Current Conditions
Temp6.6 C
RH23 %
WindENE 19 mph
RoadOpen
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Wednesday 16 May 2012
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 6 C this afternoon, 1 C this evening and 0.5 C tomorrow morning. Winds will be light and from the ENE, with seeing around 0.5-0.55 arcseconds. Precipitable water is expected to be in the 1.5-2 mm range for the night.
Discussion
The tradewind inversion will continue to cap the fairly limited supply of low-level moisture at or below 8 thousand feet and keep the mid/summit-level air mass dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear throughout the forecast period.

Precipitable water will start out near 1.75 mm for tonight, slip toward 1.5 mm for tomorrow night and probably 1.25 mm for Friday and Saturday night. It may creep back up toward 2-3 mm (or more) again for Sunday night.

Light relatively deep northerly flow at and above the summit will keep shear/turbulence in the atmosphere to a minimum and likely seeing near 0.5-0.55 arcseconds over the next 2 nights. There is a chance that shear will briefly increase in the free atmosphere, which could degrade seeing toward 0.6-0.7 arcseconds for Friday night. However, deep northerly flow is slated to fill back into the area, helping to improve seeing again for at least Saturday night. Unfortunately, there is a possibility that summit-level winds will pick up late Sunday, which could stir up boundary layer turbulence and perhaps degrade seeing for that night.

The mid/low-level ridge will continue to sit to the north of the state, promote steady/strong large-scale subsidence in the area and keep the air mass dry and stable well into next week. Upper-level flow, on the other hand, will change subtly over the next several days, but will not have access to much high clouds, thus allowing clear skies to prevail at the summit. Regardless, the Islands will remain situated between two upper-level lows, one to the far east and another near the Dateline. Neither will affect the stability of the air mass, especially with a weak upper-level ridge in the area. In fact, the presense of the ridge may help contribute to better than average seeing over the next 2 nights. There is a possibility that (the upper-level) ridge will briefly break down as the sub-tropical jet tries to fill in from the south on Friday night. This could increase shear in the free atmosphere and degrade seeing toward more average-like values for that night. The STJ is expected to sag back southward allowing the upper-level ridge to build back into the area and improve seeing once again for Saturday night. However, models suggest that this ridge will help increase summit-level winds, which could stir up boundary layer turbulence and deteriorate seeing for 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)
Wed May 16 - 2 PM0-20Clear0 / 06ENE/0-10NaN2-3
8 PM0-5Clear0 / 01ENE/0-100.45-0.551.5-2
Thu May 17 - 2 AM0-5Clear0 / 00.5ENE/0-100.45-0.551.5-2
2 PM0-20Clear0 / 05.5E/5-15NaN1.5-2.5
8 PM0-5Clear0 / 00.5E/5-150.5-0.61.25-1.75
Fri May 18 - 2 AM0-5Clear0 / 00.5E/5-150.45-0.551.25-1.75
2 PM0-20Clear0 / 05.5ESE/5-15NaN1.5-2.5
8 PM0-5Clear0 / 01E/5-150.5-0.71-1.5
Sat May 19 - 2 AM0-5Clear0 / 00.5ESE/5-150.5-0.71-1.5
2 PM0-20Clear0 / 06E/5-15NaN1-1.5
Sun May 20 - 2 AM0-5Clear0 / 01ENE/5-150.4-0.61-1.5
2 PM0-20Clear0 / 06NE/5-15NaN1.5-2.5
Mon May 21 - 2 AM0-5Clear0 / 01ENE/10-200.5-0.82-4
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 May 16 - Thu May 17 19:01 20:12 4:25 5:36 3:21 N/A 11 1 02.8 10 15
Thu May 17 - Fri May 18 19:01 20:12 4:24 5:35 3:59 N/A 6 1 48.5 13 50
Fri May 18 - Sat May 19 19:02 20:13 4:24 5:35 4:39 17:28 2 2 35.4 16 50
Sat May 19 - Sun May 20 19:02 20:14 4:23 5:35 5:22 18:19 0 3 23.7 19 07
Sun May 20 - Mon May 21 19:02 20:14 4:23 5:34 6:08 19:10 0 4 13.2 20 35
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 16 May (0300 UTC Thursday 17 May) 2012.
Additional Information
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