Current Conditions
Temp7.4 C
RH61 %
WindNE 15 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 20 July (0300 UTC Saturday 21 July) 2018
Warning(s)
Chance for moisture Sunday night.
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while broken mid/upper-level clouds fill in from the SW and contribute to extensive cloud cover through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this evening and 4.5 C tomorrow morning. Winds will be light and from the NE, with seeing near 0.5-0.6 arcseconds. Precipitable water is expected to linger near 4 mm for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 7 thousand feet and ensure the summit remains dry and stable through at least Sunday afternoon. There is a possibility that an influx of moisture and minor instability will erode the inversion and increase the risk for periods of fog, high humidity and perhaps light rain at the summit between Sunday evening and late Tuesday night. Daytime clouds will be minimal and short-lived through Sunday, but could turn extensive for the early part of next week.

Broken mid/upper-level clouds will continue to fill out of the SW and contribute to extensive cloud cover for tonight and perhaps periods of overcast skies for tomorrow night. There is a good chance that these clouds will begin to breakup and shift northward on Sunday, but mid/summit-level clouds may fill in from the east for that night and Monday night. While more more high clouds drift in from the west for the early part of next week.

Precipitable water is expected to linger near or exceed 4 mm through the next 5 nights.

Relatively calm skies, with light/moderate shear/turbulence in the free atmosphere should allow for better than average seeing over the next 2 nights. However, there is a possibility for times of variability, particularly if/when die off completely for prolong periods during these nights. An increase in low-level moisture and perhaps mid-level turbulence may contribute to some degradation or even poor seeing for Sunday night and the early part of next week.

No change since the morning forecast...The low-level ridge will continue to sit to the north of the state, while an upper-level ridge and tropical upper-tropospheric trough (TUTT) persists to the SSE and NW, respectively well into next week. Nonetheless, the ridge will promote steady large-scale subsidence in the area, which will help maintain a well-defined inversion near 7 thousand feet and ensure the summit remains dry and stable through at least Sunday afternoon. A remnant tropical wave/moisture is set to move in with the low-level trades and move through the area between early Sunday evening and Tuesday night. This moisture, combined weak instability associated with the TUTT (as well as the tropical wave) could help erode the inversion and increase the risk for fog, high humidity and light rain at the summit during that time. Last 2 model runs have taken a more aggressively wet outlook with this wave, suggesting that the atmosphere will periodically turn saturated for much of Monday and into Tuesday. I suspect this is a little overdone, but it is likely that poor/wet conditions will prevail late in the weekend and for the early part of next week. In the meantime, the tropical upper-tropospheric trough and its associated sub-tropical jet is expected to gain access to more organized/thicker high clouds filling out of the tropics over the next 6-12 hours. These clouds will stream over the summit area, contributing to extensive cloud cover if not overcast skies probably throughout most of the forecast period.
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)
Fri Jul 20 - 8 PM60-809-100 / 04ENE/5-150.45-0.653.5-4.5
Sat Jul 21 - 2 AM70-907-100 / 04.5ENE/0-100.4-0.73.5-4.5
2 PM80-1006-100 / 09.5NE/0-10NaN4-6
8 PM80-1006.5-100 / 04.5ENE/0-100.4-0.63.5-4.5
Sun Jul 22 - 2 AM80-1006.5-100 / 04E/0-100.4-0.74-6
2 PM60-806-90 / 08.5N/0-10NaN4-8
8 PM50-704-825 / 103NE/5-150.5-0.86-10
Mon Jul 23 - 2 AM60-804-875 / 252.5NE/0-100.7-1.16-10
2 PM80-1004-1090 / 605ESE/0-10NaN8-12
Tue Jul 24 - 2 AM50-704-1080 / 552E/0-100.7-1.36-10
2 PM70-904-1075 / 405.5W/0-10NaN8-12
Wed Jul 25 - 2 AM50-704-1060 / 202.5WNW/0-100.5-1.16-10
2 PM60-804-960 / 306NE/5-15NaN6-10
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
Sun Jul 22 - Mon Jul 23 19:12 20:24 4:33 5:45 N/A 2:49 83 16 42.3 -18 29
Mon Jul 23 - Tue Jul 24 19:12 20:23 4:34 5:45 N/A 3:35 89 17 33.1 -20 19
Tue Jul 24 - Wed Jul 25 19:11 20:23 4:35 5:46 N/A 4:22 95 18 24.5 -21 14
Wed Jul 25 - Thu Jul 26 19:11 20:22 4:35 5:46 17:32 5:10 98 19 15.9 -21 12
Thu Jul 26 - Fri Jul 27 19:11 20:21 4:36 5:46 18:19 6:00 100 20 07.0 -20 14
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 23 July 2018.
Additional Information
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