FXUS63 KARX 230201
AFDARX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LA CROSSE WI
801 PM CST TUE DEC 22 2009
.UPDATE...
SURGE OF MOISTURE INTO NORTHEAST IOWA AND SOUTHWEST WISCONSIN WAS
RESULTING IN FREEZING DRIZZLE AND SPOTTY FREEZING RAIN. CALLS TO
COUNTIES INDICATED ROADS BECOMING ICY. MOISTURE HAVING A HARD TIME
MOVING NORTHWARD WITH DRY EASTERLY FLOW. THUS HAVE ISSUED A FREEZING
RAIN ADVISORY FOR NORTHEAST IOWA AND PORTIONS OF SOUTHWEST WISCONSIN
OVERNIGHT THROUGH NOON WEDNESDAY.
&&
JLR
&&
.PREV DISCUSSION...
.SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT
FORECAST CONCERNS THIS PACKAGE...IMPENDING WINTER STORM AND PRECIP
TYPE/AMOUNTS FOR MOST OF THE PERIOD.
18Z SFC ANALYSIS HAD LOW PRESSURE DEEPENING OVER THE CENTRAL ROCKIES
TO WEST TX...WITH A TROUGH/WARM FRONT NORTHEAST INTO MO/IL. WV
IMAGERY DEPICTED A PORTION OF THE SHORTWAVE RESPONSIBLE FOR THE SNOW
ACROSS THE AREA MON NIGHT OVER EASTERN IA...STILL PRODUCING LIFT AND
SOME -SN ACROSS SOUTHEAST WI/NORTHERN IL. LOWER LEVEL WARM
ADVECTION/LIFT AND MOIST SFC-800MB LAYER RESPONSIBLE FOR PATCHY DZ/
FZDZ ACROSS PORTIONS OF CENTRAL IA. UNDER THE INFLUENCE OF HIGH
PRESSURE OVER WESTERN ONT...MOSTLY SUNNY SKIES OVER PORTION OF
NORTHERN WI/NORTHEAST MN EARLY THIS AFTERNOON. LOWER CLOUDS THE RULE
OVER THE REMAINDER OF THE REGION WITH WEAK 850-700MB WARM ADVECTION
OVER THE MID MS VALLEY WARM FRONT.
22.12Z NAM/GFS LOOK TO HAVE INITIALIZED WITHOUT LARGE ERRORS. BOTH
WERE 1-2MB TOO HIGH WITH SFC PRESSURES ACROSS THE CENTRAL PLAINS
WHILE PER WV IMAGERY...GFS APPEARED BETTER WITH THE SHORTWAVE
DETAILS ALONG THE WEST COAST. MODELS CONTINUE TO CONVERGE TOWARD
A COMMON SOLUTION...AND REASONABLE WELL SUPPORTED BY ECMWF/CAN-
GEM/UKMET...BUT STILL SOME DIFFERENCES AMONG THEM THAT HAVE
SIGNIFICANT IMPACTS ON THE POSSIBLE WEATHER OUTCOME FOR THE AREA
THRU THE NEXT 3 DAYS. DPROG/DT OF 500MB HGTS AT 22.12Z SHOWED
NAM/GFS/ECMWF RUNS OF 20.12Z AND 21.12Z WERE A BIT WEAK WITH THE
SHORTWAVE ACROSS SOUTHERN CA AND NEAR THE OR/WA BORDER. FOR 00-36HRS
MODELS CONVERGING ON A COMMON SOLUTION AS ONE UPPER LOW/SHORTWAVE
DROPS TOWARD MT AND THE WEST COAST ENERGY EJECTS INTO THE SOUTHERN
PLAINS. NAM A BIT OF AN OUTLIER AT 36HRS WITH A SLOWER SOUTHERN
SHORTWAVE. FOR 36-60HRS TREND IS TOWARD MORE/FASTER PHASING OF THE
NORTH/SOUTH STREAM SHORTWAVES INTO ONE UPPER LOW OVER THE CENTRAL
PLAINS...WHICH LEADS TO A FASTER OCCLUDING SFC SYSTEM. GOOD SIGNAL
FOR A DEEP UPPER LOW TO BE SOMEWHERE OVER THE MID/UPPER MS VALLEY AT
84HRS. CAN-GEM AND NAM APPEAR AS FAST AND SLOW OUTLIERS AT 84HRS.
RUN-TO-RUN CONSISTENCY ABOUT EQUAL AMONG THE MODELS AND BELOW
AVERAGE FOR THE MOST PART. CHECK OF OBS VS. MODEL DATA AT 18Z SHOWED
NAM/GFS WITH REASONABLE DEPICTIONS OF THE SFC MASS FIELDS ACROSS THE
CENTRAL CONUS. PER WV IMAGERY...BOTH LOOKED GOOD WITH THE SHORTWAVE
DETAILS ALONG THE WEST COAST WITH SLIGHT EDGE TO GFS. GIVEN THEIR
MORE SIMILAR SOLUTIONS AND NORMALLY BETTER PERFORMANCE...PREFERRED A
GFS/ECMWF COMPROMISE THIS CYCLE. EVEN SO...THIS DOES NOT SORT OUT
MANY OF THE FCST DETAILS FOR THE NEXT 3 DAYS. FORECAST CONFIDENCE
ON THE AVERAGE SIDE THIS CYCLE.
FOR THE SHORT TERM...EVEN AS MODELS CONTINUE TO CONVERGE TOWARD A
COMMON SOLUTION MANY QUESTIONS REMAIN...ESPECIALLY WITH PRECIP TYPES
ACROSS THE AREA WED NIGHT THRU THRU FRI AS THE STRONG SFC/UPPER
LEVEL LOW LIFTS TOWARD AND INTO THE REGION. MODEL SOUNDINGS/X-
SECTIONS INDICATE A SATURATED SFC-800MB LAYER OVER THE SOUTH 1/3 TO
1/2 OF THE FCST AREA TONIGHT/WED MORNING...WITH CLOUD TOP TEMPS
AROUND -5C AND SOME WEAK 925-850MB WARM ADVECTION AND 275-285K
ISENTROPIC LIFT IN THIS LAYER. SIGNAL POINTS TO -FZDZ POTENTIAL
TONIGHT/WED MORNING. 20-50 PERCENT CHANCE OF -FZDZ LOOKS REASONABLE
OVER THE SOUTH 1/3 TO 1/2 OF THE FCST AREA TONIGHT/WED MORNING. WILL
HOLD OFF ON ADVISORY TONIGHT/WED MORNING FOR NORTHEAST IA/SOUTHWEST
WI FOR NOW AND WILL PASS ALONG TO EVENING CREW TO KEEP AN EYE ON IT.
DEEPER MOISTURE/LIFT ARRIVES WED AFTERNOON IN FIRST SURGE OF 850-
700MB WARM ADVECTION/280-295K ISENTROPIC LIFT AHEAD OF THE DEEPENING
LOW/TROUGH. MODEL SOUNDINGS/X-SECTIONS INDICATE THE PRECIP SHOULD
START AS SNOW...THEN TRANSITION TO A MIX/ZR/IP OVERNIGHT AS TEMPS
WARM TO NEAR/ABOVE 0C IN THE 900-800MB LAYER. STILL PLENTY OF
DIFFERENCES IN HOW MUCH QPF IS PRODUCED IN THIS FIRST SURGE OF
MOISTURE/LIFT...AND WHICH PRECIP TYPE WILL DOMINATE. CONTINUED
WINTER STORM WATCH FOR WED AFTERNOON/NIGHT AS IS FOR NOW...AS MAY
YET NEED A FZRA/FZDZ ADVISORY ON WED BEFORE THE DEEPER MOISTURE
ARRIVES FOR ICE NUCLEATION IN THE CLOUDS AND CHANGE TO SNOW THEN
CHANGING BACK TO MIXED PRECIP TYPES. SOME MODEL CONSENSUS FOR A LUL
IN THE HEAVIER PRECIP THU MORNING INTO EARLY THU AFTERNOON AS SOME
DRIER AIR ABOVE 800MB SPREADS ACROSS THE AREA. PRECIP TYPE REMAINS
UNCERTAIN...FROM DZ OR -FZDZ TO -RA OR -SN FOR MUCH OF THU...
DEPENDING ON BOUNDARY LAYER TEMPS AND WHICH MODEL WOULD BE MORE
CORRECT. SECOND SURGE OF MOISTURE/LIFT EXPECTED TO ARRIVE LATER
THU AFTERNOON/NIGHT AS NORTH/SOUTH STREAM SHORTWAVES BEGIN TO
PHASE...UPPER LOW DEEPENS AND SFC LOW DEEPENS INTO SOUTHERN IA BY
FRI MORNING. DEPENDING ON MODEL...PLENTY OF DIFFERENCE IN PRECIP
TYPE WITH THIS SURGE OF MOISTURE/PRECIP...WITH NAM WARMER AND
INDICATING MORE -FZRA/RA OVER MOST OF THE FCST AREA...TO GFS/CAN-
GEM/UKMET COOLER AND INDICATING MORE MDT/HEAVY SNOW FOR MORE OF THE
FCST AREA. CARIBOU SNOW TOOL-COBB DATA INDICATES MIXED PRECIP TYPES
THU/THU NIGHT AT KLSE...WITH ONLY ABOUT 3 INCHES OF SNOW...WHILE
EXAMINING GFS MODEL SOUNDING/TIME-HGT X-SECTION FOR KLSE INDICATES A
MAX WET-BULB ZERO VALUE OF ABOUT 1C IN THE BOUNDARY LAYER AND
BELOW 0C THRU THE REST OF THE COLUMN...WHICH WOULD RESULT IN
PREDOMINATELY SNOW FROM 0.75 INCH OF QPF. GIVEN THIS UNCERTAINTY...
LEFT PRECIP TYPE AS MIX OF RA/FZRA/SN THU NIGHT PENDING FURTHER
CONSISTENCY ON THE LOWER LEVEL THERMAL STRUCTURE DETAILS. FRIDAY MAY
BE ANOTHER LUL IN THE PRECIP AS DRY SLOT ABOVE 800MB WRAPS AROUND
THE LOW AND OVER THE AREA. WITH WHAT WOULD BE A LACK OF ICE CRYSTALS
IN THE CLOUDS...ADDED -FZDZ MENTION TO FRI. GIVEN MULTIPLE POSSIBLE
MIXED PRECIP OUTCOMES...WINTER STORM WATCH FOR THU THRU FRI LOOKS
GOOD. DEEPER MOISTURE/COLDER AIR RETURNS FOR FRI NIGHT AS THE
VERTICALLY STACKED LOW DRIFTS OVER THE AREA. BY FRI NIGHT PRECIP
TYPE AS ALL SNOW...BUT BULK OF FORCING/LIFT HAS PASSED NORTH/EAST OF
THE AREA.
NUMERICAL TEMP GUIDANCE GENERALLY SIMILAR THROUGH THE PERIOD.
FAVORING ECMWF/GFS...GENERALLY FAVORED THE GFS TEMP GUIDANCE FOR
TONIGHT THRU THU NIGHT...THEN BLEND OF GFS MEX/ENSEMBLE MOS AND HPC
GUIDANCE FOR FRI/FRI NIGHT.
.LONG TERM...SATURDAY THROUGH TUESDAY
22.00Z MEDIUM RANGE MODELS IN MODEST AGREEMENT AT 12Z SAT...THEN
QUICKLY DIVERGE WITH THE PROGRESSIVENESS OF THE UPPER LOW BY SAT
NIGHT/SUN. ECMWF/UKMET SLOWER WITH THE UPPER LOW REMAINING OVER THE
REGION INTO SUN...CAN-GEM/GFS MORE PROGRESSIVE WITH THE TROUGH/UPPER
LOW INTO THE EASTERN GREAT LAKES BY 00Z MON. BOTH ECMWF/GFS WITH
REASONABLE RUN-TO-RUN CONSISTENCY WITH THEIR RESPECTIVE 21.00Z
RUNS...ECMWF SLOWER...GFS FASTER. BETWEEN MODEL AND RUN-TO-RUN
CONSISTENCY POOR BY MON/TUE AS MODELS STRUGGLE WITH THE INTERACTIONS
OF THE STRONGER SHORTWAVE TROUGHS IN THE FLOW AND SPEED OF THE
SHORT-TERM SYSTEM INTO EASTERN CAN. HGTS DO RISE OVER THE AREA FOR
MON/TUE...AHEAD OF SPLIT FLOW DEVELOPING OVER WESTERN NOAM. GIVEN
ALL THE BETWEEN MODEL AND RUN-TO-RUN VARIABILITY...FCST CONFIDENCE
IN THE LONG TERM AVERAGE AT BEST. ECMWF HAS LEAD THE WAY WITH THE
DEC 23-25 SYSTEM THE PAST 2-3 DAYS...WITH ITS RUN OFTEN LOOKING LIKE
A SLOW OUTLIER...THEN UKMET/GFS/CAN-GEM TRENDING TOWARD IT WITH
THEIR SUBSEQUENT RUNS...THUS PER HPC GUIDANCE...FAVORED ECMWF FOR
THE LONG-TERM. WITH THE SFC/UPPER LOW LOOKING TO LINGER OVER THE
AREA SAT INTO SUN...RAISED -SN CHANCE ON SAT TOWARD 50 PERCENT AND
ADDED FLURRIES TO SUN. EVEN WITH DIFFERENCES ALOFT AT 500MB...RIDGE
OF HIGH PRESSURE AT THE SFC BUILDS INTO THE REGION AND LEFT MON/TUE
DRY FOR NOW. COLDEST LOWER LEVEL AIRMASS WITH THE DEPARTING SYSTEM
ROTATES ACROSS THE AREA SAT/SUN...WITH WHAT SHOULD BE A CLOUD
BLANKET. 850MB TEMPS MODERATE SOME FOR MON/TUE WITH MORE OF A
WESTERLY COMPONENT IN THE SFC-850MB FLOW. APPEARS TEMPS WILL NOT BE
BITTERLY COLD BEHIND THIS SYSTEM...UNLESS WE/RE UNDER THE RIDGE AXIS
AND CLEAR SKIES SUN/MON NIGHTS...AS SAT NIGHT LOOKS TO REMAIN MOSTLY
CLOUDY. FAVORED A BLEND OF GFS MEX/ENSEMBLE MOS AND HPC GUIDANCE FOR
MAXES/MINS THRU THE PERIOD.
.AVIATION...TONIGHT AND WEDNESDAY
PRIMARY FORECAST CONCERNS WERE WITH PRECIPITATION TYPE AND FLIGHT
CATEGORIES ASSOCIATED WITH WINTER STORM TO IMPACT THE AREA WEDNESDAY
THROUGH FRIDAY. THIS STORM SHOULD HAVE SIGNIFICANT IMPACTS ON
DEICING AIRCRAFT AND SNOW AND/OR ICE REMOVAL ON AIRPORT SURFACES.
THEREFORE...AIRPORT MANAGERS...DISPATCHERS AND PILOTS WILL WANT TO
KEEP ABREAST OF LATEST FORECASTS.
THROUGH 23.18Z...WEDNESDAY NOON...LOW LEVEL RELATIVE HUMIDITY
REMAINS IN PLACE ACROSS THE AREA. DRIER AIR ALOFT FAVORS ANY
PRECIPITATION DURING THIS TIME AS FREEZING DRIZZLE. CHANCES OF THIS
APPEAR SMALL DUE TO LACK OF UPWARD VERTICAL MOTIONS...SO CONFIDENCE
NOT HIGH ENOUGH TO INCLUDE IN THE TAFS. FORECAST CONFIDENCE WAS HIGH
THAT DOWNWARD TREND INTO IFR AS PREVAILING CONDITIONS WILL OCCUR
TONIGHT INTO WEDNESDAY AT KLSE AND KRST.
LOOKING AHEAD...WINTER STORM SYSTEM DEVELOPING IN THE PLAINS IS
EXPECTED TO BRING A SIGNIFICANT AMOUNT OF PRECIPITATION INTO THE TAF
REGION...WHICH WILL LIKELY INCLUDE SNOW AND FREEZING RAIN. FORECAST
CONFIDENCE WAS HIGH THAT THESE CONDITIONS WILL OCCUR...ALONG WITH AN
EXTENDED PERIOD OF MVFR/IFR CONDITIONS THROUGH THE END OF THE WEEK.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...FREEZING RAIN ADVISORY UNTIL NOON CST WEDNESDAY FOR WIZ054-
WIZ055-WIZ061.
WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR WIZ053-WIZ054-WIZ055-WIZ061.
WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH FRIDAY
AFTERNOON FOR WIZ017-WIZ029-WIZ032-WIZ033-WIZ034-WIZ041-
WIZ042-WIZ043-WIZ044.
MN...WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR MNZ086-MNZ087-MNZ088-MNZ094-MNZ095-MNZ096.
WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH FRIDAY
AFTERNOON FOR MNZ079.
IA...FREEZING RAIN ADVISORY UNTIL NOON CST WEDNESDAY FOR IAZ008-
IAZ009-IAZ010-IAZ011-IAZ018-IAZ019-IAZ029-IAZ030.
WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR IAZ008-IAZ009-IAZ010-IAZ011-IAZ018-IAZ019-
IAZ029-IAZ030.
&&
$$
SHORT/LONG TERM...RRS
AVIATION..........THOMPSON
