Strong Wind in Michigan, September 23 to 24, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
350 PM EDT SUN SEP 23 2001

SHORT RANGE DISCUSSION -- TONIGHT THRU TUES...LATE AFTERNOON SURFACE
ANALYSIS SHOWED PRIMARY AREA OF LOW PRESSURE OVER SOUTHERN LAKE
MICHIGAN...WITH A WARM FRONT EXTENDING NE ACROSS TVC/GLR AND INTO N
LAKE HURON. ORGANIZED LIFT HAS BEEN SUPPLIED BY SHARP 500 MB TROUGH
JUST UPSTREAM...50 KNOT 500 MB SPEED MAX LIFTING NE ACROSS REGION...
AND STRONG ISENTROPIC ASCENT IN ADVANCE OF SYSTEM. THIS HAS PRODUCED
WIDESPREAD RAINFALL TODAY ACROSS THE MOST OF FORECAST AREA. LOW IS
FORECAST TO PUSH E TONIGHT AND BE POSITIONED JUST N OF LAKE ERIE BY
12Z MON...AS UPPER LOW CLOSES OFF BY LATE MON OVER EXTREME SOUTHERN
LOWER MI. FORECAST CHALLENGES INCLUDE PROGRESS OF THIS UPPER LOW...
AND CORRESPONDING RAIN CHANCES. ALSO...MAGNITUDE OF WINDS LATER
TONIGHT AND MON A CONCERN.

TONIGHT...STEADY RAINFALL IS EXPECTED TO DIMINISH TO SCATTERED
SHOWERS BY LATE EVENING ACROSS E UPPER AND MUCH OF NW LOWER AS
SURFACE LOW MOVES E AND ISENTROPIC LIFT DIMINISHES. THIS TREND IS
SUPPORTED NICELY BY RADAR AND IR/WV SATELLITE LOOPS. EXTRAPOLATION
SUGGESTS THAT RAIN WILL BECOME MORE SPORADIC IN TVC BY 00Z...AND IN
GLR/PLN/SSM CORRIDOR BY 02-03Z. 12Z MODELS MAINTAIN DEEPER MOISTURE
AND STEADIER PRECIPITATION THROUGH MOST OF THE NIGHT ACROSS NE LOWER
FROM APN S TO HTL/OSC...AND THIS SEEMS REASONABLE GIVEN 500 MB
TROUGH POSITION. AS LOW MOVES E AND PRESSURE GRADIENT TIGHTENS...
SURFACE WINDS WILL (FINALLY) PICK UP THIS EVENING. CAA AND
INCREASING OVER WATER INSTABILITY WILL ALLOW FOR STRONG VERTICAL
MIXING. THOUGH UPSTREAM WINDS HAVEN/T BEEN OVERLY IMPRESSIVE THUS
FAR...ETA 925/850 MB WINDS SUGGEST 30-40 KT GUSTS POSSIBLE BY 12Z
MON. WILL INCLUDE WIND GUST POTENTIAL IN ZONES.

MONDAY AND MONDAY NIGHT...ETA/AVN GENERALLY SIMILAR WITH CLOSED
UPPER LOW POSITION OVER S/SE LOWER MI -- THOUGH AVN IS A BIT SLOWER
AND PREFERRED. MODEL SOUNDINGS DRY MID LEVELS OUT CONSIDERABLY OVER
NW LOWER AND E UPPER...WITH SLIGHTLY HIGHER 850/700 MB RH LINGERING
OVER NE LOWER -- AND THIS IS WHERE RISK FOR SHOWERS WILL BE
GREATEST. WITH 850 MB TEMPERATURES OF -2C STREAMING S ACROSS THE
AREA...OVER WATER DELTA T/S WILL INCREASE TO NEAR 20C. HOWEVER...
THERE IS SOME QUESTION WHETHER CONVECTION WILL EXTEND TO -10C
ISOTHERM GIVEN LOWERING INVERSION HEIGHTS. AS A RESULT...ANY SHOWERS
THAT OCCUR OVER NW LOWER AND E UPPER SHOULD BE LIGHT. ETA FORECASTS
40-50 KT WINDS IN THE 925/850 MB LAYER OVER LAKE HURON WHICH...WITH
EFFECTIVE MIXING WILL ALLOW FOR GUSTY WINDS ESPECIALLY NEAR LAKE
HURON. WINDS NOT QUITE AS STRONG FARTHER W.

TUESDAY...MUCH THE SAME STORY. FEEL THAT AVN IS A BIT TOO SLOW
MOVING UPPER LOW E...WHILE ETA IS TOO PROGRESSIVE. THE COMPROMISE
SOLUTION WILL RESULT IN A CONTINUED NORTH/COOL FLOW WITH A FEW
SHOWERS LINGERING OVER MAINLY NE LOWER. WILL INTRODUCE SOME PARTLY
SUNNY SKIES FOR E UPPER...WITH MODEL SOUNDINGS CONTINUING TO SHOW A
DRYING TREND AS SURFACE HIGH NUDGES CLOSER.

EXTENDED RANGE DISCUSSION -- WED THRU SUN...THE NEW 12Z OPERATIONAL
RUNS SUGGEST THAT THE 00Z MRF HAS THE RIGHT IDEA KEEPING UPPER LOW
OVER THE EASTERN GREAT LAKES EARLY IN THE EXTENDED PERIOD (AND NOT
DIGGING UPPER LOW AS FAR S AS SOME PREVIOUS MODELS HAD SUGGESTED).
THE MRF HAS CLOSED 500 MB LOW OVER SOUTHERN ONTARIO -- JUST S OF
GEORGIAN BAY -- BY 12Z WED. ECMWF...UKMET...AND CANADIAN GEM (AND
NEW ETA) ARE ALL MORE PROGRESSIVE -- AND TAKE UPPER LOW FARTHER E
INTO NEW ENGLAND BY EARLY WED. THE MRF HAS BEEN TRENDING TOWARD A
SLIGHTLY MORE PROGRESSIVE SOLUTION THE PAST 3 RUNS. MRF ENSEMBLE
DATA ALSO INDICATES THAT THE OPERATIONAL MRF IS SLIGHTLY BIASED
TOWARD THE SLOWER UPPER LOW MOVEMENT. LASTLY...THE UKMET/ECMWF/MRF
ALL SUGGEST THAT A WEAK UPSTREAM 500 MB KICKER SHOULD PUSH NE OUT OF
THE NORTHERN ROCKIES BY MIDWEEK. THIS ALL SUGGESTS THAT A SOMEWHAT
FASTER SOLUTION MAY VERIFY BEST...AND AS A RESULT...EXTENDED
FORECAST WILL LEAN TOWARD A SLIGHTLY FASTER DEPARTURE OF UPPER LOW
THAN SUGGESTED BY THE 00Z OPERATIONAL MRF. THIS WILL KEEP A RISK OF
LINGERING SHOWERS INTO WED FOR ONLY NE LOWER...WITH DRIER WEATHER
EXPECTED IN THE THUR THRU SUN TIMEFRAME AS UPPER LOW FINALLY OPENS
AND LIFTS ENE. TEMPERATURES WILL SLOWLY MODERATE THROUGH
PERIOD...WITH NEAR NORMAL TEMPERATURES EXPECTED BY NEXT WEEKEND.

.APX...NONE.

SMITH