Extreme Cold in Michigan, February 19 to 20, 2001

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
326 PM EST MON FEB 19 2001

MODELS REASONABLY SIMILAR...WITH TIMING DIFFERENCES MINIMAL. SURFACE
COLD FRONT FINALLY PROGGED TO PULL ON THROUGH BY MIDDAY
TUESDAY...ITS PROGRESSION SLOWED SOMEWHAT BY WEAK WAVING ON SOUTHERN
PART OF FRONT INDUCED BY SHEARED MID LEVEL ENERGY PASSING SOUTH OF
THE GREAT LAKES...THEN MASSIVE COLD HIGH BUILDS IN AND TEMPERATURES
DROP IMPRESSIVELY. AT 500 MB...STRONG LOBE PIVOTS AROUND HUDSON BAY
VORTEX INTO GREAT LAKES TUESDAY AND ON OUT WEDNESDAY.

COLD FRONT EXPECTED TO LINGER IN VICINITY OF SOUTHEAST MI LONG
ENOUGH FOR TEMPERATURES TUESDAY TO WARM INTO MID 30S AHEAD OF IT
NORTH TO AROUND 40 IN FAR SOUTH. WILL GO FALLING AFTERNOON
TEMPERATURES NORTH AND CENTRAL.

GIVEN LACK OF DEEP MOISTURE TONIGHT...AND LACK OF REPORTS OF
PRECIPITATION...WILL DROP MENTION OF PRECIPITATION FOR TONIGHT.
BUFKIT SOUNDINGS SHOW MID LEVELS VERY DRY TONIGHT AND EVEN LOW MOISTURE
DIMINISHING LATE TONIGHT PARTICULARLY NORTH AND CENTRAL. GIVEN THIN
SPOTS TO THE WEST...WILL RETAIN PARTIAL CLEARING WORDING LATE
TONIGHT EXCEPT FAR SOUTH. ON TUESDAY...MOISTURE DEEPENS UP
CONSIDERABLY DURING THE MORNING...BEFORE MID AND HIGH MOISTURE PEELS
AWAY RAPIDLY LATE TUESDAY INTO TUESDAY NIGHT AS ARCTIC AIR MOVES ON
IN. SOUNDINGS AND THICKNESS CONSIDERATIONS TUESDAY WOULD SUPPORT
SNOW...EXCEPT FAR SOUTH WHERE A RAIN SNOW MIX WOULD SEEM IN ORDER.

DYNAMICS WILL BE MODEST TUESDAY...TO GO ALONG WITH THE MORE FAVORABLE
MOISTURE. 700 TO 925 MB THETA E ADVECTION SLIGHT AT BEST. SURFACE
CONVERGENCE AND 850 TO 500 MB QVECTOR CONVERGENCE MODEST TOO...
BUT 1000 TO 850 MB AND 700 MB FRONTOGENETICAL FORCING PRETTY GOOD. A
TWIN 300 MB JET STRUCTURE IN THE VICINITY OF LOWER MI TUESDAY
SUPPORTIVE OF PRECIPITATION AS WELL. NET ADIABATIC ISENTROPIC OMEGA
LIFT AT 290K SURFACE SEEN TUESDAY AFTERNOON SOUTH ALSO...WITH
CONDENSATION PRESSURE DEFICITS TUESDAY LOWERING TO 20 TO 30 MB MOST
AREAS BY AFTERNOON. WILL GO CHANCE POPS TUESDAY.

SCATTERED SNOW SHOWERS A GOOD BET INTO TUESDAY EVENING...AND VERY COLD
WITH A CHANCE OF FLURRIES YET WEDNESDAY. WILL GO CLOSE TO THE ETA
2 METER TEMPERATURES TUESDAY NIGHT AND WEDNESDAY...5 TO 15 TUESDAY
NIGHT AND 10 TO 20 WEDNESDAY.

EXTENDED FORECAST PERIODS...MODELS OVERALL SIMILAR. AT 500 MB...
MEDIUM RANGE MODELS SHOW CANADIAN VORTEX GRADUALLY SHIFTING OFF TO THE
EAST AFTER MIDWEEK...WHILE WEAK PACIFIC REGIME SHORTWAVE ENERGY
IMPULSES PASS MAINLY TO THE SOUTH OF THE GREAT LAKES. STRONGER AMPLIFIED
WESTERN TROUGH ADVANCING INTO CENTRAL USA BY 12Z SATURDAY...UK
FASTER AND WEAKER...CANADIAN GLOBAL GENERALLY MORE SIMILAR TO
MRF/ECMWF AND LATTER THREE SOLUTION PRETTY MUCH ACCEPTED. AT
SURFACE...MASSIVE ELONGATED RIDGE AXIS JUST SOUTH OF GREAT LAKES YET
THURSDAY...THEN PUSHED SOUTHEAST AS COLD FRONT APPROACHES FROM THE
NORTHWEST...MRF TENDING A BIT FASTER THAN OTHERS WITH THIS
FRONT...AND 12Z AVN EVEN FASTER AND MORE VIGOROUS...WITH 00Z MODEL
CONSENSUS SHOWING FRONT WEAKER AND LOSING MUCH OF ITS DEFINITION AS
IT GETS NEAR. WILL GO CHANCE OF SNOW SHOWERS FRIDAY...IN PREFERENCE
TO SLOWER PROGRESSION OF FRONT. A MORE VIGOROUS SURFACE SYSTEM
APPROACHING WESTERN LAKES SATURDAY...THOUGH MUCH LATITUDINAL
VARIATION OF SURFACE LOW. AT ANY RATE...NEXT WEEKEND LOOKS LIKE
SOUTHEAST MI WILL BE IN WARM SECTOR...WITH STRONG THERMAL RIDGING
AND PROBABLY SNOW TO RAIN SATURDAY AND RAIN SHOWERS CHANGING TO SNOW
SHOWERS SUNDAY. MRF SHOWS QUITE ABUNDANT QPF FOR SATURDAY AND
SATURDAY NIGHT.

.DTX...NONE.

DWD