374
FXUS63 KDVN 170445
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1045 PM CST MON DEC 16 2024
KEY MESSAGES
- ABOVE NORMAL TEMPERATURES ARE EXPECTED TUESDAY BEFORE BECOMING
MORE SEASONAL BY MID-WEEK
- A FEW CLIPPER SYSTEMS COULD APPROACH OUR AREA BY THE MID- TO
LATE-WEEK PERIOD, BUT UNCERTAINTY ON TIMING AND COVERAGE
REMAINS.
- MOST IMPACTFUL CLIPPER WILL BE THURSDAY THAT COULD BRING MINOR
ACCUMULATING SNOW DURING THE AM RUSH HOUR ACROSS OUR NORTH.
SHORT TERM /THROUGH TUESDAY/
ISSUED AT 327 AM CST MON DEC 16 2024
WE START OFF THE WORK WEEK WITH YET ANOTHER FOGGY MORNING FOR MOST,
WITH SOME DENSE FOG REPORTED FOR AREAS ALONG AND NORTH OF INTERSTATE
80. THIS MORNING'S FOG FORECAST REMAINS TRICKY AS THE FOG SEEMS TO
BE TRANSIENT, PARTICULARLY OVER OUR SOUTHEASTERN AREAS. LATEST HREF
ENSEMBLE SOUNDINGS SHOW A VERY STOUT LOW-LEVEL THERMAL INVERSION FOR
OUR NORTHWESTERN AREAS WHICH HAS HELPED TRAP MOISTURE NEAR THE
SURFACE OVER THE LAST 24 TO 30 HOURS. FOG POTENTIAL SOUTH OF
INTERSTATE 80 APPEARS TO BE LESS COMPARED TO FARTHER NORTH, BUT
THERE REMAINS UNCERTAINTY ON THE IMPACT OF A CLEAR SLOT THAT HAS
QUICKLY DEVELOPED OVER THE LAST TWO TO THREE HOURS OR SO. THE LATEST
OBSERVATIONS HAVE SHOWN VISIBILITIES TANKING QUICKLY UNDER THIS
CLEAR SLOT, WHICH SOME MODELS HAVE AND OTHERS DON'T. WILL
VISIBILITIES FALL TO 1/4 MILES UNDER THIS CLEAR SLOT? SEEMS LIKE WE
WILL GET CLOSE, IF NOT REACH THAT THRESHOLD. THE LATEST HREF
EXCEEDANCE PROBABILITIES OF QUARTER MILE OR LESS VISIBILITY IS
AROUND 60 TO 90% WHERE WE HAVE THE GOING DENSE FOG ADVISORY, SO WE
WILL JUST LET IT RIDE, WITH THE EXCEPTION FOR JEFFERSON COUNTY IN
SOUTHEAST IA, WHERE CONFIDENCE IS HIGH ENOUGH TO PULL OUT OF THE
DENSE FOG ADVISORY. THE FOG IS EXPECTED TO LAST THROUGH MID-MORNING
BEFORE DRIER AIR FILTERS IN FROM THE WEST, SLOWLY ERODING IT, BUT
LINGERING LONGEST OVER FAR NORTHEASTERN IOWA INTO NORTHWEST ILLINOIS.
THE REMAINDER OF THE DAY LOOKS DRY, BUT BREEZY, THANKS TO AN
APPROACHING MID-LEVEL TROUGH AND TIGHTENING SURFACE PRESSURE
GRADIENT. WEST WINDS LOOK TO GUST BETWEEN 20 TO 30 MPH. THE
PREVIOUSLY MENTIONED WARM AIR ADVECTION SHOULD LEAD TO MUCH WARMER
THAN AVERAGE TEMPERATURES TODAY, WITH HIGHS WARMING TO THE LOWER 40S
NORTH TO THE UPPER 40S SOUTH. THESE TEMPERATURES ARE NEARLY 10
DEGREES ABOVE AVERAGE! DRY CONDITIONS LOOK TO CONTINUE TONIGHT, WITH
LOWS IN THE 20S (COLDEST TO THE NORTHWEST).
LONG TERM /TUESDAY NIGHT THROUGH MONDAY/
ISSUED AT 220 PM CST MON DEC 16 2024
LITTLE CHANGE IN THE LONG TERM FORECAST AS WE CONTINUE TO SEE AN
ACTIVE PATTERN WITH CLIPPERS THROUGH THE PERIOD. OVERALL THE
MOST IMPACTFUL SYSTEM IS POSSIBLE THURSDAY DURING THE AM
COMMUTE. WHERE WE COULD SEE 1 TO 2 INCHES ALONG THE HIGHWAY 20
CORRIDOR. HAVE INCLUDED THE MID SHIFT DISCUSSION BELOW:
FOR TUESDAY NIGHT THROUGH FRIDAY, THE WEATHER PATTERN WILL BE FAIRLY
ACTIVE, AS WE CONTINUE TO KEEP AN EYE ON A FEW CLIPPER SYSTEMS THAT
WILL BRING CHANCES OF SNOW TO THE REGION. FIRST THE TUESDAY NIGHT
CLIPPER: MOST OF THE LATEST GLOBAL MODELS DEPICT THE COMPACT CLIPPER
TO LARGELY MISS US TO THE NORTH AS THE FGEN BAND REMAINS FARTHER
NORTH, BUT THE PARENT TROUGH SHOULD HELP ENHANCE LARGE-SCALE
FORCING, AND MOST MODEL SOUNDINGS HAVE BEGUN TO SUGGEST A SATURATED
DENDRITIC GROWTH ZONE CONCURRENT WITH THE TROUGH, SO CONFIDENCE HAS
INCREASED FOR A LIGHT SNOW EVENT. NBM EXCEEDANCE PROBABILITIES OF A
TENTH OF AN INCH OF SNOW SHOWS VALUES NOW AROUND 30 TO 50 PERCENT
OVER OUR NORTHEASTERN FORECAST AREA, WHICH IS TRENDING HIGHER, BUT
STILL NOT A GREAT SIGNAL FOR ACCUMULATING SNOW. PROBABLY THE LARGER
IMPACT FROM THIS CLIPPER WILL BE A DROP IN TEMPERATURES TO MORE
SEASONAL VALUES, WITH HIGHS WEDNESDAY BACK IN THE UPPER 20S TO LOWER
30S.
THE OTHER, LARGER CLIPPER SYSTEM WE ARE KEEPING AN EYE ON IS PROGGED
TO APPROACH THE REGION THURSDAY AND THURSDAY NIGHT. RIGHT OFF THE
BAT, THERE REMAINS UNCERTAINTY WITH HOW THIS CLIPPER SYSTEM WILL
EVOLVE, GIVEN SPATIAL DIFFERENCES AMONG THE DETERMINISTIC AND
ENSEMBLE GUIDANCE. HOWEVER, THESE DIFFERENCES AREN'T AS LARGE AS
THEY WERE 24 HOURS AGO. A BROAD UPPER-LEVEL TROUGH IS PROGGED TO
DIVE SOUTHEASTWARD FROM WESTERN CANADA, MAKING A BEELINE TOWARDS THE
UPPER MIDWEST. OVERALL, WE CONTINUE TO REMAIN ON THE SOUTHERN
PERIPHERY OF THE PRECIPITATION SHIELD, BUT WITH VARYING PATHS FOR
THE SURFACE LOW AMONG THE GUIDANCE. VARIOUS ENSEMBLE GUIDANCE
SUGGESTS AROUND 30 TO 60 PERCENT FOR MEASURABLE SNOW FOR AREAS ALONG
AND NORTH OF INTERSTATE 80, WHICH HAS BEEN A RELATIVELY BIG JUMP
OVER THE LAST 24 HOURS. OVERALL, CURRENT INDICATIONS ARE
POSSIBLY 1 TO 2 INCHES OF SNOW FOR OUR FAR NORTH.
FRIDAY THROUGH THE UPCOMING WEEKEND: ANY REMNANT SNOW WILL CEASE BY
THE DAYLIGHT HOURS FRIDAY, WITH A DRY WEEKEND AHEAD. TEMPERATURES
CONTINUE TO BE SEASONAL, WITH HIGHS IN THE 20S TO LOWER 30S, AND A
FEW CHILLY NIGHTS, TOO.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 1039 PM CST MON DEC 16 2024
MVFR CLOUDS WILL MOVE ACROSS NORTHEAST IOWA AND ALONG THE WI/IL
BORDER THROUGH AT LEAST 17Z/17 WITH SOME BRIEF PERIODS OF VFR
ALONG THE SOUTHERN EDGE OF THE CLOUDS. VERY SHORT TERM MODELS
ARE STRUGGLING WITH THESE CLOUDS BUT NBM IS CAPTURING THE 2-3
KFT AGL CIGS. OTHERWISE LLWS PROGGED BY THE RAP MODEL IS NOW
MARGINAL WITH THE MAIN JUMP IN WINDS MAINLY ABOVE 2KFT AGL.
ELSEWHERE ACROSS THE REST OF EASTERN IOWA AND NORTHERN ILLINOIS
EXPECT VFR CONDITIONS AS CLOUDS SLOWLY LOWER THROUGH 06Z/18 WITH
THE APPROACH OF A STORM SYSTEM.
DVN WATCHES/WARNINGS/ADVISORIES
IA...NONE.
IL...NONE.
MO...NONE.
SHORT TERM...GIBBS
LONG TERM...GIBBS
AVIATION...08
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