Current Conditions
Temp6.1 C
RH8 %
WindE 0 mph
Mauna Kea Observatories Forecast
5 PM HST Friday 19 July (0300 UTC Saturday 20 July) 2019
Cloud Cover and Fog/Precipitation Forecast
The summit will be mostly dry and stable through tonight. High clouds, approaching fom the SW, will stream overhead this evening, thinning and moving away through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 3.5 C this evening and 2 C tonight. Winds will be from the NNE at 15-25 mph, possibly decreasing through night. PW is likely to linger close to 4 mm. Observing conditions will start off poor to less than average but will improve some as the night progresses.
The tradewind inversion will remain in place and continue to promote mostly stable conditions at the summit at least through Saturday. Models project the inversion to lift and vanish by Sunday night as a bout of moisture, from the South, will destabilize the airmasses. Therefore episodes of high relative humidity and fog are very likely from late Sunday and through Monday and early Tuesday. The inversion is expected to rebuild afterward.

High clouds, streaming fom the SW will move over thinning and dissipating through tonight. Mostly clear skies will follow on Saturday night but mid level clouds approaching from the South will start being visible on Sunday and are likely to reach the area by Sunday day as extensive daytime clouds and through Monday, obscuring almost all of the summit skies then. They will start to clear on on Tuesday.

Precipitable water will linger close to 4 mm tonight, will quickly drop below 2 mm to range between 1 and 1.5 mm on Saturday night. Unfortunately it will increase as suddendly on Sunday and likely exceed the 4 mm threshold through the rest of this forecast period.

Observing conditions will start off poor to less than average tonight as surface winds are still sustained. Winds will slowly taper through the second night, allowing an improvement in seeing. Observing conditions are expected to be average to better than average on Saturday night, while will become unoperable on Sunday and Monday night due to saturated airmasses. An improving trend will start on Tuesday.

Not much is changed since the morning forecast... While the high pressure system north of the islands, although slighly weaker, will continue to promote a stable tradewind inversion today and tomorrow and the upper level trough/low that interested the area these past days continues to move northwestward, drier airmasses will be left behind at least through Saturday night. Unfortunately, a weak mid-upper level trough passing just over and South of the Big Island will advect tropical moisture from the South over the area and destabilize enough the airmasses to result in high relative humidity and fog from Sunday through Monday, with some moisture possibly lingering into early Tuesday. This will make it for very bad observing to unoperable conditions then. As the trough moves to the west more bening conditions will follow from late Tuesday and onward.
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)
Fri Jul 19 - 8 PM20-407-80 / 03.5NNE/20-300.7-1.14-6
Sat Jul 20 - 2 AM10-307-80 / 02NNE/15-250.55-0.853.5-4.5
2 PM0-20Clear0 / 08ESE/10-20NaN1.5-2.5
8 PM0-20Clear0 / 03ESE/10-200.5-0.81.5-2
Sun Jul 21 - 2 AM0-20Clear0 / 02.5SE/10-200.4-0.71-1.5
2 PM40-603.5-4.550 / 07SSW/10-20NaN4-6
8 PM60-803-570 / 102.5S/10-200.7-1.16-8
Mon Jul 22 - 2 AM80-1003-590 / 202.0S/10-200.8-1.26-8
2 PM80-1003-590 / 207NE/5-15NaN6-12
Tue Jul 23 - 2 AM80-1003-590 / 202E/5-150.6-16-12
2 PM30-503.5-4.550 / 09N/5-15NaN4-8
Wed Jul 24 - 2 AM10-303.5-4.510 / 03ENE/5-150.4-0.84-6
2 PM0-20Clear0 / 09ESE/5-15NaN4-6
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
Sat Jul 20 - Sun Jul 21 19:13 20:25 4:32 5:44 21:51 N/A 82 23 26.5 -9 18
Sun Jul 21 - Mon Jul 22 19:12 20:24 4:33 5:44 22:26 N/A 74 0 11.1 -4 57
Mon Jul 22 - Tue Jul 23 19:12 20:24 4:33 5:45 23:01 N/A 65 0 55.4 -0 25
Tue Jul 23 - Wed Jul 24 19:12 20:23 4:34 5:45 23:36 N/A 56 1 40.2 4 08
Wed Jul 24 - Thu Jul 25 19:11 20:23 4:34 5:46 0:12 N/A 46 2 26.2 8 35
Forecast Issued by: Tiziana Cherubini
Next update at 10 AM HST (2000 UTC) Monday 22 July 2019.
Additional Information
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