Current Conditions
Temp2.3 C
RH9 %
WindENE 38 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Wednesday 18 January (0300 UTC Thursday 19 January) 2017
Moderate/strong winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for thin high clouds along the western skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1 C tomorrow morning. Winds will be from the ESE at 35-50 mph for today, diminishing to 25-40 mph as the night progresses. Seeing will exceed 1 arcsecond, while precipitable water is expected to be in the 0.8-1 mm range for the night.
A well-defined tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived through Sunday, but could pick up for the early part of next week.

While skies overhead will remain predominately clear throughout the forecast period, there is a possibility for thin high clouds along the western skies for tonight, which are set to move to the northern skies for tomorrow night.

Precipitable water is expected to linger just below 1 mm for tonight, trend toward 2 mm through the course of tomorrow night, then settle in near 2-2.5 mm for the remainder of the week.

Moderate/strong summit-level winds will continue to stir up significant boundary layer turbulence and contribute to bad seeing for at least the next 2 nights. Winds are set to subside below 20 mph, which should help to reduce boundary layer turbulence and likely improve seeing toward 0.5-0.6 arcseconds as relatively calm skies prevail in the free atmosphere for much of Friday night. However, an influx of mid/upper-level turbulence could degrade seeing toward more poor-like values for the following 2 nights.

Little change since the morning forecast...A deep ridge sitting to north will begin to shift eastward over the next several days, then will flatten out over the state as a trough begins to fill in from the NW over the weekend. Nonetheless, the deep ridge will continue to promote strong/steady large-scale subsidence in the area, which will help maintain a well-defined inversion near 6 thousand feet over the next 3 nights. The inversion is set to weaken/lift toward 8-9 thousand feet as minor upper-level instability builds into the area over the weekend, but lack of mid/upper-level moisture will ensure the summit air mass remains dry and stable through the next 5 nights. Winds are still expected to peak this morning, then slowly but steadly decline as the ridge shifts eastward over the next 48-60 hours, eventually dropping below 20 mph by Friday night. Still, winds will continue to stir up boundary layer turbulence and contribute to bad seeing for the next 2 nights. Calmer skies should allow seeing to dramatically improve (toward 0.5-0.6 arcseconds) for Friday night, but the building trough is expected to push the southern fringe of the jet over the Big Island for the following 2 nights. This could increase mid/upper-level turbulence in the area and degrade seeing toward 0.7-0.8 arcseconds during that time. Now it should be noted that the last two runs have started to get a little more agressive with the southern progression of a dissipating cold front early next week. The latest model run actually has this front arriving around midnight Sunday, then dissipating in the area over the next 2-3 days. I suspect this is a little overdone, mainly due to the inconsistencies in previous runs (but also what is expected to be left of the front), and thus have left it out of the forecast table for Sunday night....though that could change with more consistent subsequent runs.
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)
Wed Jan 18 - 8 PM0-20Clear0 / 02ESE/30-451-20.8-1
Thu Jan 19 - 2 AM0-20Clear0 / 01ESE/25-401-20.8-1
2 PM0-20Clear0 / 06ESE/20-35NaN1-2
8 PM0-20Clear0 / 02ESE/20-350.8-1.41.25-1.75
Fri Jan 20 - 2 AM0-20Clear0 / 01ESE/15-300.7-1.31.5-2
2 PM0-20Clear0 / 07SSE/15-30NaN1.5-2.5
8 PM0-5Clear0 / 03S/15-300.4-0.71.75-2.25
Sat Jan 21 - 2 AM0-5Clear0 / 02.5SSW/10-200.45-0.651.75-2.25
2 PM0-20Clear0 / 06SW/5-15NaN2-3
Sun Jan 22 - 2 AM0-5Clear0 / 0-1ESE/5-150.6-0.92-3
2 PM0-20Clear0 / 04SSE/10-20NaN2-3
Mon Jan 23 - 2 AM0-5Clear0 / 0-1S/10-200.6-11.5-2.5
2 PM60-804-860 / 202WSW/10-20NaN4-8
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
Wed Jan 18 - Thu Jan 19 18:15 19:23 5:43 6:50 24:00 N/A 54 13 37.9 -5 52
Thu Jan 19 - Fri Jan 20 18:16 19:23 5:43 6:50 0:49 N/A 45 14 23.9 -9 25
Fri Jan 20 - Sat Jan 21 18:16 19:24 5:43 6:50 1:38 N/A 35 15 10.2 -12 33
Sat Jan 21 - Sun Jan 22 18:17 19:24 5:43 6:50 2:27 N/A 27 15 57.3 -15 10
Sun Jan 22 - Mon Jan 23 18:18 19:25 5:43 6:50 3:16 N/A 19 16 45.5 -17 10
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 19 January 2017.
Additional Information
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