Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 200001
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
601 PM CST FRI DEC 19 2014

.SHORT TERM...
237 PM CST

THROUGH SATURDAY...

UNFORTUNATELY IT LOOKS LIKE WE WILL REMAIN LOCKED IN THE CLOUDS YET
AGAIN TONIGHT...DESPITE A CLEARING WEDGE THAT EXTENDS FROM
WESTCENTRAL IL TO SOUTHERN IN. WITH HIGH PRESSURE OVERHEAD THE
ABILITY TO MIX TO THE SFC DRIER AIR HAS BEEN NONEXISTENT. WITH THE
CONSIDERABLE SOLAR SHIELDING THIS AFTERNOON...SFC TEMPS HAVE BEEN
UNABLE TO WARM MUCH. TEMPS IN MOST LOCATIONS HAVE REMAINED ARND 30
TO A FEW LOW 30S ACROSS THE FAR SOUTHERN CWFA. OVERNIGHT THE SFC
RIDGE WILL DRIFT EAST...ALLOWING LGT/VRB WINDS TO SLOWLY TURN
SOUTHWESTERLY BY DAYBREAK SAT. OVERNIGHT LOWS WILL GENERALLY BE IN
THE LOW/MID 20S...BUT IF CLOUDS REMAIN THICK ENOUGH IT IS PLAUSIBLE
THAT TEMPS COULD HOLD IN THE MID/UPR 20S. GUIDANCE HAS INDICATED A
WEAK LOBE OF VORTICITY ALONG THE NORTHERN STREAM PUSHING EAST ACROSS
THE NORTHERN PLAINS OVERNIGHT...ARRIVING ACROSS THE GREAT LAKES
REGION AROUND SAT MORNING. WHILE IT APPEARS MOST OF THE NEAR SFC
WILL REMAIN DRY...THERE IS SOME WEAK FORCING IN THE MID-LVLS ALONG
WITH MARGINAL SATURATION THAT SOME FLURRIES COULD OCCUR DURING THE
MORNING HOURS. WITH YET ANOTHER DAY OF CONTINUED CLOUDINESS SAT...IT
APPEARS LESS FAVORABLE FOR ANY BUMP TO THE TEMPS. SO HAVE NUDGED
TEMPS DOWN A DEGREE TO THE MID 30S ACROSS THE CWFA.

SATURDAY NIGHT WILL GENERALLY REMAIN DRY...HOWEVER THERE IS ANOTHER
WEAK VORT TRYING TO LIFT NORTHEAST ACROSS IOWA LATE SAT NGT/EARLY
SUN. WITH A SLIGHT WARM LAYER TRYING TO LIFT ACROSS THE
REGION...HOWEVER HAVE HELD ONTO MAINLY LGT SNOW. THERE IS SOME
CONCERN THAT TEMPS ALOFT COULD BE WARM ENOUGH TO FULLY MELT ANY
DENDRITES. THE OTHER CONCERN WORTH MENTIONING IS THAT THE LIFT/OMEGA
IS LACKING LATE SAT NGT...SO DROPLET SIZE COULD BE SMALL AND INSTEAD
OF ANY DENDRITES THERE COULD END UP BEING PATCHY FREEZING
DRIZZLE...MAINLY AFTER MIDNIGHT.

BEACHLER

&&

.LONG TERM...
237 PM CST

SUNDAY THROUGH SATURDAY...

500MB TROUGH WILL BEGIN TO DIG SOUTH ACROSS THE CENTRAL CONUS SUN
INTO MON...WITH A SERIES OF MID-LVL VORTS PROGGED TO SLIDE SOUTHEAST
ACROSS THE CANADIAN ROCKIES INTO THE NORTHERN PLAINS. THE MAIN FOCUS
WILL BE ON A STRONGER SHORTWAVE DEVELOPING SUN NGT/EARLY MON ACROSS
THE DAKOTAS...EXPECTED TO SLIDE SOUTHEAST ACROSS NORTHERN IL.
ALTHOUGH CONFIDENCE IN THE TIMING/PLACEMENT OF THIS PATH IS LOW
GIVEN CONTINUED CORRECTIONS BASED ON THE LATEST GUIDANCE CYCLES.

MOISTURE WILL BE ADVECTING NORTH OF THIS LOW MON...WITH PRECIP
ARRIVING MON MORNING LIKELY AS MAINLY RAIN OR PERHAPS A RAIN/SNOW
MIX ACROSS THE NORTHERN CWFA. THEN A QUICK PUSH OF MUCH WARMER AIR
WILL BRING TEMPS INTO THE UPR 30S/NEAR 40 MON AFTN AND SHOULD TURN
ANY PRECIP TO PLAIN RAIN. AS MON NGT PROGRESSES...THE LOW IS PROGGED
TO STEADILY DEEPEN AND LIFT NORTHEAST ACROSS NORTHERN IL EARLY TUE.
FROPA CURRENTLY PROGGED FOR TUE EVE...BRINGING COLDER AIR BACK INTO
THE FORECAST AREA AND TURNING RAIN OVER TO LGT SNOW.

MON NGT WITH THE WARM AIR STEADILY ADVECTING NORTH...TEMPS WILL
REMAIN IN THE MID/UPR 30S. TUE TEMPS COULD PUSH EVEN
WARMER...DEPENDING ON THE PLACEMENT/TIMING OF FROPA. CURRENT
INDICATIONS ARE THAT TEMPS WILL PUSH INTO THE LOW/MID 40S TUE AFTN.

CHRISTMAS EVE THROUGH CHRISTMAS DAY...
ENSEMBLES ALONG WITH OPERATIONAL SOLUTIONS HAVE BEEN TARGETING THE
SYSTEM BECOMING WRAPPED UP OVER THE GREAT LAKES REGION AND POSSIBLY
TRANSITIONING INTO ANOTHER LOW OVER SOUTHERN ONTARIO/SOUTHWEST
QUEBEC CHRISTMAS DAY. A TIGHT GRADIENT WILL REMAIN OVER THE REGION
BOTH CHRISTMAS EVE/CHRISTMAS DAY...WITH TEMPS RETURNING TO MORE
SEASONAL CONDITIONS IN THE LOW/MID 30S.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* MVFR CIGS.

ED F

//DISCUSSION...UPDATED 00Z...

PERSISTENT LOW CLOUDS AND LIGHT WINDS TO CONTINUE OVERNIGHT AND
INTO SATURDAY.  LOW STRATO CUMULUS CLOUDS REMAIN TRAPPED UNDER
TEMPERATURE INVERSION AND LITTLE TO NO FORCING PRESENT OR EXPECTED
THROUGH MIDDAY SATURDAY TO HELP MOVE THEM OUT. MAY SEE A FEW
BREAKS SATURDAY AFTERNOON BUT LOW LEVEL MOISTURE REMAINS ABUNDANT
PER MODEL FORECAST SOUNDINGS HENCE EXPECT ANY HOLES TO BE
BRIEF/SMALL. WINDS BECOME LIGHT SOUTHERLY SATURDAY AS HIGH
PRESSURE RIDGE SLOWLY MOVES OFF TO OUR EAST.

ED F


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM TO HIGH FOR CIGS.
* HIGH FOR ALL OTHER FORECAST ELEMENTS.

ED F

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
200 PM CST

HIGH PRESSURE IS OVER THE REGION AND IT WILL SLOWLY SHIFT EAST
THROUGH SUNDAY NIGHT. LIGHT WINDS BECOME SOUTHWEST OVERNIGHT. THE
NEXT LOW MOVES OVER THE DAKOTAS SUNDAY NIGHT WITH SOUTH WINDS
INCREASING TO 30 KT.  MODELS DISAGREE WITH EXACT PATH OF THIS LOW.
ONE HAS THE LOW DEEPENING OVER LAKE SUPERIOR WEDNESDAY WHILE ANOTHER
HAS THE LOW DEEPENING OVER LAKE ERIE.  SOUTHEAST WINDS AROUND 25 KT
ARE EXPECTED THROUGH MONDAY NIGHT AHEAD OF THE LOW...THEN WINDS
BECOME WEST BEHIND IT.  FOR SPEEDS WENT MIDDLE OF THE ROAD GIVEN THE
VARIABILITY.  COULD DEFINITELY SEE HIGHER GUSTS IF THE LOW DEEPENS
CLOSER TO THE LAKE.

MODELS AGREE ON VERY STRONG WINDS BEHIND THE LOW WEDNESDAY NIGHT
THROUGH THURSDAY.  HAVE HIGH END GALES IN THE FORECAST AND SOME
GUIDANCE MEMBERS SUGGEST LOW END STORM FORCE GUSTS MAY BE POSSIBLE.
DO NOT HAVE THE CONFIDENCE TO GO THAT HIGH JUST YET...BUT HAVE HIGH
CONFIDENCE IN AT LEAST GALES.  THE LOW SHIFTS NORTHEAST WITH WINDS
DIMINISHING THURSDAY NIGHT. THE NEXT LOW HOWEVER MOVES OVER THE
SOUTHERN PLAINS THURSDAY EVENING.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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