Current Conditions
Temp6.9 C
RH7 %
WindN 13 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Monday 16 October 2017
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while broken mostly thin high clouds continue to pass along the southern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 7.5 C this afternoon and 3 C for the night. Winds will be from the NE at 15-30 mph for today and 20-35 mph for the night. Seeing will likely be near 0.8-1 arcsecond, while precipitable water is expected to linger around 0.7-0.75 mm for the night.
A strong well-defined tradewind inversion will continue to cap low-level moisture near 7-8 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Scattered to broken high clouds will continue to stream along the southern skies, likely scraping the Big Island for much of tonight. This band will begin to break up and sag a touch southward thereafter, decreasing cloud cover over the following 2 nights and leaving clear skies for Thursday night. However, there is a possibility that high clouds will start to creep in from the west for Friday night.

Precipitable water is expected to plummet toward 0.7-0.75 mm for tonight, briefly increase back to 2-2.5 mm for tomorrow night, then settle in near or just below 1 mm for the following 3 nights.

Boundary layer and/or low-level turbulence will likely contribute to poor/bad seeing throughout most of the forecast period. There is a possibility that boundary layer turbulence will briefly subside and allow seeing to improve toward more average-like values for tomorrow night.

A deep ridge to the NW will continue to slowly drift eastward, invoking strong/steady subsidence in the area probably through the week. This subsidence will help maintain a very well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. PW is also expected to respond to this subsidence and plummet toward 0.7-0.75 mm for tonight. However, there is a possibility that a patch of mid-level moisture riding in with the deep northerly flow will briefly push PW back toward 2-2.5 mm for tomorrow night; PW should settle back in near 0.8-1 mm as this moisture slips southward thereafter. Unfortunately, the rather stiff persistent north to NE flow along the eastern flank of the ridge is expected to stir up boundary layer turbulence and contribute to poor/bad seeing throughout most of the forecast period. The only exception could be as the ridge subtly shifts northward, allowing winds to taper a bit and perhaps seeing to improve toward more average-like values for tomorrow night. The high clouds currently streaming along the southern skies via a rather strong sub-tropical jet are expected to gradually shift southward and dissipate as the upper portion of the ridge to the NW drifts eastward over the next few days. This should help open up summit skies and diminish turbulence in the free atmosphere, particularly after tonight. There is a possibility that more high clouds will move in from the west as the upper ridge breaks down and a large trough begins to develop near the dateline over the weekend. This trough could have the potential to bring another round of bad conditions (strong winds and moisture) to the summit for the early 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)
Mon Oct 16 - 2 PM50-709-100 / 07.5NNE/15-30NaN0.7-1.1
8 PM40-609-100 / 03NE/20-350.7-1.10.6-0.8
Tue Oct 17 - 2 AM40-609-100 / 03NE/20-350.7-1.10.65-0.85
2 PM30-509-100 / 08NNE/15-30NaN1-2
8 PM20-409.5-100 / 03.5NE/10-200.5-0.72-3
Wed Oct 18 - 2 AM20-409.5-100 / 03.5NE/10-200.5-0.71.5-2.5
2 PM10-309.5-100 / 09ENE/10-20NaN1-2
8 PM0-209.5-100 / 04.5ENE/15-300.6-10.8-1
Thu Oct 19 - 2 AM0-20Clear0 / 04ENE/15-300.7-1.10.9-1.1
2 PM0-20Clear0 / 09ENE/15-30NaN1-1.5
Fri Oct 20 - 2 AM0-5Clear0 / 04NE/20-350.7-1.10.9-1.1
2 PM0-20Clear0 / 08.5ENE/25-40NaN1-1.5
Sat Oct 21 - 2 AM20-409-100 / 03.5ENE/20-350.7-1.10.7-1.1
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
Mon Oct 16 - Tue Oct 17 18:06 19:11 5:04 6:08 4:22 N/A 6 11 50.7 3 50
Tue Oct 17 - Wed Oct 18 18:06 19:10 5:04 6:09 5:15 17:09 2 12 39.2 -0 27
Wed Oct 18 - Thu Oct 19 18:05 19:09 5:04 6:09 6:07 17:49 0 13 26.9 -4 40
Thu Oct 19 - Fri Oct 20 18:04 19:09 5:05 6:09 6:59 18:28 1 14 14.3 -8 37
Fri Oct 20 - Sat Oct 21 18:03 19:08 5:05 6:10 N/A 19:08 3 15 01.9 -12 10
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Monday 16 October (0300 UTC Tuesday 17 October) 2017.
Additional Information
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