Steering flow

Clicking on the image at left will show a 24-hr animation of the stationary front over New England on Monday 21 July, 2008. It is being distorted by small mesoscale disturbances (or low pressure systems) that advect parts of the front northward and southward as they rapidly move eastward. They also trigger local showers as they pass through a given area. These mesoscale systems are in fact smaller than the large synoptic-scale systems we usually track in the other seasons. Recent animations of New England station plots and fronts can be found and the HPC surface analysis page.

These disturbances are steered over New England by the upper flow. Clicking on the image of left for 8 AM EDT Sunday 20 January 2008 shows the jet stream on a 500 mb map dipping south of the Great Lakes and across New England roughly above the stationary front described above. It is this westerly flow that guides system eastward across New England.

The 24 hr precipitation field for 8 AM Sunday through 8 AM Monday reflects the path of small scale distirbances in the steering flow. Precipitation fall in the northern U.S. follows the same curved pattern around the Great Lakes and into New England as the systems guided by the jet stream. These maps (and more) can by found at the Daily Weather Maps webpage of the HPC.