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000
FXUS63 KMQT 200522
AFDMQT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MARQUETTE MI
122 AM EDT MON MAY 20 2013

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 353 PM EDT SUN MAY 19 2013

VERY SUBTLE FEATURES DOMINATING THE SHORT TERM FORECAST PERIOD.
LONGWAVE TROUGH IS CURRENTLY SETUP OVER MUCH OF THE EASTERN HALF OF
THE CONUS...WHILE RIDGING IS OCCURRING OVER THE EASTERN GREAT LAKES
AND A GOOD PORTION OF THE EASTERN CONUS. THIS PUTS THE AREA UNDER
THE UPPER RIDGE AXIS THIS AFTERNOON AND HAS BEEN ONE OF THE MAIN
REASONS THERE HAS BEEN LIMITED SHOWER/THUNDERSTORM OVER UPPER
MICHIGAN. WITHIN THIS UPPER TROUGH...SEVERAL SHORTWAVES HAVE BEEN
ROTATING NORTH THROUGH THE UPPER MISSISSIPPI VALLEY AND LEADING TO
SHOWER/THUNDERSTORM DEVELOPMENT. THE MAIN SHORTWAVE AND CONVECTION
THAT WILL BE INFLUENCING THIS AREA IS CURRENTLY PUSHING NORTH TH
ROUGH NORTHERN IOWA AND INTO SOUTHERN MN. THIS IS JUST SOUTH OF THE
WARM FRONT STRETCHING EAST FROM THE LOW LOCATED IN EASTERN SOUTH
DAKOTA AND THROUGH CENTRAL MINNESOTA AND INTO NORTHEAST IOWA.
CLOSER TO HOME...SHORTWAVE AND ELEVATED WARM AIR ADVECTION THAT
KICKED OFF THE SHOWERS OVER LAKE SUPERIOR AND THE KEWEENAW EARLIER
TODAY HAS BEEN MOVING NORTH AND EXPECT THAT TO SLOWLY CONTINUE AS
THE RIDGE AXIS SLOWLY MOVES NORTHEAST THIS EVENING. A POCKET OF
LOW-MID LEVEL DRY AIR UNDER THIS RIDGE HAS LIMITED THE CLOUD
DEVELOPMENT THUS FAR AND THE SPC MESO ANALYSIS ONLY INDICATES ML
CAPE VALUES AROUND 100-250 J/KG THIS AFTERNOON. EVEN THOUGH THERE
ARE SOME BREAKS IN THE CLOUDS TO ENHANCE HEATING...THINK THIS WILL
BE ENOUGH TO HOLD OFF SHOWER DEVELOPMENT THIS AFTERNOON.

THUS...THE QUESTION FOR TONIGHT INTO MONDAY IS WHAT WILL HAPPEN
TO THE DEVELOPING CONVECTION IN SOUTHERN MN...WHICH WILL PROVIDE
THE INITIAL OPPORTUNITY FOR CONVECTION FOR THE AREA. BEST
INSTABILITY...1K-2.5K J/KG OF MLCAPE...IS LOCATED OVER SOUTHERN
MN...SW WISCONSIN...AND NORTHEAST IOWA THIS AFTERNOON AND IS ALSO
WHERE THE 850MB JET HAS INTENSIFIED. WITH THE SHORTWAVE PUSHING
THROUGH THAT AREA NOW...STARTING TO SEE DEVELOPMENT SOUTH OF THE
TWIN CITIES OVER THE LAST COUPLE OF HOURS. BASED OFF THE TRACK OF
THE SHORTWAVE AND THE EXPECTED STORM MOTION FROM THE STORMS
CURRENTLY IN MN /TO THE NORTH-NORTHEAST/...WOULD EXPECT THEM TO MISS
THE LAND CWA AND JUST SLIDE ACROSS WESTERN LAKE SUPERIOR.
ALSO...WOULD EXPECT THE INTENSITY TO DIMINISH AS THEY HEAD NNE DUE
TO THE DIMINISHING INSTABILITY OVER THE AREA...MOVING INTO 250-500
J/KG OF MUCAPE AND SIMILAR TO WHAT WAS SEEN TODAY OVER LAKE
SUPERIOR. TO GET RAIN INTO THE AREA...THE THUNDERSTORMS WOULD NEED
TO BUILD SOUTHEAST INTO THE BETTER INSTABILITY...WHICH WOULD ALLOW
THE STORM MOTION TO PULL THEM OVER THE WESTERN CWA. EXPECT THAT TO
HAPPEN OVER THE NEXT FEW HOURS AND HAVE FOLLOWED THAT IDEA FOR POPS
TONIGHT...WITH THE HIGHEST OVER THE WEST AND DIMINISHING TOWARDS THE
EAST. WITH THE LIMITED AND TALL/SKINNY INSTABILITY...WOULD THINK
HEAVY RAIN WOULD BE THE MAIN THREAT...BUT THERE COULD BE HAIL FROM
ANY STRONGER STORM OVER THE FAR SOUTHWEST CWA.

MONDAY MORNING CONTINUES THE MORE FAVORABLE CONDITIONS FOR
WIDESPREAD SHOWERS AND CONVECTION...AS THE UPPER LOW BEGINS TO
SLOWLY SHIFT EAST AND THE UPPER JET FOCUSES IN WISCONSIN AND UPPER
MICHIGAN. MODELS SHOWING THE 850MB WARM FRONT LIFTING NORTH INTO
THE CWA DURING THE MORNING HOURS WHILE ANOTHER SHORTWAVE LIFTS INTO
THE UPPER GREAT LAKES TOWARDS MID DAY. THESE TWO FEATURES...ALONG
WITH THE UPPER JET FOCUSING NORTHEAT INTO THE GREAT LAKES WILL LEAD
TO THE BEST CHANCE FOR SHOWERS/THUNDERSTORMS OVER THE
CENTRAL/EASTERN CWA. HAVE SHOWN A PERIOD OF LIKELY TO DEFINITE POPS
FOR THE EXPECTED TIME OF THE PASSAGE. IT CONTINUES TO LOOK LIKE A
SHARP GRADIENT TO THE MUCAPE VALUES ACROSS THE CWA...WITH LITTLE TO
NO CAPE OVER NORTHERN LAKE SUPERIOR AND VALUES INCREASING TOWARDS
1500 J/KG ALONG AND SOUTH OF THE WARM FRONT IN THE AFTERNOON.
ALTHOUGH THERE WILL BE SOME THUNDER IN THE MORNING...THE GREATEST
CONCERN WILL BE DURING THE AFTERNOON BEHIND THE WARM FRONT WHEN THE
BEST INSTABILITY OCCURS. AT THE SAME TIME...POCKET OF DRIER AIR AT
850-700MB WILL BE MOVING THROUGH SOME PORTION OF THE UPPER GREAT
LAKES REGION TOMORROW AFTERNOON AS THE 850MB WARM FRONT MOVES OVER
THE NORTHERN HALF OF THE CWA. THIS COULD LIMIT COVERAGE OF ANY
SHOWERS/THUNDERSTORMS IN THOSE AREAS OVER THE SOUTH HALF AND WILL GO
WILL LOWER POPS IN THE AFTERNOON. MUCH OF THE FORECAST WILL DEPEND
ON THE EVOLUTION OF THE CONVECTION TONIGHT INTO TOMORROW
MORNING...SO WON/T MAKE A SIGNIFICANT LOWERING OF THE POPS AND KEEP
THEM IN THE HIGH CHANCE OR LOW LIKELY CATEGORY.

LAST ITEM OF CONCERN WILL BE FOG OVER LAKE SUPERIOR AND HOW
FAR EAST IT SPREADS...ALONG WITH COMING ON SHORE TONIGHT. HAVEN/T
SEEM MUCH FOR LOWER VISIBILITIES FROM SHIP OBS OVER THE WESTERN
LAKE...BUT A FEW BREAKS IN THE CLOUDS INDICATED LOW STRATUS OR
FOG JUST NORTHWEST OF THE APOSTLE ISLANDS. WILL CONTINUE TO
MENTION AREAS/WIDESPREAD FOG OVER THE WESTERN LAKE AND THEN TRY TO
SPREAD IT EAST THROUGH THE NIGHT AND INTO MONDAY AS PRECIPITATION
INCREASES TO THE EAST. CONFIDENCE IS LOW ON THE TIMING AND HAVE
DELAYED THE EASTWARD EXTENT SOME WHAT WITH A LATER ARRIVAL TO THE
RAIN.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 353 PM EDT SUN MAY 19 2013

MONDAY NIGHT INTO TUE...THE MID/UPPER LEVEL LOW IS EXPECTED TO
REMAIN NEARLY STATIONARY OVER THE ERN DAKOTAS WHILE THE MAIN SFC
FRONTAL BOUNDARY EXTENDS FROM THE LOW OVER NE SD THROUGH SRN MN INTO
CNTRL WI. SHRA AND POSSIBLE TSRA ARE STILL EXPECTED WITH SFC
TROUGH/FRONT JUST TO THE SOUTH...CONTINUED MODERATE 700-300 MB
QVECTOR CONV AHEAD OF THE MID LEVEL LOW. ALTHOUGH LIKELY POPS
CONTINUE...THERE IS MORE UNCERTAINTY WITH THE TIMING/POSITION OF
PCPN AREAS THAT WILL BE SUPPORTED BY THE WEAKER SHORTWAVES. MUCAPE
VALUES GENERALLY IN THE 500-1000 J/KG RANGE MAY SUPPORT SCT/ISOLD
TSRA. HOWEVER...WITH THE MARGINAL INSTABILITY...THE RISK FOR STONGER
STORMS WILL BE MINIMAL.

TUE NIGHT AND WED...MODELS WERE IN GOOD AGREEMENT THAT THE MID LEVEL
LOW WILL FINALLY BEGINS TO SHEAR AND WEAKEN RESULTING IN SLOWLY
DIMINISHING PCPN CHANCES AND INTENSITY.

THU...MODELS HAVE CONTINUED WITH THE TREND TOWARD DRY WEATHER AS NW
FLOW NRN STREAM FLOW TAKES OVER AND A SFC RIDGE BUILDS INTO THE
REGION FROM NRN ONTARIO. BREEZY NORTH TO NE WINDS WILL KEEP TEMPS
MAINLY IN THE MID AND UPPER 50S WITH EVEN SOME UPPER 40S ALONG LAKE
SUPERIOR.

FRI-SAT...WITH CONFLUENT NW MID/UPPER LEVEL FLOW THROUGH THE WRN
GREAT LAKES BTWN THE TROUGH OVER ERN CANADA AND A RIDGE OVER THE
PLAINS...HIGH PRES AND COOL DRY CONDITIONS WILL PREVAIL. 850 MB
TEMPS FROM -2C TO 2C EARLY FRIDAY...PER GFS/ECMWF...SLOWLY MODIFY TO
AROUND 6C SATURDAY AS THE SFC RIDGE MOVES EAST OF THE AREA. WELL
BELOW NORMAL TEMPERATURES FROM AROUND 50 NORTH TO 60 SOUTH ARE
EXPECTED TO CLIMB BACK INTO THE 60S SATURDAY.

SUN...THE 00Z ECMWF WAS FASTER WITH THE TRANSITION TOWARD A MORE
ZONAL PATTERN COMPARED TO THE GFS/GEFS. THE ECMWF SCENARIO WOULD
RESULT IN PCPN CHANCES BY SAT NIGHT INTO SUN AS WAA AND MOISTURE
INFLOW RETURNS INTO THE AREA. GIVEN LARGE DIFFERENCES AND LARGE
ECMWF CHANGE COMPARED TO PREVIOUS RUNS...CONFIDENCE IN OVERALL
PATTERN DETAILS AND PCPN CHANCES IS LOW.
&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 122 AM EDT MON MAY 20 2013

CHALLENGING FCST WILL CONTINUE OVER THE NEXT DAY OR SO. WITH RADAR
SHOWING PLENTY OF PCPN UPSTREAM...EXPECT SHRA/OCNL TSRA AT KIWD
OVERNIGHT WITH CONDITIONS VARYING BTWN VFR/MVFR. AFTER MID
MORNING...PCPN FCST IS MUCH MORE UNCERTAIN. WHILE THERE MAY BE
SHRA/TSRA AT TIMES...DIFFICULT TO PIN DOWN BEST TIME FRAME.
GENERALLY FAVORED VFR CONDITIONS UNDER A DOWNSLOPING ESE/SE WIND. AT
KCMX...UPSLOPE E FLOW THRU THE FCST PERIOD SUGGESTS PREVAILING LIFR
CONDITIONS...BUT AS OBS HAVE SHOWN...THERE MAY BE SOME VARIABILITY
AT TIMES. EXPECT OCNL SHRA. AT KSAW...MVFR CONDITIONS WILL LIKELY
PREVAIL THRU MUCH OF THE FCST PERIOD ALONG WITH OCNL -SHRA. MAY
BREAK OUT TO VFR THIS AFTN...BUT CONFIDENCE IS LOW.
&&

.MARINE...(FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE)
ISSUED AT 353 PM EDT SUN MAY 19 2013

A BROAD LOW PRESSURE SYSTEM CURRENTLY SPINNING IN THE
NORTHERN/CENTRAL PLAINS WILL FOCUS OVER THE UPPER GREAT LAKES
TONIGHT AND REMAIN INTO MONDAY EVENING. EXPECT THE MARINE LAYER TO
HOLD WINDS IN CHECK TONIGHT INTO MONDAY...MAINLY FROM 20-25KTS...BUT
A FEW HIGHER PLATFORMS COULD SEE GUSTS TOWARDS 30KTS OR EVEN 35KTS.
THE LOW WILL BEGIN TO SLIDE EAST ON TUESDAY AND SLOWLY MOVE ACROSS
THE LOWER GREAT LAKES ON TUESDAY NIGHT INTO THURSDAY MORNING.
EAST-NORTHEAST WINDS ARE EXPECTED DURING THIS PERIOD...MAINLY IN THE
15-25KT RANGE. CANADIAN HIGH PRESSURE WILL THEN BUILD OVER THE UPPER
GREAT LAKES THURSDAY AFTERNOON AND REMAIN INTO THE FIRST PART OF THE
WEEKEND...PRODUCING LIGHT WINDS.

WITH THE WARM/MOIST AIR MASS MOVING OVER THE COOL LAKE SUPERIOR
WATERS...EXPECT FOG TO CONTINUE OVER THE WEST AND THEN EVENTUALLY
SPREAD EAST OVER PORTIONS OF CENTRAL AND EASTERN LAKE SUPERIOR
TONIGHT INTO MONDAY. THE TIMING OF THIS EASTWARD SPREAD IS A LITTLE
UNCERTAIN...AS IT DEPENDS ON WHEN THE RAIN ARRIVES OVER THE EAST TO
PROVIDE ADDITIONAL MOISTURE. ONCE THE FOG SETS IN...IT WILL LIKELY
CONTINUE UNTIL TUESDAY NIGHT OR WEDNESDAY.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
UPPER MICHIGAN...
NONE.
LAKE SUPERIOR...
NONE.
LAKE MICHIGAN...
NONE.
&&

$$

SHORT TERM...SRF
LONG TERM...JLB
AVIATION...ROLFSON
MARINE...SRF