540
FXUS63 KDVN 180536
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1136 PM CST TUE DEC 17 2024
KEY MESSAGES
- CHANCE (30-70+%) OF SNOW, WINTRY MIX AND RAIN IN PORTIONS OF THE
CWA TONIGHT FROM NORTH TO SOUTH.
- STRONG CLIPPER THURSDAY MAY BRING A CHANCE FOR ACCUMULATING SNOW
FOR AREAS NORTH OF I-80.
- COLDER AND MAINLY DRY FRIDAY, THEN A LOW CHANCE FOR LIGHT SNOW SOMEWHERE
IN OR NEAR THE LOCAL FORECAST AREA LATE FRIDAY NIGHT INTO
SATURDAY.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED AT 251 PM CST TUE DEC 17 2024
TONIGHT...PROGRESSIVE PATTERN WITH EMBEDDED WAVES CONTINUING ACRS
THE CONUS, WITH WATER VAPOR IMAGERY SHOWING ONE UPSTREAM WAVE OF
NOTE CURRENTLY ACRS NE, WITH AND ASSOCIATED LEESIDE BAROCLINIC LEAF
FROM THE SOUTHWESTERN PLAINS TO ACRS IA. THIS FEATURE ALSO ALREADY
PRODUCING SNOW ACRS SD, SOUTHWEST MN INTO NORTHWEST IA. THE DIGGING
UPPER TROF AXIS WILL PRODUCE A SWATH OF PRECIP(SNOW) ACRS THE LOCAL
AREA FROM NORTHWEST-TO-SOUTHEAST FROM THIS EVENING AND INTO THE
OVERNIGHT, ALTHOUGH QUITE A BIT OF TOP-DOWN SATURATION TO GO WITH
IT'S INITIAL LIFT BEFORE PRECIP REACHES THE SFC. ANOTHER ELEVATED WAA
TYPE CONVEYOR FROM THE SOUTH WILL LOOK TO SPREAD SCTRD RAIN SHOWERS
UP FROM THE SOUTH AND MAKE IT INTO THE SOUTHERN QUARTER TO THIRD OF
THE DVN CWA. BACK TO THE SNOW IN THE NORTH, STRENGTH OF H8-H7 MB F-
GEN FORCING AND SATURATION MAY LAY OUT NARROW OR CONFINED SWATHS OF
HIGHER SNOW AMOUNT'S OF 1-2+ INCHES BY 12Z WED MORNING, BUT WHERE
THESE "ENHANCED" SWATHS LAY OUT THE CHALLENGE OF COURSE. BUT LOOKING
AT SOME OF THE F-GEN PROGS THAT SEEM TO BE HANDLING THE BETTER SNOW
BANDS OFF TO THE NORTHWEST CURRENTLY, THEY LAY OUT GENERALLY IN THE
VICINITY OF THE HWY 20 CORRIDOR, WITH SECONDARY FORCING BAND CLOSET
TO HWY 30.
AS THE SNOW BANDS SAG SOUTH TOWARD I80 AND SOME OF THE RAIN IN THE
SOUTH TRIES TO PUSH NORTHWARD, FCST SOUNDINGS SUGGEST A BUILDING
WARM WEDGE ALOFT ENOUGH TO PRODUCE A WINTRY MIX IN THE VICINITY OF
THE I-80 CORRIDOR TOWARD MIDNIGHT AND A FEW HOURS PAST. THE VERTICAL
PROFILES SUGGEST BOUTS OF SLEET, FREEZING RAIN AND SNOW POSSIBLE
ALONG THIS CORRIDOR(A COUNTY OR TWO EITHER SIDE OF I-80)UNTIL
NORTHERLY FLOW AND EVAPO-COOLING IN THE WARM LAYER COOL IT ENOUGH
FOR A TREND BACK TO MAINLY LIGHT SNOW. WITH SFC TEMPS HOVERING AT
OR A LITTLE BELOW FREEZING, SOME LIGHT ICE GLAZE MAY BE POSSIBLE IN
BETWEEN THE SLEET AND SNOW. CURRENT HIRES PROGS SUGGEST MOST OF THE
PRECIP EAST OF THE CWA BY THE TIME THE MORNING RUSH IS IN EARNEST,
BUT THERE MAY BE SOME LINGERING SLICK SPOTS ON UNTREATED SURFACES.
LOW TEMPERATURES TONIGHT BEHIND A PASSING SFC TROF INDUCED BY THE
WAVE ALOFT, WILL LOOK TO RANGE FROM THE LOW 20S IN THE NORTHWEST, TO
THE LOWER 30S IN THE SOUTHEAST.
WEDNESDAY...A BREEZY NORTHWEST SFC FLOW COOLING DAY IN INCOMING
RIDGE PRESSURE GRADIENT. EXTENT OF CLOUD COVER SOMEWHAT UNCERTAIN,
BUT WOULD THINK THAT WITH INCOMING SUBSIDENCE FIELDS THAT THERE
WOULD BE SOME BREAKS AT TIMES FOR AT LEAST PARTIAL SUN. COLD AND DRY
WED NIGHT UNDER LINGERING RIDGE AXIS. MAY HAVE TO THINK ABOUT SOME
PATCHY FOG, BUT TOO UNCERTAIN AT THIS POINT TO INCLUDE IN THE
GRIDS.
LONG TERM /THURSDAY THROUGH TUESDAY/
ISSUED AT 251 PM CST TUE DEC 17 2024
THURSDAY...STEERING FLOW ENSEMBLES SHOW ANOTHER DIGGING CLIPPER
SYSTEM IN THE MIDWEST FLOW, MORE VIGOROUS THAN THE ONE FOR TONIGHT.
STILL SOME VARIANCE BETWEEN THE SOLUTIONS AND ENSEMBLES OF THE EXACT
PATH OF THIS SYSTEM TAKES AND HOW FAR NORTH OR SOUTH IT JOGS. BUT THE
LATEST TRENDS IN MOST OF THE RECENT MODEL RUNS HAVE TRENDED FURTHER
SOUTH, THUS THE NORTHERN OR NORTHEASTERN THIRD TO HALF OF THE FCST
AREA MAY BE MORE UNDER THE GUN FOR SNOW WITH THIS SYSTEM BY THU
MORNING. A FEW SOLUTIONS EVEN HAVE ADVISORY LEVEL SNOW ACCUMULATIONS
IN NORTHEAST PORTIONS OF THE DVN CWA. FOR NOW WILL RAISE POPS TO 30-
60% IN THE NORTH, AND AWAIT FURTHER MODEL TRENDS/RUNS TO BETTER
DEFINE OVER THE NEXT 24 HOURS OR SO. INTERESTING THAT SOUTH OF THE
PRECIP, THE WARM DRAW OF THE PASSING CLIPPER SYSTEM MAY RAISE TEMPS
INTO THE 40S IN THE SOUTH.
FRIDAY THROUGH MONDAY...COOL CORE UPPER TROF WILL LOOK TO DEEPEN
ACRS THE MS RVR VALLEY IN THE WAKE OF THE THU CLIPPER ON FRIDAY AND
INTO THE START OF THE WEEKEND. THUS COLDER TEMP TRENDS LOOK ON TAP
FOR FRIDAY AND SATURDAY. ALSO, THE NORTHWEST-TO-SOUTHEAST ALIGNED
LLVL BAROCLINICITY MAY USHER A WEAK CLIPPER OR ISENTROPIC LIFT EVENT
DOWN ACRS THE AREA EITHER LATE FRIDAY NIGHT OR SATURDAY FOR A
POTENTIAL LIGHT SNOW EVENT IN OR NEAR THE LOCAL FCST AREA. BUT ANY
RIPPLE WILL HAVE TO BATTLE DRY AIR AND IT'S PRECIP ERODING EFFECTS.
LONGER RANGE UPPER JET FLOW AND MEAN STEERING PROGS SUGGEST A
FLATTENED FLOW FOR TEMP MODERATION LATE IN THE WEEKEND AND INTO NEXT
WEEK. OF COURSE THIS FLOW WILL ALSO LOOK TO USHER ANOTHER WAVE
SOMEWHERE ACRS THE MIDWEST LATE SUNDAY INTO MONDAY WITH INCREASING
PRECIP CHANCES AGAIN.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1124 PM CST TUE DEC 17 2024
BAND OF SNOW HAS MOVED JUST TO THE EAST OF THE CID/DBQ TERMINALS
AND WILL CONTINUE TO PROGRESS EAST OVER THE NEXT 1-3 HOURS. HAVE
MAINTAINED RASN AT MLI AS THE BAND MOVES EAST, WITH MVFR VSBYS.
PERIODS OF MVFR AND BRIEF IFR CIGS ARE EXPECTED THIS MORNING,
AS THE SURFACE TROUGH SLIDES EAST. CONFIDENCE REMAINS LOW ON
WHEN CONDITIONS IMPROVING BACK TO VFR, WITH MOST MODEL GUIDANCE
STRUGGLING WITH CURRENT CONDITIONS. CEILINGS SHOULD IMPROVE
TO VFR LATE MORNING AND EARLY AFTERNOON, WITH NORTHWEST WINDS
INCREASING OVER 10 KTS.
DVN WATCHES/WARNINGS/ADVISORIES
IA...NONE.
IL...NONE.
MO...NONE.
SHORT TERM...12
LONG TERM...12
AVIATION...GROSS
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