accumulating snow weds night/thursday??

Currently our system is spinning across mexico and will move into TX over the next 24-36 hours. the last few runs of the assorted models have moved the track of the low back further west, with the NAM being the farthest west and GFS/Euro back east with the Euro being the most consistent. HPC is also going with the Euro for now. Seems that most of the time with these split flow regimes that has the southern stream ejecting out and taking on a negative tilt. It will also depend on how far south the northern stream can dig south and if it can slow down allowing for the southern stream wave to catch it and phase with it. the earlier it can phase and the stronger it is, the farther west the low pressure will track. later phase/no phase, then the storm could run east of the Apps near the east coast.

All the models have got away for the ladder and most have a low going from northern AL up through KY/TN and then through OH/PA with the NAM taking it from west of memphis into IN then MI. if that verified then it would be slighty to west for us to get all snow, would probably go from rain to heavy snow. there is a pretty big spread between the models but hopefully by tomorrow night there will be a better agreement on the track as the northern stream energy getting sampled better with it being completely on shore.

looks to be a pretty dynamic system with it being able to draw in colder air than the previous one. I keep thinking of the 11/30/06 snowstorm that hit us pretty good with near 8 inches of snow. the NAM was the first to jump on the westward track a few days before and the other models picked up on it at the last minute. the pre-thanksgiving storm of 2004 also comes to mind as it was a setup like this with the northern stream energy running along the canada/US border and the a wave from the southern stream heading northeast. that was also forecasted by the models to end up further southeast of here but verified back northwest giving the area 4-6 inches of snow.

really dont see lack of cold air being a problem with this in the snow band, the crystal growth layers between 700-500 mb with this are pretty stinkin cold, temps range from -10 to -20C, which means good size flakes with this and the surface temps should cool rapidly with good precip rates falling into it. the snow shouldn't have any problems sticking. another thing to watch is how much moisture can be thrown back into the cold sector, GFS putting out alot of storms along the gulf coast and southeast U.S. along the CF, although im sure some of that is convective feedfack. very fun having a interesting storm to watch and forecast.

Still to early to say much about amounts but would think a general 3-6 in the defo band/trowal on the northwest side of the low. the speed of the system will not help the big accumulations. If I were to bet, id say the band ends up being from STL to ORD to western MI, would need to see more of a NW trend from the models.


Matt

two waves, second with snow.

well the first wave is moving through the area with a sfc low now on the IA/IL border southwest of the davenport area, looks almost stationary but barely moving off the northeast it looks like. we have been socked under some descent rain all afternoon as well as northwest IL, eastern IA, and southern WI. there were some thunderstorms earlier today down near macomb and still a slight chance of a rumble of thunder.

looking at upper air data off meso-analysis, the low is vertically stacked all the way up. what will be interesting to watch is what goes on around here tomorrow night into thanksgiving on thursday. the 2nd wave is still up in canada but will begin to dive southeast into the U.S. and will be in the dakotas by morning and in MN in the afternoon. this 2nd wave looks to be a tad stronger then the one moving through the area now. this will slow down the departing first low and a trough will develop and rotate around the west side of the low. it will reinforce the cold air with the upper low moving into eastern IA by late tomorrow night and bringing 850 temps down to -3 and colder.

progs are showing very nice UVV and the possibility of a trowal like feature developing tomorrow evening with the best lift setting up from eastern IA to southwest/southern WI. most models do have the defo band/trowal on them but the exact location of it is the challenge. DVN also mentioned some convective development possible due to the steep mid-level lapse rates. the question is when the changeover from rain to snow occurs. the last few runs the GFS has been a tad warmer with the boundary layer temperatures, where the NAM and EURO are colder. with as much lift associated with this system and the really cold air aloft, I would think to go with the NAM and EURO and the faster changeover, but will have to be monitored.

MKX did put out a SWS for their CWA with the possiblity of 3-4 inches of snow in a small area saying the most snow should accumulate south and west of a line from the dells down to burlington. right now think the best area for the most snow would be from the DBQ/CWI/freeport area on northeast to south of MKX but we will have to see. wouldn't be suprised to see an inch or so down this way on grassy surfaces if the band can make it this far south. some models are showing that, here is an example...

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/hiresw/12/images/hiresw_slp_048l.gif

with this being the 12hr QPF forecast

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/hiresw/12/images/hiresw_p12_048l.gif

going to interesting to see what the 0z NAM says as well as the new short range models later on. wouldn't be suprised to see a 4 inch amount somewhere if a nice band can set itself up and drop some moderate to heavy snow for a short period. nice having something exciting to watch and forecast and getting giddy with winter getting underway.



Matt