Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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445
FXUS63 KDTX 121736
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1236 PM EST FRI FEB 12 2016

.UPDATE...

ISSUED A WIND ADVISORY FOR HURON COUNTY...IN EFFECT FROM 4 PM TO
MIDNIGHT LST. LATEST GUIDANCE ARRIVED IN LOCKSTEP SUPPORTING
NORTH NORTHWESTERLY WINDS OF 40 TO 50 MPH DEVELOPING IN THE WAKE
OF THE ARCTIC FRONT...PRIMARILY ALONG THE LAKE HURON SHORELINE
THIS EVENING. GIVEN THE FETCH...EXPECTATIONS ARE THAT TUSCOLA AND
SANILAC COUNTIES WILL BE SHADOWED FROM THE GREATEST WINDS. THERE
IS RELATIVELY HIGH CONFIDENCE IN 45 TO 50 MPH WIND GUSTS ALONG THE
SHORE GIVEN A VERY DEEP...10 KFT UNSTABLE LAYER OVER THE LAKE.
THE LOOK OF THE VERTICAL WIND PROFILE SUPPORTS GRADIENT WIND
PROCESSES WITH AN EVENT THEN CONDUCIVE FOR AN INFLUENCE BY
SHORELINE CONVERGENCE. IN OTHER WORDS...50 MPH APPEARS TO BE THE
CEILING. GIVEN THE TRENDS THIS AFTERNOON...SNOW SQUALL POTENTIAL
WILL CONTINUE TO EXIST ALONG AND IMMEDIATELY BEHIND THE COLD
FRONT. WITH THE HIGHER INTENSITY SNOWFALL RATES AND THE POTENTIAL
FOR BLOWING SNOW FROM RECENT SNOW EARLIER THIS WEEK...THE THREAT
WILL EXIST FOR BRIEF/SPORADIC WHITEOUT CONDITIONS.

INCREASED POPS INTO THE CATEGORICAL RANGE FOR A SOLID PORTION OF
THE CENTRAL CWA PER TRENDS. THE PREFRONTAL TROUGH AXIS...AND
LARGER SCALE SOUTHWESTERLY FLOW CONFLUENCE AXIS HAS BECOME ACTIVE
THIS MORNING WITH ISOLATED REPORTS OF SURFACE VISIBILITIES OF LESS
THAN 1 MILE. DEEPER MOISTURE EXISTS WITHIN THIS CORRIDOR WITH
SATURATION/SUPER SATURATION WRT TO ICE BETWEEN 900-750 MB.
GUIDANCE SUGGESTS THIS ACTIVITY WILL REMAIN FAIRLY
TRANSIENT...MIGRATING FROM THE I 69 CORRIDOR AT 17Z...DOWN INTO
PORTIONS OF METRO DETROIT AFTER 19Z THIS AFTERNOON. GAUGING FROM
HERE AT THE OFFICE...ONE NEEDS TO GET DIRECTLY WITHIN THESE SMALL
DBZ CORES TO SEE THE HIGHEST SNOWFALL RATES. PLAYED IT IN THE
GRIDS OF SNOWFALL ACCUMULATIONS OF GENERALLY AN INCH OR LESS
POSSIBLE...BUT AGAIN THIS IS A LOCALIZED SNOWFALL ACCUMULATION
POTENTIAL. THERE VERY WELL COULD BE A LULL IN SNOW SHOWER
ACTIVITY AFTER THAT...UNTIL THE ARCTIC COLD FRONT ARRIVES.
ANTICIPATING THERE TO BE A SNOW SQUALL POTENTIAL ATTENDANT TO THIS
FEATURE DROPPING DUE SOUTHWARD THROUGH THE CWA BETWEEN 21-02Z.

&&

.AVIATION...ISSUED 541 AM EST FRI FEB 12 2016

VFR CEILINGS LOOK TO BE IN PLACE FOR MOST OF THE TAF PERIOD.
HOWEVER...A STRONG ARCTIC FRONT MOVING THROUGH DURING THE AFTERNOON
HOURS WILL TRIGGER SNOW SHOWERS...LIKELY CAUSING VISIBILITIES TO DIP
INTO IFR...WITH LIGHT ACCUMULATIONS EXPECTED (LESS THAN ONE INCH). IN
ADDITION...NORTHWEST WINDS WILL INCREASE BEHIND THE FRONTAL
PASSAGE...GUSTING TO 25 KNOTS OR GREATER LATE THIS AFTERNOON
INTO THE EVENING. THE POST FRONTAL ENVIRONMENT MAY SUPPORT SOME
HEAVIER BUT MORE LOCALIZED SNOW SHOWERS/SQUALLS DURING THROUGH THE
EVENING. LOW CONFIDENCE SCENARIO AT THIS STAGE GIVEN THE DIFFICULTY
IN DEFINING BOTH TIMING AND DURATION...BUT QUICK/BRIEF DISRUPTIONS OF
VISIBILITY /LIFR-IFR/ WILL BE POSSIBLE.

FOR DTW...
MID CLOUDS LOWERING WITH PERIOD OF SNOW SHOWERS THIS AFTERNOON AS A
STRONG ARCTIC FRONT SLIPS THROUGH. ACCUMULATION PROJECTIONS CURRENTLY
AT A HALF INCH OR LESS.  INCREASING NORTHWEST WINDS /300-310 DEG/
BEHIND THIS FRONT LATE AFTERNOON INTO THIS EVENING...WITH GUSTS
PEAKING OUT BETWEEN 25-30 KNOT RANGE DURING THIS TIME. POSSIBLE
HEAVIER SNOW SHOWERS/SQUALLS COULD BRING ABRUPT VISIBILITY
REDUCTIONS DOWN TO IFR-LIFR...BUT HIGH UNCERTAINTY YET IN POSSIBLE
TIMING/COVERAGE. DRY NATURE OF THE ARCTIC AIRMASS MAY PROMOTE SKIES
PARTIALLY CLEARING OUT SOONER THAN FORECASTED (9Z)...BUT RENEWED VFR
CU UP IS THEN FAVORED DURING SATURDAY.

//DTW THRESHOLD PROBABILITIES...

* LOW FOR CEILING AOB 5KFT THIS MORNING MORNING...HIGH THIS
  AFTERNOON...THEN LOW TO MEDIUM CONFIDENCE TONIGHT INTO TOMORROW.

* LOW TO REACH CROSSWIND THRESHOLDS FROM 300-310 DEGREES LATE FRIDAY
  AFTERNOON AND EVENING /21Z-03Z/

* HIGH FOR PTYPE AS SNOW.

&&

.PREV DISCUSSION...ISSUED 306 AM EST FRI FEB 12 2016

DISCUSSION...

THE STRONGEST ARCTIC FRONT OF THE SEASON...WITH H85 TEMPERATURES OF
-25F OR LOWER...IS STILL SLATED TO MOVE THROUGH THE AREA LATE THIS
AFTERNOON WITH THE ARCTIC AIRMASS THEN DEEPENING INTO SATURDAY AS
THE ARCTIC HIGH PRESSURE CENTERED SHIFT EASTWARD OVER THE CENTRAL
GREAT LAKES. WHILE SNOW SHOWERS WILL BE SOMEWHAT LIMITED WITH THIS
FRONT IN TERMS OF DURATION AND COVERAGE...STILL EXPECT NUMEROUS SNOW
SHOWERS ALONG AND BEHIND THIS FRONT...WITH LOCAL ACCUMULATIONS ON
THE ORDER OF HALF AN INCH POSSIBLE.

THE MORE NOTABLE ASPECT OF THIS SYSTEM WILL BE DANGEROUSLY COLD WIND
CHILL READINGS TONIGHT INTO SATURDAY MORNING...ESPECIALLY OVER THE
THUMB REGION WHERE NORTHWEST FLOW WILL BE ENHANCED AFTER TRAVELING
ACROSS A LARGELY FROZEN SAGINAW BAY. IN ADDITION...LOW TEMPERATURES
WILL BE COLDER...ZERO TO -5F...DUE TO THE POSITION OF THE ARCTIC AIR
MASS AND ALSO DUE TO SLIGHTLY BETTER RADIATIONAL COOLING WITH SOME
BREAKS IN THE CLOUDS AS LAKE EFFECT BANDS WILL ALIGN NNW TO
SSE...AND FOCUS FROM I-75 WESTWARD. WIND CHILL READINGS OVER THE
THUMB WILL HOVER AROUND -20F FROM LATE THIS EVENING INTO SATURDAY
MORNING WITH READINGS CLOSER TO -10F TO THE WEST AND SOUTH OF THE
ADVISORY AREA. WILL RUN THE ADVISORY FROM 03Z-16Z TO ENCOMPASSES THE
PERIOD WHERE -15F TO -20F WIND CHILL READINGS AREA EXPECTED TO BE
COMMON.

THIS ARCTIC AIRMASS WILL BE RELATIVELY SHORT LIVED AND PEAK ON
SATURDAY WITH HIGH TEMPERATURES CLIMBING ONLY INTO THE UPPER SINGLE
DIGITS OVER THE THUMB TO PERHAPS 15F DETROIT SOUTH. SCATTERED SNOW
SHOWERS WILL PERSIST AT TIMES TONIGHT INTO SUNDAY AS THE BITTERLY
COLD NORTHWEST FLOW PRODUCES AN ABUNDANCE OF LAKE EFFECT SNOW
BANDS/SHOWERS. THE NEXT DECENT CHANCE OF WIDESPREAD LIGHT SNOW WILL
COME SUNDAY NIGHT INTO MONDAY AS A CLIPPER LOW PRESSURE SYSTEM
SWEEPS INTO THE SOUTHERN GREAT LAKES AROUND THE BASE OF THE SLOWLY
EXITING ARCTIC AIR.

BY EARLY NEXT WEEK...SOUTHERN STREAM ENERGY IS EXPECTED TO PROGRESS
INTO THE CONUS FROM THE CENTRAL PACIFIC OCEAN...WITH A NORTHERN
STREAM SHORTWAVE DROPPING FROM THE VICINITY OF ALASKA INTO SOUTH
CENTRAL CANADA DURING THE SAME TIME FRAME. MEDIUM RANGE MODELS ALL
SUGGEST A DECENT PHASING OF THESE STREAMS BY THE TUESDAY/WEDNESDAY
TIME FRAME. WHILE THE RESULTANT STORM SYSTEM WILL MOST LIKELY BRUSH
THE AREA TO THE SOUTHEAST...AS A LARGE MAJORITY OF MODELS/ENSEMBLES
SUGGEST...TIMING OF THE TWO MAIN SHORTWAVES...AND THE EVENTUAL
INTERACTION OF THEM...WILL NEED TO BE MONITORED CLOSELY OVER THE
NEXT SEVERAL DAYS...AND ESPECIALLY BY LATE THIS WEEKEND WHEN THEY
ARE BETTER SAMPLED.

THE UPPER LEVEL PATTERN APPEARS TO BECOME RATHER PROGRESSIVE IN THE
WAKE OF THIS EARLY/MID WEEK SYSTEM...WITH TEMPERATURES MODERATING
FURTHER BY THE END OF NEXT WEEK AS UPPER LEVEL RIDGING BUILDS EAST
INTO THE AREA.

MARINE...

AN ARCTIC FRONT SLIDING THROUGH THE CENTRAL GREAT LAKES THIS
AFTERNOON AND EVENING WILL PRODUCE SNOW SQUALLS...AS STRONG WINDS
ALOFT AND FRIGID AIR GLIDING OVER THE WARMER LAKE WATERS WILL CREATE
UNSTABLE CONDITIONS...ALLOWING GALE FORCE WINDS TO DEVELOP OVER THE
OPEN WATERS OF LAKE HURON. HIGH-END GALE FORCE GUSTS TO 45 KNOTS ARE
EXPECTED BY EVENING...LASTING INTO THE EARLY OVERNIGHT HOURS. WINDS
WILL SUBSIDE BELOW GALE FORCE SATURDAY MORNING...THEN DECREASE
FURTHER THROUGH THE DAY AND FINALLY BECOME LIGHT SATURDAY NIGHT AS
HIGH PRESSURE SETTLES INTO THE AREA.

THE GALE FORCE WINDS COMBINED WITH LARGE WAVES AND FRIGID AIR WILL
ALSO CREATE AREAS OF HEAVY FREEZING SPRAY. A HEAVY FREEZING SPRAY
WARNING IS IN EFFECT FOR ALL OF LAKE HURON LATE FRIDAY AFTERNOON
THROUGH FRIDAY NIGHT...LASTING THROUGH SATURDAY FOR THE SOUTHERN
BASIN OF THE LAKE.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WIND ADVISORY FROM 4 PM THIS AFTERNOON TO MIDNIGHT EST TONIGHT FOR
     MIZ049.

     WIND CHILL ADVISORY FROM 10 PM THIS EVENING TO 11 AM EST SATURDAY
     FOR MIZ049-054-055-062-063.

LAKE HURON...HEAVY FREEZING SPRAY WARNING UNTIL 10 PM EST SATURDAY FOR LHZ363-
     462>464.

     GALE WARNING UNTIL 10 AM EST SATURDAY FOR LHZ363-421-441>443-
     462>464.

     HEAVY FREEZING SPRAY WARNING UNTIL 10 AM EST SATURDAY FOR LHZ421-
     441>443.

     HEAVY FREEZING SPRAY WARNING UNTIL 4 AM EST SATURDAY FOR LHZ361-362.

     GALE WARNING UNTIL 4 AM EST SATURDAY FOR LHZ361-362.

LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

UPDATE.......CB
AVIATION.....DG
DISCUSSION...DG
MARINE.......SF


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



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