Heat and humidity will climb this holiday weekend

The weather has been really quiet in much of the middle of the country today, as noted by the lack of lightning this afternoon. In contrast, thunderstorms have been widespread out East from New England to Florida.

The usual daytime buildup of scattered thunderstorms is apparent up and down the mountains of the west from Idaho and Montana south to Arizona and New Mexico. Texas also has active storm areas.

Vaisala

The comfy weather that we have enjoyed for most of this week is really going to heat up as we head into the Independence Day weekend. Increases in moisture will be measured as higher dewpoints and might build into thunderstorms at times.

Here are the expected highlights from the National Weather Service.

NWS Chanhassen

Friday should bring Minnesota highs from the mid-70s to low-80s. Saturday will be a bit warmer. Sunday will be almost hot with much of the state in the 80s, and there could be a few 90-degree readings from the Twin Cities metro area south.

In fact, Sunday could be the warmest day so far this year in the metro area where our highest temperature has been 87 on May 30.

Moisture will surge in on a broad southerly flow as well. Dewpoints that have dipped into the 40s and low 50s will climb well into the 60s on Saturday and stay in the upper 60s on Sunday.

Precipitation is, as usual, the trickiest part of the forecast. It looks as though thunderstorms will blow up in the Dakotas on Friday. Some storms might build into northwestern Minnesota later in the day, but most of us will have a dry Fourth of July right through fireworks time.

Saturday will see more storms build, mainly later in the day and especially in northern Minnesota where some storms could become strong or even severe.

Forecast map for Saturday. National Oceanic and Atmospheric Administration

Sunday is quite a meteorological question mark at this time.

Forecast models are differing on the timing of a cold front from the northwest. If that front plows rather slowly across Minnesota on Sunday, scooping up muggy air on the way, the dynamics could generate numerous thunderstorms.

In that case, some storms could be severe. On the other hand, if the cold front zips along a little faster and clears out of Minnesota before significant afternoon solar heating can occur, then fewer and weaker storms should occur. As we say, stay tuned.

Hurricane Arthur

Hurricane Arthur continues to intensify and accelerate as it heads toward the protruding parts of the East Coast. This afternoon Arthur was closing in on North Carolina. It is moving toward the north-northeast at 13 mph. Maximum sustained winds are 90 mph.

Note the distinct eye that identifies it as a “warm-core cyclone” with much thermal lift but no fronts.  In contrast, our winter storm systems are “cold-core cyclones” with cold fronts and warm fronts separating air masses, but no eye.

Hurricane Arthur displays lovely spiral cloud bands. NOAA

Current forecasts call for Arthur to intensify into a Category 2 hurricane with sustained winds of approximately 100 mph before striking the North Carolina coast, especially the very vulnerable Outer Banks, tonight.

Water levels are forecast to rise three to five feet above ground level in areas adjacent to the Pamlico Sound and along oceanfront beaches.

Rising water and waves of 15 to 20 feet will cause over-wash on the Outer Banks by Friday morning, which is what occurs when the storm surge and waves wash right across the barrier island from the Atlantic Ocean to the Pamlico Sound. This action erodes beaches, washes out dunes and sometimes destroys houses and roads.

Hurricane Arthur is forecast to cross the Outer Banks of North Carolina and then head back out over the Atlantic. National Hurricane Center

Arthur will then continue to accelerate toward the northeast and brush southeastern New England late Friday. It should weaken as it approaches and then crosses the Canadian Maritime Provinces from Nova Scotia to Newfoundland on Saturday and Sunday.