737 FXUS63 KMPX 281054 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 454 AM CST Sat Dec 28 2019 .SHORT TERM...(Today through Sunday) Issued at 445 AM CST Sat Dec 28 2019 A very complex weather event is about to unfold over the WFO MPX coverage area, starting this morning and lasting through the weekend and expected to cause potentially significant travel problems, especially over southwest Minnesota. The main low pressure center is still well off to the southwest, near the TX/OK Panhandles while high pressure is centered over the lower Great Lakes. Plenty of moisture is associated with this system, some brought over from the Pacific during its origin and additional added from a prolonged deep Gulf of Mexico plume. A potent upper level trough will aid in the propensity and strength of this system. The trough will be large and lumbering, making for a slow push of this low to the northeast through the weekend. Nevertheless, the system is already exhibiting a large precipitation shield which is moving over southern MN early this morning. Model profiles still show a sufficient enough warm low- level layer but different locations are showing different depths. In addition, multiple precip types are already being reported in northern IA as the precip moves north. Given temperatures in the mid-upper 20s in advance of the system then warming to the lower 30s with the precip, that alone gives rise to multiple icy p-types (sleet/freezing rain). The other complicating factor is that the overnight air temps are warming faster than the ground surface temps, which may lead to sustained icing issues through late morning. As the precip swath continues to move north in tandem with the surface low moving northeast through KS, the p-type will change to all rain for all of the WFO MPX coverage area except far western MN which will maintain a freezing rain/snow setup. Icing potential is exemplified over southwestern MN where upslope will be highest and upper divergence focused but still with a cold enough low layer to freeze the precip before reaching the ground. As such, have opted to issue an Ice Storm Warning for Redwood/Brown counties where ice accumulation is expected to range 0.25"-0.50". Going north from Yellow Medicine through Todd Counties, the Winter Storm Warning has been maintained due to the combination of icing up to around a quarter inch but also heavy snow accumulations, especially over western parts of those counties where 6-12" of snow is likely. Over the remainder of the coverage area, icing amounts (up to 0.10") and snow amounts (up to 3") will be much less so have issued a Winter Weather Advisory for much of the area to account for the mixed wintry precipitation this morning before the transition to rain. Rain will then persist tonight through tomorrow with rainfall amounts of around an inch for most areas. This could result in minor to moderate rises in rivers factoring in ice jams. The low will track through IA into MN tonight into Sunday morning, then the main surface low will shift east into WI while a cutoff low develops over MN. Colder air will slowly entrain into the system late Sunday into Sunday night, allowing for a gradual transition back to snow for the entire coverage area. Obviously this is a complex forecast where minor changes in temperature profiles or storm track/timing could result in significant differences in the precipitation types/amounts over short distances. Nevertheless, hazardous travel can be expected over much of southern and western Minnesota through the weekend. .LONG TERM...(Sunday night through Friday) Issued at 445 AM CST Sat Dec 28 2019 The transition to snow, or a mixture of snow/freezing drizzle/rain, will occur Sunday night as the storm system re- intensifies over the Great Lakes on Monday. Models are becoming more consistent with moisture wrapping around the intensifying surface low across the Great Lakes on Monday. Initially, and due to shallower moisture in the dry slot Sunday, light precipitation Sunday evening will become more steadier, along with more ice forming clouds developing as moisture deepens on Monday. There is still some uncertainties in the amount of deep moisture available and where the surface low deepens over the Great Lakes. There will still be enough moisture to consider accumulating snowfall on the back side of the storm as it deepens and moves off to the east slowly early next week. Current models support a few inches of snow across eastern Minnesota, and into west central Wisconsin as the storm system departs Monday night/early Tuesday. I wouldn't be surprised to see a Winter Weather Advisory issued for portions of eastern Minnesota, western Wisconsin on Monday once we have a better handle on the surface features and moisture depth. Otherwise, another weak frontal boundary moves across the region by Thursday. The mean flow aloft and where the air mass originates beyond Tuesday, remains more Pacific vs. Arctic. Not until next weekend, or the week of January 6th does any sign of Arctic air start to affect the Upper Midwest. The active weather beyond Monday's departing system will remain across Canada, and the deep south. Temperatures will average above normal with highs still expected to be in the 30s which is 10 degrees above normal. The lows are expected to be even milder with readings in the teens and 20s. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 1130 PM CST Fri Dec 27 2019 Conditions will rapidly deteriorate between 09-15z from southwest Minnesota, then northeast across southern/central Minnesota, as well as west central Wisconsin as moisture deepens and precipitation develops. The main concern is precipitation type, especially during the onset with temperatures well below freezing, and temperatures aloft are warm enough to melt any ice crystals. It looks as though a period of 1 to 3 hours of sleet, mixed with freezing rain, changing to freezing rain, then rain, will occur as the precipitation spread northward across the Upper Midwest. Only KAXN-KDXX will see mostly snow today, with a mixture of snow/rain, or freezing rain by the late afternoon/evening as warmer air continues to move northward ahead of the winter storm. Winds will start from the southeast, then become east/northeast and increase during the day. KMSP... The onset of the precipitation looks around 12-14Z, with a period of either sleet/snow or freezing rain as temperatures will remain below freezing through most of the morning hours. By the late morning/afternoon, any mix precipitation should become all rain, with periods of light to moderate rain through the afternoon/evening. Cigs will rapidly become IFR once the precipitation becomes widespread and heavier. I wouldn't be surprised to see an AWW issued for ice during the 12-18Z time frame. Winds will start from the southeast, become east and increase during the afternoon/evening. /OUTLOOK FOR KMSP/ Sun...MVFR/IFR with -RA, changing to -SN late. Wind Lgt & Vrbl. Mon...MVFR/IFR with -SN, Wind NW 10-20 kts. Tue...Mainly VFR. MVFR cigs possible. Wind NW 10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... WI...Winter Weather Advisory until 3 PM CST this afternoon for WIZ023>028. MN...Winter Weather Advisory until noon CST today for MNZ067-075>077- 083>085-092-093. Winter Storm Warning until 6 AM CST Monday for MNZ041-042-048. Winter Weather Advisory until 9 PM CST this evening for MNZ043>045-049>053. Winter Storm Warning until 6 AM CST Monday for MNZ047-054>056- 064. Winter Weather Advisory until 3 PM CST this afternoon for MNZ057>063-066-068>070-078. Winter Weather Advisory until 6 AM CST Sunday for MNZ065-082-091. Ice Storm Warning until 6 AM CST Sunday for MNZ073-074. && $$ SHORT TERM...JPC LONG TERM...JLT AVIATION...JLT