U.S.: Western storm shifting to central part, ice, severe thunderstorms, and flooding
A strong, embedded vort max ejecting over the High Plains as upper-level heights continue to fall ahead of the approaching trough will lead to intense cyclogenesis in the lee of the Rockies.
This developing storm system will produce numerous, widespread, and impactful weather hazards in the heart of the country this week.
Both flash flooding and severe weather will be a risk in the Southern Plains east into the Lower Mississippi Valley in the warm sector of the system.
Anomalously high moisture will surge northward ahead of a cold front sweeping eastward late tonight.
Increasing shear and cooling air aloft will provide the necessary ingredients for a band of intense convection to develop along the front north to south in the Central and Southern Plains.
Some intense downpours will be possible late Monday night/early Tuesday morning that may lead to isolated instances of flash flooding, and there is a Marginal Risk of excessive rainfall (level 1/4) in effect for a north-south axis from southern Kansas south through western Oklahoma and northwest Texas.
In addition, there is a Slight Risk of severe weather (level 2/5) from the Storm Prediction Center for western Kansas and the Oklahoma Panhandle in vicinity of the surface low and beneath cooling air aloft where strong wind shear and enough CAPE could produce a few instances of severe hail, wind gusts, and a tornado or two.
The greater risk for severe weather and flash flooding will be on Tuesday as height falls with the upper-level trough begin to spread farther eastward over the Plains and additional moisture surges northward from the Gulf of Mexico contributing to higher CAPE values in the warm sector over eastern Oklahoma and Texas and into the Lower Mississippi Valley.
The line of intense convection along the cold front will continue eastward with the potential for additional isolated supercells to develop in the warm sector ahead of the line.
There is a Slight Risk of Excessive Rainfall (level 2/4) centered on the Lower Mississippi Valley as a couple rounds of rainfall between the initial supercells and convective line will produce rainfall totals between 1-2 inches, with localized areas of 2-4+ inches leading to some scattered instances of flash flooding.
In addition, there is an Enhanced Risk of severe weather (level 3/5) for far northeastern Texas and northern Louisiana where severe hail, winds, and tornadoes, including the potential for a couple strong tornadoes, will accompany any initial isolated supercells ahead of the line as well as embedded supercells within the line.
A broader Slight Risk (level 2/5) is in place for eastern Texas, southern Arkansas, Louisiana, and southwestern Mississippi.
Flash flooding and severe weather threats shift eastward to the central Gulf Coast and interior portions of the Southeast on Wednesday.
Multiple rounds of heavy convective and training rainfall are forecast to develop on Wednesday as Gulf moisture surges north and interacts with a north-south oriented cold front sweeping through the region.
The heaviest axis of rainfall is likely to occur from Louisiana through north-central Mississippi and western Tennessee.
Supercell and tornado development are also possible.
Meanwhile, cold air will continue to surge southward on the backside of the low as warm air aloft surges northward leading to widespread wintry precipitation and heavy snow for portions of the Northern and Central Plains and Upper Midwest.
Snow accumulations through Tuesday morning will generally range between 6-12 inches, centered on the Northern High Plains.
The highest snow totals are currently forecast for western South Dakota and northwestern Nebraska, where upwards of 18-24 inches is possible.
Winds will rapidly strengthen as the pressure gradient increases with the deepening low pressure center, leading to the potential for blizzard conditions in some locations.
Currently, Blizzard Warnings are in effect along and near the Front Range, though the strong, gusty winds upwards of 40-50 mph will still lead to the potential for blowing snow and significant travel impacts across the region.
Farther east, accumulating sleet and ice are also expected for portions of the eastern Dakotas into the Upper Midwest.
The current risk for the greatest ice accumulations over a tenth of an inch is forecast for the eastern Dakotas, southwestern Minnesota, and northwestern Iowa.
Some locations in the Dakotas in particular will likely see both accumulating ice and snow.
Up to a quarter inch of sleet may also fall in the aforementioned areas.
Ice Storm Warnings are in effect for parts of far northeastern South Dakota.
Temperatures in the teens and 20s will spread southward from the Northern High Plains today into the Central High Plains Tuesday and the Southern Plains by Wednesday.
Snow will continue in the west under the influence of the upper-level trough as well as a Pacific cold front continuing through the Southwest and Southern Rockies and a second frontal boundary slowly meandering southward through the Central Rockies, Great Basin, and Pacific Northwest.
The snow will begin to taper off from west to east through the day Tuesday, lingering longest in the Northern and Central Rockies.
Additional accumulations between 6-12 inches, locally higher, will be possible for the mountain ranges of the central Great Basin, Central and Southern Rockies, and Arizona.
Lower elevations will continue to see a mix of some lighter rain and snow, with little to no accumulations expected.
Temperatures will remain 10-20 degrees below average for this time of year, with highs ranging from the 20s and 30s for the Great Basin and Northern and Central Rockies, 40s for the Pacific Northwest and Southern Rockies, and 50s for California and the Southwest. ■