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 021458
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1057 AM EDT WED SEP 02 2015

...VALID 15Z WED SEP 02 2015 - 12Z THU SEP 03 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...



...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 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. THE LARGER SCALE MID LEVEL TROUGH
WILL REMAIN IN PLACE...STUCK INSIDE A MEAN RIDGE POSITION. THE
SMALL CIRCULATION MAY NOT PERSIST IN ITS PRESENT FORM...BUT
PRESENCE OF THE TROUGH ALONG WITH PERSISTENT ONSHORE FLOW SHOULD
AGAIN FAVOR ISOLATED HEAVY RAINFALL ALONG THE COAST WEDNESDAY
NIGHT.


...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...BUT ALSO 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.

BURKE
$$




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