Dalfy

...While there could be some brief rain at the onset of snow for areas from central MO into southwest IL and points south, I still think that this should be brief with low levels cooling rather quickly... 0z Nam and other short term guidance has been keeping surface and lower levels warmer in St. Louis area compared to previous runs. I'd like to see what other runs show but I'm worried about the assumption of quick cooling in this area.

Here's the LSX AFD for those in eastern MO and west central iL. FXUS63 KLSX 132351 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 551 PM CST Thu Jan 13 2022 .SHORT TERM... (Through Saturday Night) Issued at 259 PM CST Thu Jan 13 2022 ...Winter Storm on track for Friday Afternoon-Saturday... It`s currently the calm before the storm across the CWA with lots of sun and above normal temps. The pockets of light rain across parts of eastern MO and western IL exited by early afternoon with clouds clearing quickly. This evening looks pretty tranquil with colder air filtering into the region as high pressure settles southeastward. Much of the latest guidance is showing a fairly strong signal for low stratus and fog developing overnight from central IL west-southwestward into western IL and parts of eastern MO. In fact some of the guidance suggests that the fog could be dense in the 10-15z time frame. I am not that confident in the dense fog aspect but it is something we will have to watch. The remainder of Friday morning should be rather tranquil with clouds thickening ahead of the winter storm. All systems still appear go for a winter storm impacting the area starting Friday afternoon and lasting possibly into early Saturday evening. This will be the first real widespread snowfall impacting the entire CWA. There are still some questions on amounts and onset times but the majority of the guidance suggest that snow will develop sometime in the afternoon across Northwest Missouri and west central IL in response to isentropic lift, weak large scale forcing, and impressive mid level frontogenetic forcing. This should lead to a rather robust and wide band of snow driven strongly by frontogenesis. The band should then widen and translate slowly south-southeastward on Friday Night and into Saturday morning as both the frontogenesis and large scale forcing attendant with the upper trof/low centered in the Plains digs southeastward. The mid level lapse rates are 6+ DegC/km suggesting a good response to the frontogenetic forcing and supporting snowfall rates in excess of a half inch per hour at times. While there could be some brief rain at the onset of snow for areas from central MO into southwest IL and points south, I still think that this should be brief with low levels cooling rather quickly. This will be a fairly wet snow with lower than normal SLRs. The longevity of the snow in the north and intensity of the forcing still highlights this region for the highest amounts. The WPC forecasts, HREF, and probabilistic guidance all support this area having potential for 6+ inches. We have decided to issue a winter storm watch for this area starting on Friday afternoon. For the remainder of the area this looks like a pretty solid 2-5 inch snowfall and will eventually lead to an advisory within the next 12-18 hours. There has been some concern about a period of heavy snowfall late Saturday afternoon/night into early Sunday morning across southeast MO/southern IL associated with the upper low and deepening cyclone as it tracks to our south. The trend in the latest ensemble and deterministic models now has the upper low digging longer and to the east of the track yesterday, and not bottoming out until Saturday night well south across the lower MS Valley and then shifting east across the deep south. This track would suggest this snow threat then will be well south of the CWA. Glass

A really satisfying trace fell, that's all I needed to enjoy my late spring walk haha. Looks great on the flowers and trees. Temp is 34.

All snow in STL, 4 hours ahead of schedule with the changeover lol. Temp is 35.

Or fill in around south central illinois. Reminds me of the classic DC snow hole

GFS continues its tease

Time sensitive:

Laramie WY webcam:

STL had a pretty intense band set up about an hr ago - ~25-30dbz. We're back down to light snow. Our AFD mentions up to an inch in our metro associated with the area of lift. [on an unrelated note: I'm really trying to expand my knowledge of some of these terms they use in the AFD - frontogenesis, isentropic lift. I'm not in any math heavy fields, and I looked through the weather 101 forum without much avail to find a conceptually-focused guides that could help me interpret better. If anyone has any good, beginner-friendly sources I'm all ears and open hands]

Very nice discussion by STL crew regarding the final days of the arctic air mass: .LONG TERM... (Thursday through Monday) Issued at 426 AM CST Tue Feb 16 2021 Deterministic guidance is now in good agreement for Thursday. Where in past runs there were a range of solutions, some producing another significant snow storm for the area, the latest GFS and ECMWF both keep the entire area dry on Thursday as the trough aloft continues to dig into the Gulf of Mexico, resulting in low level cyclogenesis along the coast. The Mid Mississippi Valley is too far back into the cold/dry Arctic air on Thursday. Even the GEFS >0.01 QPF probability map has only 10-20% over our far southern counties, and the more likely chances down across the Bootheel. I did leave some token slight chance PoPs in for parts of the area on Thursday to cover those very low chances in the ensemble, but if the trend continues we`ll be able to pull those by this afternoon. The remainder of the forecast will be characterized by a warming trend into the weekend and early next week as the upper level pattern shifts. The persistent eddy in the northern stream that`s been hanging over the CONUS and keeping us locked in such a cold surface pattern over the past week will finally fill in and move east. This pattern shift will finally shut the door to the Arctic which had been left standing open since February 6th and temperatures will begin warming back toward normal. The snow pack will slow our moderation down somewhat, and it`s unlikely highs will get above freezing until at least Saturday. However, by Monday it could be a balmy mid to upper 40s across the area. Carney

^LOL, I can imagine after what you guys have been through.

6-7'' reports in STL city, our local office was spot on. Really enjoyed this storm!

Chicago is gone... lmao: https://www.earthcam.com/usa/illinois/chicago/field/?cam=fieldmuseum

So incredible outside. It hasn't been since, maybe 2016 that I've had the chance to walk through rates as intense as this. Visibility still very low here-maybe a few blocks worth, with a very fine-grain +SN [wind is hard to gauge since I'm deep in the city]. Temp is 3 degrees. Not sure how much we've accumulated since it's all drifted around.

Yessir. Sounds about right

Glass from STL, really interesting disco: Light snow with pockets of moderate snow cover the majority of the CWA early this morning. This snow is occurring in response to a broad region of mid level frontogenetic forcing and weak isentropic upglide, with a little added help from a weak vort max moving across MO at this time. Light snow wavering in intensity is expected to persist through mid-morning and could briefly end in some areas. The ongoing winter storm will really get going after around 15z with the greatest overall intensity centered on this afternoon. Guidance is all in good agreement showing a classical evolution per conceptual models as the upper trof currently over the southern Plains ejects northeastward and becomes negatively tilted, leading to a deepening surface low tracking from the north- central GOM through the TN Valley. Strong large scale forcing associated with the upper trof, stout mid-level frontogenetic forcing associated with a cyclonically turning branch of the warm conveyor belt, and coupled ULJs will lead to robust ascent across southeast and east central MO into west central IL. This strong ascent within a deep dendritic growth zone will result in high snowfall rates and heavy snow during the aforementioned time frame. The HREF, HRRR, and RAP all are showing snowfall rates at times of 1+ in/hr. I`m in new territory estimating the SLRs as never in my 30+ years forecasting have I dealt with a major storm with this cold of an airmass. I am using 20:1 or greater and they increase with time. This results in additional snowfall from 600 am today through midnight of 5-9 inches within the winter storm warning area, the highest amounts along an axis from near Fredericktown to Salem IL. This corridor is good agreement with well established techniques from climatologies by Goree & Younkin, Browne & Younkin, and Gosselin using the track of the 850 mb low center. The model consensus of this 850 mb low track is from central AR skirting the bootheel to just north of Louisville. Gusty winds with the tightening pressure gradient and the light fluffy nature of the snow will bring concerns for blowing and drifting. To top this off we remain in the throes of bitterly cold air and dangerous wind chills. Travel is not recommended. If you become stranded it could result in a life-threatening situation. Outside of the warning area, a solid 2-5 inch snowfall looks in order. The current winter storm warning and advisory look on target. The storm system should completely exit and area by 06-09z with bitterly cold air and dangerous wind chills continuing into Tuesday morning. A few record lows may be possible Tuesday morning and the record low maxes today will again be shattered. The wind chill warning and advisory in effect until noon Tuesday looks good as well. Tuesday is still looking like a down day with weak surface high pressure dominating. Very cold temperatures will continue. There could be some flurries around in the morning due to lingering stratus. Glass

Webcam just south of Austin, TX [1:33AM CST]. Incredible:

Nice! Looking like they'll upgrade us soon. EDIT: just happened: 6-9'' call STL metro

Glass from STL CWA, stuck to his guns in the 1pm update. It's also interesting they're the only CWA to not expand wind chill warnings south of the central portion of their forecast area. Other potential areas for concern with this forecast are exactly what the SLRs will be and whether we might be a tad low on snowfall for Monday. Given the very cold air mass, snow ratios should be high with dendrites dominating. Present thinking is that storm total snowfall amounts will range from 2-3 inches in far northeast MO and west central IL to 4-6 inches encompassing the remainder of the CWA. These totals agree well with GEFS exceedance guidance using a max SLR, and are in the 50-90th percentile of the NBM. Noteworthy is our operational NBM data looked a bit light on QPF for Monday. The winter weather advisory looks on target for this event considering the aforementioned expectations and has been expanded to include the remainder of the northern CWA.

STL's criteria is >=6 inches I believe. They haven't updated their AFD or forecast since this morning at 6, before the NW shift; they were calling 4-6'' which is under their warning criteria. "Other potential areas for concern with this forecast are exactly what the SLRs will be and whether we might be a tad low on snowfall for Monday. Given the very cold air mass, snow ratios should be high with dendrites dominating. Present thinking is that storm total snowfall amounts will range from 2-3 inches in far northeast MO and west central IL to 4-6 inches encompassing the remainder of the CWA. These totals agree well with GEFS exceedance guidance using a max SLR, and are in the 50-90th percentile of the NBM. Noteworthy is our operational NBM data looked a bit light on QPF for Monday. The winter weather advisory looks on target for this event considering the aforementioned expectations and has been expanded to include the remainder of the northern CWA."

Our AFD from yesterday: "As the main surface system passes south and east of the CWA overnight Sunday into Monday, the probability of accumulating snow ramps up mainly along and south of the I-70 corridor. Upper-level divergence from the trough and mid-level frontogenesis will couple with cold air to produce efficient snow-to-liquid ratios. By the time this system departs the CWA Monday afternoon and evening, snowfall will range from 2-5 inches along and south of the I-70 corridor. I continue to have confidence in these totals, as blended and ensemble guidance continue to focus the greatest snow potential and amounts along this corridor." Learning moment: never have significant confidence in models >48 hours out, lol.

STL's AFD. They feel confident w/ call for 2-5'' along and south of I70 within their CWA

STL's AFD

LOL, I'm glad you appreciate the humor.