000 
FXUS63 KAPX 201930
AFDAPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
330 AM EDT THU SEP 20 2007

.DISCUSSION...SURFACE HIGH PRESSURE CENTER HAS PUSHED JUST EAST OF 
MICHIGAN LATE THIS AFTERNOON. STRONG SUBSIDENCE AND DRY AIR REMAIN 
IN CONTROL OF THE WX ACROSS THE STATE. UPSTREAM MCS OVER MINNESOTA 
IS MAINTAINING STRENGTH AND ORGANIZATION...FEEDING OFF OF PRONOUNCED 
850 MB THETA E RIDGING...GOOD INSTABILITY AND IMPRESSIVE WIND 
FIELDS/EXCELLENT DIRECTIONAL SHEAR. CLOSER TO HOME...LEADING EDGE OF 
THE CI SHIELD FROM THIS CONVECTION IS PUSHING TOWARD NRN LAKE 
MICHIGAN...BUT HAS YET TO REACH OUR CWA. SKIES REMAIN MOSTLY SUNNY 
ACROSS ERN UPR AND NRN LWR MICHIGAN AT THIS HOUR...WITH LIGHT WINDS 
AND SEASONAL TEMPS. WX REMAINS QUIET THRU THE OVERNIGHT HOURS. OUR 
ATTENTION THEN TURNS TO INCREASING CHANCES OF SHRA/TSRA BY FRIDAY 
AFTERNOON AS INSTABILITY...MOISTURE AND WIND SHEAR INCREASE ACROSS 
THE WRN GREAT LAKES AHEAD OF AN APPROACHING COLD FRONT.

TONIGHT AND FRIDAY...HIGH PRESSURE CENTER WILL CONTINUE NE INTO 
QUEBEC THIS EVENING...BUT SUBSIDENCE AND DRY AIR WILL REMAIN OVER 
OUR CWA. EXPECT ONLY A FEW DEBRIS CI WILL REACH NW SECTIONS OF OUR 
CWA THIS EVENING...THEN SCT-BKN MID/HIGH CLOUD WILL INCREASE FROM  
NW TO SE OVERNIGHT INTO FRIDAY MORNING. WIND SPEEDS WILL ALSO BEGIN 
TO INCREASE...FIRST ALOFT OVERNIGHT (I.E. LENDING TO LLWS) AND THEN 
PARTIALLY MIXING DOWN TO THE SURFACE BY MID TO LATE MORNING AS 
SURFACE PRESSURE GRADIENT TIGHTENS AHEAD OF THE APPROACHING COLD 
FRONT. CHANCES OF SHRA/TSRA WILL INCREASE EARLY AFTERNOON FOR 
LOCATIONS N OF A LINE FROM PAN TO GOV TO FKS AS SFC INSTABILITY AXIS 
AND 850 MB THETA E RIDGING LAYS INTO THIS LOCATION. BOTH SPEED AND 
DIRECTIONAL SHEAR WILL BE INCREASING AS THE AFTERNOON PROGRESSES AS 
WELL...WITH THE MOST IMPRESSIVE WIND SHEAR DEVELOPING ACROSS ERN UPR 
MICHIGAN BY LATE AFTERNOON. SEVERE WX IS NOT EXPECTED AS BEST 
INSTABILITY AND MOISTURE WILL STILL BE UPSTREAM ALONG AND AHEAD OF 
THE FRONT...BUT A FEW STRONG STORMS ARE CERTAINLY POSSIBLE DUE TO 
STRENGTHENING WIND SHEAR THRU THE COLUMN. WILL MAINTAIN CHANCE POPS 
FOR MUCH OF THE CWA DURING THE AFTERNOON...WITH LOCATIONS SOUTH OF 
THIS LINE REMAINING DRY UNTIL FRIDAY EVENING. STRENGTHENING WAA WILL 
BOOST HIGH TEMPS INTO THE UPPER 70S IN ERN UPR MICHIGAN AND INTO THE 
LOWER TO MID 80S IN NRN LWR MICHIGAN. 

REST OF FORECAST (FRIDAY NIGHT THROUGH THURSDAY)...SOMEWHAT TYPICAL 
EARLY FALL PATTERN EXPECTED THROUGH THE LONG TERM AS ENERGETIC 
NORTHERN STREAM FLOW SENDS A COUPLE STRONG (A SURE SIGN OF FALL) 
STORM SYSTEMS ACROSS ACROSS SOUTHERN CANADA AND THE NORTHERN CONUS. 
EARLY AFTERNOON NORTHERN HEMISPHERIC WATER VAPOR IMAGERY SHOWS 
SEVERAL KEY PLAYERS OF INTEREST. TO OUR WEST...STRONG SHORTWAVE 
DIGGING SOUTHEAST ACROSS SOUTHERN ALBERTA WITH NEXT POTENT SHORTWAVE 
FARTHER UPSTREAM OVER THE ALEUTIAN ISLAND CHAIN AND UNSEASONABLY 
STRONG MID LEVEL CLOSED LOW MEANDERING JUST OF THE CENTRAL 
CALIFORNIA COASTLINE. FINALLY...TO OUR SOUTH...DEVELOPING LOW 
PRESSURE MAKING SLOW BUT STEADY WESTWARD PROGRESS INTO THE EASTERN 
GULF OF MEXICO. FORECAST CHALLENGES THROUGH THE EXTENDED CENTER ON 
RAIN THREAT WITH PASSAGE...AND POSSIBLE INTERACTION...OF THESE 
SYSTEMS AS THEY CROSS THE NORTHERN MICHIGAN LANDSCAPE.

FRIDAY NIGHT...THIS AFTERNOONS SOUTHERN ALBERTA SHORTWAVE CUTS ACROSS 
THE NORTHERN HIGH PLAINS FRIDAY...SPAWNING RATHER DEEP SURFACE LOW 
DEVELOPMENT OVER SOUTHWEST ONTARIO BY FRIDAY AFTERNOON. THIS SYSTEM 
IS EXPECTED TO CONTINUE TO DEEPEN AS IT HEADS NORTHEAST...DRAGGING 
ITS ASSOCIATED COLD FRONT ACROSS NORTHERN MICHIGAN DURING THE 
OVERNIGHT HOURS. SEE NO REASON TO DEVIATE FROM PREVIOUS FORECASTERS 
THINKING...WITH LIKELY POPS DURING THE EVENING BASICALLY NORTH OF 
M-72...CLOSER TO BETTER SHORTWAVE DYNAMICS AND GOOD EXIT REGION JET 
DYNAMICS...AND DRYING THINGS OUT FROM WEST TO EAST AFTER MIDNIGHT. 
DESPITE GOOD DYNAMICS...NOT EXPECTING ANY TYPE OF SEVERE WEATHER 
OUTBREAK GIVING UNFAVORABLE OVERNIGHT FRONTAL PASSAGE...WITH 
CORRESPONDING MEAN LAYER CAPE OF ONLY 500 J/KG OR SO AND SOME 
LINGERING CIN TO OVERCOME (LATEST SPC DAY-2 GRAPHICS KEEP SEVERE 
THREAT CONFINED TO AREAS TO OUR WEST). HOWEVER...CANNOT RULE OUT 
ISOLATED SEVERE WIND THREAT WITH SOUNDINGS SHOWING WINDS TO 55 KNOTS 
RIGHT OFF THE DECK (925MB) AND 500MB WINDS UPWARDS OF 70 KNOTS. WILL 
CONTINUE TO HIGHLIGHT THIS POTENTIAL IN THE HWO. IT WILL BE RATHER 
WINDY OTHERWISE AS PRESSURE GRADIENT RAMPS UP WITH APPROACH OF 
SYSTEM. HELD OFF ANY MARINE HEADLINES AT THIS EARLY JUNCTURE...BUT 
COULD EASILY SEE THE NEED FOR AT LEAST SCA/S OVER MANY OF OUR 
NEARSHORE WATERS. TEMPERATURES STAY SEASONABLY MILD WITH READINGS 
DROPPING INTO THE 50S. 

SATURDAY AND SATURDAY NIGHT...MID LEVEL HEIGHTS RISE QUICKLY BEHIND 
FRIDAY NIGHTS DEPARTING SYSTEM...WHILE...AT THE SURFACE...A LARGE 
AREA OF HIGH PRESSURE DRIFTS ACROSS THE LAKES REGION. THUS...EXPECT 
MORE SEASONABLE TEMPERATURES UNDER PLENTY OF CLEAR SKIES. HIGHS 
SATURDAY SHOULD RANGE FROM THE MIDDLE 60S NORTH TO THE MID 70S FAR 
SOUTHEAST. GOOD RADIATIONAL COOLING CONDITIONS SATURDAY NIGHT UNDER 
LIGHT WIND REGIME SHOULD DROP TEMPERATURES WELL INTO THE LOW TO MID 
40S...WITH A FEW ISOLATED UPPER 30S POSSIBLE IN TYPICAL COLDER 
INTERIOR LOCATIONS OF NORTHERN LOWER MICHIGAN.

SUNDAY AND SUNDAY NIGHT...DRY WEATHER WILL PREVAIL AS MID AND 
UPPER LEVEL RIDGING GOES THROUGH FURTHER AMPLIFICATION OVER THE 
GREAT LAKES AND EASTER CONUS AS ALEUTIAN SHORTWAVE MERGES WITH 
CALIFORNIA COAST MID LEVEL LOW...EVENTUALLY CARVING OUT A DEEP 
INTERMOUNTAIN TROUGH SUNDAY. LIGHT SOUTHERLY RETURN FLOW ON BACKSIDE 
OF DEPARTING SURFACE HIGH PRESSURE WILL KICK OFF A SLOW MODERATING 
TREND. WHILE 850MB TEMPERATURES APPROACHING THE MID TEENS SUNDAY 
AFTERNOON WOULD ARGUE FOR HIGHS IN THE LOW TO MID 80S...AS IS 
TYPICAL IN THE FALL...GOOD SURFACE BASED MIXING THROUGH THIS LAYER 
WILL NOT LIKELY BE REALIZED. THEREFORE...WILL CUT THESE VALUES BY A 
GOOD 5 TO 10 DEGREES...WITH READINGS EXPECTED TO RANGE IN THE 70S 
ACROSS THE AREA. MUCH MILDER CONDITIONS EXPECTED SATURDAY 
NIGHT...WITH LOWS ONLY DROPPING INTO THE 50S.

MONDAY THROUGH TUESDAY...INTERMOUNTAIN SHORTWAVE GETS THE BOOT EAST 
AS NEXT PACIFIC SYSTEM MOVES INTO THE NORTHWEST. STILL SOME TIMING 
ISSUES WITH LATEST GFS ABOUT 6 HRS FASTER BRINGING IN SHOWER AND 
THUNDERSTORM THREAT THAN LATEST HI RESOLUTION ECMWF. GIVEN SOME 
PERSISTENCE FROM LAST SEVERAL GFS RUNS...HAVE GONE AHEAD AND SPLIT 
THE DIFFERENCE...BRINGING IN CHANCE POPS OVER EASTER UPPER AND 
NORTHWEST LOWER DURING THE AFTERNOON. SYSTEM HAS THE POTENTIAL OF 
BRINGING SOME MUCH NEEDED WIDESPREAD RAINFALL TO THE NORTHERN 
LAKES...ESPECIALLY MONDAY NIGHT...WITH MODELS SUGGESTING THAT 
REMNANT MOISTURE FROM GULF OF MEXICO LOW WILL BE DRAWN NORTH ALONG 
APPROACHING COLD FRONT. GIVEN INHERENT TIMING ISSUES AT THIS 
JUNCTURE...WILL ONLY NUDGE POPS UP TO HIGH CHANCE AT THIS TIME. 
RATHER WARM DAY ON MONDAY WITH GOOD MECHANICAL MIXING SUPPORTING 
HIGH TEMPERATURES RANGING FROM THE LOW TO MID 70S OVER EASTERN UPPER 
MICHIGAN TO THE UPPER 70S TO LOWER 80S OVER NORTHERN LOWER MICHIGAN. 
TEMPERATURES COOL DOWN SOME ON TUESDAY WITH MODEST CAA BEHIND COLD 
FRONT PASSAGE...WITH HIGHS IN THE MID 60S TO MID 70S.

WEDNESDAY THROUGH THURSDAY...HIGH PRESSURE ONCE AGAIN BUILDS INTO 
THE AREA...BRINGING WITH IT DRY CONDITIONS AND SOMEWHAT MORE 
SEASONABLE TEMPERATURES. LOOKING EVEN FARTHER OUT...CURRENT PATTERN 
IN NO HURRY TO BREAK DOWN...WITH GUIDANCE SUGGESTING WEST COAST 
TROUGH WILL RELOAD LATER NEXT WEEK. WHAT THIS MEANS FOR NORTHERN 
MICHIGAN WEATHER IS CONDITIONS REMAINING RELATIVELY MILD THROUGH AT 
LEAST NEXT WEEKEND...AND POTENTIALLY BEYOND.

MSB

&&

.AVIATION...VFR CONDITIONS WILL CONTINUE THROUGH THE 24 HOUR 
FORECAST PERIOD. SOUTHERLY FLOW WILL INCREASE ABOVE THE SURFACE 
THROUGHOUT THE NIGHT AHEAD OF AN APPROACHING STORM SYSTEM. WITH 
WINDS LIGHT AT THE SURFACE...LOW LEVEL WIND SHEAR A POSSIBILITY 
AFTER 06Z PRIMARILY AT PLN AND TVC.  

&&

.APX WATCHES/WARNINGS/ADVISORIES...NONE. 

&&

$$