Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 281754
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1254 PM EST WED JAN 28 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 326 AM EST WED JAN 28 2015

AFTER A QUIET DAY TODAY...A WINTRY MIX WILL BE ARRIVING LATE TONIGHT
ACROSS SOUTHWEST LOWER MICHIGAN...WHILE MAINLY SNOW IS EXPECTED FOR
CENTRAL LOWER.  SOME AREAS ACROSS SOUTHWEST LOWER WILL SEE A COATING
OF ICE THROUGH THURSDAY MORNING...BEFORE THE PRECIPITATION CHANGES
OVER TO SNOW THURSDAY.  MEANWHILE...1 TO 2 INCHES OF SNOW CAN BE
EXPECTED ACROSS MUCH OF CENTRAL LOWER.

IT WILL TURN COLDER WITH LAKE EFFECT SNOW SHOWERS FOR THURSDAY NIGHT
AND FRIDAY.  THERE WILL BE ANOTHER GOOD CHANCE FOR SNOW FROM SUNDAY
INTO MONDAY.  IT SHOULD GET EVEN COLDER BEHIND THIS SYSTEM WILL
HIGHS ONLY IN THE TEENS MONDAY AND TUESDAY.

&&

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 326 AM EST WED JAN 28 2015

WILL GO AHEAD AND ISSUE A WINTER WEATHER ADVISORY STARTING LATE
TONIGHT AND EXTENDING INTO THURSDAY AFTERNOON.

THE CLIPPER SYSTEM WILL ARRIVE LATE TONIGHT AND BRING A MIXED BAG OF
PCPN TYPES.  THE SYSTEM WILL BRING IN WARMER AIR ALOFT...WHILE THE
BOUNDARY LAYER HOLDS ON TO SHALLOW COLD AIR.  THIS WILL PRODUCE
MOSTLY FREEZING RAIN AND SLEET FOR THE SOUTHERN AND CENTRAL CWA.
PCPN AMOUNTS SEEM MODEST ON THE MODELS...BUT THERE IS POTENTIAL THAT
THIS SYSTEM MAY OVER-ACHIEVE.  A 45-50 KT LOW LEVEL JET NOSES INTO
LOWER MICHIGAN AFTER 06Z AND COULD CAUSE THE PCPN TO GO SOMEWHAT
CONVECTIVE...PRODUCING LOCALLY HEAVIER PCPN.  FOR NOW EXPECT MOST
AREAS WITHIN THE ADVISORY AREA WILL SEE AROUND A TENTH OF INCH OF
ICE...ALONG WITH SOME SLEET ACCUMULATION.

FURTHER NORTH...EXPECT THE PCPN TO BE MAINLY SNOW AND WILL THEREFORE
NOT HAVE THIS AREA IN THE ADVISORY.  1 TO 2 INCHES OF SNOW CAN BE
EXPECTED.  THIS COULD COME IN A QUICK BURST LATE TONIGHT GIVEN THE
DYNAMICS OF THE LLJ.  THIS AREA MAY SEE A BRIEF PERIOD OF SLEET TOO.

BY THURSDAY WE WILL GRADUALLY TRANSITION TO MOSTLY SNOW FROM NW TO
SE AS THE WARM POCKET ALOFT MOVES EAST.  HOWEVER THIS MAY TAKE MOST
OF THE MORNING UNTIL THIS OCCURS IN THE SOUTHERN CWA.  SNOW
ACCUMULATIONS SHOULD GENERALLY BE LESS THAN AN INCH ACROSS THE
CENTRAL AND...AND VERY LITTLE ACROSS THE SOUTH.

COLDER AIR ARRIVES THURSDAY NIGHT AND FRIDAY BRINGING IN SOME LAKE
EFFECT SNOWS.  INVERSION LEVELS SHOULD BE 4K FT OR LESS...SO ACCUMS
SHOULD BE ON THE LIGHT SIDE...MAINLY AN INCH OR TWO ALONG THE
LAKESHORE.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY)
ISSUED AT 326 AM EST WED JAN 28 2015

MAIN IMPACT WEATHER IN THE LONG TERM WILL BE THE OPPORTUNITY FOR
ACCUMULATING SNOW STARTING SATURDAY NIGHT AND POSSIBLY LASTING INTO
MONDAY. AT THIS TIME THE POTENTIAL EXISTS FOR SEVERAL INCHES OF SNOW
ACROSS SOUTHERN LOWER MICHIGAN DURING THIS PERIOD. THIS IS NOT A
CERTAINTY YET BUT NUMEROUS INDICATIONS ARE PRESENT IN THE LATEST 00Z
NWP SUITE.

SOME FEATURES TO WATCH FOR SATURDAY AND SUNDAY WILL BE THE
POSITIONING OF A DEVELOPING UPPER LEVEL JET (120-140 KT) OVER THE
GREAT LAKES REGION AND ASSOCIATED H500 SHORTWAVE TROUGH. IF THE JET
CAN GET FAR ENOUGH NORTH (IE. GFS AND GEM SOLUTIONS) THEN WE COULD
TAP INTO SOME RIGHT ENTRANCE REGION DIVERGENCE SATURDAY
NIGHT/SUNDAY. THE STRONGER THIS DIVERGENCE IS...THE DEEPER THE H500
SHORTWAVE AND ASSOCIATED SFC LOW DEVELOPMENT...WHICH TRENDS NW IN
THESE SITUATIONS.

REGARDING MODEL TRENDS...DECIDED TO LOOK AT H500 HEIGHTS AND SFC
MSLP DPROG/DT PLOTS OF THE GFS...ECMWF...AND GEM (DPROG/DT REVEALS
PAST MODEL RUNS FOR EACH RESPECTIVE MODEL AT A CHOSEN FORECAST
TIME). FOR THE FORECAST TIME I CHOSE 00Z MONDAY. THE 00Z GFS H500
HEIGHTS ARE DEEPER AND FURTHER WEST (TROUGH AXIS ALONG A LINE FROM
MSP TO KCI) THAN THE 12Z JAN 27 RUN...BUT SIMILAR TO THE 00Z JAN 27
RUN. THE 00Z ECMWF H500 HEIGHTS ARE SLIGHTLY DEEPER THAN PAST
AVAILABLE RUNS (TROUGH AXIS NEAR A LINE FROM MKE TO STL) BUT SIMILAR
IN NATURE GOING BACK THROUGH THE 00Z JAN 26 RUN. THE 00Z GEM IS
DEEPER AND FURTHER WEST THAN THE LAST 2 RUNS. AT THE SFC...THE GFS
AND GEM ARE SHOWING MUCH DEEPER LOWS AND FURTHER WEST THAN THE ECMWF
(GFS HAS A 994 MB LOW OVER CINCINNATI AT 12Z MONDAY...THE GEM HAS A
990 MB LOW OVER CLEVELAND...AND THE ECMWF HAS A 998 MB LOW OFF THE
COAST OF NEW JERSEY). WITH THE GFS ENSEMBLE MEAN MSLP SIMILAR IN
NATURE TO THE ECMWF I AM NOT TOTALLY CONFIDENT IN A DEEPER LOW
ACROSS OHIO JUST YET.

ALL THIS BEING SAID...A STRONGER SOLUTION WITH A FURTHER NW TRACK IS
SUGGESTED WITH THE 00Z MODEL RUNS...BUT WOULD LIKE TO SEE A FEW MORE
ITERATIONS OF THIS BEFORE CONFIDENCE BECOMES GREATER. AT THIS POINT
THE CONSENSUS MODEL QPF WHICH WEIGHTS THE MEDIUM RANGE MODELS DOES
BRING IN A THIRD OF AN INCH OR MORE OF PRECIPITATION TO MOST OF THE
CWA FROM 06Z SUN TO 18Z MON...WHICH WOULD YIELD SEVERAL INCHES OF
SNOW. UNTIL A STORM TRACK IS LOCKED IN BY THE MODELS...UNCERTAINTY
DOES EXIST WHETHER THIS WILL MATERIALIZE...BUT THERE IS A 50/50 SHOT
OR SLIGHTLY BETTER THAT IT WOULD HAPPEN.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1247 PM EST WED JAN 28 2015

CONFIDENCE INCREASING ON IMPACT CONDITIONS AT THE TAF SITES LATER
TONIGHT THROUGH THU MORNING. FREEZING RAIN...SLEET AND SNOW WILL
WORK ITS WAY IN FROM THE SOUTHWEST AND PERSIST THROUGH THU
MORNING. AHEAD OF IT THERE COULD BE WIND SHEAR AS LOW LEVEL WINDS
BACK TO THE SOUTHEAST AS A STRONGER LOW LEVEL JET ARRIVES FROM THE SOUTH.

IFR CONDITIONS MAY BE DELAYED INITIALLY DUE TO THE DRY
AIR...HOWEVER ONCE THEY ARRIVE LATER TONIGHT...THEY SHOULD PERSIST
THROUGH THE MORNING.

THE WIND WILL SHIFT SHARPLY THURSDAY MORNING AS THE WAVE OF LOW
PRESSURE TRACKS THROUGH.

&&

.HYDROLOGY...
ISSUED AT 1215 PM EST TUE JAN 27 2015

A FEW AREA RIVERS SHOWED MINOR FLUCTUATIONS OVER THE PAST 48 HOURS.
NONE OF THIS WAS TOO CONCERNING. THE ACTIVITY HAS SEEMED TO LEVEL
OFF AND STABILIZE FOR THE MOST PART. COLDER TEMPERATURES WILL HOLD
ON THROUGH MUCH OF THE WEEK WITH THE WARMEST CONDITIONS BEING FELT
THURSDAY...TO THE TUNE OF LOW TO MID 30S.

A COUPLE ROUNDS OF WINTRY PRECIPITATION ARE POSSIBLE. THE TWO MAIN
EVENTS ANTICIPATED ARE LATE WEDNESDAY INTO THURSDAY AND AGAIN BY
SUNDAY. MOISTURE WILL BE SPREAD OUT OVER TIME AND COLDER TEMPERATURES
DO NOT LOOK TO BE CAUSE FOR CONCERN. RIVERS WILL CONTINUE TO BE
MONITORED IN THE CASE THAT ANY FLUCTUATION DOES OCCUR.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY FROM 1 AM TO 4 PM EST THURSDAY FOR
     MIZ037-043-044-050>052-056>059-064>067-071>074.

LM...NONE.
&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...HOVING
AVIATION...MJS
HYDROLOGY...JAM





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