Hoosier Posted December 23, 2014 Share Posted December 23, 2014 AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 309 PM CST TUE DEC 23 2014 SHORT TERM 309 PM CST SYNOPSIS... A POWERFUL LOW PRESSURE SYSTEM WILL IMPACT NORTHERN AND CENTRAL ILLINOIS AND NORTHWEST INDIANA ON CHRISTMAS EVE. DESPITE QUITE MARGINAL TEMPERATURES FOR SNOW...THE STORM IS EXPECTED TO PRODUCE INTENSE ENOUGH PRECIPITATION TO CAUSE INITIAL RAIN OR A MIX TO CHANGE OVER TO HEAVY AT TIMES WET SNOW. A FAIRLY NARROW BAND OF INTENSE SNOW IS EXPECTED. IN THIS AREA...SIGNIFICANT ACCUMULATIONS POTENTIALLY RESULTING IN SUBSTANTIAL TRAVEL IMPACTS ON A VERY BUSY TRAVEL DAY MAY OCCUR. THIS WILL INCLUDE AT LEAST PART OF THE HEART OF THE CHICAGO METRO. WHILE CONFIDENCE REMAINS ON THE LOWER SIDE WITH THIS COMPLEX SYSTEM...FELT IT WAS PRUDENT TO ISSUE A WINTER STORM WATCH FOR MUCH OF THE CHICAGO METRO WHERE THE MOST SIGNIFICANT IMPACTS COULD OCCUR. HAVE ALSO ISSUED A WINTER WEATHER ADVISORY SURROUNDING THE WATCH AREA...WHERE HAZARDOUS TRAVEL IS EXPECTED BUT SLIGHTLY LOWER SNOWFALL AMOUNTS. WINTER STORM...TONIGHT THROUGH WEDNESDAY NIGHT... SURFACE ANALYSIS SHOWS DEVELOPING LOW PRESSURE AREA ALREADY DOWN TO JUST UNDER 1000 MB NEAR NEW ORLEANS. THERE IS A SUBSTANTIAL AMOUNT OF CONVECTION NEAR THE GULF COAST AND THE TORNADO WATCH IN EFFECT THERE SHOWS THE AMOUNT OF ENERGY AND MOISTURE ASSOCIATED WITH THIS DEVELOPING SYSTEM. MOIST PLUME SURGING NORTHWARD IS QUITE EVIDENT ON WATER VAPOR IMAGERY AND WILL CONTRIBUTE TO ANOMALOUSLY HIGH PWAT VALUES ALSO FAVORABLE FOR HEAVY PRECIPITATION. MUST NOTE THAT THE AMOUNT OF CONVECTION NEAR THE GULF MAY BE PLAYING SOME HAVOC WITH UPPER LEVEL LOW EVOLUTION AND SFC LOW TRACK FORECASTS AMONGST THE VARIOUS MODELS..PARTICULARLY THE NON- CONVECTION ALLOWING GLOBAL MODELS. AS THE SURFACE LOW TRACKS NORTHWARD TONIGHT...SHARPLY DIGGING UPPER/MID LEVEL TROUGH WILL INTENSITY THANKS TO NEARLY 140 KT UPPER JET SAMPLED BY 12Z RAOB AT GJT ROUNDING THE BASE OF THE TROUGH. INTENSIFICATION OF MID LEVEL LOW WILL ALSO TRANSLATE TO DEEPENING OF SFC LOW AS IT LIFTS NORTHWARD TOWARD THE OHIO VALLEY BY DAYBREAK AND THEN LOWER MICHIGAN BY LATER IN THE DAY DOWN TO SUB 990 MB. THIS TRACK IS TYPICALLY FAVORABLE FOR HEAVY SNOW SOMEWHERE IN OUR AREA. THE HUGE QUESSTION MARK CONTINUES TO BE THE QUITE MARGINAL THERMAL PROFILES AND ALSO THE VERY MILD TEMPERATURES THIS AFTERNOON THAT ARE CAUSING WARM ROAD SURFACES. ALSO STILL HAVE A QUESTION ON SPEED/TIMING OF SFC LOW LIFTING NORTHWARD...WITH GFS ON FASTEST SIDE AND LIKELY TOO FAST...WHILE 12Z NAM WAS LIKELY A SLOW/DEEP OUTLIER. FURTHERMORE...TYPICALLY RELIABLE ECMWF SHIFTED EASTWARD TODAY...WHICH LOWERS CONFIDENCE SOME...BUT IN COLLAB WITH WPC...FELT EC WAS A FAR EAST OUTLIER. WITH ALL THIS BEING SAID...THE RAPIDLY DEEPENING CIRCULATION IS EXPECTED TO FORM A VERY IMPRESSIVE TROWAL WRAPPING AROUND IT...WITH VERY INTENSE 850-700 MB FRONTOGENESIS AND OMEGA WITHIN THIS TROWAL/DEFORMATION AXIS. INITIAL PRECIP SPREADING NORTHWARD TOWARD DAYBREAK IS LIKELY TO BE MAINLY RAIN OR A MIX...AND HAVE PRETTY GOOD CONFIDENCE IN THIS. THE KEY TIMEFRAME WILL COME AS THE MORNING PROGRESSES ONWARD...WITH RESPECT TO DYNAMIC COOLING RESPONSE FROM THE INTENSE UPWARD MOTION IN THE DEFORMATION AXIS/TROWAL. ALSO AIDING IN THIS WILL BE THE EXISTING VERY STEEP LAPSE RATES ABOVE 600 MB PLUS PRESENCE OF NEGATIVE EPV ABOVE THE FGEN...WHICH ALSO MAKE LIGHTNING STRIKES A NON-ZERO POSSIBILITY. FEEL THAT THE HIGHER RES GUIDANCE HAS A BETTER HANDLE ON THE DYNAMIC COOLING POTENTIAL AND THE HEAVY PRECIP RATES WILL FORCE A FLIP OVER TO A VERY HEAVY WET SNOW WITH TIME AND TEMPERATURES GETTING FORCED DOWN CLOSER TO FREEZING. UNFORTUNATELY FOR HOLIDAY TRAVELERS...MUCH OF THE 12Z DATA WITH THE EXCEPTION OF THE ECMWF PLACED THE CHICAGO METRO IN THE CROSS HAIRS OF THE BEST BANDING SIGNAL. CURRENT EXPECTATION IS FOR RAIN/MIX TO CHANGE TO SNOW FROM SOUTHWEST TO NORTHEAST...GENERALLY MID/LATE MORNING INTO EARLY AFTERNOON. ASSUMING CHANGEOVER OCCURS AS WE EXPECT...AREAS WITHIN THE BAND COULD SEE 1-2"+ PER HOUR SNOWFALL RATES DURING THE EARLY TO MID AFTERNOON...POTENTIALLY MAKING TRAVEL NEARLY IMPOSSIBLE. THESE RATES WILL ALSO OVERCOME THE WARM ROAD TEMPERATURES TO ENABLE ACCUMS ON SURFACES. WHILE HEAVY SNOW RATES WILL LIKELY RESULT IN PERIODS OF VISIBILITY 1/4 MILE OR LESS...GUSTY NORTH-NORTHWEST WINDS COULD CAUSE VISIBILITY ISSUES EVEN IN LIGHTER SNOW RATES DESPITE WET NATURE OF THE SNOW. THE LOCATIONS THAT SEE THE HEAVIEST SNOW COULD VERY WELL BE NARROWER THAN WHAT IS DEPICTED IN THE GRIDS. HOWEVER...AS NOTED IN SYNOPSIS...FELT IT WAS PRUDENT TO ISSUE AN IMPACT BASED WATCH FOR THE CHICAGO METRO GIVEN THE CIRCUMSTANCES. WHILE MOST LOCATIONS LIKELY WILL NOT SEE 6" OF SNOW...SOMEWHERE WITHIN THE WATCH AREA COULD END UP WITH 6"+...WITH GENERALLY 2 TO 5 INCHES IN ADVISORY AREAS. THE SYSTEM WILL LIFT OFF TO THE NORTHEAST QUICKLY DURING THE EVENING...SO MUCH OF THE ACCUMULATING SNOW SHOULD BE OVER BY THEN. OVERALL CONFIDENCE...MEDIUM. THE MODERATE TO HEAVY SNOW ACCUMULATIONS ARE CONSIDERED A MORE LIKELY SCENARIO. HOWEVER...THE BUST POTENTIAL WITH THIS SYSTEM REMAINS HIGH GIVEN LINGERING UNCERTAINTY EVEN AT THIS LATE HOUR WITH MARGINAL BOUNDARY LAYER CONDITIONS AND TRACK OF THE SURFACE LOW/HEAVIEST PRECIP. CONTINUE TO STAY TUNED FOR THE LATEST UPDATES. RC Link to comment Share on other sites More sharing options...
A-L-E-K Posted December 23, 2014 Share Posted December 23, 2014 important nugget and something i've been mentioning during the day MUST NOTE THAT THE AMOUNT OF CONVECTION NEAR THE GULF MAY BE PLAYING SOME HAVOC WITH UPPER LEVEL LOW EVOLUTION AND SFC LOW TRACK FORECASTS AMONGST THE VARIOUS MODELS..PARTICULARLY THE NON- CONVECTION ALLOWING GLOBAL MODELS. Link to comment Share on other sites More sharing options...
geddyweather Posted December 23, 2014 Share Posted December 23, 2014 Not a shock, I also wouldn't be shocked if we see some severe warnings tomorrow with the frontal band either. Now THAT would be interesting... CLE has issued a high wind watch as well. IWX staying silent. SPC 1730z, fwiw: Link to comment Share on other sites More sharing options...
Central Illinois Posted December 23, 2014 Share Posted December 23, 2014 LSX issued a WWA for St Louis and their South Central IL counties Link to comment Share on other sites More sharing options...
huronicane Posted December 23, 2014 Share Posted December 23, 2014 Rayno continues to say east is the way to go Link to comment Share on other sites More sharing options...
Brewers Posted December 23, 2014 Share Posted December 23, 2014 Milwaukee, racine and Kenosha counties under WWA for 1-3" Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Stebo Posted December 23, 2014 Share Posted December 23, 2014 Just to note, the EPS control and the Euro ensembles mostly show the snow in western Michigan with only a handful showing snow in Chicago's area and most of those are the eastern part of LOT's CWA. Link to comment Share on other sites More sharing options...
Hoosier Posted December 23, 2014 Share Posted December 23, 2014 important nugget and something i've been mentioning during the day Indeed. How it would affect things is debatable though. Sometimes the latent heat release can result in a deeper/westward system. Link to comment Share on other sites More sharing options...
Geos Posted December 23, 2014 Share Posted December 23, 2014 important nugget and something i've been mentioning during the day Yeah I caught that too. Interesting also that the SREF plumes rose area wide at 15z... now the 21z run is coming out. Link to comment Share on other sites More sharing options...
A-L-E-K Posted December 23, 2014 Share Posted December 23, 2014 Yeah I caught that too. Interesting also that the SREF plumes rose area wide at 15z... now the 21z run is coming out. i'd guess 21z will probably come back down a tad Link to comment Share on other sites More sharing options...
Thundersnow12 Posted December 23, 2014 Share Posted December 23, 2014 Always gotta question a guy with the name of Bernie. Link to comment Share on other sites More sharing options...
Hoosier Posted December 23, 2014 Share Posted December 23, 2014 IWX mentioned the convection/latent heat release. I swear I didn't plagiarize. MAIN CONCERN FOR THE LONG TERM PERIOD IS SNOWFALL AMOUNTS WITH WRAP AROUND PRECIPITATION AND THE POTENTIAL FOR WIND ADVISORY CRITERIA TO BE REACHED WEDNESDAY EVENING. MODELS HAVE COME INTO BETTER AGREEMENT TODAY WITH RESPECT TO THE LOW POSITION. 12Z GEM/GFS/EURO ALL BRING THE SURFACE LOW BETWEEN FORT WAYNE AND LIMA NEAR 18Z WEDNESDAY. 12Z NAM IS SLOWER AND THE FURTHEST WEST SOLUTION WITH A SURFACE LOW TRACK THROUGH COLUMBIA CITY NEAR 00Z. PREFER THIS WESTWARD TRACK OVER THE OTHERS DESPITE THE RECENT EASTWARD TREND OF THE MODELS. ACTUALLY WOULD NOT BE SURPRISED TO SEE THE LOW DEEPEN A BIT MORE THAN MODELED (PERHAPS 985MB) WITH A NEGATIVELY TILTING TROUGH AND A RAPIDLY DEEPENING SURFACE CYCLONE. IN ADDITION...20Z SURFACE ANALYSIS IS ALREADY ANALYZING A 998MB CLOSED CONTOUR AT THE SURFACE IN SOUTHEASTERN LOUISIANA WHICH IS A FEW MB DEEPER THAN ANY 12Z GUIDANCE INDICATED AT 18Z. HAVE BEEN WATCHING THE LARGE AREA OF CONVECTION BLOW UP ALONG THE SOUTHERN COAST TODAY TO MONITOR TRENDS FOR ANY INDICATIONS THAT LATENT HEAT RELEASE NEAR THE SURFACE LOW MAY AID IN INTENSIFICATION...BUT IT IS STILL A BIT EARLY TO TELL WHAT EFFECT...IF ANY...IT MAY HAVE. IF THE WESTERN TRACK DOES PROVE TO BE THE WINNER...A WIND ADVISORY MAY BE NECESSARY FOR THE EASTERN 1/3RD OF THE FORECAST AREA NEAR 00Z AS THE ISALLOBARIC COMPONENT OF THE WIND INCREASES WITH THE DEEPENING SURFACE REFLECTION. Link to comment Share on other sites More sharing options...
A-L-E-K Posted December 23, 2014 Share Posted December 23, 2014 IWX mentioned the convection/latent heat release. I swear I didn't plagiarize. haha, nice such a hard call but this will be a fun one to watch unfold if the stronger solution win out Link to comment Share on other sites More sharing options...
Chicago Storm Posted December 23, 2014 Author Share Posted December 23, 2014 18z GFS went a bit east as well. Link to comment Share on other sites More sharing options...
Rainman Posted December 23, 2014 Share Posted December 23, 2014 IWX mentioned the convection/latent heat release. I swear I didn't plagiarize. I like the note by IWX that models could be under-doing the strength of the cyclone...something east coast forecasters are surely familiar with. In the Midwest it is often forgotten that the collapse in scale of features/forcing that accompanies explosive cyclogenesis is often undersimulated and results in NWP being too weak. It is usually a good bet to hedge a forecast toward the deeper solutions in these cases. Just thinking out loud...carry on. Link to comment Share on other sites More sharing options...
Hoosier Posted December 23, 2014 Share Posted December 23, 2014 18z GFS went a bit east as well. Wetter in the def band it looks like. Link to comment Share on other sites More sharing options...
Hoosier Posted December 23, 2014 Share Posted December 23, 2014 24 hour precip comparison between the 12z and 18z GFS Link to comment Share on other sites More sharing options...
Stebo Posted December 23, 2014 Share Posted December 23, 2014 24 hour precip comparison between the 12z and 18z GFS gfs.gif Wow Grand Rapids area would be in for a shocker. Link to comment Share on other sites More sharing options...
Hoosier Posted December 23, 2014 Share Posted December 23, 2014 Wow Grand Rapids area would be in for a shocker. A lot of precip but not sure how much is snow. Link to comment Share on other sites More sharing options...
TugHillMatt Posted December 23, 2014 Share Posted December 23, 2014 Milwaukee, racine and Kenosha counties under WWA for 1-3" Sent from my iPhone Winter Weather Advisory? GRR NWS considers 1-3 inches as "light snow showers"... Link to comment Share on other sites More sharing options...
TravisWx Posted December 23, 2014 Share Posted December 23, 2014 APX just issued a batch of winter storm watches for most of northern Michigan. Link to comment Share on other sites More sharing options...
TugHillMatt Posted December 23, 2014 Share Posted December 23, 2014 Wow Grand Rapids area would be in for a shocker. Looks perfect for my location. Link to comment Share on other sites More sharing options...
mimillman Posted December 23, 2014 Share Posted December 23, 2014 24 hour precip comparison between the 12z and 18z GFS gfs.gif Very similarly to the NAM, I prefer the 18z GFS solution to the 12z. Looks colder for many of the watch counties in northeastern Illinois. Link to comment Share on other sites More sharing options...
Gilbertfly Posted December 23, 2014 Share Posted December 23, 2014 21Z RAP with a 995 SLP just east of Indianapolis at 14Z 24DEC Link to comment Share on other sites More sharing options...
Brewers Posted December 23, 2014 Share Posted December 23, 2014 Winter Weather Advisory? GRR NWS considers 1-3 inches as "light snow showers"... Likely due to coordination with LOT and holiday timing. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Hoosier Posted December 23, 2014 Share Posted December 23, 2014 Not sure how well this lines up with obs. It will be nice once this thing gets more organized over land. Link to comment Share on other sites More sharing options...
Gilbertfly Posted December 23, 2014 Share Posted December 23, 2014 a little old....but 15Z plumer for JOT... Link to comment Share on other sites More sharing options...
BadgerStateWX Posted December 23, 2014 Share Posted December 23, 2014 Winter Weather Advisory? GRR NWS considers 1-3 inches as "light snow showers"... I would wildly venture because of the timming/holiday travels, uncertainty, possible 'heavier' intensity burst and the fact that's its not going to be a GRR LES fluff special are probably a few of their reasonings for a wwa for 1-3" with possible isolated higher amounts. Link to comment Share on other sites More sharing options...
M4XiMuS Posted December 23, 2014 Share Posted December 23, 2014 I would wildly venture because of the timming/holiday travels LSX openly admitted to this in their latest forecast discussion: "Given potential the impacts of slushy/slippery roads and reduced visibility on holiday travel, we have gone ahead an issued a winter weather advisory even though these amounts are generally below those we typically consider for an advisory." Link to comment Share on other sites More sharing options...
TimChgo9 Posted December 23, 2014 Share Posted December 23, 2014 important nugget and something i've been mentioning during the day I saw that and was wondering how that would play into this. Link to comment Share on other sites More sharing options...
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