Current Conditions
Temp-0.9 C
RH8 %
WindSW 41 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Thursday 16 November (0300 UTC Friday 17 November) 2017
Warning(s)
Increasing winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while banding high clouds pass along the southern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near -1 C this evening and -2 C tomorrow morning. Winds will be from the west at 10-20 mph for much of today, increasing 15-30 mph through the night. Seeing will start out near 0.6 arcseconds, but could degrade toward 0.8-0.9 arcseconds as the night progresses. Precipitable water is expected to be in the 3-4 mm range for the first half of the night and 2.5-3.5 mm range for the second half.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 7 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.

While mostly clear skies will prevail for tonight, banding high clouds are set to scrape just south of the Big Island for tonight then sag back southward through tomorrow. Thin patches/strands of cirrus will possibily spread in from the west and pass over/near the summit for Friday and Saturday night. Predominately clear skies are likely for Sunday night, but another band of high clouds may drift in from the south on Monday and could significantly increase cloud cover by later that night.

Precipitable water is expected to linger near 2.5-3 mm for the next 3 nights, then slip toward 1.5 mm for Sunday and Monday night.

Increasing summit-level winds are expected to stir up boundary layer turbulence deteriorating seeing through tonight, and likely contribute to bad seeing for at least the following 3 nights. There is a chance that winds will begin to subside, which may allow seeing to improve for Monday night.

No change since the morning forecast...A quasi-stationary large-scale trough will linger to the NE of the state and prohibit the eastward advancement of the mid/low-level ridge to the NW probably well into next week. Nevertheless, the bulk of the moisture and instability associated with trough will remain off to the SE and NE (respectively) of the Big Island, allowing the SE tip of the ridge to promote fairly steady large-scale subsidence in the area throughout the forecast period. This subsidence will help maintain a relatively well-defined inversion near 7 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Unfortunately, a short-wave trough is expected to dig in from the NW and expand/enhance the large-scale trough over the next 12-24 hours. This southward expansion will result in a drastic increase in summit-level winds over the next 48 hours, with winds likely topping 50 mph (with gusts around 75 mph) for much of the weekend. There is a possibility that winds will begin to subside as the trough retracts northward early next week. Regardless, these winds will are expected to stir up boundary layer turbulence and contribute to poor/bad seeing throughout most of the forecast period (particularly Friday, Saturday and Sunday night).
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 Nov 16 - 8 PM0-209.5-100 / 0-1W/10-200.5-0.82.5-3.5
Fri Nov 17 - 2 AM0-209.5-100 / 0-2W/15-300.6-0.92-3
2 PM0-20Clear0 / 02WSW/25-40NaN2-3
8 PM0-209.5-100 / 0-3WSW/30-451-22-3
Sat Nov 18 - 2 AM10-309.5-100 / 0-3WSW/35-501-22-3
2 PM10-309-100 / 01.5WSW/40-60NaN2-4
8 PM10-309-100 / 0-3.5WSW/40-601-22.5-3.5
Sun Nov 19 - 2 AM0-209.5-100 / 0-4WSW/40-601-22.5-3.5
2 PM0-20Clear0 / 02.5WSW/40-60NaN2-4
Mon Nov 20 - 2 AM0-5Clear0 / 0-2.5W/40-600.8-1.61-2
2 PM20-409.5-100 / 03W/25-40NaN1.5-2.5
Tue Nov 21 - 2 AM60-809-100 / 0-1W/15-300.5-0.91-2
2 PM0-20Clear0 / 04W/10-20NaN1.5-2.5
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 Nov 16 - Fri Nov 17 17:51 18:58 5:15 6:23 5:44 17:06 1 14 49.8 -11 12
Fri Nov 17 - Sat Nov 18 17:51 18:58 5:16 6:23 6:34 17:46 0 15 37.3 -14 23
Sat Nov 18 - Sun Nov 19 17:51 18:58 5:16 6:24 7:25 18:28 1 16 25.4 -16 57
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
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 17 November 2017.
Additional Information
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