Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 302045
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
345 PM EST FRI JAN 30 2015

.SHORT TERM...TONIGHT

MOSTLY CLEAR SKIES CONTINUE TO HOLD OVER THE MAJORITY OF SOUTHEAST
MICHIGAN THIS AFTERNOON ALLOWING MANY LOCATIONS TO TOP OUT AROUND 20
DEGREES. AIRMASS IS DRY...AS INDICATED BY SURFACE DEW PTS IN THE
LOWER SINGLE NUMBERS. WITH WINDS BECOMING LIGHT/CALM AROUND 00Z WITH
SURFACE RIDGE AXIS IN PLACE...TEMPS SHOULD TAKE A QUICK DIVE POST
SUNSET...AND PLANNING ON STAYING CLOSE TO THE INHERITED MINS (SINGLE
NUMBERS TO AROUND 10 DEGREES)...WHICH UNDERCUTS GUIDANCE...BUT WILL
ALLOW FOR RISE IN TEMPS OVERNIGHT. THE PROBLEM/WILD CARD IS TIMING
OF THE RETURN OF THE CLOUDS THIS EVENING. LOWER CLOUDS ARE HANGING
AROUND OVER WESTERN LOWER MICHIGAN...AND WITH WINDS BECOMING WEST
AND THEN LIGHT SOUTHWEST TOWARD MORNING...GOOD CHANCE FOR THESE
CLOUDS TO SPREAD EASTWARD ONCE DAYTIME MIXING SUBSIDES. 12Z NAM IS
MOST ADAMANT WITH THE 925 MB MOISTURE. EVEN IF THESE CLOUDS TO NOT
MATERIALIZE...MID CLOUDS WILL BE ON THE INCREASE...AS VERY COMPACT
SHORTWAVE DIVES SOUTHEAST INTO THE CENTRAL GREAT LAKES...LIFTING
WEAK WARM FRONT NORTH. BEST FORCING...WHICH ISN`T MUCH...IS OVER
NORTH HALF OF THE CWA...AND PROBABLY WILL SEE AT LEAST A FEW
FLURRIES VERY LATE TONIGHT...WITH A VERY LOW CHANCE OF MEASURABLE
SNOWFALL WITH THE MODEST MOISTURE ADVECTION/700 MB THETA-E RIDGE.

&&

.LONG TERM... SATURDAY THROUGH THURSDAY

MODEST WARM ADVECTION WILL CONTINUE DURING THE DAY SATURDAY AHEAD OF
A COLD FRONT DROPPING SEWD FROM LAKE SUPERIOR. MIDLEVEL MOISTURE
WILL BE LIMITED SO WILL GO NO HIGHER THAN LOW CHANCE POPS FOR SOME
LIGHT SNOW ACROSS THE SAGINAW VALLEY WITH LITTLE TO NO ACCUMULATION.
LOWER LEVEL MOISTURE WILL BE IN PLACE THOUGH SO EXPECTING MOSTLY
CLOUDY SKIES DURING THE DAY...POSSIBLY WITH MORE SUN BREAKS OVER THE
SOUTH.

STORM TERM...SATURDAY NIGHT THROUGH SUNDAY NIGHT

ATTENTION IS ON LOCAL IMPACTS FROM WINTER SYSTEM SET TO AFFECT A
GOOD PORTION OF THE CENTRAL US. IT IS SHAPING UP TO BE A PROLONGED
EVENT WITH THE TIME PERIOD FOR ACCUMULATING SNOW DEFINED ROUGHLY 06Z
SUNDAY THROUGH 09Z MONDAY. THIS FORECAST PACKAGE CALLS FOR AROUND 6-
8 INCHES FROM I-94 TO THE OHIO BORDER...4-6 INCHES BETWEEN M-59 AND
I-94...2-4 INCHES BETWEEN I-69 AND M-59...AND 2 INCHES OR LESS NORTH
OF I-69. IT SHOULD BE NOTED THAT WHILE CONFIDENCE IN AN IMPACTFUL
STORM FOR THE SOUTHERN PART OF OUR AREA HAS INCREASED...THE SNOWFALL
GRADIENT IS LOCATED DIRECTLY THROUGH OUR AREA. AS SUCH...SUBTLE
CHANGES IN THE STORM TRACK WILL SHIFT SNOWFALL TOTALS.

THE KEY TO THIS SYSTEM IS THE INTERACTION BETWEEN A COMPACT
SHORTWAVE NOW COMING ONSHORE OVER BRITISH COLUMBIA AND SOME ENERGY
EJECTING FROM THE CLOSED UPPER LOW OVER THE DESERT SOUTHWEST. SUNY
STONY BROOK ENSEMBLE SENSITIVITY ANALYSIS FROM THE 00Z NAEFS RUN
INDICATES MOST OF THE UNCERTAINTY WITH THE PATH AND STRENGTH OF THE
SURFACE LOW CAN BE TRACED TO THE BRITISH COLUMBIA SHORTWAVE...WITH A
STRONGER WAVE IMPLYING A MORE AMPLIFIED SYSTEM BY THE TIME IT
REACHES THE CENTRAL US. 12Z MODEL CONSENSUS HAS BEEN TO CONTINUE THE
NORTHWARD SHIFT SEEN IN THE 00Z MODELS WITH THE SYSTEM AS A
WHOLE...BOOSTING FORECASTER CONFIDENCE. HOWEVER...AS THE BRITISH
COLUMBIA SHORTWAVE HAS NOT YET BEEN SAMPLED BY RAOBS...SOME
UNCERTAINTY REMAINS. QUALITATIVELY...IT DOES APPEAR ROBUST ON WATER
VAPOR IMAGERY.

AS THE SYSTEM DEVELOPS OVER THE CENTRAL US IT WILL ENTRAIN A GOOD
DEAL OF MOISTURE NOW EVIDENT ON WATER VAPOR IMAGERY OVER THE DESERT
SOUTHWEST. THIS MOISTURE WILL BE LIFTED OVER THE LOWER/MIDDLE
TROPOSPHERIC FRONT LEADING TO A PROLONGED PERIOD OF LIGHT TO
MODERATE SNOWFALL. LIFT WILL BE ENHANCED BY THE EQUATORWARD ENTRANCE
REGION OF THE UPPER JET DOWNSTREAM OF THE TROUGH AXIS AS THE UPPER
LEVEL HEIGHT PATTERN BECOMES MORE AMPLIFIED DURING THE DAY SUNDAY.
SOME ENHANCEMENT TO THE SNOWFALL RATES WILL BE POSSIBLE IN THE 6-
HOUR PERIOD CENTERED AROUND 00Z MONDAY AS WE GET A LITTLE FGEN
RESPONSE AS THE CLOSED 850 MB CIRCULATION STRENGTHENS AS IS PASSES
ACROSS NORTHERN PORTIONS OF INDIANA AND OHIO. CROSS SECTIONS
INDICATE THAT STABILITY WILL BE RELATIVELY HIGH SO WE ARE NOT
EXPECTING MUCH CONVECTIVE ENHANCEMENT. FORECAST SOUNDINGS AT DTW
INDICATE THE DGZ RATHER HIGH IN THE COLUMN FROM ABOUT 550-700 MB AT
THE BEGINNING OF THE EVENT WITH A NEARLY ISOTHERMAL LAYER BELOW THAT
AROUND -8 TO -10C. THIS WILL TRANSLATE INTO SNOW RATIOS AROUND 12-
13:1 AT THE START OF THE EVENT INCREASING TO AROUND 15-16:1 SUNDAY
NIGHT AS COLDER AIR IS WRAPPED INTO THE SYSTEM.

TEMPERATURES WILL FALL SATURDAY NIGHT THROUGH THE EVENT AS WINDS
TURN NE ADVECTING IN COLDER AIR. LOW TO MID-20S ARE EXPECTED AT THE
START OF THE EVENT...FALLING INTO THE TEENS FOR MOST AREAS BY SUNDAY
MORNING. INCREASING NORTHEASTERLY WINDS OF 10-15 KT WILL CAUSE WIND
CHILLS TO DROP INTO THE SINGLE DIGITS ABOVE AND BELOW ZERO
SUNDAY...WITH TEENS BELOW ZERO WIDESPREAD OVER THE REGION SUNDAY
NIGHT.

REST OF EXTENDED FORECAST...

LOW PRESSURE WILL CONTINUE TO MOVE OFF TO THE EAST ON MONDAY
MORNING AS HIGH PRESSURE BUILDS INTO LOWER MICHIGAN. THIS HIGH WILL
BRING DRY CONDITIONS TO THE AREA THROUGH WEDNESDAY MORNING. THE NEXT
CLIPPER SYSTEM WILL IMPACT SOUTHEAST MICHIGAN ON WEDNESDAY. STILL
TOO EARLY TO PINPOINT ANY SNOW ACCUMULATIONS WITH THIS SYSTEM
THOUGH. HIGH PRESSURE AND DRY WEATHER RETURNS FOR THE END OF NEXT
WEEK.

&&

.MARINE...

NORTHWESTERLY WINDS WILL CONTINUE TO DIMINISH TONIGHT AS HIGH
PRESSURE BUILDS INTO THE REGION. WINDS WILL BECOME SOUTHWESTERLY AND
INCREASE ON SATURDAY AHEAD OF A COLD FRONT DROPPING SOUTHEASTWARD
FROM LAKE SUPERIOR. THIS FRONT...ACCOMPANIED BY A BLAST OF COLDER
AIR...WILL PASS THROUGH LAKE HURON SATURDAY NIGHT CAUSING WINDS TO
TURN NORTHERLY AND THEN NORTHEASTERLY ON SUNDAY. SOME GUSTS TO 25-30
KT WILL BE POSSIBLE SATURDAY NIGHT. WINDS WILL THEN DIMINISH ON
MONDAY AS A LOW PRESSURE SYSTEM PASSING THROUGH THE OHIO VALLEY
PULLS OFF OF THE EASTERN SEABOARD.

&&

.AVIATION...ISSUED 1201 PM EST FRI JAN 30 2015

BRISK NORTHWEST WINDS GUSTING AT OR SLIGHTLY ABOVE 20 KNOTS HAS
USHERED IN ENOUGH DRY LOW LEVEL AIR TO SUPPORT MOSTLY CLEAR-PARTLY
CLOUDY SKIES OVER MUCH OF SOUTHEAST MICHIGAN EARLY THIS AFTERNOON.
HOWEVER...LOW LEVEL MOISTURE...HIGH MVFR/LOW VFR CLOUDS REMAIN
LURKING OVER WESTERN LOWER MICHIGAN THIS AFTERNOON. WITH WINDS
BACKING TOWARD THE WEST...THESE CLOUDS WILL ATTEMPT TO MOVE EAST.
BANKING ON THE DAYTIME MIXING TO BE SUFFICIENT TO CONTINUE TO ERODE
THE CLOUDS AS THEY ATTEMPT TO PUSH EAST...BUT CONFIDENCE LOWERS AS
WE HEAD TOWARD SUNSET. WITH WEAK WARM FRONT LIFTING THROUGH AND VERY
LIGHT SOUTHWEST WINDS...WILL ALLOW FOR LOWER CEILINGS (AROUND 3000
FEET) TO WORK THROUGH SOUTHEAST MICHIGAN THIS EVENING/TONIGHT.

FOR DTW...THE STRONGEST NORTHWEST WINDS ARE BEHIND US...BUT FEW MORE
GUST AROUND 20 KNOTS ARE EXPECTED THIS AFTERNOON WITH WINDS QUICKLY
DROPPING OFF AROUND SUNSET. EXACT TIMING AND DURATION OF LOW CLOUDS
RETURNING IS LOW.

//DTW THRESHOLD PROBABILITIES...

* LOW CONFIDENCE IN CIGS BELOW 5000 FT THIS AFTERNOON INTO
  THIS EVENING...MEDIUM TONIGHT...LOW AGAIN TOMORROW MORNING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH LATE SUNDAY
     NIGHT FOR MIZ075-076-082-083.

LAKE HURON...HEAVY FREEZING SPRAY WARNING UNTIL 7 PM EST THIS EVENING FOR LHZ362-
     363-441-462>464.

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

$$

SHORT TERM...SF
LONG TERM....DT/RK
MARINE.......DT
AVIATION.....SF


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


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