[LeArc] Forecast Discussion : MLI@ 9/20/02 2:07:47 PM

[learc@mailman.qth.net]

The following weather message is provided by McDonough County E.S.D.A.


FXUS63 KDVN 201915
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
210 PM CDT FRI SEP 20 2002

.OVERVIEW...AUTUMN IS DEFINITELY HERE.  FIRST SIGNIFICANT COOL SEASON
STORM SYSTEM NOW MOVING EAST WITH BACK EDGE OF WRAPAROUND CLOUDS ALONG
I-35 AT 18Z.  UPPER AIR ANALYSIS SHOWS VIGOROUS JET ACROSS NORTH AMERICA
WITH EXCEPTIONAL AMOUNT OF COOL AIR IN CANADA SUPPORTING STRONG NW FLOW
WITH NEXT SHORT WAVE ENTERING MONTANA.  LONG WAVE TROUGH BECOMING
ESTABLISHED OVER CENTRAL US WITH LITTLE LARGE SCALE FORCING SUPPORTING
MAJOR SHIFT...SO OVERALL COOLER AND MORE CHANGEABLE PATTERN UNDERWAY.

...TIMING CLEARING TONIGHT WITH IMPACT ON TEMPS AND THEN MORE CLOUDS AND
POPS WITH NEXT SHORT WAVE SATURDAY NIGHT WITH EVEN COOLER AIR
AFTERWARDS...

.DIAGNOSIS AND DAYS 1-3...MODELS SIMILAR AND VERIFY OK ON CENTRAL US
SYSTEM WITH NORMAL PROBLEMS ON CLEARING LINE.  ADJUSTING FOR NOWCAST
TOOLS SUGGEST CLEARING SW AND W BY MID EVENING AND AROUND OR JUST AFTER
MIDNIGHT EAST.  LOWS WITH VERY DRY AIR BY MORNING AND PERSISTENCE
UPSTREAM WITH LIGHT WINDS SUGGEST LOW ABOUT 1 CATEGORY BELOW FWC/MAV
BLEND.  THEN NICE WARMUP SATURDAY WITH DRY AIR AND LOTS OF SUN TIL
AFTERNOON...ESPECIALLY SE 2/3 AREA.  FAST BAROCLINIC LEAF TO AFFECT AREA
SATURDAY WITH MAJOR DIFFERENCES IN MOISTURE AMONG ALL MODELS. AVN VERY
WET WITH HALF INCH AMOUNTS AS NORMAL WITH ETA/NGM/UKMET SUGGESTING FEW
HUNDREDTHS.  TREND PAST 2 RUNS IS FOR MORE MOISTURE WITH EACH RUN AS
SHORT WAVE GETS BETTER RESOLVED AND WILL GO MID WAY ON POPS WITH HIGHER
POSSIBLE AS GETS CLOSER.  HIGH CONFIDENCE OF SIGNIFICANT CLOUDS AT LEAST
WITH STRENGTH OF SYSTEM AND FOR SOME POPS AS SHORT WAVE DIVES INTO LONG
WAVE TROUGH AND GOOD BAROCLINICITY SUPPORTING SHORT WAVE.  WILL GO NEAR
GUIDANCE ON LOWS EXCEPT NW SECTIONS WHERE CLEARING AND GOOD CAA BY
SUNRISE KICKS IN. THEN MUCH COOLER AND BREEZY WITH 850 WINDS ALL 25 TO
35 KNOTS AND WITH GOOD CAA AND DECENT GRADIENT WITH HEATING FOR LOTS OF
MIXING MOMENTUM DOWNWARD TO SURFACE. HIGHS NEAR TO SLIGHTLY BELOW
GUIDANCE BLEND WITH 850 TEMPS 3-4C NORTH TO ONLY 5-6C SOUTH AT BEST WITH
SOME FAIR WEATHER MID DAY CUMULUS CLOUDS. VERY COOL SUNDAY NIGHT WITH
LIGHT WINDS AND SURFACE HIGH NEARBY SUGGEST GOOD RADIATIONAL COOLING FOR
LOWS SLIGHTLY BELOW GUIDANCE FOR FROSTY MORNING N AND AND WORD
ACCORDINGLY. IF NEXT SHORT WAVE IS DELAYED AT ALL COULD SEE SOME LOWS
NEAR FREEZING. UKMET AND AVN DIFFER ON NEXT SHORT WAVE ON MONDAY WITH
ETA HALFWAY IN BETWEEN.  HIGH ENERGY (HIGH INDEX) JET SUGGEST PROBABLY
MORE CHANGES NEXT FEW RUNS SO POOR CONFIDENCE SO WILL MENTION ONLY
SLIGHT POPS FAR NW LATE MONDAY AND INTO MONDAY NIGHT FOR NOW TO
BEGIN TREND.

.EXTENDED...(TUE-FRI)
MAJOR TIMING ISSUES WITH VIGOROUS JAMES BAY VORTEX AND ROTATING SHORT
WAVES WILL TAKE BLEND OF UKMET/AVN/ECMWF/NEW NOGAPS.  WILL LEAVE DRY FOR
NOW WITH TEMPS NEAR TO SLIGHTLY BELOW MEX/FMR...EXPECT HURRICANE ISIDORE
TO BE WILD CARD IN VERY PROBABLY AFFECTING EVOLUTION EVENTUALLY OF
CANADIAN VORTEX AND SHORT WAVE PHASING.

.DVN...
IA...NONE.
IL...NONE.
MO...NONE.

NICHOLS