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Technical Forecast Discussion for Tuesday through Thursday.

4:18AM Sunday 1/30/22

***Wintry Storm System Possible Mid-Week***

A busy week ahead in the weather department. We continue to monitor the risk for a potentially plowable accumulating snow event during what is now the Tuesday night through Thursday timeframe. This will likely come in two waves and the second wave may only occur in far southern portions of our coverage area, if it doesn’t miss south all together. Let’s tackle one at a time.

When this system was 5 to 8 days out, pretty much any model you might have chosen to look at had mid-Michigan right in the bullseye for a significant winter storm. Even with such strong model and ensemble agreement, changes can still come as things approach, and it appears that’s what we’re dealing with here.

Tuesday night into Wednesday:

The GFS and ECMWF have good agreement on this part of the forecast. Even the NAM maxed out at 84 hours is right in line as well. The first element to consider is moisture coming out of the Gulf of Mexico is rather impressive for this time of year; coming in at 200-250% of normal for early February. During the winter months when it is cold, water vapor in the troposphere is lower than it is in the summer, since colder air can’t hold as much water vapor as warmer air can. So, given these circumstances, we are anticipating being extra moist Tuesday night into Wednesday morning with PWAT values between 0.75” and 1”. This impressive moisture transport from the Gulf of Mexico into Michigan will be aided by a modest 850mb LLJ on the order of 45 to 50 knots within the strongest Low Level Jet Streak area Tuesday afternoon. As for lift, we have that as well with a cold front coming through Tuesday evening, which will be extending southward from a 992mb to 995mb Low Pressure system advancing NNE north of Lake Superior in Ontario. GFS, ECMWF, and NAM agree on this strong of a Low Pressure System developing in the left exit region of a Jet Streak extending from eastern Iowa to eastern Ontario. This is a fairly strong Low Pressure, which will tighten the pressure gradient across our area Tuesday afternoon and allow sustained winds out of the south to reach between 15 and 20 MPH. Occasional higher gusts between 25 and 30 MPH are possible, but we don’t expect anything too out of hand, since a low-level inversion around 900-950mb will make it very difficult to tap into the stronger LLJ wind speeds aloft. We expect surface temperatures to warm above freezing Tuesday afternoon as 850mb temperatures warm to the 4 to 7 degrees Celsius range. Given the cold ground and snow, the magnitude of how warm we can get will be limited, but areas with less snow on the ground would be favored to warm up the most. We also favor a Mostly Cloudy day, so not much sun comes with the southerly WAA flow. Still, highs should have no trouble warming into the upper-30s north to perhaps as warm as the mid-40s south along I-94. Another thing to consider with warm air coming over cold ground and a snowpack is fog, however given the breezy conditions expected on Tuesday afternoon, any fog issues should be minor if anything. Something that will be monitored just in case, though.

Rain should develop by late afternoon and early evening along and ahead of the cold front. Remember, we have an unusual amount of moisture in the air, so rain may be moderate. Once the cold front moves through, a transition to wet snow can be expected. There shouldn’t be any major mixing issues in between since the combination of the surface cold front moving through and evaporative cooling from moderate snow falling out of the clouds between 500-600mb should cool the entire layer quickly. Snow will likely occur behind the cold front in ana-front fashion due to weak DIV aloft within the left exit region of a 250mb Jet Stream that extends from southern Arizona to central Illinois, while also being aided by the right entrance region of the aforementioned Jet Streak responsible for our strong Low Pressure system in Ontario. As for precipitation totals, the highest amounts are favored generally across the southern half of our coverage area, particularly south and east of a Kalamazoo to Saginaw line. GFS and ECMWF are on board with a solid 0.3 to 0.5”, but the NAM suggests higher amounts of locally 0.75”+ possible. Frontogenesis aloft may setup, which would make this possible. Frontogenesis leads to locally heavier precipitation, which would lead to stronger evaporative cooling and therefore areas of locally heavy snowfall overnight. One thing the models disagree with is the timing of the rain to snow transition overnight and of course the sooner that happens the more snow we can see. This timing will need to be pinned down better in later updates as hour-by-hour specifics will be key. Several inches of snow is on the table depending on how quickly we transition. It is also very important to question how much rain we will see before transitioning. Rain to snow transitions are not ideal for driving conditions since pre-treatment cannot be applied so wet roadways turn to ice and snow falls on top. This could lead to extremely hazardous travel conditions late Tuesday night and last into the Wednesday morning commute.

Wednesday into mainly Thursday:

Solutions diverge by this timeframe. GFS and ECMWF suggest light snow and snow showers can continue for much of Wednesday, especially, once again, along and southeast of a that line from Kalamazoo to Saginaw. A few more inches are certainly possible during the day. By Wednesday night however, the snow may wind down and end. At this point, our attention turns to a strengthening area of Low Pressure developing in the TX/LA border area. This Low will form in the right entrance region of a strengthening Jet Stream and tap into Gulf Moisture. The concern is the strengthening Jet Stream, which is occurring in response to an increasing temperature gradient as a strong area of surface High Pressure advances southward out of Canada into the northern plains of the US. This high has trended stronger from 1038mb to 1042mb or so on ensemble means from both GEFS and EPS. Although the GFS continues snow on Thursday for much of our coverage area, the heaviest snow has trended southeastward. The ECMWF has made a larger adjustment southeastward to the point where it does not snow for us at all on Thursday. A stronger High Pressure would tend to want to suppress the system further south and east, so this trend makes sense. We can’t ignore the ridge over the northeastern US and northwestern Atlantic, however, which has remained fairly consistent in recent ensemble trends. Given model performance this winter and where ensemble means have trended in the latest 00Z runs on this Sunday morning, we believe it makes sense to favor the ECMWF model over the GFS in this case. We can’t throw out the GFS model completely, by any means, so trends will need to be monitored over the next 24 to 36 hours. It will also be interesting to see whether the NAM agrees with ECMWF or GFS once it comes more into view. Also during this time, GFS and ECMWF should begin to come into agreement again. We have a feeling the GFS will eventually catch on and follow the ECMWF, but again we’ll see how things look after the next few model updates. For now, the risk for the heaviest snow is now located primarily south of our coverage area across northern IN into northwest OH on Thursday. Should a further northwest solution end up unfolding, we still like the Kalamazoo to Saginaw line and points southeast to be at the highest risk within our coverage area for accumulating snow Thursday.

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