possibility for periods of high humidity, fog/ice and patches of mid-level clouds passing to the south, mainly as the night progresses; precipitation is not expected.
Summary of Key Meteorological Variables
Summit temperatures will be near -2 C this evening and -3 C tomorrow morning. Winds will start out near 30 mph for this evening, but will likely exceed 50 mph by the end of the night. Seeing will exceed 1 arcsecond, while precipitable water is expected to be in the 1.75 to 2.25 mm range for the night.
Discussion
Although the atmosphere will remain quite stable with the tradewind inversion fairly well-established near 7 thousand feet throughout the forecast period, patches of mid-level moisture scraping by could contribute to periods of fog/ice and high humidity over the next 2 nights; precipitation is not expected and dry and stable conditions will prevail for the remainder of the forecast period. Some afternoon clouds are possible over the next 2 days, then will become minimal and short-lived for Sunday and early part of next week.

There is a possibility for patches of mid-level clouds quickly passing to south of the Big Island through early tomorrow evening. High clouds may also drift along the northern skies and there is also a chance for development of lenticular clouds over the Big Island summits for tomorrow night. Predominately clear skies will prevail overhead for Sunday evening, but banding high clouds may set up along the southern later that night and could scrape the Big Island for Monday night, then shift back off toward the south on Tuesday. However, more thin strands of cirrus may drift in from the west and pass overhead for that night.

Precipitable water is expected to linger near 2 mm for tonight, increase to 4-6 mm for Saturday night, briefly slip toward 1 mm for the Sunday night, then trend back toward 2 mm over the course of the following 2 nights.

Strong increasing summit-level winds are expected to stir up boundary layer turbulence and contribute to bad seeing over the next 3 nights. While winds are set to subside on Monday, there is still a possibility that moderate boundary layer turbulence will limit much improvement in seeing.

Subtle changes have been made to the PW forecast....The SE tip of the mid/low-level ridge (to the NW) will continue to linger over the state and promote relatively strong large-scale subsidence in the area probably throughout the forecast period. While this subsidence will help maintain a fairly well-defined inversion near 7 thousand feet during this time, a band of moisture just south of the Big Island and associated with the restrengthening low to the NE is expected to briefly expand northward between late this evening and around midnight tomorrow. This moisture could allow for the developement of short-lived fog/ice and/or periods of high humidity over the next 2 nights (drier conditions are expected as this band of moisture slips southward on Sunday and early part of next week). In addition, the low is set to expand/dig southward, which will continue to increase summit-level winds over the next 24-36 hours. Winds will likely settle in the 60-80 mph range between late tomorrow evening and early Monday morning, then abruptly decrease (to 15-30 mph) for the following 2 nights. Nonetheless, winds will stir up significant boundary layer turbulence and contribute to poor/bad seeing probably throughout the forecast period. There is also a possibility that the mid-level moisture in the area, combined with strong mid-level flow and a rather stable low-level air mass will allow for the development of lenticular clouds along the Big Island summits mainly between sunrise tomorrow and early Sunday morning.
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 Nov 17 - 8 PM0-205-610 / 0-2WSW/30-450.7-1.31.75-2.25
Sat Nov 18 - 2 AM10-305-720 / 0-3WSW/35-500.8-1.61.75-2.25
2 PM60-804-860 / 151WSW/40-60NaN4-8
8 PM20-405-725 / 0-4WSW/50-701-24-6
Sun Nov 19 - 2 AM20-405-715 / 0-5WSW/60-801-24-6
2 PM0-205-60 / 01WSW/60-80NaN1-2
8 PM0-10Clear0 / 0-4WSW/60-801-21-1.5
Mon Nov 20 - 2 AM10-309-100 / 0-4W/40-601-20.9-1.1
2 PM30-508-100 / 03W/25-40NaN1-2
Tue Nov 21 - 2 AM30-509-100 / 0-1.5WSW/15-300.6-11.25-1.75
2 PM10-309.5-100 / 03W/15-30NaN1.5-2.5
Wed Nov 22 - 2 AM10-309-100 / 0-2W/15-300.55-0.951.5-2.5
2 PM0-209-100 / 03W/15-30NaN2-3
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
Sun Nov 19 - Mon Nov 20 17:51 18:58 5:17 6:24 N/A 19:12 3 17 14.3 -18 47
Mon Nov 20 - Tue Nov 21 17:51 18:58 5:17 6:25 N/A 19:57 7 18 03.7 -19 49
Tue Nov 21 - Wed Nov 22 17:51 18:58 5:18 6:25 N/A 20:44 13 18 53.4 -20 00
Wed Nov 22 - Thu Nov 23 17:51 18:58 5:18 6:26 N/A 21:33 20 19 43.0 -19 20
Thu Nov 23 - Fri Nov 24 17:51 18:58 5:19 6:27 N/A 22:23 28 20 32.4 -17 49
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 20 November 2017.
Additional Information
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