Early-Season Cold Front Bringing Big Changes This Week

Jonathan Belles
Published: September 28, 2017

A cold front is slicing across the country, bringing several big changes wrapping up the last week of September.

Backed by a robust branch of the jet stream located over the northern tier of the country, a cold front is driving much cooler temperatures through the Northeast, mid-Atlantic and Southeast. Farther west, this cold front will be left to sag in portions of the southern Plains.

(MAPS: Weekly Planner)

The upper-level pattern will switch to a trough, or southward dip in the jet stream, over the East and ridge, or northward bulge of the jet stream, over the West by late week.

Here are two things that you should know about this cold front.

1. A Southern Plains and Rockies Flood Threat

The cold front is pooling deep tropical moisture to bring several rounds of heavy rain into parts of the Plains and Rockies.

The threat for additional heavy rain through much of this week will focus on the Rio Grande Valley of Texas and New Mexico, where another 1 to 3 inches of rain may fall through Friday. 

(INTERACTIVE: Regional Radar Loop)

Locally higher amounts may fall quickly where clusters of thunderstorms stall, triggering local flash flooding.

Rainfall Forecast

Flash flooding was reported Wednesday in the Texas Big Bend. Water-covered roads were reported in several spots around Batesville, Texas, and Highway 55 was impassable near Montell, Texas.

There were numerous reports of flash flooding on Tuesday, including in Midland and Odessa, Texas. Tuesday night, water rescues occurred in Laredo, Texas, where more than 5 inches of rain fell in one day. Near Laredo, from Monday into early Wednesday morning, over 10 inches of rain was reported. For perspective, Laredo receives just over 20 inches of rain in an average year.

2. Current Summerlike Heat Wave is Slowly Coming to an End for Some

The early-fall cool front is shoving summerlike heat southward for now, but by this weekend, 90s will be vanquished everywhere except the immediate northern Gulf Coast. Even there, temperatures will be within five degrees of average.

(MAPS: Current Temperatures10-Day Forecast)

The Forecast Into Next Week

Behind the front, it will finally begin to feel more like autumn as the jet stream kicks out the upper-level high-pressure dome.

Temperatures will generally be near average for the Midwest, Northeast and South, with cooler-than-average conditions in parts of the Plains. This translates to highs in the 60s and 70s for most areas east of the Rockies, but 80s in portions of the South.

(MORE: La Niña May Develop by Fall or Winter)

This change will lead to some big temperature drops. New York City will see a noticeable change, with highs in the upper 80s on Wednesday falling into the lower 70s or even upper 60s by this weekend. A number of records were set in the Northeast and Midwest prior to the arrival of this cold front.

More than a dozen daily record highs were set Wednesday from the Midwest to the Northeast. These included Louisville, Kentucky (92); Columbus, Ohio (92); Pittsburgh (91); Harrisburg, Pennsylvania (91); Allentown, Pennsylvania (91); Scranton, Pennsylvania (91); Syracuse, New York (91); Rochester, New York (91); Burlington, Vermont (90); Concord, New Hampshire (90); Cincinnati (90) and Boston (86).

When temperatures are falling somewhere in the Lower 48, they are usually climbing somewhere else. In this case, the West will be warming up.

An upper-level ridge is building over the West Coast, and a gradual warming trend is expected on Thursday and Friday. As this ridge continues to build over the West, temperatures are expected to be slightly above average in the Northwest and closer to average for this time of year in the remainder of the region by late week.

This warm-up won't last long, up to three days in most spots, with the most anomalous temperatures occurring in the Pacific Northwest and northern Rockies on Thursday.

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