010
FXUS63 KLOT 200937
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
337 AM CST SUN JAN 20 2019
SHORT TERM
304 AM CST
THROUGH MONDAY...
ONGOING RAGGED LAKE EFFECT SNOW CONTINUES ACROSS NE IL AND NW IN
EARLY THIS MORNING. BASED OFF A FEW SNOWFALL REPORTS COMBINED WITH
WEBCAMS AND ASOS/AWOS VISIBILITIES, LITTLE ACCUMULATION HAS OCCURRED
SO FAR. DECENT DIRECTIONAL SHEAR OVER THE LOWEST 3KFT IS THE LIKELY
CULPRIT FOR THIS SOMEWHAT DISORGANIZED ACTIVITY. HOWEVER, A MORE
DOMINANT BAND APPARENT ON RADAR AND SATELLITE IS DEVELOPING JUST
OFFSHORE OF LAKE COUNTY EARLY THIS MORNING. EXPECTATION IS FOR THIS
BAND TO REMAIN SOMEWHAT WELL-ORGANIZED, WITH PERIODIC DISRUPTIONS
DUE TO THE LOW-LEVEL SHEAR, AS IT MOVES INTO COOK COUNTY OVER THE
NEXT COUPLE HOURS. BASED OFF RADAR PRESENTATION AND THE THERMO
PROFILE OVER LAKE MI, WOULD EXPECT SNOWFALL RATES IN EXCESS OF 1"/HR
AT TIMES WITHIN THIS BAND.
THE LES BAND SHOULD GRADUALLY SHIFT EAST THROUGH DAYBREAK,
ULTIMATELY SETTLING OVER LAKE AND PORTER COUNTIES DURING THE DAY.
SHORT-TERM HI-RES GUIDANCE SUGGESTS THAT THIS BAND COULD STALL FOR A
2-4HR PERIOD OVER LAKE COUNTY THIS MORNING. IF THIS OCCURS,
LOCALIZED SNOWFALL RATES OF 1"/HR TO POSSIBLY 2"/HR COULD OCCUR.
WHILE WARNING CRITERIA OF 6"/12HR FOR ANY ONE LOCATION MAY NOT BE
MET DURING THIS TIME, DID CONSIDER UPGRADING LAKE COUNTY TO WINTER
STORM WARNING TO ACCOUNT FOR THE CONDENSED PERIOD OF HEAVY SNOW THIS
MORNING. HOWEVER, GIVEN THE ODDITIES OF LAKE EFFECT SNOW
FORECASTING, CONFIDENCE IN THE LES BAND ACTUALLY STALLING FOR
SEVERAL HOURS IS TOO LOW TO UPGRADE TO A WARNING. WILL INSTEAD
HIGHLIGHT THE POTENTIAL FOR A PERIOD OF HIGHER SNOWFALL RATES WITHIN
THE ONGOING ADVISORY THIS MORNING.
BY THIS AFTERNOON, A MID-LEVEL SHORTWAVE DIGGING SE ACROSS NE MN
EARLY THIS MORNING WILL ALTER THE LOW-LEVEL WIND FIELD ENOUGH TO
DISRUPT THE SINGLE LES BAND. GRADUALLY VEERING LOW-LEVEL WINDS AHEAD
OF A SURFACE HIGH APPROACHING FROM THE NW WILL ALLOW PRIMARILY
DISORGANIZED LES WITH AN EMBEDDED MESO-LOW OR TWO TO DRIFT BACK
WEST, AND THEN NORTHWARD, TONIGHT. LIGHT TO BRIEFLY MODERATE SNOW IS
EXPECTED WITH THIS ACTIVITY IMMEDIATELY ADJACENT TO LAKE MI IN BOTH
IN AND IL. ANY REMAINING LES SHOULD EXIT THE CWA BY MID-MORNING
MONDAY AS THE SURFACE RIDGE MOVES OVER AREA AND WINDS VEER SSE.
KLUBER
LONG TERM
337 AM CST
MONDAY NIGHT THROUGH SATURDAY...
MONDAY NIGHT THROUGH WEDNESDAY: A MID-LEVEL TROUGH MOVING ACROSS THE
CENTRAL PACIFIC COAST TONIGHT WILL PHASE WITH A NW CANADIAN TROUGH
OVER THE CENTRAL GREAT PLAINS MONDAY NIGHT INTO TUESDAY. AN
ASSOCIATED SURFACE LOW WILL TRACK NE ACROSS THE CWA. GUIDANCE HAS
COME INTO SOMEWHAT BETTER AGREEMENT ON THE TRACK OF THE LOW, WITH A
CONSENSUS FORECAST PRODUCING A NORTHERN MO TO FAR SE WI MOTION.
PRECIP WILL BEGIN TO SPREAD ACROSS THE CWA BY LATE TUESDAY MORNING,
WITH WIDESPREAD PRECIP EXPECTED LATE TUESDAY AFTERNOON INTO THE
EARLY MORNING HOURS WEDNESDAY. THERMO PROFILES SUPPORT AN INITIAL P-
TYPE OF ALL SNOW TO TRANSITION TO LIQUID PRECIP FROM SOUTH TO NORTH
DURING THE AFTERNOON HOURS. HOWEVER, PRECIP WILL LIKELY REMAIN
MOSTLY IN THE FORM OF SNOW ACROSS THE NORTHERN TIER OF COUNTIES.
WITH ABUNDANT WAA ALOFT, THE TRANSITION TO LIQUID PRECIP WILL
PRECEDE SURFACE TEMPS RISING ABOVE FREEZING, SUPPORTING A PERIOD OF
FREEZING RAIN DURING THE AFTERNOON INTO THE THE EARLY EVENING. GIVEN
THE EXPECTED COLD OVER THE NEXT COUPLE DAYS, FREEZING RAIN WILL
LIKELY CONTINUE ON COLD SURFACES EVEN AFTER SURFACE AIR TEMPS RISE A
FEW DEGREES ABOVE FREEZING. CAA WILL COMMENCE OVERNIGHT TUESDAY INTO
WEDNESDAY, BUT WITH THE LOSS OF DEEP MOISTURE, PRECIP MAY TRANSITION
TO A MIX OF LIGHT SNOW AND FREEZING DRIZZLE THROUGH THE DAY
WEDNESDAY.
OVERALL, MESSY CONDITIONS ARE EXPECTED TUESDAY AFTERNOON AND NIGHT,
WITH POTENTIAL IMPACTS ACROSS MUCH OF THE AREA. BECAUSE OF THE
COMPLEXITIES OF THIS SYSTEM, DETAILS ON SNOW AND ICE AMOUNTS REMAIN
DIFFICULT TO DETERMINE. HOWEVER, AT THIS TIME, THE POTENTIAL EXISTS
FOR SEVERAL INCHES OF ACCUMULATING SNOW ACROSS THE NORTHERN TIER OF
COUNTIES, A MIX OF ICE AND SNOW ACCUMULATIONS GENERALLY BETWEEN THE
I-88 AND I-80 CORRIDORS (INCLUDING THE ENTIRE CHICAGO METRO), AND
ICE ACCUMULATIONS SOUTH OF I-80.
THURSDAY THROUGH SATURDAY: A MUCH COLDER PATTERN WILL SETTLE
ACROSS THE REGION DURING THIS TIME. THE FIRST TRUE SHOT OF ARCTIC
AIR THIS SEASON LOOKS TO CROSS THE WESTERN GREAT LAKES ON FRIDAY,
WITH A REINFORCING SHOT SATURDAY NIGHT INTO SUNDAY. MAX TEMPS
FRIDAY WILL LIKELY STRUGGLE TO RISE OUT OF THE SINGLE DIGITS ABOVE
ZERO, WHILE WIND CHILLS REMAIN WELL-BELOW ZERO THROUGH THE DAY. A
COUPLE CLIPPER SYSTEMS WILL BRING CHANCES OF SNOW DURING THIS
TIME, WITH LIGHT SNOW POSSIBLE THURSDAY AND A MORE POTENT SYSTEM
BRINGING BETTER CHANCES FRIDAY NIGHT INTO SATURDAY.
KLUBER
AVIATION
FOR THE 06Z TAFS...
PRIMARY FORECAST CONCERN IS LAKE EFFECT SNOW THROUGH THE PERIOD.
LAKE EFFECT SNOW SHOWERS HAVE BEEN SPREADING ACROSS NORTHEAST IL
THIS EVENING OCCASIONALLY LOWERING VIS INTO THE 2SM RANGE. WINDS
HAVE SHIFTED TO THE NORTH/NORTHWEST IN IL AND TO THE NORTH/
NORTHEAST IN SOUTHWEST LOWER MI SIGNALING CONVERGENCE HAS BEGUN
AND THIS MAY ALLOW ANY HEAVIER LAKE EFFECT BAND TO REMAIN EAST OF
ORD AND POSSIBLY MDW...FOCUSING MORE INTO NORTHWEST IN AND GYY.
HAVE TRENDED A BIT HIGHER WITH THIS FORECAST FOR ORD/MDW AND IF
THE BAND DOES REMAIN EAST...FURTHER IMPROVEMENT CAN BE EXPECTED.
THIS LAKE EFFECT SNOW MAY SHIFT EAST OF GYY BY EARLY SUNDAY
AFTERNOON BUT AS HIGH PRESSURE MOVES ACROSS THE AREA THE BAND IS
LEFT TO DRIFT BEFORE DISSIPATING AND THERE IS SOME CONSENSUS FROM
THE MODELS IT MAY MOVE BACK TOWARD NOT ONLY GYY BY LATE AFTERNOON
BUT TOWARD ORD/MDW LATER SUNDAY EVENING. CONFIDENCE IS VERY LOW
DURING THIS TIME PERIOD BUT MAINTAINED PROB MENTION AT GYY AND
ADDED VCSH MENTION AT ORD/MDW.
PREVAILING WINDS WILL REMAIN NORTH/NORTHWEST INTO SUNDAY EVENING.
SPEEDS/GUSTS WILL SLOWLY DIMINISH OVERNIGHT BUT SPEEDS 10-15KTS
WILL CONTINUE SUNDAY WITH SOME HIGHER GUSTS POSSIBLE. WINDS ARE
EXPECTED TO SHIFT LIGHT NORTHEASTERLY LATE SUNDAY NIGHT. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...WINTER WEATHER ADVISORY...ILZ014 UNTIL 9 AM SUNDAY.
LAKESHORE FLOOD ADVISORY...ILZ006-ILZ014 UNTIL 9 AM SUNDAY.
IN...LAKESHORE FLOOD ADVISORY...INZ001 UNTIL 9 AM SUNDAY.
WINTER WEATHER ADVISORY...INZ001-INZ002 UNTIL 4 PM SUNDAY.
LM...HEAVY FREEZING SPRAY WARNING...LMZ740-LMZ741-LMZ742-LMZ743-
GARY TO MICHIGAN CITY IN UNTIL MIDNIGHT MONDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 4 AM MONDAY.
VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)
FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page