Maunakea Weather Center

Maunakea Observatories Forecast
5 PM HST Thursday 30 November (0300 UTC Friday 1 December) 2023
Fog, ice and high humidity
Chance for convection and heavy snow

Cloud Cover and Fog/Precipitation Forecast
Extensive fog, ice, thick clouds and flurries will continue to plague the summit throughout the night. There is a possibility for convection in the area and periods of heavy snow at the summit mainly into early this evening.

Summary of Key Meteorological Variables
Summit temperatures will be near -0.5 C, with winds from the SE at 10-20 mph for this evening, switching to a more WSW direction through the night. Seeing and PW are expected to exceed 1 arcsecond and 4 mm, respectively, throughout the night.

Deep widespread moisture and instability will continue to pour into the area, contributing to extensive fog, ice and light/moderate snow for tonight, as well as the development of convection especially along the eastern skies and periods of heavy snowfall at the summit mainly through late this evening. While the bulk of the moisture/instability are expected to gradually shift off toward the NE by sunset tomorrow, pockets of moisture/instability will still persist in the area and limit the inversion from restrengthening until late in the weekend. As a result, there is still a moderate/high risk for periods of fog, ice and high humidity probably into early Sunday evening; this risk will subside thereafter. Extensive daytime clouds are likely through Saturday, but could taper for Sunday and especially early next week.

Broken to overcast thick clouds will continue to build in from the south, blanketing summit skies for tonight. These clouds will begin to shift off toward the north and east around noon tomorrowopening up portions of the sky for that night and as the weekend progresses. Clear skies should prevail for at least the latter half of Sunday night and especially Monday night.

Precipitable water is expected to exceed 4 mm through at least Sunday evening, but could slip toward 3 mm by sunrise Monday and into the 2-3 mm range for that night.

Boundary layer as well as free atmospheric turbulence and especialy an influx of deep moisture/instability will contribute to bad seeing for tonight and probably even into Friday night. There is a moderate possibility for a modest improvement in seeing as summit-level winds (and below) taper and the atmosphere begins to gradually dry out through Saturday night and especially for Sunday night night. The redevelopment of the inversion, combined with relatively deep/light NE flow in the free atmosphere could allow seeing to settle back in near 0.5-0.6 arcseconds for Monday night.

Little change since the morning forecast...The deep cut-off low to the west will remain quasi-stationary/steady remain quasi-stationary/steady for another 6-12 hours, then will lift northward and weaken through tomorrow, only to be swallowed by the westerly jet far to the north as the weekend progresses. Deep southerly flow along the eastern flank of this low and its parent trough will continue to draw deep widespread moisture out of the tropics and over the Big Island through tonight. This, combined with instability associated with the low, will contribute to inoperable conditions at the summit through tonight. There is also a possibility for convection developing particularly along the eastern skies and periods of heavy snowfall at the summit mainly into early this evening. The convection will begin to taper and become more isolated as the upper air mass warms up, stabilizing the air mass as the night progresses. The bulk of the deep moisture and instability will begin to slide off toward the north and east as the low loses its supply of tropical moisture and also lifts northward through tomorrow. However, there is still a very good chance that pockets of deep moisture will persist close enough to the Big Island, limiting improvement in summit conditions for the early part of the weekend. In fact, the residual trough axis assoicated with the eventualy decaying/departing low is set to cross through the area and another round of weak upper-level dynamic instability (in the form of diffluence) to the region around Sunday morning. This may prohibit the inversion from restrengthening until this trough axis shifts well east of the Big Island and the residual moisture detrains into the surrounding air mass later that night. That should allow more normal conditions to return to the summit perhaps as early as Monday morning, and almost certainly for Monday night.
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Thu Nov 30 - 8 PM80-1004-10100 / 95-0.5SE/10-201.5-2.515-20
Fri Dec 01 - 2 AM80-1004-10100 / 90-0.5WSW/10-201.5-2.515-20
2 PM80-1004-1095 / 753W/10-20NaN10-15
8 PM70-904-995 / 600WSW/5-150.8-1.610-15
Sat Dec 02 - 2 AM60-804-890 / 400S/5-150.7-1.38-12
2 PM60-804-890 / 404SW/5-15NaN6-10
8 PM20-405-875 / 150SW/5-150.6-16-10
Sun Dec 03 - 2 AM20-405-760 / 10-0.5WSW/5-150.5-0.96-10
2 PM20-404-560 / 153.5SSW/5-15NaN4-8
Mon Dec 04 - 2 AM0-20Clear25 / 50S/5-150.5-0.83-5
2 PM10-304-4.530 / 55SSE/5-15NaN3-5
Tue Dec 05 - 2 AM0-10Clear10 / 00.5SSE/5-150.4-0.72-3
2 PM0-20Clear0 / 06.5E/5-15NaN2-4
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 Nov 30 - Fri Dec 01 17:51 18:59 5:22 6:31 20:45 N/A 83 8 03.4 25 44
Fri Dec 01 - Sat Dec 02 17:51 18:59 5:23 6:31 21:41 N/A 75 8 55.4 22 35
Sat Dec 02 - Sun Dec 03 17:51 19:00 5:24 6:32 22:34 N/A 66 9 43.9 18 31
Sun Dec 03 - Mon Dec 04 17:51 19:00 5:24 6:33 23:25 N/A 57 10 29.4 13 48
Mon Dec 04 - Tue Dec 05 17:52 19:00 5:25 6:33 0:14 N/A 48 11 12.7 8 36
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 1 December 2023.
Additional Information
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