Severe Thunderstorm Warning 25, NWS Marquette, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MARQUETTE MI
420 PM EDT SUN JUN 18 2000

12Z RAOBS/WATER VAPOR LOOP SHOW A VORT MAX NEAR THE MINNESOTA
ARROWHEAD WITH RIDGING UPSTREAM OVER MONTANA/SASKATCHEWAN AND THE
NEXT SYSTEM DIGGING INTO THE PACIFIC NORTHWEST. SURFACE ANALYSIS
SHOWS HIGH PRESSURE OVER THE OHIO VALLEY WITH A WEAK TROUGH
STRETCHING FROM MINNESOTA INTO SOUTH DAKOTA. LOCAL RADARS SHOW
THUNDERSTORMS OVER NORTHERN MINNESOTA...WISCONSIN AND THE U.P.
SHOWERS BEGINNING TO DEVELOP BACK THROUGH SOUTHERN MINNESOTA IN
CONVERGENCE ALONG THE TROUGH.

TONIGHT...MAIN VORT MAX PUSHES EAST OF THE CWA WHILE A LOBE OF
SHEARED ENERGY TRAILS BEHIND. SURFACE TROUGH/WARM FRONT LINGERS TO
THE SOUTH OF THE CWA DURING THE NIGHT WITH DECENT 1000-700MB
MOISTURE CONVERGENCE ACROSS CENTRAL MINNESOTA AND NORTHERN
WISCONSIN. 12Z MESOETA SHOWS UVV/300K ISENTROPIC LIFT ACROSS THE
SOUTHERN CWA FOR BETTER PART OF THE NIGHT. DEEP LAYER MOISTURE
/1000-500MB RH AOA 70 PERCENT/ TRIES TO PUSH EAST OF THE CWA WITH
THE MAIN VORT...BUT REDEVELOPS ACROSS THE SOUTHERN HALF IN AREA OF
LIFT. SIS DROP TO NEAR ZERO AND LIS TO NEAR 1C AS SLIGHT 500MB
COLD POOL AROUND -19C IS OVERHEAD. WILL MAINTAIN CHANCE OF SHOWERS
FOR THE SOUTHERN TIER COUNTIES AND ADD A RUMBLE OF THUNDER TO THE
FAR SOUTH. WILL CARRY A CHANCE OVER THE EASTERN CWA FOR THE FIRST
HALF OF TONIGHT AS MOISTURE CONVERGENCE ASSOCIATED WITH SHOWERS OVER
NORTHERN MINNESOTA MOVES THROUGH.

MONDAY...UPPER TROUGH DIGS INTO THE NORTHERN PLAINS AND SURFACE LOW
BEGINS TO TAKE SHAPE TO OUR WEST. SURFACE TROUGH/FRONT OVER NORTHERN
WISCONSIN WEAKENS AS IT TRIES TO PUSH THROUGH THE CWA. 850MB TEMPS
INCREASE TO 12-15C /NE TO SW/ SIGNALING A RETURN TO MORE SEASONABLE
TEMPERATURES. WHILE THE TROUGH LOSES ANY SIGNIFICANT FORCING AS IT
MOVES ACROSS THE CWA...A SWATH OF 850-700MB RH AOA 70 PERCENT SWINGS
THROUGH WITH IT. WITH CU SCHEME /850MB TEMPS MINUS 1000MB DEW
POINTS/ NEGATIVE AND 1000-850MB LAPSE RATES NEAR 8C/KM...EXPECT MORE
CU TO DEVELOP. BELIEVE THAT INSTABILITY SHOWERS ARE NOT LIKELY GIVEN
MINIMAL CAPE AND MID-LEVEL WARMING.

MONDAY NIGHT...NEXT SYSTEM APPROACHES THE UPPER PENINSULA OVERNIGHT.
MODELS BRING QPF INTO THE WESTERN CWA MAINLY AFTER MIDNIGHT. WORDED
SCATTERED SHOWERS DEVELOPING WITH QUESTION AS TO EXACT TIMING.
TUESDAY...SHRA/TSRA SPREAD OVER THE CWA. WITH WIDESPREAD PRECIP
COVERAGE...BUMPED UP CHANCE POPS TO LIKELY...ALL DAY IN THE WESTERN
CWA AND MAINLY IN THE AFTERNOON IN THE EASTERN CWA. TUESDAY NIGHT
AND WEDNESDAY CONTINUED CHANCE SHRA/TSRA WITH UNCERTAINTY AS TO
EXACT TIMING.

FURTHER IN THE EXTENDED...MRF/CANADIAN/ECMWF/NOGAPS ARE IN
QUASI-AGREEMENT WITH TIMING THE SYSTEM OUT OF THE AREA. LOW HEIGHTS
LINGER EARLY THURSDAY BUT BEGIN REBUILDING DURING THE DAY AND INTO
FRIDAY AS THE UPPER TROUGH MOVES EAST. MRF IS SLOWEST WITH MOVEMENT
BUT STILL INDICATES DRYING DURING THE DAY. LINGERING SHOWERS ARE
POSSIBLE EARLY BUT WILL CONTINUE THE DRY FORECAST THURSDAY. MODELS
BEGIN TO DIFFER WITH STRENGTH OF THE NEXT SYSTEM LATE IN THE WEEK.
MRF HAS TRENDED WEAKER WITH THE UPPER LEVEL SUPPORT. ECMWF/NOGAPS
ARE MUCH MORE AMPLIFIED THAN BOTH THE MRF AND CANADIAN. MRF/CANADIAN
ENSEMBLE MEMBERS SUPPORT BOTH SOLUTIONS...WITH THE CANADIAN ENSEMBLE
MEAN NEARLY A FLAT LINE SATURDAY AND SUNDAY.

.MQT...NONE.

JHB