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Weather Information Update for April 15th, 2019

State of Hawai'i Weather Discussion

Weather Synopsis:

Trade wind weather will persist across the islands this week. Trade winds will become lighter by Tuesday as the high, currently north of the islands, moves east of the islands. Breezy trades will return by Friday as a strong surface ridge settles north of the islands.


There is still a little bit of wind and weather left this early Monday morning. Lanai remains windy with sustained winds of around 30 mph at times, and windward Big Island had a few brief but heavy showers move through. But both elements are on the downswing. With the trade winds, we expect the strength to be relatively strong today, although it will be trending weaker as the day progresses. This weakening trend should accelerate tonight and Tuesday as the source of the trades, a surface high north of the islands, moves off to the east. The trades should be at its weakest on Tuesday, at light to moderate speeds. Under this background flow, it will be weak enough to allow for local daytime sea breezes to develop, especially on the lee and interior areas of the smaller islands. The trades start to pick up speed once more, reaching locally strong by Wednesday evening, then moderate to strong area wide by Friday.

In term of showers, windward Big Island continues to be showery this hour. Radar is starting to pick up a few showers heading toward Kauai, but Kauai, Oahu, and Molokai, have been mostly dry thus far. Windward Maui has had some scattered showers pass through. Morning soundings from both LIH and ITO, shows an strengthening inversion, sloping from 6k feet to 10k feet, respectively. This comes about as mid level ridging takes hold at the expense of the upper trough moving away and weakening over the islands. The inversion is expected to be at its strongest this afternoon at 6k over Kauai to 8k feet over the Big Island. The mid level ridge weakens slightly tonight into Tuesday with the inversion rising to 7 to 8k feet over Kauai to 9 to 10k feet over the Big Island. With the trades at its lightest on Tuesday, this air mass should limit the convection showers to isolated. There is a 30 to 40 percent POP for the windward areas Tuesday afternoon, which could be too high. Trades will be trending stronger thereafter as a surface ridge lingers north of the islands into the weekend. This will lead to moderate to strong trades area-wide by Friday morning, and lasting into the upcoming weekend. The frequency of trade showers should be on the rise Tuesday night into Wednesday, as the low level moisture is accentuated by a passing upper level shortwave trough. Both ECMWF and GFS, are picking up on this feature. This shortwave evolves into an upper low southeast of the Big Island on Wednesday. A weaker mid level ridge over the islands, never-the- less, leads to a weaker and higher inversion, ranging between 10 and 12k feet area wide, which is supportive of more robust showers, lasting into the weekend.

The National Weather Service (NWS) reports as of 8:45 am Monday Morning, No Watches, Advisories, or Warnings are in effect for all islands.

Southern Nevada Discussion


An active first half of the work week is expected with gusty winds today followed by rain chances and a cold front passage on Tuesday. By Wednesday, conditions return to dry and mild, warming back to above normal temperatures by the weekend. UPDATE:

Approaching Pacific trough will make its way onshore this afternoon, increasing southwesterly flow over the local area and fueling showers across the southern Great Basin and the southern Sierra region this afternoon and overnight. Instability developing out ahead of the system will allow for isolated thunderstorms across central Nevada this afternoon and early evening. Outside of these areas, breezy south to southwest winds will develop today with gusts up to 35 mph possible. Slightly stronger winds with gusts in excess of 40 mph are expected across the western Mojave Desert, Owens Valley, and Death Valley NP late this afternoon and overnight which could create some issues with blowing dust. Made minor adjustments to overnight precip chances but no significant changes. SHORT TERM FORECAST THROUGH TUESDAY NIGHT

Active spring pattern in store for the next 48 hours as a potent trough diving southward from the PacNW brings gusty winds and increased shower chances to the area. Today, increasing southwesterly flow aloft ahead of the approaching trough will result in increased wind speeds across much of the forecast area. Most of the winds will be gusting below 40 mph, precluding more widespread wind advisories. However, the Western Mojave Desert and parts of Inyo county will see stronger winds developing late in the day and persisting through Tuesday and a Wind Advisory remains in effect for those areas. I did add the Owens Valley to the wind advisory as high resolution models suggest a few pockets of strong downslope winds developing late this afternoon and persisting into Tuesday morning, especially near Independence and south of Olancha. Downslope winds should taper off Tuesday morning, but northerly winds behind the cold front could keep winds going into Tuesday afternoon. In addition to the winds, a few high based showers and perhaps an isolated thunderstorm may develop this afternoon across our far northern zones, namely Esmeralda, northern Inyo, and central Nye and northern Lincoln counties. This will be in response to a developing frontal band which will sag southward overnight. On Tuesday, potent trough will develop southward from the Pacific Northwest and Great Basin region. This will result in widespread shower activity thanks to cooling temperatures aloft and strong vorticity advection into the region. By early afternoon, 500mb temperatures of -20C to -25C will be common, resulting in steep lapse rates and some marginal instability across much of the area. Given the cold pool aloft and increasingly strong April sun angle, expanded the thunder mention to include most of Southern Nevada, northwest Arizona, and parts of eastern California. This closely matches the SPC day 2 convective outlook for general thunder. This trough will close off and push into the Four Corners region on Tuesday night with shower activity diminishing from west to east along with decreasing cloud cover. However, northerly breezes will persist into Wednesday morning.

Hazardous Weather Outlook Graphic for Southern Nevada Region:

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