Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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717
FXUS63 KDVN 201149
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
649 AM CDT WED MAY 20 2015

.SYNOPSIS...
ISSUED AT 258 AM CDT WED MAY 20 2015

SPLIT FLOW ALOFT CONTINUED ACROSS NORTH AMERICA WITH A PSEUDO REX
BLOCK ACROSS WESTERN NORTH AMERICA RESULTING IN CONVERGING
NORTHERN AND SOUTHERN STREAM OVER THE UPPER MIDWEST. AT THE
SURFACE...AN INVERTED SURFACE TROUGH STRETCHED NORTHWARD INTO
EASTERN NEBRASKA THIS MORNING FROM A SURFACE LOW ACROSS EASTERN
NEBRASKA. PRECIPITATION WAS SPREADING EASTWARD INTO CENTRAL IOWA
AS OF 330 CDT.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 258 AM CDT WED MAY 20 2015

THE MAIN FORECAST CONCERN THIS PERIOD WILL BE CHANCES OF
PRECIPITATION ON WEDNESDAY. MODELS ARE IN GOOD OVERALL AGREEMENT
WITH THE SYNOPTIC PATTERN BUT THERE ARE DIFFERENCES IN MOISTURE
AND STRENGTH OF THIS SYSTEM. THE OUTLIERS ARE THE DRIER AND WEAKER
GFS AND THE STRONGER AND WETTER NAM. THE CANADIAN AND ECMWF FALL
IN BETWEEN THESE TWO SOLUTIONS.

IN THE UPPER LEVELS...A DISTURBANCE MOVING EASTWARD INTO THE
PLAINS WILL INTERACT WITH A SECOND DISTURBANCE DROPPING SOUTHWARD
ALONG A TROUGH ACROSS EASTERN CANADA. AS THIS OCCURS...A SURFACE
LOW WILL MOVE EASTWARD ALONG A STALLED FRONTAL BOUNDARY ALONG
INTERSTATE 40 DURING THE DAY ON WEDNESDAY WITH AN INVERTED SURFACE
TROUGH STRETCHING NORTHWARD INTO IOWA. A WING OF WARM ADVECTION
AHEAD OF THE INVERTED TROUGH WILL PROVIDE THE LIFT FOR
PRECIPITATION DURING THE DAY ON WEDNESDAY WITH THE BEST LIFT
ARRIVING BY 18 UTC AND QUICKLY EXITING THE REGION BY 00 UTC.

COOL EAST TO NORTHEASTERLY FLOW AHEAD OF THE TROUGH AXIS WILL
WORK AGAINST THIS LIFT AND KEEP THE ATMOSPHERE FROM SATURATING
QUICKLY. HOWEVER THE FLOW IS WEAK AND AS PRECIPITATION SPREADS
ACROSS THE REGION THE ATMOSPHERIC COLUMN WILL SATURATE FROM THE
TOP DOWN. THERE WILL BE A NORTH TO SOUTH GRADIENT IN PRECIPITATION
ACROSS THE CWA WITH THE BEST CHANCES OF SHOWERS ALONG AND SOUTH
OF A LINE FROM FAIRFIELD TO GALESBURG. LOCATIONS ALONG THE HIGHWAY
20 CORRIDOR MAY SEE LITTLE IF ANY PRECIPITATION. THE DRY AIR AT
THE SURFACE AND EVAPORATION AS THE RAIN FALLS THROUGH THE
ATMOSPHERE WILL LEAD TO EVAPORATIONAL COOLING WHICH WILL KEEP
TEMPERATURES UNSEAONABLY COOL FOR LATE MAY. HIGH TEMPERATURES WILL
GENERALLY BY THE LOWER TO MID 50S WITH A RECORD COOL MAY POSSIBLE
AT MLI. PLEASE SEE THE CLIMATE SECTION BELOW.

IN THE WAKE OF WEDNESDAYS SYSTEM COOL CANADIAN HIGH PRESSURE WILL
BUILD INTO THE CENTRAL PLAINS AND CLEAR THE CLOUDS OUT FROM NORTH
TO SOUTH OVERNIGHT. LOW TEMPERATURES ON THURSDAY MORNING WILL BE
10 TO 15 DEGREES BELOW NORMAL.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 258 AM CDT WED MAY 20 2015

FORECAST FOCUS ON THUNDERSTORMS RETURNING SOMETIME THIS WEEKEND.

THURSDAY THROUGH FRIDAY...NORTHWEST FLOW ALOFT AND SURFACE HIGH
PRESSURE WILL KEEP TEMPERATURES BELOW NORMAL ON THURSDAY.
HOWEVER...COMPARED TO WEDNESDAY THESE READINGS WILL BE MUCH WARMER.
HIGHS WILL BE IN THE UPPER 60S AT MOST LOCATIONS. ON FRIDAY A ZONAL
FLOW RETURNS WITH CONTINUED DRY CONDITIONS BUT EVEN WARMER WITH
HIGHS IN THE LOWER TO MID 70S.

SATURDAY...OPERATIONAL MODELS HAVE SLOWED THE DEEP TROUGH IN THE
ROCKIES SUCH THAT SATURDAY NOW APPEARS DRY AS HEIGHTS RISE. I HAVE
LOWERED POPS ON SATURDAY AS A STARTER BUT LATER SHIFTS MAY WANT TO
GO DRY IF THIS TREND CONTINUES. MAXIMUM TEMPERATURES SHOULD BE IN
THE LOWER TO MID 70S AGAIN...BUT IF THERE IS MORE SUNSHINE THEN
EXPECTED THESE READINGS MAY END UP A BIT WARMER.

SATURDAY NIGHT THROUGH TUESDAY...THE UPPER LEVEL RIDGING MOVES EAST
ALLOWING FOR A SOUTHWEST FLOW AHEAD OF A DEEP TROUGH IN THE ROCKIES.
THIS SYNOPTIC PATTERN WILL ALSO PULL DEEPER GULF MOISTURE INTO THE
MIDWEST. THERE SHOULD BE SEVERAL ROUNDS OF THUNDERSTORMS DURING THIS
PERIOD BUT ALSO SOME DRY TIMES...WHICH LATER SHIFTS WILL NEED TO
RESOLVE. THE WILD CARD WILL BE WHERE THE WARM FRONT WILL BE LOCATED
TO FOCUS THE MORE ORGANIZED THUNDERSTORMS. IF THIS FRONT MOVES NORTH
OF THE DVN CWA THEN POPS WOULD NEED TO BE LOWERED. THE SEVERE
WEATHER THREAT APPEARS LOW AS DEEP LAYER SHEAR LOOKS WEAK...BUT THIS
COULD CHANGE IN LATER MODEL RUNS. HIGH TEMPERATURES DURING THIS TIME
FRAME WILL BE WELL INTO THE 70S WITH LOWS IN THE 50S TO LOWER 60S.


&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 641 AM CDT WED MAY 20 2015

A STORM SYSTEM WILL BRING RAIN SHOWERS TO TAF SITES IN EASTERN
IOWA AND NORTHWEST ILLINOIS FROM 14 UTC THROUGH APPROXIMATELY 21
UTC ON WEDNESDAY. FLIGHT CONDITIONS ARE CURRENTLY VFR AND EXPECT
VFR CONDITIONS TO CONTINUE THROUGH THE TAF PERIOD. CEILINGS AND
VISIBILITIES MAY BRIEFLY LOWER TO MVFR FOR A SHORT TIME IN THE
HEAVIEST OF SHOWERS. CONFIDENCE IS LOWER THAT SHOWERS WILL OCCUR
AT KDBQ WITH THE BEST CHANCES AT KBRL. HIGH PRESSURE WILL BUILD
INTO THE PLAINS AFTER 06 UTC AND BRING A QUEST END TO THE TAF
PERIOD.

&&

.CLIMATE...
ISSUED AT 258 AM CDT WED MAY 20 2015

RECORD COOL HIGHS FOR MAY 20

DUBUQUE 44 1892
MOLINE  52 2002

&&

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

$$

SYNOPSIS...COUSINS
SHORT TERM...COUSINS
LONG TERM...HAASE
AVIATION...COUSINS
CLIMATE...COUSINS



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