01 February 2011

Snowtorious B.I.G. - FCST #2: 02/01 - 02/03/11

 Repost from the forecast I contributed too on Convective Addiction!!

Before we take a look at the forecast, here is what we have going on so far in regards to the major event which is in its early stages of development as we speak.

Taking a look at the water vapor imagery below, we can already see the powerful jet stream beginning to wrap around the base of the trough. This is what will eventually help the main surface low to spin up and really get the system underway. Such a process is often referred to as "cyclogenesis."
Not only is this main piece of energy beginning to ignite precipitation as shown above, but a piece of energy known as a "lead shortwave" has ejected into the Midwest and is currently setting off a round of snow across the Midwest. For these folks this can be referred to as an "opening act" before the main show arrives. You can see both pieces and their precipitation at work on the radar below.
The precipitation associated with the lead shortwave is nothing more than your typical wintry nuisance precipitation. For the remainder of the forecast we will focus on the main show, but we thought it was at least worth a mention, since the two areas of precipitation are somewhat related.

A historic, crippling and potentially deadly winter storm is preparing to take aim on a large portion of the CONUS over the next 48-72 hours. This will be a powerful winter storm with a range of hazards from SVR weather across the lower Mississippi River valley to significant wintery precipitation across the Middle and Upper Mississippi River valley extending E into the Eastern Great Lakes region and on into New England. In the cool sector significant ice accumulations of 0.50"+ and historic snowfall totals exceeding 24" (in some areas) will make this storm memorable. Snowtorious B.I.G. still looks to fulfill the hype that has surrounded its synoptic evolution for days.

The forecast models are pretty well converging on a solution, though some slight deviations in the final storm track are still possible. This storm will cause major disruptions of travel and commerce in metropolitan areas such as OKC, Dallas-Fort Worth, Wichita, Kansas City, St. Louis, Chicago, Indianapolis, Columbus and the northern NYC megalopolis region, to name just a few.

In the upper-levels of the atmosphere, a two dynamic jet cores exist with 140kt jet streaks embedded in each core. These jet streaks are associated with a stalwart shortwave that is gyrating eastward on the lee side of a large ridge that is building across the far eastern Pacific. The forcing dynamics associated with split jet cores are partially responsible for the magnanimous snowfall amounts progged for this event. Transverse circulation between the two jet cores will contribute to significant forcing for ascent that, along with a layer of warm air embedded aloft, could contribute to mesoscale banding with slantwise convection (thundersnow). In areas that experience said mesoscale banding, snowfall amounts could reach >4" per hour!
A skew-T from near Quincy, IL at midnight on Wednesday reveals this wedge of warm air aloft that could contribute to steeper lapse rates and reveals an environment favorable for thundersnow and mesoscale banding. Also, the 700 mb vertical velocity chart indicates the region downstream from the vorticity maxima that would suggest the greatest amount of ascent courtesy the exit region of the jet core (divergence zone) rounding the basal side of the trough in the area of maximum PVA.

The H5 vorticity chart shows the areas of both counterclockwise and clockwise spin. One will note the lifting upwind of the vorticity maxima, which indicates the extent of upward motion and divergence of wind associated with this strong system.

Another unusual feature of this system is strong winds aloft in the low levels of the atmosphere with as much 69 kts being progged at H85 (app. 5000 ft above the surface) NE of the 850 mb low for a winter system. These types of winds can easily mix down to the surface with heavier precipitation.

[caption id="" align="aligncenter" width="260" caption="850 mb profile midnight WED"][/caption]

As the surface low develops as forecast and begins to move NE, it will draw forth ample amounts of gulf moisture as it tracks towards the Ohio River valley (see below). The low is forecast to deepen to around 994 millibars and occlude somewhere north of the Ohio Valley on Wednesday. This will spread an area of very heavy snow and some ice along and NW of the main low pressure track.
The various ensembles show a variety of possible surface low tracks through midweek (see below).
The ample gulf moisture will facilitate seasonably strong QPF amounts (quantitative precipitation forecasts) as noted below by the HPC.
The ample isentropic lift and copious amounts of moisture will coalesce with a progged median depth dendritic growth zone of 2oo mb across parts of WC and NC IL overnight TUE-WED; dendrites will be favored where the omega maximums coalesce with ambient temperatures AOB -12C to -16 C. This will be associated with mean snow to liquid rations on the order of 13:1 to 17:1, with a notation that stronger winds will bring those numbers down.
Finally, our personal snowfall forecast appears below. Click on the map to see a larger image and view specific types and amounts of precipitation.
Forecast written by Convective Addiction's
Jesse Risley / Adam Lucio / Danny Neal
View Snowpocalypse in a larger map

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