Cold temperatures and overcast skies will continue to be the main weather story this week. For this afternoon, snow and light freezing drizzle are ongoing over much of mid-MO. This will likely continue into the evening, before precipitation lets up overnight and transitions mainly to scattered flurries and light pockets of freezing drizzle. Winds in the lower levels of the atmosphere will continue to be out of the north, driving temperatures further down these next few days. Another bout of snow is possible Wednesday into Thursday, and even colder air is in store towards the weekend.
Major models were doing a good job resolving the
large-scale structure of the current atmospheric regime. Thus, the NAM and GFS/GEFS were used in
this forecast for longer-range and broad pattern forecasting, with shorter range forecasting handled mostly by the SREF and RAP/HRRR.
This forecast is tricky, and much of the sensible weather at COU for the
rest of the week will be determined by small pieces of energy
passing along the polar front jet (PFJ) overhead.
At 20 UTC, a significant blocking pattern at 500-mb was noted across North America. A large occluded low was present over central Canada, per the RAP and WPC surface analysis. This occluded low was vertically-stacked and had not budged for two days. The PFJ arced southward into the central United States, setting up an active storm track.
Closer to mid-MO, a surface stationary front was shown to extend from Joplin to near Rolla. This front was associated with a small surface low centered over southern OK, which was supported aloft by a small shortwave passing through on the south side of the PFJ. Warmer and more humid air was surging northward, but progression at ground level was severely limited by potent CAA in the boundary layer. Just above the surface, however, veering profiles indicated strong WAA. This was the source for widespread light precipitation over mid-MO as of ~4:00 PM.
In the near term, models indicate that persistent WAA aloft will continue for at least more several hours. RAP isentropic analysis shows decent upglide continuing at 270 K through approximately 00 UTC, with minor upglide remaining through 08 UTC before downglide takes over and shuts off the moisture supply. Thus, light wintry precip remains likely through the early evening, with scattered snow showers and/or patchy freezing drizzle possible until 3 or 4 AM Tuesday. One concern is a lack of cloud ice, with RAP soundings showing very low saturation in the DGZ. This would lend itself to either inefficient snow production or freezing drizzle, especially once the main source of our lift moves east. In total, snowfall accumulations will likely end up between a dusting an an inch for most, with slightly higher totals possible northeast of Columbia.
For Tuesday, a cold and cloudy day is in store. The aforementioned surface low will still be skirting by to the south, but a lack of WAA overhead will keep precip chances very low. Ensemble models concur, with both the SREF and GEFS pegging the chance of precipitation on Tuesday at nearly 0%. Saturation through 850-mb will ensure ample cloud cover. Temperatures should be in the middle to upper 10s, but it is interesting to note that the SREF mean is nearly 25 degrees for Tuesday's high. Given that the SREF is currently overpredicting temperatures by about 10 degrees, it seems reasonable to go with deterministic RAP/GFS and GEFS solutions of a high somewhere between 15 and 20 degrees.
For Wednesday, deterministic guidance shows another shortwave disturbance rounding the south side of the PFJ. Cold air should be a bit more entrenched over mid-MO by then, but another broad area of isentropic upglide will likely establish itself out ahead of the approaching shortwave. The SREF is not too keen on precipitation chances, but the GEFS, deterministic GFS, NAM, and extended HRRR all support wintry precipitation. Given the similar nature of Wednesday's setup to today's, it would not be surprising to receive another trace - 1 inch of snow, with freezing drizzle possible as well. However, model soundings do show better saturation in the DGZ, which may lend itself to a more solidly-snow event with more efficient snowfall production. GEFS means are sitting at 1.5 inches for this event, which - if the moisture advection and lift are truly as strong as the GFS projects - would be doable. The only issue may come with dry air at the surface, as was seen on Saturday and Sunday. If there is a persistent dry layer (and there may be, given that CAA will be deeper on Wednesday than today), precipitation may have a hard time becoming established. Thus, we will go ahead and keep snow totals on the lower end - near or less than an inch. This will need to be monitored closely in future shifts.
Thursday, the cold pattern will continue. The aforementioned shortwave will still be in the area, affording a continued chance for snow showers into the day. The NAM is more aggressive with this than the GFS/GEFS, though snow is certainly still possible across much of the area Thursday. Arctic air will also be amassing to the north, poised to plunge into the area late this week.