Current Conditions
Temp10.4 C
RH21 %
WindNW 16 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Friday 22 May (0300 UTC Saturday 23 May) 2015
Warning(s)
Moderate winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for departing high clouds along the eastern skies for early this evening.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1 C tomorrow morning. Winds will be from the west at 20-35 mph, with seeing around 0.7-0.8 arcseconds. Precipitable water is expected to be in the 2.5-3.5 mm range for the first half of the night and 2-3 mm range or the second half.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 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.

While the high clouds to the north and south are expected to shift eastward over the next 12 hours, leaving predominately clear skies for the remainder of the forecast period, there is a possibility for departing cirrus along the eastern skies for early this evening.

Precipitable water is expected to linger near 2.5-3 mm for the next 2 nights, then increase toward 4 mm for Sundahy, Monday and Tuesday night.

Boundary layer turbulence will contribute to poor seeing over the next 2 nights. This turbulence is slated to subside through Sunday, allowing seeing to return toward 0.5-0.55 arcseconds for Sunday and Monday night. However, an influx of mid/upper-level turbulence may subtly degrade seeing for Tuesday night.

No change since the morning forecast...Although only the eastern tip of new ridge is expected to slowly fill in from the WSW over the weekend, it will still help push the mature low off toward the east and keep its associated cold from reaching the Big Island. This will not only ensure large-scale subsidence prevails in the area and the summit remains dry and stable (throughout the forecast period), but will also help clear out summit skies over the next 6 hours. Unfortunately, lingering mid/upper-level moisture will likely allow PW to linger near 2.5-3 mm over the next 2 nights, and may increase further as the easterly tip of the ridge transports more mid/upper-level moisture into the area later in the weekend. In addition, westerly flow along the southern fringe of the low will likely keep summit-level winds near 20-30 mph, which will stir up boundary layer turbulence and contribute to poor seeing over the next 2 nights. Winds are slated to taper once the low shifts further eastward, which should allow seeing to settle in near 0.5-0.55 arcseconds for Sunday and Monday night. There is a possibiltiy that a patch of mid/upper-level turbulence embedded a weak (rebuilding) tropical upper-tropospheric trough will enter into the area, which could disrupt seeing a tad for Tuesday 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)
Fri May 22 - 8 PM0-20Clear0 / 02W/20-350.6-0.92.5-3.5
Sat May 23 - 2 AM0-10Clear0 / 01W/20-350.6-0.92-3
2 PM0-20Clear0 / 07W/20-35NaN2.5-3.5
8 PM0-5Clear0 / 02.5WNW/15-300.6-0.92.5-3.5
Sun May 24 - 2 AM0-5Clear0 / 02W/15-300.6-0.82.5-3.5
2 PM0-20Clear0 / 08WNW/10-20NaN3-4
8 PM0-5Clear0 / 03.5NW/5-150.5-0.63.5-4.5
Mon May 25 - 2 AM0-5Clear0 / 03WNW/5-150.45-0.553.5-4.5
2 PM0-20Clear0 / 09W/10-20NaN4-6
Tue May 26 - 2 AM0-5Clear0 / 03W/10-200.45-0.553.5-4.5
2 PM0-20Clear0 / 08W/10-20NaN4-6
Wed May 27 - 2 AM0-5Clear0 / 02.5WSW/10-200.5-0.73.5-4.5
2 PM0-20Clear0 / 08WSW/15-30NaN3-5
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
Mon May 25 - Tue May 26 19:04 20:16 4:21 5:33 N/A 1:16 56 10 48.4 4 32
Tue May 26 - Wed May 27 19:05 20:17 4:21 5:33 N/A 1:53 65 11 33.7 0 50
Wed May 27 - Thu May 28 19:05 20:18 4:21 5:33 N/A 2:30 74 12 19.2 -2 56
Thu May 28 - Fri May 29 19:06 20:18 4:20 5:33 N/A 3:08 82 13 05.5 -6 40
Fri May 29 - Sat May 30 19:06 20:19 4:20 5:33 N/A 3:47 89 13 53.3 -10 12
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 25 May 2015.
Additional Information
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