Late-Christmas week storm to impact a large part of the country

Firsthand Weather is tracking a potent storm system that will impact much of the Southwest late-Christmas week, with impacts spreading north & east into the Plains over the weekend followed by impacts across the East by early next week. A huge dip in the jet stream will develop by mid-week across the eastern Pacific with the development of a potent upper-level low.

Figure 1: Big dip in the jet stream by mid-week across west

The initial impacts will begin across southern California late-Christmas day. Heavy valley & coastal rain will fall, which may lead to flash flooding. Rain amounts up to 2″ are possible. In higher elevations, above 3,500′, heavy snow will fall. The high deserts may pickup a couple inches of snow with close to a foot possible in the higher elevations of the mountains in southern California. Rain & snow will continue into early Friday before shifting east.

Figure 2: Precipitation totals through Friday morning

Figure 3: Snow totals through Friday

As the upper-level low moves east on Thursday, it will spread its impacts into southern Utah, Arizona, New Mexico and southern Colorado by early Friday. Heavy precipitation is likely as this low taps into adequate Pacific moisture. Valley rain of 1″ is possible with higher totals possible east of the central mountains in New Mexico. The mountains & high deserts, above 5,000′, will see heavy snow. The heaviest snow looks to impact the southern mountains of New Mexico & Arizona. Over a foot of snow is possible above 7,000′ with a couple inches down to 5,500′. Rain & snow will continue for Arizona into Saturday before ending by late in the day with precipitation continuing across New Mexico & southern Colorado into Sunday morning.

Figure 4: Precipitation totals through Sunday

Figure 5: Snow totals through Sunday

The upper-level low ejects northeast on Saturday into the Plains. The low will begin to slightly weaken and may open up into a strong wave. There are still questions about the magnitude of the weakening, which throws a wrench into the forecast. Two other variables add to this confusion: the timing and track. All three of these will have significant impacts on the forecast. Regardless, showers & storm are likely for a large part of Texas, Oklahoma, Louisiana, Arkansas, Missouri, Kansas and Illinois on Saturday. It is possible on the northern shield of the rain & storms, snow will begin to mix in. The best snow hazard exists across the Texas Panhandle, northwestern Oklahoma and Kansas. It is possible snow may shift farther north into Nebraska & Iowa, if the system track farther north. Also, shower & storm chances will increase on Sunday for Mississippi, Tennessee, and Alabama as this system drags a cold front into the South. Rain totals of 0.50″-1.00″ look possible. It is too early to evaluate snow accumulations in this region, but an area of heavy snow (several inches) may setup in the aforementioned areas.

Figure 6: Dip in jet stream advances east into central parts of the country by the weekend

Figure 7: Precipitation totals through Monday for the Southern Plains

Figure 8: Precipitation totals through Monday for Plains & Midwest

Figure 9: Snow totals through Monday for Southern Plains

Sunday into early week, the precipitation will spread into the Northeast & Southeast. Cold air will be largely lacking across the Northeast but snow is possible for Maine with a mixture of wintry precipitation in Vermont, New Hampshire and eastern New York on Sunday. Shower & thunderstorm chances increase for Georgia and the Carolinas on Monday and continue throughout the day. Widespread 1-3″ of rain possible across the Southeast from late Sunday through early Tuesday.

Figure 10: Dip in jet stream moves to East Coast by early week

Figure 11: Precipitation totals through Tuesday morning for Southeast

Figure 12: Precipitation totals through Monday for Northeast

It should be noted: the graphics provided are strictly output from the European model to paint a general idea of the upcoming storm system & weather pattern. It is generally not recommended to use one model verbatim. The European does appear to be handing this pattern decently well, however, changes will be needed throughout the week so keep checking back for updates.