Quantitative Precipitation Forecast
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FOUS30 KWBC 231429
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1029 AM EDT SAT AUG 23 2014

...VALID 15Z SAT AUG 23 2014 - 12Z SUN AUG 24 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 ENE CWEH 45 ENE CYEN 15 E CWGN 20 NE JKJ GHW 15 SSW PQN
40 SW MHE 50 NNW VTN 25 NE IKA 15 NNE GCC 15 NNE SHR 45 SSW BIL
40 NNW WYS 25 WNW BTM 55 NNE 3DU 40 SE CTB 40 ENE CWEH.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
2WX 65 NNE GCC 40 N SHR 25 NE BIL 45 NNE BZN 30 NE GFA
50 SSE CWEH 40 E CWAQ 15 ENE MOT 45 NNE K7L2 30 SE K7L2 40 S MBG
2WX.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 SE HVR 55 SSW CWVN 30 WSW GGW 15 NW JDN 20 WSW JDN
55 WSW JDN 40 ESE LWT 25 NNE LWT 50 SE HVR.


...EASTERN PORTIONS OF THE NORTHERN ROCKIES AND FOOTHILLS INTO THE
NORTHERN PLAINS...

15Z UPDATE...BASED ON THE CURRENT GUIDANCE AND RADAR TRENDS...HAVE
EXPANDED THE MODERATE RISK AREA TO INCLUDE THE WESTERN 2/3 OF
NORTH DAKOTA ALONG WITH A SMALL PORTION OF NW SOUTH DAKOTA.
EVOLVING DIFFLUENT UPPER LEVEL FLOW AND STRENGTHENING POCKET OF
UPPER LEVEL DIVERGENCE AHEAD OF THE VORT MAX CURRENTLY LIFTING
N/NNE ACROSS NERN CO AND WRN NE IS GENERATING A SEPARATE
WIDESPREAD AREA OF GENERALLY MODERATE RAINFALL ACROSS SD AND SRN
ND. OVER TIME... THE THERMODYNAMIC PROFILES OVER THIS REGION (NRN
HIGH PLAINS) WILL BECOME INCREASINGLY FAVORABLE FOR MORE OF A
CONVECTIVE CONTRIBUTION AND THUS AN ENHANCED EXCESSIVE RAINFALL
THREAT...ESPECIALLY FARTHER EAST INTO THE CENTRAL DAKOTAS...ALONG
THE N/NW PERIPHERY OF THE INSTABILITY AXIS (MUCAPES 500-1000 J/KG
PER THE ARW WITH PWATS AROUND 1.5 INCHES (WHICH WILL BE AROUND 3
STD DEVIATIONS ABOVE NORMAL OR AOA THE 99TH PERCENTILE FOR THE
AREA THIS TIME OF YEAR). DRY AIR ALOFT (STEEPENING THETA-E LAPSE
RATES) NORTH OF THE AFOREMENTIONED VORT MAX WILL LIKELY ENHANCE
CONVECTION AHEAD OF THIS VORT MAX AS IT LIFTS N/NNE THIS AFTERNOON.

THE MODEL GUIDANCE...BOTH GLOBAL AND HIGH RES...CONTINUE TO SHOW A
STRONG SIGNAL FOR A SIGNIFICANT RAINFALL EVENT ACROSS THE EASTERN
FOOTHILLS OF THE NRN ROCKIES INTO THE NRN PLAINS...WITH THE LATEST
SSEO MEAN PROBABILITIES OF EXCEEDING 3 AND 6 HOURLY FFG NOW OVER
70 PERCENT IN THE NOW HIGH RISK AREA ACROSS PORTIONS OF CENTRAL MT
ALONG THE WESTERN PERIPHERY OF THE TROWAL ZONE. 24 HOUR
AREAL-AVERAGE QPF WITHIN THE HIGH RISK AREA PER THE GLOBAL MODEL
CONSENSUS RANGES FROM 2.5 TO 5 INCHES...WHICH IS SUPPORTED BY THE
SREF AND GEFS PROBABILITIES OF 50% OR GREATER OF RECEIVING MORE
THAN 3 INCHES IN 24 HOURS. AT THE SAME TIME...VIRTUALLY ALL OF THE
HIGHER RES GUIDANCE SHOW LOCALLY HIGHER AMOUNTS OF 6+ INCHES.
FARTHER EAST INTO THE CENTRAL DAKOTAS...RAINFALL IS EXPECTED TO
AVERAGE CLOSER TO 1-3 INCHES...HOWEVER GIVEN THE GREATER
INSTABILITY TO FEED OFF OF...THERE WILL MORE DEVIATION FROM THE
MEAN WITH LOCALLY HEAVIER...POTENTIALLY EXCESSIVE AREAS OF
RAINFALL...SUPPORTED BY THE ISOLATED 4-6+ INCH BANDS PER THE
LATEST 4KM NAM CONEST AND NSSL WRF.


...PORTIONS OF THE MID MISSISSIPPI VALLEY...

THE POTENTIAL FOR 2-3 IN/HR RAINFALL RATES WITH FLASH FLOODING
SHOULD CONTINUE ACROSS ERN IOWA UNTIL ABOUT 15Z WHEN LOW LEVEL
INFLOW DIMINISHES TO LESS THAN 20 KTS. FOR FURTHER
DETAILS...PLEASE REFER TO THE LATEST MESOSCALE PRECIPITATION
DISCUSSION OR FFGMPD #314 WHICH CAN BE ACCESSED BY GOING TO
WWW.WPC.NCEP.NOAA.GOV/METWATCH/METWATCH_MPD.PHP.



HURLEY


PREVIOUS DISCUSSION BELOW...


A WIDESPREAD AND HEAVY TO ISOLATED EXCESSIVE RAINFALL EVENT
EXPECTED THIS PERIOD FROM THE NORTHERN ROCKIES OUT INTO THE
NORTHERN PLAINS..AS DEVELOPING COOL SEASON DYNAMICS COMBINE WITH
WARM SEASON MOISTURE.  THE LATEST MODEL RUNS CONTINUE TO ADVANCE
THE ALREADY IMPRESSIVE NORTHERN GREAT BASIN H5 TROF INTO AN
UNSEASONABLY STRONG H5 TROF/CLOSED LOW INTO THE NORTHERN ROCKIES
LATER THIS PERIOD.  TO THE EAST OF THIS H5 TROF...AN ANOMALOUSLY
STRONG AND MOIST EASTERLY LOW LEVEL FLOW IS SETTING UP AND WILL
PERSIST INTO THE NORTHERN HIGH PLAINS AND NORTHERN ROCKIES UNTIL
LATER SATURDAY AFTERNOON/EVENING..WHEN THE FLOW SHOULD BACK TO A
MORE NORTHEASTERLY DIRECTION BEHIND THE LIFTING OUT LOW LEVEL
CENTER.  THE STRONG MID LEVEL DYNAMICS/FORCING...THE DEVELOPMENT
OF AN INCREASINGLY FAVORABLE UPPER DIFFLUENT PATTERN AND THE VERY
MOIST AIRMASS SHOULD SUPPORT THE HEAVY TO ISOLATED EXCESSIVE RAINS
FROM THE NORTHERN HIGH PLAINS BACK INTO MUCH OF CENTRAL AND
EASTERN MT..WITH ALL OF THE MODEL QPF GUIDANCE IN AGREEMENT ON
THIS IDEA.  EXPECT AT LEAST AREAL AVERAGE 3-4 INCH RAINS IN PARTS
OF CENTRAL/EASTERN MT...WITH ISOLATED AMOUNTS IN EXCESS OF 5
INCHES POSSIBLE...AND HAVE PUT THIS AREA UNDER A MODERATE RISK OF
FLOODING.  A BIT FARTHER EAST...H5 S/WV ENERGY LIFTING
NORTH-NORTHEASTWARD OUT OF THE CENTRAL PLAINS THRU THE NORTHERN
PLAINS AHEAD OF THE MAIN UPSTREAM H5 TROF WILL COMBINE WITH A MORE
EASTERLY TO EAST-SOUTHEASTERLY STRONG LOW LEVEL JET TO PRODUCE
HEAVY RAINS/CONVECTION THRU THIS REGION INTO SATURDAY
EVENING...WITH WELL DEFINED SURFACE LOW PRESSURE JUST AHEAD OF THE
MAJOR H5 TROF SUPPORTING ADDITIONAL WRAP-AROUND HEAVY RAINS THRU
PARTS OF ND SATURDAY NIGHT.  THE RAINS OUT IN THE NORTHERN PLAINS
NOT LIKELY TO BE AS HEAVY AS BACK IN MT..BUT SOME AREAL AVERAGE
2-3 INCH TOTALS ARE EXPECTED...WITH THIS AREA BEING PUT IN A
SLIGHT RISK OF FLOODING.

TERRY
$$





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