Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 040439
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1139 PM CDT SUN MAY 3 2015

.SYNOPSIS...
ISSUED AT 330 PM CDT SUN MAY 3 2015

A VERY CHALLENGING DAY OF WARM SEASON IMPACTS HAVE BEEN OVER OUR
REGION TODAY...AS A PERSISTENTLY ACTIVE MCV HAS SLOWLY TRAVERSED
OUR CWA FROM WEST TO EAST. THE SLOW MOVEMENT ALLOWED IT TO
MAINTAIN CONTACT WITH THE PLUME OF HIGHER PWAT VALUES AROUND 1
INCH. WHILE INSTABILITY HAS NOT BEEN HIGH...ENOUGH MUCAPE (500
J/KG)...AS BEEN IN PLACE TO SUPPORT SMALL AND SHALLOW UPDRAFTS
WITH OCCASIONAL LIGHTNING. RAINS OVER THE NORTHERN 1/2 HAVE
SEEN...WHERE STORMS CROSSED THROUGH...ANYWHERE FROM 0.15 TO LIKELY
A BIT OVER 1 INCH. TEMPERATURES IN THE COLD POOL FROM THIS
ACTIVITY HAVE HELD IN THE LOWER 60S...WHILE JUST OUTSIDE/WEST HAVE
ROCKETED INTO THE UPPER 70S TO LOWER 80S. WHILE MUCH OF IOWA IS
CLEAR AND WARMING AHEAD OF THE COMING COLD FRONT...OUR EYES ARE
FOCUSED ON ANOTHER CLUSTER OF ELEVATED STORMS IN EASTERN NEBRASKA.
THIS SHOWS THE LOCATION OF THE NEXT SHORT WAVE...AND SHOULD BE THE
NEXT TRIGGER FOR CONVECTION OVER OUR CWA TONIGHT.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 330 PM CDT SUN MAY 3 2015

TODAY AND MONDAY... OUR CWA WILL REMAIN ON THE NOSE OF
MOISTURE TRANSPORT AND MUCAPE ADVECTION THROUGH THE EARLY MORNING
HOURS MONDAY. THE MAIN QUESTION FOR THE FORECAST FOR TONIGHT THROUGH
TUESDAY WILL BE TO HOW MUCH OF A DEGREE THE LLJ VEERS OR NOT...BETWEEN
ROUNDS OF STORMS. WITH THE DEVELOPING WESTERN TROF...AND LITTLE REASON
FOR INTENSE ORGANIZED/SEVERE STORMS...IT SEEMS A SCENARIO WHERE WINDS
ALOFT WILL BACK QUICKLY AFTER PASSING ROUNDS OF STORMS EXIT. THIS SETS
THE STAGE FOR REPEATING ROUNDS OF NON SEVERE STORMS...WITH HEAVY RAIN
POSSIBLY RESULTING IN THE COMING DAYS.

TONIGHT...SURFACE BASED CONVECTION SHOULD FIRE TO OUR NORTHWEST...OVER
SOUTHERN MN/NORTHERN IA...AND MOVE EAST TO SOUTHEAST WITH TIME.
MID LEVEL WESTERLIES SHOULD CARRY STORMS EAST...WHILE MOISTURE
INFLUX FROM THE SOUTHWEST ALLOWS THEM TO BUILD MOST AGGRESSIVELY
ON THE SOUTHERN FLANK. I SEE SEVERAL DRY HOURS THIS EVENING...FOLLOWED
BY THE MAIN ACTIVITY INITIALLY MOVE NORTH OF THE CWA...BUT BY MID
EVENING...THIS CONVECTION SHOULD DROP SOUTH...WITH THE MOST INTENSE
UPDRAFTS LOCATED IN NORTHEASTERN IOWA BEFORE 1 AM...AND OVER EASTERN/SOUTHEASTERN
IOWA AND WESTERN ILLINOIS AFTER THAT TIME. THIS IS DUE TO THE EXPECTED
VEERING LLJ ALOFT...BUT IN ANY CASE...COVERAGE APPEARS AT LEAST HIGH
END LIKELY...IF NOT CATEGORICAL FOR MOST LOCATIONS AFTER 10 PM. RAINFALL
TONIGHT SHOULD BE WIDESPREAD 0.25 TO 1.25...BUT AS TODAY SHOWED US...THE
ATMOSPHERE IS CAPABLE OF AMOUNTS HIGHER THAN THAT...AND SOME LOCATIONS
MAY SEE OVER 1.5 TONIGHT.

CONDITIONS MONDAY SYNOPTICALLY SUPPORT CHANCE POPS...HOWEVER...MESOSCALE
TRENDS WILL CERTAINLY RULE THE DAY...AS CONVECTION LIKELY WANES IN THE
MID MORNING HOURS...OR SETTLES SOUTH AND EAST OF THE CWA. BACKING
WINDS ALOFT MAY CERTAINLY ALLOW FOR SOME SCATTERED ACTIVITY THROUGH
THE DAY ON TOP OF THE COLD POOL/STALLED FRONT. IN ANY CASE...THE NEXT
SHORT WAVE DUE TO RIDE OVER THE FRONT SHOULD ARRIVE BY MID AFTERNOON...AND
WITH BACKING WINDS THROUGH 850MB FORECAST BY ALL GUIDANCE...AND DIVERGENCE
ALOFT...IT SEEMS LIKELY POPS ARE ONCE AGAIN WARRANTED BY MID AFTERNOON.
SINCE THIS WILL ARRIVE AT PEAK HEATING...A LOW RISK FOR AN ISOLATED
SEVERE STORM CANNOT BE RULED COMPLETELY OUT. HOWEVER...ORGANIZED SEVERE
STORMS SEEM VERY UNLIKELY GIVEN THE MID SUMMER LIKE WEAK FLOW.

LIKE TODAY...CHALLENGING TEMPERATURES ARE EXPECTED...WITH HIGHS IN THE
LOWER 70S NORTH TO AROUND 80 SOUTH A LEAST ERROR FORECAST...BUT FAR
FROM CONFIDENT. ERVIN

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 330 PM CDT SUN MAY 3 2015

OVERVIEW...THE POLAR UPPER JET WILL WILL SHIFT INTO NORTHERN CANADA
THROUGH THE WEEK. UPPER-LEVEL RIDGING BUILDING IN ACROSS THE CENTRAL
U.S. BEHIND THE POLAR JET WILL RESULT IN A SIGNIFICANT CHANGE TO A
MUCH MORE MOIST ATMOSPHERE. MEAN 850-300MB WINDS WILL SLOWLY VEER
FROM WESTERLY TO SOUTHWESTERLY DURING THE EARLY PORTION OF THE WEEK.
PWAT VALUES WILL BE ABOVE AVERAGE DURING THIS TIME.

MONDAY EVENING AND NIGHT...ANOTHER POTENTIAL CONVECTIVELY INDUCED PV
ANOMALY WILL ORIGINATE OVER THE CENTRAL ROCKIES AND PROPAGATE OVER
THE DVN CWA PROVIDING LIFT AND A GOOD CHANCE FOR SHOWERS/STORMS. THE
GREATEST COVERAGE IS PROBABLY GOING TO OCCUR BETWEEN 6PM-12AM.
INSTABILITY WILL BE DECREASE THROUGH THIS PERIOD STARTING NEAR 1500
J/KG IN THE EARLY EVENING AND FALLING BELOW 1000 J/KG BY MIDNIGHT.

A FEW STORMS MAY BE STRONG WITH SMALL HAIL AND WIND GUSTS OVER 40
MPH BUT BY AND LARGE SEVERE WEATHER IS NOT EXPECTED. THE MAIN STORY
WILL BE THE HEAVY RAIN POTENTIAL.

MOISTURE...PWAT VALUES ARE GOING TO BE RELATIVELY HIGH BETWEEN 1.25-
1.50 INCHES BUT THE NAEFS PLACES THIS IN THE 85TH-90TH PERCENTILE OR
NEAR 1.5 STANDARD DEVIATIONS ABOVE THE MEAN FOR THE BEGINNING OF
MAY. RELATIVELY DRY ANTECEDENT CONDITIONS SHOULD LIMIT OVERALL FLOOD
POTENTIAL EVEN FOR AREAS THAT RECEIVE THE HEAVIEST RAIN.

FORWARD PROPAGATING CORFIDI VECTORS SUGGEST SLOW EAST-NORTHEAST
MOVING MULTICELL STORMS AT ABOUT 20-25 MPH. 500MB WINDS WILL BE
NEARLY PARALLEL TO THE SFC-850MB BOUNDARY WHICH MEANS THE POTENTIAL
FOR TRAINING OF SHOWERS/STORMS IS THERE.

RAINFALL AMOUNTS...MOST AREAS WILL RECEIVE BETWEEN 0.25 TO 0.75
INCHES BUT THERE WILL LIKELY BE A ONE TO TWO COUNTY WIDE ZONE OF
HIGHER AMOUNTS OVER 1 INCH...AND THERE COULD BE A NARROW BAND OF 1-2
INCHES. THE PLACEMENT MAY CHANGE SLIGHTLY BUT THE HIGHWAY 30
CORRIDOR APPEARS TO BE THE MOST LIKELY AREA FOR THE HEAVIEST RAIN.

TUESDAY...A WARM FRONT WILL LIFT INTO THE NORTHERN CWA TUE AFTN.
DROPPED TEMPS DOWN BELOW CONSENSUS ACROSS THE NE THIRD OF THE CWA.
WENT AS COOL AS MID 60S NEAR FREEPORT BUT STILL HAVE LOWER 80S IN
THE FAR SOUTH. SCT SHOWERS/STORMS ARE POSSIBLE ESPECIALLY IN THE
MORNING AND EARLY AFTN.

WEDNESDAY...VERY WARM...HIGHS IN THE LOWER 80S AS THE SOUTHERLY FLOW
INCREASES AND THE RIDGING CONTINUES TO BUILD.

THURSDAY AND FRIDAY....TEMPS WILL REMAIN IN THE UPPER 70S TO LOWER
80S. AN ORGANIZED UPPER-LEVEL WILL EJECT OUT OF THE CENTRAL ROCKIES
BUT REMAIN WELL TO THE WEST OF THE MIDDLE TO UPPER MISSISSIPPI
VALLEY REGION...OVER NEBRASKA AND THE DAKOTAS.

CHANCES FOR SCT SHOWER/STORMS WILL INCREASE ESPECIALLY DURING PEAK
HEATING TIME. DISTANCE FROM THE CENTER OF THE MID-LEVEL LOW WILL
KEEP SYNOPTIC/QG FORCING RELATIVELY WEAK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1134 PM CDT SUN MAY 3 2015

A COOL FRONT WILL SLIDE INTO THE REGION OVERNIGHT AND IS BRINGING
SHOWERS AND THUNDERSTORMS WITH INTERVALS OF MVFR CONDITIONS WITH
THE HEAVIEST RAINFALL...LASTING UNTIL AROUND 04/10Z. SOUTHERLY
WINDS OF 5 TO 15 KTS WILL SHIFT TO THE NORTH AND THEN NORTHEAST AT
ALL BUT BRL TERMINAL BY MID MORNING. VFR CONDITIONS WITH SCT-BKN
CLOUDS WITH CIGS AOA 4K AGL WITH HEAVIEST COVERAGE SOUTH OF I-80
ON MONDAY. AREAS OF SHOWERS AND STORMS SHOULD REDEVELOP SOUTH OF
THE I-80 CORRIDOR AFTER 04/21Z ALONG THE STATIONARY FRONTAL BOUNDARY.
THIS IS HANDLED WITH A PROB30 GROUP AFTER 05/00Z WITH SIGNIFICANT
AREAS OF PRECIPITATION POSING HIGHER END MVFR CONDITIONS.

&&

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

&&

$$

SYNOPSIS...ERVIN
SHORT TERM...ERVIN
LONG TERM...UTTECH
AVIATION...NICHOLS


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