Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 291949
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
349 PM EDT WED APR 29 2015

.SHORT TERM...

CLOSED LOW OVER NORTHERN LAKE SUPERIOR WILL CONTINUE TO PROPAGATE
DUE SOUTH ROUGHLY PARALLEL TO THE EASTERN LAKE MICHIGAN SHORELINE
THROUGH THE SHORT TERM PERIOD. AXIS OF ENHANCED MID-LEVEL MOISTURE
CONTENT IS EVIDENT ON WATER VAPOR IMAGERY AND WILL BE ROTATING INTO
SOUTHEAST MICHIGAN DURING THE NEXT SEVERAL HOURS. A STEEP LAPSE RATE
ENVIRONMENT CHARACTERIZED BY H7-H5 LAPSE RATES OF 7.5 C/KM OR BETTER
LEADS THE LOW THE CENTER BY 150 MILES OR SO AND IS SUPPORTING AN
AGITATED CU FIELD ACROSS THE NORTHWEST CWA ALONG ITS LEAD EDGE. A
POOR COVERAGE AND INTENSITY OF SHOWERS CURRENTLY ACCOMPANIES THIS
MID-LEVEL BAROCLINIC ZONE DUE TO WEAK FORCING AND DRY AIR.

DEEP LAYER DEFORMATION IS FORECAST TO INTENSIFY WITHIN THE SOUTHEAST
QUADRANT OF THE LOW THROUGH THE NIGHT, A PROCESS JUST GETTING
UNDERWAY AS EVIDENCED BY COOLING CLOUD TOPS OVER SOUTHWEST LOWER
BETWEEN 17Z-20Z. SUPERPOSITION OF DEFORMATION FORCING AND STEEP
LAPSE RATES WILL SUPPORT SHOWERS DEVELOPING OVER THE SOUTHEAST CWA
TONIGHT. FAIRLY HIGH UNCERTAINTY REGARDING COVERAGE, EXCEPT TO SAY
THAT IT WILL BE HIGHEST DURING THE LATTER HALF OF THE OVERNIGHT. THE
RAP IS QUITE AGGRESSIVE COVERAGE-WISE BUT APPEARS TO NOT BE GIVING
DRY AIR NEARLY ENOUGH CREDIT. SIMILAR CASE WITH THE NAM, BUT NOT AS
SEVERE. STILL NO REASON NOT TO EXPECT SHOWERS IN DETROIT AND
VICINITY, BUT WEAKER FORCING ELSEWHERE WILL REALLY STRUGGLE TO
PRODUCE ANYTHING BUT VIRGA - RAP/HRRR NOTWITHSTANDING. NUDGED POPS
FURTHER INTO THE LIKELY CATEGORY ACROSS THE EASTERN TIER BUT
REMAINED CONSERVATIVE ELECTING INSTEAD TO LEAVE ROOM FOR ADJUSTMENT
ONCE THE SCENARIO BETTER SHOWS ITSELF. LOWS NEAR 40 ARE
REASONABLE...MID 40S ACROSS THE EAST WHERE CLOUDS WILL BE THICKEST
AND MOST PERSISTENT.

&&

.LONG TERM...THURSDAY THROUGH NEXT WEDNESDAY

WELL DEFINED CLOSED UPPER LOW WILL ADVANCE SOUTH OVER THE OHIO
VALLEY REGION ON THURSDAY. GOOD DEFORMATION FORCING THROUGHOUT THE
NORTHEAST QUADRANT OF THE CIRCULATION WILL SET THE STAGE FOR
CONTINUED SHOWER PROSPECTS OVER PORTIONS OF SOUTHEAST MICHIGAN.

THE NWP SUITE IS STRUGGLING WITH COMING TO AN AGREEMENT ON THE
AMOUNT OF AVAILABLE MOISTURE FOR SHOWER PRODUCTION. THE 29.12Z NAM
IS THE MOST AGRESSIVE...WITH EVERYTHING ELSE INDICATING A LESS
BULLISH OUTCOME - EVEN A DRY RUN OR TWO FROM WHICH TO CHOOSE. EXPECT
THE FAVORABLE DEEP LOWER STABILITY THERMODYNAMICS ASSOCIATED WITH
THE COLD POOL ALOFT WILL ENCOURAGE SCATTERED SHOWER ACTIVITY WITHIN
THE DEFORMATION AXIS. BEST CHANCE FOR SHOWERS WILL BE ACROSS THE
DETROIT METRO REGION...WITH DIMINISHING CHANCES NORTH AND WEST.
TEMPERATURES WILL BE TEMPERED BY THE CLOUDS AND SHOWERS...LINGERING
MAINLY IN THE 50S.

AS THE UPPER LOW EXITS STAGE SOUTH...A PROGRESSIVE JETLET CURRENTLY
OVER THE EASTERN PACIFIC WILL DRIVE EAST ALONG THE 49TH PARALLEL.
THIS WAVE WILL PILE INTO THE NORTHERN PLAINS RIDGE...FORCING IT TO
BREAK ACROSS THE REGION FRIDAY AND SATURDAY. THE SUBSIDENCE
ASSOCIATED WITH THE BREAKING SHORTWAVE RIDGE WILL KEEP CONDITIONS
QUIET AND ALLOW TEMPS TO RETURN TO THE VALUES OBSERVED THE PAST
COUPLE OF DAYS. ONLY SOME DIURNAL CUMULUS EXPECTED FRIDAY AND
THICKENING HIGH CLOUDS ON SATURDAY.

HIGH INDEX FLOW REGIME ALONG THE SOUTHERN FLANK OF AN ARCTIC
LONGWAVE TROUGH SETS UP ACROSS THE NORTHERN TIER FOR THE END OF THE
WEEKEND. RETURN MOIST FLOW OVER THE SOUTHERN AND CENTRAL PLAINS WILL
LICK EASTWARD IN THE REGION LATE SUNDAY AND WILL LINGER.
EXPECTATIONS ARE FOR A MILD AND PERIODICALLY WET PERIOD SUNDAY
THROUGH WEDNESDAY.

&&

.MARINE...

WEAK HIGH PRESSURE DRIFTING THROUGH THE CENTRAL GREAT LAKES WILL
MAINTAIN A LIGHTER WIND FIELD AND LOW WAVE CONDITIONS THROUGH TODAY.
PROLONGED PERIOD OF LIGHT NORTH TO NORTHEAST FLOW EXPECTED THROUGH
THE END OF THE WEEK.  THIS MAY PROVIDE A FAVORABLE ENVIRONMENT FOR
GREATER WAVE GROWTH UNDER LONG DURATION ONSHORE FLOW.

&&

.AVIATION...ISSUED 107 PM EDT WED APR 29 2015

CONVERGENCE AXIS IN THE DETROIT AREA HAS SUPPORTED DEVELOPMENT OF
SCT-BKN CIGS AROUND 6KFT. THIS ACTIVITY COULD GIVE RISE TO A FEW
SHOWERS DURING LATE AFTERNOON BUT AT THIS TIME COVERAGE IS EXPECTED
TO BE RATHER SPARSE. IN THE MEANTIME, EXPANSION OF THIS HIGH-BASED
CU WILL CONTINUE AS INLAND TROUGHING INCREASES WITH PEAK HEATING.
DEEPER MOISTURE WILL ARRIVE AFTER 00Z. PERSISTENT FORCING WITH A
SMALL SPATIAL FOOTPRINT WILL POTENTIALLY BRING SEVERAL HOURS OF -
SHRA TO SMALL AREA OVERNIGHT. BEST CHANCES ATTM ARE IN THE DETROIT
AREA. CIGS WILL EVENTUALLY DETERIORATE TO MVFR AS FORCING INCREASES
AFTER MIDNIGHT.

FOR DTW...CIGS AOB 5KFT WILL BE POSSIBLE WITHIN THE EXPANDING CU
DECK THIS AFTERNOON. DRY LOWER LEVELS AND A CONTINUING OF DIURNAL
BOUNDARY LAYER GROWTH SPELL LOW CONFIDENCE, HOWEVER, IN CIGS COMING
DOWN MUCH LOWER THAN THEY ALREADY ARE. THUS, WILL LEAVE MENTION OF
5KFT CIG OUT OF THE TAF FOR NOW.

//DTW THRESHOLD PROBABILITIES...

* LOW FOR CIGS AOB 5KFT THIS AFTERNOON. HIGH AFTER 02Z.

&&

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

$$

SHORT TERM...JVC
LONG TERM....MANN
MARINE.......MANN
AVIATION.....JVC


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


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