🚀 go-pugleaf

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1159 AM CST MON FEB 25 2013

DISCUSSION...
1005 AM CST

HAVE INCREASED THE FORECAST TEMPERATURES FOR TODAY ACROSS MUCH OF
THE AREA WITH LATE FEBRUARY STRONGER SUNSHINE...DIMINISHING SNOW
COVER...AND A MODIFYING LOWER TROP TOGETHER AIDING IN WARMER THAN
EXPECTED VALUES.

THE GOES SATELLITE LOOP SHOWS OUR SYSTEM FOR TUE SPINNING OVER THE
SOUTHERN PLAINS WITH UPPER AND SURFACE RIDGING STILL HOLDING TIGHT
OVER THE LOCAL AREA. THE DRY AIR AND SUPPRESSION ALOFT LOOKS TO
KEEP MOST OF THE HIGH CLOUDS AT BAY THIS AFTERNOON PER VISIBLE
SATELLITE TRENDS AND SIMULATED SATELLITE FORECASTS. MORNING RAOBS
INDICATED TEMPERATURES HAD MODERATED IN THE LOW LEVELS BY 2-3C IN
THE PAST 24 HOURS AND SURFACE TEMPERATURES ARE RUNNING MUCH WARMER
/7-10F/ THAN THIS TIME YESTERDAY. WITH ESE WINDS OFF MAINLY SNOW
FREE AREAS OF NORTHERN AND CENTRAL IN...CAN ONLY ENVISION
TEMPERATURES REACHING SEVERAL DEGREES WARMER THAN YESTERDAY. THE
RAP MODEL HAS A BETTER REPRESENTATION ON CURRENT SNOW COVER THAN
THE NAM AND HAS TEMPERATURES MODERATING INTO THE MID 40S FOR MANY
LOCATIONS SOUTH OF INTERSTATE 80. HAVE MOVED UP OUR FORECAST
FAIRLY CLOSE TO THAT...ESPECIALLY SOUTH OF THE KANKAKEE RIVER.

WITH REGARD TO THE WINTER WEATHER ON TUESDAY...NO CHANGES TO
GOING HEADLINES PLANNED THIS MORNING. UNCERTAINTY REMAINS
EXCEPTIONALLY HIGH WITH REGARDS TO ACCUMULATION POTENTIAL DURING
TUESDAY. MODELS CONTINUE TO STRUGGLE WITH 2M TEMPS AND SNOW PACK
WITH INITIALIZATION OF SNOW COVER THIS MORNING SHOWING NEARLY THE
ENTIRE STATE OF INDIANA COVERED WITH SNOW ALMOST TO THE OHIO
RIVER...WHICH VISIBLE IMAGERY THIS MORNING SHOWS VERY LITTLE SNOW
REMAINING OVER EASTERN ILLINOIS SOUTH OF I-80 OR ANYWHERE BUT THE
MICHIGAN BORDER IN INDIANA. PROGGED 2M TEMPS TOMORROW SHOW A SHARP
GRADIENT RIGHT AT THE EDGE OF WHERE THE MODEL INCORRECTLY ASSUMES
THE EDGE OF THE SNOW PACK IS WHICH RAISES SERIOUS DOUBTS ABOUT HOW
COLD PROGGED 2M TEMPS ARE TOMORROW AND THE RESULTANT PRECIP TYPE
OVER OUR CWA AND ACCUMULATION POTENTIAL WHERE THAT TYPE IS SNOW.

WOULD LIKE TO GET A LOOK AT THE FULL SUITE OF 12Z MODEL DATA
INCLUDING THE ECMWF BEFORE MAKING ANY DECISIONS WITH REGARDS TO THE
WATCH HEADLINE...BUT AT THIS POINT THINKING THAT OUR CHANCES OF
REACHING WARNING CRITERIA ARE VERY LOW ACROSS MOST OF THE WATCH
AREA. CONVECTIVE POTENTIAL TOMORROW DOES EXIST AND ANY TIME YOU GET
CONVECTIVE SNOW (WITH OR WITHOUT LIGHTNING) ALL BETS ARE OFF WITH
REGARDS TO ACCUMULATION POTENTIAL...BUT WOULD SEEM MUCH MUCH MORE
LIKELY THAT THE MAJORITY OF THE WATCH AREA WILL END UP WITH LESS
THAN 3 INCHES OF ACCUMULATION DURING THE DAY TOMORROW THAN IT WILL
WITH 6 INCHES. WILL CONTINUE TO DIG INTO DATA AND WILL AIM TO HAVE
ANY CHANGES TO WSW OUT BY 2000-2030Z AND NEW AFD BY 2100Z.

MTF/IZZI

//PREV DISCUSSION...
352 AM CST

MAIN FOCUS IS WITH LATE WINTER STORM SYSTEM THAT WILL MOVE INTO THE
AREA TUESDAY MORNING...AND THE RESULTING ISSUES OF PRECIP TYPE...
SNOW AMOUNTS AND HEADLINES. HAVE CHOSEN TO LET THE WINTER STORM
WATCH RIDE FOR NOW...WITH SOME POTENTIAL TO REACH WARNING (6+ INCH)
CRITERA SNOW ESPECIALLY IN WESTERN IL...THOUGH CONCERNS ABOUT WARM
THERMODYNAMIC PROFILES AND DECREASING STRENGHT OF OCCLUDING AND
WEAKENING SYSTEM REMAIN.

SHORT TERM...TODAY THROUGH WEDNESDAY...

NO REAL CONCERNS IN THE VERY NEAR TERM TODAY...WITH UPPER/SURFACE
HIGH PRESSURE RIDGING DRIFTING EAST OF THE AREA. INCREASING MID/HIGH
CLOUDS ARE EXPECTED THROUGH THE DAY IN ASSOCIATION WITH A SHORT WAVE
MOVING ACROSS THE UPPER MIDWEST...ESPECIALLY ACROSS THE NORTHWEST
PART OF THE CWA. RELATIVELY MILD LOWER TROPOSPHERIC AIR SHOULD
SUPPORT TEMPS WELL ABOVE FREEZING DURING THE DAY...WITH MOS HIGHS IN
THE UPPER 30S NORTH AND AROUND 40/LOW 40S IN THE SOUTHEAST WHERE
THERE IS LESS REMAINING SNOW COVER AND A LITTLE MORE SUN LIKELY.

ATTENTION THEN TURNS QUICKLY TO THE APPROACHING STORM SYSTEM OVER
THE SOUTHERN PLAINS. DEEPENING UPPER LOW CURRENTLY OVER THE TEXAS
PANHANDLE IS PROGGED TO MOVE EAST ACROSS THE RED RIVER VALLEY OF THE
SOUTH BY EVENING...AND TO NORTHEAST ARKANSAS BY TUESDAY MORNING.
GUIDANCE IS IN VERY GOOD AGREEMENT IN QUICKLY OCCLUDING THE SYSTEM
EARLY TUESDAY AS IT LIFTS NORTHEAST INOT THE LOWER OHIO VALLEY INTO
CENTRAL/SOUTHERN INDIANA BY TUESDAY EVENING. NORMALLY...THE TRACK OF
A STRONG SURFACE LOW FROM SOUTHEAST MISSOURI INTO CENTRAL INDIANA
WOULD INDICATE THE POTENTIAL FOR A SWATH OF HEAVY SNOW ACROSS
NORTHERN IL/NORTHWEST INDIANA...THOUGH THE LACK OF A REALLY COLD
AIRMASS ACROSS THE GREAT LAKES/ONTARIO AND THE FACT THAT THE
DEFORMATION BAND WILL WEAKEN CONSIDERABLY AS IT SPREADS NORTHEAST
INTO THE WFO LOT FORECAST AREA AS THE SYSTEM FILLS RAISE DOUBTS
ABOUT WIDESPREAD 6+ INCH SNOWFALL AMOUNTS.

AS PRECIPITATION SPREADS INTO THE AREA FROM THE SOUTH EARLY TUESDAY
MORNING...FORECAST SOUNDINGS DEPICT VERY DRY LOW LEVELS BELOW 700
MB. THIS SHOULD NOT BE AN ISSUE HOWEVER GIVEN THE VERY STRONG
MOISTURE ADVECTION AHEAD OF THE LOW...WITH PWATS IN THE 0.50-0.75
INCH RANGE DEPICTED BY THE GFS. THE ISSUE HOWEVER WILL BE THE WARM
NOSE OF +2 TO +4 DEG C NOTED IN GFS/ECMWF SOUNDINGS ACROSS OUR
SOUTH/SOUTHEAST COUNTIES WHICH WILL LIKELY RESULT IN A PERIOD OF
MIXED FREEZING RAIN/RAIN AND SLEET EARLY TUESDAY. EVEN AREAS NORTH
OF I-80 COULD SEE A LITTLE GRAUPLE AS PRECIP BEGINS AFTER SUNRISE
BEFORE CHANGING OVER TO WET SNOW. THERMAL PROFILES ROUGHLY
ALONG/NORTH OF A PONTIAC TO CHICAGO LINE APPEAR TO SUPPORT MAINLY
ALL SNOW ONCE THE COLUMN SATURATES...THOUGH AREAS EAST/SOUTH OF THAT
LINE WILL LIKELY SEE SOME MIX AND EVEN A CHANGE OVER TO JUST RAIN
ACROSS THE FAR SOUTHEAST. EVEN WHERE PRECIP IS ALL SNOW...THE BEST
DENDRITIC GROWTH LAYER LOOKS TO BE ABOVE 700 MB...WITH THE LOWER 10
KFT OF THE PROFILE GENERALLY WARMER THAN -8 C. WITH LOW LEVEL TEMPS
NEAR/EVEN SLIGHTLY ABOVE FREEZING THIS SUGGESTS COMPACTION ISSUES
AND A VERY WET/LOW RATIO SNOW...LIKELY LESS THAN 10:1 EXCEPT PERHAPS
IN THE FAR NORTHWEST WHERE QPF IS A LITTLE LOWER. ALL OF THIS MAKES
SNOW AMOUNT FORECASTS SOMEWHAT LOW CONFIDENCE. WITH 0.50-0.80 INCHES
OF LIQUID QPF FORECAST HOWEVER...EVEN WITH RELATIVELY LOW RATIOS
THIS COULD SUPPORT SEVERAL INCHES OF WET SNOW...AND SOME AREAS JUST
UPSTREAM OF THE LOT CWA WHERE FORCING IS STRONGER WILL LIKELY EASILY
RECEIVE 6+ INCHES. THEREFORE...WITH SOME DEGREE OF UNCERTAINTY HAVE
MAINTAINED THE WATCH FOR NOW...THOUGH SUSPECT A SOLID ADVISORY (3-6
INCH) SNOW IS MORE LIKELY. EAST-NORTHEAST WINDS GUSTING 35-40 MPH
WILL NOT HELP IMPACTS...WITH BLOWING/DRIFTING AND POOR VISIBILITY
LIKELY INTO TUESDAY EVENING.

UPPER/SURFACE LOWS CONTINUE TO DRIFT NORTHEAST FROM THE LOWER OHIO
VALLEY TO THE EASTERN GREAT LAKES TUESDAY NIGHT/WEDNESDAY...WITH CWA
REMAINING LINGERING MODEST LIFT IN COLDER/MOIST CYCLONIC REGION.
CONTINUED LIGHT SNOW/SNOW SHOWERS WILL LIKELY RESULT IN ADDITIONAL
MINOR SNOW ACCUMULATION OF 1-2" THROUGH WEDNESDAY.

RATZER

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

CLOSED UPPER LOW AND SURFACE REFLECTION WILL FINALLY SLIDE EAST AND
LOSE THEIR INFLUENCE OVER REGION. WILL CONTINUE TO CARRY A CHANCE OF
LIGHT SNOW WEDNESDAY NIGHT...HIGHEST EASTERN CWA...BEFORE SYSTEM
SLIDES FAR ENOUGH OFF TO EAST. CANNOT RULE OUT SOME VERY LIGHT
ADDITIONAL ACCUMULATIONS. TEMPERATURES WILL BE SLOW TO FALL
WEDNESDAY NIGHT AND THEN SLOW TO RISE ON THURSDAY DUE TO
OVERCAST SKIES. MAINTAINED SOME SLIGHT POPS FOR THE POTENTIAL OF
LINGERING SNOW SHOWERS FOR THURS/THURS NIGHT BUT THIS COULD BE
GENEROUS.

THERE IS THEN BROAD AGREEMENT AMONGST ENSEMBLES AND OPERATIONAL
MODELS FOR A VERY HIGH AMPLITUDE RIDGE TO SET UP SHOP LATE NEXT WEEK
OVER THE WESTERN CONUS AND A DEEP TROUGH OVER THE EASTERN
CONUS...WHICH IS A CLASSIC STRONGLY POSITIVE PNA PATTERN. THIS WILL
ALSO BE ACCOMPANIED BY A NEGATIVE NAO OR GREENLAND BLOCK.
BLOCKY UPPER PATTERN WILL RESULT IN A STAGNANT SENSIBLE WX PATTERN
FOR OUR AREA THROUGH THE WEEKEND...WITH PRIMARILY DRY AND COOLER
THAN NORMAL CONDITIONS TYPIFIED BY A POSITIVE PNA/NEGATIVE NAO
COMBO. MODELS...MOST NOTABLY THE GFS...INSIST ON LIGHT QPF IN
PERSISTENT NORTHERLY FLOW INDICATIVE OF LAKE EFFECT/LAKE ENHANCEMENT
FRIDAY THROUGH SATURDAY. HOWEVER 850 MB TEMPS ARE MARGINAL FOR LAKE
EFFECT AT AROUND -10C AND FORECAST SOUNDINGS SHOW LOW INVERSION
HEIGHTS AOB 5KFT...SO REMOVED SLIGHT POPS FROM BLENDED GUIDANCE AND
JUST WENT WITH A MENTION OF INTERMITTENT FLURRIES. WILL NEED TO
WATCH FOR IMPROVED THERMODYNAMIC SET-UP GIVEN FAVORABLE FLOW FOR
LAKE EFFECT INTO NORTHEAST IL AND NORTHWEST INDIANA.

BEYOND DAY 7...THERE IS SOME EVIDENCE ON ENSEMBLES FOR THE
DEVELOPMENT OF STRONG RIDGING OVER/NEAR ALASKA...WHICH COULD
RE-ESTABLISH CROSS POLAR FLOW OF COLD AIR INTO THE NORTHERN CONUS
AND PROLONG THE COLD PATTERN INTO THE SECOND WEEK OF MARCH WHILE THE
NORTH ATLANTIC BLOCKING PERSISTS. ALL IN ALL...THOUGH THERE DOESNT
APPEAR TO BE ANY SIGNIFICANT SYSTEMS IN THE OFFING...METEOROLOGICAL
SPRING LOOKS TO BE GETTING OFF TO A DECIDEDLY WINTRY START.

RC

&&

AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* NO SIG CONCERNS FOR THIS AFTERNOON INTO THIS EVENING.

* WINDS BECOMING ENELY AND INCREASING THROUGH THE MORNING...GUSTING
  30KT OR SLIGHTLY HIGHER.

* RAIN/SNOW MIX BEGINNING EARLY AFTERNOON...QUICKLY CHANGING OVER
  TO ALL SNOW. ACCUMULATING SNOW THROUGH THE AFTERNOON.

* CIGS/VIS QUICKLY DROPPING TO MVFR AND THEN IFR FOLLOWING THE
  ONSET OF PCPN.

KREIN

//DISCUSSION...UPDATED 18Z...

CONDITIONS WILL REMAIN FAIRLY QUIET WEATHER FOR THE REMAINDER OF
THE AFTERNOON AND THROUGH THE NIGHT. THE MAIN ISSUE TONIGHT WILL
BE WINDS BECOMING ELY AND GRADUALLY STRENGTHENING, THE NEXT
CONCERN WILL BE THE APPROACHING WINTER STORM SYSTEM CURRENTLY OVER
THE RED RIVER VALLEY OF TEXAS AND OKLAHOMA. INITIALLY...THE
TERMINALS WILL SEE INCREASING MID-LEVEL CLOUD COVER WITH ELY WINDS
STRENGTHENING THROUGH TOMORROW MORNING. THE LATEST MODEL GUIDANCE
SUGGESTS THAT PCPN ONSET WILL BE A LITTLE LATER AS THE SYSTEM IS
SLOW TO MOVE THROUGH THE SOUTH HIGH PLAINS. ALSO...THIS WILL ALLOW
FOR AN OPPORTUNITY FOR SOME WARMER AIR TO REACH NRN IL/IN AND NOW
ANTICIPATE THAT THE INITIAL PCPN WITH EITHER BE A RAIN/SNOW MIX OR
ALL RAIN. THE PCPN SHOULD CHANGE OVER TO ALL SNOW WITHIN AN HOUR
OR TWO OF ONSET. ALSO...CIG/VIS CONDITIONS WILL SIMILARLY DEGRADE
RAPIDLY WITH THE ONSET OF PCPN...QUICKLY REDUCING FROM VFR TO IFR
SHORTLY AFTER PCPN OVERSPREADS THE TERMINALS. WITH TEMPERATURES
LIKELY TO REMAIN CLOSE TO THE FREEZING MARK...THE SNOW WILL BE OF
A WET/HEAVY TYPE WITH FAIRLY LOW SNOW TO LIQUID RATIONS.
ACCUMULATING SNOW IS LIKELY TO PERSIST THROUGH THE AFTERNOON AND
INTO THE EVENING WITH ASSOCIATED IFR CIG/VIS CONDITIONS.

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS THROUGH TOMORROW
  MORNING.

* MEDIUM CONFIDENCE IN PCPN ONSET TIMING AND TYPE...WITH LOWER
  CONFIDENCE IN EXACT TIMING OF CHANGEOVER OF RAIN/SNOW MIX TO ALL
  SNOW.

* MEDIUM CONFIDENCE IN TIMING OF CIGS/VIS TO DROP TO MVFR...AND
  THEN IFR.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT THROUGH WEDNESDAY...SNOW LIKELY WITH LIGHT
ACCUMULATIONS POSSIBLE. IFR.
THURSDAY THROUGH SATURDAY...MVFR. PERIODIC LIGHT SNOW OR FLURRIES.
SUNDAY...VFR.

BMD

&&

MARINE...
310 AM CST

LOW PRESSURE WILL DEEPEN OVER THE PLAINS TODAY AND LIFT NORTHEAST
REACHING THE MID MISSISSIPPI VALLEY BY LATE TONIGHT...THEN INTO
CENTRAL INDIANA BY LATE TUESDAY EVENING. THE GRADIENT WILL TIGHTEN
OVER LAKE MICHIGAN AS THIS OCCURS WITH WINDS INCREASING TO GALES
FROM SOUTH TO NORTH ACROSS THE LAKE STARTING EARLY TUESDAY MORNING
AND OVERSPREADING THE LAKE BY MID AFTERNOON. WINDS ARE EXPECTED TO
PEAK AROUND 40 KT ACROSS THE SOUTHERN HALF OF THE LAKE TUESDAY
AFTERNOON. THE LOW CONTINUES NORTHEAST INTO THE EASTERN GREAT LAKES
REGION WEDNESDAY WITH A MODERATE TO STRONG NORTHERLY GRADIENT
REMAINING OVER LAKE MICHIGAN. CURRENT EXPECTATIONS ARE FOR WINDS TO
HOVER BETWEEN 30-35 KT THROUGH AT LEAST THURSDAY. BY LATE
THURSDAY OR FRIDAY THE LOW BEGINS TO MOVE OFF THE EAST COAST AND
THE GRADIENT WEAKENS OVER LAKE MICHIGAN ALLOWING WINDS TO
GRADUALLY DIMINISH. BMD

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022...6
     AM TUESDAY TO MIDNIGHT WEDNESDAY.

IN...NONE.
LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...6 AM TUESDAY TO 3 AM
     THURSDAY.

     GALE WATCH...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...3 AM THURSDAY TO
     MIDNIGHT FRIDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ868...3 PM TUESDAY TO 3 AM THURSDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742...4 AM TUESDAY TO 10 PM
     TUESDAY.

     GALE WARNING...LMZ743-LMZ744-LMZ745...4 AM TUESDAY TO 4 PM
     TUESDAY.

&&

$$