Current Conditions
Temp-3.5 C
RH8 %
WindSW 21 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 24 February (0300 UTC Saturday 25 February) 2017
Warning(s)
Chance for fog/ice and flurries late in the weekend
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but broken mid/upper-level clouds will continue to develop in the area and/or fill in from the NW and SW, contributing to extensive cloud cover for the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this afternoon and -4 C for the night. Winds will be from the west at 10-20 mph for today, increasing to 15-30 mph for the night. Seeing will be near 0.8-0.9 arcseconds, while precipitable water is expected to be in the 3-4 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 6-7 thousand feet and ensure the summit remains dry and stable through at least Saturday afternoon. Deep moisture is set to build into the area through the remainder of the weekend, which could help erode the inversion and saturate the bulk of the air mass for Sunday night and the early part of next week. This will significantly raise the stakes on fog, high humidity, ice and flurries at the summit after tonight (and particularly after sunrise Sunday). Periods of heavy snow at the summit and convection in the area are also possible mainly between early Sunday evening and midnight Tuesday. Daytime clouds will be minimal and short-lived through tomorrow, but could turn extensive for the remainder of the forecast period.

Broken mid/upper-level clouds will continue to fill in from the NW and SW and also begin to develop in the area, contributing to extensive cloud cover for tonight and probably overcast skies for the following 4 nights.

Precipitable water is expected to increase toward 3-4 mm for the next 2 nights, then jump toward 8-10 mm for the following 3 nights.

A combination of strong upper-level turbulence, boundary layer turbulence and/or instability will likely contribute to poor/bad seeing for the next 5 nights.

Little change since the morning forecast...Despite the absence of the mid-level ridge, subsidence associated with the low-level ridge to the north will help maintain a fairly well-defined tradewind inversion and ensure a dry/stable summit-level air mass for at least another 18 hours. However, a large digging in from the NW will reinforce a couple of lows to the north of the state and drag deep moisture/clouds up from the tropics over the weekend. While the bulk of the instability associated with the low will remain far off toward the north, the moisture/clouds moving into the area will contribute to overcast skies, particularly after tonight, and could saturate the bulk of the atmosphere as early as Sunday morning. More widespread deep moisture will follow suit thereafter, which will significantly raise the stakes on extensive fog/ice and flurries at the summit for Sunday night and early part of next week. In addition, there is a possibility that short-wave trough (SWT) slowly passing through will destabilize the atmosphere, which could allow for the development of convection in the area and periods of moderate/heavy snow at the summit mainly for Sunday and Monday night. The moisture/clouds and instability are set to shift off toward the NE with the SWT, which should help to open up skies and allow dry and stable conditions to return to the summit around Wednesday afternoon/evening. However, there is a good chance for another round of strong boundary layer turbulence as winds pick up again on Wednesday.
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 Feb 24 - 8 PM60-807.5-100 / 0-4W/10-200.6-13-4
Sat Feb 25 - 2 AM70-907-100 / 0-4W/15-300.6-1.13-4
2 PM80-1006-1010 / 02WSW/20-35NaN3-5
8 PM80-1006-1025 / 0-3WSW/20-350.8-1.23.5-4.5
Sun Feb 26 - 2 AM80-1006-1040 / 10-3WSW/15-300.7-1.33.5-4.5
2 PM80-1004-1075 / 40-1W/15-30NaN4-8
8 PM80-1004-1090 / 60-4.5W/15-300.8-1.68-12
Mon Feb 27 - 2 AM80-1004-1095 / 75-4.5W/15-300.8-1.68-12
2 PM80-1004-1095 / 80-2NW/5-15NaN8-12
Tue Feb 28 - 2 AM80-1004-1095 / 80-5NW/5-150.8-1.88-12
2 PM80-1004-1095 / 75-1SSW/5-15NaN8-12
Wed Mar 01 - 2 AM80-1004-980 / 60-4SW/20-350.8-1.68-12
2 PM0-204-760 / 20-1WSW/35-50NaN4-8
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
Fri Feb 24 - Sat Feb 25 18:34 19:39 5:31 6:35 5:58 17:10 2 21 36.5 -13 17
Sat Feb 25 - Sun Feb 26 18:35 19:39 5:30 6:34 6:43 18:06 0 22 28.7 -9 52
Sun Feb 26 - Mon Feb 27 18:35 19:40 5:29 6:34 7:27 19:03 1 23 20.9 -5 53
Mon Feb 27 - Tue Feb 28 18:35 19:40 5:29 6:33 N/A 20:01 4 0 13.3 -1 31
Tue Feb 28 - Wed Mar 01 18:36 19:40 5:28 6:32 N/A 20:59 9 1 06.2 2 59
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 27 February 2017.
Additional Information
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This message is also available at the MKWC road conditions page.
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