Flash Flood in Idaho, May 16 to 17, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO IDAHO
205 PM DT MON MAY 16 2005

.DISCUSSION...
SHORT-TERM...
NUMEROUS SHOWERS AND THUNDERSTORMS OVER THE PIH CWA.  PWS ON AREA
SOUNDINGS STILL 0.6 TO 0.8 OF AN INCH.  MESO-ANALYSIS DEPICTS 330K
SFC THETA-E MAX CENTERED OVER POWER COUNTY WITH HIGHEST DBZS
OCCURRING OVER ZONES 18/19 ALONG PERIPHERY.  STORM MOTION ON VWP AND
PROFILERS 25 TO 30 KNOTS KEEPING FLASH FLOOD POTENTIAL MINIMAL BUT
COULD SEE SOME PROBLEMS LATER TONIGHT WITH ECHO ENTRAINMENT.  AT
18Z...SFC COLD FRONT ALIGNED FROM LLJ TO BOI WITH 995 MB SFC LOW
NEAR EKO AND LIGHTNING MAXES FROM EKO TO TPH.  BASED ON THIS
PLACEMENT AND INTENSITY AND QPF DISTRIBUTIONS PAST 6
HOURS...PREFERRED THE GFS AND MM5-GFS SOLUTIONS.

PEAK LOW-LEVEL CONVERGENCE/UPPER-LEVEL DIVERGENCE COUPLET AND MOST
UNSTABLE CAPES/LIS OCCUR NEAR 00Z TUE OVER AREA AS UPPER FLOW
BECOMES MORE PARALLEL TO THE SFC FRONT.  LOW-LEVEL JET OF 30 TO 40
KNITS WILL IMPACT SOUTHERN ZONES AROUND 00Z.  POTENTIAL FOR SOME
SEVERE CELLS WITH POSSIBLE ROTATION WITH INCREASING 0-2 KM SHEAR OUT
AHEAD OF THE FRONT.  THUS WILL WATCH SOUTHERN AND EASTERN SECTIONS
OF CWA FOR SEVERE THREAT GIVEN PRESENCE OF BEST LIFT/INSTABILITY.
COLD FRONT WILL PASS BY SNAKE VALLEY BY 06Z TUE FOLLOWED BY STRONG
(+15 TO +20) MID-LEVEL DPVA.  THUS WILL CARRY HIGH POPS WITH MENTION
OF LOCALLY HEAVY RAINS/TS (THROUGH 03Z) AND SMALL HAIL WITH WET BULB
ZERO HEIGHTS ABOVE 9K FEET FOR TONIGHT AND EARLY TUE.  U/L TROUGH
EJECTS THROUGH THE PIH CWA DURING 12Z TUE WITH FLOW BACKING TO W/NW
BY TUE AFTERNOON.  THIS GIVES WAY TO A BROAD U/L RIDGE FOR TUE
AFTERNOON AND NIGHT WITH A DECREASE IN SHOWERS FOR TUE NIGHT AND
WED.

EXTENDED...
HIGH CONFIDENCE IN 00Z GFS.  U/L LOW SOUTH OF THE GULF OF ALASKA
WILL DEEPEN WHILE SUBTROPICAL JET PIVOTS TO THE FRONT SIDE OF SYSTEM
AND MOVES INLAND.  THIS WILL AMPLIFY THE BROAD U/L RIDGE NEAR THE
CONTINENTAL DIVIDE AS LOW PRESSURE SYSTEM OVER THE PLAINS DIGS INTO
SOUTH US.  THUS EXPECT PIH CWA TO BE JUST WEST OF THE SHARPENING U/L
RIDGE AXIS WITH SERIES OF WAVES TO CROSS AREA IN SW FLOW ALOFT. BASE
OF THE U/L TROUGH SWINGS INLAND BY LATE FRI.  HENCE THU-FRI WILL BE
THE DRIER DAYS WHILE SAT-MON WILL BE WETTER AS THE RIDGE BREAKS
DOWN.

04

&&

.PIH WATCHES/WARNING/ADVISORIES...NONE.
&&

WEATHER INFORMATION ON-LINE 24-HOURS A DAY
(ALL LOWER-CASE LETTERS)

WWW.WEATHER.GOV/POCATELLO

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE POCATELLO ID
500 AM MDT MON MAY 16 2005

IDZ017>025-031-032-171200-
EASTERN MAGIC VALLEY-SAWTOOTH MOUNTAINS-
UPPER SNAKE HIGHLANDS-UPPER SNAKE RIVER PLAIN-
LOWER SNAKE RIVER PLAIN-SOUTH CENTRAL HIGHLANDS-
CARIBOU HIGHLANDS-CACHE VALLEY/IDAHO PORTION-
WASATCH MOUNTAINS/IDAHO PORTION-
BIG AND LITTLE WOOD RIVER REGION-LOST RIVER/PAHSIMEROI-
500 AM MDT MON MAY 16 2005

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN IDAHO

.DAY ONE...
THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. LOW
PRESSURE WILL CROSS THE GREAT BASIN TODAY AND BRING WIDESPREAD RAIN
TO SOUTHEAST IDAHO. HALF INCH RAINFALL AMOUNTS WILL BE COMMON WITH
EMBEDDED THUNDERSTORMS PRODUCING UP TO ONE INCH OF RAIN LOCALLY.
HEAVIEST RAIN FALL AMOUNTS ARE EXPECTED SOUTH OF A LINE FROM BURLEY
TO ISLAND PARK. AREA RIVERS WILL SEE INCREASED FLOWS BUT HAVE A WAYS
TO GO BEFORE ANY MAIN STEM FLOODING CAN DEVELOP. THERE IS POTENTIAL
FOR LOCALLY HEAVY RAINS TO CAUSE FLOODING OF CITY STREETS THIS
AFTERNOON. ISOLATED THUNDERSTORMS THIS AFTERNOON MAY DEVELOP
DAMAGING WINDS IN AN AREA SOUTH OF A LINE FROM BURLEY TO SWAN
VALLEY. THE SYSTEM WILL MOVE EAST OF THE STATE AFTER MIDNIGHT WITH
SHOWERS DECREASING FROM THE WEST.

.DAYS TWO THROUGH SEVEN...
NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. A FEW SHOWERS WILL
LINGER MAINLY OVER THE EASTERN HIGHLANDS ON TUESDAY. THE NEXT LOW
PRESSURE DISTURBANCE IS EXPECTED TO BRING SHOWERS AND THUNDERSTORMS
TO THE AREA ON FRIDAY.

SPOTTER INFORMATION STATEMENT...
WE ASK ALL TRAINED SPOTTERS TO REPORT SIGNIFICANT WEATHER CONDITIONS.
THIS WOULD INCLUDE ALL HAIL...WIND...AND HEAVY RAIN AND SNOW
REPORTS.  THIS INFORMATION SHOULD BE CALLED INTO THE LOCAL NATIONAL
WEATHER SERVICE OFFICE IN POCATELLO USING THE 1-800 SEVERE WEATHER
HOTLINE...OR OTHER STANDARD OPERATING PROCEDURES.

WEATHER INFORMATION ON-LINE 24-HOURS A DAY
(ALL LOWER-CASE LETTERS)

WWW.WEATHER.GOV/POCATELLO