Current Conditions
Temp6.0 C
RH49 %
WindSW 0 mph
RoadOpen (4x4 only)
Mauna Kea Observatories Forecast
5 PM HST Thursday 27 August (0300 UTC Friday 28 August) 2015
High humidity
Cloud Cover and Fog/Precipitation Forecast
There is a small risk for fog as humidity lingers in the 50-70% range through the night. There is a possibility for linger patches of mid-level clouds for this evening and high clouds may begin to develop along the northwestern skies during the second half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this evening and 3 C tomorrow morning. Winds will be light and from the north, with seeing around 0.4 arcseconds. Precipitable water is expected to exceed 4 mm through the night.
Although the air mass will continue to stabilize as the inversion rebuilds near 6-7 thousand feet over the next 24 hours, persistent mid-level moisture will allow humidity to linger in the 50-70% range probably through Saturday evening. Consequently, there is a small risk for periods of fog, particularly during the evening hours over the next 3 nights. Tropical moisture and instability are expected to build in from the ESE beginning early Sunday morning, and may help breakdown the inversion and signicantly increase the risk for extensive fog, rain and convection for Sunday and Monday night. Some afternoon clouds are likely over the next few days, then will likely turn extensive for Sunday and early part of next week. Isolated afternoon convection along the slopes are also possible mainly for today.

There is a possibility for linger patches of mid-level clouds (from afternoon clouds) for this evening and high clouds may begin to develop along the northwestern skies during the second half of the night and into tomorrow evening. The latter set is expected to breakdown through Friday night, leaving predominately clear skies for most of Saturday. However, there is a possibility that bands of clouds may begin to fill in from the ESE early Sunday morning, with thicker more widespread clouds following suit for later that night and early part of next week.

Precipitable water is expected to exceed 4 mm throughout the forecast period.

Light winds will prevail at and above the summit, which should allow for good/excellent seeing likely through Saturday evening. However, there is a possibility that building turbulence in the atmosphere will start to degrade seeing early Sunday morning and contribute to bad seeing for the following 2 nights.

Little change since the morning forecast...Although the low-level ridge will continue to strengthen to the north and instill some degree of subsidence in the area over the next 48 hours, weak mid-level flow will allow moisture to persist in the area and keep humidity and PW near 50-70% and 4-6 mm, respectively, over the next 2-3 nights. Consequently, it wouldn't take much low-level forcing to push additional moisture up to the summit and help develop short-lived fog at the summit during this time. Fortunately, the bulk of that forcing would be most likely to come from daytime heating (as relatively weak trades prevail), which should help limit the risk for fog and certainly precipitation at the summit at night. Furthermore, the inversion is slated to strengthen signficantly after tonight, further diminishing the odds on organized moisture at the summit for Friday night and likely most of Saturday night. Beyond that, conditions near the Big Island hinges on Hurricane Ignacio. The last 6-7 model runs has been consistently expecting Ignacio to pass over or just the north of the Big Island (as a hurricane and dangerously close) around Monday; rainbands out ahead of the storm are expected to reach the area as early as sunrise Sunday and sticking around into the middle part of next week. While it should come to no surprise that there is a lot of uncertainty with respect to the track and intensity of this storm and especially its impact to lower elevation areas, the copious amount of widespread deep tropical moisture surrounding the storm is a bit more certain/consistent and very likely to negatively impact summit conditions for Sunday and Monday night. Thus, there is a very good chance that another round of extensive fog, clouds and rain will plague the summit (as well as deep/widespread convection in the area) for those nights.
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)
Thu Aug 27 - 8 PM10-304.5-525 / 104NNE/0-100.4-0.54-8
Fri Aug 28 - 2 AM10-309-1020 / 53N/0-100.35-0.454-8
2 PM20-409-1040 / 108.5N/0-10NaN4-8
8 PM10-309-1020 / 54N/0-100.35-0.454-6
Sat Aug 29 - 2 AM0-20Clear15 / 53N/0-100.35-0.454-6
2 PM20-404-4.540 / 108.5NE/0-10NaN4-8
8 PM0-20Clear20 / 53.5NE/5-150.4-0.54-8
Sun Aug 30 - 2 AM20-406-840 / 103NE/10-200.5-0.84-8
2 PM60-804-875 / 605.5NNE/20-35NaN8-12
Mon Aug 31 - 2 AM80-1004-1090 / 802NE/35-501-212-16
2 PM80-1004-1095 / 904N/40-60NaN15-20
Tue Sep 01 - 2 AM80-1004-1090 / 801W/30-401-215-20
2 PM80-1004-1090 / 756SW/20-35NaN10-15
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
Thu Aug 27 - Fri Aug 28 18:50 19:57 4:50 5:56 17:01 5:08 97 21 07.5 -13 04
Fri Aug 28 - Sat Aug 29 18:49 19:56 4:51 5:57 17:52 6:11 100 22 07.3 -9 13
Sat Aug 29 - Sun Aug 30 18:49 19:55 4:51 5:57 18:42 N/A 99 23 06.5 -4 44
Sun Aug 30 - Mon Aug 31 18:48 19:54 4:51 5:57 19:31 N/A 96 0 05.1 0 02
Mon Aug 31 - Tue Sep 01 18:47 19:53 4:52 5:57 20:19 N/A 90 1 03.1 4 43
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 28 August 2015.
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