vortex95 Posted February 19, 2015 Share Posted February 19, 2015 Today's 12z NAM has the 1000-500 thickness plunging to 492 dm forBOS in 24 hours. That is the lowest I can recall for such a value at thislocation. It isn't so much it is extreme cold at lower layers as 850 tempsbottom out "only" at -20 at BOS, but the deep layer cold throughout thethickness of the column is extreme and is what makes the value what it is.-43 at 500 mb forecast BOS is about as cold as you will ever see it here. ALB gets to 489 dm and LGA 490 dm. 500 mb temp at ALB getsas low at -46! Put it this way, -50 at 500 mb in the polar/arcticregions is close to the min value expected. 500 mb heights bottom out at 498 dm over wrn ME in 21 hr fromthe 12z NAM. Not a record, for New England, but still, to see500 mb heights below 500 dm is quite rare here. No surprise with the snow squalls occurring as I type this in easternMA. That stronger Feb sun and rapid cooling aloft is leading to excellentlow level lapse rates (for this time of year). Attached is the 24 hour NAM 1000-500 thk forecast for the NEUSand the raw model output for the 12z NAM for BOS showing thevery low values . Link to comment Share on other sites More sharing options...
Ginx snewx Posted February 19, 2015 Share Posted February 19, 2015 Today's 12z NAM has the 1000-500 thickness plunging to 492 dm for BOS in 24 hours. That is the lowest I can recall for such a value at this location. It isn't so much it is extreme cold at lower layers as 850 temps bottom out "only" at -20 at BOS, but the deep layer cold throughout the thickness of the column is extreme and is what makes the value what it is. -43 at 500 mb forecast BOS is about as cold as you will ever see it here. ALB gets to 489 dm and LGA 490 dm. 500 mb temp at ALB gets as low at -46! Put it this way, -50 at 500 mb in the polar/arctic regions is close to the min value expected. 500 mb heights bottom out at 498 dm over wrn ME in 21 hr from the 12z NAM. Not a record, for New England, but still, to see 500 mb heights below 500 dm is quite rare here. No surprise with the snow squalls occurring as I type this in eastern MA. That stronger Feb sun and rapid cooling aloft is leading to excellent low level lapse rates (for this time of year). Attached is the 24 hour NAM 1000-500 thk forecast for the NEUS and the raw model output for the 12z NAM for BOS showing the very low values . great post Link to comment Share on other sites More sharing options...
Quincy Posted February 19, 2015 Share Posted February 19, 2015 Great post. The increasing sun angle is offsetting boundary layer temps to some degree, increasing lapse rates as you said. The 850mb record low for CHH/ACK in February appears to be about -25C, but -19C falls into -2SD territory. If we were getting this type of upper level cold in early January, just imagine how much colder the near-surface layer would be. Link to comment Share on other sites More sharing options...
vortex95 Posted February 19, 2015 Author Share Posted February 19, 2015 April 7 1982...850 -20 C into New England and -25 in NY? That does it for me for an extreme given the time of year! Link to comment Share on other sites More sharing options...
Roger Smith Posted February 19, 2015 Share Posted February 19, 2015 How about that very cold mid-Jan 1994 air mass? Thicknesses must have been down around mid 480s for that one. Or Feb 9 1934 but I guess that would remain somewhat speculative. Link to comment Share on other sites More sharing options...
Quincy Posted February 19, 2015 Share Posted February 19, 2015 April 7 1982...850 -20 C into New England and -25 in NY? That does it for me for an extreme given the time of year!One of the rare recorded Arctic outbreaks to make it this far south. It even affected NYC and Long Island. How about that very cold mid-Jan 1994 air mass? Thicknesses must have been down around mid 480s for that one. Or Feb 9 1934 but I guess that would remain somewhat speculative.486dm contour down into Massachusetts with -30 to -35C 850s: Link to comment Share on other sites More sharing options...
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