Current Conditions
Temp8.3 C
RH25 %
WindSE 40 mph
RoadOpen (4x4 only)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Thursday 30 July 2015
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 9 C this afternoon and 4.5 C for the night. Winds will be from the NE at 20-30 mph for today, easing to 15-25 mph for the morning hours. Seeing will be near 0.8-0.9 arcseconds, while precipitable water is expected to be in the 3-4 mm range for the first half of the night and 2.5-3.5 mm range for the second half.
The tradewind inversion will continue to cap low-level moisture near 8 thousand feet and ensure a dry and stable summit-level air mass through at least Saturday morning. There is a chance that a patch of tropical moisture/instability filling in from the east will lift the inversion and increase the risk for periods of fog, high humidity and light rain at the summit for the following 3 nights (particularly Saturday night). Daytime clouds will be minimal and short-lived through at least Friday, but may pick up over the weekend and early part of next week.

Skies overhead will remain predominately clear through at least Friday night. There is a good chance that mid/summit-level clouds and perhaps even isolated convection will start to fill in from the east through Saturday and may contribute to extensive cloud cover for that night. The bulk of these clouds will shift along the southern skies on Sunday, but may still remain an issue into the early part of next week. Another batch of thicker more widespread clouds may follow suit early Tuesday morning.

Precipitable water is expected to dip toward 2.5-3 mm for the next 2 nights, then increase back to 4+ mm for the following 3 nights.

Boundary layer turbulence will contribute to poorer than average seeing for tonight. Decreasing winds should allow seeing to improve toward 0.4-0.45 arcseconds for Friday night, but an influx of low-level turbulence will likely degrade seeing toward more poor/bad values for Saturday and Sunday night. There is a possibility that this turbulence will briefly subside and help improve seeing toware more average-like values for Monday night.

A deep ridge will continue to sit over or just north of the Islands and promote steady/strong large-scale subsidence in the area through at least Friday night. This will help maintain a well-defined tradewind inversion near 7-8 thousand feet and ensure a dry/stable and relatively warm summit-level air mass during this time. Although the upper-portion of the ridge will keep summit-level winds near 20-25 mph and likely stir up boundary layer turbulence for tonight, winds are slated to subside as the mid-level ridge weakens a tad for tomorrow night. This may allow seeing to improve significantly withe deep subsidence prevailing in the area for Friday night. Models still suggest that the remnants of tropical depression 08E will move in from the east beginning early Saturday afternoon. The latest model run expects the bulk of the moisture associated with 08E to track over and especially along the southern half of the Big Island over the following 24 hours. The core of 08E is then slated to track off toward the SW, but leave lots of residual moisture in the area through Monday night. Some of this moisture may eventually retract eastward as the next tropical strom (Guillermo) begins to move into the area and draw in the moisture early Tuesday morning. Nonetheless, there is a very good chance that the inversion will breakdown/lift toward 15-18 thousand feet by early Saturday afternoon and allow for the development of fog at the summit and perhaps convection in the area for the next 3 nights (particularly between Saturday evening and Sunday evening). The odds on extensive/prolong fog and rain at the summit may subside a bit as the moisture tries to detrain into the surrounding area late Sunday night and especially Tuesday night. However, an influx of more widespread moisture and instability associated with Guillermo may produce another round of thick fog and rain at the summit and likely deep convection in the area for the middle part of next week. Still, there is ;ots of uncertainty with regards to the track and intensity of Guillermo at this point in 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)
Thu Jul 30 - 2 PM0-20Clear0 / 09NE/20-30NaN4-6
8 PM0-5Clear0 / 04.5NE/20-300.6-13-4
Fri Jul 31 - 2 AM0-5Clear0 / 04.5NE/15-250.6-0.92.5-3.5
2 PM0-20Clear0 / 011NE/10-20NaN3-5
8 PM0-5Clear0 / 06NE/10-200.4-0.62-3
Sat Aug 01 - 2 AM0-5Clear0 / 05.5NE/10-200.4-0.52-3
2 PM60-804-660 / 2010NNE/5-15NaN4-8
8 PM60-804-675 / 404.5NNE/5-150.6-1.24-8
Sun Aug 02 - 2 AM70-904-690 / 603.5WNW/5-150.7-1.34-8
2 PM80-1004-895 / 757WNW/5-15NaN4-8
Mon Aug 03 - 2 AM30-504-560 / 153W/5-150.6-1.24-6
2 PM60-804-560 / 207.5W/5-15NaN4-8
Tue Aug 04 - 2 AM10-304-550 / 103NW/0-100.45-0.653-5
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
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
Sat Aug 01 - Sun Aug 02 19:08 20:18 4:39 5:49 20:05 N/A 94 22 33.9 -7 20
Sun Aug 02 - Mon Aug 03 19:07 20:17 4:39 5:49 20:53 N/A 87 23 31.2 -2 46
Mon Aug 03 - Tue Aug 04 19:07 20:17 4:40 5:49 21:40 N/A 78 0 27.5 1 53
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Thursday 30 July (0300 UTC Friday 31 July) 2015.
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