Significant storms impact both coasts
Active Pattern leads to a significant storms early next week:
Significant Storms are set to take place in an active pattern across the United States will bring severe weather to the Gulf Coast and Widespread rain with heavy mountain snow to the West. These frequent West Coast fronts will eventually lead to a strong system developing in the south and moving off the coast of the Northeast.
Showers and thunderstorms are expected to be widespread tonight in association with an upper level disturbance from portions of the Gulf Coast and Southeast to the Ohio valley and portions of the Great Lakes. An evolving cluster of thunderstorms bring the risk for potentially damaging wind gusts, and perhaps a tornado or two, across southeastern Alabama and portions of the western Florida Panhandle by late this evening. An increasingly organized convective system is forecast across the region and extends the Severe risk into West Central and Southwestern Georgia overnight, but this system will continue to be just disorganized enough to only cause a few severe storms. Issuance of a watch is not likely at this time. Rain will spread northeast on Friday across portions of the Mid-Atlantic and lower Great Lakes. Farther south, another round of showers and thunderstorms is expected to develop during the afternoon and evening along the Gulf Coast, some of which could once again become severe across the lower Mississippi Valley and adjacent Gulf coastal areas. Primary convective development may occur in response to strengthening low-level warm advection on the leading edge of the deeper/more favorable low-level moisture return. This is expected across parts of the northwestern Gulf of Mexico/upper Texas and Louisiana coastal areas Friday evening, northeastward through portions of southern Louisiana and central Mississippi Friday night, primarily as a risk for severe hail. By late Friday night, forcing for ascent may become strong enough southward toward southeast Louisiana/Mississippi/Alabama coastal areas, to overcome inhibition and support increasing convective development. In the presence of increasing boundary layer based instability, the risk for supercells with potential for tornadoes, in addition to large hail and damaging winds, may increase by or shortly after Saturday morning.
Meanwhile, A Pacific frontal system will move onshore along the West coast tonight, bringing widespread rain and mountain snow. As the system moves inland, snow will spread into portions of the Great Basin and Four Corners region on Friday as this system becomes one of the significant storms expected to impact the states. Winter Storm Warnings are in effect and some of the higher elevations could see as much as 4 feet of snow fall as this system passes through. For lower elevations, rain and wind will be the issue with many counties under High Wind Warnings. Some areas in this region have already seen as much as 6 inches of rain over the last few days and flooding is an issue. Scattered convective development appears possible during the day Friday, in the presence of lower/mid tropospheric warm advection. The convective layer may be sufficient for low topped supercells, with a risk for strong surface gusts and perhaps a tornado. The severe threat dies out overnight Friday but heavy snow will be possible through Saturday morning for the mountains in California as well as areas from the Mogollon Rim to the central and southern Rockies. By late Saturday into Saturday night, rain and mountain snow will begin to increase once again from central California northward along the coast as another frontal system approaches from the Northwest. Rain and snow will start first in Washington and Oregon before shifting south across California and the Rockies. Winter Storm Watches are already beginning to go into effect for this system with the forecast calling for an additional 1 to 3 feet in the higher elevations.
On Saturday, widespread showers and thunderstorms are once again expected from the Gulf Coast and lower Mississippi valley to the Southeast along and ahead of a developing warm front. Some storms could become severe by Saturday night and Sunday morning as the trough that’s currently moving onto the west coast shifts east across the Southern Plains by Saturday evening. Any storms that form here will do so in an environment with steep midlevel lapse rates, moderate buoyancy, and sufficient deep-layer shear for supercells capable of producing large hail (potentially some very large) and damaging winds. The stronger low-level wind profiles are expected farther east and overnight in association with a lead speed max progressing inland from the Gulf. Enhancement to low-level shear from south and southeast AL into the FL Panhandle and southwest GA will favor supercells with damaging winds and potentially some tornado risk, depending on the details on the low-level shear and near-ground lapse rates inland. The Storm Prediction Center has given this area a slight risk at this time but I expect that this will increase as the forecast period gets closer.
Model guidance continues to show a fair amount of uncertainty with the significant storms at the end of this weekend. The system will be lifting from the Lower Mississippi Valley to the Northeast early next week and could potentially become a significant east coast storm, bringing severe weather to the Southeast and heavy precipitation through New England as the next system moves on shore from the pacific. The timing and strength of the significant storms has below average confidence at this time, but that will improve as we get a better look at the storm systems involved as they move over land. There is likely to be a large number of people who will see rain or snow to start next week.
Rob