555
FXUS63 KBIS 042034
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
333 PM CDT SAT JUL 4 2009
SHORT TERM...TODAY THROUGH TUESDAY
CURRENTLY...THE SUBTROPICAL RIDGE OVER TEXAS CONITNUES TO
RETROGRADE. MEANWHILE...CURRENT SATELLITE IMAGERY INDICATES THAT A
CLOSED LOW MOVING INTO THE PACIFIC NORTHWEST IS SENDING IMPULSES
OVER THIS RIDGE AND INTO THE NORTHWEST FLOW OVER THE NORTHERN
PLAINS. THE MAIN SOURCE OF FORECAST UNCERTAINITY LIES WITH
STRENGTH AND TIMING OF THESE SMALL FAST-MOVING SHORTWAVES.
TONIGHT...AN AREA OF SURFACE CONVERGENCE BENEATH MEAGER UPPER
LEVEL SUPPORT WILL MOVE SOUTHEAST ACROSS NORTH DAKOTA. ASSOCIATED
CONVECTION SHOULD BE PUSHING OUT OF THE SOUTHEAST ZONES BY
MIDNIGHT. THE MAIN THREAT APPEARS TO BE HEAVY RAIN AND SMALL HAIL.
STORMS SHOULD DECREASE IN COVERAGE AND INTENSITY AFTER LOSS OF
DAYTIME HEATING...WITH A GOOD NIGHT FOR FIREWORKS IN STORE FOR THE
AREA.
SUNDAY LOOKS VERY SIMILAR...EXCEPT THAT FORECAST THERMODYNAMIC
PROFILES SHOW A BIT MORE STABILITY. THE BEST CHANCE FOR
CONVECTION LOOKS TO BE IN THE NORTHWEST TO SOUTH CENTRAL
COUNTIES...ALONG THE FORECAST AXIS OF INSTABILITY AND SHEAR.
BY SUNDAY NIGHT...THE RIDGE OVER THE ROCKIES BEGINS TO EDGE IN OVER
THE NORTHERN PLAINS...WITH A SHORTWAVE RIDGE AXIS CROSSING OVER
NORTH DAKOTA BY TUESDAY MORNING. THE FORECAST FOR THIS TIME
PERIOD LOOKS DRY AND WARM UNTIL A SHORT WAVE RIDES OVER THE RIDGE
MONDAY NIGHT AND INTO TUESDAY....PROVIDING A GOOD CHANCE
FOR SIGNIFICANT PRECIPITATION MONDAY NIGHT AND TUESDAY.
LONG TERM...WEDNESDAY THROUGH SATURDAY NIGHT
ECMWF AND GFS MODELS ARE BEGINNING TO AGREE ON HANDLING THE WESTERN
NORTH AMERICAN TROUGH...AT LEAST FOR WEDNESDAY THROUGH FRIDAY. ON
WEDNESDAY MORNING THE WESTERN TROUGH IS SUCH THAT THE FLOW OVER
NORTH DAKOTA IS A SOUTHWEST FLOW UPSTREAM FROM THE TROUGH...AND
SENDING SHORTWAVE ENERGY THROUGH THE FLOW ACROSS THE NORTHERN
PLAINS. BY THURSDAY MORNING THE MODELS BREAK OFF A LOW FROM THE
TROUGH AND SEND IT EASTWARD ACROSS CENTRAL/SOUTHERN CANADA WHILE
KEEPING A TROUGH OVER WA/OR/BC. BY THURSDAY NIGHT THE BREAK-OFF LOW
HAS MOVED TOWARDS HUDSON BAY AND NORTH DAKOTA IS IN A WEAK RIDGE OR
ZONAL FLOW ALOFT. HENCE HAVE A CHANCE OF THUNDERSTORMS WEDNESDAY
THROUGH THURSDAY...THEN WENT DRY THURSDAY NIGHT AND FRIDAY - EXCEPT
IN THE FAR WEST. THE MODELS THEN DEEPEN THE HUDSON BAY LOW FEATURE
AND KEEP EITHER ZONAL FLOW OR A WEAK RIDGE ALOFT OVER THE STATE.
HENCE KEPT THE FORECAST DRY OR PUT ONLY SLIGHT CHANCE OF
THUNDERSTORMS - WHICH IS MAINLY CLIMATOLOGY.
AVIATION
WEAK SURFACE TROUGH THIS AFTERNOON EXTENDED FROM NEAR PEMBINA/GRAND
FORKS TO BETWEEN KBIS AND KJMS...TO NEAR KHEI. EXPECT THIS TO BE THE
FOCUS OF SHOWERS AND POSSIBLE THUNDERSHOWERS. THIS TROUGH IS PROGGED
TO MOVE SOUTHEAST AND EXPECTED TO EXTEND FROM NORTHERN MN TO EASTERN
SD AFT 03Z. ISOLATED/WIDELY SCATTERED SHOWERS/THUNDER TO AFFECT
MAINLY KJMS TAF SITE THROUGH 03Z.
HYDROLOGY
THIS MORNING THE LITTLE MUDDY RIVER GAGE NOTED A SHARP INCREASE TO
NEAR ACTION STAGE. LOCAL REPORTS HAVE SHOWN A BASIN AVERAGE OF
ABOUT 1 TO 2 INCHES OF RAIN FROM LAST NIGHT...WHICH HAS SATURATED
THE SOIL THROUGHOUT THE BASIN. LOCAL AMOUNTS OVER 2 INCHES WERE
ALSO RECEIVED. WILL KEEP AN EYE OUT FOR CONVECTION OVER THIS
AREA...AS FLASH FLOOD GUIDANCE HAS DROPPED TO BELOW AN INCH IN
SOME AREAS.
BIS WATCHES/WARNINGS/ADVISORIES
NONE.
BPN/SCHECK/JV
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