992
FXUS63 KAPX 130715
AFDAPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
314 AM EDT TUE MAY 13 2008
DISCUSSION...N-S ORIENTED SURFACE RIDGE OVER LAKE HURON
WITH
RETURN FLOW RAMPING UP WEST OF LAKE MI. INITIAL SURGE OF WARM
ADVECTION AND MID-LEVEL FGEN DID MANAGE TO CRANK OUT A FEW SPRINKLES
IN EASTERN UPPER MI SOON AFTER MIDNIGHT. THAT IS EXITING...THOUGH
LEAVING BEHIND A SUBSTANTIAL CIRRUS SHROUD ACROSS THE NORTHERN
REACHES. PRECIP TRENDS TONIGHT AND WEDNESDAY ARE THE MAIN CONCERN.
MODELS...GFS FINDS ITSELF A BIT ON THE FAST SIDE OF THE MODEL
ENVELOPE...BUT ALL IN ALL THE MODELS ARE IN MUCH BETTER AGREEMENT ON
TIMING. THE NAM IS NOW THE ONLY MODEL THAT CLOSES OFF THE UPPER TROF
PASSING TO OUR NORTH...GFS/ECMWF KEEP THE WAVE OPEN (AND ARE
PREFERRED).
TODAY...SOUTHERLY LOW LEVEL WINDS WILL INCREASE AS HIGH PRESSURE
MOVES TO THE EASTERN LAKES. 850MB TEMPS WILL RISE TO 7-9C DURING THE
DAY. SUNSHINE WILL BE MORE ABUNDANT SOUTH THAN NORTH THANKS TO LESS
CIRRUS...THOUGH THAT CIRRUS WILL TEND TO DIMINISH AT MIDDAY BEFORE
RETURNING AGAIN VERY LATE. EASTERN UPPER WILL SEE PREVAILING SE
SURFACE WINDS...AND THE HURON COAST OF NE LOWER WILL BACK SE DURING
THE DAY THANKS TO THE BIG COLD LAKE. THESE PLACES WILL STAY FAIRLY
COOL...WITH HIGHS NEAR 60 TO THE MID 60S...COOLER YET RIGHT ON THE
BEACHES. ELSEWHERE...EVEN WITHOUT LAKE INFLUENCES...MODELS ARE NOT
WARMING THE LOW LEVELS AS MUCH...AND THUS WILL SHAVE OFF A DEGREE OR
TWO IN MANY PLACES. WITH A DUE SOUTH SURFACE WIND...TVC GETS MUCHO
DOWNSLOPING AND WILL PROBABLY TOUCH 70. THE REST OF NORTHERN LOWER
LOOKS TO COME UP JUST SHORT. THIS WILL KEEP TEMPS/RH VALUES BELOW
CRITICAL FIRE WX THRESHOLDS. UPSTREAM DEEP MOISTURE/PRECIP WILL ONLY
APPROACH THE WEST SHORE OF LAKE MI BY 00Z/8PM...SO NO CHANCE OF
PRECIP.
LAST SECOND ADDITION...ONGOING MARINE FOG IS AN ISSUE ON THE HURON
COAST...WITH APN FLUTTERING BETWEEN 1/4 AND 1/2SM (BUT MAINLY AT
1/4SM)...AND OSC NOT REPORTING A VSBY BUT REPORTING AN OVC001 CIG.
FOG LOOP AND CONCEPTUAL MODELS ARGUE FOR THE FOG BEING DENSER ON THE
COAST (SAY...IN THE CITY OF ALPENA) THAN IT IS AT APN AIRPORT.
THOUGH DENSE IS NOT WIDESPREAD IN THE COASTAL COUNTIES...IT IS
IMPACTING THE MOST HIGHLY POPULATED AREAS. THUS...WILL HOIST A DENSE
FOG ADVISORY FROM APN TO TAWAS THRU 11AM. CALLS TO ARENAC COUNTY LAW
ENFORCEMENT INDICATED JUST PATCHY FOG THERE.
TONIGHT...SURFACE LOW WILL LIFT ACROSS SUPERIOR...AND DEEPEN TO
998MB OVERNIGHT NORTH OF THE BIG LAKE. UPSTREAM COLD FRONT WILL
TIGHTEN UP CONSIDERABLY AS IT ADVANCES ACROSS WI...AND WILL BE JUST
ENTERING THE FORECAST AREA AT 12Z. PRECIP SHOULD BLOSSOM AHEAD OF
THE COLD FRONT IN WI LATE TODAY. AS MENTIONED YESTERDAY...MOISTURE
IS NOT STUPENDOUS...BUT FORCING IS SUBSTANTIAL. 850MB WINDS INCREASE
TO 40-50KT IN THE WARM CONVEYOR BELT...PROVIDING RAPID MOISTURE
TRANSPORT AND SIGNIFICANT LIFT. HEIGHT FALLS ALOFT AND DIFFERENTIAL
TEMP ADVECTION WILL STEEPEN UP LAPSE RATES JUST ENOUGH (6.5 C/KM
FROM 700 TO 500MB) TO GET A LITTLE THUNDER IN THE MIX. IT WILL
RAIN...JUST A MATTER OF TIMING. WILL GO JUST A SMIDGE SLOWER THAN
THE EARLIER FORECAST...WITH CHANCY POPS IN THE FAR WEST THRU
03Z/11PM...AND RAPID EXPANSION OF LIKELY TO CATEGORICAL POPS AFTER
THAT. A GENERAL QUARTER TO HALF INCH OF RAIN SEEMS REASONABLE.
AVAILABLE MUCAPES ARE ONLY 200J/KG AT MOST...SO NO REAL SVR THREAT.
WEDNESDAY...COLD FRONT WILL CROSS THE FORECAST AREA IN THE 1ST HALF
OF THE DAY...AND EXIT THE HURON COAST AT OR JUST AFTER 18Z/2PM. WILL
HAVE CHANCE POPS WEST AND CATEGORICAL EAST TO START THE DAY...BY 18Z
WILL ONLY NEED A CHANCE ALONG THE IMMEDIATE HURON COASTLINE. DEEP
DRYING AND SUBSIDENCE SURGES IN BEHIND THE FRONT...REMOVING ANY
PRECIP THREAT IN THE PM. BETTER WRAPAROUND MOISTURE NOW LOOKS TO
STAY NORTH OF SUPERIOR. HOWEVER...THERE IS INITIALLY STILL A DECENT
AMOUNT MOISTURE TRAPPED BENEATH THE 850MB INVERSION POST-FRONT...SO
CLEARING WILL BE DELAYED. TIMING OF CLEARING WILL PROBABLY BE ONLY A
BIT FASTER THAN WE SAW ON MONDAY. SURGE OF COOL AIR BEHIND FRONT NOT
QUITE AS EMPHATIC AS WAS PROGGED YESTERDAY...WITH 850MB TEMPS ONLY
DOWN TO 0 TO 3 C BY 00Z. MAX TEMPS IN THE 50S TO AROUND 60 STILL
LOOK GOOD...BUT TEMPS WILL HOLD UP BETTER LATER IN THE DAY INSTEAD
OF FALLING OFF.
WEDNESDAY NIGHT/THURSDAY...UPPER LOW OVER HUDSON BAY...WITH
SIGNIFICANT MODEL DIFFERENCES RESOLVING THE SHORTWAVES ROTATING
AROUND IT. HOWEVER...THERE IS REASONABLE AGREEMENT THAT WHATEVER
SENSIBLE WX HAPPENS WILL STAY NORTH OF SUPERIOR. PARTLY CLOUDY TO
MOSTLY CLEAR SKIES SHOULD WORK (WITH MORE CLOUDS DURING THE DAY THAN
AT NIGHT)...WITH MINS IN THE 30S (SOME FROST POSSIBLE) AND HIGHS A
FEW DEGREES EITHER SIDE OF 60.
REST OF THE FORECAST...HARD TO HAVE A LOT OF CONFIDENCE AS TO HOW
THE LOW TO THE NORTH WILL EVOLVE. THE 00Z GFS SWINGS A REINFORCING
COLD FRONT AND SOME SHOWERS INTO THE REGION ON FRIDAY...USHERING IN
A MORE UNSETTLED PATTERN INTO THE WEEKEND. THIS IS ACTUALLY IN GOOD
AGREEMENT WITH THE CURRENT FORECAST. THAT/S GOOD ENOUGH FOR ME.
JZ
AVIATION...ISSUED 1143 PM MON MAY 12
BIGGEST PROBLEM THROUGH THE FIRST HALF OF THE FORECAST PERIOD WILL
BE AT APN...WHERE IFR CEILINGS/VISIBILITIES HAVE DRIFTED IN OFF LAKE
HURON. EXPECT THIS TO PERSIST THROUGH MID MORNING...THOUGH GIVEN
TRENDS MAY SEE "JUMPS" FROM LIFR TO VFR AND BACK FROM TIME TO TIME.
OTHERWISE VFR CONDITIONS EXPECTED INTO TUESDAY EVENING...WITH SOME
RAIN SHOWERS SPREADING IN FROM THE WEST TOWARD THE END OF THE
FORECAST PERIOD.
JPB
APX WATCHES/WARNINGS/ADVISORIES
MI...DENSE FOG ADVISORY UNTIL 11 AM EDT THIS MORNING FOR
MIZ024-030-036.
LM...NONE.
LH...NONE.
LS...NONE.
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