Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KDTX 242028
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
328 PM EST WED DEC 24 2014

.SHORT TERM...THIS EVENING THROUGH TONIGHT

THE CHRISTMAS EVE CYCLONE WILL FINALLY SHOW ITS HAND THIS EVENING AS
IT UNFOLDS OVER THE GREAT LAKES REGION. CONSOLIDATION OF UPPER
ENERGY IS FORECAST TO OCCUR SLIGHTLY NORTH AND EAST OF PREVIOUS
MODELED PROJECTIONS, LIKELY DUE TO IMPACTS OF CONVECTION OVER THE
SOUTHERN UNITED STATES. THIS HAS LED THE 12Z SUITE TO DELAY
DEEPENING OF THE CYCLONE AND MOVE IT A BIT EAST. AS A RESULT, THE
PRESSURE GRADIENT MAXIMUM THAT WILL FORM ON THE BACK SIDE OF THE LOW
WILL ONLY MANAGE TO SCRAPE THE EASTERN CWA AND WILL INSTEAD
PRIMARILY IMPACT ONTARIO. DESCENT WITHIN THE FRONTAL ZONE AND
TRAILING SUBSIDENCE/CAA MAY YET BE SUFFICIENT TO SQUEEZE OUT A FEW
45 MPH GUSTS WITHIN THE AREA ADVISED FOR WIND, BUT GENERALLY EXPECT
GUSTS TO 35 TO 40 MPH...STILL GUSTY ENOUGH TO WARRANT CONTINUING
WITH THE MARGINAL ADVISORY FOR NOW. STRONGEST WINDS ARE STILL ON
TRACK TO IMPACT THE AREA 00-04Z.

SECOND FACET OF THIS SYSTEM IS SNOW POTENTIAL. FROM A THERMODYNAMIC
STANDPOINT, THE EVOLUTION WILL BE ENTIRELY DIFFERENT THAN MODELED
OVER THE LAST SEVERAL DAYS. PREVIOUS RUNS HAVE INDICATED A
PRONOUNCED WARM AXIS WRAPPING AROUND THE LOW AND WELL INTO THE CWA,
DELAYING THE CHANGEOVER TO SNOW FOR ALMOST EVERYONE AND ALLOWING
HIGHS TO REACH WELL INTO THE 50S OVER MUCH OF THE CWA. TODAY,
HOWEVER, IT IS EVIDENT THAT HIGHS WILL STRUGGLE INTO UPPER 40S FOR
MOST LOCATIONS AND SHORT TERM PROJECTIONS INDICATE H85 TEMPS FALLING
BELOW 0C AREAWIDE BY 03Z.

FROM A SYNOPTIC/MESOSCALE STANDPOINT, COLD AIR SUPPORTIVE OF SNOW
WILL STILL BE SLOW TO INFILTRATE THE BOUNDARY LAYER OVER SOUTHEAST
MICHIGAN. HOWEVER, NAM12 CROSS-SECTIONS SHOW AN INCREDIBLY LOW
STATIC STABILITY PROFILE ACROSS THE CWA THAT WILL BE VERY RECEPTIVE
TO ANY FORCING AT ALL, AND FORCING WILL BE PRESENT IN ABUNDANCE.
FRONTOGENETIC LEFT EXIT REGION DYNAMICS, DESPITE BEING LARGELY
DISPLACED TO THE SOUTHEAST, WILL BE SUFFICIENT OVER THE AREA TO
ALLOW FOR AGGRESSIVE TILTING OF ISENTROPES IN THE 850-400MB LAYER.
THE RESULTANT DEEP FGEN RESPONSE ZONE WILL SUPPORT A BAND OF
ENHANCED ASCENT WITHIN AN ALREADY ROBUST DEFORMATION ZONE. IN FACT,
CROSS-SECTIONS BORDER ON BEING CONVECTIVELY UNSTABLE AT THE NAM12
GRID SCALE NORTHWEST OF THE GLACIAL RIDGE. EVEN IN THE CASE THAT
UPRIGHT CONVECTION DOES NOT DEVELOP, GEOSTROPHIC ANGULAR MOMENTUM
PROFILES SUGGEST CSI COULD EVEN EVOLVE IN ITS PLACE. IT HARDLY SEEMS
TO MATTER, AS ONE WAY OR ANOTHER ASCENT WILL BE INTENSE WITHIN A
POTENTIALLY NARROW BAND BETWEEN ROUGHLY SAGINAW AND FLINT. IT IS
DOUBTFUL, AND CERTAINLY PLAYING WITH FIRE SO TO SPEAK, TO EXPECT
MARGINAL BOUNDARY LAYER TEMPERATURES TO CONTINUE TO SUPPORT RAIN
WITHIN SUCH AN ENVIRONMENT. AS SUCH, EXPECT THAT RATES COULD BE
INTENSE AS WELL WITH THE POTENTIAL FOR 2-3" IN A 1-2 HOUR TIME
WINDOW WITHIN THE ADVISED AREA. THIS WOULD BE SUFFICIENT TO DISRUPT
TRAVEL AND CONFIDENCE IS HIGH ENOUGH TO WARRANT ISSUANCE OF A WINTER
WX ADVISORY FOR THE NORTHWESTERN PORTION OF THE CWA ATTM. WOULD NOT
BE TERRIBLY SURPRISED TO SEE A NARROW BAND OF MODERATE TO HEAVY SNOW
SET UP WITHIN THE ADVISORY AREA AND BE FLANKED ON EITHER SIDE BY 34
DEGREE RAIN. AT THIS TIME, HOWEVER, WILL HEDGE TOWARD A CHANGE TO
ALL SNOW IN THE NORTHWEST PORTION OF THE ADVISORY AND RAIN/SNOW MIX
SOUTHEAST. OBSERVATIONS WILL BE MONITORED THROUGH THE EVENING.

&&

.LONG TERM...CHRISTMAS THROUGH NEXT WEDNESDAY

THE STORM SYSTEM IMPACTING THE REGION TODAY WILL RAPIDLY LIFT ACROSS
QUEBEC ON CHRISTMAS. GUSTY WINDS WILL PERSIST THROUGH THE EARLY PART
OF THE DAY. LIMITED MIXING DEPTHS SHOULD KEEP THE PEAK GUSTS BELOW
30 MPH. AMPLE LOW LEVEL MOISTURE AMIDST A DEEPENING LOW LEVEL
INVERSION WILL SUSTAIN A HEALTHY STRATO CU FIELD DURING THE DAY.
THERE IS NOT A SUBSTANTIAL AMOUNT OF COLD AIR WRAPPING AROUND THIS
LOW PRESSURE SYSTEM. SO EVEN WITH THE POTENTIAL FOR SOME SNOW COVER
ACROSS THE NRN HALF OF THE FORECAST AREA...DAYTIME TEMPS SHOULD
REMAIN LARGELY ABOVE FREEZING. LOW LEVEL WARM AIR ADVECTION WILL
ALREADY GET UNDERWAY TOMORROW AFTERNOON INTO THE EVENING IN RESPONSE
TO BUILDING MID LEVEL HEIGHTS AND STRENGTHENING LOW LEVEL SW FLOW.
MODEL SOUNDINGS ARE AT LEAST SUGGESTIVE OF ENOUGH LOW LEVEL DURING TO
OFFER A POTENTIAL FOR SOME CLEARING SKIES THURS NIGHT. THIS MAY
OFFER JUST ENOUGH DECOUPLING IN THE BOUNDARY LAYER TO SOME SUBTLE
COOLING DESPITE THE LOW LEVEL WARM AIR ADVECTION.

THE BUILDING HEIGHTS ACROSS THE GREAT LAKES REGION WILL CONTINUE
INTO FRIDAY IN RESPONSE TO LONG WAVE TROUGH AMPLIFICATION ACROSS THE
CENTRAL ROCKIES. THIS WILL SUPPORT A MODEST WARM UP HEADING INTO THE
FIRST HALF OF THE WEEKEND. THE MEDIUM RANGE MODEL SUITE ARE IN
REASONABLE AGREEMENT IN SHOWING A FAST MOVING SHORTER WAVELENGTH
IMPULSE EJECTING OUT OF THE BASE OF THE LONG WAVE TROUGH AND
ROTATING ACROSS THE NORTHERN GREAT LAKES SAT INTO SAT NIGHT.
ALTHOUGH THE WAVE IS FORECAST TO BECOME HIGHLY SHEARED AS IT ROTATES
INTO THE REGION...ENHANCED UPPER JET FORCING WILL INVOKE A HEALTHY
DEEP LAYER FRONTOGENETICAL RESPONSE OVER SE MI SAT AFTN INTO SAT
NIGHT. THERMAL PROFILES WILL REMAIN WARM ENOUGH TO SUPPORT ALL RAIN
THROUGH MOST OF THIS EVENT...WITH A POSSIBLE CHANGE OVER TO SNOW SAT
NIGHT AS THE FORCING EXITS TO THE EAST.

A PATTERN SHIFT TOWARD STRONGER RIDGING OFF THE WEST COAST OF NOAM
NEXT WEAK WILL SUPPORT A TRANSITION TOWARD MORE TROUGHING OVER
EASTERN CANADA AND THE NORTHERN TIER OF THE US. THIS WILL OFFER AN
OPPORTUNITY FOR BETTER INFILTRATION OF COLDER AIR INTO THE GREAT
LAKES REGION. SO COLDER TEMPS IN COMPARISON TO THE LAST FEW WEEKS
ARE EXPECTED TO TAKE HOLD ACROSS THE REGION.

&&

.MARINE...

LOW PRESSURE OVER NORTHWEST OHIO WILL STRENGTHEN AS IT TRACKS INTO
FAR SOUTHERN LAKE HURON THIS EVENING. THE LOW WILL CONTINUE TO
DEEPEN AS IT LIFTS NORTHEAST INTO QUEBEC OVERNIGHT. THE RESULT WILL
BE A BACKING OF THE WINDS FROM NORTH TO WEST ACROSS LAKE HURON
TONIGHT...WITH THE INTENSIFICATION OF THE LOW LEADING TO GALE FORCE
WIND GUSTS.

WINDS WILL DIMINISH DURING THURSDAY AS A RIDGE OF HIGH
PRESSURE BUILDS INTO THE AREA THROUGH THE DAY...WITH LIGHT TO
MODERATE SOUTHWEST WINDS IN STORE FOR FRIDAY AHEAD OF A COLD FRONT
PASSING THROUGH ON SATURDAY.

&&

.AVIATION...ISSUED 1247 PM EST WED DEC 24 2014

THE SURFACE LOW TRACK FROM ABOUT LIMA TO DTW TO PORT HURON HAS
PROLONGED THE VLIFR RESTRICTION IN THE DTW AREA WHICH IMPROVES
MODESTLY TOWARD MBS...A LITTLE FARTHER FROM THE LOW BUT DEEPER INTO
THE PRECIPITATION SHIELD. THE COMPLEX CEILING AND VISIBILITY PATTERN
WILL IMPROVE AT THE EXPENSE OF STRONG WESTERLY WIND AS THE SYSTEM
EXITS INTO SOUTHERN ONTARIO BY EVENING. COLDER AIR RUSHING IN
THROUGH THE LOW LEVELS WILL THEN EXPEDITE A CHANGE FROM RAIN TO SNOW
MORE RAPIDLY AND A FEW HOURS EARLIER IN THE NIGHT...FROM ABOUT MID
EVENING TO MIDNIGHT ACROSS THE TERMINAL CORRIDOR. AN IFR BURST OF
SNOW IS EXPECTED FROM PTK NORTHWARD AS WESTERLY WIND GUSTS INCREASE
TO 35 KNOTS WITH A FEW HIGHER GUSTS POSSIBLE. THE SNOW WILL TAPER
OFF DURING THE OVERNIGHT HOURS AND THE WIND WILL FOLLOW A DOWNWARD
TREND DURING THE DAYLIGHT HOURS OF CHRISTMAS MORNING.

FOR DTW... THE SLIGHT IMPROVEMENT OF CEILING AND VISIBILITY OBSERVED
EARLIER AT TOL AND TTF HAS REVERSED BACK TOWARD 1/4SM JUST BEFORE
PRESS TIME. THIS WILL REQUIRE ANOTHER EXTENSION OF VLIFR CONDITIONS
AT DTW AS THE SURFACE LOW TRACKS JUST ABOUT OVERHEAD DURING THE
AFTERNOON. WESTERLY WIND GUSTS TO 35 KNOTS WILL MATERIALIZE ON THE
HEELS OF THE SYSTEM AS WILL A CHANGE FROM RAIN TO SNOW...THE
HEAVIEST OF WHICH IS EXPECTED TO OCCUR NORTH OF DTW BUT WITH SOME
MINOR ACCUMULATION STILL POSSIBLE.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CEILINGS AOB 5000 FEET THROUGHOUT THE TAF PERIOD.

* HIGH IN VISIBILITY BELOW 1/2SM AND CEILING AOB 200 FEET DURING THE
  AFTERNOON.

* HIGH FOR WIND GUSTS TO REACH 35 KNOTS FROM 250 DEGREES TONIGHT.

* HIGH CONFIDENCE IN RAIN CHANGING TO SNOW TOWARD MIDNIGHT.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO MIDNIGHT EST
     TONIGHT FOR MIZ047>049-053-054-060-061.

     WIND ADVISORY FROM 9 PM THIS EVENING TO 5 AM EST THURSDAY FOR
     MIZ049-054-055-062-063.

     WIND ADVISORY FROM 7 PM THIS EVENING TO 3 AM EST THURSDAY FOR
     MIZ069-070-075-076-082-083.

LAKE HURON...GALE WARNING FROM 7 PM THIS EVENING TO 11 AM EST THURSDAY FOR
     LHZ363-421-441>443-462>464.

     GALE WARNING FROM 7 PM THIS EVENING TO 5 AM EST THURSDAY FOR LHZ422.

     GALE WARNING FROM 11 PM THIS EVENING TO 11 AM EST THURSDAY FOR
     LHZ361-362.

LAKE ST CLAIR...GALE WARNING UNTIL 4 AM EST THURSDAY FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...LOW WATER ADVISORY FROM 9 PM THIS EVENING TO NOON EST THURSDAY FOR
     LEZ444.

     GALE WARNING UNTIL 4 AM EST THURSDAY FOR LEZ444.

&&

$$

SHORT TERM...JVC
LONG TERM....SC
MARINE.......SC
AVIATION.....BT


YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.