QPF IN WEST INCLUDING THE FRONT RANGE OF THE ROCKIES
MAP OF LOCATION AND TYPE OF SYSTEM FOR 137 HEAVY CONVECTIVE RAINFALL EVENTS
LOCATIONS OF LARGEST 13 MCS AND MCC SYSTEMS USED TO PREPARE 4 TYPES OF ATMOSPHERIC COMPOSITES
FREQUENCY OF FLASH FLOODING OR 2”/24HR RAINFALL FOR 137 EVENTS IN WEST NOTE THE HIGH FREQUENCY IN LATE JULY AND AUGUST
HEAVY RAIN EVENTS ALONG THE FRONT RANGE BIG THOMPSON, FORT COLLINS, CHEYANNE, MADISON COUNTY (VA)
A NARROW BAND OF MOIST UNCONDITIONALLY UNSTABLE AIR JUST BEHIND THE FRONT THE MOISTURE USUALLY EXTENDS TROUGH A DEEP LAYER (TO 300 MB) PWS 150-200% OR NORMAL OROGRAPHIC LIFT PROVIDES MECHANISM TO RELEASE INSTABILITY
Cells develop east of highest terrain + Cells move slowly north and northwest + redevelopment on southeast or southern flank +heaviest rain falls over a very small area
The vast majority of front range events occur during the late July and early August,
ETA MODEL FORECAST OF SFC AND 1000-500 MB THICKNESS. USING THESE FORECASTS AND THE THE MAPS TO FOLLOW, PREDICT WHERE THE HEAVIEST RAIN WILL FALL.
ETA 500H AND VORTICITY FORECASTS NOTE THE TILT OF THE UPPER RIDGE AXIS.
OBSERVED MAPS VALID 00Z JULY 29
MODELS’ 12-36 HR FORECAST OF ACCUMULATED PRECIPITATION
HOW DID YOU DO?
SUMMERTIME QPF IN THE WEST AND ALONG THE FRONT RANGE INVOLVES
MORE ON SUMMERTIME WESTERN EVENTS
Southwest, blocking high type heavy rainfall event.
Blocking anticyclone type (also is known as Maddox Type 4)
DEFORMATION TYPE HEAVY RAINFALL EVENT
An old front or surface boundary and weak mean flow are usually present
QPF IN WEST DURING WINTER
IN WEST IN WINTER CONT.
MADDOX ET AL., WINTER TYPE III
Maddox et al., Type III
Type III events typically occur in southern California when a block forms over Alaska and the Gulf of Alaska and the westerlies break through to its south.
NEED TO KNOW TERRAIN AND WIND DIRECTION THAT FAVORS UPSLOPE
A TYPE III CASE STUDY
DO THE FORECAST LOOK CONSISTENT WITH WHAT YOU SEE IN PACIFIC?
OVERLAYING MODEL OUTPUT WITH SSMI IMAGERY CAN GIVE YOU A GOOD IDEA OF THE MOISTURE THAT WILL BE FEEDING INTO THE WEST COAST. THE MODEL OUTPUT LOOKS REASONABLE
CAN LOOK AT MODEL OUTPUT FOR LIFTING DUE TO TERRAIN
THE MODEL’S TERRAIN IS AVERAGED OVER THE GRID BOX SO THE SLOPE OF THE TERRAIN IS USUALLY NOT STEEP ENOUGH
THINGS TO REMEMBER ABOUT MODEL QPFS IN COMPLEX TERRAIN DURING WINTER
WHAT ADJUSTMENTS ARE NEEDED TO THIS 24 HR QPF
WITH STRONG VERY MOIST SOUTHWESTERLY FLOW AT 850 AND 700 MB NOTE HOW CLOSELY THE PRECIPITATION CONFORMS TO THE TERRAIN
Rhea Orographic Model
Input Requirements for Rhea Orographic model
MOUNTAIN MAPPER
IN SUMMARY
Email: norman.junker@noaa.gov
Home Page: http://www.hpc.ncep.noaa.gov/research/res2.html
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