Ice Storm in Michigan, February 24, 2001

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
350 AM EST SAT FEB 24 2001

ETA GETS A NOD FOR ITS QPF MATCHING UP WELL WITH THE LEADING EDGE OF
PRECIP WORKING NORTHEAST EARLY THIS MORNING. THIS WAS SHOWN BY RADAR
AND SURFACE OBS WHICH INDICATED A MIX OF SNOW, FREEZING RAIN, AND
RAIN WORKING THROUGH ILLINOIS AND INTO WESTERN INDIANA. BANDS OF
HIGHER REFLECTIVITY ON RADAR SUGGESTED SOME SLEET WAS OCCURRING AS
WELL.

THE NGM AND AVN WERE TOO SLOW WITH THE ONSET PRECIP, BUT AT THE SAME
TIME, THEY LOOKED BETTER MATCHING UP THE RAIN SNOW LINE WITH
CRITICAL THICKNESS FOR 1000-850 AND 850-700 LAYERS. THESE VALUES ARE
CALIBRATED AT THE USUAL 1300M FOR 1000-850 WITH 1545 LOOKING GOOD
FOR THE 850-700 LAYER. THE ETA WAS TOO WARM WITH ITS 1000-850
THICKNESS BASED ON THESE OBS. IT HAS BEEN TRYING TO BRING THE WARM
AIR IN TOO FAST AS IT RAMPS UP THE SURFACE LOW TO OUR WEST, BUT BY
THIS AFTERNOON THE WARM BIAS DIMINISHES QUITE A BIT AS HEAVIER
PRECIP MOVES IN AND WET BULB COOLING WORKS INTO THE PICTURE. USING
THE ETA'S QPF AND THE NGM'S THICKNESS AS A GUIDE, AS WELL AS
FORECAST SOUNDINGS FROM BOTH, EXPECT LIGHT SNOW OR FLURRIES TO BREAK
OUT OVER SE MICHIGAN DURING THE MID TO LATE MORNING HOURS.

THE HEAVIER PRECIP WILL SLIDE IN FROM SW TO NE AND JUST GRAZE THE
DETROIT AREA THIS MORNING, SETTLING IN BETTER FROM FLINT TO PORT
HURON AND NORTH. THIS WILL OCCUR AS THE FIRST WAVE OF MOISTURE RIDES
IN ON THE LOW LEVEL JET FROM SW LOWER INTO THE THUMB. VERY
IMPRESSIVE THETA-E ADVECTION IS SHOWN ON ALL THE MODELS TODAY WITH
THE LOW LEVEL JET GETTING UP AROUND 50 KNOTS. IMPRESSIVE MODEL LIFT
IS THE RESULT WITH OMEGA GETTING UP INTO THE 5 TO 7 UB RANGE. THIS
WILL INCREASE THE PRECIPITATION RATE ENOUGH TO HELP KEEP THE PRECIP
TYPE IN THE FORM OF SNOW, ALONG WITH WET BULB COOLING. ABOUT AN INCH
OF ACCUMULATION CAN BE EXPECTED AROUND THE TRI CITIES AND THUMB,
DOWN TO PORT HURON BEFORE THE CHANGE OVER BEGINS. THE STRONG LOW
LEVEL JET WILL THEN RAPIDLY BRING IN ABOVE FREEZING TEMPERATURES
THROUGH A DEEP LAYER AND MAKE THE OCCURRENCE OF SLEET RELATIVELY
BRIEF. THE LOW LEVEL COLD POOL WILL BE DEEPER IN THE NORTH, BUT NOT
REALLY COLD ENOUGH TO REFREEZE LIQUID DROPS. FREEZING RAIN WILL BE
THE RESULT, WITH THE LONGEST DURATION AGAIN IN THE SAGINAW VALLEY
AND THUMB, ESPECIALLY GIVEN THE COLD START TO THE DAY. BAD AXE
REPORTED SINGLE DIGIT TEMPERATURES THIS MORNING, ALONG WITH TEENS IN
THE TRI CITIES AND PORT HURON. FREEZING RAIN WILL CHANGE TO RAIN BY
ABOUT 2 PM AROUND FLINT AND PONTIAC, BUT NOT BEFORE QPF REACHES 0.25
INCH. PLAN TO DISTRIBUTE THIS ABOUT 50/50 BETWEEN SNOW AND FREEZING
RAIN, THEN JUST RAIN TOWARD LATE AFTERNOON. WITH THE PRECIP TYPE
RUNNING THE BOARD AND ABOUT 0.10 INCH OF ICING, FEEL THAT A WINTER
WEATHER ADVISORY WILL BE WARRANTED FOR THE AREA MAINLY NORTH OF M
59. ICE ACCUMULATION CLOSE TO 0.2 IS POSSIBLE AROUND THE TRI CITIES
AND THUMB, AND PORT HURON.

PRECIP WILL BE ALL RAIN HEADING INTO TONIGHT, EXCEPT FOR EARLY
EVENING IN THE NORTH, WITH HEAVY RAINFALL AND THUNDER POTENTIAL THE
MAIN PROBLEMS. WITH THE DRY SLOT WORKING IN AROUND 09Z, THE 0.5 TO
1.0 INCH QPF THAT WE HAVE GOING IN OUR FLOOD POTENTIAL OUTLOOK
(ESFDTX) STILL LOOKS GOOD. THE 1 INCH AMOUNTS WILL OCCUR ON A MORE
LOCAL BASIS DEPENDING ON THE COVERAGE OF CONVECTION. THE BEST CHANCE
OF THUNDERSTORMS WILL BE ALONG THE LOW LEVEL MOIST AXIS AND LEADING
EDGE OF THE DRY SLOT. THIS IS WHERE DYNAMIC FORCING AND MID LEVEL
INSTABILITY WILL BE GREATEST. THE LATEST 06Z MESOETA ADVERTISES 850
LI GETTING CLOSE TO ZERO BY 06Z. THIS IS GOOD EVEN FOR THE WARM
SEASON, NOT TO MENTION LATE FEBRUARY.

FOG AND DRIZZLE WILL BE LEFT BEHIND FOR SUNDAY MORNING IN THE DRY
SLOT OF THE SYSTEM, FOLLOWED BY A MIX OF RAIN AND SNOW DURING THE
AFTERNOON AS THE WRAP AROUND MOISTURE WORKS IN. WINDY CONDITIONS
WILL ALSO BE HIGHLIGHTED INTO SUNDAY NIGHT WITH A 20 MB GRADIENT
ACROSS LOWER MICHIGAN.

.DTX...WINTER WEATHER ADVISORY...TODAY...MIZ047>049-053>055-
                                            060>063-068>070E
       GALE WARNING...TODAY AND THIS EVENING...LAKE HURON.

BT