A front extending from the Northern High Plains to the Great Basin will merge with a front extending from the Upper Great Lakes to the Southern High Plains overnight Wednesday, moving to the Southern Plains and Southwest by Thursday evening.
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The western boundary will produce coastal rain with embedded thunderstorms and snow over the Cascades through Wednesday morning.
Snow will also develop over parts of the Northern Intermountain Region, Great Basin, and Northern Rockies Through Wednesday morning.
On Wednesday, an upper-level low will develop over the Great Basin.
The upper-level low will draw moisture northwestward from the Gulf of Mexico.
Heavy snow will begin to develop over parts of the Central Rockies Wednesday afternoon into evening.
Furthermore, the significant and long-duration winter storm will develop across the Central and Southern Rockies beginning Wednesday, followed by a round of heavy snow for the Southern Rockies and Four Corners region Thursday night.
Further, snow probabilities are high (greater than 70% chance) for at least 1 foot for most of the Colorado Rockies, the Front Range Mountains, the Foothills, and the Palmer Divide.
Localized higher amounts are expected and could exceed 2 feet across the Front Range Mountains (30-50% chance).
Confidence is also increasing for a significant snowfall for the I-25 corridor and snow probabilities for at least 8 inches are high (greater than 70% chance).
A second phase of the winter storm will impact the Four Corners Region beginning Thursday night.
Waves of heavy snow will impact the terrain areas north of the Mogollon Rim and northeast toward the San Juans and southern Colorado Rockies.
Snow probabilities for 8 inches are moderate to high (greater than 50%).
Localized totals above a foot are possible for the higher terrain.
Hazardous to very difficult travel is expected as heavy snow and intense snow rates at times (1-2 inches plus per hour) will lead to deteriorating travel conditions beginning Wednesday and Wednesday night across the Central/Southern Rockies and beginning across the Four Corners region Thursday night.
Moreover, on Wednesday evening, as the front begins to merge with the Eastern Front, showers and severe thunderstorms will develop over parts of the Central Plains/Middle Mississippi Valley.
Therefore, the SPC has issued a Slight Risk (level 2/5) of severe thunderstorms over parts of the Central Plains/Middle Mississippi Valley from Wednesday through Thursday morning.
The hazards associated with these thunderstorms are frequent lightning, severe thunderstorm wind gusts, hail, and a few tornadoes.
Additionally, there is an increased threat of hail two inches or greater over parts of the area.
Furthermore, overnight Wednesday, showers and thunderstorms will expand along the front from the Central Plains/Middle Mississippi Valley into the Ohio Valley/Great Lakes and extend into parts of the Southern Plains/Lower Mississippi Valley.
On Thursday, showers and severe thunderstorms will extend from the Middle Mississippi Valley to the Southern Plains/Lower Mississippi Valley.
Therefore, the SPC has issued a Slight Risk (level 2/5) of severe thunderstorms over parts of the Middle Mississippi Valley to the Southern Plains/Lower Mississippi Valley on Thursday.
The hazards associated with these thunderstorms are frequent lightning, severe thunderstorm wind gusts, hail, and a few tornadoes.
The showers and thunderstorms will also have heavy rain associated with the precipitation.
Therefore, the WPC has issued a Slight Risk (level 2/4) of excessive rainfall over parts of the Southern Plains/Lower Mississippi Valley on Thursday.
The associated heavy rain will create mainly localized areas of flash flooding, with urban areas, roads, and small streams the most vulnerable. ■