Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 240852
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
352 AM EST TUE FEB 24 2015

.SHORT TERM... TODAY AND TONIGHT

EARLY MORNING SURFACE OBSERVATIONS INDICATE SOUTHWEST WIND IS
PICKING UP ABOUT ON SCHEDULE OVER THE TRI CITIES AND NORTHERN THUMB.
THE WIND...ALONG WITH THICKENING HIGH CLOUDS...WILL CONTINUE TO LIFT
TEMPERATURES INTO THE UPPER SINGLE DIGITS IN THAT AREA THROUGH
SUNRISE. FARTHER SOUTH...A FEW BELOW ZERO READINGS NEAR THE OHIO
BORDER WILL RISE INTO THE LOWER SINGLE DIGITS ABOVE ZERO AS THE WIND
CARRIES IN SLIGHTLY WARMER AIR FROM NORTHERN INDIANA. THE WARMING
TEMPERATURE TREND BEING IN STEP WITH THE INCREASING WIND WILL HELP
WIND CHILL LINGER MOSTLY WARMER THAN -15 THROUGH ABOUT MID MORNING.
ACTUAL TEMPERATURE RISING TOWARD HIGHS AROUND 20 DURING THE
AFTERNOON WILL HELP WIND CHILL CREEP ABOVE ZERO EVEN WITH SUSTAINED
WIND AROUND 20 MPH...BUT GUSTS AROUND 35 MPH ARE ALSO LIKELY WHICH
WILL DROP WIND CHILL TOWARD 10 BELOW AT TIMES AND PROVIDE NO REAL
RELIEF TO THE RECENT HARSH TEMPERATURE CONDITIONS.

THE WIND FIELD WITH THIS LOW PRESSURE SYSTEM CONTINUES TO EVOLVE AND
WILL REQUIRE MONITORING IN OBSERVATIONS. GUSTS AROUND 35 MPH WILL BE
MOST COMMON...BUT A FEW AROUND 40 MPH WILL ALSO BE POSSIBLE DURING
LATE MORNING THROUGH MID AFTERNOON. THIS IS WHEN THE LOW LEVEL JET
AXIS WILL BE OVERHEAD AND WHEN BOUNDARY LAYER MIXING WILL BE
DEEPEST. MODEL SOUNDINGS INDICATE THAT MIXING WILL ONLY REACH ABOUT
900 MB/2500 FT WHICH COULD TAP WIND NEAR 40 KNOTS AT THE INVERSION
LEVEL BEFORE THE LOW LEVEL JET AXIS EXITS EASTWARD. THE TEMPERATURE
PROFILE ABOVE THE INVERSION IS ISOTHERMAL ENOUGH TO HINT AT SOME
TURBULENCE UP TOWARD 850 MB. AT THE SAME TIME...0-1KM THETA-E LAPSE
RATES ARE 5-10 K/KM THROUGH THE AFTERNOON WITHIN THE LOW LEVEL JET
AXIS. THIS INDICATES STABILITY TYPICAL OF A WARM ADVECTION PATTERN
IN THE LEAD FLANK OF THE LOW PRESSURE SYSTEM WHICH SHOULD GUARD
AGAINST GUSTS AT WIND ADVISORY LEVELS.

TAKEN BY ITSELF...THE SNOW ASSOCIATED WITH THIS SYSTEM IS NOT MUCH
OF A CONCERN. THE WIND WILL BE BLOWING THE SNOW ALREADY ON THE
GROUND PRESENTING MORE OF A DRIFTING CONCERN VERSUS VISIBILITY
RESTRICTION AS WE ADD ROUGHLY HALF INCH OF ACCUMULATION DURING THE
AFTERNOON. THE ARM OF ISENTROPIC ASCENT SUPPORTING THE SNOW WILL
DEVELOP AHEAD OF THE PRIMARY SHORT WAVE MOVING IN FROM NORTHERN
ONTARIO. MODEL CROSS SECTIONS CONTINUE TO SHOW A SHARP MID LEVEL
THETA-E RIDGE SWINGING THROUGH LOWER MICHIGAN BUT THE OVERALL STATIC
STABILITY REMAINS ON THE HIGH SIDE. SPECIFIC HUMIDITY AROUND 1 G/KG
IN THE 850-700 MB LAYER AND THE OVERALL SPEED OF THE SYSTEM SUPPORT
JUST A FEW 100THS OF MODEL QPF DESPITE A COMPLEMENT OF STRONG
DYNAMIC FORCING WITH THE SHORT WAVE. THE APPROACH OF THE GOING
FORECAST REMAINS ON TARGET IN DEPICTING A LIKELY POP/LOW QPF/LOW
ACCUMULATION SCENARIO UNTIL THE BAND EXITS BY EVENING. AFTER
THAT...LIKELY POPS WILL BE MAINTAINED DURING THE EVENING TO COVER
THE POTENTIAL FOR SNOW SQUALLS WITHIN THE NEXT ARCTIC COLD FRONT.
THIS THEME WAS HIGHLIGHTED IN YESTERDAY`S DISCUSSION POINTING OUT
THE DEEPENING CONVECTIVE LAYER WITHIN AND IMMEDIATELY TRAILING THE
ARCTIC FRONT. MODEL SOUNDINGS AND CROSS SECTIONS MAINTAIN CONVECTIVE
DEPTH PUSHING 700 MB IN THE TRI CITIES AREA AND PLAN VIEW DEPICTIONS
OF 0-1 KM THETA-E LAPSE RATE INDICATE A SIZABLE AREA OF -1 TO -2
K/KM SWEEPING THROUGH WITH THE FRONT. AT LEAST A SMALL BOOST FROM
LAKE MICHIGAN CAN BE ADDED TO THAT ALONG WITH THE APPEARANCE OF A
SMALLER SCALE BUT INTENSE MID LEVEL CIRCULATION TO AUGMENT LIFT IN
THE CONVECTIVE LAYER. THIS CIRCULATION IS SEEN IN SATELLITE IMAGERY
TRAILING THE MAIN SHORT WAVE FROM WESTERN REACHES OF HUDSON BAY
DURING THE MORNING. AREAL COVERAGE WILL LIMIT OVERALL ACCUMULATION
BUT A LOCALIZED QUICK INCH WILL BE POSSIBLE MAINLY IN THE TRI CITIES
AND NORTHERN THUMB. A WEAKENING TREND IS THEN SHOWN IN MODEL OUTPUT
AS THE FRONT MOVES TOWARD THE OHIO BORDER BUT WILL REMAIN WORTH A
CHANCE OF SNOW SHOWERS IN THE FORECAST UNTIL THE FRONT EXITS INTO
OHIO AFTER MIDNIGHT.

&&

.LONG TERM...WEDNESDAY THROUGH MONDAY

COLD FRONT WILL SETTLE NEAR THE MICHIGAN/OHIO BORDER BY 12Z WED.
THIS WILL KEEP US IN A NEUTRAL TO WEAK COLD AIR ADVECTION THROUGH
WEDNESDAY AS HIGH PRESSURE EXPANDS INTO THE AREA. MIXING WILL REMAIN
FAIRLY SHALLOW DURING THE AFTERNOON WITH THE BASE OF A SUBSIDENCE
INVERSION NEAR 900MB. THIS AND 925MB TEMPS ONLY BETWEEN -16 AND -19C
WILL HOLD TEMPERATURES DOWN INTO THE SINGLE DIGITS TO MID-
TEENS...PROVIDING LITTLE RECOVERY FROM MORNING READINGS.

COLD AIR WILL REMAIN IN PLACE INTO THE END OF THE WEEK AS THE
EASTWARD EXPANSION OF STRONG HIGH PRESSURE OVER THE NORTHERN PLAINS
REMAINS OVER LOWER MICHIGAN. UPPER TROUGH AXIS DROPPING DOWN THROUGH
THE GREAT LAKES WILL EVEN GIVE SOME REINFORCEMENT TO COLD AIR BY
THURSDAY. OVERNIGHT LOWS WEDNESDAY NIGHT THROUGH FRIDAY NIGHT ARE
EXPECTED TO DROP BELOW ZERO. THE EXCEPTION MAY BE A FEW LOCATIONS
FROM DETROIT TO THE OHIO BORDER WEDNESDAY NIGHT...AS CLOUDS WORK
INTO THE AREA FROM OFF LOW PRESSURE TRACKING TO OUR SOUTH. THERE IS
POTENTIAL WIND CHILL ADVISORIES MAY BE NEEDED ANY OF THESE NIGHTS.

THE UPPER TROUGH AXIS DROPPING THROUGH THE GREAT LAKES SHOULD KEEP
THE CENTER OF LOW PRESSURE SOUTH OF THE AREA...AS IT DROPS FROM THE
NORTHERN PLAINS INTO THE TENNESSEE VALLEY. GFS/NAM DO HOWEVER SHOW
MID-LEVEL DEFORMATION BRUSHING THE AREA WEDNESDAY NIGHT...AND DID
INTRODUCE LOW CHANCES FOR LIGHT SNOW SHOWERS OVER LENAWEE AND MONROE
COUNTIES. 00Z EURO SHOWED A FAIRLY BIG NORTHWARD SHIFT IN THE
PLACEMENT OF THE 925MB FRONTAL FEATURE COMPARED TO THE 12Z RUN...AND
WAS NOT WILLING TO INCLUDE MORE OF THE AREA IN SNOW CHANCES QUITE
YET.

A SHIFT IN THE PATTERN OVER NOAM LOOKS TO OCCUR BY THE WEEKEND AS
ENERGY DROPPING SOUTH CARVES A TROUGH OVER THE WEST COAST AND FLOW
BECOMES MORE SOUTHWESTERLY TO ZONAL OVER THE EASTERN 2/3 OF THE
COUNTRY. THIS WILL LIFT THE MID-LEVEL BAROCLINIC ZONE UP INTO THE
CENTRAL PLAINS AND GREAT LAKES SATURDAY NIGHT INTO SUNDAY...BRINGING
WARMER TEMPERATURES AND A CHANCE FOR ACCUMULATING SNOW AS MOISTURE
AND SHORTWAVE ENERGY EJECT OUT OF THE WEST COAST TROUGH AND RIDE UP
ALONG THE FRONT...AND AS AN UPPER TROUGH TRACKS THROUGH ONTARIO. A
LITTLE EARLY TO THROW OUT SNOW AMOUNTS FOR SATURDAY NIGHT INTO
SUNDAY AS THE MAIN UPPER FEATURES HAVE YET TO BE SAMPLED...MODELS
CONTINUE TO SHOW DIFFERENCES WITH HOW UPPER FEATURES ALL
INTERACT...AND ARE WEAK WITH DEVELOPMENT OF ANY SURFACE REFLECTIONS.

&&

.MARINE...

SOUTH TO SOUTHWEST WINDS WILL CONTINUE TO INCREASE IN STRENGTH THIS
MORNING AS LOW PRESSURE PASSING THROUGH NORTHERN ONTARIO INCREASES
THE PRESSURE GRADIENT OVER THE GREAT LAKES. OBSERVATIONS AROUND THE
AREA HAVE SHOWN GALE FORCE GUSTS COMING IN OFF LAKE MICHIGAN EARLY
THIS MORNING. THESE GALE FORCE GUSTS ARE EXPECTED TO EXPAND EASTWARD
TO LAKE HURON PRIOR TO SUNRISE...AND TO THE REMAINDER OF THE CENTRAL
GREAT LAKES BY MID MORNING. THE STRONGEST WINDS WILL OCCUR OVER
CENTRAL LAKE HURON...WHERE GUSTS LOOK TO REACH 45 KNOTS. THE LATEST
IN A SERIES OF ARCTIC COLD FRONTS WILL THEN SWEEP DOWN ACROSS THE
CENTRAL GREAT LAKES TONIGHT...FLIPPING WINDS TO THE NORTHWEST. THESE
WINDS WILL REMAIN ELEVATED TONIGHT INTO WEDNESDAY OVER THE OPEN ICE
OF LAKE HURON...BUT AT THIS TIME...GUSTS LOOK TO REMAIN AROUND 30
KNOTS.

&&

.AVIATION...ISSUED 1221 AM EST TUE FEB 24 2015

EXPECT VFR CONDITIONS WITH CLOUDS AOA 10-15KFT INCREASING TONIGHT
THROUGH THE MORNING. LOWER VFR CIGS APPROACHING 6KFT WILL THEN BE
POSSIBLE LATER IN THE DAY AS A SURFACE TROUGH SETTLES INTO THE
AREA. ANY PRECIPITATION ALONG THIS BOUNDARY WILL BE LIMITED TO A
FEW -SHSN AND REALLY NOT IMPACT THE TERMINALS. STRONG SOUTHWEST
WINDS WILL DEVELOP WITH GUSTS TO 30 KNOTS OR SO POSSIBLE. BOTH
WINDS AND CLOUDS WILL DIMINISH LATE IN THE FORECAST PERIOD ONCE
THE NEXT COLD FRONT BEGINS PUSHING SOUTHEAST THROUGH THE AREA.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN SOUTHWEST WINDS...200 DEGREES...GUSTING TO 25-30
  KNOTS TUESDAY AFTERNOON.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...GALE WARNING UNTIL 7 PM EST THIS EVENING FOR LHZ361>363-421-422-
     441>443-462>464.

LAKE ST CLAIR...GALE WARNING UNTIL 7 PM EST THIS EVENING FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...GALE WARNING UNTIL 7 PM EST THIS EVENING FOR LEZ444.

&&

$$

SHORT TERM...BT
LONG TERM....HLO
MARINE.......HLO
AVIATION.....DG


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



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