Fronts Are Stronger Aloft Than At the Surface Here in the Northwest

Another strong Pacific front will come through tomorrow across western Washington State.  The temperature change will be wimpy at the surface, with a decline of only a few degrees.

But go aloft, to say 5000-10,000 ft, and major temperatures declines will occur (5-15F).

So why are fronts so wimpy at low levels around here?  The answer is below.

 Here is the forecast map for 10 AM tomorrow at 700 hPa (about 10,000 ft).  There is a trough of lower pressure along the coast (solid line), with a slug of cold air with it.  If you look closely, you will see a wind shift with the front aloft and a substantial change in temperature behind (roughly a drop from -8 to -14C, a decline of 6C or about 11F)

A map of sea level pressure and 925 hPA  (about 2500 ft) temperature at 7 AM, shows the front making landfall and a temperature drop of only a few degrees C (3-4F).

A wimpy front at low levels and a much stronger front aloft, at least in terms of temperature.  

The larger temperature changes with the front aloft are even more clear cut in a time-height cross section, which shows the temperatures (red lines), winds (barbs), and humidity (color shading) for the next few days (time increases to the left, height in pressure, with 850 being 5000 ft).  Look at the red lines (temperature)....much greater undulations aloft tomorrow (1128/12-1129/00) .

Why are the  surface temperatures variations associated with our vaunted Pacific fronts so weak around here?

Because of the influence of the vast Pacific Ocean.  At the latitude of our coast, the sea surface temperature is roughly 11 C (52F), extending for thousands of miles!

A blow up section off of our coast show 11-12C water temperatures due east of the WA Coast (below).  Cold air moves off of Asia and Alaska at all levels, but is rapidly warmed over the lower few thousand feet by the relatively warm ocean.  Over time the temperature contrasts with fronts are weakened at low levels, but remain fairly strong aloft.  Those are the fronts that reached our shores.

Want to see the process from space?  Here is a NASA MODIS satellite image from Saturday over the north Pacific.  You can see cold air streaming off of Asia to Alaska, produce lines of clouds resulting from the instability of cold air over warm water.  This process results in warming of the lower atmosphere.

from Cliff Mass Weather and Climate Blog http://ift.tt/2zJEPgp