🚀 go-pugleaf

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1048 AM CST WED FEB 27 2013

DISCUSSION...
342 AM CST

WHILE PERIODS OF LIGHT SNOW WILL LIKELY CONTINUE FOR SOME TIME...
SNOWFALL INTENSITY HAS DIMINISHED CONSIDERABLY ACROSS THE REMAINING
WINTER STORM WARNING/ADVISORY AREAS IN NORTHEAST IL AND WILL CANCEL
REMAINING WINTER HEADLINES WITH THIS FORECAST ISSUANCE.

LIGHT/OCCASIONALLY MODERATE SNOW CONTINUES TO FALL ACROSS MUCH OF
SOUTHERN WISCONSIN AND FAR NORTH/NORTHEAST IL EARLY THIS MORNING...
IN THE ELONGATED DEFORMATION REGION OF OCCLUDING STORM SYSTEM OVER
NORTHERN INDIANA AND OHIO. DRIER MID-LEVEL AIR AND LOSS OF ICE
NUCLEI IN DRY SLOT REMNANTS OVER CENTRAL IL HAS RESULTED IN ONLY
LIGHT PRECIPITATION SOUTH OF INTERSTATE 80...MAINLY IN THE FORM OF
DRIZZLE.

EARLY MORNING WATER VAPOR IMAGERY DEPICTS THE MAIN UPPER LOW
CIRCULATION OVER NORTHERN INDIANA...WITH A COUPLE OF SMALLER
AMPLITUDE SHORT WAVE VORT MAXIMA ROTATING WEST-SOUTHWEST FROM
MICHIGAN ACROSS WI AND INTO EASTERN IA. GUIDANCE DOING ITS BEST TO
INITIALIZE THESE SMALLER SCALE FEATURES...WITH MODELS GENERALLY
SHOWING SOME AGREEMENT IN WRAPPING SHORT WAVE OVER MICHIGAN THIS
MORNING WEST/SOUTHWEST ACROSS THE WFO LOT CWA DURING THE DAY AND
BRINGING LIGHT SNOW BACK ACROSS THE AREA FROM THE NORTH/NORTHEAST
LATER THIS MORNING INTO THE AFTERNOON. QPF AMOUNTS RANGE ROUGHLY
0.15-0.25 INCHES WEST TO EAST ACROSS THE CWA THROUGH 00Z...THOUGH
THESE AMOUNTS AREA LIKELY OVER DONE BASED ON CURRENT TRENDS.
RELATIVELY WARM THERMODYNAMIC PROFILES SUPPORT EXPECTED SNOW/LIQUID
RATIOS STILL ON THE LOW SIDE OF AVERAGE...ROUGHLY 10:1 OR LESS.
NONETHELESS...THIS COULD SUPPORT LOCALIZED ADDITIONAL 1-2 INCH SNOW
ACCUMULATIONS IN SOME SPOTS THROUGH THIS AFTERNOON...WITH AREAS
NORTH OF I-80 GENERALLY MORE FAVORED. PATCHY DRIZZLE/FOG AT TIMES
MIXED WITH SOME LIGHT SNOW SOUTH OF I-80 THIS MORNING ARE EXPECTED
TO CHANGE BACK OVER TO LIGHT SNOW BY AFTERNOON WITH THE APPROACH OF
THE AFOREMENTIONED SHORT WAVE. THE MAIN MID-LEVEL VORT SHIFTS SOUTH
OF THE FORECAST AREA THIS EVENING...WITH A CORRESPONDING LOSS OF
MID-LEVEL VERTICAL MOTION NOTED IN WRF-NAM AND GFS TIME/HEIGHT
PLOTS. LOW LEVELS REMAIN MOIST INTO THURSDAY MORNING HOWEVER...WITH
GUIDANCE INDICATING WEAKER SHEARED MID-LEVEL VORTICITY WRAPPING
AROUND THE WESTERN PERIPHERY OF THE UPPER LOW THOUGH TONIGHT. THIS
SUGGESTS THE POTENTIAL FOR SOME LINGERING LIGHT SNOW SHOWERS OR
FLURRIES INTO THURSDAY. RELATIVELY WARM TEMPERATURE PROFILES SUGGEST
THAT PRECIP COULD CHANGE OVER TO DRIZZLE AT TIMES TONIGHT/THURSDAY
AS MID LEVEL LIFT/SATURATION DECREASES...THOUGH CONFIDENCE FAIRLY
LOW WITH PLENTY OF HIGHER ALTITUDE MOISTURE AVAILABLE FOR SEEDING
LOWER CLOUDS.

WITH UPPER LOW CONTINUING TO MOVE SLOWLY OFF TO THE EAST AND
ASSOCIATED DECREASE IN FORCING FOR ASCENT THURSDAY...WIDESPREAD
PRECIP LOOKS TO GREATLY DIMINISH...THOUGH LONG PERIOD OF NORTHERLY
LOW LEVEL WIND FLOW DOES RAISE THE QUESTION OF LAKE EFFECT
POTENTIAL. THERMODYNAMICALLY...CONDITIONS ARE EXTREMELY MARGINAL
THROUGH THURSDAY WITH LAKE SURFACE TO 850 MB TEMP DIFFERENCE ONLY
10/11 DEG C...AND EQUILIBRIUM HEIGHTS FROM THE WRF-NAM COMPUTED AT
LESS THAN 5000 FT. ONLY CONVERGENCE ALONG THE WESTERN SHORE OF THE
LAKE WITH LONG FETCH OF NORTH-NORTHEAST WINDS IS FAVORABLE...BUT
WITH LITTLE THREAT OF PRODUCING ANY SIGNIFICANT MEASURABLE LAKE
EFFECT. MODELS DEPICT COLDER AIR EVENTUALLY SPREADING SOUTH ACROSS
THE LAKE FRIDAY NIGHT/SATURDAY AS THE OLD LOW FINALLY PULLS FARTHER
OFF TO THE EAST...WITH LAKE/850 MB DELTA-T IMPROVING TO AROUND 18
DEG WITH INVERSION HEIGHTS EXCEEDING 6000 FT ON SATURDAY. HAVE
MAINTAINED AT LEAST A LOW CHANCE POTENTIAL OF SNOW SHOWERS FOR AREAS
NEAR THE LAKE IN NORTHEAST IL/FAR NORTHWEST INDIANA THURSDAY NIGHT
THROUGH SATURDAY...BEFORE SURFACE HIGH PRESSURE RIDGE BUILDS EAST
SUNDAY AND BREAKS DOWN THE PERSISTENT NORTHERLY FETCH LATE SUNDAY.
SOME POTENTIAL FOR SOME LIGHT ACCUMULATIONS WILL LIKELY EXIST IN THE
FRIDAY-SATURDAY TIME FRAME...BUT WILL HAVE TO MONITOR OVER THE NEXT
COUPLE OF DAYS TO BETTER REFINE THE MESOSCALE ASPECTS OF THE
POTENTIAL LAKE SNOW SHOWER THREAT.

SUNDAY/MONDAY...LONGER RANGE GUIDANCE IS IN GENERAL AGREEMENT IN
BUILDING HIGH PRESSURE RIDGE SOUTHEAST ACROSS THE GREAT LAKES
REGION. GLOBAL MODELS CONTINUE TO DIG A SHORT WAVE TROUGH SOUTHEAST
ACROSS THE NORTHERN PLAINS AND MISSOURI VALLEY LATER MONDAY INTO
TUESDAY...WITH THE POTENTIAL FOR SOME LIGHT SNOW ACROSS MO/IA/IL.

AS FOR TEMPERATURES...NOT MUCH CHANGE EXPECTED TODAY AND THURSDAY AS
ONLY MODEST COLD ADVECTION INITIALLY DEVELOPS BEHIND SLOWLY
RETREATING LOW TO OUR EAST. HIGHS IN THE MID 30/LOW IN THE 20S AS
DEPICTED BY VARIOUS MODEL MOS APPEAR REASONABLE. FRIDAY-SUNDAY LOOK
TO BE A LITTLE COOLER AS COLD AIR MAKES MORE OF AN INTRUSION...HIGHS
IN THE UPPER 20S/LOW 30S AND LOWS IN THE TEENS/20S WILL PROVIDE A
SUB-AVERAGE START TO MARCH.

RATZER

&&

AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* PREVAILING IFR CEILINGS INTO TONIGHT.

* TIMING OF PERIODS OF HEAVIER SNOWFALL REDUCING VISIBILITIES TO
  IFR.

* NW WINDS GRADUALLY BECOME NNW WHILE INCREASING WITH GUSTS OF 14
  TO 18 KT DURING THE

TRS

//DISCUSSION...UPDATED 12Z...

AREA OF LOW PRESSURE OVER NORTHWESTERN OHIO EARLY THIS MORNING WILL
GRADUALLY TRANSITION EAST TODAY...BUT CYCLONIC FLOW WILL PERSIST
ACROSS NORTHERN ILLINOIS...WITH PINWHEELING VORT LOBES ROTATING
SOUTH ACROSS THE AREA KEEPING PERIODIC LIGHT SNOW AND FLURRIES IN
THE FORECAST TODAY. EXPECT SNOW TO INTENSIFY SOME THIS AFTERNOON AS
ONE OF THESE UPPER WAVES MOVES ACROSS THE AREA. VSBY MAY DROP TO A
MILE OR LESS AT TIMES...WITH LIGHT ACCUMULATIONS POSSIBLE. SEEMS THE
BEST CHANCE FOR THIS WILL BE EARLY TO MID AFTERNOON AND LASTING FOR
A FEW HOURS...BUT TIMING IS UNCERTAIN. CIGS SHOULD REMAIN IFR OR
LOW END MVFR THROUGH THE DAY. UPPER LEVEL RIDGING WILL BEGIN TO
BUILD INTO THE AREA THIS EVENING AND TONIGHT. INCREASING
SUBSIDENCE FROM THE WEST SHOULD EVENTUALLY ALLOW SNOW TO END
OVERNIGHT.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM CONFIDENCE IN CIG/VSBY TRENDS.

* MEDIUM CONFIDENCE IN TIMING OF SOMEWHAT HEAVIER SNOWFALL
  PRODUCING MINOR ACCUMULATIONS.

* MEDIUM CONFIDENCE IN WIND TRENDS.

TRS

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

THURSDAY NIGHT THROUGH SATURDAY...MVFR. PERIODIC LIGHT SNOW OR
FLURRIES.
SUNDAY...MVFR POSSIBLE.
MONDAY...VFR.
TUESDAY...CHANCE OF SNOW. MVFR.

BMD

&&

MARINE...
301 AM CST

LOW PRESSURE OVER NORTHWESTERN OHIO EARLY THIS MORNING WILL SLOWLY
MOVE EAST THROUGH THE REMAINDER OF THE WEEK...MOVING OFF INTO THE
ATLANTIC THURSDAY. MEANWHILE...STRONG HIGH PRESSURE WILL DEVELOP
OVER HUDSON BAY WITH RIDGING EXTENDING SOUTHWEST INTO THE NORTHERN
PLAINS. THIS WILL MAINTAIN A MODERATE TO STRONG GRADIENT WITH LOW
END GALES EXPECTED TO CONTINUE ACROSS MUCH OF THE LAKE THROUGH
THURSDAY...AND REMAIN FRESH THROUGH EARLY INTO THE WEEKEND. WINDS
THIS MORNING HAVE LET UP A LITTLE OVER THE SOUTH HALF OF THE
LAKE...BUT WILL INCREASE THROUGH THE DAY AND SHOULD PEAK AGAIN
OVERNIGHT AS THE GRADIENT TIGHTENS AND MODERATE PRESSURE RISES
DEVELOP BEHIND THE DEPARTING LOW AND AHEAD OF THE HIGH. LATE IN THE
WEEKEND...THE RIDGE AXIS IS EXPECTED TO SETTLE EAST INTO THE GREAT
LAKES REGION ALLOWING WINDS TO DIMINISH.

BMD

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SATURDAY.

&&

$$