430
FXUS63 KMQT 141133 AAA
AFDMQT
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MARQUETTE MI
730 AM EDT WED MAY 14 2008
UPDATED AVIATION SECTION FOR 12Z TAFS
DISCUSSION (450 AM EDT)
00Z RAOBS/LATEST WV IMAGERY AND RUC ANALYSIS SHOW FAIRLY POTENT
SHRTWV MOVING E THRU THE UPR MS VALLEY INTO THE WRN LKS EARLY THIS
MRNG. INTERACTION BTWN FAIRLY VIGOROUS DPVA/DEEP LYR H85-3 QVECTOR
CNVGC/RRQ OF H3 JET AXIS AND DEEP MSTR WITH PWAT AOA 1 INCH/H85 DWPT
AS HIGH AS 8C IS CAUSING AN AREA OF SHRA/EMBEDDED TS AHEAD OF
ATTENDANT COLD FNT NOW MOVING INTO THE WRN ZNS AT 03Z. THE MOST
WDSPRD RA IS OVER THE E UNDER AXIS OF MORE IMPRESSIVE MSTR...WITH
MORE SCT -SHRA ACRS THE W. THE BACK EDGE OF THE SHRA IS NOW APRCHG
THE WRN ZNS AT 03Z AS DRIER AIR SHOWN ON THE 00Z INL SDNG ABV H8 IS
ADVECTING EWD. HOWEVER...LLVL MSTR/SC EXTENDS WWD WELL BEHIND THE
SFC FNT UNDER H85 THERMAL TROF. DRIER LLVL AIR APRNT ON THE WELL
MIXED 00Z BIS/YQD/GGW SDNGS...BUT YQD/GGW RAOBS ALSO DEPICT HIER MID
LVL RH AT THE TOP OF THE DEEPER MIXED LYR OBSVD AT THOSE SITES. IN
FACT...SOME SHRA/LTG OCCURRED JUST W OF LK WINNIPEG IN AREA OF
DIFFERENTIAL TEMP ADVCTN WHERE H7-5 LAPSE RATES ARE STEEPEST.
MAIN FCST CONCERNS EARLY TDAY ARE TIMING THE END OF PCPN/COLD FROPA.
TEMPS/SKY WL BE THE BIGGEST CONCERN LATE TDAY INTO THU...THEN SHRA
CHCS BECOME THE FOCUS AGAIN BEGINNING THU AFTN WITH DIFFICULT TIMING
OF SHRTWVS IN PESKY NW FLOW ALF.
FOR TDAY...SHRTWV AND ACCOMPANYING SFC LO FCST TO LIFT NEWD THRU
ONTARIO...WITH SFC COLD FNT CLRG ERY BY 12Z. WL MAINTAIN SOME SCT
-SHRA OVER THE ERN ZNS UNTIL ABOUT 15Z WHEN H3 JET AXIS PROGGED TO
PUSH TO THE E AND DRY AIR ALF MOVES INTO THAT AREA. ALTHOUGH LO CLD
EXTENDING WELL BEHIND THE FNT NOW WL BE IN PLACE OVER THE ENTIRE FA
AT 12Z WITHIN LLVL THERMAL TROFFING BLO DVLPG SUBSIDENCE INVRN...
ARRIVAL OF SOMEWHAT DRIER AIR SHOWN ON THE 00Z BIS SDNG AND DAYTIME
MIXING OF LCL ABV SUBSIDENCE INVRN IN CONCERT WITH MORE ACYC FLOW WL
CAUSE THE MRNG SC TO GIVE WAY TO SOME SCT AFTN CU. DOWNSLOPING NW
FLOW MAY ACCELERATE THE DRYING TREND OVER THE SE ZNS. MIXING TO H75
OR SO ON GFS/NAM FCST SDNGS YIELD HI TEMPS ARND 60 AWAY FM LK
MODERATION... WHICH WL BE MOST PRONOUNCED IN AREAS DOWNWIND OF LK
SUP IN NW FLOW. WITH SFC DWPTS MIXING OUT AS LO AS 30 AT TIME OF
PEAK HTG...EXPECT MIN RH TO BOTTOM OUT ARND 30 PCT.
SFC HI PRES CENTER PROGGED TO DRIFT TO THE SE TNGT AND BE CENTERED
OVER LWER MI BY 12Z THU. RETURN WSW FLOW/HINT OF A WEAK SFC TROF
EMBEDDED IN NW FLOW ALF WL LIKELY RESULT IN SOME CLD COVER
ESPECIALLY OVER THE NRN TIER WHERE MSTR IS A BIT MORE SUBSTANTIAL
AND H7-5 LAPSE RATES ARE SOMEWHAT STEEPER IN LINE WITH 00Z GGW/YQD
SDNGS. BUT ARRIVAL OF THESE CONDITIONS DURING DIURNAL MIN HTG IN
ABSENCE OF SYNOPTIC SCALE FORCING WARRANTS NO PCPN FCST. THE CLD AND
LGT WSW WIND WL RESTRICT THE DIURNAL TEMP FALL...WHICH SHOULD BE
MOST SUBSTANTIAL OVER THE INTERIOR SCNTRL CLOSER TO THE DEPARTING
HI/CORE OF DRIER AIR.
SHRTWV/SFC LO PRES TROF EMBEDDED IN NW FLOW ALF PROGGED TO APRCH THU
AFTN FM NW ONTARIO WITH ACCOMPANYING DPVA/DEEP LYR H85-3 QVECTOR
CNVGC IN DIFFERENTIAL TEMP ADVCTN PATTERN THAT GFS SHOWS STEEPENING
H7-5 LAPSE RATES AOA 7.0C/KM BY 00Z OVER THE NW ZNS. NAM ACTUALLY
SHOWS THE MOST INSTABILITY WITH SBCAPES APRCHG 1000J/KG...BUT WITH
SFC DWPT RISING WELL INTO THE 40S TOWARD 50. GFS FCST DWPTS IN THE
MID 30S APRCHG 40 SEEM MORE RSNBL. FOR SFC TEMP RISING INTO THE MID
60S...A SFC DWPT OF 40 YIELDS SB CAPE OF 100-200 J/KG. THIS
INSTABILITY WITH DAYTIME HTG PLUS THE APRCH OF THE SHRTWV/DYNAMICS
AND FVRBL DIFFERENTIAL ADVCTN PATTERN FAVORS LO CHC POPS OVER THE N
AND W ZNS LATER IN THE AFTN AND THEN ACRS THE REST OF THE FA THU NGT
BEFORE THE WEAK TROF SWINGS BY. PCPN CHCS WL BE LOWER OVER THE
SCNTRL WITH BETTER H85-7 FGEN SHIFTING DUE E AND TROF ARRIVAL IN THE
EARLY MRNG HRS ON FRI MOST OUT OF SINK WITH DIURNAL HTG CYCLE. MIN
RH ON THU AFTN WITH HI TEMPS AS HI AS 68 WL BE CLOSE TO 25 PCT...AND
THIS DRY LLVL AIR WL LIMIT THE COVG/INTENSITY OF ANY SHRA.
TIMING DIFFERENCES ABOUND IN THE FRI-FRI NGT PD IN REGARD TO NEXT
POTENT SYS PROGGED TO DROP SE IN NW FLOW ALF. LAST SVRL RUNS OF THE
GFS HAVE CONSISTENTLY DEPICTED A FASTER/STRONGER SHRTWV/COLD FROPA
ON FRI AFTN/EVNG. WITH THE SUPPORT OF THE 12Z ECWMF AND RUN-TO-RUN
CONSISTENCY IN A MEAN NW FLOW PATTERN THAT FAVORS FASTER/STRONGER
FROPAS...WL TEND TOWARD THE GFS FOR FCST DETAILS. SO AFTER A BIT OF
DRYING ON FRI MRNG IN THE WAKE OF DEPARTING SHRTWV (MAINTAINED LO
CHC POPS EVEN ON FRI MRNG THOUGH TO TAKE INTO ACCOUNT TIMING
QUESTIONS)...BUMPED UP POPS AGAIN FRI AFTN/NGT. GOING SPREAD OF HIER
POPS TOWARD THE E IS CONSISTENT WITH AXIS OF H3 JET MAX ACRS FAR WRN
LK SUP AND STRONGER DPVA/DEEP LYR H85-3 QVECTOR CNVGC/STEEPER LAPSE
RATES ON CYC SIDE OF THIS FEATURE. THE ONLY OTHER SGNFT CHG BEYOND
FRI NGT WAS TO CUT POPS OVER THE FAR W WITH LO PRES TO THE E SLOWLY
DEPARTING AND UPR JET AXIS OVHD WITH SFC HI PRES RDG NOSING SWD
TOWARD THIS AREA.
AVIATION (FOR THE 12Z TAF ISSUANCE)
MVFR CIGS IN WAKE OF THE FROPA THIS MORNING. SINCE UPSTREAM SITES
OVR NE MN AND NORTHERN WI ARE NOT REPORTING IFR CIGS...HAVE OPTED TO
JUST RIDE WITH LOW MVFR CIGS EARLY THIS MORNING AT BOTH SITES.
LATEST SATELITTE LOOP SHOWS SFC RIDGE AND LOW LEVEL DRYING QUICKLY
MOVING EAST...SO PROCEEDED TO SCATTER OUT CIGS BY LATE MORNING AT
BOTH SITES. GUSTY WINDS EXPECTED BY LATE MORNING. STRONGEST WINDS
SHOULD OCCUR AT KCMX AS THEY ARE FAVORED BY NW WINDS. SCT-BKN MID
CLOUDS UPSTREAM OVR MANITOBA MOVE IN LATE TODAY BUT NO PCPN IS
EXPECTED DUE TO VERY DRY AIR REMAINING BENEATH BASE OF THE CLOUDS.
MARINE (FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)
LOW PRESSURE BETWEEN LAKE SUPERIOR AND JAMES BAY AND A HIGH PRESSURE
RIDGE OVR MN LEADS TO A TIGHT PRESSURE GRADIENT TODAY. W/NW WINDS UP
TO 30 KNOTS ARE EXPECTED OVR CNTRL AND ERN SECTIONS OF LAKE SUPERIOR
WHICH IS FAVORED FOR STRONGER WINDS IN NW FLOW. LIGHTER WINDS ARE
THEN EXPECTED THROUGH FRIDAY AS A HIGH PRESSURE RIDGE AND WEAK
TROUGH COME ACROSS THE LAKE. STRONG LOW PRESSURE WILL FOLLOW THESE
SYSTEMS INTO THE UPR GREAT LAKES ON SATURDAY AND THEN MOVE TO
SOUTHERN QUEBEC SUNDAY. THE TIGHT PRESSURE GRADIENT ON THE WEST SIDE
OF THE LOW ALONG WITH UNSEASONABLY COLD AIR SURGING INTO THE AREA
COULD PRODUCE NW WINDS TO 30KT (POSSIBLY HIGHER) MUCH OF THE
WEEKEND.
MQT WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...KC
AVIATION...JLA
MARINE...JLA
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