Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 180930
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
430 AM EST TUE NOV 18 2014

.SHORT TERM...TODAY AND TONIGHT

INITIAL LAKE EFFECT PLUME EARLY THIS MORNING SET UP ALONG THE
INTERSTATE 69 CORRIDOR WITH FILAMENTS OF VERY HEAVY SNOW SHOWERS
FILTERING EAST THROUGH THE AREA AND REDUCING THE VISIBILITIES
LOCALLY TO 1/4SM OR LESS.

RADAR TRENDS SUGGEST THE BEST CONNECTION TO LAKE MICHIGAN IS
SHIFTING A BIT SOUTHWARD...MORE INTO LINE WITH THE GOING ADVISORY AS
MAIN ACTIVITY CENTERS CLOSER TO M 59 WITH TIME EARLY THIS MORNING.
TRENDS ALSO SUGGEST A SLIGHT WEAKENING OF THE EASTWARD EXPANSION OF
THIS ACTIVITY...BUT EXPECT THAT TO REVERSE AS INCREASED MID/UPPER
LEVEL MOISTURE EXPANDS EAST OVER THE EXISTING LAKE EFFECT BANDING
AND HELPS SEED IT AND PRODUCE A GENERAL RE-EXPANSION INTO THE DAWN
TIME FRAME.

WILL MAINTAIN THE GOING ADVISORY...ALTHOUGH IT APPEARS THAT ONLY THE
NORTHWEST 1/3 OR SO OF WASHTENAW COUNTY RUNS ANY NOTABLE RISK OF
HEAVIER SNOW SQUALLS THIS MORNING. ALSO...WHILE THE OCCASIONAL HEAVY
SNOW SHOWER MAY "ESCAPE" INTO LAPEER COUNTY...THE SOUTHERLY DRIFT OF
THE MAIN BANDS OF SNOW SHOWERS ARGUES AGAINST EXPANDING THE ADVISORY
ANY FARTHER NORTHEAST INTO THIS AREA. WHILE SNOWFALL TOTALS WILL
VARY WIDELY GIVEN SUCH A SETUP...STILL EXPECT SEVERAL INCHES OF NEW
SNOW LOCALLY AS VARIOUS BANDS OF HEAVIER SNOW SHOWERS TRANSLATE
ACROSS THE AREA THROUGHOUT THE MORNING. THIS WILL COMBINE WITH WIND
GUSTS TO 25 MPH OR SO TO PRODUCE VERY POOR VISIBILITIES ON OCCASION.

THIS LAKE EFFECT SNOW SHOWER ACTIVITY WILL THEN WEAKEN AND SHIFT
QUICKLY TO THE NORTH AS LOW LEVEL FLOW BECOMES MORE SOUTHERLY IN
ADVANCE OF NEXT APPROACHING SHORTWAVE. BY TONIGHT...SCATTERED TO
NUMEROUS SNOW SHOWERS FROM LAKE EFFECT WILL BE LIMITED TO THE
SAGINAW VALLEY WITH FLURRIES/LIGHT SNOW SHOWERS FOR THE REST OF
SOUTHEAST LOWER MICHIGAN.

TEMPERATURES WILL REMAIN VERY COLD AS THE CORE OF THE CURRENT BUBBLE
OF ARCTIC AIR SHIFTS OVER THE AREA TODAY. TEMPERATURES WILL START
OUT THE DAY FROM AROUND 10F ALONG THE MICHIGAN AND OHIO STATE LINE
TO THE MID/UPPER TEENS WITHIN MODIFIED AIRMASS WITH MOISTURE PLUME
COMING OFF LAKE MICHIGAN. HIGHS WILL THEN REACH THE UPPER TEENS TO
LOWER 20S FROM SOUTH TO NORTH ACROSS THE AREA AS BRISK SOUTHWEST
FLOW REMAINS IN PLACE INTO MIDDAY. WHILE THE SHIFT A SOUTHERLY WINDS
WILL LIMIT THE FALL OF TEMPERATURES SOMEWHAT TONIGHT...A TREND TO
PARTLY CLOUDY SKIES WILL ASSIST IN RADIATIONAL COOLING...SO LOWER TO
MID TEENS WILL BE THE RULE ACROSS THE CWA AGAIN TONIGHT.

&&

.LONG TERM...WEDNESDAY THROUGH MONDAY

ACTIVE STRETCH OF COLD AND SNOWY WEATHER WILL CONTINUE THROUGH THE
WEEK WITH BIG CHANGES IN STORE BY THE BEGINNING OF NEXT WEEK. THE
DOMINATE TROUGH OVER THE GREAT LAKES WILL HOLD OVER THE REGION
THROUGH THE WEEKEND BEFORE BREAKING DOWN AS NEXT FEW WAVES MAKE
LANDFALL OVER THE SW CONUS...SHIFTING THE LONGWAVE PATTERN AND
ALLOWING A RIDGE TO BUILD OVER THE AREA. SO AFTER A FEW MORE DAYS
WITH SNOW IN THE FORECAST...AND SOME MINOR ACCUMULATIONS...A WARM UP
WILL ENSUE ALLOWING A RUN AT 50F MAX TEMPS.

FIRST THINGS FIRST...A SHORTWAVE CURRENTLY DIVING THROUGH WESTERN
CANADA INTO THE BACKSIDE OF THE LONGWAVE TROUGH WILL SWEEP THROUGH
LOWER MI ON WEDNESDAY BRINGING LIGHT SNOW ACCUMULATIONS ACROSS LOWER
MI. MODELS ARE STILL NOT ON THE SAME PAGE WITH THIS SYSTEM WHICH IS
NOW ABOUT 36 HOURS OUT. HIRES MODELS ARE JUST BEGINNING TO CAPTURE
THE SHORTWAVE BUT HINT AT A MORE SOUTHERLY TRACK AS STRONG VORT MAX
DROPS INTO...THEN PIVOTS THROUGH THE AREA PUSHING SOUTHWARD. LOOKING
AT THE SFC...A LOW PRESSURE SYSTEM WILL BEGIN OVER WESTERN ONTARIO
BUT SFC PRESSURE FALLS WILL DROP...CONCENTRATING OVER OHIO WHICH
SHOULD PULL THE CENTER OF THE LOW FURTHER SOUTH. HOW FAR SOUTH WILL
BE KEY AS MODELS ARE ADVERTISING VERY FAVORABLE ISENTROPIC ASCENT ON
THE LEAD FRONT WITH 1-2G/KG OF SPECIFIC HUMIDITY TO WORK WITH
EXTENDING UP TO 700MB AND 850MB TEMPS STILL AROUND -10 TO -15C. THE
NAM ALSO FAVORS THIS SOUTHERLY TRACK ALTHOUGH THE INCOMING 00Z EURO
SUGGESTS HOLDING IT TO THE NORTH. THE ONE THING THEY DO AGREE ON IS
MOISTURE CONTENT ALL COMING IN WITH SIMILAR SPECIFIC HUMIDITY IN THE
BL AND AROUND 0.1 INCHES OF LIQUID EQUIVALENT. WITH HIGH SNOW RATIOS
OF 15-20:1 THIS WOULD PRODUCE A WIDESPREAD COVERAGE OF AROUND 2
INCHES OF SNOW DURING THE DAY. EXPANDED THE LIKELY POPS FURTHER
SOUTH BECAUSE EVEN WITH A SLIGHT NORTHWARD JOG...IT APPEARS THEY
SHOULD RECEIVE SOME MEASURABLE SNOW.

COLD WESTERLY FLOW WILL AGAIN SET UP BEHIND THIS SYSTEM FOR THE REST
OF THE WORK WEEK WHICH WILL KICK UP LAKE EFFECT SNOW ONCE AGAIN.
ASSIGNING ANY CONFIDENCE TO WHERE THE BAND WILL SET UP AT THIS POINT
WOULD BE TOUGH SO WILL CONTINUE TO HIGHLIGHT THE TYPICAL AREA BETWEEN
I69 AND I94 TAPERING DOWN OUTWARD FROM THERE.

THE OTHER BIG STORY IN THE EXTENDED IS THE WARM UP THIS WEEKEND. THE
ALASKAN LOW WILL SEND THE NEXT FEW WAVES FURTHER SOUTH DIGGING THE
TROUGH OVER THE WESTERN CONUS...ALLOWING RIDGING OVER THE REGION. A
STRONG LOW PRESSURE SYSTEM LOOK TO DEVELOP OVER TEXAS WITHIN THIS
THROUGH...LIFTING NE THROUGH THE GREAT LAKES. AS OF NOW IT LOOKS
LIKE WE WILL GET INTO THE WARM SECTOR ALLOWING TEMPS TO CLIMB INTO
THE MID/UPPER 40S SUNDAY AND MONDAY. THIS WILL INTRODUCE PERIODS OF
MIXED PRECIP WITH AS TEMPS CLIMB AND ALSO AN EXTENDED PERIOD OF PURE
RAIN.

&&

.MARINE...

A HIGH END WESTERLY GALE EVENT IS ONGOING OVER ALL EASTERN GREAT
LAKES WATERS...PERSISTING THROUGH THIS EVENING AS VERY COLD
CONTINUES TO STREAM INTO THE REGION. AN OCCASIONAL GUST TO STORM
FORCE REMAINS A POSSIBILITY THIS AFTERNOON DURING THE PEAK OF THE
EVENT BUT SHOULD NOT PERSIST LONG AT ANY ONE LOCATION. WAVE HEIGHTS
WILL KEEP FROM BECOMING TOO ELEVATED IN THE NEARSHORE ZONES DUE TO
OFFSHORE FLOW BUT FURTHER OUT...CENTRAL LAKE HURON SIGNIFICANT WAVE
HEIGHTS WILL REACH NEAR 10 FEET FOR AN EXTENDED PERIOD WITH MAXIMUM
WAVE HEIGHTS APPROACHING 20 FEET. WIDESPREAD SNOW SQUALLS CAN BE
EXPECTED OVER THE OPEN WATERS OF LAKE HURON AS LAKE EFFECT PROCESSES
WILL BE VERY EFFICIENT. LOW WATER LEVELS ARE A CONCERN FOR BOTH
SAGINAW BAY AND LAKE ERIE...AND LOW WATER ADVISORY ARE IN EFFECT.
THE NEXT LOW PRESSURE SYSTEM WILL ARRIVE ON WEDNESDAY WITH THE
POSSIBILITY OF ANOTHER ROUND OF GALES OVER THE OPEN WATERS OF LAKE
HURON WEDNESDAY NIGHT INTO THURSDAY.

&&

.AVIATION...ISSUED 1201 AM EST TUE NOV 18 2014

//DISCUSSION...

COLD WESTERLY WINDS OFF LAKE MICHIGAN WILL MAINTAIN A FAVORABLE
ENVIRONMENT FOR SNOW SHOWERS TO SHIFT ACROSS THE DETROIT TO FLINT
CORRIDOR OVERNIGHT AND TUESDAY.  A BRIEF DOWNWARD TREND PER RECENT
RADAR RETURNS AT 06Z...BUT EXPECTATIONS REMAIN FOR AN INCREASE IN
COVERAGE THROUGH THE MORNING PERIOD.  THE MOST NUMEROUS AND INTENSE
BANDS CARRYING A LONGER DURATION WILL TEND TO CENTER ACROSS
PTK/FNT...HIGHLIGHTED BY INTERMITTENT PERIODS OF IFR WITHIN THE
HEAVIER SHOWERS.  THE DETROIT CORRIDOR WILL REMAIN AT THE PERIPHERY
OF THIS MOISTURE...THE FREQUENCY OF VSBY DISRUPTIONS BELOW MVFR
CONSIDERABLY LOWER AND NO LONGER WORTHY OF A MENTION.   OUTSIDE
THESE SNOW SHOWERS...CONDITIONS WILL RECOVER INTO VFR WITHIN AN
EXTENSIVE CANOPY OF LAKE STRATUS.  AN EASTWARD PUSH OF MVFR CEILING
REMAINS PLAUSIBLE...PARTICULARLY LATE TONIGHT AND EARLY TUESDAY.
GUSTY WEST-SOUTHWEST WINDS INTO THE 25 KNOT RANGE WILL HOLD THROUGH
TUESDAY.

FOR DTW...LIMITED COVERAGE OF SNOW SHOWERS WILL THE FOCUS ALIGNING
TO THE NORTH OVERNIGHT.  A BRIEF DISRUPTION INTO IFR REMAINS
PLAUSIBLE...BUT CONDITIONS WILL REMAIN PREDOMINATELY IN VFR.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FT THROUGH TUESDAY.

* HIGH CONFIDENCE IN PTYPE OF SNOW.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR MIZ060-061-068-069-
     075.

LAKE HURON...GALE WARNING UNTIL 4 AM EST WEDNESDAY FOR LHZ362-363-462>464.

     GALE WARNING UNTIL 10 PM EST THIS EVENING FOR LHZ361-421-422-
     441>443.

     LOW WATER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR LHZ422.

LAKE ST CLAIR...GALE WARNING UNTIL 10 PM EST THIS EVENING FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...GALE WARNING UNTIL 10 PM EST THIS EVENING FOR LEZ444.

     LOW WATER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR LEZ444.

&&

$$

SHORT TERM...DG
LONG TERM....DRK
MARINE.......DRK
AVIATION.....DG


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



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