Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EST Tue Dec 10 2024 Valid 12Z Tue Dec 10 2024 - 12Z Thu Dec 12 2024 ...Widespread heavy rain threat emerging across the central to eastern Gulf Coast region today will spread rapidly up the entire East Coast on Wednesday... ...Active Lake effect snows to begin Wednesday and continue through Thursday downwind of the Lakes... ...Record warm morning lows likely along the east coast Wednesday morning... ...Arctic air to surge south into the Northern Plains/Upper Mississippi Valley region late Tuesday into Wednesday... ...Santa Ana winds along with critical to extreme fire weather danger across portions of southern California... The upper-level flow pattern across much of North America will undergo significant amplification over the next few days, producing various types of impactful weather across mainland U.S. The most active weather in terms of precipitation and winds will be the primary focus along the East Coast through the next couple of days. Precipitation currently falling across portions of the Southeast is in its organizing stage ahead of a developing low pressure wave over the Mid-South along a cold front. As the cold air behind the front interacts with a rapidly amplifying upper trough, rain and embedded thunderstorms will rapidly expand northeastward during the day Wednesday and up the entire East Coast, producing a period of widespread heavy rainfall from the central to eastern Gulf coast, across the Southeast, Mid-Atlantic, Northeast and New England. With much of these areas currently in moderate to extreme drought conditions, this rainfall will be beneficial. Still, given the potential for periods of heavy rains over a short period, there will be a threat of localized flash flooding, especially in more urbanized regions. The cold front associated with this rapidly intensifying system will become rather potent as it sweeps across the East Coast during the day on Wednesday. There is potential for some very strong thunderstorms to form ahead of the front together with heavy downpours. Meanwhile, drastically colder air behind the front is forecast to produce accumulating snowfall up the western slopes of the Appalachians on Wednesday together with blustery northwesterly winds. The snow will then sweep across interior New England through Wednesday night into Thursday morning as a potent elongated low pressure system races northward into southeastern Canada. With a warm southerly flow strengthening ahead of this potent front, there is the potential for widespread record high morning low temperatures on Wednesday across the southern Mid-Atlantic, Mid-Atlantic and portions of the Northeast. In the wake of this front, much colder air will stream across the Great Lakes from west to east beginning on Wednesday. This will ignite active lake-effect snows, initially downwind of Lakes Superior and Michigan on Wednesday and then downwind of Lakes Erie and Ontario Wednesday night into early Thursday. Before these lake-effect snows diminish by early Friday, snowfall totals of 1 to 2 feet are possible in the favored Snow Belt across portions of northwest and western New York State, far northwest Pennsylvania, far northeastern Ohio, the Upper Peninsula of Michigan and the western portions of the Lower Peninsula of Michigan. The above-mentioned lake-effect snows will be driven by arctic air that will be first surging east southeastward late Tuesday into early Wednesday across the Northern Plains into the Upper Mississippi Valley and then eastward trough the Great Lakes into the Ohio Valley on Wednesday. While there are not expected to be any records with this arctic outbreak, temperatures will be much below average on Wednesday across the Northern Plains into the Upper Mississippi Valley. These much below average temperatures will then push farther southeast into the Great Lakes and Ohio Valley region on Thursday. Across these regions, high temperatures will be 10 to 25 degrees below average during the height of the cold temperatures during Wednesday and Thursday. In contrast to the wet and cold conditions across portions of the north-central to eastern U.S., dry condition and milder temperatures are in store across the West coast, Great Basin and Rockies region. The dry air, low relative humidities together with the latest episode of Santa Ana winds across southern California will produce critical to locally extreme fire weather danger. These fire weather conditions will be most prominent in the higher terrain areas to the north and east of the Los Angeles to San Diego region. Winds of 35 to 45 mph in the valleys and gusts of 50 to 65 mph in the mountains will help fan any fires that do develop quickly and may reduce visibility with blowing smoke and dust adding to travel concerns in the region. Across these areas, red flag warnings are currently in effect, affecting nearly 13 million people. By early on Thursday, the next round of coastal rain and mountain snow is forecast to reach northern California as the next Pacific cyclone arrives. Kong/Oravec Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php