Current Conditions
Temp4.1 C
RH5 %
WindWSW 13 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Thursday 25 April (0300 UTC Friday 26 April) 2019
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while a narrow band of isolated to scattered cirrus passes overhead during the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 3 C this evening and 2 C tomorrow morning. Winds will be light and from the WNW, while seeing will start out near 0.4 arcseconds, but will likely deteriorate toward 0.6 arcseconds as the night progresses. Precipitable water is expected to be in the 2-3 mm range for the night.
A fairly well-defined inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure the summit remains dry and stable through Friday night. There is a possibility that the inversion will begin to to breakdown as instability and moisture build into the area through Saturday, which could increase the risk for fog, ice and flurries at the summit for that night, and especially Sunday and Monday night. Daytime clouds will be minimal and short-lived through Friday, but could turn extensive over the weekend and early part of next week. There is also a possibility for afternoon convection along the interior and western slopes of the Big Island mainly for Sunday and Monday.

A narrow band of scattered to isolated cirrus is set to move in from the west and pass overhead for tomorrow night. After a brief clearing on Friday, more high clouds are expected to fill in from the SW early Saturday morning, with perhaps thicker clouds building in and/or developing overhead, contributing to periods of extensive cloud cover for Saturday and Sunday night. The bulk of these clouds will shift off toward the east through Monday, opening up skies a bit for that night.

Precipitable water is expected to increase into the 2-3 mm range for tonight, increase into the 3-4 mm range for tomorrow night, then linger near or exceed 4 mm for the weekend and early part of next week.

Relatively calm skies will allow seeing to start out near 0.4-0.45 arcseconds for this evening, but builing turbulence in the free atmosphere may begin to degrade seeing as the night progresses and into tomorrow night. An increase in instability and moisture may further degrade seeing and contribute to poor/bad seeing for Saturday, Sunday and Monday night. There is also a possibility for light/moderate boundary layer turbulence for the latter two nights.

Little change since the morning forecast...The ridge will continue to sit over the state for the next 24-36 hours, but will also gradually weaken before shifting off toward the south in response to a trough filling in from the NW over the weekend. Nevertheless, subsidence associated with the ridge will help maintain a fairly well-defined inversion at or below 9 thousand feet and ensure a dry/stable summit-level air mass through tomorrow night. While the incoming trough will not affect the stability of the atmosphere (at least initially), it will begin to rebuild the sub-tropical jet in the area, which will increase turbulence in the free atmosphere and have a negative impact on seeing as early as tonight. This downward trend in seeing will likely continue thru the following night (and probably through the weekend), while the STJ also starts to gain access to high cloud flowing out of the tropics early Saturday. In addition, the aforementioned trough is then set to deepen and slowly pass to the north over the remainder of the weekend and into the early part of next week. Instability associated with the trough could help weaken or even dismantle the inversion and increase the risk for fog, ice and light flurries at the summit during that time. There is also a small/moderate risk for convection in the area, but that should be limited to the interior or western slopes and during the afternoon hours, as the bulk of the dynamical forcing associated with the trough passes well to the north of the state.
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 Apr 25 - 8 PM10-308-90 / 03W/0-100.35-0.552-3
Fri Apr 26 - 2 AM0-208-90 / 02W/0-100.5-0.72-3
2 PM0-20Clear0 / 06.5SW/0-10NaN3-5
8 PM0-20Clear0 / 01.5SW/5-150.5-0.83-4
Sat Apr 27 - 2 AM10-309-100 / 01SSW/5-150.6-0.93-4
2 PM40-604-1040 / 105.5SW/5-15NaN4-8
8 PM60-808-1035 / 50WSW/5-150.6-13.5-4.5
Sun Apr 28 - 2 AM60-808-1040 / 10-1SW/10-200.7-1.13.5-4.5
2 PM70-904-1075 / 253W/10-20NaN4-8
Mon Apr 29 - 2 AM60-809-1065 / 40-2WSW/10-200.7-1.34-6
2 PM60-804-875 / 302WSW/15-35NaN4-8
Tue Apr 30 - 2 AM20-407-860 / 15-2W/15-300.7-1.33-5
2 PM40-604-540 / 104NNW/10-20NaN2-4
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 Apr 25 - Fri Apr 26 18:52 20:00 4:39 5:47 0:40 N/A 54 20 14.3 -21 10
Fri Apr 26 - Sat Apr 27 18:53 20:01 4:38 5:46 1:24 N/A 45 21 04.2 -19 08
Sat Apr 27 - Sun Apr 28 18:53 20:01 4:38 5:46 2:05 N/A 36 21 52.2 -16 20
Sun Apr 28 - Mon Apr 29 18:53 20:02 4:37 5:45 2:44 N/A 27 22 38.6 -12 53
Mon Apr 29 - Tue Apr 30 18:54 20:02 4:36 5:44 3:20 N/A 19 23 23.9 -8 57
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 26 April 2019.
Additional Information
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