Projecting Maximum Intensity of Today’s Southeast U.S. Squall Line

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Highlight: Projecting max intensity of today’s South U.S. squall line, why so cold in the Northeast and a much warmer 11-15-day midday forecast.

Fig. 1-2: HRRR model projects strongest cloud-to-ground lightning frequency (9PM CDT) and strongest radar reflectivity (11PM CDT) for today’s squall line.

Discussion: The ongoing severe weather event in the southern states continues to track eastward. According to the HRRR model, peak lightning intensity is around 9PM CDT near Baton Rouge, LA and northeastward to the east of Jackson, MS (Fig. 1). The maximum intensity of the squall line is at 11PM CDT stretching from just east of New Orleans northeastward to Birmingham (Fig. 2). A lot of severe weather at night – an extremely dangerous combination.

The just-ending super cold in the Northeast U.S. was caused by a classic negative phase North Atlantic oscillation (-NAO) pattern which produced a cold trough over a southeast surge of snow cover into the Interior Northeast U.S. (Fig. 3-4). The cold trough over snow cover propelled unusually cold air.

The midday 12Z GFS was slightly cooler in the East during the 6-10-day period and much warmer in the central states during the 11-15-day period (Fig. 5-6). The early April HDD forecast increases while a sharp decline is indicated for April 8-14 (Table 1).

Fig. 3-4: A classic negative North Atlantic oscillation (-NAO) pattern across a southeastward surge of snow cover into the interior Northeast U.S. caused the late season super cold.

Fig. 5-6: Midday 12Z GFS temperature anomaly forecast for the medium-range.

DatesHDD Forecast12-Hr Change24 Hours Ago10-Year NML30-Year NML
Mar. 25-31


Apr. 1-7


Apr. 8-14



 Table 1: The 12Z GFS U.S. population weight HDD forecast compared to 12 and 24 hours ago.