Current Conditions
Temp4.2 C
RH91 %
WindS 0 mph
RoadOpen (4x4 only)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Monday 27 July 2015
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable through the night. There is a possibility for high clouds along the southern skies toward the end of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 8 C this afternoon and 3 C for the night. Winds will be light and from the south, with seeing around 0.5 arcseconds. Precipitable water is expected to exceed 4 mm through the night.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure a dry and stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies overhead will remain predominately clear for most of tonight, but banding high clouds may start to creep in from the south near sunrise tomorrow and perhaps contribute to periods of extensive cloud cover for that night as well as Wednesday night. This band is slated to break up and shift off toward the northwest on Thursday, leaving only residual very thin slow-moving high clouds in the area for that night and Friday night.

Precipitable water is expected to linger near or exceed 4 mm probably throughout the forecast period.

Relatively calm flow will prevail at and above the summit, which should allow for better than average seeing through the next 5 nights. There is a very good possibility that seeing will dip toward 0.3-0.4 arcseconds as upper-level subsidence builds in overhead late Wednesday night and especially for the following 2 nights.

The mid/low-level ridge will continue to sit to the north of the Islands and promote steady/strong large-scale subsidence in the area through the week. This subsidence will easily maintain the tradewind inversion at or below 9 thousand feet and ensure a dry and stable summit-level air mass through the next 5 nights. The sub-tropical jet will also persist well north of the Big Island, which should keep turbulence in the free atmosphere to a minimum and likely allow for better than average seeing during this time. Unfortunately, a slow-building upper-level ridge to the southeast is expected to inject high clouds up its western flank, over the Big Island and into the STJ beginning around sunrise tomorrow. These clouds will likely contribute to periods of extensive cloud cover until the upper ridge starts to fill over the Big Island early Thursday morning. This will not only help to clear up summit skies, but also enhance the subsidence in the area for the second half of the forecast period. This extra subsidence will significantly warm up the summit-level air mass and potentially improve seeing toward excellent values for Thursday and Friday night (perhaps even the second half of Wednesday night as well).
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)
Mon Jul 27 - 2 PM0-20Clear0 / 08SSE/0-10NaN4-6
8 PM0-5Clear0 / 03SSE/0-100.45-0.554-6
Tue Jul 28 - 2 AM0-20Clear0 / 03S/5-150.45-0.554-6
2 PM20-409-100 / 08W/0-10NaN4-6
8 PM40-608-100 / 03.5N/0-100.45-0.554-6
Wed Jul 29 - 2 AM60-808-100 / 03.5NNE/0-100.45-0.554-6
2 PM60-807-90 / 09NE/5-15NaN4-6
8 PM60-807-90 / 04.5NE/10-200.4-0.54-6
Thu Jul 30 - 2 AM60-808-90 / 04.5ENE/10-200.35-0.454-6
2 PM20-409.5-100 / 010NE/10-20NaN4-6
Fri Jul 31 - 2 AM10-309.5-100 / 06NE/10-200.25-0.453-5
2 PM0-209.5-100 / 011NE/10-20NaN3-5
Sat Aug 01 - 2 AM0-209.5-100 / 06NE/5-150.25-0.453-5
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 Jul 27 - Tue Jul 28 19:10 20:21 4:36 5:47 N/A 3:27 88 17 36.8 -18 50
Tue Jul 28 - Wed Jul 29 19:10 20:20 4:36 5:47 N/A 4:24 94 18 35.4 -18 40
Wed Jul 29 - Thu Jul 30 19:09 20:20 4:37 5:47 17:29 5:24 98 19 35.3 -17 22
Thu Jul 30 - Fri Jul 31 19:09 20:19 4:38 5:48 18:23 6:25 100 20 35.6 -14 55
Fri Jul 31 - Sat Aug 01 19:08 20:19 4:38 5:48 19:15 N/A 99 21 35.3 -11 30
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Monday 27 July (0300 UTC Tuesday 28 July) 2015.
Additional Information
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