Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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985
FXUS63 KDTX 082307
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
607 PM EST MON FEB 8 2016


.AVIATION...

LOW PRESSURE WILL SLOWLY DEEPEN AS IT SPINS NEAR THE EASTERN SHORE
OF LAKE HURON INTO TUESDAY. VFR CIGS WILL TREND TO MVFR DURING THAT
TIME AS -SHSNS BECOME MORE PREVALENT WITH TIME OVER THE TERMINALS.
THIS WILL BE ESPECIALLY TRUE MIDDAY TUESDAY INTO TUESDAY EVENING.
NW TO WNW FLOW WILL PERSIST AROUND THIS LOW PRESSURE CENTER THRU THE
FORECAST...INCREASING ON TUESDAY AFTERNOON GIVEN TIGHTENING PRESSURE
GRADIENT AND DECENT BOUNDARY LAYER MIXING. GUSTS SHOULD APPROACH 25
KNOTS DURING THIS TIME FRAME.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN CIGS AOB 5KFT THIS EVENING...AND HIGH OVERNIGHT INTO
  TUESDAY.

* HIGH CONFIDENCE IN PRECIPITATION TYPE BEING SNOW OVERNIGHT INTO
  TUESDAY. MEDIUM CONFIDENCE IN RAIN/SNOW MIX EARLY THIS EVENING.

* LOW CONFIDENCE IN NORTHWEST CROSSWIND TUESDAY AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 314 PM EST MON FEB 8 2016

DISCUSSION...

WITH SURFACE TEMPS HOLDING IN THE UPPER 30 TO LOW 40S THIS
AFTERNOON...BOUNDARY LAYER WARMTH HAS REMAINED SUFFICIENT IN KEEPING
THE RETURNS STREAMING INTO PORT HURON AND THE EASTERN THUMB REGION
ALL RAIN. THIS PRECIPITATION WILL UNDERGO A TRANSITION TO ALL SNOW
THIS EVENING DUE BOTH TO NIGHTTIME BOUNDARY LAYER COOLING AND WEAK
LOW LEVEL COLD AIR ADVECTION. THESE RETURNS ARE ASSOCIATED WITH AN
AXIS OF MID LEVEL DEFORMATION EXTENDING FROM NRN OHIO INTO SRN LAKE
HURON. THE REGIONAL WATER VAPOR LOOP TODAY HAS INDICATED SOME
MOISTURE ADVECTION INTO THIS SYSTEM AHEAD OF A SHORT WAVE IMPULSE
NOW OVER THE OH/KY BORDER. THIS SHORT WAVE FEATURE IS ASSOCIATED
WITH THE BROAD UPPER LOW CENTERED OVER LAKE MI. THE SHORT WAVE
IMPULSE WILL BE DRIVEN TOWARD SRN LAKE HURON OVERNIGHT AS THE UPPER
LOW SLIDES INTO NRN INDIANA. THIS WILL IN TURN DRIVE THE MID LEVEL
DEFORMATION ACROSS THE THUMB REGION DURING THE NIGHT. LATEST HI RES
SUITE ALL GENERALLY SUGGEST THE STRONGER PUSH OF DEFORMATION WILL BE
A LITTLE SLOWER TO MOVE THROUGH THE THUMB REGION TONIGHT AS IT
APPEARS THE MID LEVEL IMPULSE WILL FOSTER A MORE COMPACT REGION OF
FORCING. MEANWHILE SOME CONVECTIVE SHOWERS HAVE EMERGED UNDER THE MID
LEVEL COLD POOL OVER SRN LAKE MI/SW LOWER MI. SOME OF THESE SHOWERS
MAY IMPACT THE FAR SOUTHERN SECTIONS OF THE FORECAST AREA THIS
EVENING.

ON TUESDAY...THE MID LEVEL SHORT WAVE WILL HOLD NEARLY STEADY IN THE
VICINITY OF EITHER THE ERN THUMB/SRN LAKE HURON OR JUST EAST OF
METRO DETROIT INTO TUES AFTERNOON. THE MID LEVEL IMPULSE WILL THEN
LIFT NORTHEAST AS THE UPPER LOW OPENS UP AND LIFTS EAST LATE IN THE
DAY. THERE REMAINS SOME DEGREE OF MODEL UNCERTAINTY AS TO HOW
QUICKLY THE DEFORMATION REGION OPENS UP AND TRANSITIONS WEST AND
SOUTH. RECENT MODEL TRENDS SUGGEST IT WILL TAKE UNTIL TUES
AFTERNOON/EVENING FOR THE REMNANT LARGE SCALE FORCING TO PUSH
THROUGH THE SAGINAW VALLEY AND INTO METRO DETROIT/ANN ARBOR AND PTS
SOUTH. STEADY COLD AIR ADVECTION THROUGH THE DAY WILL BEGIN TO BOOST
INSTABILITY OVER LAKE HURON. THE DEPARTURE OF THE SYSTEM TO THE EAST
TUES NIGHT MAY BE ENOUGH TO FORCE A LAKE ENHANCED SFC TROUGH INTO
THE THUMB REGION...POSSIBLY BOOSTING SNOWFALL RATES ACROSS HURON
COUNTY TUES NIGHT. EXPECT THE REMAINDER OF THE FORECAST AREA WILL
SEE SNOW TRANSITION TO NMRS/SCT SNOW SHOWERS. RESIDUAL DEEP LAYER
MOISTURE AND STEEP LOW LEVEL LAPSE RATES COULD HOWEVER SUPPORT SOME
INTENSE SNOWFALL OUT OF SOME OF THESE SNOW SHOWERS.

AS FAR AS THE WINTER WEATHER ADVISORY...THERE WILL BE NO AREAL
EXTENSION OF THE ADVISORY ATTM. THE POTENTIAL FOR LAKE ENHANCEMENT
WITHIN THE MID LEVEL DEFORMATION WILL HOWEVER SUPPORT EXTENDING THE
ADVISORY END TIME A LITTLE LATER INTO TUES EVENING. THE MAIN
FORECAST UNCERTAINTIES ATTM REVOLVE AROUND HOW FAR WEST INTO FLINT
AND THE TRI CITIES REGIONS THE STRONGER DEFORMATION WILL OCCUR ON
TUESDAY AND HOW WELL THE LARGE SCALE FORCING HOLDS TOGETHER LATE IN
THE DAY SOUTH OF THE M 59 CORRIDOR. GIVEN FAIRLY RESPECTABLE
MOISTURE QUALITY WITH 850MB MIXING RATIOS BETWEEN 2 AND 3 G/KG AND
GIVEN A FAIRLY DEEP LAYER OF LOW STATIC STABILITY WITH THE MID LEVEL
COLD POOL IN THE VICINITY...THERE IS LIKELY TO BE SOME REGIONS OF
ENHANCED FORCING WHICH MAY SUPPORT PERIODS OF HIGH INTENSITY
SNOWFALL RATES. THESE FACTORS SUGGEST SOME NEAR TERM FORECAST
UPDATES WILL BE NEEDED AS THIS EVENT UNFOLDS. TAKING INTO
CONSIDERATION LIQUID TO SNOW RATIOS AROUND 10:1 TONIGHT RISING TO
ROUGHLY 12:1 BY LATE TUESDAY AND WITH TOTAL QPF /TONIGHT THROUGH
TUES NIGHT/ POSSIBLY OVER A HALF INCH IN THE THUMB TO A TENTH OR
LESS SOUTH OF M 59...TOTAL FCST SNOWFALL OF 3 TO 7 INCHES LOOK
REASONABLE IN THE ADVISORY AREA /DROPPING TO AN INCH OR LESS SOUTH
OF THE M 59 CORRIDOR/.

REMAINDER OF THE FORECAST FOCUSES ON SNOW SHOWER POTENTIAL WEDNESDAY
AND COLD TEMPERATURES WEDNESDAY THROUGH THE WEEKEND. SURFACE LOW
CONTINUES TO PULL AWAY WEDNESDAY WITH UPPER TROUGH AXIS SWEEPING
THROUGH. SURFACE FLOW TURNS NORTHWESTERLY WHICH IS TYPICALLY A DRIER
FLOW FOR SOUTHEAST MICHIGAN. HOWEVER...850 MB TEMPS DROP TO NEAR -20
RESULTING IN GOOD INSTABILITY OVER THE LAKES. IN ADDITION...MODEL
FORECAST SOUNDINGS SHOW THE COLUMN SATURATED WRT ICE UP PAST 10KFT
EARLY IN THE DAY...WITH DEEPENING BOUNDARY LAYER RESULTING IN STEEP
LAPSE RATES AND SUPERSATURATION WRT ICE IN THE DGZ. THINK WE WILL
SEE AT LEAST A SCATTERED COVERAGE OF SNOW SHOWERS WITH POTENTIAL FOR
LOCALLY AND BRIEFLY HEAVY BURSTS OF SNOW. TOTAL ACCUMULATIONS
WEDNESDAY STILL LIKELY AROUND AN INCH OR LESS FOR MOST AREAS.

HIGH TEMPS WED THRU FRI EXPECTED TO BE A FEW DEGREES EITHER SIDE OF
20 BEFORE A REINFORCING SHOT OF ARCTIC AIR BLASTS IN FRIDAY NIGHT
INTO THE WEEKEND. THIS WILL OCCUR AS THE ARCTIC CLOSED LOW SWEEPS
INTO SOUTHEAST CANADA...AND A BACKDOOR COLD FRONT TURNS SURFACE
WINDS TO A NNW DIRECTION. FAIRLY GOOD CONFIDENCE THAT THIS WILL BE
THE COLDEST AIRMASS ALL YEAR...WITH GEFS MEAN 850 MB TEMPS DROPPING
TO AROUND -25C. HEART OF THIS COLD AIR WILL BE FRIDAY NIGHT THROUGH
SUNDAY. CURRENT FORECAST CALLS FOR LOW TEMPS IN THE SINGLE DIGITS
ABOVE AND BELOW ZERO FRI/SAT NIGHT...WITH HIGHS MAINLY IN THE SINGLE
DIGITS SAT. ECMWF MOS GUIDANCE IS EVEN COLDER. THERE IS LIGHT
SNOWFALL POTENTIAL FRIDAY ALONG THE ARCTIC FRONT AREAWIDE...WITH
SOME CONCERN FOR LAKE EFFECT SNOW ALONG THE HURON SHORELINE FRIDAY
NIGHT AND SATURDAY.

MARINE...

LOW PRESSURE WILL SETTLE OVER FAR SOUTHERN LAKE HURON
TONIGHT...STRENGTHENING IN THE PROCESS...WHICH WILL ALLOW FOR
EXPANDING SNOW SHOWER ACTIVITY THROUGH TOMORROW. WINDS WILL BE LIGHT
TONIGHT...BUT GUSTING UP TO 20 KNOTS ACROSS FAR WESTERN LAKE HURON.
AS THE LOW SLOWLY PULLS AWAY TOMORROW AND COLD AIR RUSHES INTO THE
CENTRAL GREAT LAKES...NORTHWEST WINDS LOOK TO BE RAMPING UP TO 25 TO
30 KNOTS ACROSS MUCH OF LAKE HURON TUESDAY NIGHT...AND PERSISTING
WEDNESDAY...WITH JUST A SMALL DECREASE ON THURSDAY. WITH THE AMOUNT
OF COLD AIR COMING IN...FREEZING SPRAY IS EXPECTED...AND MAY BE
HEAVY. A RENEWED SURGE OF ARCTIC AIR ARRIVES BY SATURDAY...ALLOWING
FOR ANOTHER ROUND OF STRONGER WINDS AND LIKELY FREEZING SPRAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY UNTIL 9 PM EST TUESDAY FOR MIZ049-054-055-
     062-063.

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

$$

AVIATION.....DG
DISCUSSION...SC/DT
MARINE.......SF


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



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