Special Weather Statement, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
337 AM CDT SUN AUG 9 2015

.SYNOPSIS...
ISSUED AT 308 AM CDT SUN AUG 9 2015

A WEAK SFC TROUGH EXTENDED FROM SW KANSAS NORTHEASTWARD INTO
WESTERN AND CNTRL IOWA. ABOVE THE SFC...850MB WV TRANSPORT WAS
MAXIMIZED NEAR AN 850MB INFLECTION POINT OVER NW MISSOURI BUT
LOWER VALUES DID EXTEND INTO E IOWA. UPPER LEVEL AGEO. DIVERGENCE
IN THE RIGHT ENTRANCE REGION OF A 300MB JET WAS SUPERIMPOSED ABOVE
925MB FRONTOGENESIS THAT WAS LOCATED RIGHT THROUGH THE HEART OF
THE DVN CWA. THE COMBINED FORCING FOR ASCENT FROM THESE TWO
FEATURES WAS PRODUCING MODERATE TO HEAVY SHOWERS AND THUNDERSTORMS
WHICH WERE EXPLOITING MUCAPE VALUES NEAR 500 J/KG AND ANOMALOUSLY
HIGH PWAT VALUES UP TO 2 INCHES.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 308 AM CDT SUN AUG 9 2015

THIS MORNING...A CONVECTIVE BAND OF SHOWERS AND THUNDERSTORMS
PRODUCING PERIODS OF HEAVY RAIN WAS IMPACTING THE COUNTIES ALONG I-
80...AND HAS BEEN INCREASING IN INTENSITY AND AREAL COVERAGE OVER
THE PAST FEW HOURS. PARTS OF IOWA COUNTY HAVE BEEN HARDEST
HIT...RADAR ESTIMATES ARE THAT UP TO 2-3 INCHES OF RAIN HAVE
ALREADY FALLEN.

FORECAST FOCUS WILL BE ON ZONES OF HEAVY RAIN PRODUCING SHOWERS
AND THUNDERSTORMS NOT EXITING THE EASTERN CWA UNTIL THE LATE
MORNING. SOME LOCALIZED FLASH FLOODING IS POSSIBLE.

RAINFALL...APPRECIABLE RAIN AMOUNTS WILL NOT BE WIDESPREAD BUT
WILL BE FOCUSED IN TWO MAIN CORRIDORS...THE FIRST IS IN THE
COUNTIES ROUGHLY ALONG I-80...THE SECOND IS ALONG AND SOUTH OF
HIGHWAY 34. IF YOU ARE IN ONE OF THESE TWO SECTIONS OF THE CWA
THEN 0.50 TO 1.50 INCHES OF ARE RAIN IS LIKELY WITH ISOLATED
AMOUNTS OVER 2 INCHES...WHICH HAS ALREADY OCCURRED IN
SOUTHERN/WESTERN IOWA COUNTY. RAIN AMOUNTS OUTSIDE OF THE HEAVY
ZONES WILL VARY GREATLY FROM A TRACE TO A FEW HUNDREDTHS....LOCALLY
UP TO 0.50 INCHES.

THIS AFTERNOON AND TONIGHT...CONDITIONS SHOULD SETTLE DOWN QUITE A
BIT AND POPS OF 20-30 PERCENT ON AVG REFLECT THAT IDEA. TIME-HEIGHT
SECTIONS HAVE HIGH SATURATION AT/BELOW 850MB...SIMILAR TO YESTERDAY
STRATUS OVERCAST ANTICIPATED TO LAST THROUGH THE DAY...BUT TODAY
THE CEILING HEIGHTS WILL LIKELY BE LOWER.

SPC HAS A MARGINAL RISK FOR SEVERE STORMS ACROSS THE SOUTHERN CWA
DURING THE AFTN/EVENING WHEN A SFC BOUNDARY MAY IGNITE ISOLATED TO
SCT ACTIVITY IN AN ENVIRONMENT CHARACTERIZED BY MODERATE MUCAPE
VALUES BUT WEAK 0-6KM BULK SHEAR. FOR THE OVERNIGHT...EXPECT MILD
LOWS IN THE 60S AND AREAS OF FOG.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 308 AM CDT SUN AUG 9 2015

DEVELOPING AMPLIFIED UPPER LEVEL PATTERN FORMING A NW FLOW OVER THE
REGION AND HIGH PRESSURE AT THE SURFACE...WILL FAVOR DRY WEATHER
WITH NEAR NORMAL TEMPERATURES THROUGH MOST OF THE WEEK.

MONDAY...MODELS CONTINUE TO DEPICT A WEAK MID LEVEL VORT MAX
EMBEDDED IN THE WEAKLY CYCLONIC NW FLOW SENDING A COLD FRONT WITH
POSSIBLE SHOWERS AND THUNDERSTORMS AS IT MOVES SE THROUGH THE AREA
DURING THE DAY. WILL KEEP SLIGHT TO LOW END CHANCE POPS IN PLACE
WITH HIGHS FROM THE UPPER 70S NORTH TO LOWER 80S IN THE FAR SOUTH.

TUESDAY THROUGH THURSDAY...A NW UPPER LEVEL FLOW BETWEEN A LONG WAVE
RIDGE BUILDING OVER THE ROCKIES AND LONG WAVE TROUGH OVER THE
EASTERN U.S...WILL PROVIDE AN EXTENDED PERIOD OF DRY WEATHER. HIGH
PRESSURE AT THE SURFACE WILL KEEP HUMIDITY LEVELS RELATIVELY LOW
WITH TEMPERATURES TRENDING NEAR TO SLIGHTLY BELOW NORMAL WITH HIGHS
IN THE LOWER 80S AND LOWS IN THE UPPER 50S TO LOWER 60S.

MODELS CONTINUE TO DEPICT A LOW LEVEL BOUNDARY PUSHING THROUGH THU
NIGHT INTO FRIDAY TO WARRANT LOW POPS FOR SHOWERS AND THUNDERSTORMS.
MODEL CONSENSUS CONTINUES TO SUPPORT A WARMING TREND INTO SATURDAY
BASED ON THE FLATTENING AND EASTWARD SHIFTING UPPER RIDGE SENDING
WARMER TEMPERATURES BUILDING UNDER THE RIDGE IN THE PLAINS
NORTHEASTWARD.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1131 PM CDT SAT AUG 8 2015

LOW PRESSURE WILL SPREAD EAST ALONG A STATIONARY FRONT OVERNIGHT
THROUGH SUNDAY MORNING. THIS WILL BRING WIDESPREAD SHOWERS AND
THUNDERSTORMS TO THE REGION. CONDITIONS AS OF LATE SATURDAY
EVENING ARE ALREADY DROPPING TO AREAS OF MVFR TO LOWER VFR...IN
RAIN AND WEAK THUNDERSTORMS. THIS PROCESS WILL CONTINUE TO DROP
FLIGHT CONDITIONS THROUGH THE NIGHT...WITH IFR POSSIBLE FROM 10Z
TO 15Z SUNDAY...FOLLOWED BY PERSISTENT MVFR CONDITIONS IN CIGS OF
1000 TO 2500 FT ALL SUNDAY. THERE IS LITTLE IF ANY DRY AIR MOVING
IN BEHIND THE RAIN TO LIFT CIGS...BUT WITH SUMMER TIME
CONDITIONS...IT IS UNLIKELY THAT WE WOULD GO ALL DAY WITHOUT
IMPROVEMENT.
ERVIN

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...FLASH FLOOD WATCH UNTIL NOON CDT TODAY FOR JEFFERSON-VAN BUREN.

IL...NONE.
MO...FLASH FLOOD WATCH UNTIL NOON CDT TODAY FOR SCOTLAND.

&&

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

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