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The moisture and upper-level energy will aid in producing showers and thunderstorms over parts of the Western Gulf Coast/Southern Plains that will begin to expand eastward into the Lower Mississippi Valley by Tuesday morning.
On Tuesday, the showers and thunderstorms will continue to expand eastward into parts of the Tennessee Valley/Southeast well into Wednesday morning.
Rain and snow will develop along and near the boundary from the Northeast to the Upper Midwest that will end over the Upper Midwest by Tuesday morning. MODELS CONTINUE TO LOCK ON TO A SIGNIFICANT AMPLIFICATION OF THE FLOW PATTERN THROUGH CHRISTMAS MORNING - RIDGE EXTENDING FROM THE WEST COAST TO THE ARCTIC AND A MEAN TROUGH FROM THE HUDSON BAY AREA TO THE DESERT SOUTHWEST/MEXICO.The snow will taper off to snow showers over the Upper Great Lakes and parts of Northern New England by Wednesday morning. THIS SETUP WILL FAVOR COLD AIR TO SURGE SOUTHWARD...Ziegenfelder Graphics available at gov/basicwx/basicwx_EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1102 AM EST MON DEC 18 2017 VALID 12Z THU DEC 21 2017 - 12Z MON DEC 25 2017 ... WHICH WILL CREATE A SHARP THERMAL GRADIENT ACROSS THE SOUTHERN TIER STATES AS WARM, MOIST AIR LIFTS NORTHWARD (THANKS TO A STRENGTHENING SUB-TROPICAL RIDGE OFFSHORE THE SOUTHEAST COAST).If you are in the path of a storm you should be listening to official information sources.Blog NWS: Fire Weather Threat Continues in California; Wintry Conditions in Northern Rockies, Great Lakes & Northeast Gusty winds and low humidity will again result in elevated to critical fire weather conditions across portions of California through the weekend.