| DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0357 AM CDT SUN MAY 16 2010 VALID 191200Z - 241200Z THE MEDIUM RANGE MODELS ARE IN GENERAL AGREEMENT EARLY IN THE DAY 4 TO 8 PERIOD WITH AN UPPER-LEVEL SYSTEM MOVING EWD ACROSS THE ROCKIES. IN RESPONSE...LOW-LEVEL FLOW SHOULD INCREASE ACROSS THE SRN PLAINS WITH A LARGE AREA OF MODERATE TO STRONG INSTABILITY POSSIBLE WEDNESDAY AFTERNOON/DAY 4 ACROSS MUCH OF THE SRN PLAINS. IN ADDITION...MODEL FORECASTS SUGGEST THAT DEEP LAYER SHEAR ACROSS THE WARM SECTOR WILL BE SUFFICIENT FOR ORGANIZED STORMS. IF THIS UPPER-LEVEL PATTERN MATERIALIZES...SEVERE THUNDERSTORM DEVELOPMENT WOULD BE POSSIBLE WEDNESDAY AND WEDNESDAY NIGHT FROM WRN KS SSEWD ACROSS WRN AND CNTRL OK AS A DRYLINE ORGANIZES AND MOVES EWD ACROSS THE REGION. HOWEVER...THE SYSTEM APPEARS A BIT TOO WEAK TO WARRANT AN OUTLOOK AREA. THE ECMWF AND GFS CONTINUE IN GOOD AGREEMENT MOVING THE UPPER-LEVEL TROUGH EWD ACROSS THE SRN PLAINS THURSDAY/DAY 5 AND INTO THE MID-MS VALLEY ON FRIDAY/DAY 6. STRONG THUNDERSTORMS WOULD BE POSSIBLE IN THE ARKLATEX REGION THURSDAY AND IN THE OH AND TN VALLEYS FRIDAY JUST AHEAD OF THE UPPER-LEVEL TROUGH. BY SATURDAY/DAY 7 AND SUNDAY/DAY 8...THE MODELS DEVELOP A HIGHLY MERIDIONAL UPPER-LEVEL TROUGH IN THE WRN STATES BUT ARE SIGNIFICANTLY VARIANT ON THE TIMING WITH THE GFS MUCH FASTER THAN THE ECMWF. AHEAD OF THIS SYSTEM...A BROAD LOW-LEVEL JET WOULD RESULT IN A LARGE WARM SECTOR ACROSS THE GREAT PLAINS WITH A POSSIBLE SEVERE EVENT IN THE CNTRL PLAINS/MID-MO VALLEY ON SATURDAY. HOWEVER...MUCH UNCERTAINTY EXISTS CONCERNING THE TIMING OF THE UPPER-LEVEL SYSTEM AND A SEVERE THREAT AREA CAN NOT BE DRAWN ATTM. ..BROYLES.. 05/16/2010 EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 329 PM EDT SAT MAY 15 2010 VALID 12Z TUE MAY 18 2010 - 12Z SAT MAY 22 2010 WE ARE STILL LOOKING AT TWO FAIRLY SLOW MOVG CLOSED LOW DOMINATING THE WEATHER ACROSS THE LOWER 48 FOR A SIGNIFICANT PORTION OF THE UPCOMING MED RANGE PERIOD. THE LEAD CLOSED LOW...WHICH WILL BE RESPONSIBLE FOR SIGNIFICANT RAINFALL AMTS DURG THE SHORT RANGE PERIOD ACRS PORTIONS OF THE MS...TN AND OH RIVER VALLEYS...WILL BE PUSHING FROM THE OH VALLEY INTO THE MID ATLANTIC TUE-WED (DAYS 3-4). THE MORE SRN TRACK OF THIS LOW WAS FAVORED INITIALLY THRU THE OH VALLEY ON TUE (DAY 3) AS PER THE 00Z/15 CMC...NAM...AND UKMET. THE 00Z/15 GFS WAS A NRN OUTLIER. WHILE THE 00Z/15 ECMWF WAS ALSO ON THE SRN TRACK OF THE CMC...UKMET AND NAM...IT WAS A SLOW OUTLIER. HOWEVER ITS SLOWNESS HAS SOME SUPPORT FROM THE 00Z/15 ENSEMBLE SPAGHETTI PLOTS. PCPN IS EXPECTED TO DECREASE TUE (DAY 3) COMPARED TO THE SHORT RANGE PERIOD.. HOWEVER...UNDER CYCLONIC VORTICITY ALOFT...WE KEEP THE MID ATLANTIC/APLCHNS IN AN UNSETTLED PATTERN INTO MID WEEK. ANOTHER SIGNIFICANT TROF WILL BE PUSHING INLAND INTO CA AND THE GRTBASIN MON-TUE. ENERGY FROM THIS TROF WILL BREAK OFF INTO A CLOSED SYS NEAR FOUR CORNERS REGION WED...THEN TRANSLATE INTO THE SRN/CNTRL HIGH PLAINS THU. A SLOWER EWD DRIFT OF THIS FEATURE...AS PER THE DETERMINISTIC ECMWF...IS FAVORED BY THE ENSEMBLE MEANS OF BOTH THE GFS AND ECMWF. PCPN AMTS ACRS THE WRN U.S. ARE NOT EXPECTED TO BE HEAVY WITH THESE HEIGHT FALLS. HOWEVER SIGNIFICANT CONVECTIVE PCPN IS EXPECTED TO BREAK OUT ACRS PORTIONS OF THE CNTRL TO SRN PLAINS DOWNSTREAM OF THESE HEIGHT FALLS AS LARGE SCALE LIFT STRENGTHENS INVOF THE STNRY FRONTAL BNDRY LYING ACROSS THE CNTRL TO SRN PLAINS. HEAVY TO EXCESSIVE RAINFALL AMTS POSSIBLE BEGINNING LATE MON...LASTING THRU MOST OF THE WEEK... ACROSS PORTIONS OF THE CNTRL TO SRN PLAINS. THE SLOW MOVG CLOSED UPPER LOW SHOULD MAINTAIN FAVORABLE CONDITIONS FOR CONVECTION INVOF THE AFOREMENTIONED FRONTAL BNDRY. A GFS/ECMWF BLEND WAS ALSO USED FOR THE NERN PAC CLOSED LOW EXPECTED TO PUSH A STRONG FRONTAL BNDRY INLAND INTO THE WEST BEGINNING LATE WED. DESPITE DIFFS THAT DEVELOP BY FRI-SAT (DAY 6-7) WITH THE DETAILS OF THIS STRONG SYS OVER THE W COAST STATES....THE ECMWF AND GFS MEANS WERE FAIRLY SIMILAR AT THIS TIME AND WERE USED FOR DETAILS. FLOOD |