Current Conditions
Temp1.3 C
RH75 %
WindWNW 12 mph
RoadClosed
Mauna Kea Observatories Forecast
5 PM HST Friday 22 July (0300 UTC Saturday 23 July) 2016
Warning(s)
Fog, high humidity and rain
Moderate winds
Cloud Cover and Fog/Precipitation Forecast
Fog, high humidity, clouds and/or rain are set to build in this evening and contribute to inoperable conditions for the remainder of the night (and likely the weekend).
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1 C tomorrow morning. Winds will be from the NE at 10-20 mph for today, increasing to 25-40 mph by the end of the night. Seeing will likely be near or exceed 1 arcsecond, while precipitable water is expected to start out near 3 mm for this evening, but will rapidly increase to 10+ mm by midnight.
Discussion
The tradewind inversion is set to rapidly breakdown this evening, allowing the atmosphere to become saturated through at least midnight Sunday. This will likely result in extensive fog, high humidity and rain at the summit, as well as convection in the area (especially along the northern and eastern skies) during this period. While the inversion is expected to rebuild near 5-6 thousand feet by sunrise Monday, lingering mid-level moisture may still allow for periods of fog and high humidity through that night; dry and stable conditions will return to the summit by Tuesday night. Daytime clouds may pick up today and turn very extensive over the weekend, then taper again for Monday and especially Tuesday.

Thick clouds are expected to pour in from the east early this evening, contributing to extensive cloud cover, if not overcast skies through at least Sunday evening. The bulk of these clouds will shift off toward the WNW, leaving mainly residual patches of mid/upper-level clouds to dissipate in the area for most of Monday and into early Tuesday. Clear skies will prevail for the latter night.

Precipitable water is expected to start out near 3 mm early this evening, but will jump toward 10+ mm for the remainder of the weekend and probably most of Monday night. There is a chance that it will dip toward 3-4 mm again for Tuesday night.

Inoperable conditions/skies, in addition to pockets of turbulence throughout various layers in the atmosphere will contribute to bad seeing through at least the weekend. There is a possibility for improving conditions and perhaps poor/average seeing for Monday night. However, an increase in boundary layer turbulence will limit further improvement in seeing for Tuesday night.

Little change since the morning forecast...TS Darby is still schedule to march toward the Big Island over the next 24 hours, then veer off toward the NW over the remainder of the weekend and into early part of next week. (It should be noted that the latest run has Darby passing through the Big Island, then shifting off toward the north around Sunday night.) Nonetheless, the abundant supply of moisture/clouds associated with the storm will likely contribute to inoperable conditions/skies at the summit between early this evening and at least midnight Sunday. There is a high probability for convection in the area, particularly once the center of Darby moves over/near the Big Island for Saturday night and again around Sunday afternoon. Winds at the summit may gradually increase (toward 40-50 mph) prior to this, then taper again early Sunday morning. The bulk of the moisture is set to shift off toward the NW and/or detrain into the surrounding atmosphere as Darby gradually weakens through Sunday and especially into the early part of next week. While this should permit the mid/low-level ridge to the to regain control of the air mass near the Big Island, lingering mid/upper-level moisture may still allow for periods of fog and/or high humidity through Monday night. Dry and stable conditions will return to the summit by Tuesday night, but there is a chance that winds will increase back toward 20-25 mph, which could contribute to light/moderate boundary layer turbulence and limit any improvement in seeing for that night.
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 Jul 22 - 8 PM60-804-675 / 252NE/15-300.6-1.23-6
Sat Jul 23 - 2 AM80-1004-8100 / 601ENE/20-350.8-1.66-10
2 PM80-1004-10100 / 953E/25-40NaN10-15
8 PM80-1004-10100 / 851E/30-451-210-15
Sun Jul 24 - 2 AM80-1004-10100 / 950.5E/25-401-210-15
2 PM80-1004-10100 / 904WNW/5-15NaN10-15
8 PM80-1004-995 / 601SSW/15-301-210-15
Mon Jul 25 - 2 AM60-805-990 / 300.5SSW/20-350.8-1.610-15
2 PM60-804-875 / 155S/10-20NaN8-12
Tue Jul 26 - 2 AM20-406-850 / 51ESE/10-200.5-0.86-10
2 PM20-404-525 / 56E/15-30NaN4-8
Wed Jul 27 - 2 AM0-20Clear0 / 00E/15-300.5-0.83-5
2 PM10-304-4.50 / 05E/20-35NaN3-5
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
Sun Jul 24 - Mon Jul 25 19:11 20:22 4:35 5:46 22:44 N/A 67 0 53.7 2 18
Mon Jul 25 - Tue Jul 26 19:11 20:22 4:35 5:46 23:29 N/A 56 1 47.9 6 38
Tue Jul 26 - Wed Jul 27 19:10 20:21 4:36 5:47 0:15 N/A 44 2 43.1 10 34
Wed Jul 27 - Thu Jul 28 19:10 20:21 4:36 5:47 1:04 N/A 33 3 39.4 13 51
Thu Jul 28 - Fri Jul 29 19:10 20:20 4:37 5:47 1:56 N/A 23 4 36.9 16 15
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 25 July 2016.
Additional Information
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