Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 010857
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
357 AM EST SUN MAR 1 2015

.SHORT TERM...TODAY AND TONIGHT

SYNOPTIC SCALE ASCENT ANCHORED UNDER THE LEFT EXIT QUADRANT OF A
POWERFUL ZONAL JET AXIS AND WEAK SYSTEM RELATIVE ISENTROPIC ASCENT
ARE THE MECHANISMS RESPONSIBLE FOR THE BROAD FOOTPRINT OF LIGHT SNOW
ACROSS THE REGION. THE LEAD EDGE OF THE PRECIPITATION WAS ABLE TO
LIFT NORTHWARD THROUGH THE DETROIT METRO AREA PRIOR TO 6Z...TIMING
WELL WITH A COMPACT 850MB TEMPERATURE GRADIENT. NWP DATA SUPPORTS
THIS STEEPENED FRONTAL STRUCTURE TO CONTINUE TO LIFT NORTHEASTWARD
AWAY FROM THE CWA...MAKING IT AS FAR NORTHWARD AS CENTRAL LAKE HURON
AND SOUTHERN GEORGIAN BAY BY 12Z. AN ADDITIONAL STEEPEND FRONTAL
STRUCTURE RESIDES TO THE SOUTH OF THE STATE...NOW OVER CENTRAL
SECTIONS OF INDIANA AND OHIO. THIS FEATURE IS RESPONSIBLE FOR THE
HIGHER Z RETURNS AND LOWER VSBYS IN SURFACE OBSERVATIONS. MODELS
SUPPORT THIS BAROCLINIC ZONE TO REMAIN SOUTH OF THE AREA THROUGH THE
DURATION OF THE EVENT. WITH THIS IN MIND...EXPECTATIONS ARE FOR A
STATUS QUO TO SNOWFALL RATES THROUGH 12Z WITH VERY LIGHT SNOW
ACCUMULATIONS THIS MORNING.

WITH THE UPPER LEVEL JET FORCING AND LEAD MOISTURE ADVECTION
VACATING THE PREMISES...FORCING WILL THEN DISTILL DOWN TO WEAK
ISENTROPIC ASCENT. WHILE PERSISTENT...THERE IS SERIOUS QUESTION ON
WHETHER OR NOT THIS UPGLIDE WILL BE SUFFICENT IN CONTINUING TO
GENERATE MEASURABLE PRECIPATION. CURRENT RADAR MOSAIC DOES SHOW A
DEFINITIVE BACK EDGE OF THE PRECIPATION SHIELD...WITH DRY AIR
ALREADY ADVANCING THROUGH CHICAGOLAND AND INTO FAR SOUTHWESTERN
LOWER MICHIGAN. VARIOUS SOLUTIONS THEN SUGGEST IT WILL REQUIRE THE
AGEOSTROPHIC RESPONSE TO A POSITIVE D(MAG)/DT INCREASE OF THE UPPER
LEVEL JET MAX TO ALLOW PRECIPATION TO FILL BACK IN ACROSS FAR
SOUTHERN SECTIONS OF THE CWA FOR THE AFTERNOON. THIS IS EXPECTED TO
OCCUR BETWEEN 19-00Z. GIVEN THE TRENDS IN NUMERICAL OUTPUT IN
ADDITION TO THE RADAR DATA...WAS FAIRLY AGGRESSIVE IN LOWERING POPS
AND AMOUNTS FOR AREAS NORTH OF DETROIT. IN SUM TOTAL...SNOWFALL
ACCUMULATIONS OF 1 TO 2 INCHES WILL BE POSSIBLE FROM DETROIT
SOUTHWARD WITH AN INCH POSSIBLE BETWEEN THE M 59 AND I 94 CORRIDORS.

THE MAIN MIDLEVEL TROUGH AXIS AND NORTHERN STREAM WAVE WILL CATCH UP
TO LOWER MICHIGAN TONIGHT PASSING THROUGH THE CWA AFTER 6Z.
SHALLOW...LOWER TROPOSPHERIC COLD AIR ADVECTION IS FORECASTED TO
STEEPEN LAPSE RATES IN THE 1.5 TO 5.5 KFT AGL LAYER. THE UNSTABLE
PROFILE IN COMBINATION WITH PROGGED SATURATION WRT ICE AND CYCLONIC
VORTICITY ADVECTION SUPPORTS HYDROMETEOR PRODUCTION THE LATTER HALF
OF THE NIGHT. TOTAL LACK OF QPF SUPPORTS NOTHING MORE THAN A MENTION
OF FLURRIES AT THIS TIME.

&&

.LONG TERM...

MODEL TRENDS EXPLORED DURING THE 12Z CYCLE LARGELY HOLD TRUE FOR THE
00Z RUNS WITH A BIT LESS DISPARITY IN SOLUTIONS. ESSENTIALLY...THE
BROAD AND SOMEWHAT FLAT SOUTHERN EDGE OF THE EXISTING NOAM UPPER
TROUGH WILL REMAIN IN PLACE OVER THE CONUS AS A POTENT NORTHERN
STREAM SHORTWAVE NOW EXITING ALASKA TAKES A TRACK SOUTHEASTWARD
THROUGH THE PRAIRIE PROVINCES AND THEN EAST ALONG THE SOUTHERN EDGE
OF HUDSON BAY DURING THE FIRST PART OF THIS WEEK. THIS WILL STEER
SOUTHERN STREAM ENERGY INTO THE AREA ON A RATHER FLAT TRAJECTORY. IN
THE MEANTIME...WHILE THE ARCTIC AIRMASS IN PLACE TO OUR NORTH AS
ERODED TO SOME EXTENT DURING THE PAST DAY OR TWO...IT STILL REMAINS
EXPANSIVE ENOUGH TO MAINTAIN A TIGHT TEMPERATURE GRADIENT ACROSS THE
GREAT LAKES. BETWEEN THESE TWO FACTORS...CHANCES ARE THAT COLD AIR
WILL BE DIFFICULT TO DISPLACE OVER THE AREA. THIS SHOULD LEAD TO A
FAIR AMOUNT OF THE PRECIPITATION FROM THIS SYSTEM FALLING AS SNOW.
EVEN NAM12/GFS NOW SUPPORT A BASICALLY ALL SNOW EVENT FOR THE FAR
NORTHERN CWA.

THE MAIN QUESTION WILL BE THE TIMING AND PLACEMENT OF A CHANGEOVER
TO SLEET/FREEZING RAIN AND THEN RAIN IN SOME LOCATIONS BY AFTERNOON
AS THE SURFACE LOW REFLECTION OF THIS SYSTEM CROSSES THE AREA. WILL
ONLY MAKE MINOR ADJUSTMENTS TO THE FORECAST AS MODELS DO NOT SUPPORT
A STRONG SHIFT EITHER NORTH OF SOUTH IN THE PRECIPITATION TYPE
FORECAST. GENERALLY...AREAS FROM I-69 NORTH ARE EXPECTED TO REMAIN
LARGELY SNOW OR SLEET THROUGHOUT THE EVENT. FOR THE REST OF THE
FORECAST AREA...PRECIPITATION WILL START AS SNOW TUESDAY MORNING
WITH A GRADUAL CHANGEOVER TO SLEET/FREEZING RAIN FROM SOUTH TO NORTH
AS SOME MILDER AIR WORKS INTO LOWER MICHIGAN AND THEN A CHANGE TO
RAIN THROUGH THE SOUTHERN THIRD TO HALF OF THE AREA AS SURFACE AND
BOUNDARY LAYER TEMPERATURES CLIMB INTO THE MID/UPPER 30S. OVERALL
PRECIPITATION INTENSITY FORECASTS FROM THE MODELS SUGGEST ONLY LIGHT
TO MODERATE PERIODS OVER A 8-10 HOUR PERIOD DURING THE DAY TUESDAY
SO WHILE IT WILL MOST LIKELY BECOME RATHER MESSY IN TERMS OF TRAVEL
THIS IS NOT A PARTICULARLY POWERFUL WINTER STORM.

AS FOR TEMPERATURES...RELATIVELY MILD READINGS AS COMPARED TO THE
PAST FEW WEEKS CAN BE EXPECTED MONDAY INTO TUESDAY. STILL WITH
AVERAGE HIGHS IN THE UPPER 30S/LOWER 40S FOR EARLY MARCH THE AREA
WILL REMAIN AOB AVERAGE EVEN DURING THIS PERIOD. MUCH COLDER AIR
WILL THEN DUMP INTO THE AREA BEHIND THIS SYSTEM DURING THE LAST PART
OF THE WEEK AS ANOTHER ARCTIC HIGH PRESSURE SYSTEM BUILDS SOUTHEAST
THROUGH THE EASTERN CONUS WITHIN AMPLIFYING UPPER TROUGHING PATTERN
THAT DEVELOPS AS ADDITIONAL NORTHERN STREAM SHORTWAVE ENERGY DIGS
INTO AREA BEHIND THE EXITING STORM SYSTEM. AS THIS TROUGH PROGRESSES
EASTWARD BY THE END OF THE FORECAST PERIOD...A MODERATION IS
EXPECTED INTO NEXT WEEKEND WITH TEMPERATURES AT LEAST CLIMBING BACK
INTO THE 30S.

&&

.MARINE...

A WEAK TO MODERATE SURFACE PRESSURE GRADIENT WILL MAINTAIN WINDS
BELOW 20 KNOTS THROUGH SUNDAY NIGHT. A COLD FRONT WILL GRAZE THE
NORTHERN PORTIONS OF LAKE HURON MONDAY AND BRING A FRESH NORTHWEST
BREEZE WITH GUSTS TO 30 KNOTS POSSIBLE AS COLD AND MARGINALLY
UNSTABLE CONDITIONS DEVELOP. HIGH PRESSURE WILL THEN BUILD INTO THE
AREA FROM THE WEST WITH NEARLY CALM CONDITIONS TAKING HOLD MONDAY
NIGHT BEFORE MODERATE SOUTHERLY WINDS EXPAND INTO THE REGION IN
ADVANCE OF THE NEXT STORM SYSTEM DUE INTO THE AREA BY TUESDAY.

&&

.AVIATION...ISSUED 1157 PM EST SAT FEB 28 2015

AREA OF LIGHT SNOW WILL EXPAND EAST-NORTHEAST AND ACROSS PORTIONS OF
SE MICHIGAN EARLY THIS MORNING.   A PERIOD OF MVFR CONDITIONS WILL
EXIST ACROSS THE DETROIT CORRIDOR UP THROUGH PTK...DIMINISHING
CONFIDENCE IN DURATION/OCCURRANCE AT FNT WITH THIS MOISTURE ALONG
THE PERIPHERY.  POTENTIAL FOR IFR PRIMARILY AT DTW/YIP...WORTHY OF A
TEMPO INCLUSION.  CONFIDENCE DIMINISHES IN THE WAKE OF THIS INITIAL
BURST OF SNOW FROM LATE MORNING ONWARD.  THERE WILL BE THE POTENTIAL
FOR A SECONDARY PERIOD OF LIGHT SNOW AT DTW...CENTERED DURING THE
AFTERNOON.  ANY INTERLUDE IN THE SNOWFALL MAY ALLOW CEILING HEIGHTS
TO LIFT SLIGHTLY DURING THE DAY...BUT STILL FAVOR A MARGINAL MVFR
CONDITIONS OUTSIDE OF MBS.

FOR DTW...PROGRESSIVE LOWERING OF CEILINGS JUST BEYOND THE 06Z TAF
ISSUANCE AS UPSTREAM AREA OF SNOWFALL APPROACHES THE METRO AIRSPACE.
ONSET OF LIGHT SNOWFALL TARGETED FOR 07-08ZZ WITH STEADY
DETERIORATION IN CONDITIONS THROUGH THE EARLY-MID MORNING HOURS...A
PERIOD OF IFR POSSIBLE AT THE PEAK 08Z-11Z.  ACCUMULATION LESS THAN
AN INCH WITH THE MORNING SNOWFALL...MINOR ADDITIONAL ACCUMS
POSSIBLE FOR THE AFTERNOON.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CEILINGS BELOW 5000 FT THROUGH SUNDAY.

* HIGH IN PTYPE AS SNOW TONIGHT AND SUNDAY.

&&

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

$$

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


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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).


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