Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221952
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
352 PM EDT TUE APR 22 2014

.SHORT TERM... AFTERNOON THROUGH TONIGHT

COLDER NORTHWEST LOW LEVEL FLOW WILL DOMINATE THE REST OF THE
AFTERNOON INTO THIS EVENING. IMPRESSIVE COLD ADVECTION WILL BATTLE
LATE APRIL SURFACE HEATING FOR A TEMPERATURE STALEMATE IN THE MID
40S NORTH TO MID 50S NEAR THE OHIO BORDER. THIS IS 20 TO 30 DEGREES
COLDER THAN YESTERDAY AFTERNOON AND IS A PRIME EXAMPLE OF THE WIDE
TEMPERATURE SWINGS TYPICAL DURING SPRING IN THE GREAT LAKES.
SATELLITE IMAGERY AND MODEL ANALYSIS FIELDS INDICATE THE CLOUD FIELD
IS MOSTLY DRIVEN BY THE LOW LEVEL THERMAL TROUGH...BUT THERE IS A
COMPACT WAVE MOVING THROUGH THE NW FLOW ALOFT ASSOCIATED WITH THE
LEFT EXIT REGION OF THE UPPER JET. A SLIGHTLY DEEPER MOISTURE AND
VERTICAL MOTION PROFILE FORCED BY THESE FEATURES COULD PRODUCE A
BRIEF SPRINKLE OR LIGHT SHOWER CONFINED TO LAKE HURON AND THE THUMB
REGION THROUGH ABOUT SUNSET.

THE MAIN FORECAST CHALLENGE FOR TONIGHT INVOLVES CLOUD COVER
EVOLUTION AND THE ASSOCIATED IMPACTS ON TEMPERATURE. AS MENTIONED
ABOVE...THE CLOUDS ARE BEING ENHANCED BY THE LOW LEVEL THERMAL
TROUGH BUT ALSO BY THE SURFACE PRESSURE TROUGH OVER THE NORTHERN
GREAT LAKES THAT IS TIED TO THE COMPACT SHORT WAVE AND LARGER SCALE
TROUGH. AFTERNOON SATELLITE DATA AND SURFACE ANALYSES INDICATE THE
MODELS HAVE A REASONABLE HANDLE ON THE CLOUD PATTERN OVER THE GREAT
LAKES AND SHOW A REASONABLE EASTWARD PROGRESSION OF THE SUPPORTING
UPPER LEVEL FEATURES. EXPECT THE SURFACE TROUGH TO FILL AND THE LOW
LEVEL FLOW TO TRANSITION TOWARD A MORE NEUTRAL NORTHWEST
CONFIGURATION. THIS WILL ALLOW THE DRY AIR INDICATED OVER NORTHERN
ONTARIO TO FILTER THROUGH LAKE SUPERIOR AND NORTHERN LAKE HURON INTO
SE MICHIGAN TOWARD SUNRISE WEDNESDAY. THIS WILL RESULT IN A CLEARING
TREND FROM NORTH TO SOUTH BUT LIKELY TOO LATE TO HAVE A MEANINGFUL
IMPACT ON TEMPERATURES, ESPECIALLY WITH GRADIENT WIND REMAINING
ELEVATED ENOUGH TO PREVENT EFFECTIVE RADIATIONAL COOLING. THIS MAKES
GUIDANCE FOR MIN TEMPS NEAR 30 LOOK REASONABLE ACROSS THE REGION.

&&

.LONG TERM...

UPPER LEVEL NORTHWEST CONFLUENT FLOW IN PLACE ON WEDNESDAY...WITH
GOOD SUBSIDENCE/DRYING...PW VALUES LESS THAN QUARTER OF AN
INCH...WILL SUPPORT MOSTLY SUNNY/SUNNY SKIES OVER SOUTHEAST
MICHIGAN. LATE APRIL INSOLATION IS EXPECTED TO SUPPORT LOW TO MID
50S BASED ON 850 MB TEMPS AROUND -1 C...AS SURFACE HIGH IN PLACE
WILL TEND TO LIMIT MIXING AND COULD SEE LIGHT BREEZES OFF COLDER
LAKES AS WELL. SURFACE HIGH LOOKS TO BE LINGERING WEDNESDAY
EVENING/NIGHT...LIKELY ALLOWING FOR MINS TO DROP INTO THE 30S UNDER
FAVORABLE RADIATING CONDITIONS WITH REMNANT LOW LEVEL DRY AIR IN
PLACE. ALTHOUGH...THERE WILL BE AN INCREASE IN HIGH CLOUDS WHICH
SHOULD PREVENT TEMPS FROM MATCHING THE DEW PTS WHICH LOOK TO BE
RUNNING IN THE 20S. THIS LOW LEVEL DRY AIR WILL LIKELY KEEP US DRY
DURING THURSDAY...EVEN WITH WARM/MOIST ADVECTION RAMPING UP THROUGH
THE DAY. INCREASING LOW LEVEL SOUTHEAST FLOW OFF THE COLD WATERS OF
LAKE ERIE/ST CLAIR SHOULD KEEP MAXES A BIT SUPPRESSED (PREDOMINATELY
UPPER 50S)...ALTHOUGH THE REAL WARM AIR (70S) WILL NOT BE TOO FAR
FROM THE SOUTHERN MICHIGAN BORDER. SHOWERS ARE EXPECTED THURSDAY
NIGHT AS SHORTWAVE TROUGH AND ASSOCIATED MOISTURE PLUME/850-700 MB
THETA-E RIDGE AXIS MOVES THROUGH. PW VALUES SEEN RISING TO 1 INCH OR
SLIGHTLY BETTER. MEAGER MID LEVEL LAPSE RATES/SLIGHTLY POSITIVE
SHOWALTER INDEX SUPPORTS LEAVING OUT MENTION OF THUNDER...AS LOOKS
LIKE TRIPLE POINT WORKS ALONG THE SOUTHERN MICHIGAN BORDER...WITH
MAIN SURFACE LOW TRACKING NORTH THROUGH THE WESTERN GREAT LAKES.
PRONOUNCED MID LEVEL DRY SLOW WITH WESTERLY FLOW DURING
FRIDAY...SETTING US UP FOR SNEAKY WARM DAY WITH GOOD MIXING...AND
WITH EURO ADVERTISING 850 MB TEMPS 4-7 C...TEMPS WELL INTO THE
60S...IF NOT 70+ ARE CERTAINLY IN PLAY IF SKIES END UP MOSTLY
SUNNY...BUT THERE ARE SOME TIMING CONCERNS WITH SECONDARY COLD
FRONT. AT THIS POINT...WILL TIGHTEN UP THE NORTH-SOUTH GRADIENT.

AN UPPER LEVEL TROUGH AND FRONT SLIDING ACROSS THE NORTHERN GREAT
LAKES ON FRIDAY NIGHT WILL HELP TO ENHANCE RAIN SHOWER ACTIVITY
ACROSS SOUTHEAST MICHIGAN. RAIN SHOWERS COME TO AN END BY SATURDAY
AFTERNOON AS HIGH PRESSURE BUILDS BACK INTO THE AREA. NORTHEAST
WINDS WILL STICK AROUND THROUGH THE BEGINNING OF NEXT WEEK
ALLOWING HIGH TEMPERATURES TO ONLY RISE UP INTO THE LOW TO MID
50S. THE NEXT CHANCE FOR RAIN SHOWERS LOOKS TO ARRIVE AS EARLY AS
MONDAY MORNING BUT WITH THE LOW CONSISTENCY AMONG MODELS HAVE
STUCK WITH ONLY SLIGHT CHANCE POPS AND LOW CHANCE POPS IN THE
FORECAST FOR MONDAY NIGHT AND TUESDAY FOR NOW UNTIL THIS SYSTEM
CAN BE BETTER SAMPLED.

&&

.MARINE...

STRONG NORTHWEST FLOW OF 20 TO 30 KNOTS DURING THE AFTERNOON WILL
SLOWLY DIMINISH TONIGHT AS HIGH PRESSURE BUILDS INTO THE CENTRAL
GREAT LAKES THROUGH WEDNESDAY. WILL BE MAINTAINING THE SMALL
CRAFT ADVISORIES INTO EARLY WEDNESDAY MORNING...AS WAVES WILL BE
SLOW TO SUBSIDE ACROSS SOUTHERN LAKE HURON. THE PREVIOUSLY
MENTIONED HIGH WILL PRODUCE LIGHT WINDS WEDNESDAY AND WEDNESDAY
NIGHT. SOUTHEAST WINDS WILL INCREASE THURSDAY AS A LOW PRESSURE
SYSTEM MOVES INTO THE WESTERN GREAT LAKES...BUT WARMER AIR WILL
LEAD TO STABLE PROFILES THURSDAY NIGHT...HOLDING WINDS AROUND 25
KNOTS ACROSS MUCH OF LAKE HURON. WINDS WILL SWING AROUND THE WEST
ON FRIDAY AS COLDER AIR SLOWLY WORKS BACK INTO THE AREA...BUT
WINDS ARE EXPECTED TO REMAIN PREDOMINATELY BELOW 20 KNOTS.

&&

.AVIATION...ISSUED 1248 PM EDT TUE APR 22 2014

//DISCUSSION...

MVFR STRATOCU WILL BE WIDESPREAD OVER SE MICHIGAN BUT WILL MIX INTO
LOW END VFR CEILING DURING THE AFTERNOON. THIS WILL OCCUR AS MORE
COLD AIR IS CARRIED INTO THE REGION ON NORTHWEST WIND GUSTING TO
AROUND 25 KNOTS. THE WELL MIXED CONDITIONS WILL LAST FOR A FEW HOURS
AFTER SUNSET BEFORE CEILING FILLS IN AND LOWERS BACK INTO MVFR.
AFTERNOON OBSERVATIONS OVER THE NORTHERN GREAT LAKES SUPPORT MODEL
IMPLICATIONS THAT STRATUS WILL HOLD WITHIN THE COLD LOW LEVEL
THERMAL TROUGH DURING THE NIGHT. THERE IS SOME UNCERTAINTY
INTRODUCED TO THE CLOUD FORECAST BY THE DRYING INFLUENCE OF A MORE
NEUTRAL NW FLOW EVOLVING WITH TIME...BUT OBSERVATIONS ALSO SUPPORT
MODEL SOLUTIONS THAT SUGGEST IT WILL TAKE UNTIL WEDNESDAY MORNING
BEFORE DRY BOUNDARY LAYER AIR NORTH OF LAKE SUPERIOR CAN MOVE INTO
SE MICHIGAN AND SCOUR OUT THE LOW CLOUDS.

//DTW THRESHOLD THREATS...

* MODERATE CONFIDENCE IN CEILING BELOW 5000 FEET DURING MID
AFTERNOON THROUGH TONIGHT.

* HIGH CONFIDENCE IN WIND GUSTING AROUND 25 KNOTS FROM 310 DEGREES
THROUGH MID EVENING.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...OUTER SAGINAW BAY AND THE NEARSHORE WATERS
     FROM PORT AUSTIN TO HARBOR BEACH...UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM HARBOR BEACH TO PORT
     HURON...UNTIL 10 AM WEDNESDAY.

LAKE ST CLAIR...NONE.

MI WATERS OF LAKE ERIE...NONE.

&&

$$

SHORT TERM...BT
LONG TERM....SF/RK
MARINE.......SF
AVIATION.....BT


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