Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 271626
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1226 PM EDT FRI MAR 27 2015

.AVIATION...

CLEARING TREND WILL ATTEMPT TO WORK IN FROM THE WEST/NORTHWEST AS
SUBSIDENCE OCCURS THIS AFTERNOON BEHIND UPPER LEVEL TROUGH AXIS. DO
THINK MBS WILL SCATTER OR CLEAR OUT. HOWEVER...COLD NORTHERLY FLOW
OFF LAKE HURON WILL TEND TO MAINTAIN LAKE CLOUDS AND EMBEDDED SNOW
SHOWERS FARTHER EAST. FORTUNATELY...CLOUD BASES AND VSBYS SHOULD BE
PREDOMINATELY OF THE LOW VFR VARIETY THROUGH TONIGHT...EVEN IF
CLOUDS DO IN FACT HOLD...WITH JUST LOCALIZED MVFR SNOW
SHOWERS/CEILINGS. SURFACE HIGH PRESSURE BUILDING INTO LOWER MICHIGAN
WILL ALLOW WINDS TO BACK A BIT TO THE NORTHWEST LATE TONIGHT...WHICH
SHOULD SET UP THE TAF SITES FOR MOSTLY CLEAR SKIES TOMORROW.

FOR DTW...LOW VFR CLOUDS AND BRIEF MVFR SNOW SHOWERS WILL DIMINISH
THIS AFTERNOON...WITH CONFIDENCE IN CLOUDS/CEILINGS HOLDING THEN
DIMINISHING THIS EVENING AND TONIGHT...AS DRIER AIR AND HIGH
PRESSURE ATTEMPTS TO BUILD IN FROM THE WEST.


//DTW THRESHOLD PROBABILITIES...

* HIGH CONFIDENCE IN CEILINGS AOB 5000 FT THIS AFTERNOON...MEDIUM
  CONFIDENCE THIS EVENING...LOW CONFIDENCE AFTER MIDNIGHT.

&&

.PREV DISCUSSION...ISSUED 911 AM EDT FRI MAR 27 2015

UPDATE...

12Z DTX SOUNDING INDICATED AN 850 MB TEMP OF -16 C...WITH APX
CHECKING IN AT -20 C. UPPER LEVEL TROUGH AXIS IS CURRENTLY MOVING
THROUGH THE CENTRAL GREAT LAKES. WATCHING SOUTHERN LAKE HURON SNOW
BAND(S) CLOSELY...AS EVEN KDTX RADAR PICKING UP THE SUBSTANTIAL ECHOS
(20-25 DBZ) AT THE 5500 FOOT LEVEL...WELL ABOVE THE STOUT
INVERSION INDICATED BY 12Z DTX SOUNDING...INDICATIVE OF THE LAKE
INFLUENCE. NAM/RAP13 STILL INDICTING THIS BAND WILL PUSH
SOUTH/SOUTHWEST THROUGH THE DAY BASED ON 925 MB OMEGA/CONVERGENCE
FIELDS...AND HOPEFULLY THE TRANSIENT NATURE WILL KEEP THE
LOCALIZED ACCUMULATIONS TO A COUPLE INCHES AROUND PORT HURON AREA.
FURTHER/INCREASING BOUNDARY LAYER MIXING/SUBSIDENCE BEHIND THE
UPPER LEVEL TROUGH AXIS THIS AFTERNOON AND BAND MOVING AWAY FROM
MOISTURE SOURCE SHOULD FURTHER DISRUPT THE ACTIVITY...HELPING TO
LIMIT THE ACCUMULATIONS FARTHER SOUTH. QUICK LOOK AT THE 12Z NAM
SHOWS ANOTHER LAKE BAND DEVELOPING OVER THE THUMB REGION THIS
EVENING WITH THE GOOD NORTHERLY FETCH OFF LAKE HURON...BUT
INVERSION HEIGHTS SLIGHTLY LOWER AND ADDITIONAL DRY AIR MAY LIMIT
ACCUMULATIONS TO INCH OR LESS...UNLIKE THE TWO INCHES SEEN IN
ELKTON THIS MORNING.

PREV DISCUSSION...ISSUED 410 AM EDT FRI MAR 27 2015

SHORT TERM...TODAY AND TONIGHT

A FULL LATITUDE TROUGH OVER THE EASTERN CONTINENTAL UNITED STATES
WILL LEAD TO RAW CONDITIONS OVER SOUTHEASTERN MICHIGAN TODAY. THE
SPINE OF THE COLD AIR IS FORECASTED TO SETTLE INTO EASTERN LOWER
MICHIGAN BY 21Z THIS AFTERNOON. 850MB AND 925MB TEMPERATURES ARE
FORECASTED TO BE SOLIDLY OUTSIDE OF 1 SIGMA.  A STRAIGHT MIXING
TECHNIQUE SUPPORTS READINGS LIMITING OUT IN THE 20S. THE OUTGOING
FORECAST WILL SHADE A DEGREE OR TWO WARMER THAN THE AVAILABLE RAW
MODEL OUTPUT...MIDDLE 20S IN THE THUMB TO NEAR THE FREEZING MARK
ACROSS THE SOUTH...APPROXIMATELY 20 DEGREES BELOW NORMAL. A
SHARP...NORTH WIND WILL LEAD TO WINDCHILLS IN THE TEENS TO LOWER 20S
TODAY...AND IN THE LOWER SINGLE DIGITS TONIGHT.

WILL BE WATCHING A NUMBER OF THINGS FOR MORE ORGANIZED SNOW SHOWER
ACTIVITY TODAY. THE FIRST WILL BE ALONG A SURFACE CONVERGENCE
BOUNDARY ASSOCIATED WITH A WEST TO EAST SURFACE TROUGH AXIS THAT IS
FORECASTED TO PUSH SOUTHWARD THROUGH SOUTHEASTERN MICHIGAN DURING
THE COURSE OF THE ENTIRE DAY. RECENT RADAR IMAGERY FROM EXETER
ONTARIO SUGGESTS A FAIR AMOUNT OF REFLECTORS IN THE GENERAL LOCATION
OF THE AXIS THIS MORNING. HOWEVER...OVERSHOOTING OF THE RADAR BEAM
AT THESE DISTANCES LEADS TO A HIGH AMOUNT UNCERTAINTY. THE INHERITED
FORECAST STILL REMAINS VALID CALLING FOR SNOW SHOWERS
LIKELY/NUMEROUS IN THE THUMB THIS MORNING. AFTER THE MID TO LATE
MORNING ...FORECASTED LAPSE RATES SUPPORT A FLARE UP OF ACTIVITY
DUE TO THE DEEPENING OF THE BOUNDARY LAYER FROM DAYTIME HEATING.
PLAN VIEW EVOLUTION OF LL THETA E LAPSE RATES ALONG HIRES MODEL
OUTPUT SUGGESTS THIS POTENTIAL IS FOR ALL OF SOUTHEASTERN
MICHIGAN. THIS THERMODYNAMIC SUPPORT IS IN ADDITION TO A
CONTRACTION IN THE WAVELENGTH OF THE UPPER LEVEL TROUGH.
CONCENTRATED DCVA IN COMBINATION WITH THE LOCALIZED
CONVERGENCE/NEAR SURFACE TROUGH AXIS WILL LEAD TO ENOUGH FORCING
TO SUPPORT LIGHT SNOW SHOWER ACTIVITY ACROSS MUCH OF THE AREA THIS
AFTERNOON. THE SUPERSATURATION WRT ICE SIGNAL IS GOOD ALONG WITH
THE STEEP LAPSE RATE POCKET ENCAPSULATING THE -15C ISOTHERM. A
LIGHT DUSTING...TO MINOR ACCUMULATIONS OF GENERALLY LESS THAN ONE
INCH WILL BE POSSIBLE FOR MUCH OF THE CWA TODAY. IT REMAINS
POSSIBLE FOR SNOWFALL ACCUMULATIONS OF AN INCH OR GREATER FOR THE
THUMB REGION.

LONG TERM...

CONTINUED DEEP NORTHERLY FLOW WILL START SATURDAY BEFORE THE LARGE
AREA OF COLD HIGH PRESSURE BECOMES CENTERED OVER LOWER MICHIGAN
DURING THE REST OF THE DAY. THE WIND DIRECTION FROM LAKE HURON INTO
THE THUMB WILL FAVOR LINGERING BUT DIMINISHING LAKE EFFECT
POTENTIAL. MODEL SOUNDINGS INDICATE NEAR DRY ADIABATIC LAPSE RATES
BUT ALSO SHOW CONVECTIVE DEPTH FORCED QUICKLY BELOW 850 MB/5000 FT.
THIS MAY BE GOOD FOR SOME FLURRIES BUT MORE LIKELY JUST SOME
STRATOCU WITHIN A SHALLOW LAYER OF SATURATION NEAR -15C THAT MIXES
OUT BY AFTERNOON. THE BUILDING SURFACE HIGH AND BACKING LOW LEVEL
WIND FIELD WILL NUDGE THE LOW LEVEL THERMAL TROUGH EASTWARD DURING
THE AFTERNOON. THIS...COMBINED WITH FULL LATE MARCH SUN...WILL HELP
MAX TEMPS RISE TOWARD THE MID 30S...BUT STILL A SOLID 15 DEGREES
BELOW NORMAL. THE STAGE WILL THEN BE SET FOR A COLD SATURDAY NIGHT
WITH MIN TEMPS LIKELY OCCURRING AROUND MIDNIGHT BEFORE HIGH CLOUDS
THICKEN AND SOUTHWEST WIND INCREASES OVERNIGHT THROUGH SUNRISE
SUNDAY.

THE HIGH CLOUDS SATURDAY NIGHT WILL BE THE FIRST SIGN OF THE NEXT
LOW PRESSURE SYSTEM ARRIVING IN THE GREAT LAKES. THIS SYSTEM IS
STILL OFFSHORE OVER THE GULF OF ALASKA AND WILL BE MOVING INLAND
TONIGHT BEFORE POWERING THROUGH THE LONG WAVE RIDGE OVER THE ROCKIES
DURING SATURDAY. THERE IS IMPROVED AGREEMENT IN THE 00Z MODEL RUNS
WITH RESPECT TO TIMING THE ARRIVAL OF PRECIPITATION WITH THIS SYSTEM
SUNDAY AFTERNOON IN SE MICHIGAN. THE MOISTURE PROFILE WILL BE A
HYBRID OF MID LEVEL PACIFIC AND LOW LEVEL GULF MODIFIED CONTINENTAL
WHICH IS SEEMS ADEQUATE FOR THE 0.1-0.2 MODEL QPF AND LIKELY POPS
SUNDAY AFTERNOON AND EVENING. THERE WILL BE SOME WET BULB COOLING
POTENTIAL AT ONSET BUT THE NAM IS GIVING IT TOO MUCH CREDIT FOR
COOLING THE BOUNDARY LAYER ENOUGH FOR SNOW IN THE MIDDLE OF THE DAY.
A PROFILE MORE LIKE THE GFS IS PREFERRED AND HELPS RULE OUT A
RAIN/SNOW MIX UNTIL SUNDAY NIGHT WHEN COLDER AIR SPILLS BACK INTO
THE REGION BEHIND THE SYSTEM.

GLOBAL MODELS MAINTAIN THE FRONTAL ZONE NEARBY TO START NEXT WEEK
WITH A COUPLE MORE LOW PREDICTABILITY SHORT WAVES TRAVERSING THE NW
FLOW ALOFT. EXPECT COLD AIR INTRUSIONS TO BE LESS HARSH COMPARED TO
THIS WEEKEND. AT THIS POINT...A STRONGER LOW PRESSURE SYSTEM IS
PROJECTED AROUND THE WEDNESDAY PERIOD THAT HAS POTENTIAL TO ALTER
THE LARGE SCALE PATTERN ENOUGH TO LIFT TEMPERATURES BACK TO NORMAL
FOR THE SECOND HALF OF NEXT WEEK.

MARINE...

STRONG NORTH WIND OVER LAKE HURON AND LOWER MICHIGAN WILL CARRY AIR
COLD ENOUGH FOR SNOW SHOWERS TODAY AND TONIGHT. GUSTS NEAR 30 KNOTS
WILL THEN EASE BACK DURING SATURDAY AS HIGH PRESSURE SETTLES
OVERHEAD. SOUTHWEST WIND WILL THEN RAMP UP SATURDAY NIGHT INTO
SUNDAY AS THE NEXT LOW PRESSURE SYSTEM MOVES INTO THE MIDWEST AND
WESTERN GREAT LAKES. SOUTHWEST GUSTS AROUND 25 KNOTS WILL BRING BACK
ENOUGH WARM AIR FOR MOSTLY RAIN SUNDAY AFTERNOON AND EVENING. COLDER
AIR WILL RETURN MONDAY BUT NOT AS COLD AS THIS WEEKEND.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR LHZ421-441-442.

LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

AVIATION.....SF
UPDATE.......SF
SHORT TERM...CB
LONG TERM....BT
MARINE.......BT


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


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