Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 240204
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1004 PM EDT THU OCT 23 2014

.UPDATE...

THE UPSTREAM HIGH CLOUDS HAVE BEEN STRUGGLING TO ADVANCE TOO FAR
INTO SE MI IN LIGHT OF THE SHARP MID LEVEL RIDGING HOLDING OVER
THE EASTERN GREAT LAKES. THIS RIDGE WILL BREAK DOWN OVERNIGHT AND
EVENTUALLY ALLOW THE MID AND HIGH CLOUDS NOW BLANKETING THE
WESTERN HALF OF THE STATE TO MAKE THEIR WAY EAST OVERNIGHT. THE
MORE PROLONGED CLEARING THIS EVENING /ESPECIALLY ACROSS THE THUMB/
WILL WARRANT A SLIGHT DOWNWARD ADJUSTMENT TO MIN TEMPS OVERNIGHT.

&&

.AVIATION...ISSUED 701 PM EDT THU OCT 23 2014

//DISCUSSION...

VERY DRY AIR ASSOCIATED WITH WEAK HIGH PRESSURE OVER SE MI WILL
MAINTAIN CEILINGS BELOW 12K FT THROUGH MOST OF THE NIGHT. THE SFC
TROUGH NOW PUSHING INTO LAKE MI WILL WEAKEN AS IT WORKS INTO LOWER
MI TONIGHT INTO FRIDAY. SO THE CHANCES OF RAIN WILL GREATLY DIMINISH
AS THE SYSTEM APPROACHES. AN INCREASE IN LOWER BASED CLOUDS /MAINLY
IN THE 2500 TO 5000 FT RANGE/ ARE HOWEVER EXPECTED TO ADVANCE INTO
THE TERMINALS TOWARD DAYBREAK AND PERSIST OFF AND ON DURING THE DAY
FRIDAY.

//DTW THRESHOLD THREATS...

* MEDIUM CONFIDENCE ON CEILINGS BELOW 5000 FEET FRIDAY.

&&

.PREV DISCUSSION...ISSUED 352 PM EDT THU OCT 23 2014

SHORT TERM... AFTERNOON AND TONIGHT

A PLEASANT FALL LATE AFTERNOON AND EVENING IS IN STORE FOR SE
MICHIGAN AS HIGH PRESSURE DRIFTS EASTWARD ACROSS THE REGION. THE
SURFACE HIGH WILL GIVE WAY TO INFLUENCE FROM THE NEXT WAVE OF LOW
PRESSURE SLIDING THROUGH THE MIDWEST AND NORTHWEST ONTARIO...BUT
THIS SYSTEM WILL BRING LITTLE MORE THAN AN INCREASE IN CLOUDS AND
PERHAPS EVIDENCE OF VIRGA ON RADAR LATE TONIGHT. TEMPERATURES WILL
FOLLOW THE TYPICAL EVENING SLIDE AFTER SUNSET BUT THEN STABILIZE
OVERNIGHT AS CLOUDS THICKEN FOR MINS RANGING FROM THE MID 30S TO
AROUND 40.

AFTERNOON SATELLITE IMAGERY AND RADAR MOSAICS SUPPORT MODEL ANALYSIS
FIELDS THAT INDICATE A WELL DEVELOPED UPPER TROUGH EXTENDING FROM
CENTRAL CANADA THROUGH THE MIDWEST. DISTINCT CIRCULATIONS AND
FILAMENTS OF DEFORMATION WITHIN THE TROUGH ARE WELL RESOLVED IN THE
500 MB VORTICITY FIELD AMONG THE MODEL SOLUTIONS WITHIN AN OTHERWISE
PEDESTRIAN UPPER JET CIRCULATION DOWNSTREAM OF THE TROUGH AXIS.
THE PRIMARY FORCING FOR THE SHOWERS OVER THE MIDWEST DEPICTED IN
RADAR MOSAICS IS A COMBINATION OF DCVA AND MID LEVEL THETA-E
ADVECTION...THE BULK OF WHICH REMAINS WELL WEST OF OUR AREA DURING
THE NIGHT. DRY AIR IN THE LOW LEVELS IS EXPECTED TO REMAIN
SUBSTANTIAL ENOUGH TO ERODE ANY LIGHT RAIN WITH MID LEVEL ORIGINS
WHICH ADDS CONFIDENCE TO THE DRY FORECAST BUT IT WILL DO LITTLE TO
STOP THE SUBSTANTIAL INCREASE IN HIGH CLOUDS THAT WILL PRECEDE THE
PRIMARY MID LEVEL MOISTURE AXIS. THESE CLOUDS WILL BE THE MAIN
INFLUENCE ON OUR WEATHER DURING THE NIGHT...WHICH ALONG WITH LIGHT
SOUTHWEST WIND...WILL HELP BUOY MIN TEMPERATURES IN THE MID 30S TO
AROUND 40...WHICH IS ABOUT 10 DEGREES WARMER COMPARED TO LAST
NIGHT.

LONG TERM...

SHORTWAVE TROUGH CURRENTLY OVER THE UPPER MS RIVER VALLEY/WESTERN
GREAT LAKES WILL CONTINUE TO MIGRATE WITHIN PREVAILING WESTERLY FLOW
OVER THE NEXT 24-36 HOURS. AS NOTED ON WV IMAGERY, THE TROUGH IS
ANCHORED ON THE NORTHERN END BY A CLOSED CIRCULATION OVER SOUTHERN
CANADA ALONG WITH A SECOND CIRCULATION OVER WISCONSIN THIS EVENING.
STRONGLY DIFFLUENT FLOW IN ADVANCE OF A 150+KT JET MAX FROM THE
PACIFIC NW WILL CAUSE THE TROUGH TO FRACTURE INTO TWO SEPARATE
WAVES WITH SE MICHIGAN POISED TO BE POSITIONED SAFELY BETWEEN
THEM. THIS WILL RESULT IN NOTHING MORE THAN MEAGER THETA-E
ADVECTION AND SPILL- OVER OF REMNANT CLOUD DEBRIS FOR SATURDAY.
FAVORED THE 12Z GUIDANCE WHICH OFFERS A SLOWER INTRUSION OF CLOUDS
AND A VIRGA TYPE SCENARIO THAT WILL STRUGGLE TO PRODUCE ANYTHING
THAT REACHES THE GROUND.

MID-LEVEL SUBSIDENCE WILL INCREASE FRIDAY NIGHT INTO SATURDAY AS
THIS WAVE DEPARTS AND A MUCH STRONGER SHEAR MAX ON THE NORTHERN
PERIPHERY OF THE AFOREMENTIONED JET BEGINS TO CLOSE OFF UPSTREAM.
THE RESULTANT RAMP UP OF 925-850MB THETA-E ADVECTION WILL HELP
REINFORCE THE MID-LEVEL SUBSIDENCE INVERSION. 12Z GUIDANCE INDICATE
A HEALTHY AMOUNT OF MOISTURE TRAPPED BENEATH THE 900MB LEVEL FOR THE
BALANCE OF THE DAYTIME HOURS. THIS SEEMS ADEQUATE TO WARRANT A
CONSIDERABLY MORE PESSIMISTIC CLOUD COVER FORECAST FOR SATURDAY. THE
HEALTHY SOUTHWEST GRADIENT SHOULD BE SUFFICIENT, HOWEVER, TO BUMP
H85 TEMPS UP TO 10C AND SURFACE TEMPS UP TO 60-65 EVEN IN A POORLY
MIXED ENVIRONMENT. THE STRENGTHENING WIND FIELD WILL SUPPORT GUSTS
OF 20 MPH. SHOWERS IN ADVANCE OF THE COLD FRONT ARE A POOR BET AT
THE MOMENT WITH THE BEST FORCING PROGGED TO REMAIN TO OUR NORTH AND
EAST. NONETHELESS, THE RELATIVELY CLOSE PROXIMITY OF RATHER POTENT
DYNAMICS WARRANTS MONITORING, ESPECIALLY GIVEN THAT THE BULK OF THE
ASSOCIATED REMAINS OFFSHORE ATTM. FOR NOW, THE FORECAST REMAINS DRY
THROUGH THE FIRST HALF OF THE WEEKEND. COLD AND DRY ADVECTION WILL
GET UNDERWAY ON SATURDAY EVENING SENDING DEWPOINTS DOWN ABOUT 20
DEGREES FROM THEIR DAYTIME PEAK VALUES AND HELPING OVERNIGHT LOWS
SETTLE NEAR 40 DEGREES...AVERAGE FOR LATE OCTOBER.

EXPECTING A PLEASANT FALL DAY SUNDAY WITH DIMINISHING
WINDS...THOUGH COOLER COMPARED TO SATURDAY AS THE LOW LEVEL THERMAL
FIELD IS SLOW TO RECOVER FROM SATURDAY/S FRONTAL PASSAGE. WARM
ADVECTION ENSUES IN EARNEST SUNDAY NIGHT INTO MONDAY AS UPPER RIDGE
BUILDS IN RESPONSE TO UPSTREAM NEAR-FULL LATITUDE TROUGH OVER
INTERMOUNTAIN WEST. RATHER MILD MONDAY AND TUESDAY WITH 850 MB TEMPS
OF 12-14C ADVERTISED. GLOBAL MODELS AND GEFS MEMBERS HAVE COME INTO
A LITTLE BETTER AGREEMENT WITH THIS TROUGH...SHOWING IT ASSUMING A
NEGATIVE TILT NORTHWEST OF THE LOCAL AREA AND DRAGGING A COLD FRONT
THROUGH SE MI. STILL TARGETING TUESDAY/TUESDAY NIGHT FOR HIGHEST
LIKELIHOOD OF PRECIP...WITH A COOL-DOWN FOR WEDNESDAY POST FRONT.

MARINE...

A TRANQUIL WIND REGIME WILL GIVE WAY TO DEVELOPING MODERATE
SOUTHWEST FLOW ON SATURDAY IN ADVANCE OF AN APPROACHING SYSTEM. THE
ASSOCIATED COLD FRONT WILL TRAVERSE AREA WATERS SATURDAY AFTERNOON
INTO SUNDAY EVENING. WINDS WILL QUICKLY TURN NORTHWEST AND BECOME
FRESH TO STRONG...ESPECIALLY OVER THE OPEN WATERS OF CENTRAL LAKE
HURON...WITH GUSTS TO NEAR-GALES LIKELY OVER THE NORTHERN HALF OF
LAKE HURON ON SATURDAY NIGHT. A GUSTY MODERATE TO FRESH NORTHWEST
BREEZE WILL THEN PERSIST ACROSS THE WATERS THROUGH SUNDAY.

&&

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

&&

$$

UPDATE.......SC
AVIATION.....SC
SHORT TERM...BT
LONG TERM....JVC/DT
MARINE.......JVC


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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).



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