US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 459 PM EST Wed Nov 17 2021 Valid Saturday November 20 2021 - Wednesday November 24 2021 Hazards: - Heavy precipitation across portions of Northeast, Mon-Tue, Nov 22-Nov 23. - Heavy rain across portions of the Northeast, Mon-Tue, Nov 22-Nov 23. - Flooding occurring or imminent across portions of the Pacific Northwest and the Northern Great Basin. - High winds across portions of the Northeast, Mon-Tue, Nov 22-Nov 23. - Much below normal temperatures across portions of the Northern Plains, Mon, Nov 22. - Much below normal temperatures across portions of the Southeast, Tue, Nov 23. - Much below normal temperatures across portions of the Southeast, Wed, Nov 24. - Heavy precipitation across portions of the Alaska Panhandle, Sat-Sun, Nov 20-Nov 21. - High winds across portions of mainland Alaska and the Aleutians, Sat, Nov 20. - High winds across portions of the Alaska Panhandle and mainland Alaska, Sat-Sun, Nov 20-Nov 21, and Wed, Nov 24. - Much below normal temperatures across portions of mainland Alaska, Sat-Tue, Nov 20-Nov 23. Detailed Summary: The main focus for the medium range hazards period (Saturday, November 20 to Wednesday, November 24) will be the potential for a significant storm system to impact the Northeast during the busy holiday travel period. An upper-level trough will develop in the lee of the Rockies on Sunday (November 21) and deepen as it moves over the Great Lakes and to the East Coast by Tuesday (November 23). At the surface, a low pressure system will strengthen over the Great Lakes and move to the east, along or just north of the U.S.-Canadian border. Additionally, a second low pressure system is forecast to develop ahead of the trough off the Mid-Atlantic coast Monday morning (November 22) and move northward towards New England Tuesday. The combination of a warm front advecting a moist airmass northward ahead of the Great Lakes system as additional, more significant moisture streams northward ahead and around the northern side of the coastal low will promote significant, widespread precipitation in the form of heavy rain and snow on Monday and Tuesday for portions of the interior Northeast and New England. Several inches of rain are expected across coastal areas of New England, particularly for Maine where the rain will linger longer into Tuesday as the system progresses eastward. Strong, gusty winds are also likely for coastal Maine as the low strengthens, with coastal flooding possible. The heavy precipitation outlook area is included to help delineate where more of the precipitation is expected to transition to snow. Warm air advection ahead of the system as well as late arriving cold air look to hold back this transition until later in the event and keep the snow chances further inland. However, several inches of snow are possible for interior portions of New England and upstate New York, particularly for higher elevations in the mountains where totals locally could exceed 6 inches. There is some difference in the guidance as to whether a closed upper-level low develops on Wednesday (November 24), and if precipitation lingers on the backside of the system. Additional snow is possible, especially for northern portions of interior New England and upstate New York. However, there is currently not enough confidence in significant snow on Wednesday to extend the heavy precipitation outlook area. Although the exact timing and location of heavy rain and snow totals may change as the event approaches, the trend in the model guidance for widespread, significant precipitation for the region has remained relatively consistent. On the backside of the upper-level trough, several surges of cold, Canadian air will move southward over the Northern Plains and Midwest accompanied by some strong winds. While temperatures will be chilly and winds may be gusty, the expectation is that they should not be significant enough over a widespread area to be considered hazardous. The exception will be Monday morning, when temperatures are expected to fall to near 0 degrees for portions of eastern North Dakota and northwestern Minnesota. These frigid temperatures, along with gusty winds, will combine to create hazardous below-zero wind chills, and a Much Below Normal Temperatures outlook area was introduced. Meanwhile, a cold front extending southwestward from the Great Lakes system will also advect cold air into the Southeast. An area of high pressure will develop behind the front, leading to calm, dry nights and chilly morning lows. Temperatures will likely fall below freezing and into the upper 20s Tuesday morning from the South Carolina Midlands west through central and northern portions of Georgia, Alabama, and Mississippi. Many of these areas still have vegetation susceptible to freezes and a Much Below Normal Temperatures Outlook area was retained to address this hazardous cold. An additional outlook area was included for Wednesday morning as the freezing morning lows spread further southeastward into the Lowcountry of South Carolina and southern Georgia. These lows are up to 12 degrees below normal for this time of year. Widespread rain is also likely ahead of the cold front moving from the Plains into the Southeast as Gulf moisture streams northward, particularly across the Tennessee and Ohio Valleys on Sunday (November 21). However, the cold front should move through the region quickly and any heavier rain totals are expected to remain isolated. Another storm system is forecast to move east across the Southern Plains and into the Mississippi Valley on Wednesday. There are some indications in the model guidance that widespread heavy rain could occur. However, will defer introducing an outlook area to later forecasts when there is more model consistency for this potential. In Alaska, the overall weather pattern looks to remain consistent through the period, with a storm system moving northeast from the Pacific into the Gulf of Alaska and eventually onshore across the Panhandle. Strong, gusty winds are likely ahead of the system along the coast from the Aleutians east to the Panhandle on Saturday. The gusty winds will continue Sunday for the Panhandle as the system moves further into the Gulf of Alaska. Gusty winds are also likely again on Wednesday as a cold front moves across the region. Additionally, moisture streaming northward along a warm front ahead of the system will lead to several days of heavy precipitation in the form of mountain snow and lower elevation rain and snow for the Panhandle. Heavier precipitation appears most likely on Saturday and Sunday, but may continue to remain heavy as the system moves onshore. To the north of the system, high pressure will remain in place across inland portions of the state. Much below normal temperatures are expected to continue through at least Tuesday, particularly for the Southwest where highs around 0 and lows well below 0 are up to 20 to 30 degrees below normal for this time of year. Putnam