Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 261106
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
606 AM EST THU FEB 26 2015

.SYNOPSIS...
ISSUED AT 151 AM EST THU FEB 26 2015

A LOW PRESSURE AREA WILL MOVE SOUTHEAST OUT OF THE REGION EARLY
TODAY...LEAVING SOME LIGHT SNOW ACCUMULATIONS. SNOWFALL AMOUNTS
OVER NORTHEAST ILLINOIS SHOULD RANGE FROM 1 TO 3 INCHES...WITH
AROUND AND INCH OVER NORTHERN INDIANA. MUCH COLDER AIR WILL
RETURN TO THE REGION BEHIND THIS SYSTEM...WITH HIGHS TODAY ONLY
FROM 10 TO AROUND 15. TEMPERATURES WILL PLUMMET BELOW ZERO LATE
TONIGHT.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 440 AM EST THU FEB 26 2015

A WEAK LOW PRESSURE AREA WITH LIMITED LIFT WILL MOVE SOUTHEAST OUT
OF THE AREA EARLY TODAY AS MUCH COLDER AND DRIER AIR SPREADS BACK
OVER THE FORECAST AREA. FAVOR A BLEND OF HIGH RES MODELS...INCLUDING
THE ARW...THE NMM AND 12KM NAM. UPSTREAM LAKE HURON AND EASTERN
LAKE SUPERIOR WILL NOT CONTRIBUTE MUCH MOISTURE FLUX INTO THE LOWER
ATMOSPHERE GIVEN NEAR 100 PERCENT ICE COVERAGE ON THESE LAKES. EARLY
THIS MORNING...ARCTIC AIR WAS SPREADING UNDER THE DEPARTING SYSTEM
WITH BITTERLY COLD TEMPERATURES. READINGS AT 3 AM EDT INCLUDED TEMPS
AS COLD AS -22 OVER NORTHERN LOWER MICHIGAN. GIVEN AN INITIAL
NORTHEAST FLOW...EXPECT SNOW TO END LATER TODAY WITH DRY AIR
ENTRAINMENT IN THE LOWER ATMOSPHERIC LAYERS AND ENDING ISENTROPIC
LIFT PER 285K SURFACE. KEPT SNOWFALL AMOUNTS AROUND OR UNDER AN
INCH...WITH THE LIGHTEST AMOUNTS OVER FAR SOUTHERN LOWER MICHIGAN
WHERE DRY AIR ENTRAINMENT WILL LIMIT AMOUNTS. COLD AIR ADVECTION
SHOULD OFFSET DIURNAL WARMING TODAY WITH WITH LIMITED TEMPERATURES
RISES. SOME CLEARING IS EXPECTED LATE TONIGHT WILL TEMPERATURES
DROPPING WELL BELOW ZERO MOST AREAS.

&&

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 440 AM EST THU FEB 26 2015

AN ACTIVE LONG TERM PERIOD WITH TWO POTENTIALLY SIGNIFICANT WEATHER
SYSTEMS POSSIBLE.

PERIOD WILL BEGIN QUIET AND VERY COLD WITH HIGH PRESSURE SLIDING
ACROSS THE REGION FRIDAY INTO SATURDAY. CLEAR SKIES AND LIGHT WINDS
FRIDAY NIGHT WILL ALLOW TEMPERATURES TO FALL BELOW ZERO ONCE AGAIN
WITH COLDEST READINGS EXPECTED OVER THE SOUTHEAST AND FAR EAST WHERE
INFLUENCE OF HIGH WILL KEEP WINDS LIGHT OR CALM MOST OF NIGHT. LOWS
TO BOTTOM OUT 4 TO 9 DEGREES BELOW ZERO.

FOCUS QUICKLY SHIFTS TO SNOW MAKER FOR LATE SATURDAY NIGHT AND
SUNDAY. BROAD SOUTHWEST FLOW ALOFT WILL DEVELOP AS AN UPPER LOW
SINKS SOUTH ALONG WEST COAST OF CA THIS WEEKEND. WEAK SHORT WAVES
WILL MOVE NORTHEAST WHILE UPPER LEVEL JET WILL STRENGTHEN OVER THE
GREAT LAKES SAT NIGHT AND SUNDAY. LOW LEVEL MOISTURE ADVECTION RAMPS
UP IN RESPONSE AND LOW LEVEL JET INCREASES WITH GULF OF MEXICO
BECOMING TAPPED. GFS40 AND ECMWF BOTH SHOWING 3-3.5 G/KG MIXING
RATIOS OVER THE AREA SUNDAY WITH LONG DURATION SYSTEM RELATIVE
ISENTROPIC LIFT. GARCIA METHOD CURRENTLY SUGGEST 5 TO 8 INCH TOTALS
POSSIBLE GIVEN THE 12 TO 18 HOUR WINDOW OF ISENTROPIC LIFT. BUFKIT
SOUNDINGS SHOW DGZ TO BE RATHER HIGH BUT DEEP IN THE 10-15KFT RANGE
WITH GOOD LIFT. THIS WOULD BE INDICATIVE OF SNOW RATIOS NEAR CLIMO
WHICH WOULD BE AROUND 13 TO 1. MODEL QPF SUPPORTIVE OF GARCIA
NUMBERS WITH GFS INDICATING 24HR AMOUNTS A LITTLE OVER THREE
QUARTERS OF AN INCH AND ECMWF A LITTLE OVER SIX TENTHS. ANY
POTENTIAL MESOSCALE BANDING WITH THIS MOISTURE AND LIFT COULD LEAD
TO LOCALLY HIGHER AMOUNTS. IT STILL REMAINS EARLY FOR THOSE DETAILS
AS WELL AS ANY HEADLINES BUT MODEL RUN TO RUN CONTINUITY AND
AGREEMENT HAS BEEN PRETTY GOOD LAST SEVERAL RUNS. WANTED TO BUMP
POPS FURTHER INTO CATEGORICAL RANGE BUT ENDED UP STANDING OUT
COMPARED TO NEIGHBORING OFFICES. THEREFORE KEPT POPS IN HIGH LIKELY
CATEGORY FOR NOW.

AFOREMENTIONED WEST COAST LOW WILL EVENTUALLY BE ABSORBED INTO
SOUTHWEST FLOW MONDAY AS ADDITIONAL ENERGY DROPS SOUTH INTO WESTERN
CONUS TROUGH. THIS WILL BE OUR NEXT WEATHER MAKER FOR MONDAY NIGHT
AND TUESDAY. WHILE THIS STILL REMAINS WELL INTO THE EXTENDED
PERIOD...CONCERN IS GROWING FOR A SIGNIFICANT PCPN EVENT WITH A
VARIETY OF PCPN TYPES POSSIBLE. MODELS HINTING AT A SUBTROPICAL
MOISTURE TAP AS THIS SYSTEM EJECTS INTO THE CENTRAL CONUS. WATER
VAPOR THIS MORNING SHOWS SOURCE MOISTURE LINGERING OVER THE SOUTH
CENTRAL PACIFIC OCEAN READY TO BE TAPPED. IN ADDITION...STRONG LOW
LEVEL JET WITH GULF OF MEXICO TAP ALSO BEING SHOWN LEADING TO A VERY
WET SYSTEM WITH 4-6 G/KG MIXING RATIOS AND PRECIPITABLE WATER
AMOUNTS NEARING AN INCH. LATEST MODEL SOLUTIONS AGAIN IN RATHER GOOD
AGREEMENT WITH PCPN STARTING AS SNOW MONDAY NIGHT. WARM AIR
ADVECTION QUITE STRONG WITH 850MB TEMPS PROGGED TO RISE WELL ABOVE
ZERO TUESDAY MORNING WHILE SFC TEMPS LOOK TO LAG BY SEVERAL HOURS
AND BEGIN IN THE LOW TO MID 20S. THUS FREEZING RAIN POTENTIAL
GROWING IF THESE SOLUTIONS INDEED VERIFY. 1030MB HIGH WILL BE
DRIFTING AWAY FROM THE AREA BUT IN GOOD LOCATION TO SLOW RETREAT
OF LOW LEVEL COLD WEDGE WHILE WARM AIR ADVECTION SURGES OVER TOP. IN
ADDITION...ACTUAL SURFACE TEMPS WILL BE VERY COLD GIVEN THE RECENT
PROLONGED COLD SPELL AND ANY LIQUID PCPN WILL CERTAINLY FREEZE
QUICKLY. THUS FELT IT PRUDENT TO INTRODUCE FREEZING RAIN CHANCES
INTO FORECAST AT THIS RATHER EXTENDED PROJECTION TIME. STILL PLENTY
OF TIME FOR FURTHER ADJUSTMENTS AND EXPECT MANY CHANGES SO STAY
TUNED TO LATER FORECASTS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 603 AM EST THU FEB 26 2015

A WEAK LOW PRESSURE AREA WITH WEAK LIFT WILL MOVE SOUTHEAST OUT
OF THE AREA THIS MORNING AS MUCH COLDER AND DRIER AIR SPREADS
BACK OVER NORTHERN INDIANA FROM LOWER MICHIGAN. UPSTREAM
CONDITIONS OVER LAKE HURON AND EASTERN LAKE SUPERIOR WILL NOT
CONTRIBUTE MUCH MOISTURE GIVEN NEAR 100 PERCENT ICE COVERAGE OF
THESE LAKES...SO EXPECT CONDITIONS TO IMPROVE LATER TODAY WITH DRY
AIR ENTRAINMENT IN THE LOWER ATMOSPHERIC LAYERS. TRENDED NEW 12Z
TAFS TOWARD A LITTLE SLOWER ENDING OF SNOW AND IMPROVEMENT TO VFR
ACCORDING TO THE LATEST MODEL GUIDANCE AND TRENDS. INCLUDED TEMPO
GROUPS EARLY IN THE TAF PERIOD FOR SOMEWHAT LOWER CIGS AND VSBYS.



&&

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

$$

SYNOPSIS...SKIPPER
SHORT TERM...SKIPPER
LONG TERM...LASHLEY
AVIATION...SKIPPER


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