Severe Thunderstorm Warning 66, NWS Gaylord, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
815 PM EDT MON SEP 22 2003

.TONIGHT...PER 0Z APX RAOB...850 MB TEMP DOWN TO +8C HERE...PROGGED
TO FALL TO AROUND +3C OVERNIGHT...YIELDING LAKE-850 MB DELTA TS
AROUND 15C OVER LAKE MICHIGAN. THERMODYNAMIC PARAMATERS...COMBINED
WITH 700-500 MB QG FORCING/COLD POOL ASSOCIATED WITH UPPER
LOW...ESSENTIALLY RAISING INVERSION HEIGHTS TO THE TROP...WILL SET
UP AN EXCELLENT LAKE ENHANCED SHOWER/THUNDERSTORM SITUATION IN
WESTERLY FLOW AREAS OVERNIGHT...ALREADY UNDERWAY PER RADAR TRENDS.
THUS...RAISED POPS TO 70% ACROSS THE WESTERN HALF OF NORTHERN LOWER
MI. ALSO...POTENTIAL EXISTS FOR LOCALLY HEAVY RAIN...PERHAPS
EXCEEDING 2 ADDITIONLA INCHES...WITHIN PERSISTENT RAIN BANDS
OVERNIGHT.

MEANWHILE...EARLIER LOWERED POPS TO 50% ACROSS THE EAST PER EXIT OF
WIDESPREAD WARM CONVEYOR BELT PRECIPITATION.

CONDITIONS WILL REMAIN FAVORABLE FOR WATERSPOUTS ON LAKES
MICHIGAN/HURON THROUGH THE NIGHT...GIVEN DELTA TS...DEEP/COLD
CYCLONIC FLOW...850 MB WINDS REMAINING BELOW 30 KTS AND POTENTIAL
FOR DEEP MOIST CONVECTION TO EXCEED 25 KFT IN DEPTH.

SPR

&&

.PREV DISCUSSION...ISSUED 414 PM SEP 22

SHORT TERM...MAIN FORECAST ISSUES ARE CHANCES FOR PCPN TONIGHT AND
EARLY TUESDAY...AND THE POSSIBILITY OF SOME THUNDER TONIGHT. LATEST
WATER VAPOR IMAGERY AND RUC ANALYSES SHOW A VIGOROUS UPPER TROUGH
OVER CENTRAL CANADA AND THE NORTH CENTRAL CONUS. AN INITIAL DRY
PUNCH CAN BE SEEN MOVING THROUGH LOWER MI AT THIS TIME...WHICH
CORRESPONDS WELL WITH THE BACK EDGE OF THE WIDESPREAD PCPN AS SEEN
ON 88D IMAGERY. THE SURFACE COLD FRONT IS WELL CORRELATED WITH THIS
MID LEVEL DRY AXIS...AND A DISTINCT WIND SHIFT IS PRESENT ALONG IT.
PCPN CURRENTLY MOVING THROUGH THE CWFA CONTINUES TO BE FORCED BY SOME
LINGERING ISENTROPIC LIFT AND DIFFERENTIAL POSITIVE VORTICITY
ADVECTION. THE 850-500MB Q-VECTOR CONVERGENCE PROGS FROM THE ETA
HIGHLIGHT THE GENERAL AREA OF FORCING FAIRLY WELL...AND SHOW
SUBSIDENCE WORKING INTO THE CWFA THIS EVENING...WHICH CORRELATES
WELL WITH WHERE THERE IS CURRENTLY A PCPN MINIMA FROM THE WESTERN
CWFA BACK INTO WISCONSIN.

THE MAIN UPPER LEVEL PV ANOMALY...AS SEEN ON THE 320K SURFACE...WILL
MOVE SOUTHEAST FROM ITS CURRENT POSITION OVER CENTRAL MINNESOTA TO
SOUTHEAST WISCONSIN BY 06Z. SOME SHRA CAN BE SEEN OVER MINNESOTA IN
ASSOCIATION WITH THIS FEATURE...AND WOULD EXPECT TO SEE CONTINUED
SHRA ACTIVITY ALONG ITS LEADING EDGE WHICH IS INDICATIVE OF THE
ARRIVAL OF THE MID LEVEL COLD POOL. ALTHOUGH LAPSE RATES WILL
STEEPEN...CHANCE FOR THUNDER APPEARS MARGINAL WITH ELEVATED CAPE
VALUES BELOW 300 J/KG AND POOR DIURNAL TIMING. WILL MAINTAIN A
MENTION OF ISOLATED THUNDER THROUGH TONIGHT...BUT IF THINGS ARE
HAVING A HARD TIME DEVELOPING WITH THE CURRENT SURFACE HEATING TO
THE WEST...IT MAY BE TOUGH FOR ANYTHING TO DEVELOP OVER OUR AREA.
HOWEVER...THE WARM LAKE TEMPERATURES MAY PROVIDE ENOUGH HEATING TO
OFFSET THE OTHERWISE UNFAVORABLE DIURNAL TIMING OF THE COLD POOL AND
MID LEVEL FRONT. WITH 850MB TEMPERATURES PROGGED TO DECREASE TO NEAR
2C BY 12Z...DELTA T VALUES WILL BE IN THE UPPER TEENS...SO WE SHOULD
SEE A FAIR AMOUNT OF SHOWER ACTIVITY LATE TONIGHT THROUGH THE
MORNING HOURS ON TUESDAY. WITH GENERALLY 270-300 DEGREE BOUNDARY
LAYER FLOW...THIS ACTIVITY SHOULD BE MOST PRONOUNCED OVER NORTHWEST
LOWER MI AND IN CHIPPEWA COUNTY IN THE U.P. THE IMPRESSIVE DELTA-T
VALUES WILL ALSO CREATE A FAVORABLE ENVIRONMENT FOR WATERSPOUTS
TONIGHT AND TUESDAY MORNING...SO WILL INCLUDE A MENTION IN THE
NEARSHORE MARINE FORECAST.

CYCLONIC FLOW BECOMES ANTICYCLONIC BY TUESDAY AFTERNOON...AND WAA
BEGINS AFTER 18Z...HELPING TO SIGNIFICANTLY DIMINISH BOUNDARY LAYER
RH VALUES. WILL BRING SHRA ACTIVITY TO AN END DURING THE AFTERNOON
HOURS IN LINE WITH THESE MORE UNFAVORABLE CONDITIONS. WE SHOULD ALSO
SEE A CORRESPONDING DECREASE IN CLOUD COVER BY LATE
AFTERNOON...ALTHOUGH WOULDN/T EXPECT THINGS TO IMPROVE BEYOND BKN.

STAYED FAIRLY CLOSE TO A BLEND OF ETA AND GFS MOS VALUES FOR
TEMPERATURES TONIGHT AND TUESDAY.

TRH

LONGER TERM(TUE NIGHT THROUGH THURSDAY)...THE ETA AND GFS ARE IN
GOOD AGREEMENT IN SHOWING THE WRAP AROUND MOISTURE AND CYCLONIC FLOW
TO MOVE EAST OF THE CWFA BY TUE EVENING. THIS SHOULD ALLOW FOR A DRY
OVERNIGHT PERIOD IN A WAA PATTERN AS SHORT WAVE RIDGING BUILDS INTO
THE CWFA FROM THE WEST AHEAD OF THE NEXT SYSTEM MOVING OUT OF THE
NORTHERN PLAINS. AGAIN...THE ETA AND GFS ARE IN EXCELLENT AGREEMENT
WITH THE MOVEMENT OF THIS SYSTEM...BRINING PCPN TO EASTERN UPPER
MICHIGAN AROUND 12Z ON WED AND TO NRN LOWER MICH BY LATE
MORNING/EARLY AFTERNOON.  AMOUNT OF MOISTURE RETURN AHEAD OF THE
SYSTEM IS A CONCERN...SO WILL NOT GO ANY HIGHER THAN CHC POPS AT
THIS TIME. BEST CHANCE FOR PCPN WILL BE OVER EASTERN UPPER MICHIGAN
WHERE THEY ARE CLOSEST TO THE DYNAMICS ON WEDNESDAY. ANOTHER CONCERN
WILL BE WINDS AHEAD OF THE SYSTEM LATE TUE NIGHT INTO WED. ETA BUFR
FILES FOR OVER LAKE MICHIGAN AND OVER THE CWFA SHOW WINDS IN THE
MIXED LAYER 30-38KT AS THE LOW DEEEPENS TO 992MB N OF LAKE SUPERIOR
BY WED AFTEROON. ALTHOUGH THIS MAY BE UNABLE TO MIX DOWN EARLY WED
MORNING...BY LATE MORNING THE WINDS SHOULD BE ABLE TO MIX DOWN
ALLOWING FOR BREEZY TO LOCALLY WINDY CONDITIONS OVER THE WESTERN
CWFA. ALTHOUGH THE ETA DOES NOT SHOW AS STRONG AS WINDS BEHIND THE
SYSTEM WED AFTN/EVENING...WITH THE STRONG CAA BEHIND THE FRONT AND
PRES RISES AHEAD OF THE SYSTEM...IT IS POSSIBLE THERE COULD BE WINDY
CONDITIONS BEHIND THE FRONT AS WELL. THE MODEL SHOWS A WEAK DRY SLOT
WILL MOVE THRU THE CWFA EARLY WED NIGHT WHICH MIGHT ASSIST IN THE
STRONGER WINDS OVER THE CWFA. THIS DRY SLOT WILL ALSO HELP TO DRY
OUT THE CWFA FOR A SHORT TIME WED NIGHT...HOWEVER THE COLD POOL
MOVES OVERHEAD BY THU MORNING ALLOWING FOR ANOTHER CHC OF SHOWERS.
THIS WILL BE HELPED BY STRONG CYCLONIC FLOW. 850MB TEMPS FROM THE
ETA LOWER TO -2 OVER EASTERN UPPER MICH AND FAR NRN LOWER...SO SOME
LAKE INSTABILITY MAY HELP GENERATE SOME LAKE EFFECT RAIN SHOWERS
THU. ONLY PROBLEM WILL BE INCREASED SUBSIDENCE AND LOWERING
INVERSION HEIGHTS DUE TO THE RIDGE AXIS BUILDING INTO THE CWFA.

AS FOR TEMPS...WILL GENERALLY FOLLOW PREV FCST TEMPS. WILL RAISE
TEMPS SLIGHTLY ON WED AHEAD OF THE WARM FRONT. HOWEVER...WILL NOT
RAISE INTO THE LOWER 70S LIKE THE ETA MOS SUGGESTS. WITH 850MB
TEMPS -2C OVER THE FAR N ON THU...WILL ALSO COOL TEMPS SLIGHTLY FROM
PREV FCST.

.FRIDAY THROUGH MONDAY...00Z AND 12Z RUNS OF THE GFS CONFIRM THAT A
MEAN TROUGH WILL CONTINUE OVER THE UPPER MIDWEST AND GREAT LAKES
STATES. THIS WILL ALLOW SEVERAL SHORT WAVES TO ROTATE AROUND THE
UPPER TROUGH AND AFFECT THE CWFA THROUGH THE WEEKEND. ALTHOUGH IT IS
LIKELY THAT THERE WILL BE PERIODS OF DRY WEATHER THROUGH THE
EXTENDED...IN BETWEEN SHORT WAVES...IT IS TOUGH TO DETERMINE EXACTLY
WHEN THOSE PERIODS WILL OCCUR. THEREFORE...WILL NEED TO INTRODUCE CHC
POPS IN FOR FRI-SUN.  LOOKS LIKE THE BEST CHC FOR PCPN WILL BE FRI-
SAT WHEN THE GFS SHOWS A STRONG COLD FRONT MOVING THRU THE CWFA...
WITH THE ASSOCIATED UPPER COLD POOL MOVING OVERHEAD BY SAT MORNING.
IN FACT...THE GFS SHOWS 850MB TEMPS LOWERING TO BELOW 0C OVER EASTERN
UPPER MICHIGAN BY SUNDAY MORNING. WITH LAKE SUPERIOR TEMPS AROUND
12C...AND LAKE MICHIGAN TEMPS AROUND 15C...WOULD NOT BE SURPRISED
TO SEE SOME LAKE EFFECT RAIN SHOWERS BEHIND THIS SYSTEM SUN
THROUGH MON DEPSITE INCREASED LOW LEVEL RIDGING. WILL THEREFORE
KEEP SOME LOW CHANCE POPS OVER THE N MON. OTHERWISE...WILL KEEP
TEMPS BELOW NORMAL THROUGH THE EXTENDED WITH TEMPS GENERALLY IN THE
50S N AND LOWER 60S S.

&&

MRD

&&

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

MIZ008-015>036-041-042-231100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GAYLORD MI
655 PM EDT MON SEP 22 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHERN LOWER AND EASTERN
UPPER MICHIGAN.

.DAY ONE...TONIGHT

WATERSPOUTS ARE POSSIBLE TONIGHT ACROSS NORTHERN LAKES MICHIGAN AND
HURON. ALSO...ISOLATED THUNDERSTORMS ARE EXPECTED ACROSS EASTERN
UPPER AND NORTHERN LOWER MICHIGAN TONIGHT. THUNDERSTORMS ARE NOT
EXPECTED TO BECOME SEVERE.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED.

&&

MORE INFORMATION MAY BE OBTAINED AT THE FOLLOWING URL:
HTTP://WWW.CRH.NOAA.GOV/APX (ALL LOWER CASE)

ROWLEY