Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 180523
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1123 PM CST WED DEC 17 2014

.UPDATE...
ISSUED AT 1123 PM CST WED DEC 17 2014

SKIES HAVE REMAINED MOSTLY CLEAR OVER ALL BUT THE FAR SOUTH AND
EXTREME NORTHEAST THIS EVENING. THIS...ALONG WITH VERY DRY
AIR AND LIGHT WINDS HAS ALLOWED TEMPERATURES TO DROP INTO THE MID
TEENS OVER ALL BUT THE FAR SOUTH. OVER THE PAST HOUR...SATELLITE
SHOWED HIGH CLOUDS SPREADING NORTHEAST AHEAD OF THE UPPER LEVEL
SYSTEM MOVING INTO THE CENTRAL PLAINS. THIS SHOULD END THE
TEMPERATURE PLUNGE AND PREVIOUSLY UPDATED LOW...FROM AROUND 12
NORTHWEST TO THE LOWER 20S SOUTH OF HIGHWAY 34 SHOULD HOLD. THE
LEADING EDGE OF THE LIGHT SNOW IS STILL WELL SOUTH OF THE I-70
CORRIDOR IN MO AND WITH THE DRY AIR ALOFT...NOT LIKELY TO REACH
INTO OUR NE MO COUNTIES UNTIL AFTER 12Z AS MENTIONED IN THE
PREVIOUS DISCUSSION.

&&

.SYNOPSIS...
ISSUED AT 325 PM CST WED DEC 17 2014

12Z UA ANALYSIS HAS AN 850MB RIDGE RUNNING FROM THE GULF COAST INTO
THE NORTHERN PLAINS. A STORM SYSTEM WAS OVER SOUTHERN CANADA WITH A
LLJ RUNNING FROM WEST TEXAS INTO THE CENTRAL PLAINS. SATELLITE
TRENDS THROUGH MID AFTERNOON SHOW CLEARING SKIES ACROSS THE AREA
WITH CLOUDS FROM THE NEXT SYSTEM OVER THE CENTRAL AND SOUTHERN
PLAINS.

18Z SFC ANALYSIS HAS HIGH PRESSURE OVER THE NORTHERN PLAINS AND
UPPER MIDWEST. A WEAK LOW WAS IN SOUTHEAST COLORADO WITH AN IMPLIED
BOUNDARY RUNNING FROM THE LOW INTO SOUTHWEST ARKANSAS. DEW POINTS
WERE IN THE SINGLE DIGITS AND TEENS ACROSS THE NORTHERN PLAINS AND
UPPER MIDWEST WITH 20S AND 30S FROM THE OHIO VALLEY INTO THE
SOUTHERN PLAINS.

&&

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 325 PM CST WED DEC 17 2014

QUIET CONDITIONS WITH CLEAR OR CLEARING SKIES WILL BE SEEN ACROSS
THE AREA THROUGH LATE AFTERNOON. DRY CONDITIONS WILL THEN BE SEEN
TONIGHT AND INTO THE PRE-DAWN HOURS WITH INCREASING CLOUDS. SNOW
WILL DEVELOP AND SPREAD NORTHEAST THROUGH KANSAS AND MISSOURI.
HOWEVER...DRY AIR ACROSS THE AREA WILL PREVENT ANY SNOW FROM
REACHING THE EXTREME SOUTH PRIOR TO 6 AM THURSDAY.

LOWS TONIGHT SHOULD DROP QUICKLY AFTER SUNSET AND THEN MAY BECOME
STEADY OR RISE SLIGHTLY AS CLOUDS MOVE BACK INTO THE AREA.

ON THURSDAY...STRONG FORCING WILL GO INTO SATURATING THE DRY AIR AT
THE LOW LEVELS AND ALLOW SNOW TO MOVE INTO THE FAR SOUTHERN AREAS.
THE FORCING RAPIDLY COLLAPSES BY LATE MORNING WITH MINIMAL FORCING
IN THE SATURATED ATMOSPHERE ACROSS THE SOUTH THIRD DURING THE
AFTERNOON.

THUS THE OPPORTUNITY FOR ACCUMULATING SNOW WILL OCCUR THURSDAY
MORNING IN A 4-6 HOUR WINDOW. THE BEST CHANCES FOR ANY ACCUMULATING
SNOW APPEAR TO BE SOUTH OF A KCNC...KFSW...TO KBMI LINE OR SOUTH OF
A CHARITON IOWA TO BLOOMINGTON ILLINOIS LINE. ACCUMULATIONS WILL BE
UNDER AN INCH BUT AMOUNTS APPROACHING AN INCH MAY BE SEEN ACROSS THE
EXTREME SOUTHERN PARTS OF SCOTLAND/CLARK COUNTIES IN MISSOURI AND
POSSIBLY THE SOUTHWEST CORNER OF HANCOCK COUNTY ILLINOIS.

DATA DOES SUGGEST THE POTENTIAL FOR A NARROW BAND OF SNOW IN STRONG
FORCING TO SET UP NEAR A KIRK TO KUIN LINE. A NORTHWARD SHIFT OF
THIS BAND WOULD PLACE IT ACROSS THE EXTREME SOUTHERN PARTS OF THE
AREA WITH THE POTENTIAL FOR SLIGHTLY HIGHER AMOUNTS.

HOWEVER...IF THE DRY AIR IS DEEPER THAN DEPICTED IN THE MODELS...
THEN THE SNOW BAND WOULD BE MUCH FURTHER SOUTH OF THE AREA AND SNOW
AMOUNTS ACROSS THE EXTREME SOUTH WOULD BE MUCH LESS.

THE KEY POINT IS THAT THERE WILL BE A VERY SHARP GRADIENT BETWEEN NO
SNOW AND ACCUMULATING SNOW ON THURSDAY.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 325 PM CST WED DEC 17 2014

OVERVIEW...ZONAL 500 MB FLOW WILL KEEP THINGS QUIET THROUGH SUNDAY.
UPPER LEVEL DISTURBANCE ASSOCIATED WITH THE SUBTROPICAL JET WILL
EJECT OUT OF NORTHERN MEXICO AND TRACK ACROSS THE SOUTHERN U.S.
THROUGH THE WEEKEND...REMAINING WELL SOUTH OF IOWA. A LARGE PACIFIC
JET STREAK WILL CARVE OUT A TROUGH OVER THE CENTRAL U.S. BEGINNING
MONDAY AND PERSISTING THROUGH NEXT WEEK. LIGHT RAIN AND SNOW WILL BE
POSSIBLE ON MONDAY ACROSS THE AREA.

FRIDAY AND SATURDAY...VERY QUIET PERIOD WITH HIGH TEMPS IN THE 30S
ALONG WITH DRY WEATHER. A WEAKENING TROUGH AXIS WILL MOVE THROUGH
FRIDAY NIGHT INTO SATURDAY MORNING WHICH HAS DECREASING DEFINITION
FORM THE MID-LEVELS TO THE SFC. PERIOD OF WEAK NEGATIVE OMEGA IS
FORECAST SATURDAY MORNING AS DCVA MOVES THROUGH BUT LAYER JUST BELOW
THE LIFT AT 600 MB IS VERY DRY DURING THIS TIME WITH RH NEAR 30%.

SUNDAY...SFC WINDS WILL BEGIN TO INCREASE OUT OF THE SE IN RESPONSE
TO A LEE-SIDE SFC LOW ORGANIZING OVER E MONTANA AND THE DAKOTAS.
HIGHS WILL ONCE AGAIN BE IN THE MID 30S TO NEAR 40 F.

MONDAY...PERIOD OF RAIN AND SNOW POSSIBLE AS LOW PRESSURE CENTER
REMAINS NW OF THE AREA ACROSS SW MINNESOTA AND N IOWA...NOT A
FAVORABLE LOCATION FOR MUCH ACCUMULATING SNOW TO OCCUR ACROSS THE
DVN FORECAST AREA.

TIMING AND P-TYPE ISSUE EXISTS BETWEEN THE GFS/ECMWF. ECMWF IS
COOLER AND ~6-12 HOURS SLOWER (THAN THE GFS)...IT HAS THE 850 MB 0 C
ISOTHERM TO THE SOUTH OF THE CWA INTO THE NIGHTTIME HOURS WITH
PRECIP LINGERING PAST 00Z/TUESDAY. THE GFS HAS 850 MB 0 C ISOTHERM
OVER NORTHERN CWA AND HAS MOST PRECIP OVER WITH BY THE AFTN. ECMWF
HAS LOW-LEVEL WAA RAISING 925 MB TEMPS TO +1 TO +3 C BY THE EVENING
AND BOTH MODELS FORECAST 2 METER MAX TEMPS IN THE MID TO UPPER 30S.

FORECAST SOUNDINGS HAVE WARMEST TEMPS IN THE LOWER PORTION OF THE
BOUNDARY LAYER WHICH ACTUALLY SLOWLY INCREASE THROUGH THE DAY.
THEREFORE MAY HAVE -RA/-SN MIX OR -SN TRANSITION TO -RA THROUGH THE
EVENT WITH BEST CHANCES FOR -SN ACROSS THE NORTH.

TUESDAY AND WEDNESDAY...A STRONG LOW WILL LIKELY FORM DURING THIS
TIME ALONG A DEVELOPING BAROCLINIC ZONE OVER THE SOUTHERN U.S./OHIO
VALLEY AND THEN MOVE INTO THE GREAT LAKES AREA. MODEL CONSENSUS FOR
THE DVN CWA IS COLDER AND BREEZY WITH SCT SNOW SHOWERS.

THE ECMWF IS SHOWING A STRONG LOW PRESSURE SYSTEM DEVELOPING ACROSS
ALABAMA AND TENNESSEE TUESDAY NIGHT AND THEN LIFTING NORTHWARD TO
LAKE HURON BY WEDNESDAY NIGHT WITH A CENTRAL PRESSURE DOWN TO 961
MB. THE GFS BRINGS IT TO THE SAME AREA BUT IS FURTHER SE DURING THE
CYCLOGENESIS PHASE. IT WILL BE INTERESTING TO SEE THE MODELS WORK
OUT THE POLAR-SUBTROPICAL JET PHASING ISSUES OVER THE NEXT FEW DAYS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1123 PM CST WED DEC 17 2014

A WEAK UPPER LEVEL SYSTEM WILL SPREAD LIGHT SNOW ACROSS MO INTO
CENTRAL IL ON THURSDAY. THIS MAY BRUSH THE BRL SITE...WHERE A
SEVERAL HOUR WINDOW OF MVFR CIGS/VISBYS IS FORECAST THURSDAY MORNING.
ELSEWHERE...SURFACE HIGH PRESSURE AND LIGHT NORTHWEST WINDS WILL
PROVIDE VFR CONDITIONS THROUGHOUT. FORECAST MODELS CONTINUE TO
SUGGEST A POTENTIAL FOR MVFR FOG LATE TONIGHT INTO MID MORNING
THURSDAY...WHICH HAS YET TO MATERIALIZE. WITH UNFAVORABLE
CONDITIONS DUE TO DRY AIR...DRY SURFACE CONDITIONS AND THICKENING
HIGH CLOUD COVER...THIS FOG HAS BEEN DISCOUNTED AND NOT INCLUDED IN THE
FORECASTS AT THIS TIME.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

UPDATE...SHEETS
SYNOPSIS...08
SHORT TERM...08
LONG TERM...UTTECH
AVIATION...SHEETS






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