Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 231556
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1056 AM EST TUE DEC 23 2014

.UPDATE...
VERY SOUPY BL AHEAD OF A NORTHWARD MOVING WARM FRONT WILL LEAD TO
PATCHY FOG/HAZE ACROSS ALL OF SE MI THROUGH THE EVENING.
VISIBILITIES CURRENTLY RANGE FROM ABOUT 1 TO 7 MILES BUT ARE
PRIMARILY 3 TO 4 MILES AND SHOULD STAY IN THAT GENERAL RANGE. DUE
TO THIS DECIDED TO ADD SOME PATCHY FOG TO THE FORECAST. IT WILL BE
ENOUGH TO BE NOTICEABLE BUT SHOULD NOT BE DENSE ENOUGH TO CAUSE
ANY MAJOR ISSUES. THOUGH A DRY SLOT ALOFT IS REDUCING MOISTURE IN
THE MID LEVELS...CONTINUED MOISTURE ADVECTION IN THE BL WILL KEEP
A NEARLY SATURATED LAYER FROM THE SFC TO 850MB. THIS WILL REDUCE
THE RISK OF ANY WIDESPREAD SHOWER ACTIVITY BUT SCATTERED
SHOWERS/DRIZZLE WILL BE POSSIBLE THROUGH THE DAY.

&&

.AVIATION...ISSUED 602 AM EST TUE DEC 23 2014

IFR/LOWER MVFR CIGS CAN BE EXPECTED TODAY AS LOW LEVEL MOISTURE
CONTINUES TO INCREASE. MORNING SHRAS WILL WANE INTO THE AFTERNOON
AND EVENING AS MID LEVEL DRY SLOTS SHIFTS OVER THE AREA AND SHUNTS
DEEPER MOISTURE TO THE NORTH. THIS WILL BE TEMPORARY...HOWEVER...AS
SECOND LOW PRESSURE BEGINS TO ORGANIZE TO THE SOUTH AND TRACK INTO
THE OHIO VALLEY. SHRAS WILL INCREASE 06Z ONWARD WITH CIGS REMAINING
AT LEAST IFR THROUGH THE END OF THE FORECAST. WINDS ARE EXPECTED TO
VEER TO THE SOUTH TO SOUTHEAST TODAY AND THEN SWING BACK TO
NORTHEAST AS THIS LOW APPROACHES TONIGHT.

FOR DTW...AS SHRAS BECOME LESS NUMEROUS LATER THIS MORNING INTO THIS
AFTERNOON/EARLY EVENING...CIGS WILL ACTUALLY LOWER AS INCREASED LOW
LEVEL MOISTURE FUNNELS INTO THE AREA. THESE CONDITIONS WILL PERSIST
INTO TONIGHT WHEN SHRAS WILL RE-EXPAND OF THE AREA WITH APPROACH OF
DEEPENING LOW PRESSURE.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CEILINGS AOB 5000 FEET THROUGHOUT THE FORECAST.

* LOW IN CEILINGS AOB 200 FEET AFTER 06Z TONIGHT.

&&

.PREV DISCUSSION...ISSUED 336 AM EST TUE DEC 23 2014

SHORT TERM...TODAY AND TONIGHT

EVAPORATIVE COOLING ALONG LEADING FGEN BANDING HAS LED TO A BRIEF
PERIOD IN WHICH A FEW WET SNOWFLAKES HAVE MIXED WITH RAIN. THIS HAS
HAD NO IMPACT ON THE AREA AS PRECIPITATION HAS REMAINED PRIMARILY
RAIN AND SURFACE TEMPERATURES HAVE HELD IN THE 33-35 DEGREE RANGE IN
THIS COLDEST POCKET OF AIR. IMMEDIATELY SOUTH OF THIS AREA OF FGEN
FORCING...PRECIPITATION IS CHARACTERIZED BY JUST A FEW ISOLATED
LIGHT SHOWERS WITH TEMPERATURES IN THE MID/UPPER 30S. AS THETA-E
RIDGE EXPANDS FURTHER INTO THE AREA EARLY THIS MORNING...ADDITIONAL
RAIN SHOWER ACTIVITY WILL WORK BACK INTO SOUTHEAST LOWER MICHIGAN
AND KEEP RAIN CHANCES RATHER HIGH INTO THE 15Z TIME FRAME.

THEREAFTER...THE AREA COMES UNDER THE INFLUENCE OF MID LEVEL DRY
SLOT...SO BETWEEN 15Z-21Z...SHOWERS WILL DIMINISH ACROSS THE AREA AS
MAIN CONCENTRATION LIFTS NORTH OF THE CWA. IN FACT...BY LATE IN THE
DAY...VERY LITTLE IN THE WAY OF PRECIPITATION IS EXPECTED. WARM AIR
ADVECTION WILL BE TEMPERED BY EXTENSIVE CLOUD COVER AND A PERSISTENT
EAST TO SOUTHEAST BOUNDARY LAYER FLOW. HENCE...THE MODERATION IN
TEMPERATURES WILL BE SLOW TODAY. THAT SAID...WITH MUCH OF THE AREA
SOUTH OF I 69 ALREADY RANGING BETWEEN 35-40F...THIS STILL MEANS
HIGHS BY THIS AFTERNOON WILL CLIMB INTO THE MIDDLE 40S ON AVERAGE.

RELATIVELY QUIET WEATHER WILL PERSIST THROUGH THE EVENING BEFORE THE
LEADING SURGE OF MOISTURE FROM DEVELOPING LOW PRESSURE TO THE SOUTH
BEGINS TO SPREAD INTO THE CWA AFTER MIDNIGHT. BY DAYBREAK WEDNESDAY
THIS RENEWED SHOWER ACTIVITY SHOULD ENCOMPASSES A LARGE PORTION OF
THE CWA. THERE IS LITTLE TO NO RISK OF FROZEN PRECIPITATION AS
RELATIVELY MILD READINGS REMAIN IN PLACE...WITH MOST LOCATIONS
BOTTOMING OUT BETWEEN 35 AND 40 OVERNIGHT.

LONG TERM...

COPIOUS AMOUNT OF UPPER LEVEL ENERGY DESCENDING SOUTH-SOUTHEAST
THROUGH THE ROCKIES EARLY THIS MORNING...ROUNDING THE BASE OF THE
LONGWAVE TROUGH ALONG THE SOUTHERN NEW MEXICO/TEXAS BORDER...A BIT
FARTHER WEST THAN ADVERTISED YESTERDAY. THE MID LEVEL CIRCULATION
OVER THE HEARTLAND IS ALSO A BIT MORE WEST. SO...IT IS NOT TOO
SUPRISING THE MAJORITY OF THE 00Z MODELS HAVE TRENDED WESTWARD WITH
THE RAPIDLY DEEPENING LOW PRESSURE SYSTEM ON WEDNESDAY...THROUGH
CENTRAL LOWER MICHIGAN (WEST OF SOUTHEAST MICHIGAN). THE NAM IS
STILL A TOUCH FARTHER EAST...BUT REMAINS IN CATCH UP MODE...AND WILL
BE DISCARDED. THE 00Z GFS/EURO BOTH IN GOOD AGREEMENT WITH NEAR
METEOROLOGICAL BOMB...AS LOW DEEPENS NEARLY 24 MB IN 24 HRS. WITH
THE WESTWARD TRACK AND STRENGTH OF THIS LOW...IT PRETTY MUCH SHUTS
THE DOOR ON ANY APPRECIABLE ACCUMULATING SNOW...AS DEFORMATION AXIS
REMAINS NORTHWEST. IN FACT...SURFACE LOW TRACK COULD VERY WELL END
UP CLOSE TO LAKE MICHIGAN SHORELINE...PER PARALLEL GFS/CANADIAN
SOLUTIONS. WITH THE SURGE OF LOW LEVEL WARM AIR DURING WEDNESDAY
(WILL BE BUMPING UP MAXES INTO THE 50S ACROSS FAR EASTERN
AREAS)...AS 925/850 MB TEMPS SEEN RISING UP TO 10 C...PRIMING US FOR
GOOD WIND POP WITH SURGE OF LOW LEVEL COLD (850 MB TEMPS PLUMMET -3
TO -6 C ) AIR AND 23-25 MB RISE/FALL PRESSURE COUPLET WORKING
THROUGH. THE 00Z GFS NOW SHOWING GOOD SUBSIDENCE/DESCENT WITH AROUND
60 KNOTS AT 850 MB. SO...POTENTIAL FOR 50-55 MPH OR SLIGHTLY HIGHER
WINDS IS IN PLAY...BUT CONCERN WITH A FARTHER WEST TRACK ARGUES TO
REMAIN SOMEWHAT CONSERTATIVE AND JUST PUT 45 MPH GUSTS IN THE GRIDS
AS BEST PRESSURE GRADIENT LINGERS BACK ACROSS WESTERN LOWER
MICHIGAN. THE GOOD DYNAMICS AND GULF OF MEXICO MOISTURE STREAMING
INTO THE AREA WILL SUPPORT A CHANCE OF THUNDERSTORMS AS WELL WITH
SHOWALTER INDEX GOING SLIGHTLY NEGATIVE...IN LINE WITH DAY 2 SPC
OUTLOOK.

THE GOOD NEWS IS THE INTENSE STORM SYSTEM WILL BE EXITING THE GREAT
LAKES REGION QUICKLY...AND WEATHER CONDITATIONS WILL BE SETTLING
DOWN FOR CHRISTMAS DAY ITSELF AS UPPER LEVEL RIDGE AXIS BUILDS INTO
THE WESTERN GREAT LAKES BY DAYS END. WARM ADVECTION PATTERN ON
FRIDAY AHEAD OF THE NEXT COLD FRONT...WHICH LOOKS TO BE MOVING
THROUGH ON SATURDAY. BUT PLENTY OF DIFFERENCES BETWEEN
CANADIAN/EURO/GFS ON EXACT TIMING...THERMAL PROFILES...AND FGEN
RESPONSE.

MARINE...

LOW PRESSURE OVER THE MIDWEST WILL LIFT INTO THE WESTERN GREAT LAKES
TODAY. THE MODERATE EASTERLY FLOW OVER THE CENTRAL GREAT LAKES WILL
VEER AROUND TO THE SOUTHEAST AND THEN SOUTH IN RESPONSE AND BECOME
LIGHT TONIGHT. RAPIDLY DEEPENING LOW PRESSURE WILL THEN TRACK UP
FROM THE SOUTH ON WEDNESDAY...BRINGING WITH IT RAIN AND POSSIBLE
THUNDERSTORMS. AS THE INTENSE LOW TRACKS THROUGH LAKE HURON TOWARD
MIDNIGHT....GALE FORCE WINDS ARE EXPECTED TO RAMP WITH GOOD COLD
ADVECTION INTO THURSDAY MORNING. CONFIDENCE IN GALES OVER THE OPEN
WATERS OF LAKE HURON IS HIGH...AS FEW STRAY GUSTS TO STORM FORCE ARE
NOT OUT OF THE QUESTION. HOWEVER...THE DURATION OF GALES APPEARS TO
BE RELATIVELY SHORT...ESPECIALLY FOR LAKE ST CLAIR AND LAKE
ERIE...AS A RIDGE OF HIGH PRESSURE BUILDS INTO THE AREA TOWARD THE
END OF DAY THURSDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...GALE WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY AFTERNOON FOR
     LHZ363-421-422-441>443-462>464.

     SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR LHZ421-441-442.

     GALE WATCH FROM LATE WEDNESDAY NIGHT THROUGH THURSDAY AFTERNOON FOR
     LHZ361-362.

LAKE ST CLAIR...GALE WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY MORNING FOR
     LCZ460.

MICHIGAN WATERS OF LAKE ERIE...GALE WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY MORNING FOR
     LEZ444.

&&

$$

UPDATE.......DRK
AVIATION.....DG
SHORT TERM...DG
LONG TERM....SF
MARINE.......SF


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