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The NAM and GFS models differ on the potential for thunderstorms this upcoming week based on how each handles the magnitude and timing of events.

According to the NAM the best thunderstorm potential this week looks like Tuesday afternoon rather than Wednesday. This is the SPC Day 3 convective outlook for Tuesday:day3otlk_0830

As indicated by the shading the Piedmonts of NC and VA are delineated with at least general thunderstorm potential. This morning’s 12Z NAM output takes that potential to another level with this EHI outlook for 7 pm Tuesday (courtesy of Pivotal Weather):ehi03-us_ma

In conjunction with this surface map the NAM model sounding for Southside Virginia late Tuesday afternoon hints at enough instability and shear for severe weather to be somewhat likely. This is due to the NAM’s tendency to be very aggressive at pumping Gulf moisture northward, resulting in higher dewpoints further north than the GFS.

Meanwhile the GFS – with its more conservative moisture return – doesn’t show the same severe potential for Tuesday. But interestingly enough it has slowed down Wednesday’s cold front passage as an approaching shortwave trough spawns low pressure over the NC and VA Piedmonts late that afternoon:sfctd_b-us_ma Thus the GFS holds thunderstorm potential – albeit VERY slight – for Wednesday afternoon vs. Tuesday afternoon. The backing surface winds around such a low pressure center could providing interesting helicity values such that rotating updrafts could materialize…that is, if enough surface instability is present.

It’ll be interesting to see how the short range models (RAP, HRRR, and the WRF suite) handle this setup. Chasing potential in February is always something to take notice of as an antidote for rampant SDS (supercell deprivation syndrome).

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