Current Conditions
Temp10.2 C
RH64 %
WindNE 7 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Thursday 02 August (0300 UTC Friday 3 August) 2018
Warning(s)
High humidity
Chance for fog/ice
Cloud Cover and Fog/Precipitation Forecast
There is a small/moderate risk for fog, high humidity and short-lived ice through the night; precipitation is unlikely. Scattered mid/upper-level clouds will continue to spread in from the NW throughout the night.
Summary of Key Meteorological Variables
Summit temperatures 0.5 C this evening and 0 C tomorrow morning. Winds will be light and from the north for today, switching to a more SE direction through the night. Seeing will be near 0.75-0.8 arcseconds, while precipitable water is expected to exceed 4 mm through the night.
Discussion
Although the tradewind inversion will remain fairly well-defined near 8-9 thousand feet before restrengthening near 6-7 thousand feet late in the weekend and early part of next week, lingering mid-level moisture will keep humidity near 50-70% and could allow for fog and perhaps short-lived ice over the next 3 nights; precipitation is unlikely. Humidity is expected to slip back toward 10-20% with dry/stable conditions returning to the summit for Sunday and Monday night. Extensive daytime clouds and perhaps isolated afternoon convection are possible through Saturday, then will taper for Sunday and especially early part of next week.

Scattered mid/upper-level clouds will continue to spread in from the NW for tonight, with more broken thich clouds drifting in from the SW and SE and contributing to extensive cloud cover or even periods of overcast skies between late Friday evening and early Sunday morning. The bulk fo these clouds are set to shift eastward through Sunday, leaving predominately clear skies for that night and especially Monday night.

Precipitable water is expected to exceed 4 mm probably into early Sunday evening, but should slip toward 1 mm by mid-day Monday, only to climb back to 2-3 mm for later that night.

Despite relatively calm skies in the free atmosphere, a mixture of moisture and minor instability will contribute to poor/bad seeing over the next 3 nights. A drying of the atmosphere is expected for Sunday, but an increase in boundary layer turbulence may only allow for modest improvement in seeing for that night and may even degrade seeing for Monday night.

No change since the morning forecast...The mid/low-level will continue to promote large-scale subsidence in the area, which will help maintain a relatively well-defined inversion near 7-8 thousand feet through the next 3 nights. Unfortunately, a steady influx of mid/upper-level moisture from the tropical upper-tropospheric trough (TUTT) lingering overhead will keep summit-level humidity near 50-70% and destabilize the air mass a bit into early Sunday morning. An embedded low is also set to move pass to the north, dragging more moisture/clouds in from the SE for Friday and Saturday night. Nonetheless, this moisture and instability may help contribute to periods of fog and ice at the summit, extensive cloud cover, poor seeing and PW near 8-10 mm over the next 3 nights. The risk for moisture at the summit and extensive cloud cover are expected to increase as the low shifts just northwest of the Island for Friday and Saturday night. Conditions and skies are expected to rapidly improve as the TUTT and low quickly retreat westward in response to a deep upper-level ridge building in from the east through Sunday. While this could allow humidity and PW to plummit below 20% and 2 mm, respectively by later that night, the redistribution of upper-level momentum could lead to an increase in boundary layer turbulence, limiting much of an improvement in seeing into next week. Long term GFS projections suggest that Tropical Cyclone Hector may pass through the area around the middle/later part of next week. Its still way to early to anticipate its trajectory, intensity and impact on the state, but there is a resonably high possibility it could bring moisture to the summit around Wednesday through Friday.
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)
Thu Aug 02 - 8 PM20-406-840 / 100.5N/0-200.6-0.96-10
Fri Aug 03 - 2 AM40-606-1040 / 100E/0-200.6-16-10
2 PM70-904-1080 / 404SSE/5-15NaN8-12
8 PM60-806-1060 / 200.5SE/10-200.6-16-10
Sat Aug 04 - 2 AM80-1005-1075 / 251SSE/10-200.7-1.16-10
2 PM80-1004-1090 / 506SE/10-20NaN8-12
8 PM60-805-975 / 252.5ESE/10-200.7-1.18-12
Sun Aug 05 - 2 AM40-605-850 / 102.5ESE/15-250.6-18-12
2 PM20-405-715 / 09E/15-25NaN4-8
Mon Aug 06 - 2 AM0-20Clear0 / 04E/15-250.5-0.82-4
2 PM0-20Clear0 / 010E/15-25NaN1-2
Tue Aug 07 - 2 AM0-5Clear0 / 05.5E/20-350.6-0.92-3
2 PM0-20Clear0 / 010NE/20-35NaN2-4
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
Thu Aug 02 - Fri Aug 03 19:07 20:17 4:39 5:49 22:56 N/A 63 1 42.6 4 26
Fri Aug 03 - Sat Aug 04 19:07 20:16 4:40 5:49 23:36 N/A 53 2 32.1 8 46
Sat Aug 04 - Sun Aug 05 19:06 20:16 4:40 5:50 0:19 N/A 42 3 23.9 12 45
Sun Aug 05 - Mon Aug 06 19:06 20:15 4:41 5:50 1:07 N/A 32 4 18.9 16 08
Mon Aug 06 - Tue Aug 07 19:05 20:14 4:41 5:50 1:59 N/A 21 5 17.0 18 38
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 3 August 2018.
Additional Information
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