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Monday, October 20, 2025 Squall Line Potential


weatherwiz
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A vigorous shortwave trough crosses the region late Sunday night and Monday with strong cold front and triple point moving across the region Monday morning. This system will be characterized by a potent 80+ knot mlvl jet streak and 60-70+ knots of bulk shear overspreading the region to go along with steeping mid-level lapse rates associated with cooling temperatures aloft. Out ahead of the shortwave trough, a strong southerly flow will develop pumping in an unseasonably moist low-level air mass. 

The combination of an unseasonably moist low-level airmass combined with modestly steep mid-level lapse rates (~ 6.5 C/KM) should yield upwards of 250-500 J/KG of MLCAPE. Bulk shear values in excess of 60-70 knots combined with vigorous forcing will likely promote a squall line consisting of heavy rain, thunder/lightning, and strong-to-damaging wind gusts along the leading edge, moving across the region early-to-late morning Monday. Forecast soundings exhibit enough low-level turning, particularly in the vicinity of the triple point to warrant potential for a few embedded QLCS tornadoes. 

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Looks light

Could be a rumble or two
of thunder with strongest shower activity but unfavorable time of
day and shallow progged instability should limit this. Flow fields
are pretty strong, with winds around 925 mb around 50-55 kt, but
strongest jetcore is locked in a shallow inversion. Pattern looks
similar to what we tend to find in late-Fall and the early-Spring
with a strongly-forced line of downpours with brief gusty winds but
limited severe weather potential.
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The shortwave trough arrives along with a strong surface front early
Monday morning, and moves quickly offshore by mid Monday afternoon.
Guidance is in rather good agreement on the timing of the line of
heavy rain or Fine Line.  The Fine Line should be approaching
western MA/CT between 5-7 am and arriving at the I-95 corridor
between 8-11 am. The line will then be moving offshore, likely
by 1-2 pm in the afternoon. Although Fine Line will be moving
rather quickly, it will pack a punch as it moves through and
create disruptions to the morning commute. PWATS ahead of the
line will be surging to near 1.5 inches, which, combined with
the strong forcing from the shortwave, will likely result in
rain rates exceeding 1-2 inches per hour. Strong to possibly
damaging winds may also accompany the line as low-level winds
around 2kft will be approaching 50-60mph. 
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