www.nws.noaa.gov/view/prodsByState.php?state=IL&prodtype=discussion000
FXUS63 KLOT 281137
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
537 AM CST FRI FEB 28 2014
.DISCUSSION...
317 AM CST
MAIN CONCERNS FOR THE NEXT SEVERAL DAYS WILL FOCUS ON THE POTENTIAL
FOR PERIODS OF SNOW THROUGH THE WEEKEND.
FOR THE REMAINDER OF THE OVERNIGHT HOURS AND INTO FRIDAY
MORNING...WEATHER ACROSS THE REGION WILL REMAIN QUIET...BUT COLD.
TEMPERATURES HAVE DROPPED BELOW ZERO ACROSS MUCH OF THE AREA WITH
THE EXCEPTION OF THE URBANIZED PORTIONS OF THE CHICAGO METRO AREA
AND THE FAR SRN PORTIONS OF THE CWA. THE CENTER OF THE SFC HIGH HAS
ALREADY MOVED EAST OF THE CWA AND SOME HIGH LEVEL CLOUDINESS MOVES
OVER THE REGION...TEMPS HAVE LIKELY BOTTOMED OUT AND SHOULD EITHER
HOLD STEADY OR RISE SLIGHTLY BY DAY BREAK. THE REMAINDER OF THE DAY
SHOULD REMAIN QUIET WITH INCREASING WARM ADVECTION ALLOWING
TEMPERATURES TO REBOUND TO NEAR 30F OVER THE SRN PORTIONS OF THE CWA
TO THE LOWER TO MIDDLE 20S ALONG THE WISCONSIN BORDER.
THE FIRST ROUND OF SNOW IS SETTING UP FOR LATE THIS EVENING AS A
WEAK NRN STREAM SHORTWAVE DROPS OUT OF ALBERTA AND TRACKS ACROSS THE
UPPER GREAT LAKES. THE SYSTEM WILL INITIALLY BE MOISTURE-STARVED AS
SFC RIDGING REMAINS ACROSS THE CNTRL GULF COAST...SO THE SYSTEM WILL
HAVE ONLY THE EXISTING MEAGER MOISTURE IN PLACE TO WORK WITH. THE
00Z FRIDAY SOUNDING FROM KDVN WAS VERY DRY AND EVEN BY LATE THIS
EVENING WHEN THE STRONGEST DYNAMICS WILL BE OVER THE AREA...PWATS
ARE FORECAST TO REMAIN UNDER 0.5 INCHES. SO...WHILE THERE WILL BE
ADEQUATE COLD AIR AND MID LEVEL DYNAMICS...THE LIMITED DEEP LAYER
MOISTURE WILL LIMIT SNOWFALL AMOUNTS TONIGHT AND INTO SATURDAY
MORNING TO AROUND 1 INCH NEAR THE WISCONSIN BORDER TO A HALF INCH OR
LESS SOUTH OF THE KANKAKEE AND ILLINOIS RIVERS. BY SATURDAY
AFTERNOON...THE FIRST WAVE OF SNOW SHOULD COME TO AN END AND THERE
SHOULD BE A LULL IN THE ACTIVITY INTO SATURDAY EVENING. A SECOND
WAVE OF SNOW IS SETTING UP FOR LATE SATURDAY NIGHT ASSOCIATED WITH A
MIDDLE STREAM SHORTWAVE QUICKLY TRACKING G ACROSS THE CENTRAL PLAINS
AND THROUGH THE MID MISSISSIPPI VALLEY. THIS WAVE WILL BE EMBEDDED
WITHING THE FAST ZONAL FLOW...AND COULD DROP A QUICK INCH OR TWO OF
SNOW...
WITH THE HIGHER AMOUNTS GENERALLY NORTH OF THE I-80 CORRIDOR.
THE SITUATION BECOMES A BIT MORE COMPLICATED FOR THE THIRD ROUND OF
SNOW ASSOCIATED WITH A PACIFIC SYSTEM STILL DEVELOPING OFF THE WEST
COAST. THE DEEPENING PACIFIC LOW IS TRYING TO INDUCE UPPER RIDGING
OVER THE ROCKIES...BUT A DEEP UPPER LOW OVER CANADA IS HELPING TO
DAMPEN THE MID LEVEL LONG WAVE PATTERN...KEEPING FLOW MORE ZONAL.
THIS WILL MAKE IT MORE DIFFICULT TO RESOLVE SHORTWAVE ENERGY THROUGH
A FAST FLOW PATTERN...AND BRINGS LOWER THAN COMFORTABLE CONFIDENCE
IN THE TIMING OF THE NEXT ROUND OF SNOW...ESPECIALLY SINCE THE
SYSTEM IS NOT EVEN BEING SAMPLED BY THE UPPER AIR NETWORK YET.
HOWEVER...THE LATEST MODEL RUNS ARE RELATIVELY CONSISTENT ON MOVING
THE SYSTEM ONSHORE BY SATURDAY EVENING...BUT THEN BEGIN TO DIFFER ON
HOW THEY HANDLE THE SYSTEM AS IT MOVES OUT AWAY FROM THE ROCKIES.
THE NAM IS A RELATIVELY SLOWER...WEAKER OUTLIER WHEN COMPARED TO THE
GFS/ECMWF/GEM...SO THAT SOLUTION HAS LARGELY BEEN DISCARDED. THE
MORNING FORECAST UPDATE IS LARGELY A GFS/ECMWF BLEND...WHICH HAVE
RELATIVELY CONSISTENT TIMING...BUT THE GFS IS NOW TRENDING TO A MORE
SOUTHERLY SOLUTION THAT HAS BEEN MORE CONSISTENTLY ADVERTISED BY THE
ECMWF. THE NET EFFECT OF THE CURRENTLY PREFERRED SOLUTION IS THAT
THE MAIN SWATH OF SNOW ASSOCIATED WITH THIS SYSTEM IS TRENDING
SLIGHTLY FARTHER SOUTH WITH SUCCESSIVE MODEL RUNS. WHILE THERE IS
RELATIVELY HIGH CONFIDENCE THAT THE CWA WILL SEE ACCUMULATING SNOW
FOR THE PERIOD FROM SUNDAY MORNING...THROUGH EARLY MONDAY
MORNING...THE MAIN CONCERN HAS BECOME THE TIMING OF THE PERIOD OF
THE HEAVIEST SNOW. GIVEN THE UNCERTAINTY IN EXACTLY WHEN THE
GREATEST ACCUMULATION WILL OCCUR AND EXACTLY WHERE THE HEAVIEST SNOW
WILL LINE UP...HAVE DECIDED TO HOLD OFF ON ISSUING ANY WINTER WEATHER
HEADLINES AT THIS TIME. HOWEVER...IF ALL GOES AS IS CURRENTLY
ADVERTISED...
THE FAR SOUTHERN PORTIONS OF THE CWA COULD SEE UPWARDS
OF 6 TO 8 INCHES OF SNOW. THERE SHOULD BE A RELATIVELY SHARP
GRADIENT TO THE NORTHERN EDGE OF THE SNOW...SO THE FAR NORTHERN
PORTIONS OF THE CWA...CLOSE TO THE WISCONSIN BORDER COULD SEE WELL
LESS THAN 1 INCH OF ADDITIONAL ACCUMULATION FROM THIS SYSTEM.
ALSO...SINCE THE SYSTEM SHOULD BE RELATIVELY QUICK-MOVING...IT IS
POSSIBLE THAT MOST OF THE ACCUMULATING SNOW MAY BE DONE IN TIME FOR
THE MONDAY MORNING RUSH HOURS. HOWEVER...THERE IS YET ANOTHER WILD
CARD IN THE DECK. THE GFS...IN PARTICULAR...IS INDICATING THE
POTENTIAL FOR A LAKE EFFECT PLUME TO DEVELOP BY SUNDAY MORNING AS
ANOTHER AREA OF COLD HIGH PRESSURE BUILDS OUT OF CANADA AND SPREAD
ACROSS THE GREAT LAKES. THIS SCENARIO WOULD BE CONDUCIVE TO AN
INVERTED TROUGH AND AN ENHANCED CONVERGENCE ZONE DEVELOPING OVER THE
LAKE. THIS COULD KEEP SOME LAKE EFFECT SNOW SHOWERS GOING OVER FAR
NERN IL EVEN AS THE SYNOPTIC SNOW IS SETTING UP OVER THE SRN
PORTIONS OF THE CWA...AND AS THE MAIN SYNOPTIC SYSTEM MOVES OFF TO
THE EAST. THERE IS THE POTENTIAL FOR THE LAKE EFFECT SNOW SHOWERS
TO PERSIST INTO MONDAY NIGHT.
FOR THE LONGER TERM FORECAST PERIOD...TUESDAY THROUGH FRIDAY...
CONDITIONS SHOULD REMAIN RELATIVELY UNSETTLED AS A SERIES OF
SHORTWAVES RIPPLE THROUGH THE REGION. SO THE TREND FOR THE EXTENDED
FORECAST PERIOD SHOULD BE FOR CONTINUED BELOW NORMAL
TEMPERATURES...THOUGH TRENDING WARMING TOWARD THE END OF THE
WEEK...WITH ADDITIONAL PERIODIC CHANCES FOR MORE SNOW.
HOWEVER...GIVEN THE UNCERTAINTIES OF TIMING INDIVIDUAL WEAK
SHORTWAVES...HAVE GENERALLY KEPT POPS LOW.
The words in blue has me confused.