Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 310537
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1137 PM CST FRI JAN 30 2015

.UPDATE...
ISSUED AT 855 PM CST FRI JAN 30 2015

UPDATE TO ADD ADDITIONAL NORTHERN COUNTIES TO WINTER STORM WATCH.
NO SIGNIFICANT CHANGES TO FORECAST GRIDS THIS EVENING. BOOSTED
AMOUNTS SLIGHTLY ACROSS THE WEST AND SOUTHWEST. ADDITIONAL WINTER
HEADLINES LIKELY FORTHCOMING EARLY SATURDAY MORNING. HAVE POSTED
UPDATED MULTIMEDIA WEB BRIEFING ON WEB SITE AND SOCIAL MEDIA.

&&

.SYNOPSIS...
ISSUED AT 320 PM CST FRI JAN 30 2015

HIGH PRESSURE WAS CENTERED ALMOST DIRECTLY OVERHEAD THE QUAD
CITIES THIS AFTERNOON. CLEAR SKIES AND LIGHT WINDS WERE ACROSS THE
FORECAST AREA. CURRENT SATELLITE IMAGERY DEPICTS HIGH LEVEL
CLOUDS ACROSS THE CENTRAL PLAINS. THESE CLOUDS ARE MOVING INTO THE
AREA AHEAD OF A POSSIBLE WINTER STORM THIS WEEKEND.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NOON)
ISSUED AT 320 PM CST FRI JAN 30 2015

MAIN FORECAST CONCERN FOR THE SHORT TERM IS THE APPROACHING STORM
SYSTEM AND WHETHER OR NOT WE SEE ANY PRECIPITATION BEFORE NOON ON
SATURDAY. CURRENT THINKING IS THAT THE MOISTURE WILL HOLD OFF
ACROSS THE AREA UNTIL AT LEAST NOON...18Z SATURDAY.

LOOKING AT THE MODELS...THE NAM AGAIN SEEMS TO HAVE A BL
MOISTENING PROBLEM. THIS SUGGESTS SATURATION THROUGH THE LAYER AT
BRL BETWEEN 12Z AND 18Z TOMORROW. THE GFS IS SLOWER...AND LIKELY
MORE ACCURATE WITH THE SATURATION. WHICH OCCURS BETWEEN 18Z AND
00Z SATURDAY AND SUNDAY. WHILE I DO NOT DOUBT THE FACT THAT THERE
WILL BE PRECIP ALOFT...I DO NOT THINK WE WILL SEE IT SATURATE
EARLY. THE GFS IS LIKELY MORE CORRECT ON THIS SYSTEM. THROUGHOUT
RUNS THE SYSTEM HAS BEEN SLOWING...SO BELIEVE THAT WE WILL HAVE
LITTLE TO NO PRECIP BEFORE 18Z SATURDAY. THAT SAID...IF WE DO HAVE
PRECIP...WARM TEMPS WILL KEEP IT AS RAIN ACROSS THE SE ZONES.

.LONG TERM...(SATURDAY NOON THROUGH FRIDAY) ISSUED AT 320 PM CST FRI
JAN 30 2015

ENTIRE FORECAST FOCUS IS ON THE WEEKEND WINTER STORM THAT AS IT
APPEARS NOW...WOULD BE THE MOST SIGNIFICANT OF THE SEASON SO FAR FOR
THIS AREA. A WINTER STORM WATCH WAS ISSUED EARLIER TODAY FOR THE
CENTRAL AND SOUTH FOR SATURDAY NIGHT THROUGH SUNDAY...BASED ON
INCREASING FORECAST CONFIDENCE OF THE TRACK OF THE SYSTEM. TODAY/S
12Z MODEL RUNS HAVE VERIFIED THE NORTHWARD SHIFT IN THE TRACK OF THE
SURFACE CIRCULATION AND PRECIPITATION SHIELD...A TREND STARTED IN
YESTERDAY/S 12Z MODEL RUN AND CONTINUED OVERNIGHT.

THE STORM SYSTEM TAKES SHAPE SATURDAY AFTERNOON AS THE NORTHERN
STREAM SHORTWAVE OVER BC TODAY DEEPENS AS IT GLIDES DOWN THE NW FLOW
ALOFT AND BECOMES BETTER PHASED WITH THE UPPER LEVEL TROUGH OVER THE
SOUTHEAST...MEETING A DEVELOPING FEED OF GULF MOISTURE. THIS
PROCESS IS ENHANCED BY THE RIGHT ENTRANCE REGION OF A JET CORE
SHAPING UP FROM THE GREAT LAKES TO CENTRAL ATLANTIC COAST SATURDAY
NIGHT. AT THE SURFACE...LOW PRESSURE DEVELOPING OVER KS SATURDAY
SHIFTS EAST ACROSS N CENTRAL MO INTO SOUTHERN INDIANA BY SUNDAY
NIGHT. OVER THE LOCAL AREA...THIS PROCESS INCREASES FRONTOGENESIS
ALONG AN EAST TO WEST AXIS SETUP BY A WEAK COLD FRONT DROPPING
SOUTHEAST OUT OF THE NORTHERN PLAINS. HEAVIEST PRECIPITATION SETS UP
ALONG THIS AXIS ACROSS EAST CENTRAL IA AND NORTHERN IL AS UPPER
FORCING IS MAXIMIZED SATURDAY NIGHT INTO EARLY SUNDAY OVER THE
PASSING LOW LEVEL INVERTED SURFACE TROUGH. AS THE SURFACE LOW
DEEPENS AND MOVES INTO THE OHIO VALLEY REGION...THE TIGHTENING
CYCLONIC SURFACE PRESSURE GRADIENT WILL RESULT IN WINDY CONDITIONS
SUNDAY...LIKELY RESULTING IN CONSIDERABLE DRIFTING...IF NOT ACTUAL
BLOWING SNOW.

SATURDAY AFTERNOON...RELATIVELY WARM TEMPERATURES FROM THE LOWER 30S
NORTH TO UPPER 30S SOUTH WILL RESULT IN RAIN...OR A RAIN SNOW MIX AT
ONSET AS ISENTROPIC LIFT/WARM ADVECTION DEVELOPS FROM SW TO NE IN
THE AFTERNOON. AS THE FALLING SNOW COOLS AND MOISTENS THE
COLUMN...THE PRECIPITATION SHOULD CHANGE TO ALL SNOW AS IT
INTENSIFIES OVER THE ENTIRE AREA BY EVENING. WITH THE DAYLIGHT ONSET
AND WARM TEMPERATURES...LITTLE IF ANY SNOW ACCUMULATION IS EXPECTED
IN THE AFTERNOON.

SATURDAY NIGHT...COOLING PROFILES AND INCREASING FORCING SHOULD
CHANGE PRECIPITATION TO ALL SNOW...WHICH WILL LIKELY BE MODERATE TO
HEAVY AT TIMES OVERNIGHT. SNOW ACCUMULATIONS WILL BE COMPLICATED BY
HIGHER SNOW TO LIQUID RATIOS IN THE NORTH AND LOWER RATIOS IN THE
SOUTH...WHERE HIGHER QPF AMOUNTS WILL BE FAVORED. FOR NOW...OUR
FORECAST HAS ROUGHLY 3 TO 5 INCHES OVERNIGHT FROM NW TO SE.

SUNDAY...STRONG UPPER FORCING...AND THE FAVORED TIMING OF THE
PASSING 850 MB LOW TO THE SE SUPPORTS MODERATE SNOW CONTINUING
THROUGH THE MORNING TO SUGGESTS ANOTHER 2 TO 4 INCHES
POSSIBLE...WITH HEAVIER AMOUNTS FAVORED IN THE E AND SE. LIGHTER
SNOW SHOULD THEN CONTINUE THROUGH THE AFTERNOON WITH CONTINUED LIFT
AHEAD OF THE MAIN UPPER LEVEL TROUGH. INCREASING SURFACE
WINDS...POSSIBLY AS STRONG AS 20 TO 30 MPH SUSTAINED FROM THE
NORTHEAST AND THEN NORTH DEVELOP DURING THE DAY TO BRING BRING IN A
RISK OF BLOWING/DRIFTING SNOW WITH THE FALLING TEMPERATURES ON THE
ASSOCIATED COLD AIR ADVECTION. ADDITIONAL VERY LIGHT SNOW
ACCUMULATIONS WILL BE POSSIBLE SUNDAY NIGHT AS THE SYSTEM
EXITS...WHILE A RIDGE BUILDING IN FROM THE PLAINS RESULTS IN
DIMINISHING NORTH TO NORTHWEST WINDS.

STORM TOTAL SNOWFALL ACCUMULATIONS OF WIDESPREAD 6 TO 8 INCHES ARE
NOW LOOKING LIKELY...WITH TOTALS POSSIBLY PUSHING 10 INCHES IN OUR
EAST OVER N CENTRAL IL BASED ON THE CURRENT ANTICIPATED TRACK AND
SYSTEM EVOLUTION. THE WET NATURE OF THE SNOW...ESPECIALLY SATURDAY
NIGHT...MAY RESULT IN COMPACTION THAT COULD SUPPRESS TOTALS BELOW
THIS AMOUNT OVER THE FAR SOUTH BEFORE THE SNOW CHARACTER CHANGES
WITH THE FALLING TEMPERATURES. BASED ON MOST RECENT THOUGHTS...
WEATHER HEADLINES FOR THIS EVENT MAY EVENTUALLY BE ISSUED FOR THE
ENTIRE FORECAST AREA.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1135 PM CST FRI JAN 30 2015

06Z TAFS UPDATED TO REFINE TIMING ON PRECIP ARRIVAL AND ONSET OF
CHANGE OVER THROUGH THE DAY. EXPECTING RAIN/SNOW MIX TO MOVE INTO
KBRL AROUND 16Z...THEN CONTINUE NORTH TO KMLI/KCID/KDBQ. HAVE
TRENDS CIGS AND VSBYS TO MVFR AND EVENTUALLY IFR BY EARLY SATURDAY
EVENING. A QUICK CHANGE OVER TO ALL SNOW IS EXPECTED NEAR OR
SHORTLY AFTER 00Z SATURDAY EVENING.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...WINTER STORM WATCH FROM SATURDAY EVENING THROUGH SUNDAY
     AFTERNOON FOR BENTON-CEDAR-CLINTON-DES MOINES-DUBUQUE-HENRY
     IA-IOWA-JACKSON-JEFFERSON-JOHNSON-JONES-KEOKUK-LEE-LINN-
     LOUISA-MUSCATINE-SCOTT-VAN BUREN-WASHINGTON.

IL...WINTER STORM WATCH FROM SATURDAY EVENING THROUGH SUNDAY
     AFTERNOON FOR BUREAU-CARROLL-HANCOCK-HENDERSON-HENRY IL-JO
     DAVIESS-MCDONOUGH-MERCER-PUTNAM-ROCK ISLAND-STEPHENSON-
     WARREN-WHITESIDE.

MO...WINTER STORM WATCH FROM SATURDAY EVENING THROUGH SUNDAY
     AFTERNOON FOR CLARK-SCOTLAND.

&&

$$

UPDATE...RP KINNEY
SYNOPSIS...GIBBS
SHORT TERM...GIBBS
LONG TERM...SHEETS
AVIATION...RP KINNEY





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