Fig. 1: Projected ice, snow and severe weather areas through Thursday.
Discussion: Due to the snow on the ground across much of Texas low-level cold air will make sure that incoming air is either sleet, snow or freezing rain for the overnight into Wednesday storm. Moderate to heavy snow spreads across Oklahoma into northern Texas this evening while freezing rain and accreting ice extends eastward to central Texas by midnight and eastward to Louisiana and southern Arkansas by dawn tomorrow. Freezing rain will be most widespread and heaviest around dawn tomorrow in eastern Texas (just touching west and north suburbs of Houston) and into the northern half of Louisiana. Ice accretion of near ½ in. is possible in east-central Texas to northern Louisiana and northwest Mississippi tomorrow. To the north heavy snows pile to 4-8 in. across eastern Oklahoma and into northern half of Arkansas. Severe thunderstorms are likely tomorrow across the north-central Gulf of Mexico coast.
On Thursday the storm shifts to the Northeast States. Another major icing event is forecast for central to western Virginia to the western Carolinas where >1/2 in. accretion is possible. Snow is heavier – near one foot for Pennsylvania to interior New England on Thursday.
Canadian polar air follows the storm in the southern states with recovery to above normal by Friday. However, some residual arctic air from Canada will follow the Northeast storm for late week and into the early weekend. The cold will ease next week!
Will more cold return to the U.S. in the 11-15 day period?
Fig. 2-3: GFS ENS and ECM ENS day 11-15 temperature anomaly forecast.
Fig. 4: Temperature climatology of a strong -PNA pattern.
Discussion: At midday the GFS Operational model indicated more potential cold returning to the U.S. The following GFS Ensemble was not quite as aggressive keeping most of the big chill in Canada (Fig. 1). The ECM Ensemble is farther west with the cold air mass (Fig. 2). The leading climate signal in the upcoming pattern is the Pacific North America (PNA) index. The PNA index forecast is in the vicinity of -3.0 in the medium-range which represents a strong cooling effect on the West and very warm for the Southeast (Fig. 3). The ECM ENS is the favored 11-15 day outlook.
Today’s midday cold outlook for the West and Central U.S. was overdone. The proper 11-15 day forecast is cold in the West only as supported by the -PNA index forecast. The eastern states are spared of any cold weather in the extended-range.