Current Conditions
Temp-5.2 C
RH82 %
WindWSW 8 mph
RoadClosed
Maunakea Observatories Forecast
5 PM HST Friday 09 April (0300 UTC Saturday 10 April) 2021
Warning(s)
Moderate winds through the weekend
Chance for fog/ice and thunderstorms on Sunday
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while scattered to broken high clouds fill in from the west, perhaps contributing to extensive cloud cover as the night progresses.
Summary of Key Meteorological Variables
Summit temperatures will be near 0 C, with winds from the west at 10-20 mph for this evening, increasing to 15-25 mph for the morning hors. Seeing will be near 0.65-0.7 arcseconds, while precipitable water is expected to be in the 1.5-2 mm range for the first half of the night and 2-3 mm range for the second half.
Discussion
A well-defined tradewind inversion will continue to cap low-level moisture near 7-8 thousand feet and ensure a dry/stable summit-level air mass through at least tonight. While the inversion will remain intact through Sunday morning and influx of mid-level moisture may raise the stakes on fog, ice and perhaps light flurries for Saturday night. This risk will further increase as well as the possibility for convection in the area as the inversion breaks down in response to building instability for Sunday night. The inversion will begin to restrengthen late Monday morning, which should help decrease the risk for moisture at the summit for that night and especially Tuesday night. Daytime clouds will be minimal and short-lived for today and probably tomorrow, turn extensive for Sunday, then taper for Monday and especially Tuesday.

High clouds are set to spread in from the west and may contribute to extensive cloud cover as the night progresses. While the high clouds will begin to slip eastward through tomorrow, thicker patches of clouds are expected to fill in from the NW, which will continue to block much of the sky for that night. Skies will begin to open up as these clouds move to the NE skies through Sunday night and eventually shift out of the area and allow clear skies to return to the summit for the early part of next week.

Precipitable water is expected to start out near 1.5 mm for tonight, but will increase toward 3 mm by the end of the night, linger near or exceed 4 mm for the remainder of the weekend, then trend back to 2 mm through Monday night and 1 mm through Tuesday night.

Persistent low-level and/or boundary layer turbulence will contribute to poorer than average seeing through Monday night. There is also a possibility that an elevated inversion, instability and/or moisture will further degrade seeing mainly for early Sunday morning and that night. Calmer skies and a relatively dry/stable air mass should allow seeing to improve toward 0.5-0.6 arcseconds for Tuesday night.

Little change since the morning forecast...The quasi-stationary blocking low to the NE is expected to subtly weaken and retract northward over the next 18-24 hours, then retreat back to the west and strengthen before falling apart and slipping eastward around the early part of next week. The retraction/weakening of the low will the southern edge of the ridge to persist over the state and promote steady/strong large-scale subsidence in the area probably through most of Saturday night. Although this will be enough to ensure a dry/stable summit-level air mass for tonight, mid-level moisture revolving around the western flank of the restrengthening low will begin to move into the area later tomorrow night. This will raise the stakes on fog and ice at the summit as that night progresses. Eventually, instability associated with the low and its parent trough will erode the inversion around sunrise on Sunday, which will significantly raise these stakes as well as the possibility for convection in the area and flurries at the summit for that night. The bulk of the mid-level moisture and instability will begin to slide off toward the east by sunrise on Monday. This should help to rebuild the inversion over the following 24 hours, and diminish the risk for moisture at the summit for Monday and especially Tuesday 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 Apr 09 - 8 PM40-609-100 / 00W/10-200.55-0.851.5-2
Sat Apr 10 - 2 AM60-808-100 / 00W/15-250.6-0.92-3
2 PM60-806.5-920 / 03W/20-35NaN3-5
8 PM60-806-825 / 5-3W/20-350.6-13.5-4.5
Sun Apr 11 - 2 AM60-805-740 / 10-4W/20-350.7-1.13.5-4.5
2 PM80-1004-890 / 75-2WSW/25-40NaN4-8
8 PM40-604-675 / 30-7WSW/20-350.8-1.63-4
Mon Apr 12 - 2 AM20-404-565 / 20-6WNW/15-300.7-1.33-4
2 PM60-804-565 / 30-2W/10-20NaN3-6
Tue Apr 13 - 2 AM0-204-4.540 / 10-6N/15-300.5-0.92-4
2 PM0-20Clear0 / 03NNW/15-30NaN1-2
Wed Apr 14 - 2 AM0-5Clear0 / 00E/5-150.4-0.81-2
2 PM0-20Clear0 / 04E/5-15NaN0.8-1.2
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 Apr 11 - Mon Apr 12 18:48 19:54 4:51 5:57 6:31 18:49 0 1 41.8 6 18
Mon Apr 12 - Tue Apr 13 18:48 19:54 4:50 5:56 N/A 19:38 2 2 25.4 11 04
Tue Apr 13 - Wed Apr 14 18:49 19:55 4:49 5:55 N/A 20:28 5 3 10.2 15 24
Wed Apr 14 - Thu Apr 15 18:49 19:55 4:48 5:55 N/A 21:19 9 3 56.7 19 08
Thu Apr 15 - Fri Apr 16 18:49 19:56 4:47 5:54 N/A 22:11 15 4 45.3 22 07
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 12 April 2021.
Additional Information
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