Current Conditions
Temp3.2 C
RH16 %
WindN 10 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Monday 02 May (0300 UTC Tuesday 3 May) 2016
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 3.5 C this evening and 3 C tomorrow morning. Winds will be from the NNE at 10-20 mph, while seeing will start out near 0.65-0.7 arcseconds, but should improve toward 0.5-0.55 as the night progresses. Precipitable water is expected to be in the 1-1.5 mm range for the first half of the night and 1.5-2 mm range for the second half.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 10 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived through Thursday, but could pick for Friday and over the weekend.

Skies will remain predominately clear for the next 2 nights. There is a possibility that patch of high clouds will move in from the west and pass over/near the summit area between late Wednesday night and early Thursday evening. There is also a chance that another thin band will slip through the area near sunrise on Friday; clear skies will prevail for that night.

Precipitable water is expected to start out near 1 mm for this evening, but increase toward 2 mm as the night progresses, eventually settling in near 2.5-3 mm for the remainder of the forecast period.

Lingering upper-level turbulence may contribute to poorer than average seeing for this evening, but seeing is slated to improve as this turbulence subsides through the night. While there is a good chance for calm skies and better than average seeing for tomorrow evening, light/moderate persistent turbulence in the free atmosphere may push seeing back toward more average-like values later that night and for the following 2 nights. There is a possibility that building upper-level turbulence will further negate seeing for Friday night.

No chagne since the morning forecast...The mid and especially low-level ridge will continue to sit to the north of the state and promote steady/strong large-scale subsidence in the area through the week. This will help maintain the tradewind inversion at or below 10 thousand feet and ensure the summit remains dry and stable over the next 5 nights. The inversion is actually slated to remain well-defined near 7-8 thousand feet over the next 3-4 days, but may start to lift a bit as the mid-level portion of the ridge breaks down in response to a passing upper-level trough to the north later in the week. This trough is not expected to have a big impact on the stability of the atmosphere (but may increase turbulence in the free atmosphere), and should become less of an issue as we head deeper into Spring. In fact, upper-level flow is starting to transition more toward its usual spring-time set up, with the tropical upper-tropospheric trough (TUTT) and its associated sub-tropical jet (STJ) beginning to take shape over the eastern half of the Pacific and near or just south of the state, respectively, over the last several days. The TUTT remains too weak to really affect the stability of the atmosphere at this time, but that could change as embedded upper-level lows start to take form over/near the state over the next month or two. The STJ, particularly its positioning, will likely have a direct impact on seeing through the week. Right now, it looks like the STJ is set to sag southward over the next 24 hours, which should help to reduce turbulence in the free atmosphere and improve seeing for tomorrow. However, seeing may return toward more average-like values as the STJ rebounds northward later that night and then settles in just south of the Big Island over the following 2-3 days.
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 May 02 - 8 PM0-5Clear0 / 03.5NNE/10-200.55-0.751-1.5
Tue May 03 - 2 AM0-5Clear0 / 03NE/10-200.5-0.61.5-2
2 PM0-20Clear0 / 08.5ENE/10-20NaN2-3
8 PM0-5Clear0 / 04E/10-200.4-0.52.5-3.5
Wed May 04 - 2 AM0-5Clear0 / 03E/5-150.45-0.652.5-3.5
2 PM0-20Clear0 / 08.5ESE/5-15NaN2.5-3.5
8 PM10-30Clear0 / 03.5ESE/5-150.45-0.652.5-3.5
Thu May 05 - 2 AM20-408-90 / 03SSE/5-150.45-0.652-3
2 PM40-608-90 / 08S/5-15NaN2-3
Fri May 06 - 2 AM0-208-90 / 02WSW/5-150.45-0.652.5-3.5
2 PM20-404-4.520 / 07WNW/10-20NaN3-6
Sat May 07 - 2 AM0-5Clear0 / 02N/10-200.5-0.92-4
2 PM20-404-4.520 / 08.5ENE/10-20NaN2-4
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
Mon May 02 - Tue May 03 18:55 20:04 4:33 5:42 3:21 N/A 16 23 47.3 -2 27
Tue May 03 - Wed May 04 18:56 20:05 4:32 5:42 4:08 N/A 8 0 42.8 2 09
Wed May 04 - Thu May 05 18:56 20:05 4:32 5:41 4:57 N/A 3 1 39.6 6 40
Thu May 05 - Fri May 06 18:56 20:06 4:31 5:40 5:49 18:11 0 2 38.0 10 46
Fri May 06 - Sat May 07 18:57 20:06 4:30 5:40 6:43 19:16 1 3 37.7 14 09
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 3 May 2016.
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