Issued by NWS Marquette, MI
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000 FXUS63 KMQT 150538 AFDMQT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MARQUETTE MI 140 AM EDT FRI MAY 15 2009 UPDATED FOR 06Z AVIATION DISCUSSION .SHORT TERM (TONIGHT AND FRIDAY)... A ZONAL FLOW HAS SET UP ALOFT...WITH WEAK RIDING POISED TO MOVE OVER THE CWA LATE FRIDAY MORNING...IN ADVANCE OF THE SFC LOW/UPPER TROUGH DEEPENING OVER MANITOBA LATE IN THE DAY FRIDAY. WINDS WILL CONTINUE TO WEAKEN AS THE SURFACE HIGH MOVES OVERHEAD EARLY THIS EVENING...OR AT LEAST THE RIDGE FROM THE MAIN HIGH OVER THE OHIO VALLEY. ANY LINGERING CLOUDS SHOULD QUICKLY DISSIPATE BY 02Z AS HIGH PRESSURE NOSES INTO THE FORECAST AREA. PW VALUES WILL BOTTOM OUT BETWEEN 00Z AND 06Z AROUND 0.3 INCHES...ROUGHLY 40 TO 50 PERCENT OF NORMAL. A MID DECK SHOULD ALSO SLIDE IN FROM THE WSW AFTER 06Z. WILL KEEP AN EYE UPSTREAM TO THE CURRENT MID TO HIGH CLOUDS OVER SOUTHERN SASKATCHEWAN...AND THEIR QUICK EASTWARD PROGRESSION. THESE ADDITIONAL CLOUDS...IF THEY DEVELOP...WILL KEEP TEMPERATURES FROM BOTTOMING OUT TOO LOW...AND NEAR 40 DEGREES FAR WEST NEAR IWD AND SOUTH NEAR MNM. HAVE OPTED TO TAKE PATCHY FROST OUT FOR NOW...THOUGH IT MAY NEED TO BE ADDED IN ONCE AGAIN IN THE CLEAR SKY LINGERS LONGER THAN ANTICIPATED. EXPECT SSE WINDS TO BE ON THE INCREASE FROM MID MORNING FRIDAY ON AS THE SURFACE LOW MOVES FROM THE EASTERN DAKOTAS TO WESTERN LAKE SUPERIOR BY THE CLOSE OF BUSINESS FRIDAY. A SLIGHTLY MORE WRAPPED UP SYSTEM FRIDAY AFTERNOON LOOKS TO KEEP CENTRAL AND EASTERN UPPER MICHIGAN DRY THROUGH 00Z SATURDAY. && .LONG TERM (FRIDAY NIGHT THROUGH THURSDAY)... LONG TERM PERIOD BEGINS WITH UPPER TROUGH DIGGING OVER THE NRN PLAINS AND ELONGATED SFC LOW OVER NRN MN. THIS SFC LOW WILL TRACK NE AND INTENSIFY AS IT REACHES JAMES BAY BY 00Z SUN. NAM/GFS/ECMWF/GEM ARE FAIRLY CONSISTENT WITH THE POSITIONING OF THE LOW BY 00Z SUN...BUT THE INTENSITY VARIES. THE STRONGEST RUNS ARE THE 00Z ECMWF/GEM AND THE 12 Z NAM AROUND 993MB...WITH THE 12Z GFS RUN AROUND 998MB WHICH IS A LITTLE STRONGER THAN PAST RUNS. SINCE THERE IS PRETTY GOOD AGREEMENT...HAVE DECIDED TO GO WITH A BLEND OF THE 12Z NAM AND 00Z ECMWF FOR THE FRI NIGHT THROUGH 00Z SUN PERIOD. UPPER WAVE ROTATES NE AROUND THE TROUGH AND CLOSER TO THE LOW ON FRI NIGHT...BRINGING BEST QPF ACROSS THE NW PART OF THE LK SUPERIOR. OCCLUDED FRONT LOOKS TO MOVE FROM W TO E ACROSS THE AREA ON FRI NIGHT...AS BEST WARM/COLD FRONT FORCING AND PCPN MOVES ACROSS SE WI AND CENTRAL LOWER MI. OVERALL...MODERATE ISENTROPIC ASCENT...H850-500 Q-VECTOR CONV...AND A MOIST ATMO SHOULD PRODUCE AROUND A QUARTER INCH OF PCPN ACROSS THE CWA AS THE FRONT MOVES THROUGH. THEREFORE...LIKELY POPS SEEM REASONABLE AND WILL ONLY MAKE MINOR TWEAKS TO THE TIMING. INSTABILITY IS STILL LACKING...WITH LITTLE TO NO SFC/ELEV CAPE AND H850-500 LR/S AROUND 5.5C/KM...SO WILL CONTINUE JUST THE SLIGHT CHANCE OF THUNDER. DRY SLOT BEHIND THE FRONT MOVES ACROSS THE CWA FROM W TO E STARTING FRI EVENING...WHICH SEEMS A LITTLE FASTER THAN YESTERDAYS RUNS...SO HAVE DIMINISHED POPS OVER THE W AFTER MIDNIGHT AND TRIED TO ADD A LITTLE MORE TIMING TO THE POPS. THIS SHOULD BRING SOME BREAKS IN THE CLOUDS FOR LATE FRI NIGHT AND INTO SAT MORNING...BEFORE LLVL MOISTURE ROTATING AROUND THE LOW SWEEPS ACROSS MOST OF THE CWA ON SAT AND THE UPPER TROUGH ROTATES THROUGH. VERY STRONG SURGE OF COLD AIR IS STILL SHOWN ON THE LATEST GFS/NAM RUNS...WITH H850 TEMPS DROPPING TO -7C BY 18Z SAT. THIS SHOULD KEEP THE WRN HALF OF UPPER MI 10-15 DEGREES BELOW NORMAL DURING THE AFTN...WITH TEMPS STRUGGLING TO REACH THE LOW 40S. THAT COLD H850 AIR AND THE RELATIVELY WARM LK SUP TEMPS...AROUND 2C...MAY PRODUCE A LITTLE LK ENHANCED PCPN ACROSS THE WRN CWA. THE STRONG WINDS AND MAINLY LLVL MOISTURE WILL KEEP THE CLOUDS FAIRLY SHALLOW...BUT THINK THERE WILL BE ENOUGH INSTABILITY OFF THE LK AND STEEP LLVL LR/S TO PRODUCE SOME ISOLATED SHOWERS DURING THE LATE MORNING AND AFTN. HAVE ADDED THE SLIGHT CHANCE OF PCPN IN AND MENTIONED SN IN THE MORN...AS THE COOLING TEMPS BRING THE TOP OF THE CLOUD DECK INTO THE -10-13C RANGE PER BUFKIT SOUNDINGS. THE PREVIOUSLY MENTIONED STRONG WINDS SHOULD GUST TO 35 TO 40KTS ALONG THE KEWEENAW PENINSULA...AS H925-850 WINDS ARE TO 40KTS WITH THE CAA ALLOWING THOSE WINDS TO COME DOWN. OVERALL...THE FRI NIGHT AND SAT PERIOD LOOKS TO BE VERY SIMILAR TO LAST NIGHT AND TODAY...BUT WITH SLIGHTLY COLDER H850 TEMPS. HIGH PRESSURE SLIDES OUT OF THE NRN PLAINS AND ACROSS THE AREA ON SAT NIGHT AND SUN...AS AN UPPER RIDGE BUILDS OVER THE WRN 2/3RDS OF THE CONUS. WITH THE RIDGE BUILDING N OF THE US/CANADA BORDER...A WEAK LOW DEVELOPS ALONG HUDSON BAY WITH A COLD FRONT STRETCHING SW TO A DEVELOPING LOW OVER THE NRN ROCKIES BY 12Z MON. SAT NIGHT AND SUN SHOULD BE COOL BUT NICE WX...AS HIGH PRESSURE DRIFTS ACROSS THE REGION. HAVE LOWERED SAT NIGHT LOWS INTO THE MID 20S...AS WINDS GRADUALLY DIMINISH OVERNIGHT AND SKIES CLEAR. ADDED MENTION OF FROST FOR LOCATIONS LESS THAN 32 DEGREES AND WINDS LESS THAN 10-15KTS LATE SAT NIGHT. MAIN CONCERN FOR SUN WILL BE DROPPING TD VALUES AS AREA MIXES INTO DRIER AIR ALOFT. OUR LOCAL MIXED TD TOOL GIVES VALUES IN THE HIGH SINGLE DIGITS OVER THE INTERIOR WEST HALF OF THE CWA...WHILE NAM/GFS ML TD/S ARE IN THE TEENS. THUS...HAVE SPLIT THE DIFF FOR NOW AND MAY NEED TO BE ADJUSTED DOWN ON FUTURE SHIFTS. AFTER 12Z MON...MODEL DIFFERENCES BEGIN TO APPEAR AND LEADS TO A LESS CONFIDENT FORECAST. 00Z ECMWF...LIKE THE LAST 2 RUNS...STILL SHOWS THE RIDGE BREAKING DOWN AND DRIVING THE UPPER TROUGH SE ACROSS THE GREAT LAKES REGION. THIS CAUSES THE COLD FRONT TO DIVE RIGHT THROUGH THE AREA ON MON NIGHT...ACROSS THE MID ATLANTIC STATES...AND OVER THE ATLANTIC BY 00Z THURS. ON THE OTHERHAND...THE 00Z GFS/UKMET/GEM/GFS ENS AND 12Z GFS ALL STALL THE COLD FRONT SOMEWHERE AROUND OR N OF THE CWA ON MON NIGHT...AS A LOW DEVELOPS OVER THE NRN PLAINS. WILL FOLLOW A BLEND OF THE LATTER SOLUTION...DUE TO THE BETTER AGREEMENT IN THOSE MODELS AND BASED OFF NATIONAL GUIDANCE FOLLOWING A BLEND OF GFS/ECMWF ENS MEANS. THUS...PCPN CHANCES AND TEMPS WILL DEPEND ON WHERE THE FRONT ENDS UP STALLING OUT. A FARTHER N SOLUTION...AS SHOWN ON THE 00/06Z RUNS OF THE GFS...WILL KEEP THE AREA IN THE WARM SECTOR AS THE WARM FRONT SETS UP NEAR US/CANADA BORDER. THIS WILL ALLOW SW WINDS TO BRING WARMER TEMPS TO THE AREA AND KEEP THE PCPN OVER NRN LK SUPERIOR OR SRN CANADA THROUGH THURS. WHILE THE UKMET/GEM SHOW THE FRONT STALLING RIGHT OVER THE CWA ON MON NIGHT AND TUES...BEFORE PUSHING TO THE N ON TUES AND INTO WED. BUMPED TEMPS UP ON MON THROUGH WED PERIOD DUE TO EXPECTED BOUNDARY PUSHING N...BUT DIDN/T GO AS HIGH AS GFS AND GFS ENS BASED ON THE UNCERTAINTY. ALSO...PUT LOW CHANCE POPS ACROSS THE NRN HALF OF THE CWA FOR MON THROUGH TUES NIGHT...WITH THE BEST CHANCES ON MON NIGHT...AS THE FRONT PUSHES INTO LK SUP AND THEN STALLS. && .AVIATION (FOR THE 06Z TAF ISSUANCE)... VFR CONDITIONS ARE EXPECTED TO PREVAIL TONIGHT THROUGH FRIDAY BUT EXPECT MID/HIGH CLOUDS TO MOVE IN OVERNIGHT IN ADVANCE OF THE NEXT SURFACE LOW IN THE NORTHERN PLAINS. A PERIOD OF RAIN SHOWERS IS EXPECTED AHEAD OF A COLD FRONT MOVING THROUGH THE REGION WHICH MAY BE ACCOMPANIED BY MVFR CIGS/VSBY. && .MARINE (FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE)... LOW PRESSURE NEAR JAMES BAY WILL CONTINUE TO PUSH NORTHEASTWARD INTO QUEBEC...BRINGING AN END TO OUR GALES TEMPORARILY. HIGH PRESSURE STRETCHING FROM LAKE SUPERIOR THROUGH THE OHIO VALLEY WILL STRENGTHEN ACROSS EASTERN ONTARIO AND THE LOWER GREAT LAKES FRIDAY. THIS WILL ALLOW LOW PRESSURE TO MOVE FROM THE DAKOTAS FRIDAY MORNING...TO JUST NORTH OF LAKE SUPERIOR BY LATE FRIDAY. EXPECT SOUTHERLY WINDS TO 30KTS FRIDAY AHEAD OF ANOTHER CHANCE OF GALES ONCE AGAIN SATURDAY. ON SATURDAY...THE LOW SHOULD SLIDE TO SOUTHERN JAMES BAY...WHILE HIGH PRESSURE DIVES INTO THE PLAINS STATES. THE HIGH WILL MOVE OVER THE OHIO VALLEY SUNDAY...AND SLIDE A RIDGE ACROSS LAKE SUPERIOR. EXPECT THE HIGH TO PUSH TO THE NORTHEASTERN STATES MONDAY AND TUESDAY. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN...NONE. LAKE SUPERIOR... GALE WARNING UNTIL 7 PM EDT THIS EVENING FOR LSZ244-245-264>267. GALE WARNING UNTIL 5 PM EDT THIS AFTERNOON FOR LSZ263. GALE WARNING UNTIL 6 PM EDT THIS EVENING FOR LSZ242-243-246- 249>251. GALE WARNING UNTIL 4 PM EDT THIS AFTERNOON FOR LSZ247-248. LAKE MICHIGAN...NONE. && $$ SHORT TERM...KF LONG TERM...SRF AVIATION...JLB MARINE...KF