Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 202350
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
550 PM CST THU NOV 20 2014

.SYNOPSIS...
ISSUED AT 334 PM CST THU NOV 20 2014

A LARGE MID AND UPPER LEVEL TROUGH OVER THE EASTERN THIRD OF THE
U.S. WILL PROPAGATE EASTWARD INTO THE NORTH ATLANTIC THROUGH FRIDAY.
CONSEQUENTLY...ZONAL MID-LEVEL FLOW WILL SET UP ACROSS THE CENTRAL
U.S. THROUGH SATURDAY AND SFC TEMPS WILL MODERATE INTO THE 30S AND
40S DURING THIS TIME. MOISTURE ADVECTION IN ADVANCE OF AN
APPROACHING TROUGH WILL RESULT IN WIDESPREAD RAINFALL SATURDAY NIGHT
AND SUNDAY.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 334 PM CST THU NOV 20 2014

TONIGHT...SIGNIFICANT HEIGHT RISES WILL COMMENCE LATE TONIGHT AT THE
SAME TIME THAT A SFC HIGH PRESSURE SYSTEM MOVES ACROSS THE FORECAST
AREA. THE COLDEST AIR SO FAR THIS FALL MAY OCCUR TONIGHT WITH LOW
TEMPS IN THE SINGLE DIGITS...TO NEAR ZERO IN FAVORED COLD VALLEY
LOCATIONS NORTH OF DAVENPORT. DEPENDING ON HOW QUICKLY MID/HIGH LEVEL
CLOUDS INCREASE LATE TONIGHT SOME LOCATIONS MAY DIP A FEW DEGREES
BELOW ZERO WHICH IS ABOUT 30 DEGREES BELOW AVERAGE FOR MID NOVEMBER.
LUCKILY...SFC WINDS WILL BE LIGHT SO THE WIND CHILL WILL BE
NEGLIGIBLE.

FRIDAY...THE SFC HIGH WILL BE LOCATED OVER THE OHIO VALLEY AND THE
RETURN FLOW AROUND THIS SYSTEM WILL LEAD TO A STEADY...ALBEIT
LIGHT...SSE FLOW AT THE SFC. LOW-LEVEL WAA REGIME WILL CAUSE 850
MB TEMPS TO INCREASE DRAMATICALLY. SREF HAS 850 MB TEMPS AT -10 C
THIS EVENING WARMING TO NEAR +4 C BY FRIDAY EVENING.

NAM SOUNDINGS INDICATE SIGNIFICANT MOISTENING OF THE COLUMN THROUGH
THE DAY ON FRIDAY. BY 00Z/SAT THE FAR SW PORTION OF THE CWA IS
PROJECTED TO HAVE 1000-500 MB AVG RELATIVE HUMIDITY VALUES AROUND
85-90%...PER THE NAM. FORECAST SOUNDINGS ALSO REVEAL A STRONG
LOW-LEVEL INVERSION THAT PEAKS AT +6 C AT 900 MB. INCLUDED 20-30%
POPS IN THE FAR SW FOR THE POSSIBILITY OF DRIZZLE/FREEZING DRIZZLE
DURING THE LATE AFTN. NAM IS THE COLDEST MODEL WITH REGARD TO SFC
TEMPS BUT CURRENT FORECAST IS MORE IN LINE WITH CONSENSUS WHICH HAS
MID 30S IN THIS AREA DURING THE LATE AFTN. PRECIP CHANCES WILL
INCREASE OVERNIGHT AS LOW/MID LEVEL THETA-E ADVECTION CONTINUES.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 334 PM CST THU NOV 20 2014

FOCUS IS ON THE LARGE STORM SYSTEM OVER THE WEEKEND THAT WILL
FEATURE A SHARP CHANGE TO ABOVE NORMAL TEMPERATURES AND AN EXTENDED
PERIOD OF CLOUDY...DAMP AND FOGGY CONDITIONS OVER THE FORECAST AREA.
THIS WILL RESULT FROM A LARGE...INTENSE CYCLONE EXPECTED TO DEVELOP
FROM SEPARATE NORTHERN AND SOUTHERN STREAM SYSTEMS THAT MERGE
OVER THE MID AND UPPER MS VALLEY SUNDAY AND STRENGTHEN AS IT LIFTS
NORTH-NORTHEAST INTO THE GREAT LAKES REGION MONDAY. THE 12Z MODELS
HAVE MADE A SLIGHT SOUTHEASTWARD SHIFT AND SLOWED THE SYSTEM SOME.
EVEN THE MORE CONSISTENT ECMWF NOW TRACKS THE SURFACE LOW THROUGH
CENTRAL IL ON THE WAY TO LOWER MI VS THE MUCH MORE NORTHWESTERLY PATH
DEPICTED JUST 24 HOURS AGO THAT SUGGESTED THE LOW POSSIBLY PASSING
THROUGH FAR EASTERN IA. OVERALL...THE FORECAST REMAINS ON TRACK WITH
ONLY MINIMAL TWEAKS OTHER THAN NOW FOCUSING THE BULK OF THE RAIN
INTO THE SUNDAY AND SUNDAY NIGHT PERIODS.

FRIDAY NIGHT...LOW LEVEL SOUTH TO SOUTHWESTERLY FLOW...DEVELOPING
AHEAD OF THE UPPER LEVEL SHORTWAVE EMERGING FROM AZ AND NM
WILL RESULT IN A SURGE OF STRONG LOW LEVEL MOISTURE RETURN. THIS
WAVE OF ISENTROPIC LIFT WILL SPREAD LIGHT RAIN AND DRIZZLE NORTHWARD
THROUGH THE FORECAST AREA. MODEL ANALYSIS REVEALED THE WRF/NAM HAD A
POOR INITIALIZATION OR DEPICTION OF THE SNOW COVER OVER PORTIONS OF
EASTERN IA AND NW IL THIS MORNING...WHERE IT HAD 2 TO 4 INCHES...VS
THE TRACE TO NEAR 1 INCH AMOUNTS ACTUALLY OBSERVED. THIS APPEARS TO
RESULT IN A COOL MODEL BIAS...BY AS MUCH 5 DEGREES OR MORE IN BOTH
THE RAW MODEL OUTPUT AND MET MOS GUIDANCE...WHICH WAS ALSO NOTED IN
MODEL OUTPUT YESTERDAY...AND APPEARS TO EXTEND WELL INTO THE
WEEKEND. ACCOUNTING FOR THIS...HAVE NUDGED SURFACE TEMPERATURES AND
DEWPOINTS UPWARD CLOSER TO THE WARMER ECMWF...GFS AND GEM
OUTPUT...BUT THINK FURTHER UPWARD ADJUSTMENTS MAY BE NEEDED. THE
ONLY CONCERN IS HOW MUCH THE FROZEN GROUND IMPACTS THE STRONG WARM
ADVECTION. THAT SAID...THERE IS STILL A POTENTIAL FOR A LIGHT
GLAZING OF FREEZING RAIN OR FREEZING DRIZZLE OVER THE CENTRAL AND
NORTH BEFORE AIR AND GROUND TEMPERATURES NUDGE ABOVE FREEZING BY
SATURDAY MORNING.

SATURDAY AND SATURDAY NIGHT...CONTINUED LOW LEVEL THETAE
ADVECTION...BUT LITTLE IN THE WAY OF MID OR UPPER LEVEL FORCING WILL
RESULT IN AN EXTENDED PERIOD OF POTENTIAL LIGHT RAIN OR DRIZZLE.
LATEST NON-WRF MODEL DATA SUPPORTS TEMPERATURES RISING POSSIBLY AS
HIGH AS THE MID TO UPPER 50S IN THE SOUTH...WITH UPPER 40S NORTH.
HOWEVER...WITH THE COLD GROUND AND EARLY SEASON FROST SEVERAL INCHES
DEEP...AND CONSIDERING OVERCAST CONDITIONS...HAVE KEPT HIGHS
TEMPERED FROM THE MID 40S TO LOWER 50S. THIS PROCESS WILL LIKELY
LEAD TO FOG ESPECIALLY OVER THE NORTHWEST AND HAVE KEPT IN THE
FORECAST FOR THE NW DURING THE DAY AND ENTIRE AREA SATURDAY NIGHT.
TEMPERATURES WILL LIKELY REMAIN IN THE 40S THROUGH THE OVERNIGHT.

SUNDAY INTO SUNDAY NIGHT...THE DEEPENING LOW...NEARING 3 4O 4 SIGMA
IN STRENGTH...WILL PASS TO THE SOUTHEAST ACROSS CENTRAL IL DURING
THE DAY. THE ASSOCIATED DEFORMATION ZONE AND WARM CONVEYOR BELT OF
GULF MOISTURE WILL LEAD TO WIDESPREAD LIGHT TO MODERATE RAIN THROUGH
THE DAY WITH QPF IN THE RANGE OF ONE HALF TO POSSIBLY AN INCH OR
MORE DURING THE DAYLIGHT HOURS. THIS MAY CONTINUE WELL INTO THE
EVENING WITH POSSIBLY ANOTHER HALF INCH OR MORE OVER ESPECIALLY NW
IL BEFORE THE LOW CENTER MOVES INTO SOUTHWEST LOWER MI. THIS PROCESS
WILL DRAW IN COOLER AND DRIER AIR IN THE BRISK WESTERLY WINDS IN THE
RAP AROUND BEHIND THE OCCLUDING SYSTEM. FOR NOW...WILL CONTINUE THE
IDEA OF RAIN CHANGING TO SNOW FROM WEST TO EAST OVERNIGHT...BUT THIS
COULD WIND UP WITH THE PRECIPITATION ENDING OR BECOMING VERY LIGHT
AS THE DRY SLOT ENVELOPS THE AREA BY SUNRISE.

MONDAY WILL BE A WINDY...UNSETTLED DAY AS THE WRAP AROUND MOISTURE
AND STRONG CYCLONIC FLOW RESULTING IN WIDESPREAD FLURRIES OR SNOW
SHOWERS. LIGHT ACCUMULATIONS WILL BE POSSIBLE ACROSS THE NORTHEAST.
THE REAL COLD AIR ARRIVES MONDAY NIGHT INTO TUESDAY AS A NW FLOW
DEVELOPS BEHIND THE FILLING UPPER LEVEL TROUGH...THIS WILL LOWER
MONDAY/S HIGHS IN THE 30S TO THE UPPER 20 TO AROUND 30
TUESDAY...WITH OVERNIGHT LOWS IN THE TEENS TUESDAY NIGHT WHEN THE
CYCLONIC FLOW FINALLY EXITS. BEYOND...MODELS REMAIN IN POOR AGREEMENT
WITH A HIGH AMPLITUDE PATTERN...BUT BOTH GFS AND ECMWF HAVE BACKED
AWAY FROM THE CLOSED LATE WEEK SURFACE LOW AND INSTEAD INDICATE A
POSSIBLE MID OR LATE WEEK CLIPPER SYSTEM IN A NW FLOW. THIS WILL
JUSTIFY KEEPING AT LEAST SLIGHT CHANCE POPS FOR SNOW WHILE
TEMPERATURES RETURN TO WELL BELOW NORMAL.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 537 PM CST THU NOV 20 2014

VFR CONDITIONS WILL PERSIST THROUGH FRIDAY MORNING AS HIGH PRESSURE
BUILDS IN. NORTHWEST WINDS AROUND 10 KTS WILL BECOME LIGHT AND
VARIABLE THIS EVENING. BY FRIDAY AFTERNOON THE HIGH WILL SLIDE
EAST WITH WINDS BECOMING SOUTHEAST AROUND 10 KTS. INCREASING
MOISTURE WILL BE ACCOMPANIED BY CLOUD BASES LOWERING INTO LOWER VFR
RANGE AT KCID AND KBRL TOWARD THE END OF THE TAF PERIOD... WITH A
LOW PROBABILITY OF MVFR CIGS. JUST BEYOND THE END OF THE TAF
PERIOD EXPECT MVFR TO POSSIBLY AREAS OF IFR CIGS DEVELOPING AT THE
TERMINALS WITH A CHANCE OF LIGHT RAIN/DRIZZLE... AND POSSIBLY LIGHT
FREEZING RAIN/DRIZZLE MAINLY NEAR/NORTH OF I 80.

&&

.CLIMATE...
ISSUED AT 334 PM CST THU NOV 20 2014

RECORD LOWS FOR NOVEMBER 20...

MOLINE.........8 IN 1880
CEDAR RAPIDS...5 IN 1914
DUBUQUE........5 IN 1964 AND PREVIOUS YEARS
BURLINGTON.....7 IN 1914

RECORD LOWS FOR NOVEMBER 21...

MOLINE.........1 IN 1880
CEDAR RAPIDS...0 IN 1937
DUBUQUE........-5 IN 1880
BURLINGTON.....4 IN 1937

&&

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

$$

SYNOPSIS...UTTECH
SHORT TERM...UTTECH
LONG TERM...SHEETS
AVIATION...05




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