Current Conditions
Temp4.6 C
RH31 %
WindSE 3 mph
RoadClosed
Mauna Kea Observatories Forecast
5 PM HST Thursday 19 September (0300 UTC Friday 20 September) 2019
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
There is a slight risk for high humidity and fog toward the end of the night; precipitation is not expected. Broken high clouds are set to pour in from the north, contributing to extensive cloud cover for the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this evening and 2.5 C tomorrow morning. Winds will be from the NNW at 5-15 mph, with seeing near 0.6 arcseconds for the night. Precipitable water is expected to exceed 4 mm through the night.
Discussion
Although the tradewind will remain very well-defined near 8 thousand feet through the night, an influx of mid-level moisture could raise the stakes on fog and high humidity toward the end of the night. The building moisture will combine with instability and erode the inversion through tomorrow, allowing the atmosphere to turn quite saturated, significantly increasing the risk for extensive fog, ice and light flurries/rain for the remainder of the forecast period. There is also a possibility for the development of convection in the area, which may deposit heavier snow at the summit mainly over the weekend. Extensive daytime clouds are likely through Monday, then will begin to taper again on Tuesday.

Broken high clouds are set to pour in from the north contributing to extensive cloud cover for tonight. Thick mid-level clouds are expected to follow suit just after sunrise tomorrow, while the high clouds slip off toward the SE of the Big Island for that night, then return back over the summit probably for the remainder of the weekend. Regardless, this will likely result in overcast skies until the bulk of these clouds begin to dissipate and lift off toward the NW around Monday.

Precipitable water is expected to linger near or exceed 4 mm through the next 5 nights.

Tapering winds, combined with relatively calm skies in the free atmosphere should allow for better than average seeing for much of tonight (some variability is possible near the end of the night). An influx of moisture and instability, combined with periods of moderate boundary layer turbulence are expected to degrade and contribute to poor/bad seeing for the remainder of the forecast period.

No change since the morning forecast...While the upper-level and mid-level ridge lingering overhead and to the NE, respectively, are expected to dissipate and shift off toward the SW and NE in response a deep mid/upper-level low developing to the NE, large-scale subsidence will prevail in the area for another 12 hours. This subsidence will help maintain a fairly well-defined inversion and ensure the summit steers free of fog and precipitation until just before sunrise tomorrow. Beyond that, mid-level moisture is set to quickly fill in from the NNW by late that morning, while the low slowly destabilizes the atmosphere by injecting cold mid/upper-level low into the area over the following 24 hours. While there is a chance that the warmer temperatures will build into the area as the eastern flank of the low fills in overhead, promoting southerly advection through the weekend, upper-level diffluence may also increase, maintaining instability in the area probably into the early part of next week. Furthermore, this southerly advection could send deep tropical moisture into the area during that time. Regardless of the source of instability and moisture, the inversion is set to quickly erode the inversion through tomorrow, allowing the atmosphere to turn quite saturated, significantly increasing the risk for extensive fog, ice and light flurries/rain at the summit while the low digs in over the state and progresses westward over the weekend and into early part of next week. There is a possibility for the development of convection in the area, which could deposit heavier snow/rain at the summit between tomorrow afternoon and Sunday night. Drier more stable conditions may begin to return to the summit as the low weakens and lifts northward around Tuesday.
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)
Thu Sep 19 - 8 PM60-809-100 / 04N/5-150.5-0.76-10
Fri Sep 20 - 2 AM70-907.5-1020 / 02.5NNW/5-150.45-0.756-10
2 PM80-1004-1075 / 403WSW/15-30NaN10-15
8 PM80-1004-995 / 75-1.5WSW/15-300.7-1.310-15
Sat Sep 21 - 2 AM70-904-995 / 70-1.5W/10-200.8-1.610-15
2 PM80-1004-995 / 654SSW/15-30NaN10-15
8 PM80-1004-995 / 750S/15-300.8-1.610-15
Sun Sep 22 - 2 AM80-1004-1095 / 750S/15-300.8-1.610-15
2 PM80-1004-1095 / 905SSE/15-30NaN10-15
Mon Sep 23 - 2 AM80-1004-1095 / 801SE/5-150.8-1.610-15
2 PM80-1004-890 / 657ENE/5-15NaN10-15
Tue Sep 24 - 2 AM60-804-880 / 403NNE/10-200.6-1.28-12
2 PM0-206-830 / 1010NE/10-20NaN2-4
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 Sep 19 - Fri Sep 20 18:30 19:34 4:57 6:01 22:08 N/A 67 4 25.8 18 12
Fri Sep 20 - Sat Sep 21 18:29 19:33 4:57 6:02 22:55 N/A 57 5 19.7 20 39
Sat Sep 21 - Sun Sep 22 18:28 19:32 4:58 6:02 23:47 N/A 46 6 16.3 22 03
Sun Sep 22 - Mon Sep 23 18:27 19:31 4:58 6:02 0:43 N/A 35 7 15.0 22 10
Mon Sep 23 - Tue Sep 24 18:26 19:30 4:58 6:02 1:45 N/A 25 8 14.9 20 55
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 20 September 2019.
Additional Information
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