Heavy Snow in Michigan, February 8, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
510 AM EST THU FEB 8 2001

THE MAJOR FORECAST CONCERN THIS PACKAGE REVOLVES AROUND THE STRONG
SYSTEM APPROACHING THE AREA FROM THE SOUTHWEST AND THE POSSIBILITY
OF HEAVY RAIN ACROSS NORTHERN LOWER AND A SIGNIFICANT ICING EVENT
ACROSS THE EASTERN UP.

THE LATEST WATER VAPOR LOOP SHOWS A DEEP UPPER LEVEL LOW ACROSS THE
SOUTHWESTERN US WITH A SURGE OF PACIFIC MOISTURE ADVECTING INTO THE
MISSISSIPPI VALLEY REGION AHEAD OF THE TROUGH.

TODAY...PROFILER DATA OUT OF WINCHESTER IL SHOWS A 850MB LLJ OF
AROUND 50 KTS TARGETED TOWARDS A STRONG LOW LEVEL THERMAL GRADIENT
OVER THE GREAT LAKES REGION. THIS IS LEADING TO STRONG ISENTROPIC
ASCENT ACROSS THE FORECAST AREA...WITH STRONG LOW LEVEL
FRONTOGENESIS OCCURRING...ENOUGH LIFT HAS BEEN PROVIDING TO TRIGGER
PRECIP ACROSS THE ENTIRE FORECAST AREA. KAPX RADAR HOWEVER HAS NOT
SHOWN A REAL WIDESPREAD AREA OF HEAVY SNOW ACROSS THE FORECAST AREA.
INSTEAD THE PRECIP HAS BEEN IN A BANDED STRUCTURE WITH THE
CONVECTIVE BANDS MOVING NORTHEAST...THUS NOT AFFECTING THE SAME AREA
FOR A PROLONGED PERIOD OF TIME. I SUSPECT THAT THE STRONG
FRONTOGENETICAL FORCING AND SOME WEAK CONVECTIVE INSTABILITY (ACROSS
SOUTHERN COUNTIES) HAS LED TO MORE OF A CONVECTIVE APPEARANCE TO THE
PRECIP (WITH LIGHTNING STRIKES BEING REPORTED OVER MANISTEE CO). THE
ETA AND MESO ETA PROG THE 850MB LLJ TO GRADUALLY VEER THROUGH 12Z
WITH THE 850MB GRADIENT PUSHING NORTH. THUS EXPECT THE STRONGEST
FORCING TO EXIT THE AREA BY THIS AFTERNOON. THE ETA/NGM/AVN MODEL
SOUNDINGS ARE ALSO SHOW THE 700-400MB LAYER DRYING DURING THE
AFTERNOON...THUS ALLOWING THE PRECIP TO TAPER TO DRIZZLE/FREEZING
DRIZZLE. AS FOR THE WARNING...I HAVE DROPPED IT TO A WINTER WEATHER
ADVISORY DUE TO LOWER PRECIP AMOUNTS THAN EXPECTED. THIS WILL
CONTINUE TO BE MONITORED THIS MORNING AS CONVECTIVE ELEMENTS MAY
STILL PRODUCE A BRIF PERIOD OF HEAVY PRECIP. ALTHOUGH MODEL
SOUNDINGS SUGGEST THAT ABOVE ZERO LAYER WILL NOT WORK INTO NORTHERN
LOWER UNTIL THIS AFTERNOON...SURFACE REPORTS ACROSS SOUTHERN
COUNTIES ARE SHOWING THAT THE PRECIP IS OCCASIONALLY CHANGING OVER
TO SLEET AND FREEZING RAIN. SINCE THE LOW LEVEL WARM AIR ADVECTION
IS SO STRONG...I WILL PUT A MENTION OF MIXED PRECIP IN ALL NORTHERN
LOWER ZONES THIS MORNING (ALTHOUGH LOCATIONS NORTH OF M-72 WILL SEE
PRIMARILY SNOW).

TONIGHT...DIFFERENCES BEGIN TO ARISE AMONG THE MODELS WITH RESPECT
TO THE DEVELOPMENT OF THE SURFACE LOW TO OUR SOUTHWEST. THE ETA
WANTS TO PHASE THE 500MB TROUGH OVER THE SOUTHWEST WITH THE NORTHERN
STREAM TROUGH AS IT PROPAGATES NE. THE AVN (AND TO A LESSOR EXTENT
THE NGM) KEEP THE SOUTHERN STREAM TROUGH SEPARATE. THIS IS REFLECTED
AT THE SURFACE WITH THE ETA DEVELOPING A SURFACE LOW OVER THE
SOUTHERN GREAT LAKES AND QUICKLY MOVING IT NORTHEAST...WITH THE AVN
MUCH SLOWER IN THE DEVELOPMENT AND MOVEMENT OF THE SURFACE LOW INTO
THE AREA. BASED ON THE STRENGTH OF THE SOUTHERN STREAM TROUGH (PER
WATER VAPOR LOOP) I WILL SIDE WITH THE AVN. WITH THIS SAID THE AVN
PROGGS A SURFACE WARM FROM TO MOVE NORTH ACROSS NORTHERN LOWER
OVERNIGHT. A TREMENDOUS AMOUNT OF MOISTURE (PRECIPITABLE WATER VALUES
AROUND 1 INCH) IS ADVECTED INTO THE AREA WITH ANOTHER PUSH OF LOW
LEVEL WAA/ISENTROPIC ASCENT. THIS COULD PRODUCE UP TO AN INCH OF
RAINFALL ACROSS NORTHERN LOWER. ACROSS THE EASTERN UP...HOWEVER
MODEL SOUNDING INDICATE THAT THE PRECIP WILL START OFF AS SNOW...BUT
CHANGE OVER TO SLEET AND FREEZING RAIN. AT THIS POINT...AVN AND ETA
MODEL SOUNDINGS ARE HINTING A LITTLE MORE TOWARDS SLEET (WITH MAX
TEMP IN THE WARM LAYER AROUND +2C) HOWEVER GIVEN THE STRONG SURGE OF
LOW LEVEL WARM AIR...I PREFER TO LEAN THE PRECIP TYPE MORE TOWARDS
FREEZING RAIN. WITH SUCH HIGH AMOUNTS OF MOISTURE ADVECTING INTO THE
AREA (ALONG WITH SURFACE TEMPS PROGGED TO REMAIN BELOW
FREEZING)...THIS COULD BE A SIGNIFICANT ICING EVENT ACROSS THE
EASTERN UP. THUS THE WATCH STILL LOOKS JUSTIFIED.

FRIDAY/FRIDAY NIGHT...WILL GO WITH THE AVN SOLUTION WHICH SLOWLY
MOVES THE SURFACE LOW TO THE EAST...BRINGING VERY COLD AIR IN BEHIND
IT (850MB TEMPS DROPPING TO -20C OVER THE NORTHERN LAKES BY 12Z
SATURDAY). THUS WILL SEE THE RAIN GRADUALLY CHANGE OVER TO SNOW FROM
NORTHWEST TO SOUTHEAST. I KEPT THE MENTION OF THUNDER IN GIVEN THE
STRENGTH OF THE PASSING SURFACE FRONT.

.APX...WINTER WEATHER ADVISORY...THIS MORNING...MIZ025>036-041-042.
       WINTER STORM WATCH...TONIGHT AND FRIDAY...MIZ008>015.

CONSIDINE