Current Conditions
Temp2.7 C
RH12 %
WindSW 16 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Wednesday 22 November 2017
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while scattered high clouds pass along the southern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this afternoon and -2 C for the night. Winds will be from the WNW at 15-30 mph, with seeing near 0.65-0.7 arcseconds. Precipitable water is expected to be in the 1.25-1.75 mm range for the night.
Discussion
A 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 at least Friday night. There is a chance that building instability will begin to erode the inversion beginning Saturday morning, which will increase the risk for fog, ice and high humidity for the remainder of the weekend. There is also a possibility for convection in the area and periods of flurries at the summit mainly for Sunday and Monday. Daytime clouds will be minimal and short-lived through Friday, but could turn extensive for the weekend and early part of next week.

Scattered thin high clouds will continue to pass along the southern skies and occasionally overhead for the next 2 nights, then become more organized/widespread, thicker and creep northward through Friday night and into the weekend. This will increase cloud cover for Friday night and likely lead to overcast skies for the following 2 nights.

Precipitable water is expected to linger near 1.5 mm for tonight, settle in near or just below 1 mm, then begin to climb toward 4 mm through Saturday night and likely exceed 8 mm for Sunday night.

Light/moderate boundary layer turbulence, combined with persistent turbulence in the free atmosphere will likely contribute to poorer than average seeing over the next 2 nights. The former set of turbulence is expected to subside, which should allow for a modest improvement in seeing for Friday night. However, increasing instability and eventually turbulence and moisture in the atmosphere will likely degrade seeing over the next 2 nights.

The SE tip of the ridge to the NW will continue to sit over or just north of the state and promote strong/steady large-scale subsidence in the area through at least Saturday morning. This subsidence will help maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass over the next 3 nights. Unfortuntely, the persistent low/trough to the NE has been a little slow to retreat, which may allow winds to linger near 20-25 mph over the next 2 nights. While the direction of the winds are expected to switch (clockwise) from a more westerly direction to a more ENE direction, winds will continue to stir up light/moderate boundary layer turbulence and contribute to poorer than average seeing during this time. In addition, the departing trough will leave behind a rather broad/strong sub-tropical jet (STJ) over or just south of the state, which will eventually rebound northward and further strengthen as a new short-wave trough (SWT) digs in from the NW over the weekend. Regardless, the STJ will allow moderate/strong turbulence to persist in the free atmosphere and shuttle thin scattered high clouds over or just south of the Big Island during the next 3 nights. These clouds are expected to thicken, become more widespread and creep northward with the jet through Friday night and will likely contribute to overcast skies for the following 2 nights. The aforementioned SWT is also expected to destabilize the air mass, which will likely erode the inversion through Saturday night and lead to a fairly saturated/unstable air mass for much of Sunday. Nonetheless, this will increase the risk for fog, ice and high humidity at the summit mainly between midnight Saturday and the early part of next week. There is also a chance that for convection in the area and periods of flurries at the summit mainly between Sunday morning and midnight Monday.
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 Nov 22 - 2 PM0-209.5-100 / 02WNW/15-30NaN1.5-2.5
8 PM0-209.5-100 / 0-2W/15-300.6-0.91.25-1.75
Thu Nov 23 - 2 AM0-209.5-100 / 0-2.5WNW/15-300.55-0.851.25-1.75
2 PM10-309.5-100 / 02NNE/10-20NaN1-2
8 PM10-309-100 / 0-2NE/15-300.6-0.90.9-1.1
Fri Nov 24 - 2 AM0-209.5-100 / 0-2E/15-300.55-0.850.9-1.1
2 PM0-209.5-100 / 04ESE/5-15NaN1-2
8 PM20-409-100 / 0-1.5ENE/5-150.45-0.650.8-1
Sat Nov 25 - 2 AM40-608-100 / 0-1.5E/0-100.45-0.650.9-1.1
2 PM60-808-1025 / 53W/0-10NaN2-4
Sun Nov 26 - 2 AM80-1008-1050 / 25-2SW/5-150.5-0.93-5
2 PM80-1004-1090 / 751SW/5-15NaN6-10
Mon Nov 27 - 2 AM80-1004-1090 / 75-1.5W/10-200.7-1.38-12
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 Nov 22 - Thu Nov 23 17:51 18:58 5:18 6:26 N/A 21:33 20 19 43.0 -19 20
Thu Nov 23 - Fri Nov 24 17:51 18:58 5:19 6:27 N/A 22:23 28 20 32.4 -17 49
Fri Nov 24 - Sat Nov 25 17:51 18:58 5:20 6:27 N/A 23:13 37 21 21.5 -15 31
Sat Nov 25 - Sun Nov 26 17:51 18:58 5:20 6:28 N/A 0:05 46 22 10.3 -12 30
Sun Nov 26 - Mon Nov 27 17:51 18:59 5:21 6:28 N/A 0:57 56 22 59.2 -8 51
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 22 November (0300 UTC Thursday 23 November) 2017.
Additional Information
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