April 13-16 Plains/MW/OV/GL Severe Weather, SPC Risk Level: Day 1 Moderate Risk - Forecasts & OBS Options

[jdrenken]

This thread is for the main player that will become our severe threat this upcoming weekend. If one watches a loop of the 500mb, you will see the energy is different from the 12-13th system.

[WeatherMonger]

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
905 AM EDT SUN APR 08 2012

VALID 12Z THU APR 12 2012 - 12Z SUN APR 15 2012

...SEVERE THUNDERSTORMS POSSIBLE ACROSS THE SOUTHERN PLAINS FROM
WEDNESDAY THROUGH NEXT SATURDAY...

THE GENERAL FLOW PATTERN WILL CONTINUE TO FEATURE TROUGHING ACROSS
THE NORTHEAST AND JUST OFFSHORE WESTERN NORTH AMERICA THROUGH THIS
WEEK...BEFORE RIDGING ACROSS THE FAR NORTHERN PACIFIC OCEAN CAUSES
A RETROGRESSION IN THE EASTERN PACIFIC TROUGH. THE GLOBAL
GUIDANCE AND ENSEMBLE MEANS ARE IN EXCELLENT AGREEMENT THROUGH THE
PERIOD CONCERNING THIS AMPLIFIED FLOW PATTERN...WHICH LEADS TO
BETTER THAN AVERAGE CONFIDENCE. THE 00Z GLOBAL ENSEMBLE GUIDANCE
SPREAD IS SIMILAR TO THE CURRENT DETERMINISTIC MODEL SPREAD THIS
WEEKEND ACROSS CENTRAL NORTH AMERICA. SINCE THE AGREEMENT IS SO
GOOD...WENT WITH A 40/30/30 BLEND OF THE 00Z UKMET/06Z GFS/00Z
ECMWF THROUGH FRIDAY BEFORE SWITCHING TO A SIMPLE 50/50 BLEND OF
THE 06Z GFS/00Z ECMWF WHICH LED TO REASONABLE CONTINUITY. THIS
BLEND ACCOUNTS FOR ISSUES SEEN ACROSS THE NORTHERN PLAINS LATE IN
THE PERIOD...WHERE THE 06Z GFS IS LIKELY TOO STRONG ALOFT.

MUCH OF THE PRECIPITATION THIS PERIOD SHOULD FALL ACROSS THE
WEST...PLAINS/MIDWEST...AND OHIO VALLEY...WITH RAINS POSSIBLY
SPREADING INTO THE MID-ATLANTIC STATES NEXT SATURDAY. THE WESTERN
PRECIPITATION SHOULD BE DUE TO A COMBINATION OF PERSISTENT ONSHORE
FLOW AND THE PASSAGE OF A COUPLE UPPER LEVEL DISTURBANCES WHICH
SHOULD KEEP THE ATMOSPHERE UNSETTLED AND PRECIPITATION FOCUSED
INTO WEST AND SOUTHWEST-FACING SLOPES OF THE ROCKIES AND COASTAL
RANGES OF CALIFORNIA.

IN THE PLAINS...THE AVAILABILITY OF PRECIPITATION WATER AMOUNTS OF
OVER AN INCH SHOULD ALLOW CONVECTION TO DEVELOP CLOSE TO SURFACE
BOUNDARIES. PER THE STORM PREDICTION CENTER /SPC/...SEVERE
WEATHER REMAINS A THREAT ACROSS THE SOUTHERN AND CENTRAL PLAINS
THROUGH THE PERIOD...WITH AN AREA DEPICTED ACROSS KANSAS AND
OKLAHOMA THURSDAY. LATE THIS WEEK...THUNDERSTORMS INITIATE NEAR A
SLOWLY MOVING WARM FRONT BEFORE THE THEY MOVE/PROPAGATE SOUTHEAST
INTO THE WARM SECTOR. THE MANUAL DAY 4-5 QPF PLAYED DOWN THE 00Z
ECMWF SOLUTION /WHICH FITS THE PREFERRED MODEL BLEND AT THIS TIME
RANGE/ THAT LOOKED PARTICULARLY SHARP/DYNAMIC ALOFT AND FORMED
CONVECTION WELL NORTHWARD INTO THE COLD SECTOR.

ANOTHER BOUT OF SEVERE THUNDERSTORMS IS POSSIBLE SATURDAY ACROSS
OKLAHOMA AND KANSAS /WHERE SPC HAS DEPICTED ANOTHER AREA/ DUE TO
THE APPROACH OF A DEEP/CLOSED CYCLONE MOVING THROUGH THE WEST AND
ROCKIES...WITH CONVECTION MOVING ALONG A MORE EASTERLY TRAJECTORY
NEXT WEEKEND AS THE RIDGING IN THE SOUTHEAST BUILDS. THE 00Z/06Z
GFS RUNS DISAGREED AS TO WHETHER OR NOT THIS PRECIPITATION WOULD
SNEAK INTO THE MID-ATLANTIC STATES UNDER THE BASE OF THE
NORTHEASTERN TROUGH...THOUGH THE 00Z ECMWF AGREED IN GENERAL THAT
LIGHT TO MODERATE RAINS WERE POSSIBLE NEXT SATURDAY...EVEN IF THE
AXES IN THE 00Z ECMWF/06Z GFS WERE A BIT DIFFERENT ON THEIR WAY
TOWARDS THE MID-ATLANTIC STATES RUNNING THROUGH THE GREAT
LAKES/MID-SOUTH RESPECTIVELY.

ROTH

[The Snowman]

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CDT SUN APR 08 2012

VALID 111200Z - 161200Z

FOR D7/SAT...THE GFS/ECMWF ARE IN BETTER AGREEMENT AGAIN WITH
RESPECT TO THE DISTRIBUTION OF LOW LEVEL MOISTURE AND WARM SECTOR
SETUP ACROSS TX INTO KS. GREATEST JUXTAPOSITION OF INSTABILITY AND
STRONG DEEP LAYER SHEAR SUPPORTS ANOTHER REGIONAL SEVERE WEATHER
THREAT AREA SIMILAR TO D5 ACROSS OK/KS.

[jdrenken]

Mike Smith's thoughts...

Sunday, April 8, 2012
Uh, Oh! Keep an Eye on the Weather This Week
If you live in the states of Texas, Oklahoma, Kansas, Missouri, Nebraska, and Arkansas pay attention to the weather this week. It appears, roughly from Tuesday night through next Sunday, we will have the first weather pattern of 2012 to set up a multi-day severe weather situation.

[jdrenken]

LOT is thinking that this will slow down even more...

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1051 AM CDT SUN APR 8 2012

IN THE EXTENDED...SOUTHWEST UPPER FLOW AND SURFACE LOW PRESSURE IS
EXPECTED TO PREVAIL ACROSS THE CENTRAL PLAINS FOR MUCH OF THURSDAY
THROUGH NEXT SUNDAY. THIS WILL BE ASSOCIATED WITH A DEVELOPING
UPPER TROUGH ACROSS THE WEST. MULTIPLE SHORT WAVE IMPULSES ARE
PROJECTED FROM THE CENTRAL PLAINS TOWARD THE GREAT LAKES REGION
DURING THE END OF THE WEEK...ALONG WITH AN OVERALL ELEVATED WARM
AIR ADVECTION PATTERN. THE HIGHER PRECIPITABLE WATER AIR...AND
GENERAL INSTABILITY TO SUPPORT THUNDERSTORMS APPEARS TO ARRIVE
FRIDAY OR FRIDAY NIGHT AT THIS TIME. THE WHOLE LONG WAVE TROUGH ON
THE WEST DOES NOT APPEAR TO SHIFT EAST ENOUGH TO BRING A WELL-
ORGANIZED SURFACE SYSTEM OUR WAY UNTIL EARLY NEXT WEEK...AND ITS
POSSIBLE THAT SLOWS MORE. IT WILL BE SOMETHING TO KEEP AN EYE ON.
AT THIS TIME...HAVE THUNDER CHANCES FOR FRIDAY THROUGH
SUNDAY...AND INEVITABLY THERE WILL BE PERIODS IN THERE WHICH ARE
BETTER DEFINED AS THIS WEEK PROGRESSES.

MTF

[jdrenken]

SGF's view...

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPRINGFIELD MO
653 AM CDT SUN APR 8 2012

THE MODEL GUIDANCE IS SUGGESTING A MORE ACTIVE WEATHER PATTERN FOR
THE AREA NEXT WEEKEND WITH A STRONGER AND MORE SOUTHERN TRACK
SYSTEM MOVING OUT ACROSS THE CENTRAL PLAINS INTO THE MIDWEST NEXT
WEEKEND. THIS COULD BE A BETTER SETUP FOR SOME SEVERE WEATHER FOR
THE REGION. IT IS TOO EARLY TO PINPOINT DOWN TIMING AND DETAILS
BUT IT WILL BE SOMETHING TO WATCH IN LATER MODEL GUIDANCE AS WE
GET CLOSER TO NEXT WEEKEND. OVERALL...EXPECT A MORE ACTIVE AND
STORMY WEATHER PATTERN FOR LATE NEXT WEEK WITH TEMPERATURES
WARMING UP ABOVE NORMAL.

GRIFFIN

[jdrenken]

Here is our early next week storm of interest...

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[jdrenken]

Adam Lucio's thoughts...

[andyhb]

Yikes, can't remember the last time we had 3 straight days outlined in a Day 4-8 outlook...I still think Saturday, as Peters mentions here, has the best outbreak potential given that it is the day that is likely to have the least capping problems and strongest wind profiles.

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CDT MON APR 09 2012

VALID 121200Z - 171200Z

...DISCUSSION...
MEDIUM RANGE MODELS CONTINUE TO INDICATE A PATTERN CHANGE...WHICH
EXPECTED TO START ON D3/WED...WILL PROGRESS THROUGH MUCH OF THE
EXTENDED FORECAST PERIOD. THIS WILL RESULT IN THE DEVELOPMENT OF
SWLY MID-UPPER LEVEL FLOW FROM THE SWRN STATES THROUGH OK AND
CENTRAL PLAINS TO THE UPPER MS VALLEY/GREAT LAKES REGION AS A DEEP
LONGWAVE TROUGH EVOLVES IN THE WEST.

MODELS REMAIN CONSISTENT IN FORECASTING AN INCREASE IN SEVERE
WEATHER ACROSS PARTS OF THE SRN AND CENTRAL PLAINS DURING D4/THU
THROUGH D6/SAT. SLY LOW LEVEL WINDS TO THE EAST OF A SURFACE LOW
DEVELOPING OVER WRN KS WILL RESULT IN RICH MOISTURE RETURN INTO
OK/KS ON D4/D5 AND THEN EXTENDING INTO PARTS OF THE MID/UPPER MS
VALLEY ON D6. THIS COMBINED WITH ENEWD EXTENSION OF STEEP MIDLEVEL
LAPSE RATES WILL RESULT IN MODERATE TO STRONG INSTABILITY DEVELOPING
THROUGH D6. SWLY MIDLEVEL WINDS WILL STRENGTHEN FROM MID TO LATE
THIS WEEK ACROSS THE REGIONAL SEVERE WEATHER THREAT AREAS SUCH THAT
ORGANIZED STORMS INCLUDING SUPERCELLS CAN BE EXPECTED DURING
D4...D5...AND D6. THE STRONGEST BULK SHEAR IS EXPECTED ON D6/SAT
WITH THE SEVERE WEATHER THREAT AREA ALSO EXPANDING SWD SOME INTO N
TX AND NEWD INTO SWRN IA.

BEYOND D6...THE SEVERE WEATHER THREAT MAY CONTINUE ACROSS THE SRN
PLAINS...BUT MODEL UNCERTAINTIES PRECLUDE THE INCLUSION OF ANY
ADDITIONAL REGIONAL SEVERE WEATHER THREAT AREAS.

..PETERS.. 04/09/2012

This post has been edited by andyhb: Apr 9 2012, 04:10 AM

[jdrenken]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
635 AM CDT MON APR 9 2012

.PREV DISCUSSION... /ISSUED 358 AM CDT MON APR 9 2012/

.DISCUSSION...LIGHT WINDS AND MOIST BOUNDARY LAYER HAS RESULTED IN
WIDESPREAD FOG THIS MORNING WITH SOME AREAS OF DENSE FOG. WILL
CONTINUE WITH DENSE FOG ADVISORY AS IS THROUGH 10 AM WITH
VISIBILITIES EXPECTED TO IMPROVE LATER THIS MORNING. SURFACE LOW
EXPECTED TO DEVELOP LATER TODAY IN SOUTHWEST KS WITH DRYLINE
EXTENDING ALONG THE WRN BORDER OF OK AND WARM FRONT ARCING SEWD
FROM THE LOW ACROSS OK. EXPECT THUNDERSTORM DEVELOPMENT THIS
AFTERNOON INITIALLY IN NW OK WITH ACTIVITY INCREASING AND
SPREADING SOUTHEASTWARD THROUGH THE LATE AFTERNOON AND EVENING
WITH A THREAT OF SEVERE STORMS AS PER SWODY1. SHOWERS AND
THUNDERSTORMS AGAIN POSSIBLE TUESDAY AND WEDNESDAY AS MOISTURE
REMAINS POOLED ALONG FRONTAL BOUNDARY DRAPED ACROSS THE AREA.
UPPER RIDGE AXIS GRADUALLY MOVES EAST OF THE AREA WITH INCREASING
SOUTHWESTERLY MID LEVEL FLOW SPREADING OVER THE SOUTHERN PLAINS
AS UPPER TROUGH MOVES INTO THE WESTERN U.S. THIS WILL KEEP MOIST
SOUTHERLY LOW LEVEL FLOW ACROSS THE FA WITH A DRYLINE POSITIONED
NEAR THE WESTERN BORDER. AS A RESULT THUNDERSTORM CHANCES WILL
CONTINUE THROUGH MUCH OF THE WEEK. MORE WIDESPREAD RAIN AND
THUNDERSTORMS WITH A THREAT OF SEVERE STORMS AND HEAVY RAIN IS
EXPECTED LATER IN THE PERIOD AS UPPER TROUGH SHARPENS AND
GRADUALLY ADVANCES EASTWARD WITH A SLOW MOVING FRONTAL BOUNDARY
ALSO PUSHING INTO THE AREA.

[jdrenken]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WICHITA KS
303 AM CDT MON APR 9 2012


THURSDAY-SUNDAY:
LONGWAVE UPPER TROUGH WILL BE SLOWLY MOVING THROUGH THE WESTERN
STATES DURING THE PERIOD...WITH A STRONG UPPER LOW IN THE SOUTHERN
PORTION OF THIS TROUGH. GULF MOISTURE/INSTABILITY WILL BE
TRANSPORTED NORTHWARD INTO THE CENTRAL/SOUTHERN PLAINS WITH A
CLASSIC WARM SECTOR WITH DRYLINE SETUP. DEEP LAYER WIND SHEAR WILL
ALSO INCREASE AS THE UPPER TROUGH APPROACHES THE PLAINS. THERE ARE
SOME DIFFERENCES IN THE MEDIUM RANGE MODELS REGARDING MAINLY SURFACE
SYNOPTIC FEATURE PLACEMENT AT TIMES. A FEW EPISODES OF THUNDERSTORMS
DURING THE PERIOD APPEAR LIKELY. THE DEGREE OF INSTABILITY/SHEAR
SUGGEST HIGH END SEVERE WEATHER WILL BE POSSIBLE. STAY TUNED FOR
LATER FORECASTS...AS THE DETAILS WILL BECOME CLEARER OVER THE NEXT
FEW DAYS.

JMC

[jdrenken]

Play the warm front ladies and gentlemen!

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
627 AM CDT Mon Apr 9 2012

Medium Range (Thursday through Sunday)...

In general not much change to specifics of going forecast as weather
becomes more active late in the week into next weekend. ECMWF coming
into good agreement with GFS breaking down the central US ridge and
establishing a deep longwave trough across the west. A
strengthening low level jet and associated warm air advection
coupled with periodic shortwaves ejecting from the trough should
provide the threat for shower and thunderstorm activity for the
later half of the week into the weekend. A surface warm front is
expected to push northward on Saturday and then stall near the
Missouri-Iowa border on Sunday in response to an area of low
pressure moving out into the northern Plains. With front in the
region and longwave trough remaining to the west of the forecast
area the threat for thunderstorm activity will linger through at
least Sunday. As mentioned in previous mid-range discussion with
repeated rounds of thunderstorms through the period the potential
for flooding will need to be monitored.

MJM

[jdrenken]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPRINGFIELD MO
708 AM CDT MON APR 9 2012

AN UPPER LEVEL RIDGE WILL TRANSVERSE ACROSS THE CENTRAL U.S
EASTWARD DURING THE MIDDLE AND END OF THE WEEK WHILE A TROUGH DIGS
ACROSS THE MOUNTAIN WEST. THIS WILL PUT THE CENTRAL PLAINS AND THE
MISSOURI OZARKS IN A SOUTHWEST FLOW BY THE END OF THE WEEK INTO
THE WEEKEND. WHILE THERE ARE SOME MODEL DIFFERENCES IN TIMING AND
POSITION OF MID LEVEL FEATURES AND EXACT PLACEMENT OF SURFACE
LOWS...THE OVERALL MESSAGE IS CONSISTENCE WITH A MORE UNSETTLED
AND POTENTIALLY ACTIVE WEATHER PATTERN FOR THE AREA BY NEXT
WEEKEND. EXPECTING TO SEE SEVERAL ROUNDS OF SHOWERS AND
THUNDERSTORMS AHEAD OF IMPULSES MOVING OUT FROM THE SOUTHWEST
FLOW. IT APPEARS MOST OF THE POTENTIAL FOR SEVERE STORMS WILL BE
JUST TO OUR WEST ACROSS KANSAS BUT WILL WATCH MODEL TRENDS FOR A
BETTER HANDLE OF THIS SETUP LATER THIS WEEK. THERE COULD BE SOME
POTENTIAL FOR SOME STRONG TO SEVERE STORMS OF PORTIONS OF OUR AREA
BY NEXT WEEKEND. TEMPERATURES WILL ALSO BE WARMING UP TO SLIGHTLY
ABOVE AVERAGE BY THE END OF THIS WEEK.

GRIFFIN

[jdrenken]

This could get interesting in our backyard...

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[Illinois blizzar...]

Henry..
Active Week of Severe Weather.

[andyhb]

12z GFS is, for lack of a better word, disgusting.

[ChiWxWatcher]

Dr. Greg Forbes's thoughts:

SATURDAY APR 14
Numerical models begin to disagree, with both having a surface low move toward Lake Superior, but the GFS having another strong low over KS that would make a large difference for the severe thunderstorm forecast. Thus, confidence is reduced in the details that follow. Severe thunderstorms in IA, southeast NE, east KS, central and east OK, northeast and north-central TX.

[ChiWxWatcher]

LOT is discussing possible severe weather Sunday in their AFD, but model differences make it difficult.

EXTENDED...THURSDAY NIGHT THROUGH TUESDAY

A TRANSITION TO A MILDER AND MORE ACTIVE WEATHER PATTERN IS NOTED
FOR THE END OF THE WEEK AND THE WEEKEND...THOUGH MODEL UNCERTAINTY
DOES INCREASE WITH TIMING AND DETAILS DURING THE PERIOD.

UPPER TROUGH ACROSS EASTERN NORTH AMERICA IS MOVING OFF TO THE EAST
BY THURSDAY NIGHT...WITH SURFACE HIGH PRESSURE RIDGE DRIFTING OFF
ACROSS THE GREAT LAKES TO OUR EAST. FARTHER WEST...BROAD UPPER
TROUGH IS DEPICTED OVER MUCH OF THE WESTERN CONUS WITH SURFACE
PRESSURE FALLS DEVELOPING ACROSS THE PLAINS IN RESPONSE TO UPPER JET
STREAK THAT EJECTS FROM THE DESERT SOUTHWEST. THIS RESULTS IN
DEVELOPMENT OF SOUTHEAST LOW LEVEL FLOW ACROSS THE FORECAST AREA...
WITH LOW LEVEL WARM ADVECTION DEVELOPING PARTICULARLY WEST OF THE
MISSISSIPPI VALLEY. ECMWF AND GEM ARE A LITTLE SLOWER THAN OUR
DOMESTIC MODELS WITH THE EASTWARD PROGRESSION OF THE UPPER RIDGE
AXIS AND THIS IS PREFERRED GIVEN HIGH AMPLITUDE OF THE PATTERN. DRY
LOW LEVEL AIR ASSOCIATED WITH RETREATING SURFACE HIGH SHOULD HELP TO
KEEP WARM ADVECTION PRECIPITATION AT BAY AS WELL...ESPECIALLY IN THE
EASTERN PARTS OF THE CWA AND HAVE THUS TRIMMED POPS THERE ALONG THE
LINES OF THE GEM WHICH IS BETWEEN THE DRY ECMWF AND MORE MOIST GFS
IN TERMS OF PRECIP COVERAGE BY FRIDAY MORNING.

PRECIPITATION CHANCES INCREASE FRIDAY AS UPPER RIDGE MOVES EAST AND
UPPER JET STREAK CONTINUES TO SPREAD NORTHEAST INTO THE MIDWEST.
GUIDANCE DIFFERS WITH DEGREE OF SURFACE LOW DEVELOPMENT ACROSS THE
PLAINS AND UPPER MIDWEST...THOUGH WEAK WAVE AND WARM FRONT SHOULD
DEVELOP INTO IOWA/MINNESOTA BY FRIDAY NIGHT PER GEM SOLUTION. THIS
WOULD SUPPORT SOLID CHANCE POPS WITH A FEW PERIODS OF ELEVATED
SHOWERS/THUNDERSTORMS POSSIBLE INTO SATURDAY...AS WARM FRONT LIFTS
NORTH ACROSS THE CWA. SECOND/STRONGER UPPER WAVE LIFTS OUT ACROSS
THE REGION SATURDAY NIGHT INTO SUNDAY...MAINTAINING SHOWER AND
THUNDERSTORM THREAT THROUGH THE WEEKEND.

BY SUNDAY...SIGNIFICANT DIFFERENCES ARE EVIDENT IN EVOLUTION OF
DETAILS OF SURFACE PATTERN AND TIMING OF COLD FRONTAL PASSAGE. GFS
IS STRONGER/MORE CLOSED WITH A STRONGER SURFACE LOW REFLECTION WITH
THE INITIAL WAVE FROM FRIDAY NIGHT/SATURDAY...WHICH RESULTS IN
SECOND LOW TAKING A MORE EAST/SOUTH TRACK ACROSS THE FORECAST AREA
EARLY SUNDAY. ECMWF...WITH A WEAKER SURFACE REFLECTION OF THE
INITIAL SHORT WAVE...HOLDS THE SECOND LOW OFF TO OUR NORTH/NORTHWEST
ON SUNDAY...WITH A LATER COLD FROPA SUNDAY AFTERNOON. CONTINUE TO
PREFER A MORE ECMWF-LIKE SOLUTION...RESULTING IN WARMER TEMPS DURING
THE DAY SUNDAY...AND A POTENTIALLY GREATER THREAT OF SEVERE
WEATHER LOCALLY. WIDE-OPEN FLOW OFF THE GULF OF MEXICO ALSO
SUGGESTS SOME POTENTIALLY FOR LOCALLY HEAVY CONVECTIVE RAINFALL
DURING THE SATURDAY-SUNDAY PERIOD...WITH 12Z GEFS INDICATING
PRECIPITABLE WATER VALUES RUNNING 2-3 STANDARD DEVIATIONS ABOVE
CLIMO.

FRONT SAGS SOUTH OF THE AREA SUNDAY NIGHT INTO EARLY NEXT
WEEK...KEEPING AN OVERRUNNING PRECIP THREAT POTENTIALLY
CLOSE WHILE COOLER/STABLE SURFACE AIR PREVAILS ACROSS THE CWA IN
NORTHERLY LOW LEVEL FLOW.

RATZER

[jdrenken]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
255 PM CDT MON APR 9 2012


THE PATTERN CHANGE ALLUDED TO OVER THE LAST FEW DAYS COMMENCES ON
THURSDAY AND THURSDAY NIGHT AS THE ERN U.S. UPPER TROF PROGRESSES
INTO THE WESTERN ATLANTIC AND THE UPPER RIDGE AXIS SLIDES ACROSS THE
CWA. THE SPEED AT WHICH THIS RIDGE AXIS SLIDES TO THE EAST WILL
LARGELY DICTATE THE ONSET OF PRECIPITATION CHANCES. IN GENERAL THE
TREND IS SLOWER...ALBEIT THE NAM AND CMC GEM ARE A LITTLE FASTER AND
HENCE THE AFTERNOON POPS IN NE AND CENTRAL MO. THEREAFTER A DEEP
TROF TAKES SHAPE OVER THE WESTERN CONUS WITH SW FLOW ALOFT THROUGH
THE MS VALLEY AND A PERIOD OF UNSETTLED WEATHER WITH BOUTS OF
SHOWERS AND THUNDERSTORMS THURSDAY NIGHT THROUGH MONDAY.

GLASS

[jdrenken]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
316 PM CDT MON APR 9 2012

THU NIGHT THROUGH MON...150KT JET DIVING INTO THE WESTERN SIDE OF
THE LARGE UPPER LOW OFF THE PACIFIC NW IS SHOWN PLOWING INTO THE SW
U.S...SENDING THE UPPER RIDGE EASTWARD. THIS RESULTS IN A DEVELOPING
SW FLOW OVER THE CENTRAL U.S...AN OPEN FLOW OF GULF MOISTURE...AND
AN ACTIVE WEATHER PATTERN FOR THE LOCAL AREA. MODELS CONTINUE TO
VARY IN THE DETAILS AND TIMING OF THE LEAD ENERGY AND SURFACE LOW
TRACK...WITH THE GFS A NOTABLE OUTLIER WITH A FASTER INITIAL LOW IN
THE 12Z RUN THAT LIFTS ACROSS THE UPPER MS VALLEY FRI NIGHT INTO
SAT. IN THIS UNSETTLED PATTERN WITH LOW CONFIDENCE IN DETAILS...WILL
KEEP CHANCES FOR SHOWERS AND AT LEAST ISOLATES THUNDERSTORMS GOING
FROM THU NIGHT THROUGH EARLY MONDAY. MODELS DO CONTINUE TO TARGET
THE SATURDAY NIGHT PERIOD FOR RAIN CHANCES AND POPS HAVE BEEN
INCREASED TO LIKELY OVER PART OF THE AREA. TEMPERATURES SHOULD
RETURN TO THE 60S TO LOWER 70S FOR HIGHS...WHILE HIGHER
DEWPOINTS AND POTENTIAL FOR SIGNIFICANT CLOUD COVER HOLDS OVERNIGHT
LOWS IN THE 50S.

SHEETS