Current Conditions
Temp1.1 C
RH72 %
WindENE 17 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Monday 16 July (0300 UTC Tuesday 17 July) 2018
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while scattered thin high clouds pass over or just north the summit 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 ENE at 15-25 mph, with seeing near 0.7 arcseconds. Precipitable water is expected to exceed 4 mm through the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 6-7 thousand feet and ensure the summit remains dry and stable for tonight. There is a possibility that the inversion will briefly lift toward 13-14 thousand feet, which will increase the risk for fog, high humidity and light rain at the summit for tomorrow night. The inversion is set to quickly recover near 6-7 thousand feet, allowing dry/stable conditions to return to the summit for the remainder of the forecast period. Daytime clouds could pick up a tad over the next 2 days, then taper again for the remainder of the week.

Scattered thin high clouds will continue to pass over and especially along the northern skies through the next 3 nights. There is a good chance that more organized/thicker widespread clouds will fill in from the SW beginning late Thursday morning, contributing to periods of extensive cloud cover for that night and Friday night.

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

Despite relatively calm skies in the free atmosphere, light/moderate boundary layer turbulence will likely contribute to poorer than average seeing for over the next 2 nights. There is also a possibility that an influx of moisture will further degrade seeing for Tuesday night. Although there is a chance for an increase in free atmospheric turbulence, lighter summit-level winds and a drier air mass should allow seeing to improve and settle in near 0.5-0.6 arcseconds for the following 3 nights.

No change since the morning forecast...The mid/low-level ridge will continue to sit to the north/northeast of the state while a rather broad but weak tropical upper-tropospheric trough (TUTT) and its associated sub-tropical jet (STJ) persists to the NW probably through the week. The ridge will promote steady/strong large-scale subsidence in the area, which will help maintain the tradewind inversion primarily near 7 thousand feet and ensure a dry/stable summit-level air mass throughout most of the forecast period. The only exception could be as a developing weak tropical system passes to the south of the Big Island, bring focused moisture and/or instability to the area mainly for the second half of Tuesday night. This could increase the risk for periods of fog, high humidity and light rain at the summit during that time. An uptick of the wind ahead of and during the passage of this system may stir up boundary layer turbulence and contribute to poor seeing over the next 2 nights (the influx of moisture may also further degrade seeing for tomorrow night). Fortunately, the presence of the TUTT and STJ will limit the development/strengthening of this system as the latter strengthens and broadens southward around the middle of the week. The low-level trades will also help usher the system westward, drying the low-level air mass by Wednesday afternoon and ensure the summit steers free of fog/precipitation into the weekend. The strengthening of the jet may increase turbulence in the free atmosphere a tad, but not enough to deterimentally impact seeing for the latter half 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)
Mon Jul 16 - 8 PM10-308-90 / 03.5ENE/15-250.55-0.854-6
Tue Jul 17 - 2 AM0-208-90 / 03ENE/15-250.55-0.854-6
2 PM0-209.5-1015 / 59ENE/15-25NaN4-8
8 PM10-309.5-1040 / 104ENE/15-250.6-14-6
Wed Jul 18 - 2 AM20-409-1060 / 153.5E/15-250.7-1.34-6
2 PM10-308-920 / 58ESE/5-15NaN4-8
8 PM0-209.5-100 / 02.5ENE/5-150.5-0.73.5-4.5
Thu Jul 19 - 2 AM0-209.5-100 / 02ENE/5-150.45-0.653.5-4.5
2 PM20-406-80 / 07.5NE/5-15NaN4-6
Fri Jul 20 - 2 AM60-806-100 / 02.5NNE/5-150.45-0.654-6
2 PM60-806-100 / 08.5NE/5-15NaN4-6
Sat Jul 21 - 2 AM70-906-100 / 03.5NNE/5-150.45-0.654-6
2 PM60-806-90 / 08.5ENE/5-15NaN4-8
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 Jul 16 - Tue Jul 17 19:14 20:26 4:30 5:43 N/A 22:41 24 11 42.1 5 31
Tue Jul 17 - Wed Jul 18 19:13 20:26 4:31 5:43 N/A 23:24 34 12 34.0 0 43
Wed Jul 18 - Thu Jul 19 19:13 20:25 4:31 5:43 N/A 0:04 45 13 24.2 -4 00
Thu Jul 19 - Fri Jul 20 19:13 20:25 4:32 5:44 N/A 0:44 56 14 13.5 -8 27
Fri Jul 20 - Sat Jul 21 19:13 20:24 4:32 5:44 N/A 1:25 66 15 02.6 -12 26
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 17 July 2018.
Additional Information
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