Fig. 1: Midday 12Z GFS and the 120-hour snowfall forecast.
Discussion: The 12Z GFS indicates a long-duration snowfall event along and trailing a cold front which shifts eastward slowly this week. The snow begins tomorrow night in the south/east Great Plains and stretches to the Ohio Valley and then eastward into New England for later this week. GFS grinds out 1-2 feet of snow across this large area – which is likely excessive, but the model certainly makes its point (Fig. 1). Arctic air moves into the frontal zone to cause the wintery precipitation which (near the frontal zone) could be mainly sleet and freezing rain. A very unsettled pattern for affected areas!
The GFS is (and has been) correct with the general 15-day upper air pattern forecast (Fig. 2). An amplified ridge sits in the Northeast Pacific and is compensated for by a downstream upper trough over central North America. Consequently, the Central/East-central U.S. cold is difficult to shake.
The midday GWHDD forecast indicates a steady somewhat colder than normal forecast (nationally) for this week and next week (Table 1). The forecast for Feb. 11-17 remains colder than normal but somewhat less cold than the forecast from 24 hours ago.
Fig. 2: Midday 12Z GFS and the 15-day upper air forecast.
|Dates||HDD Forecast||12-Hr Change||24 Hours Ago||10-Year NML||30-Year NML|
|Jn. 28-Fb. 3|
Table 1: Indicated is the 12Z GFS projected gas population weight HDD for the U.S. compared to 12 and 24 hours ago through the first half of February.