Current Conditions
Temp2.3 C
RH24 %
WindNE 16 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Tuesday 21 August (0300 UTC Wednesday 22 August) 2018
Warning(s)
Chance for fog/rain
Cloud Cover and Fog/Precipitation Forecast
There is a risk for fog, high humidity and light rain mainly toward the end of the night. Mostly patches of thin high clouds will brush the Big Island for the start of the night, but broken clouds thicker clouds may begin to drift in from the SE toward the end of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2.5, with winds from the ENE at 10-20 mph and seeing near 0.6-0.7 arcseconds. Precipitable water is expected to be in the 2.5-3.5 mm range for the first half of the night and 3-4 mm range for the second half.
Discussion
The tradewind inversion will remain fairly well-established near 6-7 thousand feet through early this evening, then will begin to rapidly breakdown as moisture and instability builds into the area and raises the stakes on fog, high humidity and light rain as the night progresses. The inversion will eventually fall apart by midday tomorrow, and allow the atmosphere to become saturated and unstable, almost certainly ensuring extensive fog, rain and perhaps ice plagues the summit probably for the remainder of the week. There is also a high probability for convection in the area and heavy rain at the summit at virtually any time during this period, but particularly Thursday night. Daytime clouds will be minimal and short-lived for today, but will turn extensive for the remainder of the week.

Patches of thin cirrus will continue to brush the Big Island from the SE through this evening, then more broken thicker clouds may begin to drift in from the SE through the second half of the night. More widespread thick clouds and convection will eventually fill into the area, blanketing skies for Wednesday, Thursday and probably most of Friday night. While there is a chance that these clouds will begin to break up through the latter night, residual patches thick clouds will linger in the area, contributing to extensive cloud cover probably through the weekend.

Precipitable water is expected to settle in near 3 mm for most of the night, but could trend toward 4 mm by sunrise and likely exceed 12 mm for the following 4 nights.

While seeing will start out near average-like values for this evening, an increase in free atmospheric turbulence may start an degradation trend as the night progresses. A copious supply of moisture/instability and turbulence throughout various layers in the atmosphere will contribute to bad seeing for the following 4 nights.

Little change since the morning forecast...The mid/low-level ridge to the NE is set to gradually weaken and shift subtly off toward the east, allowing Hurricane Lane to drift northward over the next 24-48 hours. Initially, subsidence associated with the ridge will maintain a fairly well-defined inversion near 6-7 thousand feet into early this evening. However, outer rainbands associated with Lane will start to fill in from the SE as the night progresses. These rainbands may begin to erode the inversion and thus increase the risk for fog and light rain at the summit more towards the end of the night. Various Models (and embedded runs) disagree with the expected track and intensity of Lane, which is fairly normal. Currently, Lane is scheduled to scrape the western portion of the Big Island between Wednesday and Friday, but will also weaken as it encounters increasing shear associated with the sub-tropical jet to the north of the state. It will then rapidly breakdown over/near the state, leaving lots of residual moisture and instability in the area probably into the early part of next week. Nevertheless, a copious supply of widespread moisture surrounding Lane will eventually dismantle the inversion through tomorrow and allow the atmosphere to turn saturated and unstable probably for the remainder of the week. This will almost certainly result in inoperable conditions as overcast skies, extensive fog, heavy rains and occasionally ice plagues the summit after tonight. There is also a high probability for deep convection in the area and strong winds at the summit as Lane brushes the Big Island between late Thursday morning and Friday afternoon (there is a chance that gusts will approach 100 mph early Friday morning). Any convection thereafter should be more isolated in nature and favor the afternoon or sunrise hours.
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 Aug 21 - 8 PM20-409-1010 / 02.5E/10-200.5-0.72.5-3.5
Wed Aug 22 - 2 AM40-608-1060 / 202.5E/10-200.6-0.83-4
2 PM80-1004-1095 / 854E/15-30NaN10-15
8 PM80-1004-10100 / 901ESE/20-351-215-20
Thu Aug 23 - 2 AM80-1004-10100 / 950.5SE/30-451-215-20
2 PM80-1004-10100 / 952SSE/40-60NaN15-20
8 PM80-1004-10100 / 95-1SSE/60-801-315-20
Fri Aug 24 - 2 AM80-1004-10100 / 950SSW/60-801-315-20
2 PM80-1004-10100 / 902SW/40-60NaN15-20
Sat Aug 25 - 2 AM70-904-995 / 850WSW/25-401-215-20
2 PM80-1004-1095 / 903WNW/15-30NaN15-20
Sun Aug 26 - 2 AM70-904-995 / 901N/5-151-215-20
2 PM80-1004-1090 / 853.5E/10-20NaN12-16
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 Aug 21 - Wed Aug 22 18:55 20:02 4:48 5:55 N/A 3:07 85 19 01.1 -21 15
Wed Aug 22 - Thu Aug 23 18:54 20:01 4:48 5:55 N/A 3:56 91 19 52.1 -20 33
Thu Aug 23 - Fri Aug 24 18:53 20:00 4:49 5:56 17:01 4:46 96 20 42.5 -18 56
Fri Aug 24 - Sat Aug 25 18:52 19:59 4:49 5:56 17:44 5:36 99 21 32.1 -16 30
Sat Aug 25 - Sun Aug 26 18:52 19:58 4:50 5:56 18:25 6:27 100 22 20.7 -13 21
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 22 August 2018.
Additional Information
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