Current Conditions
Temp-1.7 C
RH13 %
WindE 45 mph
Mauna Kea Observatories Forecast
5 PM HST Tuesday 15 April (0300 UTC Wednesday 16 April) 2014
Moderate/strong winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, there is a slight a chance for light cirrus along the northern skies mainly during the second half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 0 C, with winds from the NE at 25-40 mph for this evening, easing to 20-35 mph and switching to more ENE direction through the night. Precipitable water is expected to be in the 1-1.5 mm range, with seeing around 0.9-1 arcsecond.
The tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and keep the summit-level air mass dry and stable through at least Friday night. While the inversion will remain in tact through the weekend, mid-level moisture is expected to fill into the area, which could increase summit-level humidity toward 60-80% and perhaps the risk for fog, ice and light flurries at the summit for Saturday night. Daytime clouds will be minimal and short-lived through Friday, but could pick up over the weekend.

There is a possibility for light dissipating cirrus along the northern for one more night. Banding high clouds are expected to set up along the southeastern skies over the next 24 hours and gradually creep toward the summit through tomorrow night. There is a good chance that this band will move over the summit and thicken, through Thursday, blanketing skies for later that night and most of Friday and Saturday. This band is slated to shift off toward the east through the latter night, but there is a chance for lingering patches of mid-level clouds well into Sunday.

Precipitable water is expected to linger near or just below 1 mm through Thursday night, increase to 2-4 mm through Friday night and perhaps exceed 4 mm for Saturday night.

Boundary layer turbulence will contribute to poor/bad seeing for at least one more night. This turbulence is slated to subside a bit for subsequent night, but there is a possibility for lingering low-level turbulence through Thursday night and mid/upper-level turbulence may build into the area for Friday and Saturday night. Nonetheless, seeing should improve back to average to slightly poorer than average seeing after tonight.

No change since the morning forecast....The low to the east of the state is expected to fall apart over the next 12-24 hours, allowing the ridge to rebuild to the north of the state and progress eastward through the remainder of the week. Nonetheless, the ridge will continue to promote strong/steady large-scale subsidence in the area and maintain a well-defined tradewind inversion near 8 thousand feet through the week. While this will be more than enough to keep the summit-level air mass dry and stable through at least Friday night, models expect mid-level moisture to fill in from the south and saturate the air mass above 16 thousand feet later in the weekend. Still, winds are slated to subside as the wind gradient become more relaxed with the dissipation of the low over the next 24 hours. This may help to improve seeing back toward more average-like values for tomorrow night, but the sub-tropical jet is slated to drift in from the south and bring free atmospheric turbulence and lots of high clouds into the area through Thursday night. These clouds will likely blanket skies for Friday night and most of Saturday night. As alluded to earlier, there is a chance that the jet will deepen into the mid-levels and advect moisture over the summit area around Saturday. I suspect this is a little overdone, but I did increase the risk for fog, ice, high humidity and light flurries at the summit for Saturday 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)
Tue Apr 15 - 8 PM0-209.5-100 / 00NE/25-400.7-1.31-1.5
Wed Apr 16 - 2 AM0-209.5-100 / 00ENE/20-350.6-1.21-1.5
2 PM0-20Clear0 / 07ENE/15-30NaN0.8-1.2
8 PM0-20Clear0 / 02ENE/10-200.5-0.80.8-1
Thu Apr 17 - 2 AM10-309.5-100 / 02E/10-200.5-0.70.8-1
2 PM20-409-100 / 07.5E/10-20NaN0.8-1.2
8 PM40-608.5-100 / 03E/10-200.5-0.80.8-1
Fri Apr 18 - 2 AM60-808-100 / 02E/15-250.5-0.80.9-1.1
2 PM80-1007-100 / 07E/15-25NaN1-2
Sat Apr 19 - 2 AM80-1007-100 / 02ESE/15-250.5-0.72-4
2 PM80-1004-1050 / 256E/10-20NaN4-8
Sun Apr 20 - 2 AM70-905-1050 / 250E/10-200.5-0.84-8
2 PM40-604-940 / 205ENE/10-20NaN4-8
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
Tue Apr 15 - Wed Apr 16 18:49 19:56 4:48 5:54 19:16 N/A 99 14 32.1 -14 17
Wed Apr 16 - Thu Apr 17 18:49 19:56 4:47 5:53 20:13 N/A 95 15 28.0 -16 59
Thu Apr 17 - Fri Apr 18 18:50 19:56 4:46 5:53 21:11 N/A 89 16 26.0 -18 45
Fri Apr 18 - Sat Apr 19 18:50 19:57 4:45 5:52 22:09 N/A 80 17 25.2 -19 24
Sat Apr 19 - Sun Apr 20 18:50 19:57 4:44 5:51 23:06 N/A 71 18 24.8 -18 54
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 16 April 2014.
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