Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 121713
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
113 PM EDT SAT APR 12 2014

.AVIATION...

//DISCUSSION...

CONVECTION ACROSS OVER SOUTHERN LAKE MICHIGAN IS THE FIRST ORDER OF
BUSINESS FOR THE TERMINAL FORECASTS.  ENOUGH EVIDENCE SUGGESTS THE
THUNDERSTORMS NEAR CHICAGO HAVE A GOOD CHANCE TO TRAVEL EASTWARD
WITH SOME LEVEL OF INTEGRITY THROUGH THE BALANCE OF THE AFTERNOON.
THEREFORE...HAVE INTRODUCED THUNDER INTO THE DETROIT AREA FORECASTS
AND REFINED TIMING FOR THE SAGINAW AND FLINT FORECASTS. MEANWHILE...
WINDS WILL CONTINUE TO INCREASE FROM THE SOUTH AS THE STORMS
APPROACH /EXCEPTION BEING MBS WHERE WINDS WILL HOLD A GREATER
EASTERLY COMPONENT/.  SHOWERS AND EMBEDDED STORMS WILL LINGER ACROSS
THE SAGINAW VALLEY THIS EVENING AS THE WARM FRONT STALLS OUT ACROSS
THE REGION.

//DTW THRESHOLD THREATS...
* MEDIUM CONFIDENCE IN THUNDERSTORMS BETWEEN 21-00Z.

* MEDIUM CONFIDENCE IN CIGS BELOW 5000 FEET LATE THIS AFTERNOON
  WITHIN THUNDERSTORMS.

* MEDIUM CONFIDENCE IN CIGS BELOW 5000 FEET SUNDAY MORNING WITH
  INCREASED LOW LEVEL MOISTURE.

&&

.PREV DISCUSSION...ISSUED 1130 AM EDT SAT APR 12 2014

UPDATE...

LOWER TROPOSPHERIC WARM FRONTAL SLOPE IS CURRENT DRAPED ACROSS
SOUTHERN LOWER MICHIGAN. MOISTURE TRANSPORT INTO THIS FEATURE IS
RAPIDLY ON THE INCREASE JUST UPSTREAM OF LAKE MICHIGAN. AS A
RESULT...AN ELEVATED AREA OF CONVECTION HAS SPROUTED AND IS
MAINTAINING A RELATIVELY HIGH DEGREE OF INTEGRITY AS IT APPROACHES
THE LAKE. FURTHERMORE...THERE IS SOME ORGANIZED MID-LEVEL SUPPORT IN
THE FORM OF A JETLET IN THE 700-500MB LAYER /EVIDENCED IN THE
WATER VAPOR IMAGERY/. REGIONAL SOUNDINGS INDICATE ADEQUATE ELEVATED
INSTABILITY TO SUPPORT A CONTINUATION OF CONVECTION THROUGH THE
DIURNAL CYCLE. SURFACE DEWPOINTS ARE EXPECTED TO CREEP INTO THE
40S AS THE RETURN FLOW ON THE TRAILING PERIPHERY OF THE SURFACE
HIGH ESTABLISHES A RIBBON OF HIGHER MOMENTUM USHERING IN AN
AIRMASS WITH BETTER MOISTURE QUALITY /PER 12Z ILX RAOB/.

NWP SUITE IS STRUGGLING WITH THE OVERALL CHARACTER OF THE
CONVECTIVE CLUSTERS. THE BEST DEPICTION IS OFFERED BY THE 12.12Z
REGIONAL GEM...WHICH CONTINUES TO ADVANCE SOME SEMBLANCE OF A
RESPONSE ALONG AND NORTH OF M-59 LATE THIS AFTERNOON. FORECAST
ADJUSTMENTS WILL CENTER ON REFINEMENT OF TIMING AND POSITIONING OF
THUNDERSTORM CHANCES LATE THIS AFTERNOON AND EVENING.

PREV DISCUSSION...ISSUED 312 AM EDT SAT APR 12 2014

SHORT TERM...TODAY AND TONIGHT

RIDGE AMPLIFICATION WILL COMMENCE TODAY IN RESPONSE TO STRONG
LONGWAVE TROUGH AXIS DIGGING SOUTHWARD ACROSS WESTERN PORTIONS OF
CANADA. SOUTHEASTERN MICHIGAN WILL REMAIN ON THE COOL SIDE OF THIS
INBOUND RIDGE INITIALLY...FINALLY GIVING WAY TO INCREASING SOUTHERLY
FLOW FOR THIS AFTERNOON. 300K SYSTEM RELATIVE ISENTROPIC WILL
INCREASE MARKEDLY AFTER 18Z...BUT DRY AIR WILL NEED TO BE OVERCOME
IN THE LOWEST 12 KFT. TEMPERATURES ARE AGAIN EXPECTED TO OVERACHIEVE
REACHING THE MID 60S NORTH TO THE LOWER 70S SOUTH. THE EARLY DAY
RETURN FLOW IS FORECASTED TO ARRIVE OFF OF THE DRY ATLANTIC
ANTICYCLONE. THIS WILL EVENTUALLY SWITCH AS TRAJECTORIES DURING THE
LATE AFTERNOON SUGGEST A PIECE OF MUCH HIGHER THETA E CONTENT WILL
BREAK OFF NEAR IOWA AND ADVECT DUE EASTERLY INTO LOWER MICHIGAN.

WHAT MAKES THE LATE AFTERNOON AND EVENING FORECAST SO DIFFICULT IS
THE SPEED OR HOW RAPID FORCING FOR ASCENT WILL BE SPREADING EAST
INTO THE GREAT LAKES. UPPER LEVEL DEFORMATION FORCING WITHIN THE
LEAD ISENTROPIC ASCENT WING OF INBOUND THERMAL RIDGE WILL BE SUPERB
WHICH WILL SUPPORT A DEVELOPING AND TIGHT THERMAL GRADIENT ALOFT.
GIVEN THIS WARM FRONT...THERE IS A CONSIDERABLE AMOUNT OF BUST
POTENTIAL WITH REGARDS TO DURATION OF SHOWERS AND THUNDERSTORMS IN
ADDITION TO QPF AMOUNTS. DID NOT GO VERBATIM WITH PRECIPITATION
CHANCES BASED ON QPF...RATHER...BEGAN THE CHANCES AFTER 21Z THIS
AFTERNOON WITH THE ARRIVAL OF THE 850-700MB FRONT. CERTAINLY
POSSIBLE SOME ACTIVITY MAY SNEAK AHEAD OF THESE THERMAL
GRADIENTS...HOWEVER...WANTED TO COMMUNICATE A PRIMARILY DRY DAY.

THE INITIAL SURGE OF SHOWERS AND THUNDERSTORMS DURING THE EVENING
MAY BE THE MOST ORGANIZED ACTIVITY FOR TONIGHT. FORCING WILL BE
LINED UP WITH INITIAL WARM ADVECTION TIED TO AN OLD MOMENTUM SURGE
OF THE REMNANT LOW LEVEL JET. INDICATIONS ARE THIS ACTIVITY WILL
PASS THROUGH AS A WAVE WITH SOME SUBSIDENCE SETTING UP IN THE WAKE
OF EVENING ROUND OF CONVECTION. FOR AREAS SOUTH OF I
69...GEOPOTENTIAL HEIGHT GRADIENT ALONG WITH FORECAST SOUNDINGS
SUGGESTS A CAPPED ENVIRONMENT UNDER THE SHELTER OF THE RIDGE. FOR
THE SAGINAW VALLEY AND THUMB...PLUME OF RICHEST THETA E WILL BECOME
QUASI-STATIONARY. DESPITE INITIAL WAA SURGE EXITING TO THE
NORTHEAST...THE REGION WILL REMAIN WITHIN THE DIRECT LINE OF THE
FIRE HOSE FROM SOUTHWESTERLY FLOW. MODELS ARE NOISY...BUT VARIOUS
SHREDS OF CONVECTIVE GENERATED VORTICITY MAXIMUMS ARE EXPECTED TO
PASS DIRECTLY OVERHEAD. FOR THIS REASON...WILL MAINTAIN A NARROW
AXIS WITH POPS IN THE LIKELY CATEGORY THROUGH 12Z TO ACCOUNT FOR ANY
TRAINING ACTIVITY. THUNDERSTORMS TONIGHT WILL BE ELEVATED. THIS IN
COMBINATION WITH MEAGER CAPE VALUES OF A FEW HUNDRED J/KG...NO
EXPECTATION FOR STRONG STORMS EXISTS. WITH THE LACK OF VIGOROUS
CONVECTION LIQUID AMOUNTS ARE NOT EXPECTED TO EXCEED A HALF INCH.

LONG TERM...SUNDAY THROUGH FRIDAY

THE AMPLIFICATION OF THE CURRENTLY ZONAL LONG WAVE PATTERN WILL RAMP
UP ON SUNDAY AS A LONGWAVE TROUGH CURRENTLY SEEN ON WATER VAPOR OVER
BRITISH COLUMBIA SINKS SOUTH AND AMPLIFIES OVER THE PLAINS SUNDAY
AND SUNDAY NIGHT. THESE HEIGHT FALLS OVER THE PLAINS WILL RESULT IN
HEIGHTS INCREASING DOWNSTREAM OVER THE EAST COAST AS THE PATTERN
AMPLIFIES OVER THE CONUS.  THE RESULT WILL BE A WELL DEFINED
BAROCLINIC ZONE OVER THE CENTRAL GREAT LAKES WITH SOUTHWESTERLY
WINDS ADVECTING IN A HEALTHY AMOUNT OF MOISTURE FROM THE GULF OF
MEXICO INTO THE GREAT LAKES REGION THROUGH EARLY NEXT WEEK. WITH
SEVERAL SHORTWAVES TRACKING ALONG THIS BAROCLINIC BOUNDARY SUNDAY
AND MONDAY...A VERY ACTIVE PERIOD IS IN STORE FOR THE CENTRAL GREAT
LAKES REGION AS THESE IMPULSES TAKE ADVANTAGE OF THE
MOISTURE...INSTABILITY AND LIFT FROM THE BAROCLINIC ZONE.

THE BEST CHANCES WILL BE ACROSS THE NORTH SUNDAY AND SUNDAY NIGHT
WHICH WILL BE CLOSE TO THE BAROCLINIC ZONE. THE AFOREMENTIONED
SHORTWAVES TRACKING ALONG THIS BOUNDARY WILL PROVIDE MULTIPLE
OPPORTUNITIES FOR HEAVY RAIN AND FLOODING GIVEN THE ABUNDANT GULF
MOISTURE THAT WILL BE AVAILABLE AS EVIDENCED BY SURFACE DEW POINTS
WELL INTO THE 50S. THE BAROCLINIC ZONE WILL ALSO HAVE ASSISTANCE IN
THE UPPER LEVELS UNDER THE RIGHT ENTRANCE REGION OF A STRONG 130
KNOT UPPER LEVEL JET OVER CENTRAL ONTARIO. INSTABILITY SOUTH OF THE
FRONT...WHICH WILL GLIDE ALONG THE SLOPE OF THE WARM FRONT...WILL
BRING THE CHANCE FOR THUNDERSTORMS WITH THE RAIN
SHOWERS...INCREASING THE CHANCE FOR A BURST OF HEAVY RAIN AND
LOCALIZED FLOODING ACROSS THE NORTH DURING THIS PERIOD.

THE AFOREMENTIONED MID LEVEL TROUGH WILL PUSH EAST OVER THE WESTERN
GREAT LAKES ON MONDAY...PUSHING THE BAROCLINIC ZONE EAST AS A COLD
FRONT ON MONDAY. THIS WILL BRING THE OPPORTUNITY FOR HEAVY RAIN TO
THE ENTIRE CWA ON MONDAY AS THIS FRONT AND ASSOCIATED MOISTURE PUSH
EAST ACROSS SOUTHEAST MICHIGAN. THE PROGRESSION OF THE FRONT...ALONG
WITH MOST OF THE PREVIOUS RAINFALL FALLING TO THE NORTH AND
WEST...SHOULD MITIGATE FLOODING CONCERNS ACROSS THE SOUTHERN AND
EASTERN CWA ON MONDAY DESPITE THE HEAVY RAINFALL. THE MAIN CHANGE TO
THE PREVIOUS FORECAST DURING THIS TIME WAS ADJUSTING THE TIMING OF
THE COLD AIR ADVECTION MONDAY AND MONDAY NIGHT WHICH MEANS
THUNDERSTORMS HANG AROUND INTO MONDAY ACROSS THE SOUTHEASTERN CWA
AND THE TRANSITION TO SNOW ACROSS THE NORTH WILL BE SLOWER. ANY
ADDITIONAL RAINFALL ACROSS THE NORTH ON MONDAY WILL ONLY EXACERBATE
THE FLOODING CONCERNS OVER THIS AREA.

WHILE THERE ARE CERTAINLY MODEL SOLUTIONS THAT ARE FAIRLY BULLISH
WITH RESPECT TO QPF AMOUNTS OVER THE SAGINAW VALLEY AND NORTHERN
THUMB DURING THIS PERIOD...THERE ARE OTHER SOLUTIONS THAT FOCUS MUCH
OF THE HEAVY RAIN A FEW COUNTIES NORTH AND WEST WHICH WOULD HELP
MINIMIZE FLOODING CONCERNS OVER THESE AREAS. IN ADDITION THE
RAINFALL APPEARS TO BE A LONG DRAWN OUT EVENT RATHER THAN 2 TO 3
INCHES OVER A FEW HOUR PERIOD. THEREFORE WILL CONTINUE TO HOLD OFF
ON ISSUING ANY FLOOD HEADLINES WITH THIS FORECAST ISSUANCE.

WHILE THE NAM SLOWS THE PROGRESSION OF THE TROUGH...WHICH WOULD
BRING ANOTHER ROUND OF PRECIPITATION MONDAY NIGHT AND TUESDAY...THE
GFS AND ECMWF MODELS ARE MORE PROGRESSIVE WITH MOSTLY DRY CONDITIONS
BY TUESDAY. WITH THE OUTCOME STILL UNCERTAIN...AS THE 12Z ECMWF
AGREEING WITH THIS SLOWER SOLUTION...WILL MAINTAIN CHANCY POPS AT
THIS JUNCTURE. BEHIND THIS TROUGH LONGWAVE RIDGING TAKES CONTROL OF
THE WEATHER FOR THE REST OF THE WEEK WITH COOLER TEMPERATURES AND
DRY WEATHER EXPECTED OVER SOUTHEAST MICHIGAN.

MARINE...

WINDS WILL SHIFT TO A SOUTHERLY DIRECTION TODAY AS WARM FRONT
LIFTS INTO THE REGION.  THIS ACTIVE FRONTAL BOUNDARY WILL PROVIDE
THE FOCUS FOR ROUNDS OF SHOWERS AND THUNDERSTORMS FROM LATE TODAY
INTO MONDAY.  MODERATE SOUTH TO SOUTHWEST WINDS WILL HOLD SOUTH OF
THIS FRONTAL BOUNDARY THROUGH THE LATTER HALF OF THE WEEKEND.  GUSTY
NORTHWEST WINDS WILL EMERGE AS THE FRONT SAGS SOUTHEAST MONDAY AND
MONDAY NIGHT.

&&

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

&&

$$

AVIATION.....MANN
UPDATE.......MANN
SHORT TERM...CB
LONG TERM....KURIMSKI
MARINE.......KURIMSKI


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






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