Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 210809
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
309 AM CDT THU MAY 21 2015

.SYNOPSIS...
ISSUED AT 309 AM CDT THU MAY 21 2015

THE LARGE SCALE FEATURES A BLOCKING SPLIT FLOW UPPER LEVEL PATTERN
WITH A NORTHERN MERIDIONAL NORTHERN STREAM FLOW OUT OF CENTRAL
CANADA MERGING INTO THE NEARLY ZONAL SOUTHERN STREAM OVER THE
CENTRAL U.S.  THIS WAS KEEPING GULF MOISTURE AND ACTIVE WEATHER
CONFINED WELL TO THE SOUTH ACROSS OK AND TX. A WEAK VORT MAX EVIDENT
ON WV IMAGERY WAS SETTLING SOUTH ACROSS THE UPPER MS VALLEY...
ACCOMPANIED BY LITTLE MORE THAN A FEW AC OVER SE MN INTO W CENTRAL
WI. OVER THE LOCAL AREA...THE STRATUS THAT BLANKETED THE AREA
WEDNESDAY DAY WAS ERODING AND SETTLING SE WHILE HIGH PRESSURE OVER
THE CENTRAL PLAINS WAS PROVIDING LIGHT W-NW WINDS. THANKS TO THE
RAIN-COOLED AIRMASS AND COLD 850 MB TEMPERATURES...EVIDENT BY DVN
850 MB TEMP OF -3 C ON THE 00Z SOUNDING...SURFACE READINGS AT 2 AM
WERE ONLY IN THE UPPER 30S TO LOWER 40S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 309 AM CDT THU MAY 21 2015

TEMPERATURES ARE THE PRIMARY CHALLENGE THROUGHOUT AS THE SURFACE
RIDGE OVER THE PLAINS MIGRATES EAST-SE UNDER A SLIGHTLY CONFLUENT
NWRLY MID AND UPPER LEVEL FLOW. THE NW FLOW WILL ADVECT WARMER AND
LARGELY DRY AIR...AS EVIDENT BY 00Z SOUNDINGS OVER THE NORTHERN
PLAINS...INTO THE LOCAL AREA. RESULTING MOSTLY SUNNY SKIES AND DEEP
MIXING TO AT LEAST 800 MB YIELDS HIGHS NEAR GUIDANCE FROM THE MID
60S TO AROUND 70...WHICH LOOKS REASONABLE AND CLOSE TO THE PREVIOUS
FORECAST. THE DEEP MIXING AND AN INCREASING SURFACE PRESSURE
GRADIENT...BETWEEN THE SOUTHERN PLAINS HIGH CENTER AND A WEAK COLD
FRONT DROPPING SOUTH INTO THE WESTERN GREAT LAKES...WILL PROVIDE
BREEZY WEST WINDS BY AFTERNOON.

TONIGHT...THE AFOREMENTIONED WEAK SURFACE FRONT DROPS SOUTH THROUGH
THE FORECAST AREA LATE. THIS WILL BE ACCOMPANIED BY LITTLE FANFARE
AS IT WILL HAVE LITTLE MOISTURE TO WORK WITH...AND ALSO AS IT WILL
BE ADVANCING INTO AN AREA OF WEAK UPPER LEVEL SUBSIDENCE.
THUS...ONLY A MINOR SHIFT IN LIGHT WINDS FROM WEST TO NW OR NORTH
IS EXPECTED UNDER MOSTLY CLEAR SKIES. THE CLEAR SKIES...LIGHT
WINDS AND DRY AIR WILL LEAD TO ANOTHER NIGHT OF BELOW NORMAL
TEMPERATURES WITH MINS FROM THE LOWER 40S NORTH TO UPPER 40S
SOUTH.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 309 AM CDT THU MAY 21 2015

FORECAST FOCUS ON THUNDERSTORM CHANCES LATER THIS WEEKEND AND INTO
NEXT WEEK.

FRIDAY THROUGH SATURDAY...WE START THE HOLIDAY WEEKEND WITH DRY AND
PLEASANT WEATHER AS RIDGING ALOFT AND AT THE SURFACE WILL BE IN
CONTROL. THIS SHOULD BE AN EXCELLENT TIME TO BE OUTDOORS WITH
AFTERNOON TEMPERATURES BOTH DAYS IN THE LOWER TO MID 70S. THERE
SHOULD BE PLENTY OF SUNSHINE ON FRIDAY WITH INCREASING CLOUDS ON
SATURDAY.

SATURDAY NIGHT THROUGH MEMORIAL DAY...THE RIDGE BREAKS DOWN ALLOWING
FOR A SOUTHWEST FLOW ALOFT AS A DEEP UPPER LEVEL TROUGH SETS UP SHOP
IN THE ROCKIES. OPERATIONAL MODELS INDICATE A STRENGTHENING LOW
LEVEL JET WHICH WILL TRANSPORT DEEP GULF MOISTURE NORTHWARD INTO THE
REGION. AS OF NOW THE MOST WIDESPREAD SHOWERS AND THUNDERSTORMS LOOK
TO BE SUNDAY AND SUNDAY NIGHT WITH CHANCE POPS ON MEMORIAL DAY.
MAXIMIM TEMPERATURES WILL BE IN THE 70S. ONCE AGAIN...DEEP LAYER
SHEAR DOES NOT LOOK OVERLY IMPRESSIVE SO THE SEVERE WEATHER RISK
APPEARS LOW.

TUESDAY THROUGH WEDNESDAY...A SERIES OF UPPER LEVEL WAVES IN THE
SOUTHWEST FLOW WILL BRING CHANCES OF SHOWERS AND THUNDERSTORMS...BUT
TIMING OF THESE WAVES IS TRICKY THIS FAR OUT. MAXIMUM TEMPERATURES
WILL AGAIN BE IN THE 70S.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1134 PM CDT WED MAY 20 2015

VFR CONDITIONS WILL BECOME MORE WIDESPREAD THROUGH SUNRISE ACROSS
EASTERN IOWA AND NORTHERN ILLINOIS AS THE STORM SYSTEM MOVES
FURTHER EAST INTO THE OHIO VALLEY. SOME BRIEF PERIODS OF MVFR
CIGS MAY BE POSSIBLE UNTIL SKIES CLEAR. AFT 12Z/21 VFR CONDITIONS
ARE EXPECTED THROUGH 00Z/22.

&&

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

$$

SYNOPSIS...SHEETS
SHORT TERM...SHEETS
LONG TERM...HAASE
AVIATION...08



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