Current Conditions
Temp-3.3 C
RH13 %
WindSW 40 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Thursday 17 January (0300 UTC Friday 18 January) 2019
Warning(s)
Moderate/strong winds
Chance for fog/ice and high humidity
Cloud Cover and Fog/Precipitation Forecast
The summit will start out dry and clear, but there is a possibliity for fog/ice and patches of mid-level clouds approaching from the NW during the second half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near -2 C this evening and -3 C tomorrow morning. Winds will be from the WSW at 30-45 mph, while seeing will exceed 1 arcsecond. Precipitable water is expected to be in the 1-1.5 mm range for the first half of the night and 1.25-1.75 mm range for the second half.
Discussion
Although the tradewind inversion will start our fairly well-defined near 7 thousand feet for this evening, it is set to weaken through the night, perhaps allowing for periods of fog, ice and high humidity near sunrise and for the early half of tomorrow night; flurries are unlikely. The inversion is set to recover through Saturday morning, becoming well-established near 7 thousand feet and ensuring the summit remains dry and stable for that night as well as the following 2 nights. Daytime clouds are expected to turn extensive for tomorrow, only to become minimal and short-lived over the weekend and Monday, then may pick up again on Tuesday.

There is a possibility that a patches of mid/upper-level clouds will drift in from the west as the night progresses. These clouds may persist in the area into tomorrow evening, then will slip eastward and dissipate through that night, leaving predominately clear skies for Saturday, Sunday and Monday night.

Precipitable water is expected to subtly increase toward 1.25-1.5 mm for tonight and probably 2-4 mm for early tomorrow evening, then abruptly drop below 1 mm by early Saturday morning and likely the remainder of the weekend. There is a good chance that it will increase back toward 3 mm again for Monday night.

Strong boundary layer turbulence will contribute to bad seeing through tomorrow night. This turbulence is set to diminish early Saturday morning, but there is a very good chance that mid-level turbulence and/or gravity waves will pass through the area, limiting seeing from improving much until early Sunday morning. There is a possibility that calmer skies will prevail, allowing for better than average seeing for that night, but another round of boundary layer turbulence will probably degrade seeing again for Monday night.

No change since the morning forecast...A relatively sharp trough/low building in from the NW will continue to usher the ridge off toward the east, and tighten the mid-level wind gradient in the area over the next 12-18 hours. The latter will likely push summit-level winds toward 40 mph, which will contribute to boundary layer turbulence and bad seeing for tonight. Instability associated with the trough will also begin to erode the inversion, increasing the risk for fog, ice and high humidity at the night progresses. The trough's associated low will also send a cold front through much of the state beginning late tonight, with this front set to arrive along the western shores of the Big Island (on a dissipating trend), late tomorrow morning. Nonetheless, this front could further weaken/lift the inversion and increase the risk for fog/ice for that afternoon/evening. Fortunately, both the trough/low and front are set to take off toward the NE, which should help rebuild the inversion and weaken summit-level winds as that night progresses. However, lingering boundary layer turbulence combined with the passage of mid-level turbulence and/or gravity wave in the wake of the front will limit seeing from improving until early Sunday morning. A relatively tight ridge is set to build in from the west and expand off toward the NE over the weekend. This will help rebuild the inversion near 6-7 thousand feet and ensure the summit remains dry and stable for Saturday, Sunday and Monday night. Calmer skies will briefly settle in overhead once the bulk of the turbulence passes eastward, allowing seeing to improve toward 0.5-0.6 arcseconds for Sunday night. However, models suggest that a broad trough may begin to develop to the NW, which could tighten the wind gradient in the area and increase boundary layer turbulence once again for the early part of next week. Long-term projections suggest that this trough could begin to destabilize the air mass and perhaps increase the risk for moisture at the summit around the middle part of next week.
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)
Thu Jan 17 - 8 PM0-207.5-85 / 0-2WSW/30-451-21-1.5
Fri Jan 18 - 2 AM20-407-840 / 10-3WSW/30-451-21.25-1.75
2 PM60-804-875 / 25-1WSW/30-45NaN3-6
8 PM20-406-765 / 10-5WNW/20-350.8-1.62-4
Sat Jan 19 - 2 AM0-207.5-830 / 5-4N/15-300.8-1.40.7-1
2 PM0-20Clear0 / 03NE/10-20NaN0.8-1.2
8 PM0-5Clear0 / 0-1.5N/5-150.6-1.20.7-0.9
Sun Jan 20 - 2 AM0-5Clear0 / 00NNW/5-150.5-0.80.7-0.9
2 PM0-20Clear0 / 05N/5-15NaN0.8-1.2
Mon Jan 21 - 2 AM0-5Clear0 / 0-0.5NNW/5-150.45-0.650.7-1
2 PM0-20Clear0 / 04NNW/5-15NaN1-2
Tue Jan 22 - 2 AM0-5Clear0 / 0-2NW/15-300.6-12-4
2 PM0-20Clear20 / 02NW/20-35NaN3-5
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
Thu Jan 17 - Fri Jan 18 18:14 19:22 5:42 6:50 N/A 4:36 89 5 12.3 19 44
Fri Jan 18 - Sat Jan 19 18:15 19:22 5:42 6:50 N/A 5:40 95 6 15.2 21 19
Sat Jan 19 - Sun Jan 20 18:16 19:23 5:43 6:50 16:45 6:42 99 7 20.4 21 25
Sun Jan 20 - Mon Jan 21 18:16 19:24 5:43 6:50 17:50 7:42 100 8 26.2 19 55
Mon Jan 21 - Tue Jan 22 18:17 19:24 5:43 6:50 18:57 N/A 98 9 30.3 16 57
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 18 January 2019.
Additional Information
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