HAMweather.com Area Forecast Discussion for County Warning Area DTX

Thu, 16 Feb 2012 07:37:13 GMT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1148 PM EST WED FEB 15 2012

.AVIATION...

//DISCUSSION...

THE INFLUX OF LOW LEVEL MOISTURE IN ADVANCE OF LOW PRESSURE LIFTING 
UP FROM MISSOURI/WRN ILLINOIS WILL CONTINUE TO CAUSE CEILINGS TO 
LOWER THROUGH THE EARLY MORNING HOURS. THE SURFACE LOW IS FORECAST 
ACROSS CENTRAL MICHIGAN BETWEEN 12Z AND 15Z. UPSTREAM OBSERVATIONS 
ACROSS ILLINOIS SHOW PLENTY OF LOW CLOUDS BASED AT OR BELOW 400 FT 
AND QUITE A BIT OF FOG. GIVEN THE TRACK OF THIS SYSTEM...THESE LIFR 
AND VLIFR CONDITIONS ARE LIKELY TO LIFT INTO SE MI TOWARD DAYBREAK 
AND SHOULD PERSIST UNTIL AFTER 15Z WITH THE PASSAGE OF A WEAK COLD 
FRONT. THIS FRONT WILL VEER THE WINDS TO THE WEST AND BEGIN TO 
ADVECT SOME DRIER AIR INTO THE REGION. PRECIP TYPE WILL REMAIN ALL 
RAIN...WITH THE EXCEPTION OF MBS WHERE SLIGHTLY COLDER AIR MAY ALLOW 
FOR SOME SNOW TO MIX IN. 

FOR DTW...CEILINGS SHOULD FALL BELOW 1000 FT WITHIN THE NEXT COUPLE 
OF HOURS WITH CONDITIONS DETERIORATING THROUGH DAYBREAK. 
OBSERVATIONS ACROSS ILLINOIS SUPPORT LOWERING CEILINGS AND 
VISIBILITIES IN THE 10Z TO 15Z TIME FRAME.  

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS WILL REMAIN BELOW 5000 FT THROUGH THE 
MORNING.

* MEDIUM CONFIDENCE IN CEILINGS OR VISIBILITIES DROPPING BELOW 200FT 
OR 1/2SM AROUND DAYBREAK THURSDAY.

.PREV DISCUSSION...ISSUED 926 PM EST WED FEB 15 2012 

UPDATE...

RAIN CONTINUES TO OVERSPREAD SE MI WITHIN INCREASING MOIST
ISENTROPIC ASCENT IN ADVANCE OF THE UPPER WAVE NOW LIFTING ACROSS
MISSOURI. THE LEADING EDGE OF THE MOISTURE ADVECTION HAS HAD A
LITTLE BETTER CONVECTIVE COMPONENT WHICH IS LIKELY CAUSING SOME
LOCALIZED SMALL GRAUPEL/SLEET. THE ISENTROPIC ASCENT WILL PERSIST
THROUGH THE NIGHT AND INTO THURS MORNING. THE MID LEVEL WAVE IS
STILL EXPECTED TO DAMPEN AS IT LIFTS INTO THE NRN OHIO VALLEY AND 
SRN GR LKS LATE TONIGHT/EARLY THURS MORNING. MODEL SOLUTIONS DO
HOWEVER SUGGEST SOME ENHANCED MID TROPOSPHERIC FGEN/DEFORMATION
TOWARD DAYBREAK IN RESPONSE TO A HIGHER AMPLITUDE NORTHERN STREAM
TROUGH DROPPING INTO NRN MN...WHICH MAY TIGHTEN THE THERMAL
GRADIENT OVER CENTRAL LOWER MI. NAM/RUC/GFS MODEL SOUNDINGS ALL
INDICATE A DEEP ISOTHERMAL LAYER NEAR 0C FROM THE SFC UP TO 900MB
ACROSS MIDLAND/BAY/NRN SAGINAW COUNTIES LATE TONIGHT. IF PRECIP
RATES ARE HIGH ENOUGH...THIS THERMAL PROFILE SUGGESTS A
POSSIBILITY OF A PERIODIC CHANGE OVER TO SNOW AT TIMES. CERTAINLY
A SUBTLE FEATURE...BUT ONE TO WATCH. FOR THE TIME BEING...HAVE
INCREASED SNOW CHANCES IN THESE LOCALS AND ADDED SOME MINOR
ACCUMS.

AS FOR THE REST OF THE AREA...CONTINUED WEAK LOW LEVEL WARM AIR
ADVECTION SHOULD ENSURE PRECIP REMAINS MAINLY RAIN. 

PREV DISCUSSION...ISSUED 358 PM EST WED FEB 15 2012 

SHORT TERM...

THE LATEST SATELLITE IMAGERY SHOWS AN OPEN WAVE OVER THE SOUTH 
CENTRAL PLAINS THAT WILL LIFT NORTHEAST TOWARD THE GREAT LAKES 
OVERNIGHT AHEAD OF A DIGGING NORTHERN STREAM TROUGH. WATER VAPOR 
IMAGERY SUPPORTS RECENT MOISTURE TRANSPORT AND PWAT PROGS WHICH 
INDICATE THAT SUBSTANTIAL MOISTURE CONTENT WILL CONTINUE TO BE DRAWN 
NORTHWARD WITHIN THE DEEP SOUTHWESTERLY FLOW AHEAD OF THIS SYSTEM. 
RADAR RETURNS ACROSS THE OHIO VALLEY WILL CONTINUE TO SPREAD 
NORTHWARD ALONG AN ARM OF STRENGTHENING SYSTEM RELATIVE ISENTROPIC 
ASCENT THAT WILL BE LIFTING INTO THE AREA LATE THIS AFTERNOON INTO 
THE EARLY EVENING HOURS. RAIN SHOWER COVERAGE AND INTENSITY WILL 
SLOWLY THEN SLOWLY INCREASE COVERAGE AS THE SYSTEM EJECTS OUT OF THE 
SOUTHERN PLAINS FOLLOWED BY A MORE NOTABLE UPTICK IN 
COVERAGE/INTENSITY THAT IS EXPECTED TO GET UNDERWAY AROUND MIDNIGHT. 
THIS WILL BE COINCIDENT WITH THE ARRIVAL OF THE STRONGEST MID LEVEL 
FORCING AND FGEN FORCING. AT THE SAME TIME, LEFT EXIT JET SUPPORT 
WILL EXPAND IN COVERAGE AS A JET CORE OVER THE OHIO VALLEY 
STRENGTHENS TO 165 KTS. THIS, COMBINED WITH AN INCREASE IN SPEED 
DIVERGENCE AS THE DOWNSTREAM RIDGE BECOMES MORE AMPLIFIED, WILL 
PROMOTE DEEP TROPOSPHERIC ASCENT THROUGH THE DEPTH OF THE COLUMN, 
WHICH WILL FEATURE PWATS BETWEEN 0.6" AND 0.7". A WIDESPREAD QUARTER 
OF AN INCH OF TOTAL RAINFALL IS PLAUSIBLE SOUTH OF I-69, BUT SOME 
HIGHER AMOUNTS WILL BE POSSIBLE IF LOW LEVEL FGEN FORCING CAN BECOME 
SUFFICIENTLY ORGANIZED. ASIDE FROM A FEW FLAKES OR A BRIEF PERIOD OF 
FROZEN PRECIP MIXING IN ALONG AND NORTH OF I-69 AS PRECIP GETS 
UNDERWAY, THERMAL PROFILES WILL BE SUFFICIENTLY WARM TO SUPPORT RAIN 
EVERYWHERE. MARGINAL PROFILES IN THE SAGINAW VALLEY AREA, 
PARTICULARLY FOR MIDLAND AND BAY COUNTIES, WILL SUPPORT OCCASIONAL 
MIXING WITH SNOW THROUGH THE NIGHT, BUT NO ACCUMULATION EXPECTED.

LONG TERM...THURSDAY THROUGH WEDNESDAY

UPPER WAVE OVER THE SOUTH-CENTRAL PLAINS WILL LIFT ACROSS THE 
SOUTHERN GREAT LAKES EARLY TOMORROW...WHILE THE OTHER UPPER WAVE NOW 
OVER NORTH DAKOTA AND MANITOBA TRACKS EAST ACROSS NORTHERN MICHIGAN 
DURING THE AFTERNOON AND EVENING. SURFACE REFLECTIONS FROM THESE TWO 
FEATURES WILL CONSOLIDATE OVER MICHIGAN...PULLING A COLD FRONT 
ACROSS THE AREA DURING THE AFTERNOON/EVENING. RAIN WILL CHANGE TO 
SNOW FROM NORTHWEST TO SOUTHEAST TOMORROW AS THE FRONT DROPS ACROSS 
THE AREA. PRECIPITATION WILL ALSO TAPER OFF DURING THE AFTERNOON AS 
THE SYSTEM MOVES EAST AND DRIER AIR ADVECTS INTO THE AREA. MOST 
PRECIPITATION WILL THEREFORE FALL AS RAIN TOMORROW...WITH MAYBE SOME 
AREAS OF DRIZZLE TOWARDS AFTERNOON. THE HIGHEST SNOWFALL TOTALS WILL 
BE NORTH OF SAGINAW AND ACROSS HURON COUNTY...BUT AMOUNTS ARE 
EXPECTED TO REMAIN LESS THAN AN INCH. LITTLE TO NO ACCUMULATION IS 
EXPECTED ELSEWHERE. TEMPERATURES WILL BE SEASONABLY MILD TOMORROW 
AHEAD OF THE FRONT...WITH HIGHS REACHING THE UPPER 30S TO MID 40S 
BEFORE THEY START TO FALL BEHIND THE FRONTAL PASSAGE.

NEXT UPPER WAVE IS EXPECTED TO TRACK ACROSS THE GREAT LAKES DURING 
THE FIRST HALF OF THE WEEKEND. THIS SHORTWAVE CAN NOW BE SEEN ON 
WATER VAPOR IMAGERY DROPPING INTO NORTHERN ALBERTA. MODELS ARE STILL 
STRUGGLING WITH HOW FAR SOUTH INTO THE DAKOTAS AND CORN BELT TO DROP 
THIS WAVE. UNCERTAINTY CENTERS IN PART WITH HOW MODELS HANDLE THE 
EASTWARD PROGRESSION OF THE UPPER LOW OVER NEVADA. PREFERENCE DOES 
LIE HOWEVER WITH THE FURTHER NORTH SOLUTIONS OFFERED BY THE GFS AND 
EURO...AS THESE MODELS HAVE BEEN MORE CONSISTENT WITH THE TRACK THAN 
THE FURTHER SOUTH NAM/GEM. SURFACE LOW ACTUALLY BEGINS TO APPROACH 
THE AREA ON FRIDAY...TIGHTENING THE THERMAL GRADIENT OVER 
SOUTH-CENTRAL LOWER MICHIGAN. DO THINK WE WILL SEE CLOUD COVER 
INCREASE BUT CHANCES FOR PRECIPITATION LOOK VERY LOW AS MODELS SHOW 
NEUTRAL TO NEGATIVE SYSTEM RELATIVE ISENTROPIC ASCENT. BETTER CHANCE 
FOR PRECIPITATION WILL ARRIVE FRIDAY NIGHT INTO SATURDAY AS A WEAK 
WARM FRONT LIFTS UP INTO THE AREA (FRI NIGHT)...AND IS FOLLOWED 
QUICKLY BY A COLD FRONTAL PASSAGE ON SATURDAY. THERMAL PROFILES 
SUGGEST PRECIPITATION WILL FALL AS SNOW. LATEST FORECAST SOUNDINGS 
FROM THE GFS JUST BARELY SUPPORT A PERIOD OF RAIN DOWN TOWARDS 
TOLEDO...HOWEVER WITH THE GFS BEING AN OUTLIER WITH THE STRENGTH OF 
THE SURFACE SYSTEM...DID NOT INCLUDE ANY MIXED PRECIP IN THE 
FORECAST. GIVEN ALL THE RECENT VARIATION IN MODEL TRACKS...ONLY FELT 
COMFORTABLE GOING WITH HIGH CHANCE POPS FOR NOW. SNOW AMOUNTS WILL 
BE LIMITED BY QUICK FORWARD SPEED OF THE WAVE...WITH MAYBE AN INCH 
TO INCH AND HALF OF SNOW IN THE HEAVIEST SWATH.

HIGH PRESSURE LOOKS TO BUILD OVER THE AREA SUNDAY AND MONDAY FOR A 
DRY FORECAST. BIG MODEL DIFFERENCES THEN LEAD TO QUITE A BIT OF 
UNCERTAINTY BY MID-WEEK. BOTH THE GFS AND EURO DROP ENERGY INTO THE 
SOUTHERN ROCKIES AND EVENTUALLY LIFT IT UP TOWARDS THE GREAT LAKES. 
THESE MODELS HOWEVER SHOW LARGE DIFFERENCES IN WHEN AND WHERE THEY 
RE-PHASE THIS ENERGY WITH THE NORTHERN STREAM. BOTH FIRST BRING A 
QUICK NORTHERN STREAM WAVE ACROSS NORTHER MICHIGAN ON TUESDAY BEFORE 
LIFTING AN AREA OF LOW PRESSURE UP TOWARDS THE GREAT LAKES. 12Z GFS 
TAKES THIS SYSTEM MORE TOWARDS THE CENTRAL GREAT LAKES BY 
WEDNESDAY...SPREADING MOSTLY RAIN INTO THE AREA. THE 12Z EURO NOW 
LIFTS THE SYSTEM INTO THE EASTERN GREAT LAKES...WHICH WOULD BRING 
MUCH LOWER CHANCES FOR PRECIPITATION.

MARINE...

LIGHT SOUTHERLY WINDS TODAY WILL BACK TO SOUTHEASTERLY TONIGHT IN 
ADVANCE OF AN APPROACHING LOW PRESSURE SYSTEM. THIS LOW WILL LIFT 
ACROSS THE REGION ON THURSDAY, WITH COLDER AIR EXPECTED TO 
OVERSPREAD AREA WATERS IN ITS WAKE. NORTHWESTERLY WINDS MAY APPROACH 
25-30 KTS OVER THE OPEN WATERS ON THURSDAY EVENING BUT WILL LIKELY 
REMAIN BELOW GALE FORCE. THE PATTERN WILL REMAIN FAIRLY ACTIVE WITH 
OCCASIONAL BREEZY PERIODS, BUT NO SIGNIFICANT WIND EVENTS ARE 
FORECAST FOR THE NEXT SEVEN DAYS.

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