Scientific Forecaster Discussion

000 fxus63 kmpx 171946 afdmpx Area forecast discussion National Weather Service Twin Cities/Chanhassen Minnesota 146 PM CST sun Feb 17 2019 Short term...(this evening through Monday night) issued at 135 PM CST sun Feb 17 2019 Light snow event to the north of an h5 low down over Iowa will slowly wind down through the afternoon as that low slowly gets sheared out and absorbed into the main flow associated with the 150-180 kt upper jet from the Texas Panhandle to western New York. Snow reports have been somewhat underwhelming when compared to what was forecast and the culprit has been the snow ratios. Weak lift in the dendritic growth zone has resulted in more a thin Needles and plates type of crystals, which has resulted in snow ratios down closer to 10:1 as opposed to up in the 18-20:1 range. Biggest nearby snow report we've seen so far was from Austin with 4.3", which is about 1-1.5" lower than we were forecasting. Another example of the next nut we have yet to crack when it comes to forecasting snowfall is determining Crystal types that will be generated and the resultant snow ratio. Not much happening the rest of the short term as we have a 1040mb high incoming. The main question tonight through Monday night is what will the extent of cloud cover be. We look to mostly clear out the mid-level clouds Monday/Monday night, but the question is how much, if any status do we see. Forecast soundings are fairly robust with their low level moisture and stratus potential, but think this is a bit overdone and we'll see partly cloudy skies on the whole Monday/Monday night. With the lower cloud cover in mind, did lower forecast lows a few degrees from the previous forecast for Monday night, though there's potential for them to be several degrees lower depending on what we see for cloud cover. Long term...(tuesday through sunday) issued at 135 PM CST sun Feb 17 2019 The anomalous longwave trough will remain over the western Continental U.S. With anomalous ridging over the southeast Continental U.S. Through this period. So, the active weather pattern will continue with mostly below normal temperatures The threat for accumulating snow continues for Tuesday night and Wednesday. This system is somewhat similar to today's on-going system with a mid-level closed low forming and aided lift from an inverted surface trough behind a surface low. With the jet becoming more meridionally-oriented, the mid-week system will have a more northerly track than today's system. This will bring more forcing over Minnesota/WI, and better potential for more widespread 3-6 inches of snowfall. There are still differences in the exact location of this system with the 17.12 GFS continuing to show the deepening surface low crossing through the Iowa/WI/IL border at 18z Wednesday and the heaviest snowfall totals over Iowa. The 17.00 European model (ecmwf) showed the deepening low trekking through southern Minnesota and thus, bringing higher snowfall amounts farther northward. The 17.12 European model (ecmwf) is in slightly better agreement with the GFS as it brings the surface low through the Minnesota/IA/WI border. However, the European model (ecmwf) solution would still bring higher snowfall amounts to southern Minnesota. A ~1026 surface high and upper-level ridging will follow the mid- week system, allowing for dry conditions on Thursday. The western Continental U.S. Trough will begin to deepen and shift eastward late Thursday and Friday. Recent model trends indicate that split flow will occur once the trough exits The Rockies. The 17.00 European model (ecmwf) developed a surface low over the Oklahoma Panhandle that continued to deepen as it lifted toward Illinois with a closed mid-level low over the Central Plains. That would bring widespread accumulating snowfall into southern Minnesota and central WI. However, the 17.12 European model (ecmwf) is more in-line with the GFS by not phasing the energy from the northern and southern streams. Both develop a surface low further to the south of the 17.00 European model (ecmwf) and only bring a shortwave trough to the northern plains. This would still provide an opportunity for accumulating snow on Saturday, but lesser amounts. Overall, model consensus indicates that there is near a 50% chance for over 0.25 inch liquid equivalent of snow between Friday night and Sunday morning. && Aviation...(for the 18z tafs through 18z Monday afternoon) issued at 1156 am CST sun Feb 17 2019 Light snow is as far north as it is going to make it today. Expect a fairly steady state in conditions through 22z before snow slowly tapers off from north to south, ending at mkt around 5z. We're seeing good drying of the low levels across central Minnesota and northwest WI to the north of the snow shield and as the snow slides south, expect the VFR conditions to drop south as well, with VFR conditions expected across most of the area late tonight through Monday morning. With a 1040mb high dropping in on Monday, expect mainly clear low level skies, though GFS/NAM soundings showing plenty of low level moist, so can't completely rule out seeing MVFR cigs Monday. Kmsp...not many changes to the going tafs, with VFR conditions expected to replace the snow as it slides south. GFS and NAM forecast soundings show potential for MVFR cigs Monday afternoon, but with a 1040mb high coming in, thinks subsidence wins out and results in a partly cloudy, though chilly president's day. /Outlook for kmsp/ Tue...mainly VFR. Wind SW 5 kts becoming southeast. Wed...IFR with snow. Wind east 5 kts. Thu...MVFR cigs. Wind west-southwest 5 kts. && Mpx watches/warnings/advisories... WI...none. Minnesota...Winter Weather Advisory until midnight CST tonight for mnz082>085-091>093. Winter Weather Advisory until 9 PM CST this evening for mnz054- 064-073>075. && $$

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