Quantitative Precipitation Forecast
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FOUS30 KWBC 021615
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1215 PM EDT WED SEP 02 2015

...VALID 1615Z WED SEP 02 2015 - 12Z THU SEP 03 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 NNW TCS 65 E DUG 65 SSW DUG 50 SW OLS 25 SSE CGZ 35 SSW INW
50 W RQE 45 N RQE 45 SSE FMN 30 W AEG 30 NNW TCS.


...SOUTHWEST U.S...

A MONSOONAL PLUME HAD BEEN FIRMLY ESTABLISHED...AND ISOLATED FLASH
FLOODING HAD BEEN REPORTED OR INDICATED BY RADAR IN RECENT DAYS.
WEDNESDAY AND WEDNESDAY NIGHT AGAIN HOLD POTENTIAL TO BE
ACTIVE...ESPECIALLY WITHIN THE PLUME OF 1.25 TO 1.65 INCH PW
VALUES OVER CENTRAL AND EASTERN ARIZONA AND WESTERN NEW
MEXICO...BUT ALSO POTENTIALLY EXTENDING TOWARD SE UT / SW CO WHERE
PW VALUES WILL APPROACH 1.00 INCH. THERE IS SOME WEAK CONNECTION
TO HIGH ALTITUDE MOISTURE STREAMING NORTHWARD FROM TROPICAL
DEPRESSION 14-E. MODELS DIFFER IN THE DETAILS...BUT ALL FORECAST
ENHANCEMENT OF MID LEVEL CYCLONIC VORTICITY ACROSS EASTERN AZ
TODAY...WITH AN EVENTUAL TRACK OF THE RESULTING SHORTWAVE TOWARD
THE FOUR CORNERS. THIS MAY ORGANIZE PRECIPITATION ONTO LARGER
SCALES...MAKE IT MORE PERSISTENT OVER A GIVEN LOCATION...AND
ENHANCE INFLOW NEAR THE TOP OF THE BOUNDARY LAYER. UNIDIRECTIONAL
FLOW IN THE CLOUD LAYER ALSO ARGUES FOR SOME TRAINING. THE MODEL
PRECIPITATION SIGNAL IS NOT PARTICULARLY STRONG IN THIS
REGION...BUT MANY OF THE INGREDIENTS ARE IN PLACE FOR AN ORGANIZED
FLASH FLOOD RISK ON LOCAL SCALES. INTRODUCED A SLIGHT RISK AREA IN
COORDINATION WITH THE LOCAL NWS FORECAST OFFICES.


...UPPER MISSISSIPPI VALLEY / WESTERN GREAT LAKES...

THUNDERSTORMS PRODUCING HEAVY RAIN RATES WILL OCCUR AHEAD OF A
COMPACT MID LEVEL TROUGH...BUT ALSO IMMEDIATELY BEHIND THE TROUGH
IN AN AREA OF ENHANCED LOW LEVEL INFLOW. THE TROUGH WILL TRACK
FROM THE VICINITY OF THE MN/WI BORDER THIS MORNING TO LOWER
MICHIGAN BY THURSDAY MORNING...WITH THE LEADING THUNDERSTORM
ACTIVITY MIGRATING ALONG A LOOSELY DEFINED WARM FRONT FROM THE
WESTERN END OF LAKE SUPERIOR DOWN TO LOWER MICHIGAN. THE TRAILING
ACTIVITY WILL REDEVELOP EASTWARD AND SOUTHEASTWARD FROM THE
MINNEAPOLIS AREA TOWARD NORTHERN INDIANA. MANY OF THE MODEL
FORECASTS WERE THOUGHT TO NOT BE PROGRESSIVE ENOUGH...AND LIKELY
DISPLAY A SLIGHT NORTHWARD BIAS TO THEIR QPF. WPC PREFERRED THE
00Z SPC WRF...WHICH SHOWED SOME AGREEMENT WITH THE NSSL WRF AND
ECMWF.

GENERALLY THE SHORT WAVELENGTH OF THE MID LEVEL TROUGH...ALONG
WITH REASONABLY STRONG DOWNDRAFT CAPE...SHOULD PROMOTE FORWARD
PROGRESSION...AND ACT AGAINST FLASH FLOODING...ALTHOUGH
PRECIPITABLE WATER VALUES NEAR 1.5 INCHES WILL SUPPORT BRIEF
STRONG RAIN RATES. THE GREATEST CONCERN FOR FLASH FLOODING MAY BE
WITH THE NARROW BANDS OF CONVECTION WHICH FORM ON THE TRAILING
SIDE OF THE TROUGH...IN THE BETTER LOW LEVEL INFLOW. ONE SUCH BAND
HAD SET UP WEDNESDAY MORNING IN WESTERN WISCONSIN WHERE RADAR
ESTIMATED MORE THAN AN INCH IN AN HOUR WAS FALLING AT 1430Z. PER
RECENT DRY WEATHER AND RELATIVELY LARGE FLASH FLOOD GUIDANCE
VALUES REQUIRING ABOUT 2.5 INCHES IN 3 HOURS...THE FLASH FLOOD
THREAT IS NOT VERY PRONOUNCED...BUT ISOLATED FLASH FLOODING COULD
OCCUR.


...TEXAS AND LOUISIANA GULF COAST...

A SMALL SCALE CIRCULATION EMBEDDED IN A MID LEVEL TROUGH HAD
FLARED UP WITH CONVECTION FOR A SECOND STRAIGHT MORNING ALONG THE
TEXAS GULF COAST. GALVESTON MEASURED A RAPID ACCUMULATION OF MORE
THAN 2 INCHES OF RAIN IN THE EARLY MORNING HOURS BEFORE OUTFLOW
PUSHED THE CONVECTION OFFSHORE. HEAVY...EFFICIENT RAINFALL WAS
ALSO NOTED ALONG THE LOUISIANA COAST FARTHER UP THE LENGTH OF THE
TROUGH AXIS...AND AGAIN WITHIN A WEAK ONSHORE FLOW COMPONENT AT
LOW LEVELS. THE LARGER SCALE MID LEVEL TROUGH WILL REMAIN IN
PLACE...STUCK INSIDE A MEAN RIDGE POSITION...BUT IT WILL START TO
FRACTURE AS RIDGING OVER THE GULF CONNECTS WITH RIDGING IN THE
PLAINS STATES TO FORM A COL POSITION OVER SOUTHERN LOUISIANA. THIS
WILL FAVOR PROLONGED WEAK ASCENT OVER LOUISIANA...CAPABLE OF
SUPPORTING HEAVY RAIN THROUGH TONIGHT. ALONG THE TEXAS PORTION OF
THE TROUGH THE SMALL CIRCULATION MAY NOT PERSIST IN ITS PRESENT
FORM...BUT PERSISTENT ONSHORE FLOW SHOULD AGAIN FAVOR ISOLATED
HEAVY RAINFALL WEDNESDAY NIGHT.

BURKE
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.