Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 282011
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
311 PM EST SAT FEB 28 2015

.SHORT TERM...TONIGHT AND SUNDAY

THE NORTHERN EDGE OF THE REGION OF LIGHT SNOW NOW EXPANDING ACROSS
MO AND SRN IA WILL ADVANCE INTO SE MI BETWEEN 03Z AND 06Z TONIGHT.
THIS SNOW IS OCCURRING DUE TO MOISTURE ADVECTION WITHIN A BROAD
REGION OF ISENTROPIC ASCENT AHEAD OF MID LEVEL SHORT WAVE IMPULSE.
MODEL CROSS SECTIONS SUGGEST SPECIFIC HUMIDITIES OF 2 G/KG UP THROUGH
700 MB ADVECTING INTO THE FAR SRN PORTIONS OF THE AREA /METRO
DETROIT SOUTH/ OVERNIGHT...WITH UP TO 1 G/KG INTO SAGINAW. THE
ASCENT OVER MOST OF THE FORECAST AREA WILL BE QUITE ELEVATED THROUGH
MOST OF THE NIGHT...AT TEMPERATURE REGIMES NOT SUPPORTIVE OF GOOD
DENDRITES. THIS AND THE INITIAL WEDGE OF DEPARTING LOW LEVEL DRY AIR
WILL KEEP SNOWFALL INTENSITY RATHER LIGHT WELL INTO THE NIGHT.

STRENGTHENING DEEP LAYER FRONTOGENESIS WILL EXPAND ACROSS THE NRN
OHIO VALLEY LATE TONIGHT INTO SUN MORNING WITHIN THE EXIT REGION OF
AN UPPER JET MAX NOSING INTO THE MID MS/NRN OHIO VALLEYS. THE LOW
LEVEL PORTIONS OF THE FRONTAL SLOPE /WHERE DEEP LAYER STATIC
STABILITY WILL BE LOWER AND MOISTURE MORE PLENTIFUL/ ARE EXPECTED TO
BE MOST ACTIVE. THIS WILL LARGELY OCCUR SOUTH OF THE MI BORDER.
METRO DETROIT/ANN ARBOR AND POINTS SOUTH WILL HOWEVER BE CLOSE
ENOUGH TO SOME ENHANCED FORCING WITHIN THE MID LEVEL PORTIONS OF THE
FRONT TO POTENTIALLY SEE SOME PERIODS OF HIGHER INTENSITY SNOW /LATE
TONIGHT THROUGH SUN MORNING/. THERE IS EXPECTED TO BE SOME
CONTRACTION OF THE FRONTAL CIRCULATION SUN MORNING...WHICH MAY BRING
SOME MID LEVEL DRYING AND SUBSIDENCE INTO THE NORTHERN HALF OF THE
FORECAST AREA BY LATE MORNING. THIS SUPPORTS LOWERING POPS AND SNOW
ACCUMS NORTH OF THE M 59 CORRIDOR. THE BULK OF THE 12Z MODEL SUITE
NOW SHOW THE BETTER FRONTAL DYNAMICS SLIDING A BIT FARTHER SOUTH SUN
AFTERNOON...SUGGESTING THE MORE WIDESPREAD SNOW SHOULD COME TO AN
END FROM NORTH TO SOUTH AFTER 17Z.

WHILE LIQUID TO SNOW RATIOS WILL BE RATHER HIGH AT 15 TO 18:1...THE
LACK OF GOOD DENDRITES WILL HAVE AN IMPACT ON ACCUMULATION RATES.
LOCATIONS TO THE SOUTH OF A MT CLEMENS TO HOWELL LINE ARE EXPECTED
TO SEE A GENERAL 1 TO 3 INCHES FROM TONIGHT THROUGH SUN AFTERNOON
/WITH THE HIGHER AMOUNTS CONFINED LARGELY TO LENAWEE...MONROE AND
SRN WAYNE COUNTIES/. TO THE NORTH...WEAKER FORCING AND LESS MOISTURE
CONTENT WILL SUPPORT JUST CHANCE POPS WITH ACCUMULATIONS AROUND A
HALF AN INCH OR LESS.

&&

.LONG TERM...

MONDAY AND MONDAY NIGHT...SHORTWAVE RIDGING AND EXPANSIVE SURFACE
HIGH PRESSURE BENEATH NOTHING MORE THAN A PARTIAL COVERAGE OF HIGH
CLOUDS WILL SUPPORT VERY WARM TEMPS IN THE UPPER 20S ON MONDAY.
AIDED BY INCREASING CLOUD COVER AND DEVELOPING LIGHT SOUTHERLY FLOW
MONDAY NIGHT, LOWS WILL BE LIKEWISE BE RELATIVELY MILD, RANGING FROM
5 IN THE THUMB TO 15 FROM THE METRO AREA SOUTH.

TUESDAY...STRONG ARGUMENT FOR A 12Z ECMWF/GEM BLEND ACROSS THE BOARD
FOR THE TUESDAY STORM. ANALYSIS OF MODEL PROGS REVEALS NO SHORTAGE
OF MOVING PARTS TO COMPLICATE MATTERS, SO EXERCISED SIMPLICITY IN
APPROACHING THE GRIDS, PARTICULARLY GIVEN THIS WINTER`S
CHARACTERISTIC POOR PREDICTABILITY.

KEY COMPONENTS ARE THE WAVE THAT CROSSED THE BERING STRAIT THIS
MORNING, A COMPACT LOW JUST NORTH OVER THE ARCTIC OCEAN AND OUT OF
VIEW OF THE GOES SATELLITES, ALONG WITH ENERGY CUTTING OFF OVER
CALIFORNIA TODAY. SUNY STONY BROOK NCEP+CMC ENSEMBLE EOF SENSITIVITY
ANALYSIS CONFIRMS SUSPICIONS THAT THE MOST SENSITIVE PART OF THE
TUESDAY FORECAST, AND POTENTIAL TIPPING POINT, RESIDES IN THE
EVOLUTION OF THE NORTHERN TROUGH, IN PARTICULAR THAT PORTION WHICH
STEMS FROM THE EVOLUTION OF THE ALASKAN SHORTWAVE TROUGH WITH THE
COMPACT ARCTIC CIRCULATION. NOTABLE DIFFERENCES REMAIN BETWEEN THE
ECMWF/GEM, BUT THEY ARE IN CONSIDERABLY BETTER AGREEMENT THAN THE
GFS AND ARE BETTER GENERALLY BETTER TRUSTED OVER THE DATA-SPARSE
ARCTIC. BEST ILLUSTRATION IS HOUR 00Z WEDNESDAY, WHEN THE GFS IS
CONSIDERABLY MORE AGGRESSIVE DIGGING THIS ENERGY, HELPING TO AMPLIFY
THE LONGWAVE AND ACCESS A BIT MORE OF THE PV RESERVOIR OVER THE
SOUTHWEST. THE VORTMAX OVER NORTH DAKOTA IS HELD OVER
ALBERTA/SASKATCHEWAN BY THE GEM/EC.  THE SUBSEQUENTLY MORE AMPLIFIED
SOLUTION OFFERED BY THE IS AN OUTLIER AMONG THE GUIDANCE.

THIS PROVIDES A GOOD SEGUE INTO TODAY`S DOMINANT 12Z TREND, WHICH
WAS TOWARD A DECIDEDLY FLATTER EVOLUTION. LESS CONNECTION WITH THE
SOUTHWEST LOW THAT WILL BE CLOSING OFF WEST OF SOUTHERN CALIFORNIA
BETWEEN NOW AND 12Z TUESDAY IS SHOWN. THIS IS PREDOMINANTLY DUE TO
SLIGHTLY LESS AMPLIFIED NORTHERN STREAM. QUICKER TROUGH PROGRESSION
ALLOWS EXISTING SOUTHWEST ENERGY TO KICK OUT CONSIDERABLY FASTER,
HELPING TO SUPPRESS THE DOWNSTREAM RIDGE OVER THE GREAT LAKES. EVEN
THE GFS TRENDED IN THIS DIRECTION TO A CERTAIN DEGREE. IN ALL CASES,
SUBSTANTIAL ISENTROPIC ASCENT AND LARGE SCALE FORCING WILL PRODUCE
WIDESPREAD PRECIPITATION ACROSS THE AREA ON TUESDAY. HOWEVER, THE
WEAKER/MORE OPEN SURFACE CIRCULATION DEPICTED BY THE EC/GEM SUGGESTS
HOLDING THE RAIN/SNOW LINE SOMEWHERE SOUTH OF M59. AT THE PRESENT
TIME, LOOKS LIKE A QUICK HIT OF MODERATE TO HEAVY SNOW FOLLOWED BY A
TRANSITION TO SNOW PELLETS/IP/FZRA AND DRY SLOT, WHICH IS STILL
POORLY DEPICTED IN MODEL QPF FIELDS. IF CURRENT TRENDS HOLD, HAVE A
FEELING DRIZZLE WILL BE THE THEME TUESDAY EVENING. RAMPED UP POPS,
BUT ONLY MADE VERY MINOR CHANGES TO PTYPE DISTRIBUTION AT THIS EARLY
STAGE.

THE 12Z FORECAST PACKAGE SHARPENS ALSO THE HIGH TEMPERATURE GRADIENT
ACROSS THE AREA TUESDAY, RANGING FROM 25 IN THE NORTH TO NEAR 40 IN
THE SOUTH. EVEN AREAS WITH HIGHS IN THE LOW/MID 30S COULD FEASIBLY
SEE PREDOMINANTLY SNOW GIVEN EXPECTED TEMP RISE AFTER DRY SLOT
INTRUSION. AS ALLUDED TO ABOVE, SUBFREEZING SURFACE DEWPOINTS AND
BEST CHANCE FOR ALL SNOW ARE MAINTAINED M59 NORTH. BROAD BRUSHED
INTRODUCTORY SNOW ACCUMS...1-3"...LESS TOWARD OHIO AND MORE TOWARD
THE THUMB.

AS THE LOW PRESSURE SYSTEM MOVES OFF TO THE EAST...COLDER AIR
RETURNS TO THE GREAT LAKES REGION. HIGHS ARE FORECASTED TO BE IN THE
MID TO UPPER 20S ON WEDNESDAY WITH LOWS DROPPING BACK DOWN INTO THE
SINGLE DIGITS ON WEDNESDAY NIGHT. THERE WILL ALSO BE A CHANCE FOR
SOME LAKE EFFECT SNOW ON WEDNESDAY AS NORTHWEST WINDS INCREASE
THROUGHOUT THE DAY. HIGH PRESSURE THEN RETURNS FOR THE REMAINDER OF
THE WEEK BRINGING DRY CONDITIONS AND PLENTY OF SUNSHINE TO SOUTHEAST
MICHIGAN. HIGH TEMPERATURES WILL GRADUALLY INCREASE FROM THE UPPER
TEENS ON THURSDAY INTO THE MID 30S BY SATURDAY.

&&

.MARINE...

WEAK TO MODERATE SURFACE PRESSURE GRADIENT WILL MAINTAIN WINDS BELOW
20 KNOTS THROUGH SUNDAY NIGHT. APPROACHING HIGH PRESSURE FROM THE
WEST WILL ALLOW A FRESH NORTHWEST BREEZE TO DEVELOP OVER THE
NORTHERN HALF OF LAKE HURON DURING THE DAY MONDAY WITH COLD AND
MARGINALLY UNSTABLE CONDITIONS SUPPORTING A POTENTIAL BORDERLINE
GALE SCENARIO. THIS PERIOD WILL BE MONITORED FOR WATCH ISSUANCE.
NEARLY CALM CONDITIONS WILL TAKE HOLD MONDAY EVENING INTO MONDAY
NIGHT BEFORE MODERATE SOUTHERLY WINDS EMERGE AHEAD OF ANOTHER STORM
SYSTEM.

&&

.AVIATION...ISSUED 1158 AM EST SAT FEB 28 2015

ARCTIC HIGH PRESSURE WILL LINGER OVER SE MI THROUGH THE
EVENING...MAINTAINING RELATIVELY LIGHT WINDS AND CLEAR SKIES BELOW
12K FT. AN INFLUX OF MOISTURE ALOFT OVERNIGHT INTO SUNDAY MORNING
WILL LEAD TO THE ARRIVAL OF SOME LIGHT SNOW AND LOWERING CEILING
HEIGHTS. THE POTENTIAL FOR MINOR SNOW ACCUMS /UP TO A HALF INCH/ BY
DAYBREAK SUN REMAINS MORE LIKELY ACROSS THE METRO DETROIT
TERMINALS...WITH LESS IF ANY NORTH OF PTK.

FOR DTW...THE BETTER PUSH OF MOISTURE WILL FORCE A 4-5K FT CEILING
INTO METRO IN THE 4Z TO 6Z TIME FRAME. SOME ADDITIONAL LOWERING OF
THE CLOUD BASE IS EXPECTED INTO EARLY SUNDAY MORNING. THERE IS SOME
UNCERTAINTY AS TO HOW QUICKLY THIS MOISTURE PUSH WILL DISPLACE THE
SHALLOW DRY ARCTIC AIR IN PLACE...WHICH ADDS A DEGREE OF UNCERTAINTY
AS TO HOW QUICKLY CEILINGS WILL DROP TO MVFR.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CEILINGS BELOW 5000 FT OVERNIGHT AND SUNDAY MORNING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

SHORT TERM...SC
LONG TERM....JVC/RK
MARINE.......JVC
AVIATION.....SC


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



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