Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 140353
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1153 PM EDT SUN JUL 13 2014


.AVIATION...

//DISCUSSION...

A SLOW MOVING FRONTAL BOUNDARY WILL EXTEND ACROSS SE MI MON MORNING
INTO LATE AFTERNOON. THIS FRONT WILL SUSTAIN SOME WIDELY SCATTERED
SHOWERS DURING THE EARLY MORNING HOURS. ENOUGH LOW LEVEL DRY AIR IS
PRESENT TO WHERE BASES WILL REMAIN VFR. DAYTIME HEATING WILL MAKE
SHOWERS AND A FEW THUNDERSTORMS POSSIBLY BY LATE MONDAY
AFTERNOON...PARTICULARLY SOUTH OF PTK WHERE INSTABILITY IS EXPECTED
TO BE HIGHER.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE IN THUNDERSTORM POTENTIAL LATE MONDAY AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 855 PM EDT SUN JUL 13 2014

UPDATE...

SOME SHOWERS MANAGED TO DEVELOP THIS EVENING ALONG A MID LEVEL
MOISTURE GRADIENT. THIS GRADIENT NOW EXTENDS FROM NRN IL INTO CNTRL
LOWER MI AND THE THUMB REGION. THESE SHOWERS FLARED UP TOWARD THE
END OF THE DIURNAL HEATING CYCLE. THE 00Z DTX SOUNDING SHOWED A
CAP IN THE 650-450MB LAYER. THIS IS LIKELY THE REASON THE
SHOWERS... WHICH HAVE BEEN IMPACTING PORTIONS OF THE SAGINAW
VALLEY/THUMB... HAVE BEEN FAIRLY LOW TOPPED. ALTHOUGH VERY
LOCALIZED...RADAR HAS SUGGESTED SOME FAIRLY GOOD RAIN RATES OUT OF
SOME OF THESE SHOWERS. WHILE THERE IS LIKELY TO BE SOME
DIMINISHING TREND TO THE ONGOING REGION OF SHOWERS AS NOCTURNAL
COOLING SETS IN...THERE HAS BEEN SOME INCREASE NOTED IN RADAR
RETURNS OVER SRN LAKE MI. THE MID LEVEL MOISTURE GRADIENT WILL
SLOWLY SINK SOUTH INTO THE REMAINDER OF THE FORECAST AREA
TONIGHT...WITH SOME UPPER JET SUPPORT SPREADING ACROSS SRN MI.
THIS ALONG WITH RADAR TRENDS OVER SRN LAKE MI WILL SUPPORT A
SLIGHT INCREASE IN POPS DURING THE REMAINDER OF THE EVENING AND
INTO THE OVERNIGHT.

PREV DISCUSSION...ISSUED 358 PM EDT SUN JUL 13 2014

SHORT TERM...THIS AFTERNOON AND TONIGHT

THE MAIN FEATURE TO NOTE IS THE EDGE OR GRADIENT OF THE CLOSED
HEIGHT ANOMALY WHICH IS NOW IN PLACE OVER THE NORTHERN GREAT
LAKES...EDGING THROUGH NORTHERN LOWER MICHIGAN. IT IS BEHIND THIS
BOUNDARY WHERE THE COOL MIDLEVEL AIR RESIDES. MODELS SUGGEST THE
ANOMALY AND CORRESPONDING LEAD EDGE WILL VIRTUALLY STALL OUT OVER
THE NEXT 12 TO EVEN 24 HOURS AS TWO COMPETING VORTICITY MAXIMA
WITHIN THE CLOSED LOW SHEAR AWAY FROM EACH OTHER. THIS WILL
ESSENTIALLY INCREASE THE WAVELENGTH OF THE CLOSED LOW AND TAKE THE
STEAM OUT OF ITS EQUATERWARD MIGRATION. THUS...RELATIVELY HIGHER LOW
LEVEL THETA E CONTENT WILL PERSIST OVER THE STATE. NWP IN VARIOUS
SOLUTIONS...HAS BEEN SHOWING SOME LIGHT PRECIPITATION POTENTIAL
FIRST ALONG THE GRADIENT THIS AFTERNOON/EARLY EVENING ACROSS
PORTIONS OF NORTHERN LOWER MICHIGAN DOWN INTO THE TRI CITIES AND
SAGINAW BAY AREA...THEN OVER THE SOUTHERN TWO THIRDS OF THE CWA
BETWEEN 6-12Z TONIGHT. FROM A BROAD LOOK THIS IS A GOOD LOCATION FOR
A SECONDARY JET MAXIMUM AND INCREASED DEFORMATION. HOWEVER...THE
PROBLEM IS OBSERVATIONAL AND NWP DATASETS ARE NOT REALLY SHOWING
ANYTHING. GIVEN VERY DRY AIR IN PLACE ABOVE 700MB....ANY POTENTIAL
REMAINS VERY LOW. ONE CAN WATCH UPSTREAM THIS EVENING OVER SOUTHERN
WISCONSIN WHERE SOME INITIATION IS PROGGED DURING THE AFTERNOON. IT
WOULD BE THAT ACTIVITY THAT COULD FUNNEL EASTWARD AND ADVECT INTO
THE CWA THE LATTER HALF OF TONIGHT. DECIDED TO LIMIT ANY LIQUID
MENTION AS A CHANCE OF SPRINKLES. LOWS TONIGHT ARE EXPECTED TO BE
RELATIVELY MILD...UPPER 50S NORTH TO THE MID 60S IN THE DETROIT
URBAN HEAT ISLAND.

LONG TERM...

CYCLONICALLY CURVED MID-LEVEL MOISTURE AXIS IS EVIDENT ON THIS
AFTERNOON`S WV IMAGERY AND MODEL MOISTURE FIELDS STRETCHING FROM
ALBERTA INTO THE UPPER MISSISSIPPI VALLEY. EXPANDING CLOUD COVERAGE
AND SCATTERED SHOWERS DEVELOPING OVER EASTERN NEBRASKA AT 19Z ARE
SYMPTOMATIC OF A LOW AMPLITUDE SHORTWAVE THAT IS FORECAST TO
PROPAGATE INTO THE AREA MONDAY MORNING. IN CONJUNCTION WITH
INCREASING BACKGROUND 310K ISENTROPIC ASCENT, THE WAVE MAY BE
SUFFICIENT TO TRIGGER A FEW SHOWERS ACROSS THE NORTHEAST HALF OF THE
CWA DURING THE MORNING, ESPECIALLY WITH THE HELP OF A LATE MORNING
BOOST TO DIURNAL HEATING. THE BETTER CHANCE FOR SHOWERS LOOKS TO BE
CONFINED TO THE FAR EASTERN AND SOUTHERN PORTION OF THE CWA ALONG
AND AHEAD OF THE 500MB FRONTAL ZONE. THE MID-LEVEL THETA-E GRADIENT
WILL SHARPEN CONSIDERABLY AS LONGWAVE TROUGH AMPLIFICATION GETS
UNDERWAY ACROSS THE GREAT LAKES. REORIENTATION OF THE FRONTAL ZONE
ALONG A SW-NE AXIS WILL ALLOW MODEST MOISTURE TRANSPORT TO SPREAD
INTO THE METRO AREA AND POINTS SOUTH. INCREASING COVERAGE OF SHOWERS
IS LIKELY ALONG/AHEAD OF THE CONVERGENT AXIS WITHIN THE BACKGROUND
OF INCREASING LARGE SCALE ASCENT. BUMPED POPS UP INTO THE HIGH
CHANCE CATEGORY FOR THE MOST PART, AND A FURTHER INCREASE MAY YET BE
NECESSARY. THE EXPECTED SHARP CUTOFF DEPICTED BY THE ECMWF AND
HIGH-RES ARW/NMM, HOWEVER, PRECLUDES GOING ANY HIGHER WITH POPS AT
THIS TIME. ONGOING HEIGHT FALLS WILL EASE THE MID-LEVEL FRONT SOUTH
OF THE AREA MONDAY EVENING, BRINGING AN END TO ANY SHOWER ACTIVITY.

A BRIEF BREAK IN FORCING WILL ENSUE, BUT AN UNSEASONABLY STRONG PV
ANOMALY WILL ROTATE ACROSS THEN AREA MONDAY NIGHT INTO TUESDAY
TRIGGERING CYCLOGENESIS EAST OF THE CWA, MOST LIKELY INVOF SOUTHERN
ONTARIO IF THE 12Z NWP ARE TO BE BELIEVED. SOLUTION SPACE REMAINS
RATHER LARGE AT THIS TIME, THOUGH THE TENDENCY TOWARD CONSENSUS ON
THE LOCATION OF CYCLOGENESIS ADDS SOME CONFIDENCE TO THE 12Z ECMWF
TREND OF INCREASING DEFORMATION WRAPPING AROUND THE SURFACE INTO
TUESDAY. TRENDED THE FORECAST IN THIS DIRECTION BY RAISING POPS
ACROSS THE BOARD, ESPECIALLY ACROSS THE NORTH. HOWEVER, GIVEN THE
STRENGTH OF LARGE SCALE FORCING AND THE PRESENCE OF THE COLD
POOL/STEEP LAPSE RATES ALOFT, FIGURE EXPANSION OF SHOWER ACTIVITY
DURING THE DAYTIME HOURS ON TUESDAY IS A PRETTY GOOD BET REGARDLESS
OF THE FINER DETAILS OF POTENTIAL DEFORMATION.

THE AREA WILL STILL BE WITHIN THE UPPER LEVEL TROUGH OVERNIGHT
WEDNESDAY AS IT CONTINUES TO SHIFT OFF TO THE EAST.  RIDGING ALONG
WITH SURFACE HIGH PRESSURE FROM THE PLAINS STARTS BUILDING IN
BEHIND THE DEPARTING TROUGH ON THURSDAY.  THIS WILL BRING A PERIOD
OF QUIETER CONDITIONS THROUGH THE END OF THE WEEK.  MODELS ARE THEN
HINTING AT A SHORTWAVE TRACKING UP THROUGH THE AREA BEGINNING THIS
NEXT WEEKEND WHICH MAY BRING THE NEXT PRECIPITATION POTENTIAL.
TEMPERATURES IN THE EXTENDED SLOWLY BEGIN WARMING UP TO NEAR 80 BY
SATURDAY.

MARINE...

A FEW THUNDERSTORMS WILL BE POSSIBLE AS A FRONT SAGS THROUGH THE
AREA ON MONDAY...MAINLY FOR THE SOUTHERN WATERS OF LAKE HURON AND
POINTS SOUTH. COVERAGE IS EXPECTED TO BE MINIMAL...HOWEVER...AND
WINDS WILL REMAIN ON THE LIGHT SIDE THROUGH MONDAY NIGHT. MUCH
COOLER AIR WILL THEN SPREAD INTO THE AREA THROUGH TUESDAY BRINGING
WITH IT AN INCREASE IN WESTERLY WINDS WHICH MAY GUST TO 20 KNOTS ON
TUESDAY AFTERNOON...MAINLY FOR NEARSHORE AREAS. SMALL CRAFT ADVISORY
CONDITIONS MAY BE ACHIEVABLE DURING THE DAYTIME HOURS TUESDAY. IN
ADDITION...THE COOLER AIR WILL CREATE AN ENVIRONMENT FAVORABLE FOR
WATERSPOUTS OVER AREAS OF WARMER WATER...NAMELY THE SOUTHERN HALF OF
LAKE HURON...LAKE SAINT CLAIR...AND LAKE ERIE. A CHANCE OF
WATERSPOUTS HAS BEEN ADDED TO THE FORECAST FOR THESE AREAS.

&&

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

&&

$$

AVIATION.....SC
UPDATE.......SC
SHORT TERM...CB
LONG TERM....JVC/SS
MARINE.......JVC


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