Heavy Snow in Michigan, April 28, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MARQUETTE MI
414 AM EDT SUN APR 28 2002

FORECAST PROBLEMS THIS MORNING INCLUDE LINGERING SNOW WITH THE STORM
MOVING BY TO OUR SOUTH...AND CLOUD COVER AND MINOR PCPN ISSUES FOR
THE REMAINDER OF THE PERIOD.

LATEST WATER VAPOR IMAGERY AND RUC ANALYSES SHOW A MASSIVE UPPER
RIDGE OVER THE EASTERN PACIFIC EXTENDED NORTH INTO SOUTHERN
ALASKA...WITH A CUTOFF LOW SLIPPING SOUTH ALONG THE WEST COAST. THE
SHORTWAVE TO OUR SOUTH IS CAUGHT UP IN FAIRLY QUICK ZONAL FLOW AND
IS SHEARING OUT WITH TIME...ALTHOUGH IT IS STILL QUITE POTENT AT THE
CURRENT TIME. IR IMAGERY HAS SHOWN WARMING CLOUD TOPS OVER UPPER
MICHIGAN OVER THE PAST FEW HOURS...AND RADAR TRENDS HAVE BEEN ON THE
DOWNTURN AS WELL. COOLING TOPS AND ENHANCED PCPN...WITH SOME
EMBEDDED CONVECTION...IS APPARENT TO THE SOUTH OVER CENTRAL
WISCONSIN IN ASSOCIATION WITH THE UPPER LOW AND MAIN VOT MAX. THE
DECREASING TREND WHICH HAS BEEN SEEN OVER UPPER MICHIGAN IS IN LINE
WITH GUIDANCE FROM THE 00Z ETA. THE ENHANCED BANDED PCPN WHICH MOVED
ACROSS THE CWFA EARLIER TONIGHT WAS IN ASSOCIATION WITH STRONG H7-H6
FRONTOGENESIS ACTING IN CONCERT WITH UPPER LEVEL DIVERGENCE DUE TO
THE COUPLED JET STRUCTURE WHICH WAS IN PLACE. SATURATED EQUIVALENT
POTENTIAL VORTICITY PROGS FROM H65-H55 INDICATED SYMMETRIC
INSTABILITY ALONG THE WI-MI BORDER EARLIER TONIGHT...WHICH LINED UP
WELL WITH THE OBSERVED THUNDER WHICH OCCURRED.

UPPER DIVERGENCE AND FRONTOGENESIS HAVE WEAKENED CONSIDERABLY OVER
THE PAST FEW HOURS...AND ARE PROGGED TO CONTINUE TO DO SO THROUGH
THE MORNING...SO WOULD EXPECT THE NORTHERN AREA OF PCPN CURRENTLY
OVER THE UP TO CONTINUE TO MOVE OUT AND WEAKEN. ANY HEAVIER PCPN FOR
THE REMAINDER OF THIS EVENT WILL BE DUE TO THE UPPER LOW AND
ASSOCIATED VOT MAX AS THEY MOVE ENE ACROSS EASTERN WI AND LAKE
MICHIGAN THROUGH EARLY THIS MORNING. CURRENT TRENDS SUGGEST THIS
AREA OF PCPN MAY CLIP THE FAR SOUTHERN AND SOUTHEASTERN CWFA THROUGH
15Z. WILL CARRY CATEGORICAL POPS EVERYWHERE TO ACCOUNT FOR ONGOING
PCPN...BUT WILL OTHERWISE TAPER THINGS OFF FROM WEST TO EAST THROUGH
THE MORNING AND EARLY AFTERNOON. WILL STICK CLOSE TO PREVIOUSLY
FORECAST NUMBERS FOR ADDITIONAL ACCUMULATIONS...WITH LITTLE OR
NOTHING WEST...AND INCH OR SO CENTRAL...AND 1 TO 3 INCHES SOUTH AND
EAST.

THE 00Z ETA AND AVN ARE IN GOOD AGREEMENT THROUGH THE EARLY PART OF
THE FORECAST...BUT DIVERGE A FAIR AMOUNT BY MONDAY EVENING. THE AVN
DEVELOPS A MUCH STRONGER SURFACE LOW MONDAY NIGHT IN RESPONSE TO THE
SHORTWAVE DROPPING IN FROM THE NORTHERN PLAINS. THE ETA PROGS A
BROAD...AND MUCH WEAKER...AREA OF LOW PRESSURE. THIS DIFFERENCE MAY
NOT HAVE A HUGE IMPACT ON THE FORECAST...SINCE ITS EFFECTS WOULD BE
MAINLY FELT AT THE EASTERN FRINGE OF THE CWFA. THE AVN/S DEVELOPMENT
OF A STRONGER SYSTEM SEEMS PREDICATED ON ITS HANDLING OF TWO
SHORTWAVES. ONE WAVE IS CURRENTLY SINKING SOUTH THROUGH
ALBERTA...WHILE THE OTHER IS BEGINNING TO DESCEND THE UPPER RIDGE
OVER ALASKA AND IS SLIDING RAPIDLY SOUTHEAST THROUGH FAR NW CANADA.
WOULD TYPICALLY FAVOR THE AVN/S HANDLING OF SUCH FEATURES...SINCE
ITS LATER DATA CUTOFF TIME USUALLY GIVES IT A BETTER HANDLE ON SUCH
THINGS. HOWEVER...AM NOT WILLING TO TOTALLY BUY INTO ITS DEPICTION
OF THINGS AT THIS POINT...ESPECIALLY WITHOUT ANY CORROBORATION FROM
OTHER GUIDANCE...SO WILL GO WITH A COMPROMISE OF THE ETA AND AVN FOR
NOW.

THIS MORNING/S SHORTWAVE WILL EXIT TO THE EAST TODAY AS DISCUSSED
PREVIOUSLY...WITH GOOD MID LEVEL SUBSIDENCE WORKING INTO THE AREA IN
ITS WAKE. THIS SUBSIDENCE WILL WORK TO DRY OUT THE MID LEVELS FROM
WEST TO EAST THIS AFTERNOON AND TONIGHT. HOWEVER...LOW LEVEL CAA AND
SUBSIDENCE ARE VIRTUALLY NOT EXISTENT...SO WE WILL BE LEFT WITH
PLENTY OF LOW LEVEL MOISTURE (BELOW 6K FEET) THROUGH TONIGHT.
WITHOUT ANYTHING WORKING TO SCOUR OUT THE LOW CLOUDS...WILL KEEP
THINGS PREDOMINANTLY CLOUDY THROUGH TONIGHT. WE COULD HAVE SOME
CONCERNS WITH DRIZZLE THIS AFTERNOON AND POSSIBLY SOME FZDZ TONIGHT
DUE TO THE LINGERING LOW LEVEL MOISTURE. HOWEVER...AM NOT TOO
IMPRESSED WITH ANY LINGERING SOURCE OF UPWARD MOTION IN THE BOUNDARY
LAYER BY TONIGHT...WITH UPPER MICHIGAN ESSENTIALLY SITTING IN A COL
FROM THE SURFACE THROUGH H85. SO...MAY MENTION SOME PATCHY DRIZZLE
IN THE CYCLONIC FLOW AND UPSLOPE THIS AFTERNOON...BUT WILL KEEP
THINGS DRY TONIGHT.

THE SHORTWAVE CURRENTLY SINKING SOUTH THROUGH EASTERN ALBERTA WILL
BEGIN TO SLIDE OUR WAY LATE TONIGHT AND ON MONDAY. WEAK 290-295K
ISENTROPIC LIFT AND SOME DPVA COMBINE TO PRODUCE SOME MODEST H85-H5
Q-VECTOR CONVERGENCE OVER THE CWFA ON MONDAY. THIS AREA OF LIFT
TRAVERSES THE CWFA FROM WEST TO EAST FROM EARLY MORNING THROUGH LATE
AFTERNOON. MOISTURE IS NOT IMPRESSIVE...BUT SHOULD BE SUFFICIENT TO
PRODUCE SOME SCATTERED RAIN AND SNOW SHOWERS. THIS SHORTWAVE WILL
HELP BRING SOME DEEPER COLD AIR FARTHER SOUTH...AND A SECONDARY
SHORTWAVE WILL SLIDE THROUGH MONDAY NIGHT...HELPING TO FURTHER COOL
THINGS OFF. WILL SIMPLY MENTION SOME SPRINKLES OR FLURRIES MONDAY
NIGHT...WITH SOME WEAK LIFT AND MOISTURE LINGERING IN THE AREA.

WILL MAKE A FEW ADJUSTMENTS TO THE EXTENDED PORTION OF THE FORECAST
TO ACCOUNT FOR CHANGES IN THE LATEST GUIDANCE. THERE IS STILL SOME
DISAGREEMENT IN THE EXTENDED BEYOND TUESDAY...BUT THINGS ARE COMING
INTO BETTER AGREEMENT. TODAY/S ECMWF AND TONIGHT/S CANADIAN RUNS ARE
IN DECENT AGREEMENT FOR THE SECOND HALF OF THE WEEK. BOTH MODELS
PUSH THE POLAR FRONT SOUTH THROUGH THE AREA TUESDAY...AND KEEP THIS
DEEPER POOL OF COOL AIR ACROSS THE NORTHERN GREAT LAKES THROUGH
EARLY WEDNESDAY BEFORE HEIGHTS BEGIN TO RISE AHEAD OF AN APPROACHING
SHORTWAVE. THE LATEST ETA AND AVN ARE SUPPORTIVE OF THIS TREND...SO
HAVE LOWERED TEMPERATURES A BIT DURING THE TUESDAY-THURSDAY TIME
FRAME. THURSDAY/S SHORTWAVE IS THE REMNANTS OF THE UPPER LOW
CURRENTLY CUTOFF ALONG THE CALIFORNIA COAST. BOTH SOLUTIONS ARE
SLOWER TO EJECT THIS UPPER LOW OUT OF THE SOUTHWEST US IN COMPARISON
TO LAST NIGHT/S MRF...AND WAIT UNTIL WEDNESDAY BEFORE SENDING THIS
FEATURE EASTWARD. THE LATEST AVN IS TRENDING TOWARD A SLOWER
EVOLUTION AS WELL...WHICH MAKES SENSE GIVEN THIS FEATURES POSITION
WELL SOUTHWEST OF ANY DIGGING NORTHERN STREAM SHORTWAVES. THIS
FEATURE SHEARS OUT AND WEAKENS AS IT MOVES OUR WAY...AND SWINGS
THROUGH AS A POSITIVELY TILTED OPEN WAVE ON THURSDAY. WITH BROAD
WESTERLY FLOW...THIS SYSTEM WILL NOT HAVE MUCH MOISTURE WITH WHICH
TO WORK...AND THERE IS SOME DISAGREEMENT BETWEEN THE ECMWF AND
CANADIAN AS TO WHETHER OR NOT IT WILL HAVE MUCH OF A SURFACE
REFLECTION. HOWEVER...WILL KEEP A MENTION OF PCPN IN THE FORECAST.
HAVE NO PERSUASIVE EVIDENCE TO ADJUST THE THINGS BEYOND
THURSDAY...SO WILL LEAVE THE REMAINDER OF THE EXTENDED FORECAST
INTACT.

.MQT...WINTER STORM WARNING EARLY THIS MORNING MIZ012-013
       SNOW ADVISORY EARLY THIS MORNING MIZ006-007-014.

TRH