Maunakea Weather Center

Maunakea Observatories Forecast
6 AM HST (1600 UTC) Thursday 22 February 2024
Warning(s)
None

Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 8 C this afternoon, 3 C this evening and 2.5 C tomorrow morning. Winds will be from the west at 5-15 mph, with seeing near 0.4-0.5 arcseconds for the night. Precipitable water is exected to be in the 0.5-0.7 mm range for the night.

Discussion
A well-defined inversion will continue to cap low-level moisture primarily near 7 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies overhead will remain predominately clear for tonight, there is a possibility for light cirrus building in from the north toward the end of the night. A narrow band of mid/upper-level clouds is expected to briefly develop near/over the summit area for Friday night then will shift off toward the east on Saturday. Another patch of quick-moving cirrus is projected to fill in from the WSW and briefly pass mainly along the southern half of the Big Island for Saturday night. Clear skies will prevail for Sunday and Monday night.

Precipitable water is expected to settle in the 0.5-0.7 mm range for tonight, trend toward 3 mm through Friday night and probably linger near 3-3.5 mm for Saturday night. There is a good chance that it will decrease toward 2 mm over the course of Sunday night and probably below 1 mm for Monday night.

Despite steady upper-level shear in the free atmosphere, light/calm winds at the summit combined with mainly laminar westerly flow overhead should allow seeing to settle in around 0.4-0.5 arcseconds for at least tonight. A subtle increase in upper-level flow could result in a slight degradation toward 0.5-0.55 arcseconds for the next 3 nights. Strong westerly flow (> 100 mph) aloft could further degrade seeing for the early part of next week

The mid/surface ridge will continue to sit to the north-northeast of the state and promote steady/strong large-scale subsidence in the area probably through the week. This subsidence will easily maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. While the westerly jet will remain quite active/intense, it will sustain a fairly zonal orientation and split into two further west of the Dateline. The latter will result in a more shallow jet overhead, which will allow for relatively calm winds near summit-level probably well into next week. The strength of the jet will still promote steady upper-level shear, but seeing should still settle in around 0.45-0.55 arcseconds through the weekend. Initially, PW will also benefit from this wide-spread subsidence and the zonal/shallow jet overhead, lingering in around 0.6-0.7 mm for tonight. However, there is a possibility that a developing low in the NE Pacific will begin to draw moisture out of the tropics, which could result in an increase in CC and PW portions of over the weekend. PW and CC should improve as these clouds/moisture is drawn off toward the east late in the weekend, but there is a good chance that this low will strengthen the southern portion of the westerly jet early next week. This could result in upper-level westerly flow around 120-130 mph, which will contribute to significant shear and probably a degration in seeing (toward 0.6-00.65 arcseconds) 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 Feb 22 - 2 PM0-20Clear0 / 08W/5-15NaN0.6-1
8 PM0-5Clear0 / 03W/5-150.35-0.550.5-0.7
Fri Feb 23 - 2 AM0-10Clear0 / 02.5W/5-150.35-0.550.5-0.7
2 PM20-407-80 / 07.5SW/5-15NaN0.6-1
8 PM20-407-90 / 02WSW/5-150.4-0.61-2
Sat Feb 24 - 2 AM20-406-80 / 01W/5-150.45-0.652-3
2 PM20-408-90 / 04.5NW/5-15NaN3-5
8 PM40-607-90 / 0-1NNW/5-150.45-0.653-4
Sun Feb 25 - 2 AM20-407-90 / 0-1.5NNW/5-150.45-0.653-4
2 PM0-20Clear0 / 03NNE/5-15NaN2-4
Mon Feb 26 - 2 AM0-5Clear0 / 0-2N/0-100.425-0.6752-3
2 PM0-20Clear0 / 03NNE/0-10NaN1-2
Tue Feb 27 - 2 AM0-5Clear0 / 0-2N/5-150.45-0.750.6-1
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 Feb 22 - Fri Feb 23 18:33 19:38 5:32 6:37 17:04 6:40 99 9 44.0 18 00
Fri Feb 23 - Sat Feb 24 18:34 19:38 5:32 6:36 17:56 7:14 100 10 29.8 13 06
Sat Feb 24 - Sun Feb 25 18:34 19:39 5:31 6:36 18:45 N/A 99 11 13.6 7 43
Sun Feb 25 - Mon Feb 26 18:34 19:39 5:31 6:35 19:33 N/A 97 11 56.1 2 05
Mon Feb 26 - Tue Feb 27 18:35 19:39 5:30 6:34 20:20 N/A 92 12 38.3 -3 37
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Thursday 22 February (0300 UTC Friday 23 February) 2024.
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