A so-called “Bermuda High” weather pattern is forecast to bring Baltimore's first prolonged heat wave of the season, according to the National Weather Service.
High pressure is expected to settle off the Atlantic Coast starting Wednesday, leading to mostly sunny skies for a few days and circulating up hot, humid air from the Gulf of Mexico. High pressure systems circulate clockwise.
Weather service meteorologists said that will mean hot and humid conditions with temperatures rising into the 90s, and with plenty of sunshine starting Thursday. The pattern is forecast to last through Saturday or Sunday.
According to a weather service forecast discussion:
UPPER-LEVEL HIGH PRESSURE REMAIN OVER THE REGION THURSDAY THROUGH SATURDAY WHILE BERMUDA HIGH REMAINS OVER THE ATLANTIC. HOT AND HUMID CONDITIONS ARE EXPECTED DURING THIS TIME...WHICH WILL LEAD TO THIS SEASONS FIRST HEAT WAVE. MAX TEMPS WILL REACH THE 90S ACROSS MANY LOCATIONS EACH DAY UNDER PLENTY OF SUNSHINE.
High temperatures are forecast close to or above 90 degrees Wednesday through Sunday in Baltimore, according to the weather service. Other outlets show similar forecasts, including AccuWeather.com, the Weather Channel and the Weather Underground.
Forecasts are mixed on whether some of those days will get out of the 80s, though all are calling for at least a few days in the 90s. The Weather Channel's outlook was the hottest, with highs forecast in the 90s for five straight days, reaching a peak of 95 degrees Thursday.
There is a chance such heat during the day could lead to afternoon and evening thunderstorms over that stretch, according to the weather service. A 30 percent chance of storms is forecast Sunday, but otherwise, the outlook is dry, however.
There are typically 30 days a year at or above 90 degrees in Baltimore, according to the National Climatic Data Center, with two in May and six in June in a typical year. There haven't been any yet this month at BWI Marshall Airport, though there was one in April.
Record highs this time of year are in the upper 90s in Baltimore.
BWI's last five-day stretch in the 90s was from Aug. 2 to Aug. 6 of last year.
Baltimore city officials typically declare “Code Red” heat emergencies when the heat index, which factors in both humidity and temperature, rises to 105 degrees. The heat index is forecast to reach the mid-90s this week.
Heat was a factor in 45 deaths in 2012.