Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 020053
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
753 PM CDT SAT AUG 1 2015

.UPDATE...
ISSUED AT 747 PM CDT SAT AUG 1 2015

A WEAK DISTURBANCE ALOFT THAT HELPED GENERATE A FEW SHOWERS AND
THUNDERSTORMS IN NORTHWEST ILLINOIS LATE THIS AFTERNOON IS
DEPARTING THE AREA. QUIET WEATHER IS NOW ON TAP THROUGH MIDNIGHT
ACROSS THE AREA. HOWEVER...ANOTHER UPPER LEVEL DISTURBANCE IS
MOVING EAST SOUTHEAST THROUGH THE DAKOTAS.

INTERNALLY...THE MODELS ARE MIXED WITH REGARDS TO WHAT WILL OCCUR
AFTER MIDNIGHT. THE CONSENSUS IS THAT A NOCTURNAL THUNDERSTORM
COMPLEX WILL DEVELOP IN THE EASTERN PLAINS AND GENERALLY MOVE EAST
OVERNIGHT. THE WHEN AND WHERE THE COMPLEX DEVELOPS ARE WHAT THE
MODELS DISAGREE UPON. THE EVENING UPPER AIR DATA SHOULD HELP SHED
SOME LIGHT ON THE WHEN AND WHERE.

&&

.SYNOPSIS...
ISSUED AT 333 PM CDT SAT AUG 1 2015

SURFACE HIGH PRESSURE WAS SPRAWLED OUT FROM OK TO SOUTHERN
PORTIONS OF IL AND INDIANA THIS AFTERNOON. SPLITTING THE ILL-
DEFINED HIGH PRESSURE CENTERS WAS A NEARLY STATIONARY FRONT
EXTENDING FROM THE KY/TN BORDER NW ACROSS CENTRAL MO TO SW IA AND
EASTERN NEB...WHERE A MESO-HIGH FROM OVERNIGHT CONVECTION HAD
BECOME THE DOMINANT FEATURE. A LOW LEVEL THETAE RIDGE WAS
RESULTING IN SURFACE DEWPOINTS IN THE LOWER 70S REACHING FROM
EASTERN KS...THROUGH NW MO INTO CENTRAL IA PUSHING INTO EAST
CENTRAL IA AT MID AFTERNOON. ALONG THE MS RIVER AND
EASTWARD...DEWPOINTS WERE STILL MAINLY IN THE 60S. SURFACE WIND
AND PRESSURE FIELDS...AND CU FIELDS ON SATELLITE IMAGERY...
INDICATED A WEAK SURFACE TROUGH FROM SOUTHERN WI WEST ALONG THE
HIGHWAY 20 CORRIDOR IN EASTERN IA. SO FAR...THE ONLY THUNDERSTORMS
THAT HAVE DEVELOPED THIS AFTERNOON WERE OVER CENTRAL MO...WHERE
DEEPER MOISTURE WAS INTERACTING WITH THE SURFACE BOUNDARY.
WEAK IMPULSES WERE EVIDENT ON WATER VAPOR IMAGERY EMBEDDED IN THE
NW FLOW ACROSS THE DAKOTAS AND NEB...WHICH WILL BE THE TRIGGER FOR
CONVECTIVE DEVELOPMENT IN THE LOCAL AREA LATER TONIGHT.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 333 PM CDT SAT AUG 1 2015

A COMPLEX...AND CONTINUED LOW CONFIDENCE...CONVECTIVE FORECAST
CONTINUES TO BE THE FOCUS. IN THE IMMEDIATE NEAR TERM...HAVE
ADDED SLIGHT CHANCES FOR THUNDERSTORMS LATE THIS AFTERNOON INTO
EARLY EVENING ALONG THE AFOREMENTIONED BOUNDARY ACROSS THE NORTH.
A LEAD IMPULSE IN THE NW FLOW OVER SW MN IS CURRENTLY ON TRACK TO
REACH THIS BOUNDARY TOWARD 6 PM...WHERE LOW LEVEL MOISTURE
CONVERGENCE AND ADVECTION WAS DRIVING DEWPOINTS INTO THE UPPER 60S
AND LOWER 70S IN EASTERN IA. ASSOCIATED BUILDING HIGH SBCAPES OF
3000 J/KG OR GREATER...AND LOW LEVEL CONVERGENCE SHOULD BE
SUFFICIENT TO TRIGGER AT LEAST ISOLATED THUNDERSTORMS EARLY THIS
EVENING...BUT THE LACK OF STRONG SHEAR SHOULD KEEP THIS LIMITED
IN COVERAGE WITH A LOW POTENTIAL FOR SEVERE WEATHER.

THE NEXT FOCUS WILL BE A LARGER VORT MAX CURRENTLY OVER THE WESTERN
DAKOTAS THAT WILL PUSH INTO THE FORECAST AREA AFTER MIDNIGHT. LACK
OF STEEP SHEAR AND UNFAVORABLE LATE NIGHT TIMING SHOULD PRECLUDE A
SIGNIFICANT THREAT OF SEVERE STORMS...AND SPC HAS SHIFTED ITS
SLIGHT RISK AREA WELL TO THE NORTH TO SOUTHERN MN INTO WESTERN
WI...LEAVING A MARGINAL RISK NORTH ROUGHLY NORTH OF HIGHWAY 30
WHERE 850 MB WINDS ARE GREATEST. DUE TO LOW CONFIDENCE IN THE NEAR
TERM CONVECTIVE TRENDS...WILL KEEP LOW CHANCES GOING IN THE FAR NW
IN THE EVENING. OVERNIGHT...WILL STAY WITH CHANCE POPS AS THE MID
LEVEL FORCING WITH THE DAKOTAS VORT MAX MOVES THROUGH THE AREA
LATER TONIGHT. THE MAIN THREAT WITH THESE STORMS WILL BE STRONG
WIND GUSTS AND HEAVY RAINFALL. DEWPOINTS WILL CONTINUE TO EDGE
UPWARD FROM WEST TO EAST TONIGHT...LEADING TO MORE HUMID
CONDITIONS AND LIMITING LOWS TO THE UPPER 60S TO LOWER 70S.

SUNDAY...THE OVERNIGHT COMPLEX MAY BE ONGOING OVER ESPECIALLY THE
EAST IN THE MORNING...THEN A BREAK IS SUGGESTED OVER EASTERN IA
BEFORE THE MAIN SURFACE FRONT APPROACHES IN THE AFTERNOON TO
POSSIBLY TRIGGER ADDITIONAL CONVECTION. WILL KEEP CHANCE CATEGORY
POPS TRENDED ALONG THESE LINES. BRISK SW WINDS IN THE PREFRONTAL SW
FLOW AND WARM ADVECTION ALOFT WILL LEAD TO HIGHS NEAR...TO PERHAPS
A FEW DEGREES WARMER THAN TODAY...DEPENDING ON CLOUD TRENDS. SPC
HAS A SLIGHT RISK INTO NW IL...WHERE STRONGER SHEAR WILL BE
POSSIBLE IN THE LATE AFTERNOON...WHILE A MARGINAL RISK COVERS MOST
OF THE REST OF THE FORECAST AREA.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 333 PM CDT SAT AUG 1 2015

SUNDAY EVENING AND NIGHT...A SHORTWAVE TROUGH AND ASSOCIATED MID-
LEVEL POSITIVE VORTICITY MAX WILL ROTATE CYCLONICALLY...AROUND A
DEEP LOW CENTERED OVER NORTHERN ONTARIO...FROM NW TO SE ACROSS
MN/WI/MI. 500MB HEIGHT FALLS OF 30 METERS/12 HRS OR GREATER ARE
FORECAST TO OCCUR TO THE NE OF E IOWA/NW ILLINOIS/NE MISSOURI.
THUS...PRIMARY FOCUS LOCALLY WILL BE ON A COLD FRONT/NORTHWESTERLY
WIND SHIFT MOVING FROM NW TO SE THROUGH THE DVN CWA WHICH SHOULD SET
OFF ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS.

PRECIP TIMING...CHANCES FOR PRECIP BETWEEN 7 PM AND 1 AM CDT ARE
HIGHEST OVER THE NORTHEAST CWA...NEAR 50 PERCENT...AND DECREASE TO
20 PERCENT OVER THE WEST AND FAR SOUTHWEST. CONFIDENCE IS MODERATE
TO HIGH THAT A FEW STORMS WILL FORM...BUT THE SCATTERED NATURE
SUPPORTS POPS IN THE CHANCE CATEGORY AND NOT HIGHER. CONSIDERING THE
EXPECTED WEAK SYNOPTIC FORCING DO NOT SEE CONVECTIVE ACTIVITY
BECOMING WIDESPREAD.

CONVECTIVE POTENTIAL...AVG MUCAPE OF 4000 J/KG AND SUFFICIENTLY
STRONG DEEP LAYER SHEAR NEAR 40-45 KTS...COULD CAUSE A FEW STORMS TO
REACH SEVERE LEVELS CAPABLE OF DAMAGING WINDS AND LARGE HAIL. SPC
HAS A SLIGHT RISK FOR SEVERE STORMS OVER THE FAR EASTERN AND
NORTHEASTERN SECTIONS OF THE FORECAST AREA...WELL EAST OF THE
MISSISSIPPI RIVER AT THIS TIME. PWATS OF ONLY 1.00-1.30 INCHES ARE A
REFLECTION OF THE ABSENCE OF A TROPICAL MOISTURE CONNECTION AND DRY
AIR IN THE 850-500MB LAYER WITH RH VALUES AS LOW AS 20-30 PERCENT.

MONDAY THROUGH WEDNESDAY...SFC FRONTAL BOUNDARY IS FORECAST TO STALL
OUT ACROSS NORTHERN MISSOURI...KEEPING EXTREME HEAT/HUMIDITY TO THE
SOUTH. THE EXACT POSITION OF THE FRONT AT ANY GIVEN TIME WILL BE
LARGELY DEPENDENT ON WHERE RESIDUAL OUTFLOW BOUNDARIES SET UP AFTER
CONVECTIVE COMPLEXES MOVE THROUGH. HIGHEST POPS ARE BETWEEN 30-50
PERCENT ALONG AND SOUTH OF HIGHWAY 34. THE OVERALL SEVERE
THUNDERSTORM THREAT IS LOW DUE TO LOWER INSTABILITY LEVELS.

THURSDAY AND FRIDAY...THE COOL DOWN CONTINUES. HIGHS WILL BE
SLIGHTLY BELOW AVG IN THE MID TO UPPER 70S. THERE IS A CHANCE FOR
ISOLATED TO SCATTERED SHOWERS AND STORMS ON THURSDAY AS A SHORTWAVE
APPROACHES.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 624 PM CDT SAT AUG 1 2015

VFR CONDITIONS WILL BE SEEN THROUGH 08Z/02 AS A SMALL HIGH
PRESSURE MOVES TOWARD THE GREAT LAKES. A THUNDERSTORM COMPLEX IS
FORECAST TO DEVELOP IN THE EASTERN PLAINS THIS EVENING BUT THE
MODELS OFFER DIFFERING OPINIONS ON WHEN AND WHERE IT DEVELOPS AND
MOVES. THE POTENTIAL FOR VCTS AT KCID/KDBQ/KMLI/KBRL WILL BE ON
THE INCREASE AFT 08Z/02. IF A TSRA AFFECTS A TAF SITE AFT
08Z/02...THE POTENTIAL IS THERE FOR BRIEF MVFR OR EVEN IFR
CONDITIONS.


&&

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

$$

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



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