April 10-13 Plains/MW/OV/GL Severe Weather, SPC Risk Level: Day 3 Slight Risk - Forecasts & OBS Options

[andyhb]

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

VALID 111200Z - 161200Z

...DISCUSSION...
ALTHOUGH MEDIUM RANGE MODELS /00Z ECMWF AND GFS/ DIFFER IN THE TRACK
OF A TROUGH INTO THE CENTRAL U.S. ON D5/THU AND TO SOME DEGREE ON
D7/SAT...THESE MODELS DO AGREE IN A PATTERN CHANGE ACROSS THE CONUS
FROM MID WEEK TO NEXT WEEKEND. A BLOCKING PATTERN WITH A NWLY FLOW
REGIME OVER THE CENTRAL TO SERN U.S. WILL PERSIST INTO D4/WED WITH A
THREAT FOR SEVERE STORMS ACROSS THE SRN AND CENTRAL HIGH PLAINS.
THE PATTERN CHANGE BEGINS ON D5 AS SWLY FLOW DEVELOPS INTO THE
PLAINS DOWNSTREAM OF A LONGWAVE TROUGH EVOLVING OVER THE WRN STATES
THROUGH THE REST OF THE EXTENDED PERIOD.

FOR D5/THU...THE GFS AND ECMWF CONTINUE TO DIFFER WITH THE TRACK OF
THE SHORTWAVE TROUGH FROM LATE D4/WED THROUGH D5. ALTHOUGH THE GFS
IS MAINTAINING A NRN TRACK BIAS WITH WEAKER FORCING ACROSS
KS/OK...THE WARM SECTORS IN EACH MODEL ARE SIMILAR. NORMALLY THESE
TYPES OF MODEL VARIANCES IN THE MID-UPPER LEVELS WOULD RESULT IN NOT
INCLUDING A REGIONAL SEVERE WEATHER THREAT AREA. HOWEVER...GFS
FORECAST SOUNDINGS SUGGEST THE POTENTIAL FOR SUPERCELLS ALONG THE
DRY LINE...BUT WITH LOWER COVERAGE. THIS FACTOR COMBINED WITH THE
FORECAST FOR STRONGER WIND FIELDS PER THE ECMWF SUGGESTS THE
REGIONAL SEVERE WEATHER THREAT AREA WILL BE MAINTAINED INTO D5 WITH
THE POTENTIAL FOR LARGE HAIL AND TORNADOES.

THE MODEL DIFFERENCES WITH THE TRACK OF THE D5/THU TROUGH AFFECT THE
SEVERE WEATHER FORECAST FOR D6/FRI...WITH THE GFS FAVORING A MORE
NRN TRACK ACROSS KS/NEB INTO IA...WHILE THE ECMWF INDICATED A
GREATER THREAT FARTHER TO THE SSE.

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.

..PETERS.. 04/08/2012

[WeatherMonger]

From the Chicago Weather Blog, no article or prediction of an outbreak. Just found it interesting, and almost looks as if they're hinting the signs are there for the plains later this week.

[jdrenken]

I have decided to split this in two threads. This will be two seperate waves of energy hitting the West Coast. The first wave hits the coast late on the 11th, while the second/stronger wave hits the coast on the 14th.

[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

[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]

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0229 AM CDT SUN APR 08 2012

VALID 101200Z - 111200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN HIGH
PLAINS INTO WRN OK...

...SYNOPSIS...
PART OF A SHORTWAVE TROUGH...CURRENTLY MOVING THROUGH THE ALEUTIAN
ISLANDS PER WATER VAPOR IMAGERY...IS EXPECTED AMPLIFY INTO THE BASE
OF THE ERN PACIFIC LONGWAVE TROUGH DURING D3/TUE. THIS SHORTWAVE
TROUGH WILL REACH THE SRN CA COAST BY 12Z WED AS THE PARENT TROUGH
SHIFTS INLAND TO THE WRN STATES. MEANWHILE...THE ERN LONGWAVE
TROUGH IS EXPECTED TO DEEPEN AS THE CLOSED LOW OVER QUEBEC MOVES SWD
TOWARD THE U.S./CANADA BORDER...AND A SERIES OF SHORTWAVE TROUGHS
TRACK SEWD FROM THE UPPER MIDWEST TO THE MID ATLANTIC STATES/
CAROLINAS. A NWLY FLOW REGIME WILL PREVAIL ACROSS THE CENTRAL U.S.
TO THE GULF COAST AND SERN STATES AS THE UPPER RIDGE AXIS SHIFTS
SLOWLY EWD. AT THE SURFACE...A FRONT EXTENDING FROM THE MID SOUTH
WWD INTO OK AND THE TX PANHANDLE EARLY TUESDAY MORNING WILL SHIFT
SWD ON D3...WITH SOME MODEL UNCERTAINTY WITH RESPECT TO HOW FAR S
THIS BOUNDARY MOVES BY 12Z WEDNESDAY.

...PARTS OF W TX INTO THE OK PANHANDLE AND WRN OK...
SELY LOW LEVEL WINDS DEVELOPING INTO THE SRN HIGH PLAINS ON TUESDAY
WILL ALLOW MOISTURE TO BEGIN RETURNING WNWWD INTO THIS REGION
BENEATH STEEP MIDLEVEL LAPSE RATES /7.5-8 C PER KM/. THESE FACTORS
COMBINED WITH SURFACE HEATING WILL CONTRIBUTE TO MARGINAL-MODERATE
INSTABILITY DEVELOPING BY PEAK HEATING AND WEAKENING INHIBITION FOR
SURFACE BASED TSTM DEVELOPMENT. GIVEN THE RIDGE AXIS SHIFTING EWD
ACROSS THIS REGION AND OVERALL LACK OF FORCING ALOFT...DIURNAL TSTM
COVERAGE MAY TEND TO BE LOW...BUT VERTICALLY VEERING WIND PROFILES
AND EFFECTIVE BULK SHEAR AROUND 35 KT WILL SUPPORT STORM
ORGANIZATION. THUS...HAIL AND STRONG WIND GUSTS WILL BE THE PRIMARY
THREATS. SINCE A FEW MODELS SUGGEST UPSCALE GROWTH OF TSTMS TUESDAY
EVENING/NIGHT ACROSS W TX INTO WRN OK AS THE LLJ VEERS...SEVERE
WEATHER THREAT THROUGH PERIOD WARRANTS A SLIGHT RISK AREA.

...SRN MS/LA WWD INTO CENTRAL/NRN TX...
A CLUSTER OF STORMS /POTENTIALLY A FORWARD PROPAGATING MCS/ SHOULD
BE ONGOING ACROSS PARTS OF ERN OK/AR INTO NERN TX AND NRN LA AT 12Z
TUESDAY. SURFACE HEATING ALONG AND S OF THE ONGOING ACTIVITY
COMBINED WITH SURFACE DEWPOINTS IN THE 60S AND MODEST MIDLEVEL LAPSE
RATES /NEAR 7 C PER KM/ SHOULD RESULT IN AT LEAST MARGINAL
INSTABILITY EXTENDING WWD FROM SRN MS/LA INTO CENTRAL/NRN TX.
DESPITE RELATIVELY WEAK LOW LEVEL WINDS/SHEAR...30-35 KT NWLY
MIDLEVEL WINDS WILL RESULT IN STRONGER BULK SHEAR FOR ORGANIZED
STORMS. MARGINAL INSTABILITY WILL LIMIT OVERALL COVERAGE...AND THUS
ONLY WARRANTS LOW SEVERE PROBABILITIES AT THIS TIME FOR A PRIMARY
THREAT OF ISOLATED DAMAGING WINDS.

..PETERS.. 04/08/2012

[snowlover2]

Is the severe threat tomorrow part of this thread? If so, begining date needs adjusted to the 9th.

[jdrenken]

Is the severe threat tomorrow part of this thread? If so, begining date needs adjusted to the 9th.

This thread is associated with a different system than tomorrow as a cold front comes South thru the Plains with a new SLP developing on the far end of the front when it stalls out.