Today's National Weather Service summary map looks pretty spectacular:
|Fig 1 -- NWS watches and warnings as of 2300Z, January 30, 2011.|
"NEEDLESS TO SAY THIS COULD BE A HISTORIC BLIZZARD CAPABLE OF
PARALYZING PARTS OF SOUTHEAST WISCONSIN."
Pretty powerful words. So what's the setup for this?
Right now, there is a highly amplified ridge over the west coast with broad scale troughing aloft across the eastern half of the country:
|Fig 2 -- GFS 12Z analysis of 500 mb geopotential heights and vorticity on Jan 30, 2011. From the HOOT website.|
|Fgi 3 -- GFS 60 hour forecast of 500 mb geopotential height and vorticity valid 00Z, Wednesday, Feb. 2, 2011. From the HOOT website.|
|Fig 4 -- GFS 30 hour forecast of 850mb temperatures and geopotential heights valid 18Z, Monday, Jan. 31, 2011. From the HOOT website.|
Of course, there's already very warm air to the south in Texas and along the Gulf Coast. As the cold air moves south, this is going to increase the temperature gradient across the central part of the country. You can already see how quickly the 850mb temperature changes from Nebraska into Oklahoma on the image above. This increasing temperature gradient means two things:
- Frontogenesis is going on at the low-levels--a cold front is most likely developing from Iowa down through Oklahoma at the time above.
- Based on those thermal wind arguments (yes, those again...), the increasing temperature gradients below translate to strengthening winds aloft parallel to the forming front.
|Fig 5 -- GFS 36 hour forecast of 300mb winds and geopotential height at 00Z, Tuesday, Feb 1, 2011. From the HOOT website.|
|Fig 6 -- Same as figure 5 but annotated with the four-quadrant model showing regions of convergence and divergence associated with jet streaks.|
We see that divergence regions of both of these jet streaks almost "coincide" over the same region. This is a form of a phenomenon known as "jet streak coupling", where the combined effect of multiple jet streaks can really enhance the divergence (or convergence) aloft. Of course, with this huge amount of divergence going on aloft, the pressure at the surface is going to fall rapidly:
|Fig 6 -- GFS 60 hour forecast of surface (2m) temperature, MSLP and wind barbs valid 00Z, Wednesday, Feb 2, 2011. From the HOOT website.|
But what about snowfall amounts? How cold will it get? We'll take a look at the models again tomorrow sometime and see how things are continuing to shape up. For now, just be on the lookout for a strong winter storm during the middle of this week.