BETHLEHEM, Pa. - The risk of frost in the Lehigh Valley typically begins around the first week of October, meteorologists say. And by the end of the month, we're almost certain to have received a frost event.
Split the difference with expected timing, and it makes the region a bit of an overachiever with the upcoming weekend forecast.
"Frost will be possible"Sarah Johnson, NWS meteorologist
Temperatures should be 5 to 15 degrees below normal on Saturday, according to the National Weather Service, with daytime highs in the mid to upper 50s and a chilly breeze out of the northwest.
In an area forecast discussion, NWS meteorologist Sarah Johnson said clear skies and lighter winds should lead to efficient radiational cooling Saturday night — the process that occurs when heat escapes from the earth's surface into the atmosphere.
"Consequently, frost will be possible, especially in the southern Poconos and NW NJ. It is less certain, but still possible that patchy frost could develop in the Lehigh Valley," Johnson wrote.
How we got here
October temperatures have trended 5.8 degrees below normal so far in the Lehigh Valley.
Between Oct. 1-5, temperatures trended 13.8 degrees below normal, according to data from the Northeast Regional Climate Center — among the top 5 coldest starts to the month ever. It made the weather more comparable to places like Eureka, California, with similar temperatures usually felt in the region closer to the middle of November.
Forecasters say we have Hurricane Ian to blame.
Since the remnants of the storm moved into the region last weekend, there have been mostly soggy, unseasonable conditions. A coastal storm born from Ian parked itself just offshore and doused the Allentown area with 2.08" of rainfall on Tuesday — breaking a record for the date that had stood for almost 100 years.
The rest of the month is trending cooler than average, says meteorologist Bobby Martrich of EPAWA Weather Consulting.
Martrich laid out the four keys to frost this weekend for the Lehigh Valley, saying we need:
- Clear skies
- Temperatures in the mid 30s
- A dew point below freezing
- Light wind
'Shots of cold air' ahead
Martrich said we'll see transient shots of unseasonable air throughout the month, really making it feel like fall.
"Temperatures will likely moderate every 4 to 5 days," he said, describing a pattern like the one that finally ended our stretch of winterlike cold this week and pushed temperatures into the mid 70s on Thursday.
EPAWA's 10/6 and week ahead outlook, covering:
— Bobby Martrich | EPAWA Meteorologist ☈ (@epawawx) October 6, 2022
■ Sun returns FINALLY with warmer temperatures
■ Transient cool trough arrives over the weekend
■ Next chance(s) for rain in the next 7 dayshttps://t.co/J2f7zxzDBo
Martrich said these cold air intrusions are coming in from Canada and he expects them to continue.
Going into the 5-to-6 weeks of lead time he usually examines with weather patterns, he also didn't hesitate to suggest Halloween could be much cooler this year.
"Not like the 60-something degrees it was last year," he said.
