HPC regarding next week's SVR/Flooding Threat/Blizzard

[Stormsfury]

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
229 PM EST SAT MAR 15 2003

VALID 12Z TUE MAR 18 2003 - 12Z SAT MAR 22 2003

...PATTERN...MODEL OVERVIEW...AND REGIONAL HIGHLIGHTS...

A DEEP MEAN TROF OVER THE CENTRAL/SRN PLAINS WILL
DOMINATE ALMOST THE ENTIRE LOWER 48 STATES THRU DAY 5.
BY FRI DAY 6...A NEW SYS WILL ENTERS THE SWRN STATES. BY
THEN...THERE WILL BE AN OVERALL TREND FOR THE LONGWAVE
PATTERN TO DE-AMPLIFY AND BECOME MORE ZONAL.

THE MAIN CONCERNS TODAY ARE NOT SO MUCH DIFFERENCES
AMONG THE MODELS...BUT THE SENSIBLE WEATHER DEVELOPING
WITH THE HUGE SLOW MOVING STORM DEVELOPING IN THE
NATIONS HEARTLAND DURING THE NEXT SEVERAL DAYS. IN OUR
PRELIM RELEASE...WE WENT ALONG WITH THE 06Z/15 GFS...WHICH
WAS VERY SIMILAR TO THE 00Z/15 GFS THRU THU DAY 5. IN OUR
FINAL RELEASE...WE DID NOT WANT TO STAY TOO FAR FROM THE
06Z/15 GFS...SO WE CREATED A BLEND OF 40% 12Z/15 GFS AND 60%
00Z/15 GFS ENSEMBLE MEAN. THE 12Z/15 GFS SEEMS AFFLICTED
WITH SEVERAL SPURIOUS CONVECTIVE FEEDBACK BLOWUPS...ONE
OF WHICH IT DEVELOPS OVER ERN TN TUE AND MOVES EWD TO
OFF THE CAROLINA COAST WED.

00Z MODEL RUNS HAD CONVERGED ON A SOLUTION WITH THIS
GIANT PLAINS SYS FROM YESTERDAY. THE 12Z/15 GFS FORECAST
SEEMED TO DROP THE MAIN SURFACE LOW TOO FAR S INTO OK BY
THU DAY 5. THEREFORE...WE STAYED CLOSER TO CONSENSUS OF
THE 00Z GFS ENSEMBLE MEAN AND OTHER MODELS WITH THE
SURFACE LOW POSITION DAYS 5-7.

...CENTRAL US...

THE MAIN PROBLEM HERE WILL BE QPF. IN GENERAL...WE THINK
THAT THE 12 GFS QPF IS OVERDONE IN NE/IA THOUGH NOT QUITE
AS MUCH AS THE 00Z RUN. ONE AREA THAT THE 12Z/15 GFS QPF IS
MUCH HEAVIER THAN ITS 00Z RUN IS IN THE NRN HIGH PLAINS.
THOUGH QPF LOOKS OVERDONE THERE AS WELL...TOTAL LIQUID
EXCEEDED 3" IS POSSIBLE IN THE WRN DAKOTAS/ERN MT WHERE
VERY HEAVY WET SNOW IS A GOOD BET ON THE BACK SIDE OF THE
MAIN UPPER/SURFACE SYS TUE-WED. MAN ADJUSTMENTS TO
WERE MADE TO MOS FOR CLOUDS/PCPN. SEE GRAPHICS.

....ERN US...

AGAIN...QPF AND POSSIBLY STRONG CONVECTION ARE THE MAIN
CONCERNS. REPEATED MCS COMPLEXES MOVING INTO THE SRN
APLCNS LATE TUE INTO FRI SUGGEST EXCESSIVE RA TOTALS. THE
5-DAY GFS QPF EXCEEDING 5" E OF THE SRN APLCNS LOOKS
REASONABLE AND COULD EVEN BE UNDERDONE IF SUFFICIENT
TRAINING OF HEAVY CONVECTION OCCURS OVER A GIVEN AREA.
SOME OF THESE HEAVY RAINS COULD EXTEND NEWD INTO VA/PA
BY THU DAY 5.

...WRN US...

NEXT SYS MOVING INTO THE SWRN STATES LATE NEXT WEEK
MIGHT STILL BE STRONGER THAN PORTRAYED BY THE
GFS/ECMWF.. OF NEW 12Z MODEL DATA HOWEVER...ONLY THE
NOGAPS SUPPORTED A DEEPER SYS. THERE IS STILL A CHANCE
OF SOMEWHAT HIGHER-THAN-GFS QPF AMOUNTS/LOCALLY HEAVY
SNOWS OVER THE CENTRAL INTERMOUNTAIN REGION AND NRN
AZ/NM BY FRI DAY 6. TEMPS AND POPS WERE ADJUSTED
ACCORDINGLY.

...THE ERN PACIFIC AND AK...

FAST BROADLY CYCLONIC POLAR JET ACROSS THE PACIFIC WILL
SLAM ONE SYS AFTER ANOTHER INTO VANCOUVER/BC AND
EXTREME SERN ALASKA. THIS MEAN PATTERN WILL KEEP AN
ALMOST DAILY THREAT OF MDT TO HVY PCPN OVER FAVORED
TERRAIN OF SCNTRL AND SERN ALASKA. FARTHER INLAND...NOT
MUCH EVIDENCE OF SPRING YET. UNDER A MEAN TROF
ALOFT...EXPECT COLDER THAN NORMAL TEMPS WITH OCCASIONAL
PERIODS OF LIGHT SN. INDEED...IT REMAIN BE BITTERLY COLD
ABOVE THE BROOKS RANGE WITH TEMPS THERE STAYING MOSTLY
BELOW ZERO.

FLOOD

GRAPHICS AVAILABLE ON THE WEB AT http://www.hpc.ncep.noaa.gov