Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 312154
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
454 PM EST SAT JAN 31 2015

LATEST UPDATE...
CORRECTED WATCHES/WARNINGS/ADVISORIES SECTION AT BOTTOM

.SYNOPSIS...
ISSUED AT 300 PM EST SAT JAN 31 2015

SIGNIFICANT SNOWFALL IS IN STORE FOR SOUTHERN LOWER MICHIGAN AS AN
APPROACHING WINTER STORM WILL IMPACT THE AREA LATE TONIGHT AND
INTO EARLY MONDAY MORNING. GUSTY WINDS WILL LEAD TO BLOWING SNOW
AT TIMES WITH DANGEROUS TRAVEL ESPECIALLY FROM SOUTH HAVEN TO
KALAMAZOO TO JACKSON. ARCTIC AIR SETTLES IN LATER SUNDAY AND LASTS
THROUGH MUCH OF THIS UPCOMING WEEK. OCCASIONAL SNOW SHOWERS CAN BE
EXPECTED.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 300 PM EST SAT JAN 31 2015

A WINTER STORM WARNING WILL REPLACE THE WINTER WEATHER ADVISORY
FOR THE SOUTHERN TWO ROWS OF COUNTIES...IN COORDINATION WITH IWX
AND DTX AS WELL AS THE LATEST 12Z GUIDANCE SUPPORTING A SLIGHTLY FURTHER
NORTHWARD NUDGE OF EXPECTED SIGNIFICANT SNOWFALL. OVERALL...THE
HIGHEST IMPACTS FROM THIS STORM ARE EXPECTED TO CENTER ALONG AND
SOUTH OF A LINE FROM SOUTH HAVEN TO KALAMAZOO TO JACKSON...WHERE
TOTAL SNOWFALL IS EXPECTED TO BE 10"-12" BY EARLY MONDAY
MORNING...COINCIDENT WITH GUSTY WINDS THAT WILL LEAD TO BLOWING
SNOW AND DANGEROUS TRAVEL. LESS SNOW IS EXPECTED NORTH OF THERE
BUT SEVERAL INCHES WILL FALL NONETHELESS AND TRAVEL DELAYS CAN BE
EXPECTED.

AS HAS BEEN SEEN FOR SEVERAL MODEL RUNS OVER THE LAST FEW
DAYS...TRENDS HAVE BEEN POINTING TO A SLIGHTLY FURTHER NORTH
TRACK OF THIS STORM SYSTEM. DPROG/DT ANALYSIS OF THE H850 LOW
TRACK FOR THE GFS AND ECMWF HAS REVEALED THIS TREND AND THE 12Z
NWP SUITE OVERALL CONTINUES TO SUPPORT THIS NOTION. A FEW KEY
THINGS TO MONITOR WITH THIS SYSTEM INCLUDE THE SFC LOW TRACK/H850
LOW TRENDS...MULTI- LAYER F-VECTOR CONVERGENCE (FN)...AND LOCATION
OF THE DEFORMATION ZONE. THE 12Z GFS IS A BIT OF AN OUTLIER WITH
THIS SYSTEM IN REGARD TO A DEEPER LOW...MORE FAVORABLE H850 LOW
TRACK FROM STL TO IND TO TOL AND ASSOCIATED DRY SLOT NUDGING
TOWARD THE MI/OH BORDER. THIS WOULD BRING IN FAVORABLE CONVECTIVE
INSTABILITY (-EPV) CLOSE TO OUR FAR SE FORECAST AREA NEAR JACKSON.
MULTI-LAYER F-VECTOR CONVERGENCE (FN) IS SHOWN TO BE MAXIMIZED
FIRST IN NORTHERN IL AND IN BUT THEN SHIFTING TO FAR SOUTHERN
LOWER MI...POSSIBLY OVER MUCH OF THE I-94 REGION. EVEN WITHOUT
THIS SOLUTION VERIFYING...A CONSENSUS OF 12Z MODEL GUIDANCE
SUPPORTS TOTAL PRECIP AMOUNTS OF AT LEAST 0.7"-0.8" FOR OUR
SOUTHERN ROW. WITH SNOW RATIOS AT OR SLIGHTLY ABOVE 15:1...ACCUMS
WILL LIKELY REACH THE 10"-12" RANGE FOR THE I-94 CORRIDOR (SOME
LOCALLY HIGHER AMOUNTS POSSIBLE). RAW ACCUMS FROM THE GFS APPEAR
TOO HIGH WITH THIS EVENT (14"-20" FOR SOME LOCATIONS).

REGARDING DEFORMATION ZONE PRECIP...THIS WILL NEED TO BE WATCHED
CLOSELY. RIGHT NOW THE ECMWF IS SHOWING THE GREATEST DEFORMATION
TO OCCUR ACROSS NORTHERN IL/IN/OH...POSSIBLY CREEPING UP INTO FAR
SOUTHERN LOWER MI. AS THIS WILL NOT BE A VERY DEEP LOW...NOT
EXPECTING EXCESSIVE SNOWFALL RATES IN THE DEFORMATION AREA...BUT
RATES APPROACHING 1" PER HOUR MAY BE POSSIBLE DURING THE HEIGHT OF
THE EVENT SUNDAY AFTERNOON AND EVENING. AS YOU MIGHT EXPECT...THE
12Z GFS BRINGS IN A SOLID DEFORMATION ZONE INTO OUR SE
CWA...ADDING SOME CONCERN THAT ACCUMS COULD BE HIGHER THAN
FORECAST THERE. WITH THE ECMWF SLIGHTLY FURTHER SOUTH AND WEAKER
WITH THIS FEATURE (AND OVERALL SFC LOW/H850 LOW TRACK) AS WELL AS
THE GEM (FURTHER SOUTH YET)...NOT WILLING TO GO ALL CHIPS IN ON
THE 12Z GFS SOLUTION AND WOULD PREFER A WEIGHTED BLEND OF
AVAILABLE GUIDANCE FOR THIS STORM.

THE SNOWFALL GRADIENT ACROSS SOUTHERN LOWER MICHIGAN WILL BE
READILY APPARENT AS THIS STORM COMES TO FRUITION. AMOUNTS ARE
EXPECTED TO TAPER OFF TOWARD THE I-96 CORRIDOR...WITH GENERALLY
5"-8" STILL EXPECTED FROM MKG TO GRR TO LAN...WITH 8" OR MORE
POSSIBLE FOR AREAS IN BETWEEN. AFTER LOOKING AT HI-RES MODEL
GUIDANCE (WRF-ARW...WRF-NMM...NAMDNG5) AND COMPARING TO THE
GFS...ECMWF...NAM...GEM...AND UKMET...I BELIEVE OUR FORECAST
AMOUNTS ARE RIGHT IN LINE WITH A CONSENSUS OF THESE MODEL
SOLUTIONS...WHICH ALL AGREE THAT THE HIGHEST AMOUNTS WILL BE NEAR
I-94.

WINDS WILL BE A FACTOR WITH THIS SYSTEM. GIVEN THE NE FLOW AS THE
STORM MOVES INTO THE REGION...COULD EASILY SEE WIND GUSTS
OVERACHIEVING ACROSS OUR CENTRAL AND EASTERN CWA GIVEN THE FLOW
OFF LAKE HURON AND FETCH OFF SAGINAW BAY. HAVE DECIDED TO BUMP UP
WIND GUSTS AS A RESULT. STILL GENERALLY LOOKING AT 25 TO 35 MPH
GUSTS...BUT 40 MPH IS NOT OUT OF THE QUESTION ESPECIALLY GIVEN THE
12Z GFS SOLUTION. THE BOTTOM LINE IS THERE WILL BE BLOWING AND
DRIFTING SNOW AT TIMES...AND GIVEN THE DRY NATURE OF THIS SNOW THE
VISIBILITIES WILL BE GREATLY REDUCED.

ALTHOUGH THIS STORM WILL BE WINDING DOWN EARLY MONDAY
MORNING...COULD SEE SOME LINGERING IMPACTS IN TERMS OF SNOW
COVERED ROADS AND SLICK TRAVEL FOR THE MONDAY MORNING COMMUTE...SO
CONTINUED DELAYS ARE PROBABLE. A FEW LIGHT LAKE EFFECT SNOW
SHOWERS MAY MOVE IN DURING THE DAY BUT WILL BE SMALL POTATOES
COMPARED TO THE WINTER STORM ON SUNDAY.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 300 PM EST SAT JAN 31 2015

AN UPPER LEVEL PV ANOMALY FOLLOWED BY AN ARCTIC COLD FRONT WILL
COMBINE TO BRING SOME SNOW TUESDAY AND TUESDAY NIGHT. A SIGNIFICANT
SNOW EVENT IS NOT LIKELY BUT SOME LIGHT SNOW ACCUMULATIONS ARE
EXPECTED MAINLY FROM TUESDAY AFTERNOON THROUGH TUESDAY NIGHT.

A COLD AIRMASS WILL ADVECT IN BEHIND THAT FRONT LATE WEDNESDAY
THROUGH LATE WEEK. MAX TEMPS THURSDAY AND FRIDAY WILL ONLY REACH THE
TEENS TO PERHAPS LOWER 20S.

LAKE EFFECT SNOW SHOWER POTENTIAL CONTINUES TO LOOK MINIMAL LATE IN
THE WEEK DUE TO THE DRY AIRMASS AND UNFAVORABLE SNOW MICROPHYSICS
AND LOW INVERSION HEIGHTS. TEMPS SHOULD MODERATE SOMEWHAT BACK TO
CLOSER TO NORMAL BY NEXT WEEKEND AS THE UPPER LEVEL PATTERN BECOMES
ZONAL AND UNAMPLIFIED.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY)
ISSUED AT 1150 AM EST SAT JAN 31 2015

VFR CONDITIONS THIS AFTERNOON WILL GRADUALLY DETERIORATE TO MVFR
THEN IFR OVERNIGHT AS LOWER CIGS AND SNOW MOVE IN. THE SNOW WILL
MOVE IN FROM WSW TO ENE AND AFFECT ALL THE TERMINALS AFTER MIDNIGHT
THROUGH DAYBREAK.

SNOW WILL GRADUALLY INCREASE IN INTENSITY FROM AROUND DAYBREAK
THROUGH 18Z SUNDAY RESULTING IN FURTHER DETERIORATION OF CONDITIONS
INTO THE LIFR FLIGHT CATEGORY AT ALL THE TERMINALS. SNOW WILL BECOME
HEAVIEST ALONG THE I-94 CORRIDOR.

WINDS WILL BE OUT OF THE WEST TO NORTHWEST THROUGH THIS EVENING
BEFORE GRADUALLY VEERING TO THE NORTHEAST OVERNIGHT. WINDS WILL
CONTINUE TO VEER SLOWLY TO THE ENE SUNDAY MORNING AND INCREASE
TO 15 TO 25 KTS.


&&

.HYDROLOGY...
ISSUED AT 300 PM EST SAT JAN 31 2015

ICE FORMATION ON RIVERS IS THE IMMEDIATE HYDRO CONCERN. ARCTIC AIR
MOVES BACK IN ON SUNDAY WITH TEMPERATURES FALLING THROUGH THE TEENS
THROUGHOUT THE DAY. LOWS SUNDAY NIGHT AND MONDAY MORNING WILL DROP
INTO THE SINGLE DIGITS. STORM TOTAL QPF FOR THE SNOW EVENT BEGINNING
TONIGHT WILL BE AROUND A HALF INCH ALONG I-96 THROUGH MONDAY
MORNING. QPF INCREASES AS YOU MOVE SOUTH... WITH A MAX OF AROUND
THREE QUARTERS TO AN INCH OVER THE KALAMAZOO BASIN. COLD
TEMPERATURES ARE EXPECTED THROUGH THE REST OF THE WEEK.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY UNTIL 6 AM EST MONDAY FOR MIZ043>046-
     050>052-056>059.

     WINTER STORM WARNING UNTIL 6 AM EST MONDAY FOR MIZ064>067-
     071>074.

LM...NONE.
&&

$$

SYNOPSIS...HOVING
SHORT TERM...HOVING
LONG TERM...LAURENS
AVIATION...LAURENS
HYDROLOGY...EBW






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