BETHLEHEM, Pa. — Big crowds are anticipated for a number of weekend events in the Lehigh Valley, but the weather may not cooperate.
Planned events around the area include Allentown’s 17th annual Blues, Brews & Barbeque, which is slated to run noon to 8 p.m. Saturday.
The Joyous at Juneteenth Festival also will be held at 3 p.m. Saturday at the ArtsQuest Center at SteelStacks in Bethlehem.
Unfortunately, the National Weather Service says “the short-term period through the weekend will be characterized by cloudy, showery, drizzly and humid conditions with below-normal temperatures.”
The latest NWS forecast discussion details a frontal boundary expected to “stall out” across the Mid Atlantic, where it will remain for the next few days.
That setup will trigger “several waves of low pressure with showers and storms” that will impact the region through early next week.
“Bermuda high pressure will then begin to take hold toward the middle of next week with increasing temperatures and daily chances of showers and storms remaining,” the forecast discussion said.
Why a stalled boundary is bad news
Stalled frontal boundaries are problematic for weather forecasters because they can lead to prolonged and somewhat unpredictable conditions.
A stalled front means the boundary between two air masses isn't moving much, and moist air repeatedly lifts along the boundary, leading to days of rain or storms in the same area.
Temperature contrasts also are very noticeable — one side of the front can be hot and humid, the other cool and damp.
Overall, forecasting challenges are plentiful as unpredictable motion and slow progression of the front makes it hard to model, with small shifts capable of dramatically changing the weather outcome.
What to expect across the region
NWS forecasters say there is “fairly low predictability” for the weekend regarding any details of timing and coverage for rain and storms.
“With that said, the daytime Saturday looks to have the highest probability of measurable rain for the entire weekend, though there will be chances of showers through the period,” the forecast discussion said.
“PWats, or precipitable water values, will be high (1.5 to 2 inches), so any robust and persistent convection that can develop will be capable of locally heavy rainfall.”
For temperatures, highs will be mainly in the mid-60s to low 70s across the region Saturday and Sunday.
Sunday is likely to be the cooler of the two days, the weather service said, noting some record coolest high temperatures could be in jeopardy.
The Lehigh Valley has yet to see a 90-degree day this year, and won't have another shot at it until late next week.
