Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 072049
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
349 PM EST SUN FEB 7 2016

.DISCUSSION...

THE AMPLIFICATION AND EVENTUAL BROADENING OF AN UPPER LEVEL TROUGH
OVER SOUTHEASTERN MICHIGAN IS RESULTING IN A VERY CHALLENGING
FORECAST FOR THE EARLY WEEK PERIOD. SPECIFICALLY...THERE IS LOW
PREDICTABILITY IN THE INTEGRITY AND TIMING OF INDIVIDUAL SHORTWAVE
ENERGY THAT WILL BE HARBORED WITHIN THE UPPER LEVEL TROUGH AXIS.

DISTINCT UPPER LEVEL ABSOLUTE VORTICITY CENTERS ARE DIGGING
SOUTHEASTWARD OUT OF THE NORTHERN PLAINS THIS AFTERNOON. FORECAST
DATA SUPPORTS THE LEAD EDGE OR GRADIENT OF THE PARENT PV ANOMALY TO
PUSH ACROSS LAKE MICHIGAN AND TO IMPINGE UPON WESTERN LOWER MICHIGAN
PRIOR TO 00Z THIS EVENING. MODELS ARE STRONGLY IN FAVOR OF A
RELATIVELY MESSY JET EVOLUTION DURING THE NEXT 6-12 HOURS WHERE A
DISORGANIZED UPPER LEVEL JET STREAM ELEMENT WILL RAPIDLY BECOME
ANTICYCLONIC IN CURVATURE AND BECOME PHASED WITHIN THE ENTRANCE
REGION OF THE MUCH MORE DOMINANT NE U.S. JET BRANCH. THE NET RESULT
IS FOR SOME DECENT TO STRONG RIGHT ENTRANCE REGION DYNAMICS
DEVELOPING OVER SOUTHEASTERN MICHIGAN. WHAT IS LIKELY MORE FAVORABLE
FROM A DYNAMICAL STANDPOINT IS THE CONVERGENCE BOUNDARY/FRONT THAT
WILL BECOME SHARPER THIS EVENING ALONG THE PV GRADIENT WHERE FORCING
WILL BE MAXIMIZED DUE TO THE MASS ADJUSTMENT CAUSED BY THE
TROPOPAUSE FOLD ARRIVAL. NUMERICAL OUTPUT SUPPORTS A CORRIDOR OF
LIGHT RAIN SHOWER DEVELOPMENT (WARM SFC TEMPERATURES) OVER MUCH OF
SOUTHEASTERN MICHIGAN BETWEEN 01-04Z. PRETTY INCONSEQUENTIAL...WITH
VERY LIGHT QPF AMOUNTS OF A COUPLE HUNDREDTHS OF QPF OR LESS.

THE LOW PREDICTABILITY THEN BEGINS IN EARNEST ALREADY LATE TONIGHT
AS INTRA-INTER MODEL CONTINUITY HAS BEEN EXTREMELY POOR WITH REGARDS
TO AMOUNT OF LOW LEVEL MOISTURE THAT WILL SATURATE/DEVELOP OVER THE
EXTREME SOUTHEASTERN SECTIONS OF THE CWA...NEAR DETROIT RIVER/LAKE
ST CLAIR. EARLIER DETERMINISTIC AND HIRES SOLUTIONS SHOWED AN
INCREASING LOW LEVEL MOISTURE PLUME AND PRECIPITATION DURING THE 10-
12Z TIMEFRAME ACROSS SECTIONS OF SOUTH CENTRAL LOWER MICHIGAN AND
OVER THE FAR WESTERN LAKE ERIE BASIN. THE NEW 07.12Z ITERATIONS OF
THESE SAME MODELS ARRIVED AND BACKED WAY OFF. PREFERENCE SIDES WITH
A DRIER SOLUTION FOR THE MONDAY MORNING COMMUTE TIME FOR A COUPLE OF
REASONS...1. THERE IS NO LOW LEVEL JET FEATURE DRIVING
ADVECTION...2. LOW LEVEL SATURATION WHILE BEING AIDED BY RIGHT
ENTRANCE REGION DYNAMICS ALOFT IS STILL LIKELY DEPENDENT ON A GOOD
AMOUNT OF PRECIPITATION/HYDROMETEOR PRODUCTION THIS EVENING. THE NAM
IS SHOWING A MINIMUM CORRIDOR OF 850-700MB SPECIFIC HUMIDITY
DIRECTLY IN PLACE AT 12Z MONDAY.

THE MODEL SOLUTIONS NOW SUPPORT THE CORRIDOR OF LIGHT
PRECIPITATIONPROGRESSING EAST OF LOWER MICHIGAN FOR THE MONDAY
PERIOD SETTING UP WHAT SHOULD BE FAIRLY WIDESPREAD DRY CONDITIONS.
WHILE A CLASSIC MIDLEVEL DRY SLOT IS NOT RESOLVED FOR
MONDAY...THERE IS A GOOD AMOUNT OF DRY AIR ENTRAINED WITHIN THE
MIDLEVEL TROUGH AXIS. ADDITIONALLY...MODEL DATA SUPPORTS NEUTRAL
TO ISENTROPIC DOWNGLIDE OVER SOUTHEASTERN MICHIGAN. CARRYING A LOW
CHANCE FOR SNOW SHOWERS IN MANY AREAS. THE ONE ITEM TO WATCH FOR
IS SOME POSSIBLE CONVECTIVE SHOWER DEVELOPMENT ALONG A SECONDARY
COLD FRONT/GRADIENT FEATURE THAT WILL PUSH INTO THE FAR WESTERN
CWA/SAGINAW VALLEY BETWEEN 21- 24Z MONDAY. NO TANGIBLE HEIGHT
RISES WILL SUPPORT VERY LITTLE COLD ADVECTION ON MONDAY.
PREFERENCE SIDES WITH WARMER TEMPERATURES IN THE UPPER 30S TO NEAR
40 DEGREES.

THE MODEL TREND TODAY HAS BEEN FOR MORE OF A SOUTHWARD SOLUTION WITH
THE MAIN VORTICITY ENERGY WITHIN THE TROUGH AXIS BY TUESDAY. THIS
SUGGESTS POSSIBLY MORE OF AN EASTWARD LEAK TO THE SURFACE
LOW/REFLECTION THAN WHAT WAS EARLIER ADVERTISED. THE BEST CVA WOULD
SHIFT SOUTH AND EAST OF THE CWA WHICH WOULD TAKE THE MAIN DYNAMICAL
SUPPORT FOR PRECIPITATION WITH IT. WHAT REMAINS OVER SOUTHEASTERN
MICHIGAN IS MORE IN THE WAY OF NORTHWESTERLY FLOW WHICH IS A DRY ONE
FOR THE AREA. THE LAKE EFFECT POTENTIAL STILL REMAINS FOR TUESDAY
AND WEDNESDAY WITH VERY COLD TEMPERATURES OF -12 TO -20C 850MB
EXPANDING ACROSS THE AREA. THE ONE ITEM OF PARTICULAR INTEREST IS A
POTENTIAL LAKE AGGREGATE TROUGH WHICH COULD LEAD TO A GOOD POTENTIAL
FOR SHOVEL-ABLE SNOWS OVER PORTIONS OF THE THUMB...PRIMARILY ON
WEDNESDAY.

THERE IS GROWING CONFIDENCE THAT WE WILL SEE SOME OF THE COLDEST AIR
OF THE SEASON SO FAR LATE NEXT WEEK INTO NEXT WEEKEND. 12Z GFS/GEFS
MEAN/ECMWF CONTINUE TO HIGHLIGHT -15 TO -20C 850 MB TEMPS WED/THU.
POTENTIAL FOR EVEN COLDER AIR NEXT WEEKEND WITH THE ARCTIC CLOSED
LOW SWEEPING INTO SOUTHEAST CANADA. STILL SOME UNCERTAINTY WITH THE
MAGNITUDE OF COLD AIR AS IT LOOKS TO BE A GLANCING BLOW WITH THE
HEART OF THE COLD AIR OVER THE NORTHEAST US...BUT EVEN A GLANCING
BLOW WOULD LIKELY PUT 850 MB TEMPS NEAR -20 TO -25C WHICH WOULD BE
THE COLDEST AIRMASS SO FAR THIS WINTER. LAKE EFFECT SNOW SHOWER
ACTIVITY WILL BE AROUND...ESPECIALLY WEDNESDAY...BUT LIKELY ON A
DIMINISHING TREND INTO THE END OF THE WEEK AS COLDER...DRIER NW FLOW
SETS UP.

&&

.MARINE...

MODERATE SOUTH-SOUTHWEST OF 15 TO 25 KNOTS WINDS WILL CONTINUE INTO
THIS EVENING BEFORE DIMINISHING CONSIDERABLY TONIGHT INTO TUESDAY AS
EXPANSIVE LOW PRESSURE SETTLES ACROSS THE GREAT LAKES. WINDS WILL
BACK TO NORTHWESTERLY BY LATE TUESDAY INTO WEDNESDAY AND INCREASE AS
LOW PRESSURE DEPARTS DURING THE MIDWEEK PERIOD. GUSTS OF 25 TO 30
KNOTS ARE ANTICIPATED OVER SOUTHERN LAKE HURON...ALONG WITH SNOW
SQUALLS...AS MUCH COLDER FILTERS INTO THE GREAT LAKES REGION OVER
THE UPCOMING WEEK.

&&

.AVIATION...ISSUED 1200 PM EST SUN FEB 7 2016

MID CLOUDS AND SOUTHERLY FLOW GUSTING TO 20 KNOTS OR BETTER THIS
AFTERNOON. THE 12Z DTX SOUNDING SHOWED A DRY SUB 700 MB
LAYER...BUT STRONG SOUTH-SOUTHWEST WINDS ADVECTING SOME MODEST
MOISTURE...AND 12Z MODELS SUGGESTING A FLARE UP OF LIGHT
RAIN/SPRINKLES AND AT LEAST MVFR CEILINGS AS SURFACE FRONT TRACKS
THROUGH DURING THE EVENING HOURS OVER SOUTHEAST MICHIGAN. IT IS A
DIFFICULT FORECAST...AS UPSTREAM OBSERVATIONS AROUND ST LOUIS
EXTENDING INTO THE WESTERN OHIO VALLEY DO NOT INDICATE THIS...BUT
THERE IS SOME VIRGA TRANSLATING THROUGH LOWER MICHIGAN AT THE
MOMENT. ALSO...SURFACE DEW PTS ARE RUNNING CLOSER TO 30
DEGREES...AND NOT SURE WE WILL RISE INTO THE UPPER 30S AS
SUGGESTED. NONE-THE-LESS...STILL ENOUGH EVIDENCE TO CARRY
BORDERLINE VFR/MVFR CEILINGS FOR THIS EVENING AND TONIGHT...WITH
JUST ENOUGH DRYING AND COLD ADVECTION MONDAY MORNING TO SCOUR OUT
THE LOW CLOUDS BEFORE RETURNING DURING THE AFTERNOON HOURS.

AT DTW... SOUTH-SOUTHWEST WINDS GUSTING TO 20 KNOTS OR BETTER THIS
AFTERNOON WILL TRANSPORT MODEST MOISTURE...EXPECTED TO GENERATE A
FEW SPRINKLES OR LIGHT RAIN SHOWERS THIS EVENING (1-4Z)...WHICH WILL
HELP DROP CEILINGS AROUND 3000 FEET...PERSISTING FOR A GOOD PORTION
OF THE NIGHT. CONFIDENCE IN CLEARING OCCURRING TOWARD SUNRISE IS
AVERAGE TO LOW...AS A BORDERLINE MVFR/IFR CEILING IS NOT OUT OF THE
QUESTION MONDAY MORNING AS ADDITIONAL MOISTURE ATTEMPTS TO MOVE UP
FROM THE SOUTH.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CIGS AOB 5KFT AFTER 00Z THROUGH 10Z...LOW DURING MONDAY
  MORNING...WITH MEDIUM CONFIDENCE DURING THE AFTERNOON.

* HIGH CONFIDENCE IN PRECIPITATION FALLING AS LIGHT RAIN DURING
  EVENING.

&&

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

$$

DISCUSSION...CB/DT
MARINE.......SF
AVIATION.....SF


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