Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 181714
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
114 PM EDT MON AUG 18 2014


.AVIATION...

//DISCUSSION...

A RIDGE OF HIGH PRESSURE WILL HOLD FOR THE FIRST HALF HALF OF THE
TAF PERIOD...BUT ENOUGH LOW LEVEL MOISTURE AROUND THIS AFTERNOON TO
SUPPORT SCT TO BKN LOW VFR CEILINGS. A LOW PRESSURE SYSTEM ENTERING
THE WESTERN GREAT LAKES TONIGHT WILL THEN LEAD TO AN INCREASING
CHANCE OF SHOWERS AND THUNDERSTORMS LATE TONIGHT INTO
TOMORROW...WITH SHOWERS AND EMBEDDED THUNDERSTORMS LIKELY BY
TOMORROW AFTERNOON. A FURTHER INCREASE IN MOISTURE TONIGHT SHOULD
SUPPORT CEILINGS AT OR BELOW 5000 FEET BY SUNRISE TUESDAY.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE CEILINGS WILL BE AOB 5000 FEET THROUGH
  TONIGHT...MEDIUM CONFIDENCE TOMORROW MORNING.

* LOW CONFIDENCE IN THUNDERSTORMS TOMORROW.

&&

.PREV DISCUSSION...ISSUED 346 AM EDT MON AUG 18 2014

SHORT TERM...TODAY AND TONIGHT

A STRATOCU FIELD HAS ADVECTED IN FROM THE NORTHWEST...HALTING MUCH
OF THE FOG PRODUCTION THAT WAS ONGOING EARLIER IN THE NIGHT. WITH
THIS CLOUD FIELD EXPECTED TO REMAIN THIS MORNING...HAVE CUT BACK ON
THE FOG BY REMOVING IT FROM THE SOUTH AND GOING FROM AREAS OF TO
PATCHY ACROSS THE NORTH WHERE SOME LIGHT FOG STILL LINGERS.

FOR THE REST OF THE DAY THINGS LOOK FAIRLY QUIET AS LOW PRESSURE
DEVELOPS OVER THE UPPER MISSISSIPPI VALLEY. WHILE THERE IS SOME
LIGHT QPF DEVELOPMENT ACROSS THE SOUTHERN CWA THIS AFTERNOON
ASSOCIATED WITH SOME LOW LEVEL MOISTURE...MODEL CROSS SECTIONS DO
NOT SHOW THE FORCING NECESSARY TO PRODUCE LIGHT RAIN SHOWERS.
THEREFORE WILL CONTINUE TO LEAVE THE CWA DRY DURING THE DAYTIME
HOURS.

THINGS CHANGE A BIT OVERNIGHT AS THE AFOREMENTIONED LOW SLIDES EAST
TOWARDS THE WESTERN GREAT LAKES. THIS WILL SATURATE THE COLUMN
ACROSS SOUTHEAST MICHIGAN OVERNIGHT AS A SURFACE WARM FRONT LIFTS
NORTH...A SHORTWAVE TRACKS THROUGH THE SOUTHERN GREAT LAKES AND LOW
LEVEL THETA-E ADVECTION TRACKS IN FROM THE WEST.  THE SOONER ARRIVAL
OF THESE FEATURES WILL LEAD TO RAIN CHANCES BEING INTRODUCED ACROSS
THE AREA AFTER MIDNIGHT WITH BETTER CHANCES AS TUESDAY MORNING
ARRIVES.

LONG TERM...TUESDAY THROUGH SUNDAY

A WEAK AN UNORGANIZED LOW PRESSURE SYSTEM WILL PLAGUE THE REGION
WITH UNSETTLED WEATHER FOR THE MIDDLE PORTION OF THE WEEK. THE UPPER
LEVEL ENERGY WILL BE HARBORED INSIDE OF A PSEUDO PLANETARY SCALE
RIDGE STRUCTURE. THEREFORE...THE LOW WILL BE DETACHED FROM ANY
SIGNIFICANT WESTERLIES AND WILL PROVE TO BE SLUGGISH AND SLOW MOVING.

FORCING ARRIVES AT THE START OF THE PERIOD TUESDAY AND WILL BE
OVERHEAD THROUGHOUT THE DAY. OVERALL...MODEL DATA SUGGESTS A FAIRLY
WELL STRUCTURED SWATH OF PRECIPITATION LIFTING NORTH AND EASTWARD
DURING THE LATE MORNING AND AFTERNOON. PROBLEM IS FORCING IS NOT
STRONG...NOR CLEAN...WITH THE FORECAST SOUNDINGS SHOWING NOTHING IN
THE WAY OF A GOOD FRONTAL INVERSION STRUCTURE. BEST GUESS ON FORCING
WILL BE VERY BROAD SYNOPTIC SCALE ASCENT TYPE...AS SOME LEAD AND
DIFFUSE SHORTWAVE ENERGY UNDERCUTS THE MAIN PV ANOMALY AND GETS
CAUGHT AND STRUNG OUT IN THE FAVORABLE ZONE OF UPPER LEVEL SHEARING
DEFORMATION. USUALLY SEE SOME GOOD ISENTROPIC ASCENT HERE IN THE
LEAD WING...BUT THE FAVORABLE SIGNAL IS NOT THERE. SO...EXPECTING
MAINLY PRE-EXISTING PRECIPITATION TO TRACK THROUGH THE CWA DURING THE
DAY...AND NOT ANTICIPATING MUCH FLARE UP IN ACTIVITY DURING THE
AFTERNOON. PWATS ARE NOTEWORTHY INCREASING TO IMPRESSIVE 1.80 INCHES
DURING THE AFTERNOON. ATTM...NOT CALLING FOR A HEAVY RAIN
THREAT...BUT WILL NEED TO GET A BETTER HANDLE ON POTENTIAL LONGER
DURATION OF PRECIPITATION FOR THE NORTHEASTERN CWA...PARTICULARLY
THE THUMB. THIS IS WHERE A PIVOT POINT MAY SETUP. SLOW ARRIVAL OF
NEAR SURFACE WARM FRONT ALONG WITH CLOUDS SHOULD HOLD TEMPERATURES
IN THE 70S TO NEAR 80 DEGREE MARK.

THE UPPER LEVEL LOW WILL SLOWLY MEANDER INTO SOUTHEASTERN MICHIGAN
BY WEDNESDAY AFTERNOON. THE SOLUTIONS ARE EXTREMELY NOISY WHICH
MAKES PINPOINTING CHANCES/TIMING DIFFICULT FROM TUESDAY NIGHT
THROUGH WEDNESDAY EVENING. DID NOT FEEL COMFORTABLE GOING ABOVE A
HIGH CHANCE POP. LARGE SCALE FORCING SEEMS IT WILL MAXIMIZE
WEDNESDAY AFTERNOON WITH THE CLOSED HEIGHT ANOMALY AND VORTICITY
MAXIMUM DIRECTLY HITTING THE CWA. GIVEN PRIME PLACEMENT OF WARM AIR
ADVECTION OCCURRING AHEAD OF THE LOW...CONDITIONS ON WEDNESDAY
SHOULD BE VERY MUGGY...HIGHS CLIMBING TO 80 DEGREES WITH DEWPOINTS
PUSHING 70 DEGREES.

UPPER LEVEL RIDGE IS THEN EXPECTED TO AMPLIFY OVER THE MIDWEST FOR
THE END OF THE WEEK AND INTO THE WEEKEND. MODELS ARE FAIRLY SET IN
SLOWING THE PROGRESSION OF THE HIGHEST THETA E INTO THE CENTRAL
GREAT LAKES. THE IMPORTANCE OF THIS IS THAT PRECIPITATION CHANCES
SHOULD HOLD OFF WITH THE INSTABILITY MAXIMUM REMAINING TO THE
SOUTHWEST. A GOOD STRETCH OF SUMMER WEATHER WITH DRY CONDITIONS AND
TEMPERATURES CLIMBING ABOVE 80 DEGREES...FRIDAY/SATURDAY/SUNDAY.

MARINE...

WITH HIGH PRESSURE CENTERED JUST NORTH AND NORTHEAST OF THE AREA AND
FIRMLY ESTABLISHED INTO THE CENTRAL GREAT LAKES...MARINE CONDITIONS
WILL REMAIN QUITE FAVORABLE INTO TUESDAY WITH LIGHT NORTHEAST TO
EAST FLOW AND MINIMAL WAVE DEVELOPMENT. AN APPROACHING LOW PRESSURE
SYSTEM WILL EVENTUALLY BRING ANOTHER CHANCE OF SHOWERS AND STORMS BY
LATE TUESDAY AND TUESDAY NIGHT...BUT WITH VERY LITTLE BAROCLINICITY
WITH THIS SYSTEM...THE FLOW OVER THE REGION WILL REMAIN WEAK AND
WINDS AND WAVES WILL REMAIN SUBDUED.

&&

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

&&

$$

AVIATION.....SF
SHORT TERM...KURIMSKI
LONG TERM....CB
MARINE.......CB


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





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