Current Conditions
Temp4.1 C
RH12 %
WindSSE 40 mph
Mauna Kea Observatories Forecast
5 PM HST Friday 19 December (0300 UTC Saturday 20 December) 2014
Moderate/strong winds through Sunday AM
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 0 C this evening and -0.5 C tomorrow morning. Winds will be from the east at 20-35 mph for today, increasing to 30-45 mph as the night progresses (gusts exceeding 50 mph are possible). Precipitable water is expected to be in the 0.7-0.9 mm range, while seeing will exceed 1 arcsecond.
The tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure a dry and stable mid/summit-level air mass through Sunday night. There is a possibility that the inversion will weaken/lift toward 13 thousand feet, which will raise the stakes on fog, ice, high humidity and flurries for Monday and Tuesday night. There is also a possibility for convection in the area mainly for Tuesday. Daytime clouds will be minimal and short-lived through Sunday, but could turn extensive for the early part of next week, then taper again on Wednesday.

Skies will remain predominately clear through Sunday night. Thick clouds are expected to build in from the north and south through Monday, perhaps blanketing skies for that night and into the early part of Tuesday night. The bulk of these clouds are slated to shift off toward the east during the latter night, opening up skies by sunrise Wednesday.

Precipitable water is expected to linger near 0.8-0.85 mm for the next 3 nights, then increase toward 2-4+ mm for Monday and Tuesday night.

Moderate/strong summit-level winds will continue to stir up boundary layer turbulence and contribute to poor/bad seeing for the next 2 nights. There is a possibility that seeing will briefly improve toward average (or slightly better) seeing for Sunday night. However, building mid/upper-level turbulence will likely contribute to another round of poor/bad seeing for Monday and Tuesday night.

The mid/low-level ridge will continue to sit to the north of the state for the next 48 hours, then shift off toward the SE as a large trough approaches from the northwest through Sunday and into Monday. Regardless, strong/steady large-scale subsidence will prevail in the area, which will help maintain the tradewind inversion near 7-8 thousand feet and ensure a very dry/stable and clear summit-level air mass over the next 3 nights. While PW is also expected to linger near 0.8 mm during those nights, strong easterly winds to the south of the ridge will continue to stir up boundary layer turbulence and contribute to poor/bad seeing through Saturday night. Winds are slated to subside as the ridge shifts closer to the Big Island, which should allow seeing to dramatically improve for Sunday night. However, the approaching trough is expected to bring mid/upper-level turbulence to the area as well as destabilize the atmosphere for the early part of next week. The latter could result in poor/wet summit-level conditions and perhaps light flurries for Monday and Tuesday night. The bulk of the heavy convection associated with the trough should linger off toward the north, which will minimize the risk of heavy snow during this trough's tenure.
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 Dec 19 - 8 PM0-5Clear0 / 00E/25-400.8-1.60.7-0.9
Sat Dec 20 - 2 AM0-5Clear0 / 0-0.5E/30-451-20.7-0.9
2 PM0-20Clear0 / 03E/25-40NaN0.8-1.2
8 PM0-5Clear0 / 0-1E/25-400.8-1.60.7-0.9
Sun Dec 21 - 2 AM0-5Clear0 / 0-1.5ESE/20-350.7-1.30.7-0.9
2 PM0-20Clear0 / 04SE/10-20NaN0.8-1.2
8 PM0-5Clear0 / 00ESE/5-150.45-0.650.7-0.9
Mon Dec 22 - 2 AM0-10Clear0 / 0-0.5ESE/5-150.4-0.60.7-0.9
2 PM60-804-860 / 303N/10-15NaN3-6
Tue Dec 23 - 2 AM80-1004-1075 / 50-2.5N/5-150.8-1.62-4
2 PM80-1004-1090 / 601N/5-15NaN4-8
Wed Dec 24 - 2 AM40-605-760 / 30-2.5N/5-150.8-1.63-6
2 PM20-402-2.520 / 52N/10-20NaN2-4
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
Sat Dec 20 - Sun Dec 21 17:57 19:06 5:33 6:42 6:18 17:09 1 17 21.7 -18 37
Sun Dec 21 - Mon Dec 22 17:58 19:07 5:34 6:43 7:16 18:07 0 18 21.0 -18 26
Mon Dec 22 - Tue Dec 23 17:58 19:07 5:34 6:43 N/A 19:08 3 19 20.7 -17 06
Tue Dec 23 - Wed Dec 24 17:59 19:08 5:35 6:44 N/A 20:10 7 20 19.7 -14 41
Wed Dec 24 - Thu Dec 25 17:59 19:08 5:35 6:44 N/A 21:12 15 21 17.5 -11 20
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 22 December 2014.
Additional Information
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This message is also available at the MKWC road conditions page.
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