Current Conditions
Temp11.3 C
RH28 %
WindNNE 1 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 21 September (0300 UTC Saturday 22 September) 2018
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while scattered high clouds drift in from the west, particularly as the night progresses.
Summary of Key Meteorological Variables
Summit temperatures will be neaer 8.5 C this afternoon and 3.5 C for the night. Winds will be from the east at 10-20 mph, with seeing near 0.45-0.5 arseconds. Precipitable water is expected to linger near 4 mm for the night.
Discussion
The tradewind inversion will continue to restrengthen near 5-6 thousand feet over the next 12 hours, and ensure the summit remains dry and stable for at least the next 3 nights. There is a possiblity that the inversion will begin to breakdown as instability and modest moisture fills into the area, increasing the risk for high humidity and perhaps short-lived fog at the summit for Monday and Tuesday night; precipitation is unlikely. Daytime clouds will become minimal and short-lived over the weekend, only to pick up again for the early part of next week. There is also an outside chance for isolated afternoon convection along the western slopes for Monday and especially Tuesday/Wednesday.

Scattered to broken high clouds are set to spread in from the west as the night progresses, then break up a bit for the early part of Saturday night, then reorganize along the western skies on Sunday, and slowly creep toward the summit through that night. The bulk of these clouds will stop short of covering the Big Island, but there is still a possiblity that stray high clouds will pass overhead and contribute to brief periods of extensive cloud cover mainly for Monday and Tuesday night.

Precipitable water is expected to linger near 4 mm for the next 2 nights, briefly slip toward 2-3 mm for Sunday night, then jump back to 4+ mm for the early part of next week.

Light relatively uniform winds at and above the summit, combined with deep subsidence in the free atmosphere, should allow seeing to settle in near 0.45-0.5 arcseconds over the next 3 nights. AN influx of instability, moisture and minor mid/upper-level turbulence could degrade seeing toward more poor-like values for Monday and Tuesday night.

No change since the morning forecast...A tight upper-level ridge settling in overhead, combined with a mid and low-level ridge to the east and NE, respectively, will continue to promote strong/steady large-scale subsidence in the area through at least the weekend. This subsidence will easily maintain a well-defined inversion near 6 thousand feet and ensure a dry/stable summit-level air mass during this time. Unfortunately, residual mid/upper-level moisture caught up within the ridge will likely keep PW near 4 mm, while a developing mid/upper-level trough to the west periodically sends waves of high clouds into the area during most of this period. Seeing, on the other hand, will benefit from the extra subsidence and calm skies within the upper-level ridge, likely settling in near 0.45-0.5 arcseconds over the next 3 nights. Global models still suggest that the aforementioned trough will creep eastward, bring weak/widespread instability and perhaps moisture into the area beginning late Monday morning. While the bulk of the moisture/instability will remain over the western half of the state, it could still weaken the inversion near the Big Island and raise summit-level humidity toward 60-80% and increase the risk for fog/rain at the summit and afternoon convection, particularly along the interior and western slopes of the Big island for early to middle part of next week.
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 Sep 21 - 8 PM20-409-100 / 03.5E/10-200.4-0.63.5-4.5
Sat Sep 22 - 2 AM40-608-100 / 03.5E/10-200.35-0.553.5-4.5
2 PM50-708-100 / 09.5SE/5-15NaN4-6
8 PM30-509-100 / 04.5SSE/5-150.35-0.553.5-4.5
Sun Sep 23 - 2 AM10-309.5-100 / 04SSE/5-150.35-0.553.5-4.5
2 PM0-20Clear0 / 09S/5-15NaN3-5
8 PM0-20Clear0 / 04S/5-150.35-0.552.5-3.5
Mon Sep 24 - 2 AM0-20Clear0 / 03.5SSW/10-200.4-0.62-3
2 PM60-804-860 / 208SSW/10-20NaN3-6
Tue Sep 25 - 2 AM50-706-1050 / 103SW/10-200.5-0.94-8
2 PM70-904-1075 / 306SSW/10-20NaN8-12
Wed Sep 26 - 2 AM60-806-1060 / 152.5S/10-200.7-1.16-10
2 PM70-904-965 / 257ESE/10-20NaN6-10
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 Sep 23 - Mon Sep 24 18:26 19:30 4:58 6:02 17:41 6:02 99 23 41.0 -6 37
Mon Sep 24 - Tue Sep 25 18:25 19:29 4:58 6:03 18:19 6:53 100 0 28.7 -2 10
Tue Sep 25 - Wed Sep 26 18:24 19:28 4:59 6:03 18:57 N/A 98 1 16.9 2 27
Wed Sep 26 - Thu Sep 27 18:23 19:27 4:59 6:03 19:36 N/A 94 2 06.3 7 01
Thu Sep 27 - Fri Sep 28 18:22 19:26 4:59 6:03 20:17 N/A 88 2 57.4 11 18
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 24 September 2018.
Additional Information
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