161 FXUS63 KLSX 041219 AFDLSX AREA FORECAST DISCUSSION...UPDATED AVIATION NATIONAL WEATHER SERVICE ST LOUIS MO 619 AM CST Sat Jan 4 2014 .SHORT TERM: (Through Late This Afternoon) Issued at 315 AM CST Sat Jan 4 2014 (Today) A cold front is expected to move through northwestern portions of the area during the day today. By 2100 UTC...the front into portions of central and northeastern Missouri. Precipitation chances will increase over northeastern Missouri and west-central Illinois as NWP guidance is beginning to hit a band of primarily frontogentically driven snow in this region beginning very late this afternoon. Along and ahead of the front...precipitation chances should be very low. Look for a warmer day today with highs in the low 40s for most areas with the exception of the far northern CWFA where temperatures are expected to top out in the mid to upper 30s. (Saturday night - Sunday) A wave of low pressure is forecast to develop along the slowly moving baroclinic zone in response to increasing forcing for large-scale ascent as midlevel trough amplifies. Precipitation should commence behind the boundary over the area by early to mid evening. The precipitation may start briefly as rain and/or sleet over southern sections of the area...especially across southeast Missouri...before changing over to snow. Some concerns of how quick this transition may be along and south of a KFAM>>KSAR line as sleet may linger a bit longer. NAM soundings depict this scenario whereas GFS BUFKIT data would suggest a quicker changeover. Either way...this should not have a huge impact on snow totals as heavier QPF should begin later on Saturday night as potent shortwave trough approaches from the west. Synoptic scale forcing will really be on the increase by early Sunday morning. 500-hPa trough becomes neutrally to slightly negatively tilted between 1200 and 1800 UTC decreasing the wavelength with the ridge. Concurrently...UL divergence will be strengthening beneath right-entrance region of 120-kt jet streak over northwestern Indiana. In addition...model soundings as well as planar plots show strong deformation of the wind field with height...indicating low/midlevel frontogenesis suggesting banding potential/increased snow totals. Snow should end from west to east by Sunday afternoon. Although models have come into a nice agreement with both key synoptic features...i.e., track of 500-hPa vort max and weak 850-hPa circulation...model QPF output leaves lots to be desired. Leaned heavily on ECMWF and to a lesser degree the CMC GEM for both QPF and snow totals given increasing strong large-scale forcing for ascent. Believe NAM/GFS event total precipitation to be much too low...though did see latest 0600 UTC NAM is coming into better agreement with foreign global models. Plotting out track of consensus 500-hPa vorticity maxima and 850-hPa low/circulation would suggest the heavier QPF/snow totals a bit further to the NW than NWP output per Goree/Younkin/Brown techniques. Would not be surprised if highest totals end up a bit further to the northwest than currently depicted...though surge of cold air southward does suggest higher totals closer to 500-hPa vort and 850-hPa circulation. In addition...mid/upper level analysis does depict strongest forcing for large-scale ascent further to the NW as well...roughly along the I-44 corridor in Missouri and I-70 corridor in Illinois. Overall...did not make too many adjustments to previous forecast as not too much as changed over the past 12-24 hours. Six to 10 inches of snow is expected for most areas south and east of a Chamois, MO to White Hall, IL line with an area of 10-12 inches just to the southeast of downtown St. Louis. Will be upgrading vast majority of winter storm watch to a warning with exception of Cole...Callaway...Pike MO...and Pike IL where sub warning-criteria snow is expected. Further to the NW...will be issuing a winter weather advisory beginning late this afternoon through Sunday morning for 3-5 inches of snow. Wind chills will also approach -15 degrees on Sunday within portions of the advisory area due to northerly winds around 15-20 mph with gusts to 25-30 mph. (Sunday night) Main story Sunday night and beyond will be bitterly and dangerously cold temperatures. Surface temperatures will go well below zero with forecast lows ranging from -3F to -14F. Combine that with the northwest winds...and wind chill readings will be between -25 and -35 degrees for the northern half of the area. Further south...wind chills will range from -10 to -25 degrees. After coordinating with surrounding offices...will hold off on any wind chill watches/warnings for now focusing in on heavy snow event beginning tonight/Sunday. However...it does appear that this bitterly cold air will be every bit the threat to public safety as the heavy snow. Will issue an SPS highlighting this threat for the time being. Gosselin .LONG TERM: (Tonight through Friday) Issued at 315 AM CST Sat Jan 4 2014 (Monday - Friday) Forecast remains basically unchanged for this coming work week. The biggest weather story will be the cold and wind chill values Monday through Tuesday morning. Monday morning temperatures look brutal with lows around -3 in southeast Missouri down to -13 in northeast Missouri/west central Illinois. Expecting a 10 degree or less diurnal rise Monday, so highs will struggle to crack 0. This Arctic air combined with winds of 10 to 15 mph with gusts up to 25 mph will produce wind chill values ranging from -15 in southeast Missouri to -30 in northeast Missouri and west central Illinois which will persist all day Monday, Monday night, and into the first few hours of daylight Tuesday. Temperatures should moderate on Tuesday in return flow on the western periphery of the Arctic high. Should see temps rise into the teens across most of the area, and even the low 20s in central Missouri. Warm advection will continue ahead of the next shortwave Tuesday night and a strong low level jet will produce isentropic lift over the area, continuing on Wednesday. Medium range models are in pretty good agreement that there will be some kind of precip over the area Wednesday through Friday as a series of shortwaves ripples over the area and the mean flow becomes southwesterly. Thermal profiles suggest snow initially on Wednesday, but then get messy as the lower troposphere warms. Cannot rule out almost any precip type including snow, sleet, and freezing rain for a period of time Wednesday night into Thursday, but eventually it should warm up enough for just liquid rain. Carney && .AVIATION: (For the 12z TAFs through 12z Sunday Morning) Issued at 551 AM CST Sat Jan 4 2014 VFR flight conditions will prevail across the area for much of the day. However, strong low level wind shear will be present for a few more hours this morning as a 50-60kt southwesterly low level jet moves over the area. A strong cold front will push into northern Missouri later in the day, bringing MVFR ceilings with it. These lower ceilings will overspread the remainder of the area through the evening. Precipitation will develop as the front moves south and interacts with an upper level disturbance. The majority of the precipitation will fall as all snow, but there may be a brief mix of rain, sleet, and snow along and south of the I-44 corridor this evening. Flight conditions will rapidly fall to IFR tonight and stay down through Sunday morning. Specifics for KSTL: VFR flight conditions will prevail across the area for much of the day. However, strong low level wind shear will be present for a few more hours this morning as a 50-60kt southwesterly low level jet moves over the area. A strong cold front will push into northern Missouri later in the day, and is expected to move through the terminal between 03-05Z. MVFR ceilings will precede the front as precipitation develops. Expect the majority of the precipitation to fall as snow, but there may be a brief period of rain or sleet mixed in at the onset this evening. Flight conditions will rapidly fall to IFR tonight and stay down through Sunday. Expect snow to taper off and end between 18Z and 21Z Sunday. Carney && .CLIMATE: Issued at 1130 PM CST Thu Jan 2 2014 Last occurrence of a min temp of zero degrees or lower at KSTL: 0 on January 21, 2011 -5 on January 5, 1999 RECORD LOW TEMPERATURES January 3 January 6 January 7 St. Louis -12/1879 -11/1884 -14/1912 Columbia -11/1919 -12/1912 -20/1912 Quincy -16/1904 -9/1970 -19/1912 RECORD LOW MAXIMUM TEMPERATURES January 3 January 6 January 7 St. Louis 1/1879 0/1912 0/1912 Columbia -3/1919 -3/1912 2/1912 Quincy 4/1911 -3/1912 -2/1912 Phillipson && .PRELIMINARY POINT TEMPS/POPS: Saint Louis 41 13 16 -7 / 20 100 100 10 Quincy 35 6 8 -14 / 50 100 60 5 Columbia 39 10 10 -10 / 30 100 70 5 Jefferson City 41 12 13 -7 / 30 100 70 5 Salem 38 20 24 -9 / 5 100 100 20 Farmington 41 17 21 -6 / 10 100 100 10 && .LSX WATCHES/WARNINGS/ADVISORIES: MO...WINTER STORM WARNING from Midnight tonight to 3 PM CST Sunday FOR Crawford MO-Iron MO-Jefferson MO-Madison MO-Reynolds MO- St. Francois MO-Ste. Genevieve MO-Washington MO. WINTER STORM WARNING from 9 PM this evening to Noon CST Sunday FOR Franklin MO-Gasconade MO-Lincoln MO-Montgomery MO-Osage MO-St. Charles MO-St. Louis City MO-St. Louis MO-Warren MO. WINTER WEATHER ADVISORY from 3 PM this afternoon to 9 AM CST Sunday FOR Audrain MO-Boone MO-Callaway MO-Cole MO-Knox MO- Lewis MO-Marion MO-Moniteau MO-Monroe MO-Pike MO-Ralls MO- Shelby MO. IL...WINTER STORM WARNING from Midnight tonight to 3 PM CST Sunday FOR Bond IL-Clinton IL-Fayette IL-Marion IL-Monroe IL- Montgomery IL-Randolph IL-St. Clair IL-Washington IL. WINTER STORM WARNING from 9 PM this evening to Noon CST Sunday FOR Calhoun IL-Greene IL-Jersey IL-Macoupin IL-Madison IL. WINTER WEATHER ADVISORY from 3 PM this afternoon to 9 AM CST Sunday FOR Adams IL-Brown IL-Pike IL. && $$ WFO LSX