Friday, February 25, 2011

Two Different Cyclones and Ongoing Forecast Challenges

Today provides an excellent opportunity to examine the differences between a western US "Intermountain" cyclone and an eastern US cyclone.

Radar composite with RUC2 sea level pressure (white contours)
and 850-mb temperature (red contours) at 1400 UTC 25 Feb 2011
In the eastern United States, the cyclone is an event.  Midlatitude cyclones are responsible for much of the cool-season precipitation in the east, including most of the major winter storms.  The precipitation shield accompanying today's cyclone is extensive, although those with a good eye may notice that to the south of the low center, precipitation is falling well ahead of the surface cold front.  This is not unusual in this part of the world and indeed overnight a very impressive pre-frontal squall line with numerous severe weather reports rumbled through the southeast.

In contrast, your Intermountain cyclone is a sub-synoptic-scale event.  The frontal structure is presently quite disorganized, although that will change during the day today.  Further, orography is presently playing a dominant role in the precipitation distribution, with heavy precipitation over northern California.  Over the Intermountain West, precipitation is trying to organize along a frontal trough that is developing over northern Nevada and Utah.  It is this trough and its placement has caused meteorologists, especially yours truly, much consternation the past couple of days.  Forecast models have placed the frontal trough and snowband anywhere from central Utah to the Utah-Idaho border.

The observations coming in this morning are consistent with a frontal band developing over northern Utah today during Intermountain cyclogenesis.  We'll see some rain or snow showers in the Salt Lake Valley, but the strong front and snowband eventually develop near the Utah-Idaho border this evening.

As discussed ad nauseam in previous posts, the predictability of the location of the frontal band has been very low.  Nevertheless, I think we can have some confidence now that this evening the real action will be to the north of the Salt Lake Valley, but the subsequent fate of the front remains uncertain.  I'm not making any wagers for late tonight and tomorrow.

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