Current Conditions
Temp-2.4 C
RH79 %
WindSW 39 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Tuesday 12 December (0300 UTC Wednesday 13 December) 2017
Warning(s)
Moderate winds
Chance for fog/ice
Cloud Cover and Fog/Precipitation Forecast
There is a small risk for short-lived fog, high humidity and ice through the night; precipitation is not expected. Scattered patches of mid/upper-level clouds will continue to fill in from the northwest and pass over the area through 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 25-40 mph, while seeing and precipitable water linger near or exceed 1 arcseconds and 4 mm, respectively, through the night.
Discussion
Although the inverison will remain fairly well intact near 6-8 thousand feet through at least Thursday evening, a passing/developing cold front may allow for the development of short-lived fog and ice for tonight; dry and stable conditions are expected for Wednesday and most of Thursday night. There is a chance that building instability and moisture to the north of the state may begin to erode the inversion and increase the risk for periods of fog, ice, high humidity and flurries at the summit for Friday and Saturday. There is also a possibility for convection along the slopes and just north of the Big Island during that time. Daytime clouds will be minimal and short-lived through Thursday, but could pick up for Friday and the weekend.

Scattered patches of mid/upper-level clouds will continue to fill in from the northwest and pass over the area through the night. Clear skies will prevail for at least Wednesday and Thursday night, but there is a possibility that patches of mid-level clouds will develop/build along the northern skies and may occasionally stray overhead for Friday and Saturday night.

Precipitable water is expected to increase to4 mm for tonight, plummet toward 0.8-0.9 mm for Wednesday and Thursday night, then rebound back toward 4 mm for the following 2 nights.

A mixture of moderate/strong boundary layer turbulence and mid/upper-level turbulence will contribute to bad seeing through the next 5 nights.

Little change since the morning forecast...A large trough strengthening to the north will send a developing cold front through the state and squash the ridge just south of the Big Island for tonight. There is a chance that the passage of the cold front will briefly weaken the inversion and/or allow for the development of fog and ice at the summit during that time. Still, the odds are quite low and subsidence associated with the ridge will quickly restore a well-defined/strong inversion near 6-7 thousand feet and ensure a dry/stable summit-level air mass for Wednesday and Thursday night. Unfortunately, moderate/strong winds will remain an issue probably through the week. Initially, the southern flank of the trough will sit over the state and promote moderate/strong westerly winds. Winds willturn to a more northerly direction and strengthen as the ridge tries to build in from the west, but is blocked as the trough deposits a low to the NE later tomorrow and into Thursday. This may allow winds to approach 60-80 mph for much of Thursday and perhaps into Friday. Winds may taper a bit as this low loses its support/momentum from the westerly jet and begins to retrograde westward during the latter day and into the weekend. Models runs have been a little inconsistent with the placement/trajectory of the low over the last several days, but it appears that it is settling on keep the bulk of the moisture to the north of the Big Island. Nevertheless, the low will still pass close enough to destabilize the air mass and bring some moisture to the area, which could raise the stakes on more fog, ice and perhaps even light flurries at the summit for Friday and over the weekend. It may also allow for the development of mostly isolated convection to the northern skies and perhaps the southern slopes of the Big Island during that time.
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)
Tue Dec 12 - 8 PM20-407-1025 / 0-2WSW/25-400.8-1.63.5-4.5
Wed Dec 13 - 2 AM10-307-1025 / 0-3WSW/25-401-23.5-4.5
2 PM0-20Clear0 / 00WNW/30-45NaN1-2
8 PM0-10Clear0 / 0-5NNW/50-701-30.7-0.9
Thu Dec 14 - 2 AM0-5Clear0 / 0-6NW/40-601-30.7-0.9
2 PM0-20Clear0 / 01N/60-80NaN1-2
8 PM0-5Clear0 / 0-4NNW/50-701-30.8-1
Fri Dec 15 - 2 AM0-10Clear15 / 5-5NNW/40-601-30.8-1.2
2 PM60-804-840 / 10-0.5WNW/50-70NaN3-6
Sat Dec 16 - 2 AM20-405-840 / 10-4.5WNW/35-500.8-1.63-5
2 PM60-804-860 / 150.5W/25-40NaN4-8
Sun Dec 17 - 2 AM20-405-840 / 10-3W/20-350.7-1.33-5
2 PM0-204-730 / 106WSW/15-30NaN3-6
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
Tue Dec 12 - Wed Dec 13 17:54 19:03 5:29 6:38 2:50 N/A 20 13 53.4 -6 29
Wed Dec 13 - Thu Dec 14 17:54 19:03 5:30 6:39 3:40 N/A 13 14 40.0 -10 16
Thu Dec 14 - Fri Dec 15 17:55 19:04 5:30 6:39 4:30 N/A 7 15 26.9 -13 35
Fri Dec 15 - Sat Dec 16 17:55 19:04 5:31 6:40 5:21 16:26 3 16 14.6 -16 20
Sat Dec 16 - Sun Dec 17 17:56 19:05 5:32 6:40 6:10 17:09 1 17 03.0 -18 22
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 13 December 2017.
Additional Information
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