Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 290820
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
220 AM CST MON DEC 29 2014

.SHORT TERM...
220 AM CST

THROUGH TUESDAY...

PRIMARY FORECAST CHALLENGE IN THE SHORT TERM IS WITH LAKE EFFECT
POTENTIAL THROUGH TONIGHT. DESPITE MODERATELY COLD AIR MASS IN PLACE
LAKE EFFECT THUS FAR TONIGHT HAS BEEN ABSENT AND THERMODYNAMICS ARE
NOT EXPECTED TO IMPROVE THIS MORNING SO PLAN TO JUST HOLD ON TO
SLIGHT CHANCE OF SNOW SHOWERS AND CHANCE OF FLURRIES ALONG THE
ILLINOIS LAKE SHORE THIS MORNING. BEST HOPE OF LAKE EFFECT SNOW
SHOWERS/FLURRIES THIS MORNING WILL HINGE ON MID LEVEL CLOUDINESS
BEGINNING TO SPREAD IN ACTUALLY SEEDING THE LAKE STRATOCUMULUS.

LOW LEVEL FLOW WILL GRADUALLY BACK TO NORTH THIS AFTERNOON THEN
NORTH-NORTHWEST WITH THE RESULTANT LAKE EFFECT POTENTIAL PIVOTING
AROUND THE SOUTH RIM OF LAKE MICHIGAN THROUGH TONIGHT.
THERMODYNAMICS COULD IMPROVE SLIGHTLY THIS AFTERNOON...THOUGH
GETTING INTO A DIURNALLY UNFAVORABLE TIME OF DAY CONSIDERING THE
STILL MARGINAL SET UP FOR LAKE EFFECT SNOW TO GET CRANKING THIS
AFTERNOON. PLAN TO JUST GRADUALLY SHIFT FLURRIES/SMALL SNOW SHOWERS
CHANCES EAST FOCUSING MORE INTO NW INDY AND EXTREME SE COOK THIS
AFTERNOON.

MORE FAVORABLE THERMODYNAMIC ENVIRONMENT WILL DEVELOP THIS EVENING
AND CONTINUE OVERNIGHT WITH IMPROVED INSTABILITY AND SLIGHTLY HIGHER
INVERSION HEIGHTS. WILL MAINTAIN HIGH CHANCE/LOW END LIKELY POPS
NEAR THE LAKE TONIGHT BUT ACCUMULATIONS WILL PROBABLY BE PRETTY
MINOR BECAUSE AS THERMAL INSTABILITY INCREASES...MODELS ALSO PROG
INCREASINGLY DRY AIR TO SPREAD IN JUST ABOVE THE BOUNDARY LAYER
INVERSION WHICH GIVEN THE MARGINAL TEMPS IN THE CLOUD BARING LAYER
REALLY DOES NOT BODE WELL FOR EFFICIENTLY ACCUMULATING SNOW. CURRENT
THINKING IS NO ACCUMULATION IN NE IL AND MOSTLY LESS THAN AN INCH IN
NW INDY TONIGHT...THOUGH ISOLATED AMOUNTS OF 1 TO POSSIBLY UP TO 2
INCHES WOULD BE ON THE HIGH SIDE. LAKE EFFECT THREAT WILL SHIFT EAST
OUT OF THE CWA TUESDAY AND SHOULD SEE CLOUDS CLEAR OUT AND SKIES
BECOME SUNNY...BUT THE SUNSHINE WILL BE MORE FOR SHOW THAN ANYTHING
ELSE AS TEMPS STRUGGLE TO REACH 20F.

IZZI

&&

.LONG TERM...
220 AM CST

TUESDAY NIGHT THROUGH SUNDAY...

COLD AIR MASS WILL REMAIN ENTRENCHED WEDNESDAY BUT MAGNITUDE OF THE
COLD WILL NO DOUBT BE TEMPERED BY THE LACK OF SNOW COVER HERE OR
EVEN FAR UPSTREAM...SO WHILE IT WILL BE COLD HAVE GONE WITH TEMPS A
BIT ABOVE WHAT 850MB/925MB CLIMO WOULD SUPPORT. WARM ADVECTION
BEGINS WEDNESDAY NIGHT AND REALLY CRANKS INTO GEAR THURSDAY ALLOWING
FOR A NICE REBOUND IN TEMPS...THOUGH THE WARMING WILL BE MORE
ACADEMIC THAN ACTUALLY FELT AS GUSTY SOUTHWEST WINDS PRODUCE STILL
CHILLY WIND CHILLS THURSDAY. TEMPS SHOULD CONTINUE TO MODERATE ON
FRIDAY WITH PRECIPITATION LOOKING PRETTY UNLIKELY FRIDAY.

STRONG TROUGH WILL TO DIG INTO THE DESERT SOUTHWEST NEW YEARS EVE
AND IS FORECAST TO PRODUCE ACCUMULATING SNOW ON THE LAS VEGAS STRIP
NEW YEARS EVE WHERE WINTER STORM WATCHES ARE IN EFFECT! THIS
POWERFUL SYSTEM IS PROGGED TO CLOSE OFF A LARGE DEEP CIRCULATION
THAT BECOMES CUT OFF FROM THE WESTERLIES. A SET UP LIKE THIS MORE
OFTEN THAN NOT SPELLS BIG TROUBLES FOR PREDICTABILITY IN THE MEDIUM
RANGE AS THIS SYSTEM WILL PRESENT A COUPLE OF THE THINGS THAT MODELS
STRUGGLE WITH...FIRST HANDLING TRACK/TIMING OF EJECTING SOUTHWEST
CUT OFFS AND SECOND THE POTENTIAL FOR PHASING WITH NORTHERN STREAM
SHORTWAVE ENERGY.

THE RANGE OF POSSIBILITIES FOR THE WEEKEND IN OUR AREA TRULY RUN THE
GAMUT FROM DRY CONDITIONS ALL WEEKEND TO RAIN...ACCUMULATING
SNOW...A WINTRY MIX...OR SOME COMBINATION OF THE ABOVE. THE
OPERATIONAL GFS IS MOST GUNG-HO WITH PHASING AND FASTEST EJECTING
THE LOW EASTWARD...WHICH WOULD SEEM TO COUNTER WHAT IS TYPICAL IN
THESE SCENARIOS. THE PARALLEL GFS AND ECMWF ARE BOTH SOUTH AND
SLOWER WITH THE SYSTEM AND WOULD LEAD TO A DRY WEEKEND IN OUR AREA.
THE BLENDED MODEL POPS FOR THE WEEKEND HAVE COME DOWN FROM PREVIOUS
CYCLES AND AM NOT PLANNING ANY CHANGES TO THEM AS PREDICTABILITY IS
JUST TOO LOW AT THIS POINT. AT THIS POINT THE CHANCES OF THE LAS
VEGAS STRIP SEEING MORE ACCUMULATING SNOW THE NEXT 7 DAYS IS
CURRENTLY HIGHER THAN HERE IN OUR CWA...QUITE ATYPICAL AND
DEFINITELY NOT SOMETHING THAT ONE WOULD TYPICALLY WAGER WOULD BE
THE CASE!

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CIGS DEVELOPING OVERNIGHT...AND CONTINUING AT TIMES MONDAY.
* LAKE EFFECT FLURRIES MONDAY AND MONDAY EVENING.
* NORTH/NORTHEAST WINDS APPROACHING 10KT MONDAY AFTERNOON.

KMD

//DISCUSSION...UPDATED 06Z...

MVFR CIGS OVER SOUTHERN WI WILL MOVE SOUTH DURING THE EARLY
MORNING HOURS LIKELY SPREADING INTO NORTHERN ILLINOIS IN THE COMING
HOURS.  MEANWHILE...ADDITIONAL LOW CLOUDS OVER THE LAKE WILL
SPREAD INTO NE ILLINOIS TOWARD DAYBREAK WITH MVFR CIGS CONTINUING
MONDAY. LOW- MEDIUM CONFIDENCE REGARDING HOW SOON THESE CIGS WILL
ARRIVE BUT ONCE THEY DO...EXPECT THEM TO LINGER THROUGH THE
MORNING...AND THROUGH THE AFTERNOON CLOSE TO THE LAKEFRONT. NE
WINDS LOOK TO GET AROUND 10 KT THIS AFTERNOON WITH THESE LOWER
CIGS IN PLACE.

AS COLDER AIR SPREADS ACROSS THE AREA...LAKE EFFECT FLURRIES OR
SNOW SHOWERS ARE POSSIBLE MONDAY INTO MONDAY NIGHT. HRRR/RAP
SUGGEST A PERIOD OF FLURRIES OR LIGHT SNOW SHOWERS THIS MORNING
AFTER 13Z AS THE LEADING EDGE OF COLDER AIR SPREADS SOUTH...POSSIBLY
LASTING OFF AN ON FOR SEVERAL HOURS. NO ACCUMULATIONS ARE EXPECTED
UNLESS A SHOWER COMES RIGHT OVER A TERMINAL. ALL OF THIS IS EAST
OF RFD/DPA. MAINTAINED A PROB30 FOR SHOWER ACTIVITY AND WILL
MONITOR AS THINGS MATERIALIZE OR NOT LATER THIS MORNING. THEN
THERE APPEARS TO BE A LULL IN ANYTHING MORE THAN LAKE CLOUDS. BEST
CHANCES FOR LAKE EFFECT SNOW SHOWERS AT GYY COULD BE MONDAY
EVENING.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH FOR MVFR CIGS...MEDIUM FOR TIMING.
* MEDIUM FOR LAKE EFFECT FLURRIES MONDAY/MONDAY EVENING.
* MEDIUM FOR WINDS THRU THE PERIOD.

KMD

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

* TUESDAY...DRY. MVFR CIGS POSSIBLE. NORTHWEST WINDS.
* WEDNESDAY AND THURSDAY...DRY/VFR. GUSTY WESTERLY WINDS.
* FRIDAY...CHANCE OF SNOW. MVFR POSSIBLE. SOUTH/SOUTHEAST WINDS.
* SATURDAY...CHANCE OF RAIN OR SNOW. IFR POSSIBLE. SOUTH WINDS
  BECOMING WEST.

&&

.MARINE...
326 PM CST

LIGHTER SPEEDS HAVE BEEN OBSERVED OVER THE LAKE TODAY...WHILE A
NORTHWEST DIRECTION PREVAILED. A LINGERING TROUGH OF LOW PRESSURE
OVER SOUTHEAST ONTARIO IS HELPING FOR SLIGHTLY HIGHER SPEEDS OVER
THE NORTHERN HALF OF THE LAKE WHERE 15 TO 25 KT WINDS CONTINUE TO
BE OBSERVED...WITH 10 TO 20 KT BEING OBSERVED OVER THE SOUTHERN
HALF. THIS WILL LIKELY CONTINUE TONIGHT AS A FRONT PUSHES SOUTH
DOWN THE LAKE...AND THEN AS HIGH PRESSURE BUILDS SOUTHEAST THROUGH
THE UPPER MIDWEST AND GREAT LAKES. THIS HIGH WILL THEN CONTINUE TO
BUILD SOUTHEAST ON MONDAY...WITH THE CENTER OF THE STRONG HIGH
BUILDING SOUTH ACROSS THE PLAINS TUESDAY INTO WEDNESDAY. THIS WILL
HELP WITH A NORTH TO NORTHWEST WIND TO REMAIN IN PLACE DURING THIS
PERIOD...BEFORE WINDS TURN MORE WESTERLY TUESDAY NIGHT INTO
WEDNESDAY. EXPECT WINDS TO SIGNIFICANTLY INCREASE DURING THE DAY
WEDNESDAY WITH GALES APPEARING TO BE LIKELY...AS THE STRONG HIGH
REMAINS TO THE SOUTHWEST AND DEVELOPING LOW PRESSURE MOVES SOUTH
THROUGH HUDSON BAY.

RODRIGUEZ

&&

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

$$

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