000
FXUS63 KGRR 291259
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
759 AM EST THU JAN 29 2015

LATEST UPDATE...
UPDATE

.SYNOPSIS...
ISSUED AT 318 AM EST THU JAN 29 2015

A WINTRY MIX WILL CONTINUE TODAY.  SOME AREAS MAY SEE UP TO A TENTH
OF INCH OF ICE BY MID DAY.  THE PRECIPITATION WILL BE CHANGING OVER
TO MOSTLY SNOW BY THIS AFTERNOON.  AND AS COLDER AIR MOVES IN...SOME
LAKE EFFECT SNOW WILL DEVELOP TONIGHT AND CONTINUE INTO FRIDAY.
HOWEVER SNOW ACCUMULATIONS ARE EXPECTED TO BE LIGHT...GENERALLY AN
INCH OR TWO.  AFTER HIGHS IN THE 30S TODAY...IT WILL COOL TO ONLY
AROUND 20 BY FRIDAY.

A STORM SYSTEM WILL MOVE SOUTH OF THE AREA SUNDAY AND MONDAY.  WE
WILL HAVE TO KEEP AN EYE ON THIS AS IT MAY GIVE SOUTHWEST MICHIGAN
MORE SNOW.  EITHER WAY...IT WILL GET MUCH COLDER INTO NEXT WEEK WITH
DAYTIME HIGHS ONLY IN THE TEENS SUNDAY THROUGH WEDNESDAY.

&&

.UPDATE...
ISSUED AT 759 AM EST THU JAN 29 2015

WE ARE IN THE EXPECTED LULL BETWEEN FREEZING RAIN THAT EXITED EAST
AND AN UPSTREAM BATCH OF PRECIPITATION CROSSING WISCONSIN AND
NORTHERN LOWER MI. THIS UPSTREAM PRECIPITATION IS ASSOCIATED WITH
AN UPPER DEFORMATION ZONE AND EXPECTED TO REMAIN ALL SNOW OVER
CENTRAL AND NORTHERN LOWER MI. FARTHER SOUTH THE FORECAST WILL BE
MORE COMPLEX. THE SURFACE LOW CURRENTLY NEAR CHICAGO IS EXPECTED
TO MOVE EAST ACROSS NRN IN/OH TODAY...SHIFTING THE LOW LEVEL JET
EAST.

A RECENT AIRCRAFT DESCENT SOUNDING INTO GRAND RAPIDS FROM THE
KALAMAZOO VICINITY SHOWED A NEARLY ISOTHERMAL LAYER JUST BELOW
FREEZING THAT EXTENDING UP TO ABOUT 6000 FT. THE WARM NOSE AT THE
TOP OF THIS LAYER...ASSOCIATED WITH THE LLJ...IS WEAK /AROUND 1
C/. ALL ELSE BEING EQUAL...THIS WOULD SUPPORT MOSTLY SNOW WITH SOME
FZRA. DO NOT EXPECT THE WARM LAYER TO REINTENSIFY AS THE LLJ PEELS
OFF TO THE EAST AND UNDERGOES DIURNAL WEAKENING THIS MORNING. FZRA
NEAR I-96 THIS MORNING SHOULD BE BECOME RAIN BY THIS AFTERNOON...
ALTHOUGH THERE COULD BE A DELAY IN SURFACE TEMPERATURES CLIMBING
ABOVE FREEZING AFTER AIR TEMPERATURES DO.

&&

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 318 AM EST THU JAN 29 2015

WILL MAINTAIN THE HEADLINE AS IS.  THE WINTRY MIX WILL CONTINUE...
ALTHOUGH IT WILL TREND TOWARD MORE SNOW FROM NW TO SE THROUGH THE
MORNING.

COMPLICATED FORECAST DAY AS WE WILL SEE EBBS AND FLOWS IN THE PCPN
TODAY.  AS OF 08Z WE WERE SEEING AN AREA OF MIXED PCPN MOVING INTO
THE REGION.  THIS WAS ON THE NOSE OF THE LOW LEVEL JET.  IT WAS A
FAIRLY NARROW BAND THAT WAS MOVING NE AT 30 KNOTS.  SO THIS WON/T BE
OVER ANY ONE AREA FOR MUCH MORE THAN A COUPLE HOURS...BUT ENOUGH TO
PUT DOWN A LIGHT GLAZE AND IMPACT THE MORNING COMMUTE.

IT APPEARS WE WILL THAN HAVE A SHORT BREAK IN THE PCPN AROUND MID
MORNING...THEN THE DEFORMATION ZONE MOVES IN LATE MORNING/EARLY
AFTERNOON.  THIS SHOULD BE MOSTLY SNOW...WITH PERHAPS SOME MIX STILL
ALONG I-94.  FINALLY...ONCE THE DEEPER MOISTURE EXITS WE MAY SEE A
PERIOD OF FREEZING DRIZZLE AS THE DGZ BECOMES UNSATURATED.  THE
NORTHERN CWA APPEARS SETUP BEST FOR THIS AS SOME OMEGA IS STILL SEEN
WITHIN THE CLOUD LAYER.  THE FZDZ COULD LAST THROUGH THE LATTER HALF
OF THE AFTERNOON...BEFORE IT COMES AN END.  ALL-IN-ALL A MESSY DAY.
HOWEVER ANY ICE ACCUMULATION SHOULD REMAIN UNDER A TENTH OF AN
INCH.  SNOW ACCUMULATIONS SHOULD BE LESS THAN AN INCH ALONG I-96...
AND UP TO TWO INCHES TOWARD HIGHWAY 10.

WE WILL GET INTO A PERIOD OF LIGHT LAKE EFFECT SNOWS TONIGHT AND
FRIDAY AS -15C H8 AIR MOVES OVER THE LAKE.  THE MEAN LOW LEVEL FLOW
WILL BE 318-330 WHICH WILL FAVOR AREAS WEST OF U.S. 131.  INVERSION
LEVELS REMAIN LOW...4500 FT OR LESS...SO NOT EXPECTING ANYTHING
HEAVY.  AN INCH OR TWO CAN BE EXPECTED HERE...WHILE INLAND AREAS SEE
LESS THAN AN INCH.  IT WILL TURN SHARPLY COLDER WITH LOWS OF 10 TO
15 TONIGHT AND FRIDAY NIGHT...WHILE FRIDAY/S HIGHS WILL ONLY BE
AROUND 20.

A COLD FRONT WILL SLOWLY DROP IN FROM THE NW BY LATE SATURDAY.  THE
FRONT LOOKS FAIRLY MOISTURE STARVED...BUT COMBINED WITH SOME LAKE
ENHANCEMENT WE MAY BE ABLE TO SQUEEZE OUT UP TO AN INCH OF SNOW OVER
THE NW CWA AS IT COMES IN.  SW WINDS AHEAD OF THE FRONT WILL HELP
TEMPS APPROACH 30.

.LONG TERM...(SATURDAY NIGHT THROUGH THURSDAY)
ISSUED AT 318 AM EST THU JAN 29 2015

LITTLE CHANGE TO THE PREVIOUS FORECAST EXCEPT TO LOWER POPS/QPF
FURTHER ON SUNDAY. CONFIDENCE IS GROWING THAT BEST PROSPECTS FOR
MEASURABLE SNOW LOOK TO BE SOUTH OF I-96...IF NOT SOUTH OF I-94.

NEXT NOTABLE CHANCE FOR SNOW IS TUESDAY WITH A BURST OF WARM
ADVECTION THAT IS PORTRAYED MORE AGGRESSIVELY BY THE GFS THAN THE
ECMWF. THIS WILL BE FOLLOWED BY A SIGNIFICANT INTRUSION OF COLD AIR
WEDNESDAY AND THURSDAY...WITH THE 29/00Z ECMWF DOWN TO -25C AT 850
MB BY THURSDAY MORNING. THIS WILL BE FAVORABLE FOR LAKE EFFECT
SNOW...BUT AMOUNTS SHOULD BE GREATLY CURTAILED BY UNFAVORABLE
MICROPHYSICS ASSOCIATED WITH THE VERY COLD AIR. ADVERTISED HIGHS
THURSDAY ARE CURRENTLY IN THE TEENS...BUT THIS MAY NEED TO BE
LOWERED IF THE ECWMF TRENDS CONTINUE.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 720 AM EST THU JAN 29 2015

RADAR INDICATES THAT THE AREA OF FREEZING RAIN HAS MOVED INTO EASTERN
LOWER MI. THE FORECAST CHALLENGE NOW TURNS TO ASSESSING THE TIMING
AND CHARACTER OF THE NEXT BATCH OF PRECIPITATION. THIS WILL BE DEPENDENT
ON THE SURFACE LOW PRESSURE SYSTEM CURRENTLY CENTERED NEAR
CHICAGO. AS THIS LOW MOVES EAST ACROSS NORTHERN IN/OH TODAY...THERE
WILL BE A SHIFT TO NORTHWEST WINDS...GRADUAL COOLING...AND AN
EVENTUAL TRANSITION TO ALL SNOW.

NEXT AREA OF PRECIPITATION CURRENTLY SEEN UPSTREAM OVER WI IS
EXPECTED TO ENTER THE AREA IN THE 14-16Z TIMEFRAME. LATEST
GUIDANCE SUGGESTS THAT THERE WILL BE AN INITIAL RAIN/SNOW
MIX...HOWEVER SPOTTY PL IS ALSO POSSIBLE. SURFACE TEMPERATURES
AROUND THE GRR AND LAN TERMINALS COULD REMAIN BELOW FREEZING THE
REST OF THE MORNING...CONTINUING THE FZRA THREAT.

IT IS UNCERTAIN HOW QUICKLY THE TRANSITION TO SNOW WILL OCCUR.
EARLIER FORECASTS AND GUIDANCE SUGGESTED A MUCH MORE ABRUPT
TRANSITION...WHEREAS THIS UPDATE FEATURES A TRANSITION PERIOD OF
RAIN/SNOW DUE TO WARMER AIR BEING BROUGHT INTO THE AREA BY THE
LOW. THE MOST LIKELY ALTERNATE OUTCOME WOULD BE A CLEAN TRANSITION
FROM RA/FZRA TO SNOW SOMETIME THIS AFTERNOON.


&&

.HYDROLOGY...
ISSUED AT 328 PM EST WED JAN 28 2015

COLD WEATHER WITH ONLY LIGHT PRECIPITATION SHOULD MEAN NO
SIGNIFICANT TRENDS IN THE RIVERS. ICE WILL FORM OVER THE WEEKEND
AS THE COLD INTENSIFIES.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR MIZ037-
     043-044-050>052-056>059-064>067-071>074.

LM...NONE.
&&

$$

UPDATE...TJT
SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...TJT
AVIATION...TJT
HYDROLOGY...OSTUNO