Winter Storm in Michigan, February 7 to 8, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
515 PM EST WED FEB 7 2001

12Z MODEL RUNS OF ETA AND AVN MUCH CLOSER IN AGREEMENT WITH THE
APPROACHING STORM SYSTEM THAN PREV RUNS HAD BEEN. FORECAST IS BASED
ON ETA/AVN COMPROMISE...LEANING TOWARD THE FASTER ETA SOLUTION BUT
SLIGHTLY WARMER AVN SOLUTION. MODELS AGREE THAT THE INGREDIENTS WILL
COME TOGETHER TO BRING SIGNIFICANT WINTRY AND LIQUID PCPN TO THE
FORECAST AREA OVER THE NEXT 48 TO 60 HOURS. MANY FORECAST CONCERNS
WITH THIS PACKAGE...INCLUDING WINTRY PCPN...HEAVY RAINFALL...
THUNDERSTORM POTENTIAL...HIGH WINDS...AND ACCUMULATING SNOWFALL
BEHIND THE SYSTEM.

FOR TONIGHT...PARAMETERS LOOK QUITE IMPRESSIVE FOR SIGNIFICANT
ISENTROPIC/WARM ADVECTION PCPN EVENT WITH ETA THE MOST AGRESSIVE
WITH PCPN AMOUNTS. COUPLED JET STRUCTURE WILL PROVIDE EXTREME LIFT
WITH TIGHT THERMAL GRADIENT DEVELOPING IN THE MID LEVELS. MID-LEVEL
FRONTOGENESIS BECOMES STRONG BY 06Z WITH CONDENSATION PRES DEFICITS
FALLING TO LESS THAN 10 MB. THERE IS A LAYER OF DRIER AIR IN THE LOW
LEVELS...BUT SHOULDN'T TAKE LONG TO SATURATE WITH PCPN EXPECTED TO
BECOME MODERATE TO HEAVY SHORTLY AFTER IT STARTS. EXPECT PCPN TO
BREAK OUT OVER THE WRN COUNTIES BETWEEN 01Z AND 03Z...REACHING ERN
COUNTIES BY 04Z. CONDITIONS LOOK FAVORABLE FOR CONDITIONAL SYMMETRIC
INSTABILILTY ACROSS THE NRN COUNTIES AND THESE AREAS APPEAR MOST
LIKELY TO RECEIVE GREATER THAN ONE-QUARTER INCH PCPN AMOUNTS
OVERNIGHT. THERE MAY BE A FINE LINE BETWEEN MODERATE TO HEAVY PCPN
IN THE 0.25 TO 0.50 INCH AMOUNTS AND LIGHT PCPN AMOUNTS OF 0.10 INCH
OR LESS. EXPECT THIS LINE TO FALL SOMEWHERE ALONG THE INTERSTATE 96
CORRIDOR. BASED ON ETA/AVN COMPROMISE...EXPECT THE SFC FREEZING LINE
TO REACH INTERSTATE 94 AROUND 06Z...THEN SLOWLY MOVE NWD TOWARD
INTERSTATE 96...REACHING KGRR...KMKG...AND KLAN AROUND 11Z OR 12Z.
EXPECT SFC TEMPS TO RISE ABOVE FREEZING FROM S TO N ACROSS THE
WARNING AREA BETWEEN 12Z AND 17Z.

EXPECT A LULL IN PCPN THU AFTERNOON BEFORE A STRONG SHORTWAVE EJECTS
OUT OF THE AMPLIFYING AND APPROACHING TROUGH. WIDESPREAD RAIN IS
EXPECTED TO RETURN THU EVENING AND CONTINUE THROUGH FRI...BEFORE
CHANGING TO SNOW AS MUCH COLD AIR RUSHES IN BEHIND THE SFC LOW
PASSAGE. FORECAST CONCERNS CENTER AROUND RAIN AMOUNTS AND POSSIBLE
HYDRO CONCERNS GIVEN MELTING SNOW. ANOTHER MAJOR CONCERN FOR THU
NIGHT AND FRI IS FOR HIGH WINDS. ETA FORECAST SOUNDINGS INDICATE
WIND SPEEDS IN THE 60 TO 80 KNOT RANGE BETWEEN 3K AND 5K FT LATE THU
NIGHT AND AHEAD OF THE FRONT ON FRI...WITH SOME DECREASE IN WIND
SPEED BUT EXTREME COLD ADVECTION BEHIND FRONTAL PASSAGE FRI. THIS
WILL NEED TO BE CLOSELY WATCHED AND A HIGH WIND WATCH MAY BE NEEDED
FOR THU NIGHT AND FRI IF LATER MODEL RUNS ARE CONSISTENT.

THUNDERSTORM THREAT LOOKS MINIMAL WITH THIS SYSTEM...BUT A FEW
RUMBLES WITH ELEVATED CONVECTION CAN NOT BE RULED OUT FOR TONIGHT
ACROSS THE NRN HALF OF THE FORECAST AREA. THE BETTER THREAT FOR
THUNDER WILL BE WITH THE FRONTAL PASSAGE LATE THU NIGHT AND FRI
MORNING...AS 850MB TEMPS/DEWPOINTS SOAR TO NEAR 10C WITH SFC TEMPS
AROUND 50 DEG F ACROSS SRN COUNTIES AROUND THE 12Z FRI TIME FRAME.
WITH DYNAMICAL FORCING AND ELEVATED INSTABILITY...EXPECT A FEW
ISOLATED THUNDERSTORMS TO FORM IN THE PREFRONTAL RAIN BAND.

AS COLD ADVECTION RACES IN BEHIND SFC LOW PASSAGE...EXPECT WRAP
AROUND MOISTURE TO RESULT IN RAIN CHANGING TO SNOW WITH MUCH OF THE
FORECAST AREA PRONE TO SOME LIGHT ACCUMULATIONS. BEST MOISTURE WILL
BE ACROSS THE NRN COUNTIES BUT LAKE ENHANCEMENT MAY COME INTO PLAY
AS 850MB TEMPS ARE FORECASTED TO FALL TO -15 TO -18C. EXPECT LAKE
EFFECT SNOW SHOWERS TO PERSIST FRI NIGHT WITH ADDITIONAL ACCUMS
POSSIBLE.

HYDRO...FLOOD POTENTIAL OUTLOOK ISSUED OUTLINING THE POTENTIAL FOR
MINOR TO MODERATE FLOODING OF MAINSTEM RIVERS...CREEKS AND STREAMS
IN THE FORECAST AREA DUE TO EXPECTED PCPN AND SNOWMELT. DEPENDING ON
PCPN AMOUNTS WHICH FALL TONIGHT AND EXPECTED RAINFALL AMOUNTS THU
THROUGH FRI BASED ON LATER MODEL RUNS...OUR OFFICE MAY ISSUE FLOOD
WATCHES AND/OR WARNINGS ON THU TO ADDRESS THE AREAS OF MOST CONCERN.

THANKS FOR COORDINATION CONFERENCE...APX AND DTX.

GREENE

EXTENDED FORECAST DISCUSSION...
MAIN FORECAST PROBLEM IN EXTENDED IS FOR THE CHANCE OF SNOW ON
SATURDAY. AVN DRIES THINGS OUT BY SATURDAY MORNING...WHILE CANADIAN
MODEL LIFTS A SOUTHERN STREAM SYSTEM UP THE OHIO RIVER VALLEY ON FRI
NIGHT/SAT...GIVING US A SNOWSTORM. I HAVE DISCOUNTED THE CANADIAN
SINCE IT IS AN OUTLIER IN KEEPING THE NORTHERN AND SOUTHERN STREAMS
SEPARATE. PREFERRED THE DEEPER PHASED 980 MB SYSTEM PROGGED BY THE
ETA AT 60 HOURS...WHICH WOULD GIVE US SOME WRAP AROUND MOISTURE AND
STRONGER CAA FRIDAY NIGHT AND SATURDAY. WITH LL MOISTURE AND
CYCLONIC FLOW CONTINUING INTO EARLY SATURDAY...LOOKS LIKE LES
SHOWERS WILL HANG AROUND THROUGH THE MORNING...THEN CUT OFF BY
AFTERNOON AS LARGE SCALE SUBSIDENCE KICKS IN. FAIRLY QUIET WEATHER
REST OF THE PERIOD WITH ONLY A WEAK SYSTEM ON MON-TUE BRINGING A
CHANCE OF SNOW OR RAIN. BY LATE TUESDAY...ANOTHER DEEPENING WESTERN
U.S. H5 TROUGH HAS SET UP...WITH ECMWF SHOWING A SOUTHERN PLAINS LOW
FORMING...WHILE MRF IS LESS OMINOUS...KEEPING HIGH PRESSURE IN
CONTROL OF WESTERN AND CENTRAL U.S. WILL KEEP WEDNESDAY DRY.

OSTUNO

.GRR...WINTER STORM WARNING T|ONIGHT AND THURSDAY MORNING...
MIZ037>040-043>046-051-052.
.......WINTER WEATHER ADVISORY TONIGHT AND EARLY THURSDAY MORNING...
MIZ050-056>059-064>067.