Flood in Michigan, February 12 to 13, 2001

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
330 PM EST MON FEB 12 2001

VISIBLE SATELLITE LOOP SHOWS SC CLOUD FIELD ADVANCING NORTHWARD
THROUGH THE OHIO VALLEY INTO FAR SOUTHEAST LOWER AT 20Z. WEAK WARM
AIR ADVECTION/ISENTROPIC LIFT ON BACK SIDE OF SURFACE HIGH SHOULD
PUSH CLOUD FIELD NORTHWARD INTO THE SOUTHERN THIRD OF THE CWA THIS
EVENING. HOWEVER ISENTROPIC LIFT ON THE 290K SURFACE BECOMES NIL BY
6Z WITH WINDS PARALLEL TO THE ISOBARS. HOWEVER CLOUDS LIKELY TO MOVE
INTO THE NORTHERN PORTION OF THE CWA AS WELL...AS UPPER WAVE MOVES
ACROSS NORTHERN LOWER OVERNIGHT...AND LOW LEVEL MOISTURE FIELD
STEAMING NORTHEAST IN WEAK SURFACE TROF SLOWLY SLIDES TO THE EAST
OVERNIGHT.

MODELS IN GENERAL AGREEMENT THROUGH 60 HOURS OVER THE GREAT LAKES
REGION...HOWEVER THE AVN HAS BEEN SHOWING A LARGE NEGATIVE HEIGHT
BIAS OVER THE WESTERN GREAT LAKES LAST SEVERAL RUNS...AND GREATLY
AMPLIFIES UPPER LOW MOVING OVER THE NORTHERN LAKES REGION 48-60
HOURS. MORE CONSISTENT AND LESS AGGRESSIVE ETA MODEL WILL BE THE
MODEL OF CHOICE FOR THIS PACKAGE. THE ETA SOLUTION WILL RESULT IN A
FASTER EASTWARD PROGRESSION OF BOTH THE SURFACE AND UPPER LOW...AND
AS A RESULT MORE AGGRESSIVE COLD AIR ADVECTION WEDNESDAY AFTERNOON
ACROSS SOUTHEAST LOWER.

MAIN CONCERN WILL BE PRECIPITATION TYPE TUESDAY NIGHT AND WEDNESDAY
BEFORE COLD AIR RETURNS. WARM AIR ADVECTION FIELD TONIGHT WILL BE
SHORT LIVED AS ASSOCIATED SURFACE LOW MIGRATES NORTHEAST. HOWEVER AS
THE STRONGER SECONDARY LOW APPROACHES THE REGION TUESDAY NIGHT A MORE
SUBSTANTIAL WARM AIR ADVECTION FIELD DEVELOPS OVER THE NORTHERN OHIO
VALLEY. THE LACK OF UPPER SUPPORT HOWEVER WILL KEEP THE MOISTURE
FIELD RATHER SHALLOW...AND THUS ICE NUCLEATION BECOMES A PROBLEM.
MODELS SHOW SOUTHERN TWO THIRDS OF CWA IN AN AREA WHERE THE MOISTURE
FIELD ONLY EXTENDS INTO TEMPERATURES OF -5 TO -10C. THUS ANTICIPATE
ALL SUPERCOOLED LIQUID AND THE POSSIBILITY OF LIGHT FREEZING RAIN
OVER THE CENTRAL PORTION OF THE CWA...BETWEEN PTK AND FNT. ONSET OF
PRECIPITATION IN THIS REGION SHOULD HOLD OFF UNTIL AFTER
MIDNIGHT...THUS ALLOWING SURFACE TEMPERATURES TO COOL OF SEVERAL
DEGREES DURING THE EVENING.

UPPER WAVE AND LEFT FRONT QUADRANT OF THE UPPER JET SHOULD DEEPEN
MOIST LAYER ON WEDNESDAY...ESPECIALLY OVER THE SAGINAW
VALLEY...RESULTING IN MAINLY SNOW THERE. DEEPER MOISTURE FURTHER
SOUTH...BUT MODELS STILL SHOW TOP OF MOIST LAYER SHY OF THE -13 TO
-15C TEMPERATURE RANGE. THUS...MORE LIGHT RAIN ON WEDNESDAY MORNING.
STRONG COLD AIR ADVECTION WEDNESDAY AFTERNOON WILL ALSO BE COUPLED
WITH AGGRESSIVE MID LEVEL DRY SLOTTING. ONCE AGAIN LIMITING THE LOW
LEVEL MOISTURE TO TEMPERATURES WARMER THAN -15C. WILL THEREFORE HAVE
TO INCLUDE MENTION OF DRIZZLE WEDNESDAY.

FWC AND MAV GUIDANCE TEMPERATURES LOOK TOO WARM AND TOO LEAN ON
CLOUD COVER. THUS WILL TRIM AUFTERNOON HIGHS 4 TO 8 DEGREES.

.DTX...NONE.

GSS