Current Conditions
Temp2.4 C
RH8 %
WindSSE 3 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Monday 23 May (0300 UTC Tuesday 24 May) 2016
Warning(s)
Chance for fog/high humidity
Cloud Cover and Fog/Precipitation Forecast
There is a small/moderate risk for periods of fog and high humidity throughout the night; precipitation is not expected. There is also a chance for thin high clouds along the southern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 1.5 C this evening and 0.5 C tomorrow morning. Winds will be from the west at 5-15 mph, with seeing near 0.6-0.65 arcseconds. Precipitable water is expected to be in the 2.5-3.5 mm range for the first half of the night and 3-4 mm range for the second half.
Discussion
After strengthening overnight, building instability is set to weaken/lift the inversion toward 12-13 thousand feet for tonight, and perhaps dismantle it all together for Tuesday and especially Wednesday night. This will raise the stakes on periods of fog, high humidity, ice and/or light rain/flurries at the summit over the next 3 nights. The inversion is expected to slowly rebuild through Thursday, which should help reduce the risk for moisture at the summit for that night and particularly Friday night. Daytime clouds will likely turn extensive for the next 3 days, then taper again for Friday and over the weekend.

Skies overhead will remain predominately clear, but there is a possibility for thin cirrus along the southern skies for tonight. There is also a chance for pockets of mid/summit-level clouds in the area for Tuesday and especially Wednesday night. These clouds are expected to shift off toward the NE on Thursday, but banding high clouds are set to fill in from the south later that night, likely contributing to periods of extensive cloud cover for much of Friday; a clearing trend is expected for early Saturday morning.

Precipitable water is expected to drift toward 4 mm through the course of the night and likely linger near or exceed that value for Tuesday, Wednesday and most of Thursday night. There is a good chance that PW will slip below 2 mm for Friday night.

Moderate turbulence in the free atmosphere will likely contribute to poorer than average seeing for tonight. Building instability and turbulence in the free atmosphere as well as moisture in the area, will further degrade seeing for Tuesday and Wednesday night. There is a good chance that seeing will improve with conditions through Thursday night, and will likely settle in near average-like values again for Friday night.

No change since the morning forecast...Although the low-level ridge will continue to sit to the north of the state and maintain the easterly trades through the week, the mid-level ridge is set to fall apart while a short-wave trough (SWT) builds into the northwest over the next 24-48 hours and eventually passes to the north around Wednesday night. In addition, the tropical upper-tropospheric trough and its associated sub-tropical jet will remain quasi-stationary over or just west of the state, providing large-scale but relatively weak instability in the area probably through the week. Nonetheless, the SWT is expected to enhance the instability in the area, which in turn will weaken/lift the inversion toward 12-13 thousand feet over the next 24 hours. As the trough shifts closer it will begin to congregate mid/low-level moisture near the Big Island, which could further dismantle the inversion between late Tuesday evening and sunrise Thursday. Thus, while there is a small/moderate risk for fog/high humidity at the summit for tonight, there is a very good chance for that this risk will increase for the following 2 nights. Light flurries/rain, ice and isolated convection are also possible for much of Wednesday. The atmosphere is expected to gradually stabilize and dry out as this SWT shifts off toward the NE through Thursday, likely allowing more normal conditions to return to the summit for the weekend. However, the sub-tropical jet is expected to briefly stream banding high clouds over the summit mainly for Friday.
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)
Mon May 23 - 8 PM0-209.5-1025 / 01WNW/5-150.5-0.72.5-3.5
Tue May 24 - 2 AM0-209.5-1040 / 00.5WSW/5-150.5-0.83-4
2 PM40-604-560 / 154W/10-20NaN4-6
8 PM0-204-4.560 / 10-0.5WNW/5-150.6-13.5-4.5
Wed May 25 - 2 AM20-404-575 / 25-2W/5-150.7-1.14-6
2 PM80-1004-895 / 752SW/5-15NaN6-10
8 PM60-804-690 / 60-3WSW/10-200.8-1.24-8
Thu May 26 - 2 AM40-604-4.575 / 25-2W/10-200.7-1.14-6
2 PM40-604-4.560 / 204WSW/10-20NaN3-5
Fri May 27 - 2 AM60-809-1025 / 5-0.5WSW/10-200.5-0.73-5
2 PM80-1008-100 / 06W/15-25NaN2-3
Sat May 28 - 2 AM20-409-100 / 01.5W/15-250.45-0.651-2
2 PM0-20Clear0 / 06WNW/15-25NaN1-2
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
Mon May 23 - Tue May 24 19:04 20:16 4:22 5:34 20:34 N/A 94 18 11.8 -19 04
Tue May 24 - Wed May 25 19:04 20:16 4:21 5:33 21:24 N/A 88 19 05.2 -18 37
Wed May 25 - Thu May 26 19:05 20:17 4:21 5:33 22:13 N/A 80 19 58.8 -17 15
Thu May 26 - Fri May 27 19:05 20:17 4:21 5:33 23:00 N/A 71 20 52.2 -15 00
Fri May 27 - Sat May 28 19:05 20:18 4:20 5:33 23:46 N/A 61 21 45.3 -11 57
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 24 May 2016.
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