Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 281722
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1222 PM EST WED JAN 28 2015

.SYNOPSIS...
ISSUED AT 401 AM EST WED JAN 28 2015

CLOUDS WILL INCREASE TODAY AS A RIDGE OF HIGH PRESSURE SHIFTS OFF TO
THE EAST. AN UPPER LEVEL DISTURBANCE ACROSS THE ROCKIES WILL TRACK
INTO THE GREAT LAKES AND OHIO VALLEY REGIONS TONIGHT BRINGING A
WINTRY MIX LATE TONIGHT INTO THURSDAY. SOME MINOR ICE AND SNOW
ACCUMULATIONS ARE POSSIBLE...PARTICULARLY ACROSS FAR NORTHERN
INDIANA...MUCH OF LOWER MICHIGAN...AND NORTHWEST OHIO. HIGH
TEMPERATURES TODAY WILL RANGE FROM THE UPPER 30S ACROSS NORTHEAST
ILLINOIS TO THE UPPER 20S ACROSS NORTHWEST OHIO AND SOUTHEAST LOWER
MICHIGAN. STEADY OR SLOWLY RISING TEMPERATURES ARE EXPECTED THROUGH
MUCH OF TONIGHT.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 401 AM EST WED JAN 28 2015

AFTER CONTINUED QUIET WEATHER CONDITIONS TODAY...ATTENTION FOR
TONIGHT WILL TURN TO NEXT SYSTEM THAT COULD BRING A WINTRY MIX TO
THE AREA INTO THURSDAY.

LARGE SCALE SUBSIDENCE CONTINUES EARLY THIS MORNING AS UPSTREAM
UPPER LEVEL RIDGE AXIS BEGINS TO SHIFT EASTWARD ACROSS THE SOUTHERN
GREAT LAKES TODAY. SOUTHERLY FLOW WILL INCREASE TOADY AS LOW LEVEL
ANTICYCLONE SHIFTS EASTWARD...WITH MAINLY JUST AN INCREASE IN MID
AND HIGH LEVEL CLOUDINESS THROUGH THE DAY AS MID LEVEL WAA
STRENGTHENS MORE SUBSTANTIALLY LATE THIS AFTERNOON. DESPITE
STRENGTHENING LOW LEVEL WAA LATER...A VERY STRONG LOW LEVEL
INVERSION WILL LIMIT AFTERNOON TEMPS...ESPECIALLY CONSIDERING
THICKENING MID LEVEL CLOUDS LATER THIS AFTERNOON. PREVIOUS
FORECASTED MAX TEMPS FROM LOWER TO MID 30S WEST...TO UPPER 20S
EAST...STILL APPEAR REASONABLE.

A FAIRLY ROBUST UPPER LEVEL PV ANOMALY APPROACHING THE ROCKIES
THIS MORNING WILL REACH THE SOUTHERN GREAT LAKES/OHIO VALLEY BY
EARLY THURSDAY MORNING. AN AXIS OF 40-50 KNOT SOUTHWESTERLY LOW
LEVEL FLOW PRECEDING THIS UPPER PV ANOMALY WILL ALLOW FOR ZONE OF
STRONG ISENTROPIC LIFT AND AN AXIS OF LOW/MID LEVEL MOISTURE
CONVERGENCE WORKING FROM WEST TO EAST ACROSS THE AREA THIS EVENING
INTO THE EARLY PORTIONS OF THE OVERNIGHT. DIFFERENTIAL WARM
ADVECTION WILL ALSO ALLOW PLUME OF FAIRLY STEEP MID LEVEL LAPSE
RATES TO OVERSPREAD THE AREA DURING THE EVENING HOURS. WHILE UPPER
FORCING WILL STILL LAG TO THE WEST FOR MUCH OF THE NIGHT...NAM/GFS
DO DEPICT STRENGTHENING 850-700 HPA QVEC CONVG SIGNAL OVERSPREADING
AREA THIS EVENING...WHICH WILL BE FOLLOWED BY PERIOD OF MORE
PRONOUNCED UPPER FORCING LATE TONIGHT INTO EARLY THURSDAY.

PTYPE QUESTIONS STILL ARE THE MAIN CONCERN WITH THIS SYSTEM AS
SUBSTANTIAL LOW LEVEL WARM LAYER ADVECTING INTO THE AREA AND AN
INITIALLY DRY LOW/MID LEVEL AIR MASS (EVAPORATIVE COOLING EFFECTS)
WILL MAKE FOR CHALLENGING FORECAST. DID MAINTAIN SOME LOW TO MID
RANGE CHANCE POPS LATE EVENING INTO THE EARLY PORTION OF OVERNIGHT
GIVEN AXIS OF STRONG LOW/MID LEVEL THETAE ADVECTION AND STEEPENING
MID LEVEL LAPSE RATES...WITH SOME LIGHT FREEZING RAIN POSSIBLE
ESPECIALLY AT PRECIP ONSET. IT DOES APPEAR AS THOUGH PRECIP ACROSS
THE WEST SHOULD TRANSITION TO LIQUID AS PRIMARY LOW LEVEL MOISTURE
AXIS SHIFTS INTO THE AREA ALONG WITH NON-DIURNAL TEMP CURVE AND
TEMPS RISING INTO THE MID 30S. ACROSS THE FAR NORTH AND
PARTICULARLY THE NORTHEAST PORTIONS OF THE CWA WHERE A WEAKER WARM
LAYER IS EXPECTED...MIXED PRECIP IN THE FORM OF LIGHT FREEZING
RAIN/SLEET/SNOW MAY BE MORE OF AN ISSUE THROUGH EARLY THURSDAY
MORNING. SOME LIGHT ICE ACCUMULATION IS POSSIBLE MAINLY NORTH OF
ROUTE 30...WITH PERHAPS BEST CHANCE OF MEASURABLE ICE ACCUMULATION
ACROSS EXTREME NORTHEAST INDIANA INTO PORTIONS OF SOUTH CENTRAL
LOWER MICHIGAN AND NORTHWEST OHIO. CONFIDENCE IN MIXED PRECIP
DURATION/LOCATION A BIT TOO LOW FOR ANY HEADLINES AT THIS TIME BUT
WILL NEED TO MONITOR THIS CLOSELY DUE TO TIMING WITH THURSDAY
MORNING COMMUTE. THE POSSIBILITY DOES EXIST THAT AN ADVISORY WILL
BE NEEDED FOR THIS PERIOD FOR PORTIONS OF THE AREA.

&&

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 401 AM EST WED JAN 28 2015

ACTIVE LONG TERM PERIOD WITH NUMEROUS ISSUES TO DISCUSS. THURSDAY`S
WINTRY MIX AND POTENTIAL SUNDAY STORM ARE THE PRIMARY ITEMS OF NOTE
BUT THERE WILL BE INTERMEDIATE PERIODS OF LAKE EFFECT SNOW AS WELL
AND AT LEAST A BRIEF RETURN TO MUCH COLDER TEMPS EARLY NEXT WEEK.

PRECIP TYPES FOR THURSDAY STILL APPEAR VERY MESSY. CONTINUED WARM
AND MOIST AIR ADVECTION WITH STRONG SOUTHERLY WINDS AT THE SURFACE
WILL PUSH WET BULB TEMPS ABOVE FREEZING BY THURSDAY MORNING.
FREEZING RAIN SHOULD TRANSITION TO JUST RAIN BY 12Z THURSDAY IN ALL
BUT OUR FAR NORTHEAST COUNTIES WHERE IT MAY PERSIST FOR AN HOUR OR
TWO LONGER. HOWEVER...ARRIVAL OF SECONDARY NORTHERN STREAM VORT MAX
WILL DO TWO THINGS. ONE...INCREASE COVERAGE OF MEASURABLE PRECIP IN
OUR CWA FOR THE MIDDAY PERIOD WITH AN ADDED BUMP OF CVA-FORCED
ASCENT IN A VERY MOIST ENVIRONMENT. AND TWO...ALLOW COLDER AIR TO
FILTER BACK INTO THE AREA BEHIND SURFACE LOW TRACKING EASTWARD. THIS
WILL FORCE A CHANGEOVER TO SNOW FROM NORTH TO SOUTH DURING THE
AFTERNOON WITH A PERIOD OF SLEET ALSO POSSIBLE DURING THE
TRANSITION. EXPECTING LITTLE IF ANY ACCUMULATION THOUGH. TROWAL AXIS
AND BEST MIDLEVEL CVA BYPASS US TO THE NORTH AND WARM/WET GROUND
WILL PREVENT MOST OF WHAT DOES FALL FROM ACCUMULATING. THINK A FEW
TENTHS AT BEST FOR MOST AREAS WITH UP TO AN INCH POSSIBLE IN OUR FAR
NORTHEAST COUNTIES.

SYNOPTICALLY DRIVEN SNOW WILL EXIT BY THURSDAY EVENING BUT LAKE
EFFECT WILL LIKELY CRANK UP TO SOME DEGREE OVERNIGHT. 850MB TEMPS
WILL DROP TO ROUGHLY -16C BEHIND A THIRD SHORTWAVE DIVING THROUGH
THE CENTRAL GREAT LAKES AROUND 06Z. NEARLY IDEAL 340 DEGREE FETCH
DEVELOPS BUT LAKE INDUCED CONVECTION WILL BE BATTLING INCREASING DRY
AIR ENTRAINMENT AND A STRENGTHENING SUBSIDENCE INVERSION. CONVECTIVE
DEPTHS ARE ONLY AROUND 5 KFT AND DROP EVEN LOWER BY FRIDAY MORNING.
ON THE OTHER HAND...MUCH OF THE LAKE EFFECT CLOUD LAYER WILL BE IN
THE PREFERRED -12 TO -18C DENDRITIC GROWTH ZONE (ESPECIALLY BY LATE
THURSDAY NIGHT) AND BOTH NAM AND GFS BUFR SOUNDINGS SHOW GOOD
SUPERSATURATION WITH RESPECT TO ICE IN THAT LAYER. NOT EXPECTING ANY
SIGNIFICANT ACCUMULATIONS BUT AN INCH OR TWO IS CERTAINLY POSSIBLE
IN BERRIEN COUNTY AND HAVE RAISED POPS ACCORDINGLY. OTHER COUNTIES
MAY ALSO SEE A LIGHT DUSTING WITH STRONG BOUNDARY LAYER WINDS LIKELY
PUSHING ORPHANED BANDS PRETTY FAR INLAND.

NOW ON TO THE ELEPHANT IN THE ROOM. 00Z DETERMINISTIC GUIDANCE
TRENDED MUCH SLOWER...DEEPER...AND FURTHER NORTHWEST WITH THE
MIDLATITUDE CYCLONE SLATED TO DEVELOP OVER THE EASTERN CONUS LATE
SUNDAY. 00Z GFS IN PARTICULAR PAINTS AN OMINOUS PICTURE. HOWEVER...A
PRUDENT AND JUDICIOUS APPROACH IS DEMANDED AT THESE TIME RANGES.
CIRCUMSTANCES THAT CONSPIRE TO PRODUCE STORM DEPICTED IN THE 00Z GFS
ARE COMPLICATED TO SAY THE LEAST...INVOLVING THE INTERACTION OF
SOUTHWEST CONUS CUTOFF LOW AND TWO DISTINCT NORTHERN STREAM
SHORTWAVES THAT ARE SHOWN TO PHASE AND PRODUCE A STRONG/NEGATIVELY
TILTED TROUGH OVER THE OHIO VALLEY. SHORTWAVES IN QUESTION HAVE NOT
EVEN DEVELOPED YET MUCH LESS BEEN SAMPLED. FURTHERMORE...ENSEMBLE
MEMBERS STILL SHOW A HIGH DEGREE OF SPREAD AND ECMWF DEPICTS A LESS
ROBUST CYCLONE. RUN TO RUN VARIABILITY HAS ALSO BEEN VERY HIGH FOR
THIS TIME RANGE. ALL OF THIS IS TO SAY THAT FORECAST CONFIDENCE IS
VERY LOW AT THIS POINT...MUCH LOWER THAN EVEN A TYPICAL DAY5
FORECAST. CERTAINLY THE CHANCES FOR PRECIP ON SUNDAY ARE INCREASING
AND THE NEW FORECAST REFLECTS THAT BUT DETAILS REGARDING AMOUNTS AND
TYPES ARE VERY MUCH IN FLUX. STAY TUNED TO THE LATEST FORECASTS OVER
THE COMING DAYS AS DETAILS ARE ALMOST CERTAIN TO CHANGE.

STILL EXPECTING A BLAST OF MUCH COLDER AIR BEHIND THIS SYSTEM EARLY
NEXT WEEK. HIGHS WILL LIKELY REMAIN IN THE TEENS WITH OVERNIGHT LOWS
POTENTIALLY IN THE NEGATIVE SINGLE DIGITS. A BRIEF SHOT OF LAKE
EFFECT SNOW IS ALSO POSSIBLE IN THE COLD WAKE OF EXITING CYCLONE.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1213 PM EST WED JAN 28 2015

VFR WITH A GRADUAL INCREASE IN SOUTHERLY WINDS AND MID-HIGH LEVEL
CLOUDS CAN BE EXPECTED THIS AFTERNOON AS WARM ADVECTION COMMENCES.
MOISTURE CHANNEL WITHIN RAMPING LOW LEVEL JET WILL DRIFT EAST OVER
NORTHERN INDIANA LATER TONIGHT INTO EARLY THURSDAY MORNING IN
ADVANCE OF AN APPROACHING MID LEVEL DISTURBANCE AND ELONGATED SFC
TROUGH. THE RESULT WILL BE DETERIORATING FLIGHT CONDITIONS AND
INCREASING CHANCES FOR RAIN SHOWERS (FREEZING RAIN POSSIBLE AT
ONSET) DURING THIS TIME.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SYNOPSIS...MARSILI
SHORT TERM...MARSILI
LONG TERM...AGD
AVIATION...STEINWEDEL


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