Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 310800
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
400 AM EDT TUE MAR 31 2015

.SHORT TERM... TODAY AND TONIGHT

THE SMALL BUT INTENSE WAVE OF LOW PRESSURE IS ON TRACK TO MOVE ALONG
THE SOUTHERN MICHIGAN BORDER BEFORE SUNRISE AND EXIT TO OUR EAST BY
MID MORNING. THE GENERAL DISTRIBUTION OF PRECIPITATION TYPE REMAINS
ALL RAIN IN THE DETROIT AREA...MIXED RAIN AND SNOW AS FAR NORTH AS
THE I-69 CORRIDOR...AND ALL SNOW TRI CITIES AND NORTHERN THUMB. THE
I-69 TO M-59 CORRIDORS WILL SEE PRECIPITATION TYPE STRONGLY
INFLUENCED BY RATE THROUGH THE REST OF THE EVENT. OBSERVATIONS
LOCALLY HAVE ALREADY RANGED FROM LIGHT RAIN TO HEAVY/WET SNOW AND
BACK TO LIGHT RAIN SINCE 2 AM RESULTING IN NEARLY 2 INCHES OF
ACCUMULATION. THE RAIN/SNOW TRANSITIONS WILL CONTINUE BUT TREND
TOWARD MORE SNOW THROUGH SUNRISE. BACKING LOW LEVEL FLOW AS THE LOW
SLIDES TO THE SOUTH WILL DRAW COLDER AIR SOUTHWARD WHILE THE MID
LEVEL DEFORMATION FOCUSES THE MOST INTENSE VERTICAL MOTION THROUGH
CENTRAL SECTIONS OF OUR AREA. EXPECT AND ADDITIONAL INCH OR TWO OF
SLUSHY ACCUMULATION WITHIN THIS MAIN BAND BEFORE IT SLIDES EASTWARD.
THE MORNING FORECAST ISSUANCE ALSO BROADENS ACCUMULATION OF AN INCH
OR LESS FARTHER NORTH TO CAPTURE SOME HIGHER ALTITUDE
FGEN/DEFORMATION ACTIVATION THAT WILL PRODUCE ALL SNOW IN THE TRI
CITIES AND NORTHERN THUMB.

THE LOW PRESSURE SYSTEM WILL EXIT EASTWARD BY LATE MORNING LEAVING
SOME IMPROVEMENT IN CONDITIONS FOR THE REST OF THE DAY. LOW LEVEL
COLD ADVECTION TRAILING THE SYSTEM WILL BECOME NEUTRAL ON LIGHT WIND
DURING THE AFTERNOON. THIS...ALONG WITH SOME BREAKS IN THE CLOUDS
WILL ALLOW TEMPERATURES TO RECOVER BACK INTO THE 40S MOST LOCATIONS
OUTSIDE OF THE THUMB.

ATTENTION THEN TURNS TO A SIMILAR SHORT WAVE MOVING OVER LAKE
SUPERIOR TODAY WHICH WILL SLIDE OVER NORTHERN LOWER TONIGHT AND
BRUSH THE TRI CITIES AND THUMB AFTER MIDNIGHT. THIS SYSTEM IS
SIMILAR TO THIS MORNING`S WAVE IN TERMS OF DYNAMICS BUT WILL HAVE
LESS MOISTURE TO WORK WITH AND WILL BE SUBJECT TO NEGATIVE
ALTERATION BY THE LARGER SCALE UPPER AIR EVOLUTION DURING THE NIGHT.
THE NEW MODEL CYCLE INDICATES THE SYSTEM WILL BE SHEARED APART BY A
COMBINATION OF RISING HEIGHTS ASSOCIATED WITH THE LONG WAVE RIDGE
OVER THE PLAINS AND HEIGHT FALLS OVER THE ATLANTIC COAST AS THE
MORNING SYSTEM MOVES EASTWARD. THE TREND AMONG THE 00Z MODELS SHOWS
THE WAVE HANGING ON LONG ENOUGH INTO NORTHERN LOWER MICHIGAN FOR A
CHANCE OF SNOW SHOWERS NW TO SE FROM THE TRI CITIES THROUGH THE
THUMB REGION FOR A FEW HOURS OVERNIGHT BUT BEFORE SUNRISE WEDNESDAY.

&&

.LONG TERM...

EASTWARD TRANSLATION OF THE LONG WAVELENGTH UPPER LEVEL RIDGE INTO
THE GREAT LAKES REGION DURING THE DAY WEDNESDAY WILL MAINTAIN
SURFACE RIDGING OVER SOUTHEASTERN MICHIGAN. MODELS SHOW A BAGGY MSLP
GRADIENT OVER SOUTHEASTERN MICHIGAN TO THE START THE DAY. THIS IN
COMBINATION WITH THE SUBSTANTIAL...PROGRESSIVE BEHAVIOR OF THE LARGE
SCALE RIDGE WILL CAUSE A WARM FRONT TO SHARPEN DURING THE AFTERNOON
HOURS IMMEDIATELY TO THE NORTH AND EAST OF THE CWA. VERY STABLE
PROFILE FROM 2 TO 13 KFT AGL LIMITS ANY PRECIPITATION POTENTIAL
OUT OF THE WARM ADVECTION. PERSISTENT EASTERLY COMPONENT IN THE
FLOW TRAJECTORY WILL LIMIT HIGHS ON WEDNESDAY...ALTHOUGH GOOD
MODERATION IN TEMPS EXPECTED WITH READINGS CLIMBING ABOVE THE 50
DEGREE MARK AWAY FROM AREA WATERS. WILL LIKELY WITNESS CHILLY
CONDITIONS FOR THOSE PEOPLE NEAR THE LAKE.

AN INITIAL SLUG OF MOISTURE AND PRECIPITATION WILL PASS NORTH OF THE
CWA WEDNESDAY NIGHT. A RIDGE RIDER TYPE SYSTEM WILL ORGANIZE IN A
TRIPLE POINT REGION...AHEAD OF THE STRONG UPPER LEVEL PV ANOMALY AND
NOSE OF THE LOW LEVEL JET.

AN IMPRESSIVE UPPER LEVEL RIDGE WITH 850MB TEMPERATURES OF 10C WILL
BE DIRECTLY OVERHEAD OF THE CWA AT THE START OF THE DAY THURSDAY.
MODELS FORECAST A WELL MIXED ENVIRONMENT WITH SURFACE
SOUTHWESTERLIES. FIRST FORECAST QUESTION IS ON HIGH TEMPERATURES FOR
THURSDAY AFTERNOON. BIGGEST CAUSE OF UNCERTAINTY IS ON WHAT THE
OVERALL POTENTIAL IS FOR A PREFRONTAL TROUGH TO BRING IN
CLOUDS/PRECIPITATION EARLY AND MUDDY THE SITUATION. GFS/ECMWF BOTH
SUPPORT A SOLUTION THAT TRACKS PRE EXISTING CONVECTION FROM MN/IA/SD
INTO SOUTHEASTERN MICHIGAN RELATIVELY EARLY IN THE DAY ON THURSDAY.
CONTINUE TO FAVOR THE CONSERVATIVE SIDE WITH FORECASTED HIGHS IN THE
MID TO UPPER 60S. THERE IS A GOOD SIGNAL FOR COOLER TEMPERATURES
AGAIN NEAR THE LAKE. THE OTHER FORECAST QUESTION MARK IS ON OVERALL
POTENTIAL FOR THUNDERSTORMS ON THURSDAY. A SLOWER PRECIPITATION
ONSET WILL BE MORE FAVORABLE FOR THE DIURNAL AFTERNOON DEVELOPMENT
OF THUNDERSTORMS. NAM GUIDANCE SUGGESTS UP TO 750 J/KG OF SURFACE
BASED CAPE POSSIBLE BY THURSDAY AFTERNOON. WHILE THE OTHER MODELS DO
NOT AGREE WITH THE MAGNITUDE OF CAPE VALUES...THERE IS CONVECTIVE
INSTABILITY FORECASTED ON THE BACK OF STEEP 800-600 MB LAPSE RATES.
DID GO AHEAD AND INTRODUCE A CHANCE OF THUNDERSTORMS FOR THURSDAY.

THE OTHER IMPORTANT MATTER TO HIGHLIGHT IN THIS PACKAGE IS THE
POTENTIAL FOR ACCUMULATING SNOWFALL FRIDAY AFTERNOON/EVENING. MODELS
SOLUTIONS ARE SHOWING STRONG DYNAMIC FORCING STRIPING ACROSS THE
STATE IN RESPONSE TO A TRAILING ZONAL UPPER LEVEL JETLET PUSHING
THROUGH IN A FAVORABLE LOCATION. STRONG LEFT EXIT REGION DYNAMICS
ARE PROGGED FOR THE REGION ALONG WITH A VERY STRONG BAROCLINIC ZONE
IMMEDIATELY TO THE SOUTH AND EAST OF THE STATE. DEFINITELY
INTERESTING. FOR NOW MID TO HIGH CHANCE POPS REMAINS ADEQUATE.

&&

.MARINE...

LOW PRESSURE WILL TRACK ALONG THE SOUTHERN MICHIGAN BORDER THIS
MORNING. WINDS WILL UNIFORMLY RESPOND NORTHEASTERLY THIS MORNING BUT
REMAIN RELATIVELY MUTED WITH GUSTS IN THE 15 TO 20 KNOT RANGE ACROSS
THE SOUTHERN BASIN OF LAKE HURON. HIGH PRESSURE IN PLACE TONIGHT AND
WEDNESDAY WILL PROVIDE LIGHT WINDS AND LOW WAVES. SOUTHERLY WINDS
WILL INCREASE WEDNESDAY NIGHT AHEAD OF A COLD FRONT...WHICH IS
EXPECTED TO MOVE THROUGH LATE THURSDAY. WARM PUSH OF AIR AHEAD OF
THE COLD FRONT WILL LEAD TO STABLE PROFILES...WITH WIND SPEEDS
LIKELY REMAINING MOSTLY BELOW 25 KNOTS.

&&

.AVIATION...ISSUED 1158 PM EDT MON MAR 30 2015

LEAD BAND OF -RA WITHIN ISENTROPIC LIFT IN ADVANCE OF SHORTWAVE WILL
WORK INTO TERMINALS AS THE FORECAST BEGINS. CIGS WILL DROP TO MVFR
WITH TIME AND THEN IFR AS THE SHORTWAVE CROSSES THE AREA AND FGEN
FORCING INCREASES. WITHIN THE STRONG FORCING...FNT AND PTK...PRECIP
WILL MOST LIKELY CHANGE TO SNOW WITH A FEW INCHES OF ACCUMULATION
POSSIBLE. THE I 94 TERMINALS WILL MOST LIKELY REMAIN LARGELY RAIN
WITH JUST SOME SNOWFLAKES MIXED IN LATE TONIGHT. THIS SYSTEM WILL
CONTINUE QUICKLY TO THE EAST WITH IMPROVING CONDITIONS ON TUESDAY AS
VFR CIGS RETURN BY MIDDAY TO EARLY AFTERNOON.

FOR DTW...FGEN WILL BRING RAIN TO THE TERMINAL BY 06Z WITH PRECIP
PERSISTING OVERNIGHT AS CIGS DROP TO MVFR AND EVENTUALLY IFR AT
TIMES. WHILE A FEW SNOWFLAKES MAY MIX WITH THE RAIN...EXPECT RAIN
PRIMARILY WITH LITTLE TO NO ACCUMULATION.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CEILING AOB 5000 FEET OVERNIGHT AND TUESDAY MORNING.

* LOW CONFIDENCE IN BRIEF PERIOD OF RAIN-SNOW MIX AS PTYPE 09-12Z.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.

&&

$$

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


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