061
FXUS02 KWBC 031914
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
313 PM EDT THU JUL 03 2008
VALID 12Z SUN JUL 06 2008 - 12Z THU JUL 10 2008
..FINAL MEDIUM RANGE FORECAST DISCUSSION
FINAL MEDIUM RANGE PROGS MADE NO MAJOR CHANGES TO THE UPDATED
PRELIM GRAPHICS.
THE 12Z/03 GFS APPEARS TO LOWER HEIGHTS A BIT TOO QUICKLY OVER THE
NE PACIFIC BY DAYS 5-6. THIS CHANGE CONTRIBUTES TO THE NEW GFS
GETTING SERIOUSLY OUT OF KILTER WITH ITS OWN 06Z AND 12Z
SHORTWAVE CONTINUITY OVER THE ERN CONUS BY THE MIDDLE OF NEXT
WEEK...DAYS 6-7. THE LATEST UKMET BRINGS EVEN MORE HEIGHT FALL
INTO VANCOUVER/BC THAN THE NEW GFS ON DAY 5-6...AND IS SUSPECT.
THE CANADIAN KEPT HIGHER HEIGHTS OFF THE PACIFIC NW COAST DAYS 5-6
BUT STILL LOWER THAN THE 00Z ECMWF. THE 12Z/03 ECMWF IS AN
OUTLIER...DEFYING ALMOST ALL OTHER OPERATIONAL AND ENSEMBLE
GUIDANCE WITH A FAIRLY STRONG RIDGE OFF THE PACIFIC NW COAST DAYS
5-6. NO MATTER HOW YOU SLICE IT THERE IS STILL A FAIR AMOUNT OF
MODEL AND ENSEMBLE SPREAD IN THE NRN BRANCH OF WESTERLIES IN THE
NE PACIFIC EWD ACROSS THE US/CANADIAN BORDER...WITH SOMEWHAT LESS
PREDICTABILITY THAN AVERAGE IN THAT STREAM.
EARLIER THIS MORNING...THE 00Z GEFS MEAN WAS SUSPECT WITH THE
DEPTH OF THE TROUGH IT DEPICTED ALONG THE WESTERN CANADIAN BORDER
LATE IN THE PERIOD. IT WAS DEEPER THAN EITHER THE 00Z/03
DETERMINISTIC ECMWF OR THE 00Z/03 GFS...SO WE LEANED AWAY FROM THE
00Z GEFS SOLUTION. THAT LEFT US WITH THE 12Z/02 AND 00Z/03 ECMWF
AND ITS ENSEMBLE MEANS...WHICH HAD EXCELLENT RUN TO RUN
CONTINUITY...FOR CONSTRUCTION OF THE MID-MORNING AND FINAL FRONTS
AND PRESSURES. AT THIS TIME HPC PREFERS TO STAY ON THE MORE
CLIMATOLOGICAL 00Z ECMWF ENSEMBLE SIDE OF THE ENVELOPE OF
SOLUTIONS.
THE LONGWAVE PATTERN DURING THE MEDIUM RANGE PERIOD BEARS THE
CHARACTERISTIC STAMP OF MIDSUMMER ACROSS NORTH AMERICA...WITH THE
POLAR JET RETREATED TO CANADA...AND THE FAR SOUTHERN UNITED STATES
GRADUALLY BECOMING SUBJECT TO DISTURBANCES IN THE EASTERLIES. THE
GENERAL LONGWAVE PATTERN SHOWS A VERY BROAD RIDGE-TROF=RIDGE
ACROSS THE US/CANADIAN BORDER...WITH A TENDENCY FOR THE SRN
PORTION OF THE MS VLY MEAN UPPER TROF TO BREAK OFF AND MOVE WWD.
THIS SCENARIO WOULD LEAVE BEHIND A WWD DRIFTING UPPER TROF/LOW
OVER SRN TX AROUND TUE DAY 5. THERE IS A FAIR AMOUNT OF MODEL
SPREAD CONCERNING THIS INVERTED UPPER TROF FEATURE...SO WE ARE
LESS THAN CONFIDENT WITH ITS PRECISE DETAILS.
..REGIONAL HIGHLIGHTS
ABUNDANT MOISTURE WILL CHARACTERIZE THE WEATHER ALONG THE GULF AND
ATLANTIC COASTS DURING THIS MEDIUM RANGE PERIOD...INDEED FOR SOME
DISTANCE INLAND FROM THE COASTS. THERE WILL BE NO DEFINITIVE
FRONTAL PASSAGES SOUTH OF 40 DEGREES LATITUDE...AND EVEN THOSE
FROPA AFFECTING NEW ENG AND THE GRT LAKES ON THE SRN EDGE OF THE
WESTERLIES SHOULD BE WEAK THOUGH FOLLOWED BY DRIER AIR. THERE
SHOULD BE A HIGHLY DIURNAL CYCLE OF SCTD TO NUMEROUS SHRA/TSRA
FROM THE MID ATLANTIC COASTAL PLAIN SWWD THEN WWD ALONG THE S
ATLANTIC AND GULF COASTS. MODELS BRING A MORE ORGANIZED AREA OF
UPWARD MOTION INTO THE EXTREMELY MOIST AIRMASS ALONG THE MID AND S
ATLANTIC COASTS SUN-MON. THE INTERACTION OF AN UPPER SYS WITH HIGH
PWS AND A LOW LEVEL SSW JET ALONG THE MID ATLANTIC COASTAL PLAIN
SUGGESTS WIDESPREAD CONVECTION AND LOCALLY HEAVY DOWNPOURS SAT
NIGHT/SUN. THE UPPER SYS MOVING ACROSS S TX THE FIRST PART OF NEXT
WEEK COULD BRING SOME LOCALLY HEAVY RAINS THERE ALSO.
...MIDWEST...
ANOTHER ROUND OF STORMS AND THEIR LOCALLY EXCESSIVE RAINFALL IS
EXPECTED TO AFFLICT THE N CENTRAL PLAINS AND THE MIDWEST BEGINNING
IN EARNEST SUN EVE...THEN CONTINUING AT INTERVALS RIGHT INTO TUE.
PLEASE REFER TO LATEST STATEMENTS FROM SPC AND HPCQPF CONCERNING
THE SEVERE WEATHER AND FLOOD POTENTIAL OF THIS LATEST BATCH OF
HEAVY TSTMS. THESE STORMS WILL BE TRIGGERED BY WEAK IMPULSES ALONG
THE SRN EDGE OF THE WESTERLIES INTERSECTING MOIST SWLY LOW LEVEL
FLOW IN THE PLAINS STATES.
WESTERN STATES....
MONSOONAL MOISTURE WILL BE SUFFICIENT FOR SCTD DAILY DIURNAL
CONVECTION THRU THE ROCKIES AND WWD INTO THE SRN HALF OF AZ.
ELSEWHERE...DRY AND HOT.
FLOOD
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