More snow for Monday is in the forecast – what a surprise. The usual merchants of hype have been pegging this storm as a “big one” and the typical sources of bad meteorology have been throwing out numbers or model snow maps (with the usual lame caveats) all veiled with dubious scientific explanations.
While some snow (>2″) seems like a pretty good bet (60-70% chance) – and significant snow (>6″) a somewhat lower certainty (say on the order of 20 or 30%) – here’s what we know.
The upper level disturbance responsible for Monday’s snow is still really, really, really far away. In fact it’s many hundreds of miles west of San Francisco. Drought-stricken California is about to get a doozy of a storm. Flooding, mudslides, feet of mountain snow, and maybe some hail or weak tornadoes thrown in for good measure. Cue the weather frenzy with the “this storm is coming here!” proclamations.
This is a somewhat silly way to demonstrate what will happen to this storm over the next 96 hours but here it goes anyway. This is a look at the storm at 00z Saturday (7 p.m. Friday) just off of California.
But take a look at what happens in 4 days. 96 hours can do a number on a storm! The big reservoir of cold across the northern tier of the U.S. and southern Canada is going to do a pulverize on our Pacific Storm. The upper level disturbance will go through an atmospheric meat grinder as it heads east. The piece of the Polar Vortex lurking to our north will eat this thing alive. Here’s a look at the 500mb GFS forecast valid 00z Tuesday (7 p.m. Monday).
That impressive bowling ball of energy in the Pacific has been reduced to a strung out piece of atmospheric mediocrity. Womp womp.
While not particularly intense (and pretty ugly to look at) this storm will have some things “going for it” when it reaches the east coast. To start, the storm is initially loaded with moisture. The sub-tropical Pacific is open for business with a long plume of high PWAT (precipitable water) air streaming into this thing.
The storm will be a juicy one with some remnant Pacific moisture and a bit of Gulf of Mexico moisture that gets thrown in for good measure. A very tight thermal gradient will exist between the very cold air across Quebec and the Canadian Maritimes and relatively mild air across the Carolinas. Here’s the GFS 850mb temperature anomalies showing that big gradient.
This storm won’t be a nor’easter and it won’t be intense. What it will be capable of doing is producing a relatively narrow band of heavy snow across the U.S. as it moves east. The strong temperature gradient (also known as a baroclinic zone) will promote strong lift ahead of the upper level energy moving east from the Pacific. Think of a tight baroclinic zone as giving you more bang for your buck – relatively weak upper level forcing can result in more lift through stronger frontogenesis and stronger isentropic upglide.
But, before we get too excited, this storm is fraught with caution flags.
Where the Pacific disturbance tracks and the orientation of the polar vortex will be crucial in figuring out what happens in the northeast. A wobble of the PV to the south or a change in orientation of the PV could mean curatins for significant snow. The 18z GEFS show a fair amount of spread and operational runs have shown some pretty noisy run-to-tun consistency.
The normally steadfast European model was showing a northern track yesterday with sleet/ice issues here in Connecticut and has now shifted to a southern track with us getting only clipped by the heavier snows. The European ensembles show a 30-40% of QPF exceeding 0.5″ here in Connecticut on Monday – still not a huge signal.
Odds favor a few inches of snow on Monday but beware the caution flags. Still a lot of questions on this one. I probably won’t feel comfortable throwing out any numbers until Saturday morning.