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Area Forecast Discussion

000
FXUS63 KIWX 212300
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
600 PM EST SUN DEC 21 2014

.SYNOPSIS...
ISSUED AT 1217 AM EST SUN DEC 21 2014

HIGH PRESSURE OVER THE EASTERN U.S. WILL CONTINUE TO CAUSE FAIR
WEATHER ACROSS OUR AREA TONIGHT. A LOW PRESSURE SYSTEM WILL MOVE
SOUTHEAST INTO THE CENTRAL PLAINS MONDAY. RAIN ASSOCIATED WITH
THIS SYSTEM WILL LIKELY SPREAD INTO WESTERN PORTIONS OF THE AREA
MONDAY AFTERNOON... WHILE EASTERN COUNTIES SHOULD STAY DRY THROUGH
EARLY EVENING. LOWS TONIGHT WILL BE IN THE UPPER 20S AND LOWER
30S... WITH HIGHS ON MONDAY IN THE LOWER AND MIDDLE 40S.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 332 PM EST SUN DEC 21 2014

POCKET OF DRIER AIR IN LOW LEVELS HAS SPREAD N-NW FROM THE OH VALLEY 
INTO OUR AREA AS SFC RIDGE CONTS TO MOVE SLOWLY EAST ACROSS THE ERN 
CONUS. BROAD UPR LEVEL TROF OVER THE PLAINS WILL AMPLIFY TONIGHT AND 
MONDAY AS SHRTWV OVER MT AND ACCOMPANYING STRONG JET OVER THE PAC 
NW/ERN PAC DIGS SEWD WITH SYSTEM CLOSING OFF AND BECOMING
VERTICALLY STACKED IN THE VCNTY OF OMA BY MON EVE. WARM FRONT
EXTENDING SE FROM THE LOW TO THE LOWER OHIO VALLEY MONDAY MORNING
WILL LIFT N-NE DURING THE DAY. BEST FORCING/MOISTURE TRANSPORT
ASSOCIATED WITH THE WARM FRONT WILL OVERSPREAD WRN PORTIONS OF THE
CWA AND POINTS WESTWARD MONDAY SUGGESTING RAIN LIKELY MOVG INTO
THIS AREA DURING THE AFTN... WHILE JUST A SLIGHT CHC OF PRECIP
REACHING THE EASTERN COUNTIES.

ALTHOUGH WAA WILL STRENGTHEN ACROSS THE AREA OVERNIGHT... JUST SOME 
HIGH THIN CLOUDS DURING THE EVE WITH STILL FAIRLY LIGHT WINDS SHOULD 
ALLOW TEMPS TO FALL INTO THE U20S/L30S. STAYED CLOSE TO PREVIOUS
FCST HIGHS MONDAY WHICH WERE GENERALLY ON THE WARM END OF 12Z MOS
GUIDANCE AS EXPECT CONTD WAA AND INCREASED GRADIENT WINDS/MIXING
WILL ALLOW TEMPS TO REACH THE L-M40S.
 

&&

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 332 PM EST SUN DEC 21 2014

FRUSTRATING MODEL INCONSISTENCIES CONTINUE WITH RESPECT TO POTENTIAL 
CHRISTMAS EVE STORM. TREND SEEN IN LAST NIGHT'S 00Z DATA FOR A LATER 
PHASE/MORE PROGRESSIVE SURFACE LOW IN OUR AREA CONTINUED TO SOME 
DEGREE INTO THIS MORNING BUT STILL A HIGH DEGREE OF INTERMODEL AND 
RUN-TO-RUN VARIABILITY IN THE FINE SCALE DETAILS. 170+ KT UPPER 
LEVEL JET THAT WILL DRIVE THIS EVENT IS JUST NOW COMING ONSHORE. 
HOPEFULLY WILL HAVE SOME MORE DEFINITIVE ANSWERS BY TOMORROW AS THIS 
JET IS FULLY SAMPLED BY THE NOAM RAOB NETWORK.

INCREASING WAA AHEAD OF LEAD WAVE WILL BRING WIDESPREAD RAINFALL TO 
THE AREA MONDAY NIGHT INTO TUESDAY. EFFICIENT MOISTURE TRANSPORT AND 
290-295K ISENTROPIC ASCENT ASSOCIATED WITH INCREASING SOUTHERLY LLJ 
SUPPORT CATEGORICAL POPS DESPITE SOME LINGERING UNCERTAINTY AS TO 
EXACT TIMING AND TOTAL QPF AMOUNTS. MAIN JET CORE AND ATTENDANT PV 
ANOMALY WILL THEN ROUND THE BASE OF LONGWAVE TROUGH TUESDAY NIGHT 
INTO WEDNESDAY AND SUPPORT SECONDARY CYCLOGENESIS SOMEWHERE OVER THE 
OHIO VALLEY. IT IS THE EXACT TIMING AND LOCATION OF THIS SECONDARY 
WAVE THAT HAS CAUSED SO MUCH DIFFICULTY FOR THE VARIOUS NWP 
SOLUTIONS. AS NOTED EARLIER...OVERALL TREND IN THE PAST FEW CYCLES 
HAS BEEN FOR A MORE PROGRESSIVE/OPEN TROUGH THROUGH OUR AREA...NOT 
BECOMING NEGATIVELY TILTED/RAPIDLY DEEPENING UNTIL IT REACHES 
CANADA. AS HAS BEEN MENTIONED FREQUENTLY...THERE IS NO GOOD SOURCE 
OF COLD AIR UPSTREAM AND A WEAKER/MORE PROGRESSIVE SURFACE LOW WILL 
STRUGGLE TO PULL IN SUB-FREEZING AIR BEFORE THE BEST FORCING FOR 
ASCENT EXITS. AND WHILE THE LATEST CONSENSUS TRACK IS SLIGHTLY 
FURTHER EAST...STILL LOOKS LIKE A LIMITED WINDOW FOR ANY SIGNIFICANT 
SNOWFALL ACCUMULATIONS LATE WEDNESDAY. THAT WILL BE ESPECIALLY TRUE 
GIVEN WARM/WET GROUND CONDITIONS AND VERY MARGINAL THERMAL PROFILES.
A QUICK LOOK AT THE NEW 12Z ECMWF SHOWS A STRONGER OHIO VALLEY LOW 
BUT SURFACE WET BULBS STILL HOVERING RIGHT AROUND FREEZING. TAKING A 
MORE HOLISTIC APPROACH...DECIDED ON NO MAJOR CHANGES TO THE GOING 
FORECAST GIVEN THE LEVEL OF UNCERTAINTY. STILL SUSPECT AT LEAST A 
BRIEF PERIOD OF LIGHT SNOW AND GUSTY WINDS WEDNESDAY EVENING BUT THE 
MAGNITUDE OF WHICH IS YET INDETERMINABLE.

WHILE CHANCES FOR A SIGNIFICANT EVENT APPEAR LOW...THERE IS STILL 
LITTLE CONFIDENCE IN ANY ONE PARTICULAR SOLUTION. ANYONE WITH 
CHRISTMAS EVE TRAVEL PLANS SHOULD STILL KEEP AN EYE ON THE LATEST 
FORECASTS. EVEN AN ADVISORY-LEVEL EVENT CAN CAUSE LARGE DISRUPTIONS 
ON A BUSY TRAVEL DAY.

THERE IS ANOTHER CHANCE FOR RAIN OR SNOW ON FRIDAY BUT WILL HAVE TO 
GET CHRISTMAS EVE STORM SORTED OUT BEFORE ANY MEANINGFUL DISCUSSION 
OF FRIDAY. DOES APPEAR TO GET COLDER HEADING INTO THE WEEKEND AND 
EARLY NEXT WEEK THOUGH...WITH A RETURN TO NORTHWEST FLOW AND ARCTIC 
AIR AT LEAST MAKING A RUN FOR OUR LOCAL AREA.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 600 PM EST SUN DEC 21 2014

DRIER BNDRY LYR AIR HAD FILTERED THROUGH THE CWA THIS AFTN AND HAS
SCOURED OUT STRATUS PLAGUE OF LATE. HWVR FAIRLY INTENSE LOW PRES
PROGGED TO ORGANIZE THROUGH THE CNTRL PLAINS ON MONDAY W/RESULTANT
SIG DOWNSTREAM MSTR ADVTN TAKING SHAPE. THUS XPC FLIGHT CONDS WILL
DETERIORATE CONSIDERABLY MONDAY AFTN AS RAIN DVLPS.

&&

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

$$

SYNOPSIS...JT
SHORT TERM...JT
LONG TERM...AGD
AVIATION...T

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