[LeArc] Forecast Discussion : MLI@ 5/21/2003 3:00:28 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 211957
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
ISSUED BY NWS LA CROSSE WI
257 PM CDT WED MAY 21 2003

FORECAST CONCERNS THIS PACKAGE...INTERMITTENT SMALL -SHRA CHANCES
THRU THE UPCOMING HOLIDAY WEEKEND.

IN BACK-UP MODE FROM WFO LA CROSSE WI THIS AFTERNOON AS WFO DVN/MLI
UPGRADES THEIR COMPUTER SYSTEMS.

18Z DATA ANALYSIS SHOWS CANADIAN HIGH PRESSURE CENTERED OVER THE
GREAT LAKES...WITH RIDGING TO THE SOUTHWEST INTO KS. VIS/IR IMAGERY
SHOWING SCT-BKN CI DRIFTING EAST ACROSS WI/IL/MO. EXTENSIVE AREA OF
CUMULUS EXTENDED FROM EAST-CENTRAL MN...SOUTH THRU MUCH OF IA INTO
NORTH-CENTRAL MO. 12Z MODEL 850MB MOISTURE FIELDS HANDLING THIS CLOUD
DECK QUITE WELL EARLY THIS AFTERNOON. COMBINATION OF PARTLY SUNNY
SKIES AND COOL EASTERLY FLOW UNDER THE CANADIAN HIGH WERE MAKING FOR
A SEASONABLY COOL DAY ACROSS MUCH OF THE REGION.

NO MAJOR INITIALIZATION ERRORS NOTED WITH 12Z MODELS...AND ALL
LOOK TO REFLECT REALITY QUITE WELL AT 18Z...WITH A FEW EXCEPTIONS.
BOTH ETA/GFS LOOK OVERDONE WITH A SHORTWAVE OVER OK/AR EARLY THIS
AFTERNOON...AND NEITHER DOING REALLY WELL WITH SHORTWAVES ROTATING
AROUND THE UPPER LOW IN GULF AK NEAR 50N 150W. HAVE TO GIVE EDGE TO
AVN SFC PRESSURE FIELD...WHILE ETA/NGM BETTER ON DEW POINTS ACROSS
THE REGION. MODEL SOLUTIONS REASONABLY SIMILAR THRU THU NIGHT...THEN
BEGIN TO DIVERGE. FOLLOWED A COMPROMISE OF ETA/GFS THIS CYCLE.

FOR THE SHORT TERM...DRY AND RATHER COOL HIGH PRESSURE REMAINS IN
CONTROL OF THE AREA/S WEATHER TONIGHT/THU. MAY YET ADD MENTION OF
PATCHY FROST IN LOW-LYING AREAS IN THE NORTHEAST CORNER OF THE
FORECAST AREA WHERE LOWS LIKELY TO DIP INTO THE MID/UPPER 30S IN
THE SHELTERED VALLEYS. GUIDANCE LOWS TONIGHT QUITE SIMILAR AND LOOK
ACCEPTABLE. WITH PARTLY CLOUDY/PARTLY SUNNY SKIES THU AND LATE MAY
SUNSHINE...FAVORED WARMER NGM/ETA-MOS HIGHS. ALL MODELS DROP THE
NEXT MORE SIGNIFICANT NORTHERN STREAM SOUTHEAST AND CARVE OUT AN
UPPER TROUGH/LOW OVER THE WESTERN GREAT LAKES BY FRI MORNING. PV
ADVECTION AND MID/UPPER LEVEL Q-G CONVERGENCE PUSH ACROSS THU NIGHT
AHEAD OF THE SHORTWAVE...HOWEVER MOISTURE REMAINS LIMITED AT ALL
LEVELS WITH THIS FEATURE. THEREFORE WILL LIMIT -SHRA TO CHANCE
WEST...SLIGHT CHANCE EAST THU NIGHT. GUIDANCE LOWS SIMILAR AND LOOK
GOOD FOR THU NIGHT. MID LEVEL COLD POOL SETTLES OVER THE AREA FRI.
PREVIOUS FORECAST OF SLIGHT CHANCE -SHRA ON FRI LOOKS REASONABLE FOR
NOW...HOWEVER BETTER PART OF THIS CHANCE APPEARS TO BE OVER THE
WESTERN HALF OF THE FORECAST AREA WHERE SFC DEWPOINTS WILL BE A BIT
HIGHER. FAVORED BLEND OF GUIDANCE HIGHS FOR FRI.

CONFIDENCE WITH FORECAST LOWERS FOR FRI NIGHT AND BEYOND AS MODELS
DIVERGE WITH HANDLING OF THE NEXT STRONGER SHORTWAVE DROPPING DOWN
THE WEST SIDE OF THE UPPER LOW/TROUGH OVER THE GREAT LAKES.
CONSENSUS IS BEST PV-ADVECTION AND MID/UPPER LEVEL Q-G CONVERGENCE
WITH THIS WAVE PUSHES OVER THE FORECAST AREA SAT NIGHT. LOW/MID
MOISTURE REMAIN LIMITED AS THE SFC RIDGE OF HIGH PRESSURE REMAINS
OVER THE REGION. WILL HONOR THE SHORTWAVE WITH CHANCE POPS NORTH
SAT NIGHT...AND SLIGHT CHANCE ELSEWHERE. GIVEN VARYING MODEL
SOLUTIONS...LEFT PREVIOUS FORECAST AS IS FOR SUN AND BEYOND...
EXCEPT FOR SOME MINOR ADJUSTMENTS TO HIGHS/LOWS.

MEDIUM RANGE MODELS INDICATE SHARP RIDGING TO BUILD INTO CENTRAL CAN
SUN/MON...AS THE UPPER LOW PROGRESSES INTO THE EASTERN GREAT LAKES.
21/00Z GFS ENSEMBLES SHOWED QUITE A BIT OF VARIABILITY FOR MON AND
BEYOND...WITH A COUPLE MEMBERS SHOWING A REX BLOCK DEVELOPING AND THE
GREAT LAKES UPPER LOW RETROGRESSING TO THE SOUTHWEST FOR EARLY NEXT
WEEK. 21/12Z GFS ENSEMBLES SHOWING THE TROUGH/RIDGE TO BE MUCH MORE
PROGRESSIVE FOR THE MIDDLE OF NEXT WEEK AS STRONG SHORTWAVE ENERGY
PUSHES THROUGH THE NORTHWEST U.S.  EITHER WAY...A SEASONABLY COOL
PERIOD SUN/MON UNDER NORTHERLY FLOW ALOFT...GIVING WAY TO WARMING
TEMPS TUE/WED AS STRONG RIDGING ALOFT BUILDS OVER THE AREA.

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

$$
RRS