Current Conditions
Temp3.8 C
RH35 %
WindN 6 mph
RoadOpen (4x4 only)
Mauna Kea Observatories Forecast
5 PM HST Monday 03 August (0300 UTC Tuesday 4 August) 2015
Warning(s)
Cloud Cover and Fog/Precipitation Forecast
There is a moderate/high risk for fog, summit-level clouds and rain particularly during the first half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 3.5 C this evening and 2.5 C tomorrow morning. Winds will be from the NNW at 5-15 mph, while seeing will start out near 0.8-1 arcseconds, but may improve toward 0.5-0.6 arcseconds during the second half of the night (some degradation is possible again near sunrise). Precipitable water is expected to exceed 4 mm through the night.
Discussion
Lingering tropical moisture will keep the inversion rather weak/elevated, which may allow for more fog and perhaps light rain mainly through this evening. There is a possibility the inversion will restrengthen a bit during the second half of the night, but an influx of widespread/deep tropical moisture is expected to erode the inversion and increase the odds on fog/rain at the summit and convection in the area between early Tuesday evening and Friday morning (especially for Wednesday). The inversion is slated to recover again near 6 thousand feet through Friday, ensuring a dry/stable summit-level air mass for that night. Extensive daytime clouds are possible through Thursday, but will taper for Friday.

There is a possibility for lingering summit-level clouds mainly for this evening, and thicker more widespread clouds are expected to fill in from the east through tomorrow, likely blanketing skies for most of that night and especially Wednesday night. These clouds will start to shift off toward the NW through Thursday, leaving only residual mid/summit-level clouds in the area for that night; clear skies will likely prevail for Friday night.

Precipitable water is expected to linger near or exceed 4 mm through at least Thursday night, but could slip toward 3 mm for Friday night.

Residual low-level turbulence will likely contribute to poor seeing through most of tonight (there is a possibility for periods of average - perhaps even slightly better - seeing during the second half of tonight). An influx stronger turbulence will result in poor/bad seeing for the following 3 nights. This turbulence is slated to subside on Friday, just as deep subsidence fills into the area, which could allow for good/excellent seeing for Friday night.

Very little change since the morning forecast...Remnant moisture from tropical depression 08E will continue to linger in the area and keep the inversion rather weak/elevated and negate the affects of the ridge to the north of the Islands probably through most of today. While this will likely allow for more fog/moisture at the summit through this evening, there is a possibility that subsidence out ahead of Guillermo will help rebuild the inversion and squash the odds on fog/rain and clouds as the night progresses. It may also allow for average (perhaps slightly better) seeing and clear skies mainly near/after midnight. However, increasing turbulence associated with Guillermo may start to degrade seeing near sunrise tomorrow and definitely contribute to poor/bad seeing for the following 3 nights. Guillermo is scheduled to continue a gradual weakening trend as it encounters the sub-tropical jet to the north while approaching and passes through or just north of the Islands over the next 4 days. Unfortunately an abundant supply of widespread/deep tropical moisture associated with Guillermo is still expected to pass over the Big Island between Tuesday evening and early Friday morning. This moisture will likely erode the inversion and bring more extensive fog/rain at the summit and islolated convection to the area during that time, and particularly between Wednesday morning and Thursday morning. The bulk of the moisture will shift off toward the NW as a deep ridge fills in from the east through Thursday night. Subsidence associated with this ridge will help rebuild the inversion near 6-7 thousand feet and ensure a dry/stable summit-level air mass for Friday night and the remainder of the weekend. It could also dramatically improve seeing (toward good/excellent values) during that time.
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 Aug 03 - 8 PM20-404-575 / 253.5N/5-150.6-13.5-4.5
Tue Aug 04 - 2 AM0-204-4.550 / 102.5N/5-150.4-0.73.5-4.5
2 PM60-804-560 / 308N/5-15NaN4-8
8 PM60-804-675 / 603.5NNE/5-150.3-1.34-8
Wed Aug 05 - 2 AM80-1004-895 / 903.5NE/10-201-26-10
2 PM80-1004-10100 / 955W/10-20NaN8-12
8 PM80-1004-9100 / 903SW/10-201-28-12
Thu Aug 06 - 2 AM80-1004-790 / 753SSW/10-201-28-12
2 PM80-1004-675 / 506S/10-20NaN4-8
Fri Aug 07 - 2 AM40-604-560 / 203S/5-150.6-1.24-8
2 PM0-20Clear10 / 08ESE/10-20NaN4-6
Sat Aug 08 - 2 AM0-5Clear0 / 04E/10-200.35-0.553-4
2 PM0-20Clear0 / 010E/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 Aug 03 - Tue Aug 04 19:07 20:17 4:40 5:49 21:40 N/A 78 0 27.5 1 53
Tue Aug 04 - Wed Aug 05 19:06 20:16 4:40 5:50 22:26 N/A 68 1 23.1 6 18
Wed Aug 05 - Thu Aug 06 19:06 20:15 4:41 5:50 23:13 N/A 57 2 18.4 10 14
Thu Aug 06 - Fri Aug 07 19:05 20:15 4:41 5:50 0:00 N/A 46 3 13.5 13 28
Fri Aug 07 - Sat Aug 08 19:05 20:14 4:42 5:51 0:49 N/A 35 4 08.6 15 51
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 4 August 2015.
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