Current Conditions
Temp2.4 C
RH15 %
WindSSW 17 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Tuesday 19 September (0300 UTC Wednesday 20 September) 2017
Warning(s)
Chance for fog/high humidity and light rain
Cloud Cover and Fog/Precipitation Forecast
There is a high risk for fog and high humidity throughout the night; light precipitation is also possible mainly toward the end of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C this evening and 1.5 C tomorrow morning. Winds will be from the ESE at 10-20 mph for the first half of the night, decreasing to 5-15 mph by the end of the night. Seeing will be near 0.65-0.7 arcseconds, while precipitable water is expected to be in the 2-3 mm range for this evening and 2.5-3.5 mm range for the morning hours.
Discussion
The tradewind inversion will remain weak/elevated near 12-13 thousand feet, which may allow for periods of extensive fog, high humidity and perhaps light rain through early tomorrow evening. The inversion is set to recover near 7 thousand feet by late tomorrow evening and remain quite strong thereafter, ensuring the summit steers free of moisture for the remainder of the forecast period. Extensive daytime clouds are possible for tomorrow, but will become minimal and short-lived for the remainder of the week.

Skies overhead will remain predominately clear through early Thursday evening, but there is a possibility for patches of summit-level clouds through early Wednesday evening. Banding high clouds are also expected to set up along the southern Thursday night. This band is set to break up a bit on Friday, but also creep northward, scraping the tip of the Big Island for that night and the early part of Saturday night, then will quickly retreat southward thereafter.

Precipitable water is expected to increase toward 3 mm for tonight, trend back toward 1 mm over the course of tomorrow night, settle in near that value for Thursday and Friday night, then bump back up toward 1.5-2 mm for Saturday night.

Lingering boundary layer turbulence as well as an increase in upper-level turbulence will likely contribute to slightly poorer than average seeing for tonight. The latter is expected to persist and limit much improvement in seeing for the following 4 nights, and may even strengthen further over the weekend.

Little change since the morning forecast...A mid-level low meandering to the south of the Big Island will continue to bring mid/low-level tropical moisture into the area over the next 24 hours. This will help keep the inversion weak/elevated near 13 thousand feet and further increase the risk for extensive fog, high humidity, light rain and perhaps patches of mid/summit-level clouds for much of tonight and perhaps into early tomorrow evening. Fortunately, the mid-level low is expected to dissipate and push off toward the west as the tropical upper-tropospheric trough (TUTT) builds back over the state and an embedded rather deep low forms to the NE during the latter night. This new low and the TUTT are not expected to affect the stability of the atmosphere during its rather prolong tenure over the next week or so. Actually the placement of the low (relatively to the state) could enhance subsidence in the area and together with the ridge to the NE, are expected to rebuild the inversion near 7 thousand feet and ensure a dry/stable air mass during this time. However, the low/TUTT will also allow for the redevelopment of the sub-tropical jet (STJ) over the Big Island, which could bringing banding high clouds along the southern skies and upper-level turbulence to the area during much of this time. The latter will limit much improvement in seeing once the boundary layer turbulence subsides after this evening.
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)
Tue Sep 19 - 8 PM0-204-4.575 / 402.5ESE/10-200.5-0.92-3
Wed Sep 20 - 2 AM20-404-590 / 601.5E/5-150.5-0.82.5-3.5
2 PM60-804-675 / 256.5NNE/5-15NaN3-6
8 PM0-20Clear25 / 52NNE/5-150.5-0.71.5-2
Thu Sep 21 - 2 AM0-20Clear5 / 01.5NNE/5-150.5-0.71-1.5
2 PM0-20Clear0 / 07.5NW/5-15NaN1-2
8 PM10-309.5-100 / 02.5NNW/5-150.5-0.70.8-1.2
Fri Sep 22 - 2 AM20-409.5-100 / 02.5NW/5-150.5-0.70.9-1.3
2 PM20-409-100 / 08NW/10-20NaN1-2
Sat Sep 23 - 2 AM40-609-100 / 03NW/10-200.5-0.81.25-1.75
2 PM30-509-100 / 08NW/10-20NaN1.5-2.5
Sun Sep 24 - 2 AM0-20Clear0 / 02.5NW/10-200.5-0.81.25-1.75
2 PM0-20Clear0 / 06.5N/10-20NaN1.5-2.5
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
Tue Sep 19 - Wed Sep 20 18:29 19:34 4:57 6:02 6:30 18:32 0 12 04.2 2 28
Wed Sep 20 - Thu Sep 21 18:28 19:33 4:57 6:02 N/A 19:13 2 12 53.2 -1 50
Thu Sep 21 - Fri Sep 22 18:27 19:32 4:58 6:02 N/A 19:52 5 13 41.2 -5 59
Fri Sep 22 - Sat Sep 23 18:26 19:31 4:58 6:02 N/A 20:32 10 14 28.9 -9 48
Sat Sep 23 - Sun Sep 24 18:26 19:30 4:58 6:02 N/A 21:13 17 15 16.6 -13 10
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 20 September 2017.
Additional Information
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