Geopotential heights are contoured
purple every 30 gpm (geopotential meters). Isotherms are contoured red every 3 °C. Plots are standard, except water vapor mixing ratio (g vapor per kg dry air) is at bottom right.The main feature is a geopotential Low just N & E of central IL. I drew some fronts on this
map - the fronts retain their identity well above the surface. Wind shifts and strong temperature
gradients are evident at the locations of both fronts. Particularly, noTe the bulge of isotherms
over W PA behind the 850 mb front, which corresponds very well with the location of the surface
trof. The Low center is WNW of its surface position, and the fronts are likewise at a different
location; similar with the diagram to right.
I drew 2 trofs -
one extending NNE from the Low center, which the data clearly supports; and another extending
WNW from it over IA, which requires some imagination because data is lacking. The sharp wind
shift was my reasoning for supposing a trof exists here, and it corresponds well with the similar
feature on the surface chart. A prefrontal trof is also hinted @. Cold air was pouring SSEward
behind the cyclone, as the isotherms there illustrate.
Considering the general pattern, the correspondence of winds and geopotential height contours
as discussed is evident. You may notice quite significant cross-contour flow over VA & the
Carolinas. Interestingly enough, this is where friction is most significant in the region - 850
mb being much nearer the surface of the Appalachians than at other locations. The wind at SW QB
does not correspond with contours; but that could be for many reasons, including atmospheric
phenomena or a data error. A part of one relevant contour (not extremely far from the cyclone
center, though definitely not ruining the analysis) is clearly incorrect -
can you tell me which & why ?
Text and embedded images are copyright of Joseph Bartlo, though may be used with proper crediting.