FXUS63 KAPX 211958
AFDAPN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
358 PM EDT WED MAY 21 2003

SURFACE HIGH PRESSURE REMAINS CENTERED OVER MICHIGAN LATE THIS 
AFTERNOON...WITH SKIES STILL MAINLY CLEAR ACROSS THE LOWER PENINSULA.
CI SHIELD ASSOCIATED WITH THE RRQ OF AN 80 KT 300 MB JET MAX AND AN 
AREA OF 70 PCT 500-250 MB RH CONTINUES TO GRADUALLY MAKE ITS WAY 
EASTWARD THRU WI AND UPPER MICHIGAN. CLOUD COVER IS GENERALLY ABOVE
12 KFT AND RATHER THIN PER LATEST VSBL SATELLITE LOOP. MAIN FORECAST 
CONCERN FOR THE SHORT TERM IS POTENTIAL FOR WIDESPREAD FROST 
DEVELOPMENT OVERNIGHT WITH COLD HIGH PRESSURE STILL IN PLACE. WX 
REMAINS QUIET THROUGH THURSDAY NIGHT. NEXT SIGNIFICANT FORECAST 
ISSUE WILL BE THE CHANCE OF SHOWERS BY FRIDAY AFTERNOON AS MOISTURE 
WRAPS INTO NORTHERN MICHIGAN ON THE NW SIDE OF A SURFACE LOW RIDING 
UP THE NEW ENGLAND COAST.

TONIGHT...ETA AND AVN BOTH HOLD THE SURFACE RIDGE AXIS OVER THE CWA 
THRU TONIGHT AS THE SURFACE HIGH CENTER PUSHES NE INTO QUEBEC. 
AFOREMENTIONED CU SHIELD WILL DRIFT OVERHEAD TONIGHT...BUT WILL NOT 
BE THICK ENOUGH TO PRECLUDE GOOD RADIATIONAL COOLING CONDITIONS. ETA 
IN FACT SUGGESTS SOME THINNING OF THE CI SHIELD...ESPECIALLY ACROSS 
SRN SECTIONS OF THE CWA AS THE JET STREAK AND ASSOCIATED HIGH LEVEL 
MOISTURE DEPART TO THE NORTHEAST. DEWPOINTS HAVE FALLEN NICELY THIS 
AFTERNOON ACROSS THE CWA AS DRIER AIR HAS MIXED DOWN...WITH MOST 
LOCATIONS NOW REPORTING DEWPOINTS IN THE MID 20S TO AROUND 30 (WITH 
THE EXCEPTION OF A FEW COASTAL AREAS ALONG LAKE MICHIGAN). IN 
COORDINATION WITH GRR AND DTX...WILL ISSUE A FROST ADVISORY FOR ALL 
OF NRN LWR MI TONIGHT. SOME LOW LYING PLACES MAY ACTUALLY SEE FREEZE 
WARNING CONDITIONS...BUT THEY SHOULD BE FEW AND FAR BETWEEN. PLACES 
ALONG THE IMMEDIATE LAKESHORES WILL LIKELY NOT ACHIEVE THE COLD 
TEMPS NEEDED FOR WIDESPREAD FROST DEVELOPMENT...BUT INLAND AREAS 
WITHIN THOSE COUNTIES SHOULD SEE A GOOD AMOUNT OF FROST OVERNIGHT.

THURSDAY AND THURSDAY NIGHT...UPPER TROUGH BEGINS TO DIG INTO THE 
GREAT LAKES BY THURSDAY EVENING...AS A DEEPENING SURFACE LOW OVER 
THE GULF COAST STATES BEGINS TO TRACK NORTHWARD ALONG THE MID 
ATLANTIC COAST. IN THE MEANTIME...SURFACE RIDGE AXIS ACTUALLY HOLDS 
IN PLACE ACROSS MICHIGAN ON THURSDAY AND MUCH OF THURSDAY NIGHT. 
UPPER LEVEL MOISTURE DOES INCREASE THURSDAY NIGHT AS ATLANTIC 
MOISTURE STARTS TO BE DRAWN BACK INTO LOWER MICHIGAN IN THE NORTHERN 
EDGE OF THE INVERTED TROUGH THAT DEVELOPS ALONG THE EASTERN 
SEABOARD. LOW AND MID LEVELS REMAIN DRY THRU THURSDAY NIGHT...WITH 
NO PRECIP EXPECTED UNTIL LATER FRIDAY. ONLY ISSUE ON THURSDAY WILL 
BE LAKE BREEZE DEVELOPMENT...WHICH SHOULD OCCUR WITH 950 MB WINDS 
STAYING JUST BELOW 15 KTS AND LAND/LAKE DELTA T'S AROUND 15 DEGREES 
OR SO. EXPECT INCREASING DEWPOINTS...WINDS AND CLOUD COVER (ALBEIT HIGH) 
WILL NOT ALLOW FOR CONDITIONS NEEDED FOR WIDESPREAD FROST 
DEVELOPMENT THURSDAY NIGHT.

FRIDAY AND FRIDAY NIGHT...LOW/MID LEVEL MOISTURE BEGIN TO WRAP BACK 
INTO NORTHERN MICHIGAN BY FRIDAY AFTERNOON AS THE 500 MB LOW CLOSES 
OFF OVER THE GREAT LAKES AND THE SURFACE LOW ALONG THE EAST COAST 
TRAVELS FURTHER NORTHWARD TOWARD NEW ENGLAND. STILL DOES NOT LOOK 
LIKE A HIGH POP EVENT...BUT WILL RECEIVE JUST ENOUGH ATLANTIC MOISTURE 
AND LIFT VIA LOW LEVEL CONVERGENCE AND WEAK ISENTROPIC ASCENT (I295) 
TO JUSTIFY MAINTAINING CHANCE POPS FOR ALL ZONES (HIGHEST CHANCE 
ACROSS NE SECTIONS OF THE CWA).

SATURDAY THROUGH WEDNESDAY...LATEST MEDIUM RANGE MODELS ARE SIMILAR 
TO YESTERDAY'S RUN...SHOWING A PERSISTENT CLOSED 500 MB LOW OVER THE 
GREAT LAKES REGION THRU THE WEEKEND AND INTO EARLY NEXT WEEK. AS 
SUSPECTED WOULD HAPPEN...MODELS HAVE DELAYED THE BREAKDOWN AND 
EASTWARD PUSH OF THIS UPPER LOW UNTIL MID WEEK. SURFACE LOW OVER THE 
MID ATLANTIC COAST SLOWLY RIDES NORTHWARD ALONG THE NEW ENGLAND 
COAST OVER THE WEEKEND AND SLIGHTLY RETROGRADES INTO THE GREAT LAKES 
REGION. ATLANTIC MOISTURE WILL BE PULL BACK INTO THE GREAT LAKES ON 
THE NRN EDGE OF THE SURFACE LOW. WEEKEND DOES NOT LOOK LIKE A TOTAL 
WASHOUT...BUT WITH DEEP UPPER LOW OVERHEAD AND SURFACE LOW JUST EAST 
OF THE REGION PULLING ATLANTIC MOISTURE INTO THE GREAT LAKES...EXPECT 
CLOUDY SKIES...TEMPS 5 TO 10 DEGREES BELOW NORMAL AND A CHANCE OF 
RAIN FOR SATURDAY THRU MONDAY (AT LEAST). DRY FORECAST CURRENTLY 
ADVERTISED FOR TUESDAY IS BECOMING A BIT QUESTIONABLE CONSIDERING 
THE DELAY IN THE BREAKDOWN OF THE UPPER LOW. AT THIS POINT...WILL 
CONTINUE TO SIDE WITH A MORE OPTIMISTIC FORECAST...BUT WILL KEEP AN 
EYE ON TRENDS FOR TUESDAY IN SUBSEQUENT MODELS RUNS. HIGH PRESSURE 
SHOULD FINALLY MOVE IN FOR WEDNESDAY AS THE 500 MB LOW SHIFTS EAST 
INTO NEW ENGLAND. WEDNESDAY SHOULD BE A FAIRLY NICE DAY...WITH TEMPS 
POPPING BACK UP TO NEAR (MAY JUST ABOVE) NORMAL.

.APX...FROST ADVISORY...TONIGHT...MIZ016>036-041-042.

$$

EME