Surface weather maps show high pressure over Michigan moving southeast. This will help bring more dry stable air over Maryland and the Baltimore area tonight and tomorrow. Given lots of sunshine afternoon readings are not having any trouble warming to near normal. That will be the case again tomorrow. Dew points are down into the lower to mid 50’s across the viewing area and this will support low temperatures down into the very comfortable lower 60’s tonight and tomorrow night. The high will move off to the east on Saturday and the lower level wind flow will turn back out of the south Saturday night and Sunday. Upper air maps show a well defined upper level trough or dip in the Polar Jet stream over the eastern U.S. This is helping to bring a northwest flow aloft over the viewing area. This trough will be forced to move eastward as a large upper level high in the south central U.S. expands eastward Friday and Saturday. This eastward expansion will help bring warmer temperatures on Friday and 90 plus heat for Saturday and Sunday.
Meanwhile a unusually strong upper level storm system over north central California is going to ride up and over the large upper level high during the next few days. A part of this upper level system will nose dive southeast in two pieces towards the Maryland Area. This first piece might help support some nighttime showers and thunderstorms over the region Saturday night into Sunday. The second impulse will ridge over the region later Sunday. This will support a weak cool front that should sweep through the Baltimore area Sunday night. Ahead of the front we see more opportunity for showers and thunderstorms. But the coverage might be spread out due to the weakness of the upper level features. If all goes as planned another weak high pressure area will build in across Pennsylvania into Maryland on the 4th of July. This should bring a dry and stable weather pattern for Independence Day. We see the return of moist unstable air again Tuesday night and Wednesday of next week.
Tropical storm Arlene will move into Mexico near the city of Tuxpan early tomorrow morning. The storm might become a strong tropical storm and perhaps even a minimal hurricane before making landfall well south of the U.S. Mexican border. We see no other tropical development across the Atlantic Basin through the rest of this week and through the 4th of July Weekend.