Current Conditions
Temp12.2 C
RH31 %
WindN 9 mph
RoadOpen
Mauna Kea Observatories Forecast
8 AM HST (1800 UTC) Wednesday 19 June 2013
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but high clouds will continue to stream along SE skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 10 C this afternoon, 4.5 C this evening and 4 C tomorrow morning. Winds will be light and from the SE, with seeing around 0.55-0.6 arcseconds. Precipitable water is expected to linger near 4 mm for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 6-8 thousand feet and keep the mid/summit-level air mass dry and stable through the next 5 nights. Daytime clouds will be fairly minimal and short-lived throughout the forecast period.

High clouds will continue to stream just southeast of the summit for tonight, then will likely drift overhead for Thursday and especially Friday night. This could result in extensive cloud cover or even overcast skies during the latter two nights, but this band will start to breakdown and progress further northward, which should help open up skies a bit for Saturday night and especially Sunday night.

Precipitable water will continue to linger near or exceed 4 mm probably throughout the forecast period.

Increasing turbulence in the free atmosphere will likely contribute to average to slightly poorer than average seeing for the next 3 nights. Seeing is slated to improve toward 0.4-0.5 arcseconds as this turbulence subsides and strong/deep subsidence fills into the area for Saturday and especially Sunday night.

The mid/low-level ridge will continue to sit the north of the state, which will help promote steady/strong large-scale subsidence in the area, maintain a well-defined tradewind inversion near 6-8 thousand feet and ensure the summit-level air mass remains dry and stable throughout the forecast period. Unfortunately, the sub-tropical jet will continue to build in overhead during the next 12 hours, then linger before departing toward the NW late in the weekend. The STJ will increase turbulence in the free atmosphere, which will likely contribute to fairly average-like seeing over the next 3 nights. It will also bring more banding high clouds to the area, probably resulting in extensive cloud cover or even overcast skies during this time. Cloud cover and seeing are expected to improve as the STJ slips northwestward in response to a deep upper-level ridge filling in from the SE beginning late Saturday night and over the following 2-3 days.
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)
Wed Jun 19 - 2 PM40-608-90 / 010SSE/0-10NaN4-6
8 PM40-608-90 / 04.5SE/0-100.5-0.63.5-4.5
Thu Jun 20 - 2 AM60-808-90 / 04SE/0-100.55-0.653.5-4.5
2 PM70-908-100 / 09ENE/0-10NaN4-6
8 PM70-908-100 / 03.5NE/0-100.55-0.653.5-4.5
Fri Jun 21 - 2 AM80-1008-100 / 04E/0-100.5-0.63.5-4.5
2 PM80-1008-100 / 09ESE/0-10NaN4-6
8 PM80-1007-100 / 04ESE/5-150.55-0.653.5-4.5
Sat Jun 22 - 2 AM80-1006-100 / 04SE/5-150.6-0.74-6
2 PM70-905-100 / 09E/5-15NaN4-8
Sun Jun 23 - 2 AM50-706-90 / 04E/5-150.4-0.64-6
2 PM30-507-90 / 010ENE/5-15NaN4-6
Mon Jun 24 - 2 AM10-307-80 / 05NE/5-150.3-0.53.5-4.5
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
Wed Jun 19 - Thu Jun 20 19:13 20:27 4:20 5:34 N/A 3:12 86 14 52.5 -17 13
Thu Jun 20 - Fri Jun 21 19:13 20:27 4:20 5:34 N/A 4:09 93 15 54.5 -19 39
Fri Jun 21 - Sat Jun 22 19:14 20:28 4:20 5:34 17:24 5:10 98 16 59.4 -20 48
Sat Jun 22 - Sun Jun 23 19:14 20:28 4:20 5:35 18:27 6:15 100 18 05.4 -20 26
Sun Jun 23 - Mon Jun 24 19:14 20:28 4:21 5:35 19:28 N/A 98 19 10.5 -18 36
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 19 June (0300 UTC Thursday 20 June) 2013.
Additional Information
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This message is also available at the MKWC road conditions page.
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